Supply Chain - Renewables & Energy Management

Mogden STW is one of Thames Water’s Tideway treatment works and in AMP6, a combined heat and power (CHP) installation was constructed at the site. Once the ongoing (AMP7) sludge and AD facility upgrade is completed, biogas yield is set to increase again and, in line with its net zero strategy, at the start of 2022, Thames Water opted to add a biomethane gas-to-grid plant at Mogden during AMP7.

Project brief and site-specific challenges

The gas-to-grid plant at Mogden was conceived to complement the AMP6 CHP facility. As such, the plant was sized to process a third of the site’s anaerobic digestion (AD) biogas output.  In order to successfully complement the CHPs, the control of the gas-to-grid plant would need to be appropriately integrated into the existing process control system.

With neighbours on all boundaries and an ever-increasing local population, the Mogden STW site is especially constrained for space. The design development and delivery of the gas-to-grid project was further complicated by the aforementioned AMP7 sludge and AD facility upgrade. The layout, plant configuration and plant control would all need to consider construction, interim and legacy phase site arrangements.

Innovative deployment of a fully proven solution

On placement of the design and build order, SGN Green Gas Solutions set about tailoring a well proven membrane upgrader-based solution for the specific requirements of the Mogden project. Fundamentally, the solution is fairly typical of a current generation biomethane gas-to-grid plant.

The biogas supply for the gas-to-grid plant was taken off the existing supply to the CHP engines. To help overcome the challenges routing this supply to the main gas-to-grid plant compound, SGN Green Gas Solutions located the biogas dehydration equipment close to the point of connection. A combination of above-ground stainless steel and buried PE pipework could then be used to convey the dry biogas.

SGN Green Gas Solutions developed an elongated design for the main plant to work given space constraints. The plant layout had to accommodate HV/LV transformers to supply the membrane upgrader and associated ancillaries and an appropriate route was found for the biomethane product pipework.

Construction

A remotely operated valve delineates the biomethane plant from the gas network and due to its location, the SGN team had to design and install a 315mm diameter, PE export pipeline over a complex 1.2km route crossing a road with high traffic flows into a medium pressure (MP) system. Although convoluted, this connection option guaranteed year-round export capacity.

With established supply chain partnerships and relationships, SGN Green Gas Solutions was able to sequence design, procurement, site works and plant installation to optimise the programme and limit the amount of work required on site. The grid connection pipeline commenced in the summer months of 2022.

Mobilisation on the Mogden site was in January 2023 and civils work peaked in June. Package plant items arrived in quick succession throughout August, and by the end of November 2023, site installation and site commissioning were substantially complete.

[caption id="attachment_13204" align="alignnone" width="1200"] Activated carbon pre-treatment units - Courtesy of SGN Green Gas Solutions[/caption]

Operational flexibility and integrated control

Given the aspiration to operate the gas-to-grid plant in conjunction with the existing CHPs, a significant amount of thought went into the control philosophy for the plant and the control interface between the plant and the wider site. Being a large sewage treatment works, Mogden has a sophisticated process control system, power management system and SCADA.

The existing CHPs normall operation includes automatic start, ramp and stop based on the common level of the site’s floating-roof AD tanks. It was agreed that the biomethane plant start, ramp and stop commands would also need to be driven from the existing process control system based on configurable set-points. The values used for these set-points would then allow the site’s process control engineers to optimise the conversion of biogas in real time based on prevailing conditions.

When there is surplus in electricity generation capacity, more of the site’s biogas can be directed to the gas-to-grid plant to be used (and to an extent ‘stored’) in the gas network.

Renewable generation capacity with intelligent features like this help the UK better match energy supply and demand as the country transitions away from fossil fuels.

Commissioning & commercial operation

Commissioning of the gas-to-grid plant commenced in November 2023, with the first green gas being injected in December. From January the plant effectively commenced commercial operation, with optimisation work, performance tests and reliability trials continuing through the spring.

The output from the plant will provide sufficient green gas to supply over 4,000 local homes, offsetting 8,000 tonnes of fossil carbon emissions each year. The project has further shown how gas-to-grid technology can be rapidly deployed and fully integrated in a high-profile municipal wastewater treatment context.

Between 2015 and 2020, Affinity Water reduced abstraction from chalk groundwater sources by 42 million litres per day (MLD) and aims to cut an additional 36 MLD by 2025. These efforts are crucial for sustainably providing high-quality drinking water to their customers. While Affinity Water does not manage sewage, it plays a key role in maintaining the ecological health of rivers by reducing water abstraction and making other environmental improvements. To protect chalk streams and their wildlife, Affinity Water is importing more water from Anglian Water’s Grafham Water Reservoir. Affinity Water has acquired Sundon Reservoir, an underground clean water facility reservoir near Luton, originally built by Anglian Water. As part of the plans, a treatment facility was constructed to adjust the Larson-Skold Index and free chlorine levels, as well as refurbishing the reservoir with a dividing wall for improved resilience.

Purpose of the new water treatment facility

The treated water from Grafham Water Treatment Works (WTW) has a different water chemistry to that of the vast majority of treated water in Affinity’s network.

The Larson-Skold Index (LSI) is an empirical scale that measures the corrosivity of water towards mild steel. During an early feasibility study, it was noted that the LSI of the water from Grafham will be much higher than that of water treated by Affinity. Therefore, if Affinity Water is to import such an increased amount from Grafham WTW to Sundon, then further water treatment would  be required.

Reservoir additions and modifications

The first phase of this project saw some work being undertaken on the existing concrete reservoir structure. The tank was bypassed and drained, with work being carried out in off-peak months as to make the most of the lower demand period. A reinforced concrete in situ dividing wall was constructed down the centre of the tank to split the single cell reservoir into two. This provides storage resilience during decennial inspections.

[caption id="attachment_14285" align="alignnone" width="1200"] Sundon Reservoir and Water Treatment Facility - Courtesy of Ward & Burke[/caption]

The incoming twin mains were brought together and a new DN800 ABB flow meter was installed. Tapering up to DN1200, the main was brought above ground into the new building before diving back down and on towards the reservoir. Existing inlet, outlet, overflow and washout pipes were reused for one cell, while new ones were installed for the second cell.

Other modifications included new access hatches, ladders, pipe hop-overs and overbanding on existing concrete joints. A baffle curtain was installed in each cell to channel the water down to one end of the reservoir and back before leaving, creating the contact time required for the chlorine to reach ‘breakpoint’ (see the following section).

As such, the reservoir used for storage as a primary purpose, was also being used as a contact tank. Prior to returning the cells to service, the structure was inspected, hydrostatically tested, thoroughly cleaned and subsequently sampled.

Chemical dosing

Sodium hypochlorite dosing: There are two components to the dosing of sodium hypochlorite:

1. To destroy the chloramines (breakpoint).
2. To leave a free chlorine residual in the outgoing water.

The dosing is calculated using the results from the import water quality analysers; Hach’s ammonia analyser and Swan Analytical’s free and total chlorine analysers. To determine the free chlorine levels after breakpoint chlorination had been reached, a vessel was used to simulate 30-minute old water before being analysed. This 30-minute value was arrived at experimentally through a bench test in outline design. Finally, the calculated dose per litre of water is then multiplied up to be flow proportional using the new flow meter.

[caption id="attachment_14281" align="alignnone" width="1200"] Water quality analysers - Courtesy of Ward & Burke[/caption]

Bulk quantities of sodium hypochlorite at 14-15% w/w concentration are stored in vertical cylindrical tanks, manufactured by Forbes Technologies Ltd. The tanks are manufactured from GRP with a uPVC lining inside, with typical connections for inlet, outlet, drain, vent and overflow. Pressure instruments installed at low level are used for chemical level readings as to remove any working at height. The duty tank is selected using an actuated valve on the tank’s outlet, taking the chemical into the dosing skid.

Grundfos manufactured the dosing skid for this project. Two duty/standby configured Grundfos DDA120 smart pumps are used in a standard dosing skid configuration with components including, but not limited to, pulsation dampers, loading valves and PRVs.

Duty/standby outlets are provided for two dosing hoses that connect the dosing skid in one building, to the point of application (POA) cabinet in another building. The dosing hoses used, stretching a distance of around 50m, is PF Detect dual contained, leak detection hosing from FT Water Treatment. This hose-inside-a-hose has two copper wires in a helix sandwiched between the two hoses. In the case of the internal carrier hose bursting, chemical leaks into the gap between hoses and by capillary action, fills the gap until a short is created across the two copper wires, indicating a fault at the control panel. This automatically switches to the standby dosing line immediately, preventing any further leakage. Note that the leakage is contained thanks to the outer hose’s extremely high burst pressure. This has allowed for transfer of chemicals through ducts over a great length without using catchpots and rigid outer piping.

The POA cabinet is situated adjacent to the static mixer on the water main. It is of typical construction with a loading valve and flow switch. Finally, withdrawable injection lances are used in the DN1200 static mixer to dose the sodium hypochlorite into the water main.

[caption id="attachment_14287" align="alignnone" width="1200"] Chemical injection at static mixer - Courtesy of Ward & Burke[/caption]

Sodium hydroxide dosing: The Larson-Skold Index (LSI) is an empirical scale to measure the corrosivity of water towards mild steel. This is an issue for Affinity’s network that has not seen such a high LSI as it can lead to pipe deterioration and water discolouration. It is a ratio of sulphate and chloride content, to alkalinity content (in the form of bicarbonate and carbonate).

The sulphate and chloride content of the import water is measured using some of Hach’s EZ4000 series analysers, and does not change very much day on day. As such, in order to reduce the LSI, alkalinity is increased by the addition of sodium hydroxide. The alkalinity is measured at the import, as well as after dosing, using a Hach EZ4000 series also. A trim function is coded in to bring the dosing closer to the set-point if it is slightly out. As a bi-product of this dosing however, the pH of the water would increase, and this is where carbon dioxide dosing comes in (see following section).

The sodium hydroxide is stored in bulk quantities at a concentration of 50% w/w. Similar tanks are used, however are of HDPE PE100 construction, also manufactured by Forbes.

The connections and instrumentation are identical to that of the sodium hypochlorite tanks, with the addition of a temperature transmitter and heater. Sodium hydroxide at this concentration has a freezing temperature of +7°C and as a result, the tanks’ contents are maintained at 25°C. The temperature transmitter informs of any drop in temperature before it is too late. It should be noted that the tanks’ stainless-steel fill and outlet lines were all heat traced and lagged also.

Grundfos also manufactured the dosing skid for this chemical. Three DME940 pumps were used in a duty/assist/standby configuration, along with the usual components as above. The same PF Detect hosing was used to get the chemical to the POA cabinet and these lines were heat traced and lagged. Furthermore, the dosing skid and POA cabinet each contained heaters.

Components in the POA cabinet were identical to that of the sodium hypochlorite, with withdrawable stainless steel injection lances in the static mixer to complete the dosing.

[caption id="attachment_14286" align="alignnone" width="1200"] (top left) Sodium hypochlorite storage and dosing, (top right) sodium hydroxide storage, (bottom left) sodium hydroxide dosing, and (bottom right) point of application cabinets - Courtesy of Ward & Burke[/caption]

Carbon dioxide dosing: Working in tandem with the sodium hydroxide dosing, the gaseous carbon dioxide is dosed into the water to bring the pH back down to the set-point. This means that both dosing systems must be working at the same time. It should be noted that the carbon dioxide does not affect the LSI at all.

As with most industrial gas use, the storage vessels are rented from the gas supplier. Nippon Gases are the supplier of carbon dioxide for this project. Delivery and storage is in liquid form, with the storage vessels being insulated with a vacuum layer, akin to a Thermos flask. Vaporisers are also rented from Nippon Gases UK and convert the liquid carbon dioxide into gaseous form for dosing. The gas is heated using trim heaters before the pressure is reduced, prior to going through flow control valves and a flow meter to control quantities for dosing.

Sundon Water Treatment Facility: Supply chain - key participants

• Client: Affinity Water
• Principal designer & contractor: Ward & Burke
• CFD analysis: Wilde Analysis
• Precast concrete: Shay Murtagh Precast
• Electrical installation: Enisca Ltd
• System integration: Riverside Automation
• Concrete repair: Concrete Repairs Ltd
• Stainless steel pipework: ABC Stainless Ltd
• Dosing skids & pumps: Grundfos
• CO₂ storage & vaporisation: Nippon Gases
• Water quality monitors: Swan Analytical UK Ltd
• Water quality monitors: Hach
• Water quality monitors: ABB Ltd
• MCC & panels: Motrol (now Profitec)
• Static mixer: Statiflo International
• Permanent generator: Bells Power
• Solar panels: GeoGreen Power
• Chemical filling kiosk: Northern Pump Suppliers
• Chemical storage tanks: Forbes Technologies Ltd
• PF Detect dual contained hoses: FT Water Treatment
• DI pipework: Saint Gobain PAM UK
• Heat tracing & lagging: Jade Insulation
• Heating & ventilation: Air Technology Systems Ltd
• Lightning protection: Bailey International

New buildings & compound

Two new buildings were constructed:

1. The chemical building to store chemicals and dosing equipment.
2. The control building to house the static mixer, water quality monitors and main MCC.

[caption id="attachment_14282" align="alignnone" width="1200"] Chemical delivery area & carbon dioxide vessels - Courtesy of Ward & Burke[/caption]

Despite their differences in size, both buildings were constructed with an in situ RC base, with precast concrete columns, beams and wall panels. Purlins in the chemical building were precast too. The precast concrete avenue was first explored due to a requirement to construct buildings with a 60 year design life. Due to the nature of the off-gassing of sodium hypochlorite degrading metals over time, a steel portal frame construction was not an option. Since concrete walls were required for satisfying security ratings anyway, the precast concrete route was a perfect option. An additional benefit of this design for manufacturing and assembly (DfMA) approach was the considerable reduction of on-site construction risks related to working at height and handling of tall and heavy rebar cages. Other notable benefits included fewer concrete wagons on local roads, less material waste and reduced construction time.

Both buildings were clad with insulated Kingspan cladding to the planning permission colour and security rated doors supplied by Bradbury were installed. Heating and ventilation systems in all rooms were designed and installed by Air Technology Systems, with duty/standby fans in rooms with critical ventilation requirements. Finally, lightning protection systems were installed by Bailey International on all buildings, as well as other plant at risk on site.

A fenced slab was constructed for all the carbon dioxide equipment in proximity to the road for deliveries. Outside the chemical building is the chemical delivery area for the sodium hypochlorite and hydroxide. It features a security rated fill kiosk with connections for each of the tanks, a tepid water emergency shower and blind tank with an interlock valve. This valve’s purpose is to isolate the rainwater drainage system during a tanker discharge to contain any spill. The valve must be shut to release a key to open to the fill kiosk door to prevent human error.

Electrical

A new MCC with ICA section was supplied by Motrol (now Profitec) in collaboration with Enisca Ltd completing the electrical installation. Said MCC was housed in a dedicated room in the control building with a trench beneath it, cast in situ during base construction allowing for easy and tidy bottom cable entry. A remote IO (RIO) panel was installed in the chemical building with an HMI to monitor and control the process.

[caption id="attachment_14280" align="alignnone" width="1200"] New MCC - Courtesy of Ward & Burke[/caption]

With Anglian Water owning the pumping station feeding Sundon, there was a focus on ensuring raw signals of reservoir level were provided to both water authorities. In contrast, any other interfaces were minimised as far as reasonably practicable to expedite any future maintenance or works that would have previously required both company’s inputs.

Solar panels were installed to provide power to the MCC at all times, with any surplus required made up by mains power. In the event of a mains power outage, an auto-changeover in the MCC will call on the permanent generator to kick in to keep the site running until mains power is restored.

Commissioning

As of August 2024, the plant is in its commissioning phase, with chemical dosing being brought online after extensive offline testing. In the coming months, Affinity Water will focus on fine-tuning and optimising the plant’s chemical usage to meet network requirements.

In line with the Scottish Government’s move towards a Low Carbon Economy, Scottish Water has committed to achieving its strategic ambition of ‘Beyond Net Zero’ by 2040. Driven by this ambition, the public utility tasked its commercial subsidiary, Scottish Water Horizons, to review its asset base to identify and accelerate opportunities for renewable energy generation. Previously, most hydropower projects developed within the water industry have focused on raw and clean water sources. By adopting a different perspective, Scottish Water Horizons identified an opportunity to generate green energy via hydropower at a wastewater treatment works (WwTW).

Background to the project

This pioneering project will see Scottish Water harness hydropower from wastewater and the scheme is:

• The first mid-process wastewater hydropower install in the UK that optimises energy potential.
• The first containerised hydropower install in Scotland which not only reduces construction carbon emissions; it also saves time and costs. This solution can also be replicated on other wastewater assets as well as other applications including raw and treated water.

Design

Hydropower opportunities across Scottish Water’s estate are identified and developed through a combination of data analytics techniques (flow and pressure data in particular), GIS analysis, whilst also tapping into the first-hand knowledge of local system operators.

One of the sites with hydropower potential that emerged from this exercise was Hamilton WwTW in South Lanarkshire, near the city of Glasgow. Hamilton WwTW is a fairly typical site with the flow passing through initial 6mm inlet screening, grit removal, primary settlement, aeration tanks and final settlement unit operations before returning to the local water course which is the River Clyde.

The aeration tanks which are in operation are relatively new to the site, having been installed approximately 17 years ago with the original aeration lanes now treated as a redundant asset.

The new aeration lanes were built above-ground and therefore sit proud of the rest of the works.

[caption id="attachment_10115" align="alignnone" width="1200"] Above-ground aeration lanes - Courtesy of Scottish Water Horizons[/caption]

Hamilton WwTW serves a population of around 57,000 people and therefore has a high electrical consumption. Thus, any electricity generated from the hydro turbine can be utilised on site, helping to green Scottish Water operations and reduce reliance on grid electricity.

After an initial desk-based investigation into the feasibility of the site, on-site operators at Hamilton WwTW were engaged, with loggers deployed to further understand the flow and head parameters. It was determined that capturing the flow between the new aeration tanks and the final settlement would provide 10m of head which is further extended to 11.5m by use of a draft tube, and an average annual flow of 432 l/s.

Through a process of data verification, site surveys, and extensive liaison with both internal and external stakeholders, a clear opportunity was identified to develop a 48 kW hydropower scheme.

Turbine location within the WwTW

By installing the turbine mid-process this allowed Scottish Water Horizons to capture not only the flows through the WwTW but also harness the recirculating flows. This makes the turbine an integral part of the works and therefore every attempt was made to incorporate safeguards to ensure the turbine will not conflict with the overall site operations. This has been addressed by adopting several measures:

• A level sensor has been installed at the aeration tanks to ensure that the turbine does not cause the tanks to either empty or overflow.
• A bypass valve has been designed in which, should the flow be too high for the turbine to function efficiently and safely, the flow will be redirected and continue onto the final settlement tanks uninterrupted. This bypass valve also allows for safe maintenance of the system.
• If a mechanical problem was to occur on the turbine system, the bypass valve will open automatically, therefore imposing no conflict to site operations.

A secondary benefit was realised;  when the effluent passes through the turbine it becomes aerated, thus aiding the treatment process. As a result, the quantity of air required to be used for aeration can be reduced on the existing asset which further reduces the energy consumption on site.

[caption id="attachment_10495" align="alignnone" width="1200"] (left) The original flume and (right) container is on site with thrust restraint in progress on the left - Courtesy of Scottish Water Horizons[/caption]

Varying flow rates

As Hamilton WwTW is an operational site the flow rates are largely influenced by the level of rain in the catchment. Loggers captured the average annual flow rate to be 432 l/s.

The section of the works where the turbine is located is subject to large flow fluctuations varying from 300 l/s to 1200 l/s. This prompted the incorporation of a bleed valve at the inlet to the pipework arrangement which allows excess flows to be diverted away from the turbine, allowing the turbine to continue generating at exceptionally high flow rates.

Effluent considerations

As this is Scottish Water’s first hydropower scheme to be installed on a wastewater asset, there was the aspect of using effluent to be considered. By using the flow from the gravity return pipe at the aeration tank, the effluent had been through several treatment processes such as screening, grit removal and primary settlement to remove the bulk of solids as well as through the aeration process itself. At this point in the treatment process the reactivated sludge and water combination will be denser than fully treated effluent therefore may boost the turbines power output.

Scottish Water Horizons had to consider that finer particles may find their way into the system, and it was important to understand the implications this could have on the turbine and use this knowledge to select a suitable turbine design choice.

Turbine design choice

A Crossflow turbine was selected as the most suitable machine for Hamilton WwTW.

[caption id="attachment_10110" align="alignnone" width="1200"] Crossflow turbine from CINK Hydro-Energy k.s. - Courtesy of Scottish Water Horizons[/caption]

This cost-efficient turbine solution allows for dependable operation over a wide range of flows whilst maintaining efficiency^[1]. The turbine is also capable of ‘self-cleaning’ to an extent. If debris becomes stuck on the blades, it is typically dislodged by either the outflowing water or the centrifugal force generated by the turbine rotating. This addressed concerns about using effluent to power the turbine as the maintenance risk of the turbine becoming clogged with debris such as rags has been partially mitigated against.

A Crossflow design turbine also requires lower maintenance due to the simplicity of the system with only three moving parts. It is typically only the rotor that has a bespoke design to match the hydraulic profile of the application.

Hamilton WwTW Hydropower: Supply chain - key participants

• Design & project delivery: FES Support Services Ltd
• Specialist hydro consultant: Glen Hydro
• Civil works: Calforth Construction Ltd
• Mechanical installation: Dustacco Engineering Ltd
• Turbine supplier: CINK Hydro-Energy k.s.
• Valves: Glenfield Invicta

Construction work

Construction started on site in April 2023 with the removal of the existing flume taking place in May. A temporary flume was then installed to allow the effluent to flow past the working area. This mitigated the risk of contractors encountering effluent when working.

[caption id="attachment_10112" align="alignnone" width="1200"] (left) Old flume removal and (right) temporary flume in situ - Courtesy of Scottish Water Horizons[/caption]

Works then started on the concrete sub-structure and tail-race upon which the turbine house is installed.

The existing pipework was retrofitted with a bespoke ‘Y’ section of pipe along with relevant bypass and bleed valves. A level sensor was installed at the outlet to the aeration tanks which communicates with the turbine control system adjusting the valves and turbine guide vanes to match the flow conditions.

A pre-fabricated containerised turbine house

Once the concrete foundations were completed the containerised turbine house was then delivered to site; the pre-fabricated unit having been assembled by CINK at their factory.

The container was crane lifted into place. Adopting off-site construction methods allowed Scottish Water to reduce its carbon footprint associated with construction and condensed time on site.

Once the container was in situ and all pipework installed, testing and commissioning began. This included pipeline stress tests and multiple mechanical and electrical tests on the equipment to prove the system functioned as the manufacturer intended.

This construction approach has an eye on standardisation which could lead to wide ranging applications within Scottish Water’s assets based on the lean principle of ‘minimum viable product’. This includes minimising capital and carbon expenditure whilst maximising energy recovery.

[caption id="attachment_10111" align="alignnone" width="1200"] Bespoke ‘Y’ piece in situ showing bypass and manual isolation valves - Courtesy of Scottish Water Horizons[/caption]

Conclusion

The system was connected to the grid (G99 accreditation) at the end of November 2023 and is now generating on site, providing green electricity to the works. This helps to not only reduce the reliance on importing electricity from the grid but also reduces on-site energy costs.

The scheme is estimated to generate 420,000 kWh of green electricity per year which will offset around 14% of the site’s annual energy demand. It is also projected to save around 64 tonnes of carbon emissions each year.

Re-using existing land and assets also meant a reduction in carbon emissions during construction, supporting Scottish Water’s strategic ambition of going ‘Beyond Net Zero’.

From conception to starting on site, the Hamilton Hydropower project took around 21 months, with a construction period lasting a further nine months. This shows the efficiency of the containerised methodology which will enable future similar schemes to be delivered at pace.

This project has demonstrated that hydropower generation can be achieved on a wastewater asset and can offset the heavy cost of electricity on wastewater sites. There are many similar opportunities available across other wastewater sites and other industries such as petrochemical and outfalls from power plants. This would drive down the carbon associated with capital investment and operational activities.

References

^[1] CINK Hydro Energy, “Crossflow Turbines,” [Online]. Available: https://www.cink-hydro-energy.com/crossflow-turbines.

Goddards Green Wastewater Treatment Works (WwTW) is a Sludge Treatment Centre (STC) located near Burgess Hill in West Sussex. The catchment serves the towns of Burgess Hill, Hassocks, Hurstpierpoint and surrounding villages, providing for 54,789 people. The project implements an innovative approach to mitigate the likely odour from the processes at the WwTW to prevent any potential impact on the planned Northern Arc development in the surrounding area.  To enable the new development to proceed in the surroundings of the WwTW, there was a planning requirement for the odour of the WwTW to be limited to 1.5 OUE/m³ odour contour.

Existing works

The main components of the WwTW consist of inlet works (screening and grit removal), storm tanks, a primary settlement tank, anoxic tanks, oxidation ditches, returned activated sludge pumping station, final settlement tanks and disc filters. Treated final effluent is discharged into the River Adur East. Besides indigenous sludge, the STC also processes imported sludge (liquid and cake). The main components of the STC consist of sludge reception and storage facilities, screening and screened sludge storage, drum thickening, anaerobic digestion, digested sludge storage tanks, centrifuge dewatering and cake storage bays. Liquors from the sludge treatment process are treated in a cyclic activated sludge system (CASS) plant before being returned to the WwTW. Hot water for digester heating is produced by burning biogas either in hot water boilers or in the 800 kW CHP (combined heat and power) engine.

Northern Arc development

The Burgess Hill Northern Arc is a development in the southern part of the parish between Ansty and Burgess Hill. The project spans a period of over 15 years. Once complete it will provide 3500 houses with 30% affordable housing, four hectares of employment land, a community centre, two primary schools and a secondary school. The project is being run by a government agency, Homes England, and is a strategic development which is part of the Mid-Sussex District Council Development Plan. Southern Water’s project at Goddards Green WwTW aims to deliver a range of odour mitigation improvement measures; removing barriers to the housing development at the Northern Arc. Southern Water have committed to delivering a scheme that achieves a 1.5 OUE/m³ limit for a boundary as defined by the odour contour image (see below). [caption id="" align="alignnone" width="1200"] Odour model emission contours for selected solution - Google Maps[/caption]

Project synopsis

This scheme is being delivered in two phases. Phase 1 was delivered in May 2020 with the installation of a new odour control unit and odour covers to reduce odour emissions at the site. Phase 2 comprises the installation of a thermal hydrolysis plant (THP) with associated equipment, provision of a cake reception building to control odour during deliveries and a cake barn to protect the product from the weather. The THP will reduce odour emissions from the sludge treatment process, improve sludge quality and enhance gas yields from the digesters. The outcome will mean that new housing developments in the area will be better protected from odour emissions. Output of the THP process will provide enhanced treated sludge for farmers to spread to land as well as greater green energy production from the existing CHP engine, reducing the site’s need to draw power from the National Grid.

Funding

Mid Sussex District Council, in collaboration with Southern Water and West Sussex County Council, successfully secured government funding of £10.54m under the Local Enterprise Partnership (LEP) Growth Deal (Programme) and the Homes England Housing Infrastructure Fund. Southern Water has invested an additional £17m to deliver the odour and sludge treatment upgrade project.

Phase 1 scope

Phase 1 was delivered in May 2020 and comprised the installation of a new odour control unit and odour covers to reduce odour emissions. High odour emitting existing asset sources as identified from the odour model were covered. These assets included the primary settlement tanks, liquid sludge reception tank and oxidation ditch distribution chamber. [caption id="" align="alignnone" width="1200"] Phase 1 odour control unit from ERG (Air Pollution Control) Ltd - Courtesy of Galliford Try[/caption]

Phase 2 scope

The current practice of blending imported cake with indigenous liquid sludge has been retained. The blended sludge is then screened using existing strain presses and thickened using existing drum thickeners. New centrifuge feed pumps have been installed to feed thickened sludge to the existing centrifuges - these were previously used for digested sludge dewatering but have been repurposed to produce raw cake for the new THP process. Conveyors transfer the dewatered sludge to duty/standby cake hopper pumps which deliver raw cake to a 130m³ cake storage silo. Cake from the silo is discharged to duty/standby hopper pumps where dilution water is added to achieve a target dry solids content of 16.5% DS in the THP feed sludge. A single Cambi B2-4 THP stream is provided, capable of processing up to 24 tDS/d. The first vessel in the THP is the pulper which homogenises and pre-heats the sludge. Pre-heated sludge from the pulper is fed to the reactors in a sequential process that ensures sealed batches of sludge in each reactor. Steam is injected to raise the temperature of the sludge in the reactor to 165°C at a pressure of about 6 bar. At the end of the hydrolysis period, hydrolysed sludge is discharged from the reactor to the flash tank, which operates at about 0.2 bar. The sudden drop in pressure ruptures any remaining biological cells in the sludge. Flash steam generated by the pressure drop is returned to the pulper to preheat the incoming sludge. Thermal hydrolysis of sludge generates a highly odorous off-gas (referred to as ‘process gas’) which is continuously extracted from the pulper and passed through a cooler, with condensate from the cooler gravitating back into the pulper. Non-condensable gases pass from the cooler to the process gas unit where they are pressurised and injected into the digester feed lines (downstream of the sludge coolers). [caption id="" align="alignnone" width="1200"] (top & bottom left) BIM models showing the THP plant area and (bottom right) Phase 2 THP area looking north-west - Courtesy of Galliford Try[/caption] Digester feed pumps are used to pump hydrolysed sludge from the flash tank to the digesters. Disinfected process water is added to the suction side of the digester feed pumps to dilute the hydrolysed sludge to achieve the target digester feed sludge dry solids content. Diluted hydrolysed sludge is combined with recirculated digested sludge before being cooled while passing to the two existing digesters. The new digested sludge dewatering stage comprises new duty/standby centrifuges and an associated polymer preparation/dosing system. Enhanced treated cake is conveyed to the new cake barn. There is an existing 800 kW CHP engine. High grade waste heat from the CHP engine exhaust gas is recovered in a new composite steam boiler. Low grade heat is also recovered from the CHP engine jacket cooling water and used to pre-heat the boiler feed water. These heat recovery systems help to minimise the consumption of supplementary fuel (biogas or diesel) required to meet the THP steam demand. A new final effluent (FE) pumping station supplies cooling water to the sludge coolers. All applications requiring dilution or carrier water are supplied with filtered FE that has been UV-disinfected, ensuring that an enhanced treated cake is produced. The schematic diagram below shows the process stages with the additional odour reduction measures undertaken in Phase 1 (in green) and the main changes to the sludge treatment process for Phase 2 (in orange). [caption id="" align="alignnone" width="1200"] Schematic showing the process stages - Phase 1: Additional odour reduction measures (green) and, Phase 2: The main changes to the sludge treatment process (orange)[/caption]

Design

Galliford Try’s (GT) inhouse engineering team based in Stafford, have undertaken and coordinated the detailed design process, supplemented by specialist suppliers. Atkins were also contracted to undertake the civil engineering design on behalf of Galliford Try. Southern Water carried out the process design. Regular design coordination meetings have been held between all parties to ensure a coordinated approach to the design. 3D and Building Information Modelling (BIM) modelling has been used throughout the scheme to coordinate and manage the design process. Viewpoint for Projects was used as the project’s cloud-based collaboration tool throughout. The use of 3D modelling was particularly useful in spotting clashes and to enable early process plant operator involvement and feedback. This has been beneficial in highlighting access and maintenance issues, prior to construction work beginning. [caption id="" align="alignnone" width="1200"] View looking at Serpecon conveyors and pre-THP silo feed pumps - Courtesy of Galliford Try[/caption]

Goddards Green WwTW - Supply chain: key participants

• Client: Southern Water
• Main contractor: Galliford Try
• Outline design: Stantec UK
• Detailed design: Atkins
• THP plant: Cambi AS
• Cake reception building/cake barn: APT Engineering Ltd
• Imported cake reception silo: Saxlund International Ltd
• Steam boiler package: Dunphy Combustion Ltd
• Groundworks drainage: TC Jones Groundworks
• Concrete cutting/diamond drilling: Castle & Pryor Ltd
• Workforce supply: Hercules Site Services
• Workforce supply: Fortel Group
• Kiosks: Morgan Marine
• UV Treatment: Xylem Water Solutions - Wedeco
• FE booster set & portable water booster set: KGN Pillinger
• Pre-THP centrifuge screw conveyors: Serpecon Ltd
• Vehicle exhaust: Air Technology Systems
• CHP exhaust flue: Rung Heating
• CHP pipework modifications: Edina UK Ltd
• MCCs: Blackburn Starling Ltd
• LV Switchboard/MCC 10: MCS Control Systems Ltd
• Final dewatering units & access platform: Alfa Laval
• Biogas booster system: DSL Building Services
• Final dewatering polymer system (powder): Richard Alan Engineering
• Mechanical/electrical installation: Field Systems Design Ltd
• Submersible centrifugal pumps: Xylem Water Solutions - Flygt Pumps
• Concrete: Hanson Aggregates
• Muck-away: Hesus UK Ltd
• Sub-base materials: Day Group Ltd
• Drainage materials: Jewson Civils Frazer
• Heat exchangers: HRS Heat Exchangers Ltd
• Reinforcement: Hy-ten Ltd
• Pumps: P&M Pumps Ltd
• Draeger control units: Draeger Safety UK Ltd
• DS monitors: Flow Technology Services Ltd
• Valves & instruments: ABB Ltd
• Valves & instruments: Siemens
• Valves & instruments: Glenfield Invicta Ltd
• Valves & instruments: Xylem Water Solutions
• Instrumentation: IFM Electronic Ltd
• Performance monitoring & operational support: PBJ Engineering Services Ltd
• Supply of steam boiler water treatment chemicals: EB Critical Engineering Services Ltd

Construction

Construction of the Phase 2 works commenced in the spring of 2021 with the clearing of existing cake bays and the construction of new openings to the existing structure. Castle & Pryor Ltd undertook the work to create new openings, utilising track saws and robotic demolition techniques. The decision for this technique was taken to minimise the health and safety risks associated with more traditional demolition methods. Once the new openings were formed, Galliford Try went on to construct new foundations to accommodate the new process units. Hercules Site Services and Fortel Group were engaged to supply the necessary skilled workforce to work directly under Galliford Try’s own control. [caption id="" align="alignnone" width="1200"] THP area looking north east - Courtesy of Galliford Try[/caption] This approach has proved successful throughout the first three years of the current programming AMP7 period (2020-2025) as it affords greater flexibility and control. Wherever possible the existing structure was retained and re-purposed to speed up the construction, and to reduce overall costs and the carbon footprint of the scheme. Before reusing the foundations, detailed in situ and pull-out testing was undertaken. The Cambi B2 unit and associated ancillary equipment are all located within the original cake drying beds. In parallel to the cake bay works, construction was undertaken within the existing plant to facilitate the installation of the other process units. This required close collaborative working between the contractor and the onsite operations team, to minimise disruption to day-to-day activities and the running of the treatment plant. Throughout the scheme, this close cooperation has continued, ensuring all stakeholders are kept up to date with activities and progress. Field Systems Design Ltd was engaged by Galliford Try to undertake the detailed design and installation of the complex interconnecting cabling and mechanical piping systems throughout the scheme. This included high voltage cabling and transformer upgrade works, low voltage power cables, signal cables and fibre optic networks. The scope of the mechanical supply included all piping and access arrangements, steam lines and pressure networks. In total, 48 kilometres of cable, 2.5 kilometres of pipes and associated support systems have been installed. These systems are predominantly placed above ground for ease of future maintenance, and to mitigate the risks of burying equipment within an already congested plant. Collaborative planning and design management have been undertaken between the site team and Galliford Try, to ensure the smooth flow of the mechanical and electrical phase of the works. Overall, the scheme is now (June 2023) approaching 200,000 hours worked without any lost time or other significant incidents. [caption id="" align="alignnone" width="1200"] View looking north-east towards the Saxlund pre-THP cake silo - Courtesy of Galliford Try[/caption]

Risk management

De-risking of the construction phase was considered key to the delivery of project. To achieve this, regular risk reviews and workshops have been undertaken throughout with significant benefits being realised. For example, the project team identified early on that Southern Water were best placed to deliver the improvements to the existing on site gas storage facility and flaring arrangement in advance of the main Phase 2 works starting. It also identified the need to procure longer lead-in items in advance of the main contract award being in place. This meant that the Cambi B2 unit, Dunphy boiler building, and Saxlund pre-THP silo were all procured under an early works agreement. This joined up approach to risk management meant that the scheme was able to rapidly adapt to the challenges posed by the worldwide semi-conductor shortage. The shortage affected the project, due to the multiple control panels and complex equipment being procured. The team agreed to utilise refurbished parts within the panels to enable off-site fabrication and factory testing to take place. These refurbished parts will then be replaced on site once the delayed components become available, which has saved many weeks of further delay.

Stakeholder management

As Southern Water had obtained funding from Homes England to undertake the odour reduction scheme at Goddards Green, they were identified by the project team as key stakeholders. It was therefore essential that they were kept informed of progress throughout the delivery phase. To achieve this, the project team held regular site tours and liaison meetings with the representatives of Homes England and the local council members, fielding questions and explaining the process and progress on site. [caption id="" align="alignnone" width="1200"] (top left) BIM model showing the steam boiler system, (top right) the rear of the steam boiler building and emissions stack, (bottom left) the front of the steam boiler building and emissions stack, and (bottom right) the Dunpy boiler package - Courtesy of Galliford Try[/caption]

DfMA - Design for Manufacture and Assembly

Design collaboration from the earliest stages of the project has provided tangible benefits in terms of costs, speed, sustainability of the project, and health and safety benefits. These small but practical examples are a core part of Galliford Try’s sustainable growth strategy. Galliford Try’s installation of the steam boiler at Goddards Green WwTW using an off-site solution, has reduced construction time on site as well as bringing health, safety, carbon, and community benefits. Manufactured and installed by Dunphy, the modularised plant room was fully fired and tested off site before delivery in two days using DfMA to allow modular construction of the building and plant, reducing the amount of time spent on site during the installation. The reduction of time spent working on site also has health and safety benefits, as more work is completed in a safer factory setting, and many of the hazards of a live site can be reduced or avoided.

Conclusion

At the time of writing (June 2023) the Goddards Green WwTW project’s construction phase is nearing completion and commissioning works have commenced on ancillary equipment. Beneficial use is currently forecast for the end of 2023. The use of THP is the first of its kind within Southern Water. Therefore, despite being utilised to manage odour, it will also alter the way the sludge is managed on site, contributing to several economic and environmental benefits.

Northern Ireland Water (NI Water) is one of the first public sector organisations to install a state-of-the-art battery energy storage system (BESS). The 4.1 MW battery helps store surplus energy from on-site solar panels at one of NI’s largest water treatment plants; Dunore Point, Antrim. The battery has a 5.6 MWh (megawatt hour) total capacity which helps to store surplus energy generated from approximately 24,000 solar panels. The battery means that during periods of low customer demand, NI Water can store this surplus renewable energy to use later during peak times. The company can therefore power its operations at a lower cost and keep water flowing. This is a vital step in NI Water’s journey to net zero, balancing supply and demand on the local grid, providing improved site resilience and security of water supply.

Primary drivers

The purpose and drivers for this project were as follows:

• Contribute to NI Water’s 2050 energy strategy and strategic objectives/priorities.
• Generating additional revenue.
• Reducing impact of price volatility.
• Increasing the use of renewable energy to mitigate the effects of climate change.
• Reducing emissions related to the use of fossil fuels/toward zero carbon.
• Facilitating opportunities to harness further renewable technology and market participation which NIW may take advantage of in the future.
• Improve resilience of NI Water’s energy supply to protect and serve our customers.

[caption id="attachment_13147" align="alignnone" width="1200"] (top left) Installation of precast concrete troughs and concrete slabs, (bottom left & top right) installation of BESS cubes, (bottom right) installation of the transformers - Courtesy of GRAHAM Construction[/caption]

Early Contractor Involvement (ECI)

Arup was appointed as Project Manager and technical advisor.

Contractor GRAHAM was appointed by NI Water to complete an Early Contractor Involvement (ECI) stage. GRAHAM provided multi-disciplinary detailed design, project and supply chain management and all civil engineering and MEICA works for the contract from start to completion. The ECI phase allowed GRAHAM to consider supply chain partners, complete site surveys, accurate scheme costing and detailed design to meet project objectives which enabled an earliest programme completion date to meet DS3 Service Delivery deadline of April 2024.

Arup provided techno-economic modelling to support business case development and viability of the project. Collaborative working between the project partners via ECI enabled a smooth transition into the construction stage where Arup was NEC Project Manager and Supervisor for the works. The proactive approach from the project team led to enhanced collaboration, innovation, value, efficiency and reduced whole life costs for the project.

Key risks

Numerous strategic risks associated with the delivery of the energy transition were identified, along with project-specific risks such as battery procurement and delivery, as well as site-specific risk. These included interface with stakeholders including NIW Alpha that operates the vital Water Treatment Works. The impacts of these risks through stakeholder engagement and early design development and devised appropriate mitigation measures (e.g. temporary and permanent security arrangements, early engagement with Northern Ireland Electricity (NIE) Networks, HV electrical works design etc). During ECI stage a detailed costed risk register was prepared and completed by the project team. This approach ensured cost certainty and accurate budgeting.

[caption id="attachment_13148" align="alignnone" width="1200"] (main image) Site overview and (inset) site layout - Courtesy of NI Water and GRAHAM Construction[/caption]

Some of the key risks associated with the project are listed below:

Grid code compliance: This was the first large scale battery connected at 33kV in Northern Ireland which presented a complex set of challenges. Ensuring grid compatibility and integration with existing infrastructure was critical, and this involved coordination with protection and control systems to maintain stability and safety.

The design phase required careful site selection and the development of a robust integration plan with current grid components. Regulatory hurdles included ensuring compliance with stringent safety and environmental standards.

Operationally, maintaining long-term reliability and establishing effective monitoring systems was essential. Additionally, integrating with renewable energy sources required managing intermittency and balancing real-time supply and demand.

Finally, community and stakeholder engagement with parties such as Northern Ireland Electricity, SONI and Grid Beyond was crucial for addressing public concerns and aligning interests across utilities, regulators, and local authorities. Each of these factors demanded a coordinated, multidisciplinary approach to ensure successful implementation.

[caption id="attachment_13145" align="alignnone" width="1200"] (left) BESS cubes and (right) inside of BESS cubes and gridstack layout - Courtesy of NI Water and GRAHAM Construction[/caption]

Security & NI Water Alpha requirements: The WTW is critical to NI’s water supply, and it was essential that the new installation integrated fully with the existing installation. As a section of this site was to be re-purposed for the construction of the access road it was crucial to involve NIW Alpha from the outset to ensure that they were aware of the works and how to ensure the site security and operation were unaffected during construction. Key tasks, such as installing new security fencing, implementing CCTV, and working near critical assets, were coordinated with NIW Alpha to prevent any disruption or delay.

Fire mitigation: This BESS was the first installation for this council area. It was critical that the BESS met all legislation and mitigation measures to meet the requirements noted below:

• Identify the fire hazards and risks associated with the premises, materials, processes and materials.
• Identify the people at risk including those who may be especially at risk.
• Demonstrate that the risks will be removed and reduced as far as reasonably practicable.
• Put in place general fire precautions to deal with any remaining risks.
• Set out appropriate emergency procedures in the event of fire.
• Set out additional preventative and protective measures if flammable or explosive substances are to be used or stored on the premises.
• Make provision for fire safety training for staff.
• Set out arrangements for logging significant actions and incidents.
• Set out proposals for reviewing the risk assessment periodically or after significant changes in the workforce.

To align with the information above a Fire Risk and Mitigation Strategy was developed alongside Fluence (the BESS provider) to highlight how this would be managed. A copy of this was provided to Northern Ireland Fire and Rescue Service to ensure they are aware of the requirements if an event was to ever occur.

[caption id="attachment_13144" align="alignnone" width="1200"] Dunore Point BESS completion - Courtesy of NI Water and GRAHAM Construction[/caption]

BESS Costs: During the early stages of the project there were unforeseen pressures across the globe on the price and availability of batteries and commodities. This was driven by shortages in battery supply vs demand, fast rising inflation, rising energy costs, and lithium carbonate, electrolyte, copper, steel, and other energy storage materials being in a volatile state which drove shorter offer validity periods and price fluctuation.

On review of the battery market conditions over the 2021, LFP cathode prices rose around 150% and between June and October 2022, these prices rose around 10%. Therefore, given the external market conditions appropriate measures had to be taken to ensure that the project was viable which included monitoring exchange rates, monitoring price of materials etc. An NEC4 ECC Option E contract was selected, which allowed the supply chain to progress rapidly and not price high levels of risk. These risks were managed well, and in turn the battery was made operational on time to meet DS3 Service Delivery and within budget.

Future-proofing: It was necessary to include consideration in business case coordination with a future solar farm in adjacent land. Therefore, as mitigation techno-economic modelling of this longer-term scenario was undertaken to ensure its feasibility and to future-proof NIW’s wider site plan, ensuring the site is capable for the addition of future solar.

BESS revenue

The BESS will provide revenue and cost savings through a diverse ‘revenue stack’:

DS3 Services

EirGrid and SONI procure system services under the Delivering a Secure Sustainable Electricity System (DS3) programme. These services help to balance the electricity system in real-time, keeping the system secure and stable. Participants in a service are required to use or supply power in response to a grid signal like frequency. The BESS bids for contracts to provide these services and is paid for each hour it is available to provide the service.

Energy Arbitrage

Energy arbitrage is the process of buying energy at a lower price and selling it at a higher price, with revenue generated by the difference in price. The BESS has two means to ‘buy’ energy – charging from the grid or from the on-site solar PV. The BESS also has two means to ‘sell’ energy – supplying the grid or supplying the Dunore WTW site. Excess solar PV generation is the cheapest form of energy the BESS can charge with, while the cost savings of reducing Dunore WTW’s grid import are greater than price received from selling to the grid.

Capacity Market

The battery system enters a contract to commit its capacity to provide security of supply to the electricity system. The BESS is available to provide energy when there is a system stress event, helping to safeguard against a potential blackout. These events are very rare!

The operation of the BESS is optimised to maximise revenue and site cost savings.

The BESS is operated by an aggregator, whose AI-driven platform optimises when to charge, discharge and engage in DS3 services to maximise revenue and site cost savings. DS3 services are expected to be the largest revenue stream, followed by energy arbitrage. Capacity market revenues form a smaller part of the ‘revenue stack’.

[caption id="attachment_13141" align="alignnone" width="1200"] Dunore Point BESS completion - Courtesy of NI Water and GRAHAM Construction[/caption]

Dunore Point BESS Project: Supply chain - key participants

As principal contractor, GRAHAM had overall responsibility to deliver the project on time and within budget, which they succeeded in doing by working collaboratively with NI Water, Project Manager Arup, suppliers and subcontractors to identify and plan for key project milestones.

Doran Consulting provided civil, structural and geotechnical design services, including the initial enabling and investigatory works carried out at the Early Contractor Involvement (ECI) stage, as well as the detailed design for construction. Scotts Electrical Services were responsible for designing and delivering the HV electrical works alongside Fluence who were responsible for designing and delivering the BESS.

• Project management: Arup
• Principal designer/contractor: Graham Construction
• Civil design: Doran Consulting
• HV designer & HV/LV contractor: Scotts Electrical Services
• BESS supplier & designer: Fluence
• Transformers: GBE Power

[caption id="attachment_13143" align="alignnone" width="1200"] Dunore Point BESS Completion – Courtesy of NI Water and GRAHAMs Construction[/caption]

Collaboration

The success of this project was largely attributed to the outstanding collaboration among all the project team. From the beginning, everyone was dedicated to maintaining clear and open lines of communication. Regular check-ins and collaborative tools kept everyone on the same page, enabling us to address issues promptly and adapt to changes when required. This included not only the project team but external parties also including SONI and Northern Ireland Electricity. As a result, the project was completed on time, within budget, and to a high standard of quality, demonstrating the power of effective teamwork.

Outcome

Through collaboration with key stakeholders, including NIE and SONI, NI Water, Arup, GRAHAM, and the broader supply chain successfully tackled challenging obstacles. Efforts by all resulted in the delivery of a sustainable, cutting-edge battery system that meets stringent requirements. This achievement helps to position NI Water to play a crucial role in advancing the green economy and ensuring climate resilience for their customers.

In recent years, the village of Boherbue in north-west Cork has undergone considerable expansion, resulting in increased demand for housing. This growth has presented challenges, particularly for the existing wastewater treatment facility, which has struggled to cope with the surge in population. Additionally, the plant has fallen short of the Environmental Protection Agency’s treatment standards, underscoring the pressing need for an upgrade. Of particular concern is the discharge of treated wastewater into the River Brogeen, a protected conservation area that serves as the habitat for the freshwater pearl mussel. In collaboration with Uisce Éireann (Irish Water) and Cork County Council, a comprehensive project has been undertaken to modernise and enhance the capacity of the treatment plant. This initiative not only addresses the immediate needs of Boherbue’s growing community but also ensures compliance with environmental regulations.

Early Contractor Involvement

The project, delivered under the innovative Early Contractor Involvement (ECI) framework, aimed to address the overloaded and outdated infrastructure while ensuring compliance with regulatory standards and meeting the evolving needs of the community. The innovation in this project lies in its multifaceted approach to efficiently treat wastewater, reduce carbon emissions, and protect natural ecosystems.

Leveraging the ECI framework allowed for the integration of innovative solutions such as solar energy, natural sludge drying reed beds, and the preservation of existing constructed wetlands for stormwater overflow. This innovative approach not only sets a new standard for sustainable wastewater treatment but also ensures long-term environmental benefits for Boherbue and its natural surroundings.

[caption id="attachment_16527" align="alignnone" width="1200"] Google Earth image of Boherbue[/caption]

The scope of works for the upgraded facility included:

1. A new inlet works.
2. A stormwater storage tank.
3. Biological treatment processes.
4. Tertiary solids removal cloth filtration system.
5. Sludge drying reed beds.

A description of these key features follows.

New inlet works

An inlet works with fine screening to 6mm in 2D and a manual bypass screen to 19mm with a stone trap upstream of the screens were installed. The screens were designed to cater for the Phase 2 Formula A flows of 23.2 l/s screens are to be designed to cope with a minimum of 150% of the design capacity for works under 2,500 PE, i.e. a design capacity of 35 l/s based on the Design Formula A. The hydraulic design of the inlet works was also based on the fine screen(s) being blinded by a minimum factor of 70%. The screen selected by the ECI team was the Definitive Ecology SF/T3 in-tank screw screen, with SDACA (specially designed anti-clog auger) system to ensure compliance with the screening handling requirements.

[caption id="attachment_16526" align="alignnone" width="1200"] Inlet works preliminary treatment - Courtesy of Glanua[/caption]

Stormwater tank

Flows exceeding the plant’s peak design flow, overflow by gravity (weir discharging via overflow screen) to the stormwater holding tank, which has been designed to provide a retention time of two hours for the difference between the Design Formula A and FFT flows plus 40 l/PE for SWO compliance as only 1:7.1 dilutions will be available for the WwTP effluent in the Brogeen River (based on DWF and 95th percentile river flow).

The stormwater holding tank is provided with a Eliquo Hydrok CWF flushing bell in order to automatically clean the tank once the storm flows have abated and the tank has been emptied; which is an innovative approach to this, requiring no energy input.

The CWF Storm Flush system is a highly effective non-powered cleaning system for all stormwater retention tanks, utilising the sewage stormwater for the flushing process thus requiring no additional fresh water. Storm return pumps located in a sump within the storm tank, which will reduce retention of larger volumes of waste and reduce the risk of odour.

Biological treatment processes

The secondary treatment stage for Boherbue includes the following:

• Two anaerobic selector tanks with three separate selector cell volumes.
• Two 624m³ aeration tanks with 109m³ of anoxic volume each for denitrification.
• Settlement provided by two 5m diameter/3.5m side wall depth secondary settlement tanks.

[caption id="attachment_16524" align="alignnone" width="1200"] Secondary aeration treatment - Courtesy of Glanua[/caption]

Each aeration tank is 15.6m length x 5m width x 4m working depth. Aeration is provided to the tanks using a fine bubble diffused aeration system designed to achieve an overall peak standard oxygen transfer rate of 66.15 kgO₂/h (i.e. 33kg O₂/h per cell).

The aeration system comprised three screw blowers from Kaeser Kompressoren operating on a duty/duty/standby basis, with automatic changeover of the standby blower on a time-basis; ensuring equal use of the equipment. Air from the blowers is forwarded to each aeration cell by an air header, which feeds individual branches into the aerobic cells. The diffusers are disc membrane units from Xylem Water Solutions.

Tertiary solids removal systems

Following settlement, secondary treated effluent is passed onto a tertiary solids removal treatment stage for final effluent polishing prior to discharge to the Brogeen River. The TSR process was required in order to ensure compliance with the WwDL ELVs, and in particular with the phosphorus ELV of 0.25mg/l, through coagulation/flocculation and filtration treatment.

[caption id="attachment_16528" align="alignnone" width="1200"] Cloth filter tertiary treatment - Courtesy of Glanua[/caption]

During the design stage and evaluation of the ECI team, the supplier Eliquo Hydrok was found to have the most reliable, energy and cost-efficient equipment that includes both flocculation and filtering stage. The package unit includes a flocculation stage comprised of one stream with two chambers that split into the cloth filters.

Sludge drying reed beds

The implementation of sludge drying reed beds (SDRB), which significantly increases sludge concentration to up to 40% dry solids (DS) after 10 years of operation is a key innovation. This revolutionary approach reduces sludge export volumes by more than tenfold compared to conventional methods, thereby minimising transportation and dewatering costs while substantially reducing the carbon footprint of the Boherbue WwTP. SDRB sludge can also be directly land spread without the need for additional chemical conditioning, further enhancing its environmental benefits.

There are numerous benefits in the inclusion of the sludge drying reed beds vs traditional sludge management practices. These include but are not limited to the following:

• Reduction of carbon footprint of the plant by approximately 45 T over a 10-year period.
• Carbon capture via natural plant growth.
• Up to 25% organic matter removal due to mineralisation.
• Dewatering process completed with zero energy consumption.
• At full design loads, the SDRBs will remove over 49 (No.) 20,000 litre tankers from the road per annum.

[caption id="attachment_16533" align="alignnone" width="1200"] Sludge drying reed beds to process wastewater sludge naturally - Courtesy of Glanua[/caption]

The construction of the sludge drying reed beds (SDRBs) commenced in early February 2023, incorporating earth embankments and precast concrete wall sections for formation. Each cell was meticulously lined to ensure water-tightness, with feed and drainage pipework installed for optimal functionality. Reeds were planted in late April to establish and grow during the summer months, aided by the importation of sludge to promote growth. This comprehensive approach ensures the effectiveness and sustainability of the SDRBs in treating wastewater and reducing the carbon footprint of the Boherbue WwTP.

Solar technology

The use of solar technology underscores the project’s commitment to renewable energy sources, contributing to further reductions in carbon emissions. By leveraging these innovative technologies and practices, the initiative sets a new standard for sustainable wastewater treatment, offering a replicable model for other treatment plants to follow. This holistic approach not only improves operational efficiency but also promotes environmental stewardship, paving the way for a cleaner and more sustainable future in the wastewater sector.

50Kw solar panels from The Low Carbon Energy Company Ltd have been installed which will produce 42,500Kwh of electricity per year. This alone will introduce a carbon saving of 13.7T/CO₂ per year which shows significant savings versus a traditionally built wastewater treatment plant of this kind.

[caption id="attachment_16532" align="alignnone" width="1200"] Solar panels for clean, renewable energy - Courtesy of Glanua[/caption]

Reuse of constructed wetlands

The integration of the existing constructed wetlands into the wastewater treatment facility which was core to the design development brought a multitude of benefits, ranging from low operational costs, support for diverse ecosystems as well as sustainable water management. The wetlands improve water quality of streams and rivers in surrounding area creating conditions for aquatic life to thrive, and also create a scenic area in the village, promoting biodiversity and providing a habitat for small animals.

Boherbue WwTP: Supply chain - key participants

• Precast concrete: Glanua Group
• Designers: Jennings O’Donovan & Partners
• Designers: Construct Engineering
• Precast concrete: Shay Murtagh Precast
• Precast concrete: Carlow Tanks
• Precast concrete: FLI Precast Solutions
• Precast concrete: Tracey Concrete
• PLCs & automation: UMAC Systems
• Inlet screens: Definitive Ecology
• Tertiary solids removal cloth filters: Eliquo Hydrok Ltd
• Aeration blowers: Kaeser Kompressoren
• Aeration diffusers: Xylem Water Solutions
• Solar panels: The Low Carbon Energy Company Ltd
• CWF Storm Flush system: Eliquo Hydrok Ltd
• Steel modular buildings: Shanette

[caption id="attachment_16530" align="alignnone" width="1200"] (left) Precast concrete aeration tanks reduced construction time and safety risks and (right) view of final clarifiers and cloth filters - Courtesy of Glanua[/caption]

Innovative construction methods

Throughout the entire design process, Glanua Group and Uisce Éireann’s PMO team evaluated several project aspects such as energy efficiency (BEP), TOTEX costs, and environmental impact.

• Energy efficiency of all motors and equipment (BEP).
• Process and equipment selected on TOTEX costs (including CAPEX, OPEX and capital replacement at end of life).
• The impact to the local environment was carefully assessed for all design options considered during the planning phase.

Modular and off-site construction

Modular/off-site construction was used to reduce the carbon footprint and on-site safety risks, with precast panels and BCAR-compliant steel modular buildings used to promote efficient delivery and enhance safety.

Precast panels were instrumental in constructing the main aeration tank, reducing construction time and mitigating safety risks compared to traditional in situ methods. Precast wall sections were used to separate the sludge drying reed beds sections to reduce the footprint size and again to reduce construction time and safety risks. Throughout the project, precast process tanks were used extensively contributing to streamlined construction processes and improved safety measures.

A BCAR-compliant steel modular building from Shanette was used for the control room, laboratory, and caretaker’s office facilities. This has a significantly lower carbon footprint than that of a conventional block-built structure and in turn reduced health and safety risks significantly during construction due to fabrication being completed before assembly on site.

[caption id="attachment_16529" align="alignnone" width="1200"] Off-site fabrication of steel building, fully assembled as works have been completed (April 2024) - Courtesy of Glanua[/caption]

Sustainability

The construction of the Boherbue Wastewater Treatment Plant is an example of Uisce Éireann and Glanua Group’s commitment to sustainability across various dimensions, including environmental, social, and economic considerations.

The inclusion of sludge drying reed beds demonstrates dedication to environmental sustainability. These beds offer an innovative solution for sludge management, reducing the environmental impact of waste disposal while also providing opportunities for ecological conservation.

By using nature-based solutions to treat and manage sludge, the carbon footprint associated with traditional disposal methods is minimised; thereby mitigating environmental harm. The SDRBs also significantly reduces operational costs, providing a long-term cost-effective solution.

The integration of solar technology underscores the commitment to renewable energy and carbon reduction. By harnessing solar power to supplement the energy needs of the wastewater treatment plant, reliance on fossil fuels is reduced, contributing to the transition towards a more sustainable energy future. This not only reduces operational costs but also mitigates greenhouse gas emissions, thereby supporting climate action efforts and environmental preservation.

Socially, the decision to reuse the existing wetlands demonstrates dedication to maintaining and sustaining biodiversity in the Boherbue community. By incorporating natural elements into the design, not only is disruption to local ecosystems minimised, but also to the overall health and vitality of the local environment.

Darran O’Leary, Programme Manager at Uisce Éireann said:

“We are delighted to have delivered this important project for the community of Boherbue. The modernisation and improvement of the wastewater infrastructure will accommodate further growth in the area and ensure that cleaner and safer treated wastewater is being discharged into the Brogeen River.

“It also adds biodiversity value to the area and remains sensitive to the surrounding landscape. This, coupled with the use of solar energy, demonstrates our commitment to putting sustainability at the heart of everything we do”.

Boherbue WwTP upgrade works is a flagship project for sustainable and carbon saving treatment processes and will serve as a reference project for future similar projects within the industry.

By demonstrating the feasibility and benefits of integrating renewable energy, advanced treatment technologies, and ecological conservation practices, this project sets a precedent for industry-wide innovation and best practices.

It complies with stringent Environmental Protection Agency (EPA) discharge consent standards, while minimising impact on the existing landscape, demonstrates a commitment to environmental sustainability, operational efficiency, and community well-being, making it a catalyst for positive change within the wastewater treatment sector and beyond.

Cardiff and Afan WwTWs are in South Wales and are owned and operated by Dŵr Cymru Welsh Water. The Cardiff WwTW serves a population equivalent of 974,869 with a flow to full treatment of 6,060 l/s, and Afan WwTW located on the TATA Steelworks site at Port Talbot, has a flow to full treatment of 2,423 l/s - a combined flow capable of filling an Olympic size swimming pool in just five minutes. At both sites, surplus activated sludge is pumped to a sludge treatment building where it is mixed with polymer, thickened, and then pumped (along with imported sludge) to a Cambi advanced aerobic digestion (AAD) process for further treatment. Methane produced in the Cambi AAD is used in the CHP engines to produce electricity.

Background

The CHP plants at both Cardiff and Afan treatment works were constructed in 2010, however the CHPs and associated ancillary assets at both sites face continued degradation, exposing Operations to volatile energy prices and increased maintenance costs. These assets are not currently performing to their designed capability, meaning the potential energy recovery savings are not being fully realised.

Samples of the biogas entering the CHPs have highlighted that the siloxane composition is at unacceptable levels, causing a risk to the CHP condition. The scope will include for replacing the existing siloxane plant with a new carbon filter which will increase delivered pressure of biogas to the CHPs and boilers to help increase performance.

[caption id="attachment_13304" align="alignnone" width="1200"] (left) Cardiff WwTW and (right) Afan WwTW - Courtesy of Google Earth[/caption]

Project drivers

Morgan Sindall Infrastructure was appointed as principal contractor and principal designer to successfully deliver a scope of work at both sites to meet the following main drivers for the project:

• Increased CHP plant availability.
• Ability to run all CHP engines and boilers while using the gas clean-up equipment.
• Operational health & safety: the ability to work safely on boilers while the associated CHP boiler is running.
• Reduce energy and maintenance costs.
• Operational health & safety at Afan WwTW: relocate the CHP exhaust bursting discs to outside of the operational building.

Being one of the designers working for Morgan Sindall Infrastructure on Welsh Water’s AMP7 framework, and because of their previous experience on similar projects, Arcadis were selected by Morgan Sindall as the design consultants for the Cardiff and Afan WwTWs CHP Optimisation Project.

Due to the commonality between the two sites, both projects were developed using the same principal contractor, design consultants, sub-contractors, and supply chain. This helped realise significant design and programme savings across the two sites.

CHP process description

For both sites, at each CHP engine the hot exhaust gases are directed to a dedicated composite steam boiler to recover heat. Each CHP package includes a biogas booster pump which is used to increase the pressure of the biogas supplied to the CHP engine.

[caption id="attachment_13326" align="alignnone" width="1200"] ADD process diagram - Courtesy of Dŵr Cymru Welsh Water[/caption] The pipework from the biogas booster pump to the container includes connections for a gas analyser and an in-line gas meter, as well as a safety slam-shut valve. The gas analyser monitors the levels of methane, carbon dioxide, oxygen, and hydrogen sulphide in the biogas. The readings are used by the CHP control system to adjust the engine performance, or to trip on high levels. The in-line gas meter monitors the flow rate of biogas to each CHP engine and the gas slam-shut valve is used to isolate the container in the event of a gas leak or fire alarm.

Design solution for both sites

• Removal of siloxane plant and installation of carbon gas cleaning.
• Chiller installation to include:
• Shell and tube heat exchanger.
• Recuperator.
• Lagging to exchanger and recuperator.
• Inlet and outlet temperature probes.
• Condensate pot (drained locally).
• Parker WFB2380CSB3180A-316 biogas cooler/separator.
• Parker ICE183B4003501P15FF0LA000 biogas process chiller.
• Parker HDF220BE biogas float drains.
• Gas booster to ensure boiler and combined heat and power operation, to include:
• Control panel booster and chiller with SCADA access and HMI.
• Gas booster motor 1 and 2 starters.
• VSD control.
• Pressure and temperature protection.
• Pipework and manifolds.
• Interconnecting pipework between the booster set and chiller including valves and purge points.
• Safety measures to enable a CHP to be operated and allow boiler safe isolation.
• Gas flow meter installation (on each digester).
• Afan Works only: Relocation of the CHP exhaust bursting discs to outside the existing boiler house.

[caption id="attachment_13308" align="alignnone" width="1200"] New biogas booster set install at Cardiff WwTW – courtesy of Morgan Sindall[/caption]

Design figures

• Maximum biogas throughput:
  • Cardiff WwTW: 3,000 Nm³/hour.
  • Afan WwTW: 2,500 Nm³/hour.
• Assumed biogas composition:
  • CH₄/CO₂/N₂/O₂): 65/35/0/0 %.
• Assumed biogas methane content range: 60-70%.
• Dehumidified gas temperature from chiller: 5⁰C.
• Combined siloxane level required following carbon filter treatment: 10 ppm.

Supplier selection

Early in the project it was recognised that the management of multiple key suppliers and lead-in times of up to six months were two key risks to a successful delivery. Selecting the same suppliers, contractors and designers across both projects, together with a clear collaborative approach from the start helped mitigate these risks.

1. Endress+Hauser was selected as suppliers of the biogas flow meters due to their proven accuracy at a similar project completed at Five Fords WwTW in North Wales.
2. CC Jensen Ltd was selected as a specialist carbon filter supplier they based on their work on previous CHP installations.
3. Dunphy Combustion Ltd was selected based on their technical capabilities and previous performance at Cog Moors WwTW.
4. Uniflare Group was selected based on programme delivery and the previous work undertaken at Cog Moors WwTW.

[caption id="attachment_13305" align="alignnone" width="1200"] Installation of foam probe and suppression nozzles at Cardiff WwTW - Courtesy of Morgan Sindall[/caption]

Cardiff & Afan CHP Optimisation: Supply chain - key participants

• Principal contractor & designer: Morgan Sindall Infrastructure
• Consulting designer: Arcadis
• Mechanical installation & biogas scrubber supplier: CC Jensen Ltd
• Electrical installer: Protocol Control Systems Ltd
• Biogas flow meter installation: Marches Biogas Ltd
• MCC modifications: GPS Group
• Systems integration: GPS Links
• Biogas boosters & chillers supplier: Uniflare Group
• Steam boiler dampers & ducting supplier: Dunphy Combustion Ltd
• Biogas flow meter & control panel: Endress+Hauser

Project benefits

As part of its response to climate change, and to reduce greenhouse gas emissions, Welsh Water have invested in a renewable energy generation and energy efficiency portfolio, split as follows:

• 45% hydro electric
• 45% Combined heat & power
• 5% wind energy
• 5% solar energy

Source: latest figures taken from dwrcymru.com - June 2024 [caption id="attachment_13309" align="alignnone" width="1200"] Installation of new Endress+Hauser prosonic gas flow meters at Cardiff - Courtesy of Morgan Sindall[/caption]

At Cardiff WwTW, the current average power generation is 20.25 GWh, and at Afan WwTW is 10 GWh. The target to achieve a 3 GWh improvement at each site will generate a combined revenue of £930,000 per annum and contribute significantly to Welsh Water’s renewable energy totals while reducing greenhouse gas emissions. The carbon benefit is assessed to be approximately 1,000 tonnes/year for both sites combined.

Project status

At the time of writing (June 2024), both projects are progressing well, and at Cardiff WwTW the civils works are now complete. The mechanical installation is expected to be complete by the end of June, with handover back to Welsh Water targeted for August 2024.

The Afan project trails Cardiff, providing the opportunity to benefit from any lessons learnt during the Cardiff installation. The work at Afan WwTW is scheduled to be commissioned in August and handed back to the Welsh Water to operate in October 2024.

These projects will meet all the client drivers to improve operational health & safety, reduce energy and maintenance costs, and increase CHP availability and output. The carbon benefits will also contribute to Welsh Water’s overall carbon reduction strategy and journey to net zero.

The Ards Peninsula is a scenic area in County Down, situated on the north-east coast of Northern Ireland. It separates Strangford Lough from the north channel of the Irish Sea and its coastal towns and villages are popular with day trippers and caravanners alike. By 2020, the wastewater treatment works serving the villages of Carrowdore and Ballywalter were operating at full capacity. NI Water investment was required to ensure that these areas could meet future EU and Northern Ireland Environment Agency (NIEA) standards. The area of Ballywhiskin only had primary settlement, which was not deemed sufficient, and the caravan parks and small settlements in the Ballywalter area were served by septic tanks, which again only offered primary settlement of wastewater before discharge to nearby watercourses. The beaches in the area represent significant tourist amenity and an extensive treatment scheme was essential to meet future bathing water quality standards in line with NIEA standards.

What the scheme involved

The two-year Ards North Wastewater Improvement Scheme involved the rationalisation of the Carrowdore, Ballywhiskin and Ballywalter catchments so that all wastewater flows from these areas could be transferred to a new state-of-the-art wastewater treatment works (WwTW) constructed on a greenfield site off the Ganaway Road in Ballywalter. In addition to these catchments, the new treatment works has been designed to treat wastewater flows from nearby caravan parks and small settlements, which previously had no treatment facilities. The scheme was split into two contracts; one for the design and construction of new pumping stations, pipelines and a modern wastewater treatment works, which was awarded to BSG Civil Engineering, and another for the design and installation of a new long sea outfall, which was awarded to Farrans. Project management/technical support for both contracts was provided by Tetra Tech. This article focuses on the work carried out to construct the new WwTW, pumping stations and pipelines by BSG Civil Engineering to serve the combined catchments and cope with seasonal fluctuations in population to protect the tourism potential of the area for many years to come. [caption id="" align="alignnone" width="1200"] Bulk excavation - Courtesy of BSG Civil Engineering Ltd[/caption]

Early contractor involvement/design and build contract

BSG Civil Engineering was appointed by NI Water as the main contractor in November 2018 under an NEC 3 Early Contractor Involvement (ECI) contract. BSG provided multi-disciplinary design, project and supply chain management and all civil engineering, process and MIECA works for the contract from start to completion. The ECI phase allowed BSG to align resources and integrate objectives with NI Water and their project management team from Tetra Tech at an early stage to benefit delivery. This proactive approach led to enhanced collaboration, innovation, value, efficiency and reduced whole life costs for the project.

Primary drivers

The purpose and drivers for this project were as follows:

• Achieve compliance with current and future EU directives on effluent discharge standards.
• Meet Registered Discharge Standards set by the Northern Ireland Environment Agency (NIEA).
• Provide a flexible design to cater for future flows and the significant summer/winter fluctuations.
• Minimise impacts to community and environment.
• Support local development, tourism and economic growth.
• Deliver best value for money construction making use of existing assets.

[caption id="" align="alignnone" width="1200"] Ards North WwTW - Inlet works overview - Courtesy of BSG Civil Engineering Ltd[/caption]

Scope of works

The main elements of work included:

• Installation of 14km of pumping main between WwTW & new/upgraded pumping stations via directional drilling and open cut methods.
• 2km of gravity sewer installed between pumping stations.
• 6mm inlet screening and storm storage for 2 hours/3x DWF)
• Grit treatment and removal.
• 3 (No.) 131m³ primary settlement tanks with automatic desludge and scum removal.
• Return activated sludge (RAS)/surplus activated sludge (SAS) pumping station.
• Anti-septicity treatment at source at the pumping stations.
• 3 (No.) 12m diameter final settlement tanks with automatic desludge and scum removal.
• Sludge holding tank.
• Sludge thickening and processing.
• Two-stage odour control plant.
• 330KVA standby power generation.
• 52.28 kwP roof mounted solar PV array, complete with dual 22kWh EV charging points.
• Process flows, levels, and quality monitoring; ancillary processes to support the main process units and intelligent motor control centre (MCC) with telemetry.
• Programmable logic controller (PLC) and human machine interface (HMI) control system.
• Installation of new long sea outfall pipe (detailed in a separate article).

Design criteria for the Ards North WwTW

Due to the large number of caravans in the area expected to be served by the new Ards North WwTW, the plant needed to be designed to deal with significant variations in flow and load to ensure satisfactory treatment could be achieved throughout the year. This meant that the works had to cope with a summer population equivalent (PE) of 8508 and a PE of 4809 in winter months.

Inlet works & flow control/balancing

Flows up to Formula A from the outlying stations can arrive at WwTW simultaneously. The inlet balancing chamber balances out flows going forward to the inlet screening plant. The inlet screening plant consists of two duty/standby incline screens and a cross conveyor. Each screen has a manual inlet penstock installed to enable isolation for maintenance purposes, or for bypass through the static 6mm bar screen. [caption id="" align="alignnone" width="1200"] Inlet works side view - Courtesy of BSG Civil Engineering Ltd[/caption] Screened raw sewage continues to the grit removal plant. The grit settles in a sump underneath the grit paddle. Any grit that settles in this sump is periodically aerated using the grit blower and then removed. From here the grit is transported out of the grit plant by the grit classifier and is deposited into the grit skip. From here it is removed off site for disposal. After the wastewater has passed through the grit removal plant, flow continues to the FFT pumping station. Here influent is collected, and FFT of 48.2 l/s (summer) & 29.6 l/s (winter) is pumped to the PST flow splitting chamber.

Ards North Wastewater Improvement Scheme: Supply chain - key participants

• Client: NI Water
• Project management: Tetra Tech
• Principal designer/contractor: BSG Civil Engineering Ltd
• Structural, hydraulic & process design: Doran Consulting
• MEICA design: BSG Civil Engineering Ltd
• Temporary works design: MEA Ltd
• Electrical installations: AW Control Systems
• Dewatering: Causeway Geotech
• Aeration equipment: Xylem Water Solutions
• Aeration blowers: Aerzen Machines
• Sludge thickeners: Huber Technology
• MCC: LMP Controls
• Inlet screening: M and N Electrical and Mechanical Services | Hydro International
• Grit treatment: Jacopa
• Storm screening: Eliquo Hydrok Ltd
• Actuators: Rotork
• Septicity dosing & booster pumps: FM Environmental
• Half bridge scrapers & access flooring/metalwork: Graham Steelworks & Engineering Ltd
• Odour control plant: John Cockerill Environment
• Pipes & fittings: APP Fusion Group
• Standby generators: PM Power
• Poly dosing plant: ProMinent Fluid Controls (UK) Ltd
• Micro-strainers: Whitewater Care
• Photovoltaic solar farm: Solmatix Renewables Ltd
• DO/MLSS & turbidity instrumentations: Hach Lange
• Flow meters & ultrasonics: Siemens
• Tipping buckets: CSO Group Ltd
• Precast concrete supplies: FP McCann

Stormwater storage

When incoming flows exceed FFT, the FFT pumping station will start to fill and eventually overflow to the blind storm tank. Once the blind storm tank has reached maximum capacity, flow will backup, allowing the level within the FFT pumping station to increase further. A higher-level overflow pipe allows flows to pass to the online storm tank. Once maximum capacity is reached here, flows will pass to the Ganaway Burn via the 6mm overflow screen and flow meter. Storm return will occur when the FFT pumping station is at a suitable low level. The storm tanks will return flow to the FFT pumping station in sequence i.e. blind tank first. Both tanks are fitted with automated penstocks which will open to return the contents of each storm tank to the FFT pumping station. Both storm tanks are fitted with tipping bucket cleaning systems from CSO Group Ltd, which help prevent build-up on the tank floor to achieve that ‘brushed floor effect’ when empty. The tipping bucket will operate when each of the storm tanks has reached the empty level. [caption id="" align="alignnone" width="1200"] (left) Ards North WwTW - Courtesy of NI Water, and (right) storm tanks tipping bucket installation - Courtesy of BSG Civil Engineering Ltd[/caption]

Primary treatment

The PST flow splitting chamber receives flows from the FFT pumping station and return liquors pumping station. Flow from the PST flow splitting chamber passes to three primary settlement tanks. These tanks are hopper bottomed and are desludged using automated valves to the primary sludge pumping station. Wastewater continues through to the PST collection manhole which mixes with RAS upstream of the ASP distribution chamber to feed the three ASP lanes. Sludge and scum drawn from the three PSTs arrives in the primary sludge pumping station. This station consists of two submersible pumps in duty/standby arrangement and is used to transfer sludge and scum removed from the PSTs to the thin sludge tank.

Activated sludge plant

The ASP lanes are identical in design and equipment. Each lane comprises an anoxic zone and an aeration zone. Each anoxic zone is equipped with a mixer. Each aeration zone is equipped with an aeration grid, air control actuator, air flow meter transmitter, two dissolved oxygen probes and an MLSS probe. Each aeration zone is fitted with mixers and aeration grids with fine bubble disc diffusers, which are attached to a central manifold which then connects to the ASP blowers. The influent entering these zones is controlled to maintain a set dissolved oxygen and MLSS level. The dissolved oxygen demand is supplied via the ASP blowers, configured in a duty/assist/standby arrangement. The blowers’ manifold is monitored by a pressure transmitter, a temperature transmitter and an air flow meter transmitter. [caption id="" align="alignnone" width="1200"] Aeration plant air manifold control valves and instrumentation - Courtesy of BSG Civil Engineering Ltd[/caption]

Final treatment

Flow from the ASP Lanes gravitates to the FST flow split chamber, fitted with adjustable weirs where the flow is split evenly to the three final settlement tanks. Each tank is identical and is equipped with a half bridge scraper, sludge blanket detector, ladder position switch and a proximity switch. Scum travels to the scum collection chamber and furthermore to the FST scum pumping station. The station is equipped with a duty/standby pump set which pumps its contents to the thin sludge tank. The tanks desludge is controlled via flow meters through actuated hydrostatic valves located in separate chambers that adjoin the RAS/SAS pumping station. Each tank’s settled effluent hydraulically discharges into the tank’s outlet launder channel to the final effluent/washwater pumping station.

Final effluent

Final effluent flows into the final effluent/washwater pumping station and on to the final effluent sample chamber. Here, the final effluent is monitored for turbidity and temperature levels and is also the dedicated location for the auto sampler. The final effluent/washwater pumping station contains two submersible fixed speed final effluent/washwater pumps in a duty/standby arrangement. These are used for supplying the washwater tank with the necessary effluent for washing the screens, sludge thickeners, etc. Final effluent is returned through a packaged plant automatic backwash strainer system located inside the control building. The automatic backwash strainer system, situated inside the sludge thickening building, is a filter that is used to remove particles from the final effluent returned from the final effluent/washwater pumping station. Final effluent flows from the sample chamber which is connected to the long sea outfall pipe.

Sludge pumping, treatment & storage

The RAS/SAS pumping station is equipped with two sets of pumps. RAS pumps and SAS pumps, a level ultrasonic and high-level floats are used to control both sets of pumps. The duty pump returns the desludge from all FSTs back to the PST collection manhole, continuing to the aeration distribution channel. The SAS pumps, also arranged in a duty/standby configuration, periodically pump forward sludge to the thin sludge tank. The frequency is operative set to maintain a desirable MLSS level within the ASP lanes. [caption id="" align="alignnone" width="1200"] RAS/SAS pumping station - Courtesy of BSG Civil Engineering Ltd[/caption] The thin sludge tank is equipped with an external mixer for the blending of the tank’s contents to feed the sludge thickening plant. A level ultrasonic with low and high-level floats are used in the control of the mixer. Mixed sludge from the thin sludge tank is pumped to the sludge thickening plant via the two thickeners feed pumps. These pumps are progressive cavity pumps and are arranged in duty/standby configuration. The pumps are VSD controlled to allow the flow to the thickening plant to be controlled. There are two sludge thickeners, with an individual throughput of 8.3 m³/hr @ 1.3% DS with a discharge of no more than 6%, based on a 5-hour day, 7-days per week operation at 100% of the maximum design load. The thickeners are arranged in a duty/standby configuration with two actuated isolation valves installed on the feed pipework allow this to be fully automated. If one thickener was to develop a fault, the standby thickener can resume operations without manual intervention. Polyelectrolyte is made up on site to be added to the sludge fed to the sludge thickening plant. The addition of this chemical aids flocculation and makes thickening easier. This plant is a liquid polymer set. The liquid poly is delivered within IBCs for the makeup process. The set mixes the poly from the IBC with water to a preset concentration rate and is then transferred to the poly storage tank. The duty poly dosing pump doses to the thickener’s sludge feed pipework from here. Thickened sludge from the sludge thickening plant is transferred to the thick sludge tank. Here thickened sludge is stored for removal off site. A collection tanker removes the tank’s contents off site by coupling to the tank’s Bauer Coupler connector. [caption id="" align="alignnone" width="1200"] PST No 1 & control building - Courtesy of BSG Civil Engineering Ltd[/caption] The tank is equipped with a decant valve arrangement to facilitate settlement of the tank’s contents. The tank is also equipped with a level ultrasonic, low and high-level floats for level status and control of an externally fitted mixer for tank agitation. The return liquors pumping station receives liquors from the following areas: inlet works drains, thin sludge tank decants and overflow, thick sludge tank decants and overflow, sludge thickening plant bund, FE and washwater drains and odour control plant drains. The station comprises of two fixed speed pumps, which are arranged in duty/standby arrangement. These return liquors to the activated PST splitting chamber.

Washwater pumping

The final effluent washwater & potable water booster sets are positioned within the sludge building. A ’dual washwater tank’ system is in place to feed both sets of pumps. The GRP dual washwater tank is designed with a lower compartment which holds 6m³ and an upper compartment which holds 1m³. The lower compartment is designed to contain the final effluent delivered via the final effluent/washwater pumping station, which in turn feeds the final effluent booster set which boosts the pressure as required for the washwater of the inlet screens, sludge thickeners, odour control, and the storm tank tipping buckets. The upper compartment is designed to contain potable water which in turn feeds the potable water booster set, which boosts the pressure as required for the nine retractable hose reels around the site for wash down, poly makeup plant water and poly carrier water. [caption id="" align="alignnone" width="1200"] Low level structures RC concrete installation - Courtesy of BSG Civil Engineering Ltd[/caption]

Odour control plant

The 2-stage odour control unit (bio & carbon filter) is connected to the various strategic areas. The odour control unit comprises of two odour fans, which are arranged in duty/standby arrangement. Actuated valve, flow meters, pressure transmitters and temperature transmitters are used to control the odour control system. Only odour omitted from the sludge thickening building (due to their extreme odorous compounds) will bypass the biofilter and go directly to carbon filter for treatment.

Outlying pumping stations

Existing treatment facilities at Ballywhiskin and Carrowdore were decommissioned and replaced with new pumping stations, while a completely new pumping facility was constructed at Sandycove Caravan Park where no NI Water asset previously existed. The last of the outlying WwPS to be upgraded was Ballywalter Fowler Terminal Pumping Station (TPS). This facility was completely refurbished with larger capacity pumps, a new MCC and additional storm storage capacity. Fowler Way TPS pumps to Sandycove WwPS which in turn pumps to the new Ards North WwTW, while the pumping stations at Ballywhiskin and Carrowdore pump directly to Ards North. [caption id="" align="alignnone" width="1200"] (left) Ballywhiskin TPS - Courtesy of NI Water, and (right) Carrowdore WwPS - Courtesy of BSG Civil Engineering Ltd[/caption]

Civil construction challenges

There were various challenges throughout the construction phase of the works that had to be overcome to ensure that the contract programme was achieved. As the project spanned over a 20km distance, there were varying ground conditions to deal with from very loose running sand in the gravity pipeline sections at Sandycove; soft, deep peat at Carrowdore WwPS; extremely hard rock at Ballywhisken to stiff clays with loose gravels at the WwTW site. This led to a variety of temporary works systems having to be designed and employed to deliver the works safely. Groundwater levels also varied across the scheme with various dewatering techniques used to maintain dry working spaces. Artesian water pressure and groundwater under tidal influence presented difficulties during the construction of these works. Overhead services also presented a construction issue at the WwTW site. As a result, carefully planned construction sequencing and specialised plant were employed. 13.5km of pumping main was installed along roads within this rural area. In order to keep to programme, pipe installation had to be carried out using a minimum of two separate teams at all times. Due to the limited options for suitable diversionary routes in the area, the pipe installation programme had to be carefully managed and continually communicated to the roads authority to ensure both pipe installation squads had consecutive sequencing of works throughout the pipeline installation phase of the scheme. [caption id="" align="alignnone" width="1200"] (left) Sandycove WwPS and (right) Ballywalter Fowler Way TPS - Courtesy of NI Water[/caption]

Sustainability

To boost the sustainability of the treatment facility, 138 solar PV panels from Solmatix Renewables Ltd were fitted to the roof of the new control building which will produce over 45,000 kWh per annum. This renewable energy could save NI Water up to £300k over 25 years. Charging points for NI Water’s growing fleet of electric vehicles have also been installed at the new treatment works.

Communications & PR

NI Water and its project management team developed a proactive comms and PR strategy for the Ards North Wastewater Improvement Scheme which included circulation of project brochure, issuing of regular press releases, letters to residents, briefings for elected representatives, circulation of progress updates, safety events with children, and face-to-face meetings with landowners. Myriad stakeholders were kept up to date with progress and informed in advance of pipelaying works and associated traffic management arrangements. Following completion of the project, a site tour of the new WwTW was organised to give local elected representatives the opportunity to view the modern facility first hand. Feedback from the visit was extremely positive. [caption id="" align="alignnone" width="1200"] NI Water, TetraTech, BSG Civil Engineering Ltd and Farrans along with local elected representatives to mark completion of the £18m Ards North Wastewater Improvement Scheme - Courtesy of NI Water[/caption]

Conclusion

A collaborative, forward-thinking approach between NI Water, BSG Civil Engineering and Tetra Tech has produced whole-life cost, programme and carbon savings in the delivery of this project. Phased flows were brought into the new Ards North WwTW between the months of November 2022 and January 2023. During this time, a process optimisation phase took place before the plant was rigorously tested and commissioned under varying flow and load scenarios. The plant was then put through a period of intensive detailed process sampling achieving highly performing results during separate 14 and 28-day sampling periods during Spring 2023. The project was successfully completed and handed over to NI Water ahead of the 2023 summer tourist season. The new Ards North WwTW is ensuring that high-quality effluent is being discharged out to sea, helping to improve the bathing water quality along this part of the Ards Peninsula in line with the project objectives.