Supply Chain - Sewerage - Products

Yorkshire Water’s Esholt Sewage Treatment Works is located northwest of Leeds and serves a population of approximately 400,000. The STW treats the majority of sewage flows from Bradford and parts of northern Leeds, with a flow to full treatment of 3200 l/s. The project driver is part of the Water Industry National Environmental Programme (WINEP), which aims to reduce overall phosphorus concentrations in the final effluent to 0.5mg/l, thereby improving water quality in the River Aire. To achieve this new consent, YWS contracted Mott MacDonald Bentley (MMB) to undertake the detailed design, construction and commissioning of the work. The project scope included a new coagulant dosing system and tertiary treatment to ensure the new phosphorus consent was met. Coagulant dosing system

The dosing system involved the implementation of a 40m3 external ferric sulphate dosing tank with a chemical dosing system, with the point of application prior to the primary settlement tanks. MMB utilised the YWS standard product which is a DfMA solution in partnership with framework supplier, Northern Pump Suppliers Ltd (NPS).

The ferric storage tank, the dosing kiosk (which came pre-assembled with all the mechanical equipment and control panel), and the point of application cabinets were all manufactured off-site and could be dropped into place in delivery.

This reduced multiple different interfaces and enabled the site team to build all the other elements ready for the delivery. The ferric dosing system was placed strategically at the bottom of an existing hydro-turbine to utilise the turbulence caused by the screw in operation which provided optimal mixing for the chemical; no additional mixing was required.

[caption id="attachment_14176" align="alignnone" width="1200"] Primary ferric point of application cabinets - Courtesy of MMB[/caption] Challenging designs & re-use of existing structures

Due to the additional ferric being added into the sewage, the site required tertiary solids removal (TSR) to capture any remaining particles before going out to river, ensuring compliance with iron consent limits. Esholt has an existing TSR which consists of 12 deep-bed sand filters cells (DBSF). The DBSF works by allowing effluent to flow down through the bed, with residual solids being captured by the granular material in the bed. In 2015, the works was damaged by an extreme flood, and subsequently the DBSF has remained out of service ever since.

To avoid the need to install new TSRs, the proposed scope included the refurbishment of the abandoned DBSF. Using this ‘build less’ approach saved on capital costs and reduced embodied carbon emissions, but did introduce its own challenges.

Following the previous abandonment, part of the dirty backwash system had been re-purposed for alternative use, meaning that a new solution for returning the backwash flows was required. To address this, a new pumping station was proposed to regulate flows back into the process. Due to the poor ground conditions and high-water table, the design required the pumping station to be of wet caisson construction. The pumping station featured a 280m-long rising main, directing flows back to the existing humus tanks. The pumping station itself was planned to be 12m in diameter and 7m deep, located adjacent to the DBSF.

During design development, MMB reviewed the need for the proposed storage requirement, agreeing a slightly different operating regime for the pumps and DBSF backwash control. As a result, the team identified an opportunity to re-purpose an existing dry well structure nearby. By adapting this structure, they could house the new return pumps without the need to construct an entirely new pumping station.

[caption id="attachment_14174" align="alignnone" width="1200"] Deep bed sand filter, post refurbishment - Courtesy of MMB[/caption] Laser scanning

To verify this opportunity, and to ensure that the detail design could be completed with minimal changes, the team utilised GeoSlam Horizon. This handheld laser scanning technology took half a day to survey the existing dry well, and enabled MMB’s digital delivery technician to model the output in Revit. The model was then exported to virtual reality (VR) in which the project team held collaborative review sessions to confirm the design and ensure that the proposal would be compliant against the clients engineering standards. This also aiding access lifting and maintenance reviews with the client to ensure the refurbishment included aligning the design to the new client engineering specification.

By challenging the design requirements, MMB took out the need for a new pump station by re-purposing the existing structure. This removed the difficult caisson construction and by doing so achieved substantial costs savings for this element of work, and enhanced safety conditions for the construction team. This approach also significantly reduced the embodied carbon footprint. The team utilised the Mott MacDonald Moata Carbon Portal to undertake rapid calculations to understand the benefits of the proposed change, showing a capital carbon saving of ~248 tCO2e.

Rising main

The 280m rising main that directed dirty backwash flows back into the existing humus tanks was originally proposed below ground. The pipe was routed along the Industrial Emissions Directive (IED) boundary and the initial assessment concluded that the pipe required dual containment to mitigate the risk of any pollution.

[caption id="attachment_14173" align="alignnone" width="1200"] Dirty backwash rising main - Courtesy of MMB[/caption]

MMB worked collaboratively with the client to better understand the risk and consequence of a failure, as the media contained within was backwash water and not sludge, which is typically with focus under IED. In addition to this, a review was undertaken on programme and cost impact, as well as the risks during the construction phase.

The outcome of this review was an agreement with the Environment Agency to undertake a more pragmatic approach. The carbon saving calculated on the Moata Carbon Portal tool is estimated to be ~37t CO2eq moving from a dual contained below-ground pipe, to an above-ground single skin ductile iron pipe.

MCC

The existing MCC in this area had reached the end of its asset life and was insufficient in terms of capacity. To meet the power and control requirements of the refurbished sand filters, the new backwash arrangement, and associated equipment, a replacement was essential. However, the location of the existing MCC posed challenges, in that it could not accommodate the new MCC while complying with the latest Engineering Specification.

To achieve the upgrade, MMB proposed a hybrid approach to the design. Instead of installing the entire new panel in a separate GRP kiosk raised above the flood zone on a steel frame, the team opted for a more efficient solution. They integrated sections of the new MCC within the existing building, ensuring compliance with current specifications, minimising the length of the MCC which required a new structure. This reduced not only the kiosk size but all the periphery infrastructure including civils works, raised steel frame and security fencing.

[caption id="attachment_14178" align="alignnone" width="1200"] Side view of primary ferric dosing compound - Courtesy of MMB[/caption] Esholt STW: Supply chain - key participants Designer & delivery contractor: Mott MacDonald Bentley Dosing system subcontractor: Northern Pump Suppliers Ltd Chemical dosing trays subcontractor: APT Marine Engineering Ltd 3D printing subcontractor: Hyperion Robotics UK Ltd Electrical installation: Circle Control & Design Systems Ltd DBSF mechanical refurbishment: De Nora Water Technologies UK MCC platform subcontractor: AJ Engineering & Construction Services Ltd Thinwall stainless steel pipework: GTS Nitrogen Services Ltd Systems integration: Actemium Civil engineering/site engineers: Day Civils Ltd Access platforms subcontractor: GT Fabrications Security fencing subcontractor: Burn Fencing Ltd MCC security kiosks subcontractor: Technocover Ltd Electrical panels: Technical Control Systems Pumps: Xylem Water Solutions DI pipework: Electrosteel Castings (UK) Ltd 3D concrete printing

To take the electrical ducts around the site and between the two panels for power and control cables, multiple large scale draw-pits were required at changes of direction. These draw-pits, typically measuring 2m2 by 2m deep, typically involve in situ concrete casting with 0.25m-thick walls. Their construction can be carbon-intensive, time-consuming due to intricate formwork, and pose safety risks for the construction team working in excavations over extended periods.

After meeting at a Yorkshire Water-led Net Zero event, MMB began forming a strategic relationship with Hyperion Robotics. Hyperion create 3D printed structures with a cementitious grout, printing only what the structure actually requires to be structurally integral. Early discussions used the proposed draw-pits as a test case of how their innovative 3D printing technology could support the water industry’s need for innovation and a drive towards Net Zero.

[caption id="attachment_14177" align="alignnone" width="1200"] Delivery of 3D printed draw-pits - Courtesy of Mott MacDonald Bentley[/caption]

The process involved working with Hyperion to create a bespoke design, to allow incorporation of the specific electrical duct penetrations and angles, and sizing of the chambers. This process reduced the materials required by 40%. Collaborative reviews were held with MMB, Hyperion, Tarmac and Yorkshire Water to ensure adequate buy in to this new technology.

3D concrete printing involved printing cementitious grout in layers, by using this technology the time taken to print the 2m high 1.9mØ draw-pits required at Esholt was only two hours. This DfMA approach also had huge safety and programme benefits as the time required working within excavations was significantly reduced since the site team could directly lift the draw-pit into the excavation from the wagon.

The technology provides improved quality control and ensures precise application to meet the exact dimensions in a controlled environment. The 3D-printed design achieves a 40% reduction in embodied carbon, a 10% cost reduction, and a 50% improvement in programme for drawpit construction, compared to conventional in situ.

Progress

Esholt STW is on track to meet its compliance date of 0.5 mg/l of phosphorus by December 2024. The scheme has been a success by challenging the design to get the best value for the client but to leave a positive impact on the environment. MMB have kept in touch with the continuously growing construction industry, trialing new technology including utilising laser scans, VR and 3D printing.

Esholt is a prime example of how challenging design and reusing existing structures where possible reduces the impact the construction has and accelerates progress towards a net-zero built environment.

The WINEP Durham Transfers Project was designed to improve the quality of the Blackdene Burn, a watercourse located in the north Durham area. During AMP7, sewage treatment works (STW) sites within Northumbrian Water Group (NWG) ownership were identified for improvements in phosphorus concentrations within final effluent discharge to the environment. The scope of this project is to address the improvements at both Plawsworth STW and Pity Me STW, which currently discharge to the Blackdene Burn. Background

Esh-Stantec was appointed by NWG to progress the proposed solution; a phased approach whereby, during AMP7, final effluent from both STWs will be transferred to a discharge point on the River Wear via transfer pumping stations. The transfer of flows will be facilitated via new rising mains and gravity sewerage which will connect immediately upstream of the existing outfall from Brasside STW. In line with the phased approach, planned upgrades to Brasside STW in AMP8 will increase its treatment capacity and allow for the eventual abandonment of Plawsworth and Pity Me STWs along with chemical dosing to meet planned phosphorus limits discharging to the River Wear.

The designed solution allows for projected growth across the Plawsworth and Pity Me catchments (including the completion of the significant Sniperley development) with an AMP8 solution transferring all raw flows from Plawsworth and Pity Me to the upgraded Brasside STW for treatment, with final effluent from Brasside STW ultimately discharging to the River Wear.

The objective of this appointment is to provide the assets required to enable to the transfer of flows from Pity Me and Plawsworth STWs in the AMP7 and AMP8 scenarios. It is anticipated that the project will be completed in December 2024.

[caption id="attachment_18551" align="alignnone" width="1200"] Piling operations by Francis & Lewis International Ltd, for the construction of the pipe bridge substructure - Courtesy of Esh-Stantec[/caption] WINEP Durham Transfer: Supply chain - key participants Client: Northumbrian Water Principal designer & contractor: Esh-Stantec Esh Group Stantec UK Structural consultant: James Christopher Consulting Ltd M&E, including supply & installation of generators, MCCs & pumps to wet wells: Retroflo Ltd Directional drilling of 3km of rising main & installation of all AV chambers: Ken Rodney Construction Ltd Auger boring under the East Coast Mainline, coordinating with Network Rail, & supply/installation of track monitoring: Terra Solutions Ltd Design, manufacture, & installation of pipe bridge: Francis & Lewis International Ltd Design & sinking of segmental shafts: Active Tunnelling Ltd Temporary works/shoring: MGF Ltd New transfer stations

The first stage of the scheme involves the transfer of fully treated, final effluent to the River Wear, meaning that Plawsworth and Pity Me STWs remain fully operational throughout the construction of all assets which will become live prior to the upgrade of Brasside STW.

Plawsworth Transfer Station: The new transfer assets at Plawsworth STW were carefully designed and sequenced around the limited working room in the site and the requirement to maintain treatment operations during construction. The Plawsworth Transfer Pumping Station comprises:

A 4m diameter, 6m deep wet well shaft (sunk as a caisson). MCC and associated kiosk. Generator and associated kiosk. Above-ground valve arrangement. Flow meter chamber and all associated interconnecting pipework and ducting.

In AMP7, final effluent flows are intercepted and directed into the new wet well before being pumped to the River Wear. Due to the transfer of final effluent, a reduced emergency storage volume has been provided within the new wet well.

In AMP8, following upgrades to Brasside STW, raw flows will be intercepted upstream of the inlet works and diverted to the new SPS for transfer to Brasside via a new 250mm rising main. As part of the conversion from a treatment works to a terminal pumping station, the existing humus tank will be re-purposed to provide additional emergency storage in line with EA guidelines for the transfer of raw sewage flows and minimise emergency overflow spills to the environment.

In addition to emergency storage, a permanent standby generator has been incorporated into the design which will automatically cut in if there is a loss of power to the site.

The pumping station was designed as a three pump station (duty/assist/standby) to transfer ultimate AMP8 flows up to 32 l/s, however, in the AMP7 scenario,  the pumping station will operate as a duty/standby/standby station, with the individual pumps sized to transfer 24 l/s of final effluent to maintain a minimum velocity in the rising main.

Pity Me Transfer Station: The main works at Pity Me STW comprises the following:

A 6m diameter, 9m deep wet well shaft (sunk as a caisson) with built-in emergency storage volume sized for ultimate raw flows. MCC and associated kiosk. Generator and associated kiosk. Valve chamber. Flow meter chamber and all associated interconnecting pipework and ducting.

Similar to Plawsworth, the pumping station was designed as a three pump station to transfer 34 l/s in AMP7, with a duty/standby/standby arrangement, and up to 61 l/s in AMP8, after conversion to a duty/assist/standby arrangement. In both the final effluent and raw flow scenarios, pumped flows will exit the works via a new 280mm rising main.

[caption id="attachment_18550" align="alignnone" width="1200"] Active Tunnelling constructing the new wet well shaft at Pity Me STWCourtesy of Esh-Stantec[/caption] Transfer rising mains

Approximately 2.1km of 250mm PE rising main and associated air valve/washout chambers has been installed from Plawsworth STW. The rising main pipework was installed predominantly via a trenchless technique, namely horizontal directional drilling (HDD), primarily due to lack of available access from the adjacent A167 highway to facilitate traditional open cut construction, as well as unfavourable ground conditions.

A new 280mm  rising main was installed over an 850m length from Pity Me STW. Due to a tight working corridor situated between a garden centre and the Blackdene Burn, as well as the requirement to cross beneath the A167, a highly trafficked highway, the rising mains was also installed via HDD. This use of a trenchless installation technique minimised disruption to local business and removed the requirement for traffic management on a busy commuter route.

eDNA samples taken from ponds adjacent to Pity Me in the feasibility stage confirmed the presents of great crested newts. In lieu of protracted traditional population surveys and subsequent licenced activities to mitigation including fencing and capture to clear the working area, a District Level License (DLL) was secured from Natural England and works were completed under an approved method statement with supervision from a consultant ecologist.

The 280mm and 250mm rising mains from Pity Me and Plawsworth connect to a common chamber located at the high point of the new network, where they will discharge flows to a new DN400 gravity sewer.

[caption id="attachment_18547" align="alignnone" width="1200"] Construction of new valve chamber and associated pipework at Pity Me STW - Courtesy of Esh-Stantec[/caption] New gravity sewerage

2.4km of new DN400 gravity sewerage, with associated manhole chambers, was constructed to receive the pumped flows from both Pity Me and Plawsworth STWs. Careful consideration was given to the design of the new sewerage to ensure capacity (including future growth) and self-cleansing requirements are met in all flow scenarios, including when Pity Me and Plawsworth transfer pumps operate either in isolation or in parallel.

The construction of the new gravity sewer poses some complex crossings and challenging ground conditions. The crossing of Chester Low Road, another busy road for both commuters and customers of a popular local retail park, The Arnison Centre, was originally planned for open cut excavation. However, subsequent on-site observations with regard to topography, a number of high-risk services including high voltage electric cables and a uPVC water main, and running sands within nearby open cut trenches led to the conclusion that it would not be possible to safely support the excavation during construction. Therefore, the road crossing was completed via guided auger bore. Not only did this mitigate the disruption and health and safety risks associated with damaging services, but it also minimised disruption to local businesses and residents as the road remained operational throughout the process.

East Coast Main Line crossing

Further downstream, the new gravity line is also set to cross beneath Network Rail’s East Coast Main Line. The proposal is to install a 610mm sacrificial steel sleeve via a guided auger bore beneath the embankment, once complete the 400mm NB gravity pipe will be sleeved and the anulus grouted. Extensive liaison is ongoing with Network Rail in the lead up to the under track crossing (UTX) to gain the necessary approvals and fully understand the constraints which must be met during construction. These constraints include but are not limited to 24/7 working for the duration of the tunnelling works, installation of track monitoring and an approved contractor on standby in case there is a requirement for emergency track repair.

[caption id="attachment_18549" align="alignnone" width="1200"] Aerial view of working area at Brasside STW - Courtesy of Esh-Stantec[/caption] Brasside pipe bridge

Approximately 800m upstream of the Brasside STW outfall connection, the sewer crosses a watercourse located within a steep ravine and dense woodland at the existing Brasside Sewage Pumping Station (SPS).

At the optioneering stage of the project, it was proposed that this crossing would take place via an inverted siphon arrangement. However, subsequent hydraulic modelling deemed that, due to topography constraints, it would not be feasible to achieve sufficient capacity while maintaining self-cleansing velocities in both the AMP7 and AMP8 flow scenarios without connecting to the existing outfall further downstream. This would have required construction works within ancient woodland, imposing the requirement for Environmental Impact Assessment (EIA) and potentially preventing the obtention of a Lawful Development Certificate.

Therefore, to mitigate the risk of repeat maintenance issues and potential asset failure, a pipe bridge was progressed as the preferred option having discounted a further interstage pumping station at the low point due to a lack of space within the existing Brasside SPS site and the associated operational carbon and expenditure.

The route of the pipe bridge was designed to mitigate environmental impact, by including bends within the bridge structure and above ground pipework to take advantage of existing operational land and avoid clearance of significant trees within a conservation area. The interface between the bridge structure and the above ground ductile iron pipework has been carefully modelled and iteratively designed to assess the impact of bridge movement and deflection on the pipe joints and select joints which provide appropriate tolerances for these movements.

[caption id="attachment_18552" align="alignnone" width="1200"] Construction of pipe bridge structure by Francis & Lewis International Ltd - Courtesy of Esh-Stantec[/caption] Conclusion

The design of the WINEP Durham Transfers Scheme serves to meet regulatory deadlines by achieving a sustainable multi-stage solution which meets the needs of the current and future catchment population.

At the time of writing (July 2024), construction is progressing well, and all rising main pipework and transfer station substructures have been installed. The gravity sewer is predominantly complete with the two key crossings remaining, pending final Network Rail approval to complete the rail crossing and final structural design of the pipe bridge to install the above-ground pipework adjacent to Brasside SPS.

The current construction programme shows that flows will be turned in December 2024, transferring final effluent to the River Wear in the interim and, in AMP8, transferring raw flows to Brasside STW for treatment. This will achieve the removal of treated effluent from the Blackdene Burn, in turn significantly improving water quality while meeting WINEP obligations. Furthermore, the completion of the scheme in AMP8 will serve to rationalise the NWG sewage network in the area and improve the resilience of the network by serving catchment growth and improving treatment capacity.

Ballygowan is a small village situated in County Down, within the Ards & North Down Borough Council area. The towns of Comber and Saintfield are both approximately 4 miles to the north-east, and to the south respectively, with the city of Belfast 7 miles north-west. The 2021 Census indicates that the population of Ballygowan is approximately 3,138. The existing WwTW was constructed in the village in the 1950s and comprised an inlet works, a CAS basin, a storm tank and a small sludge holding tank, as well as an MCC building to control the works and was designed to treat a population equivalent (PE) of 2,700. The existing works was therefore beyond capacity to treat the present day population, and the structures had exceeded their design life. An extensive upgrade was required to provide effective and robust wastewater treatment services for the future catchment area, allowing economic growth, while improving the local environment and adhering to a much tighter discharge consent of 7mg/l BOD, 10mg/l total suspended solids, and 1.5mg/l ammonia. The new fully automated works will serve a PE of 4,513. Primary drivers for the upgrade The existing wastewater treatment works (WwTW) was undersized for the current flows coming into the works. The existing works was not complaint with the Northern Ireland Environment Agency’s discharge consent standard for Ballygowan WwTW. Future planning applications for residential properties in the Ballygowan area had been put on hold due to the existing WwTW operating beyond its intended design capacity. The existing works was not capable of fulfilling the requirements of NI Water’s long-term strategy to enhance wastewater services and ensure environmental compliance and was expensive to operate and maintain. An even tighter NIEA standard was imminent. [caption id="" align="alignnone" width="1200"] (left) Existing Ballygowan WwTW - Courtesy of NI Water and (right) demolition in progress: (top) the existing storm tank and (bottom) the existing CAS basin tank - Courtesy of  GEDA Construction[/caption] Project description & scope Designed for a 2045 population equivalent of 4,500, the new Combined Activated Sludge Plant (CASP) at Ballygowan WwTW, was to be constructed east of Dickson Park in Ballygowan, in a green field site that bordered the southern boundary of the existing site: The preliminary treatment process comprising of 6mm inlet screening and forward flow-control equivalent to Formula ‘A’. A new storm storage management facility including a CSO storage tank, and two storm tanks providing a total capacity of 224m3. The CSO storage tank and two storm tanks are equipped with a tipping bucket system for effective cleaning of the storm tank floor. Flows equivalent to Full Flow to Treatment (FFT) are pumped forward via a new interstage pumping station. FFT is then split with equal flows going to two CAS basin tanks. The selector chamber was carefully designed to assist with controlling filamentous bulking in activated sludge systems which can be a common operational challenge issue in activated sludge plants. Downsteam of the flow split chamber, there are two CAS tanks complete with final settlement tanks (FSTs) accommodated centrally, each aeration stream comprising of an anoxic zone to aid denitrification, and three individual aeration zones equipped with tapered aeration diffuser grids. The design and construction of the biological treatment process on this site was critical and to ensure compliance with an extremely stringent discharge consent of 1 mg/l ammonia alkaline was dosed at this stage in the process, detailed below. Due to the restricted footprint available for the site, the CAS tanks were selected to accommodate the final settlement stage within the biological treatment footprint. Two FSTs were constructed, with the CAS (anoxic and aeration zones) wrapped around the FSTs. [caption id="" align="alignnone" width="1200"] CAS basins  - Courtesy of NI Water[/caption] Following final settlement, the treated effluent gravitates to a tertiary treatment plant for further solids removal prior to discharge at the final effluent outfall location. A new combined RAS/SAS pumping station was constructed adjacent to the selector/flow split chamber to aid best use of available footprint. This pumping station houses two RAS pumps to replenish the bacteria within the biological treatment system and maintain the required MLSS levels for effective treatment. A further two SAS pumps are also provided to pump away sludge to the new sludge storage facilities should the MLSS levels within the treatment process exceed the desired levels. The new Ballygowan WwTW includes two sludge storage tanks, one mechanical sludge thickener and a polymer chemical dosing plant for processing sludge prior to being tankered offsite. To ensure a robust solution was provided for the client to meet the 1 mg/l ammonia consent, a supplementary alkalinity chemical dosing plant was provided for dosing into the aeration lanes. The provision of this dosing plant which utilises sodium carbonate ensures there is sufficient alkalinity available within the biological treatment process for effective and complete nitrification under all flow and load conditions. The works also comprises a new MCC room which controls all mechanical and electrical plant equipment and instrumentation, a welfare unit, a standby backup generator, and associated access and drainage. As the treatment works was built in close proximity to a neighbouring residential area, the odour model highlighted areas of the treatment process that required covers with passive odour abatement being provided. The site was also landscaped to include a site bund to reduce the visual impact on the neighbouring residential area of Dickson Park. [caption id="" align="alignnone" width="1200"] New storm tank being utilised during construction - Courtesy of GEDA Construction[/caption] Main challenges for design/construction Discharge consent The key challenge around the design and construction of the new Ballygowan WwTW, was ensuring that the new WwTW would comply with a very tight water order consent (WOC) set by NIEA. The WOC is one of the tightest consents in Northern Ireland. The discharge consent was originally advised as 7:10:1.5 mg/L (BOD/TSS/ammonia), however the design and construction was further challenged when NIEA confirmed that the ammonia consent would be restricted to 1mg/l ammonia. GEDA Construction, in conjunction with their MEICA and process subcontractor Water Solutions Ireland Ltd, reviewed the design and construction proposal to provide a solution which incorporated minimal changes, minimising costs to NI Water, but still providing effluent treatment compliance. Site location The WwTW site is bordered by agricultural land to the north and east, and has a housing development to the west. To construct the new WwTW and keep the existing plant operational, NI Water purchased an area of land (formerly a football pitch) to the south of the site belonging to the local council. The existing WwTW access road is through Dickson Park housing estate and runs directly alongside a children’s playpark. In advance of construction the project team took the proactive decision to look at creating a temporary construction access to the south of the site through agricultural land so that all construction traffic would not have to travel near Dickson Park or the children’s playpark. Extensive consultation took place with local landowners, the residents’ association and roads authority and the temporary road was successfully constructed ahead of construction start. Due to the close proximity of the new WwTW to the housing development, consideration was also given to any potential visual and odour implications to the neighbouring housing development. It was decided at an early stage to design the structures in such a way that they would have minimal visual impact. This meant designing and constructing structures as low in the ground as possible to keep them out of view of the neighbouring properties. An earth bund was also constructed to the west boundary of the site and planted with trees/bushes and shrubs in order to further hide the treatment works as well as helping to combat any odours coming from the site. [caption id="" align="alignnone" width="1200"] Ballygowan WwTW under construction (December 2021) - Courtesy of NI Water[/caption] Interface between new and old works during construction The majority of the new WwTW works was to be built on a greenfield site which allowed GEDA Construction to build most of the new structures without having to work around existing infrastructure. However, in order to construct pipelines which would eventually take the flow into the new works, and to construct the new WwTW access road, it was necessary to demolish the existing storm tank in the old works prior to the new works becoming live. GEDA Construction carried these works out by utilising the newly-constructed storm tank and incorporating a carefully developed phasing plan. A temporary 300mm gravity fed sewer was laid from the existing inlet works to the new storm tank, which in turn rendered the existing storm tank surplus to requirements, as all storm flows had been diverted away from it. GEDA Construction also had to lay a temporary 200mm pumped sewer from the new storm tank complete with temporary pumps to send the storm flows back to the existing pumping station in order for the influent to then go through the treatment process. This in turn allowed us to demolish the existing storm tank and construct the new permanent inlet sewers to the new works ahead of turning flows. This process had to be carefully managed both hydraulically and biologically to ensure the treatment process was optimised and effluent compliance was maintained at all times. [caption id="" align="alignnone" width="1200"] New permanent high-level sewer under construction - Courtesy of GEDA Construction[/caption] Turn of flows Influent flows were successfully diverted into the new works in early May 2022. In order to bring the new biological treatment process online, several tanker loads of seeded sludge were brought to site from another treatment facility and were introduced into the new CAS basin tanks to promote bacteria growth. With flows diverted, and effective treatment established through a rigorous sampling regime, approval was received from NI Water to proceed with the demolition of the remainder of the existing treatment works. Once the existing works were decommissioned and demolished, the entire new WwTW site was able to be finished and access roads completed. Demolition Post turn of flows in early May 2022, the existing treatment works was decommissioned and then demolished. Reusable mechanical and electrical assets from the old treatment process were removed for future use by NI Water, while the effluent left in the old CAS basin and pumping station was removed from the site to allow demolition to commence. Effluent was filtered through the new treatment process to minimise unnecessary removal and disposal from site. Project team As principal contractor, GEDA Construction had overall responsibility to deliver the project on time and within budget, which they succeeded in doing by working collaboratively with NI Water, project managers Tetra Tech, key suppliers and subcontractors to identify and plan for key project milestones. McAdam 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. Water Solutions Ireland (WSI) were responsible for designing and delivering a full turnkey MEICA, process design and build solution for the new works. Ballygowan WwTW: Supply chain - key participants Civil contractor: GEDA Construction Project managers: Tetra Tech MEICA contractor: Water Solutions Ireland Civil, structural & geotechnical design: McAdam Electrical design: SBE Design Mechanical design: McWall Drawing & Design PLC software & commissioning: Ashdale Engineering Odour control: Anua Clean Air UK Storm screens: Eliquo Hydrok Ltd Grit removal plant: Jacopa 6mm inlet screening: Hydro International (M and N Electrical and Mechanical Services) Aeration blowers: Aerzen Machines MCC: Greenville IDC Pumps, mixers, fine bubble diffusers: Xylem Water Solutions Tertiary treatment plant: WPL Chemical dosing: Richard Alan Engineering Instrumentation: Park Electrical Systems Flow measurement: Siris Environmental Ltd Flow measurement: AMPM Flow & Energy Services Ltd Penstocks, valves & actuators: Flow Technology Services Storm tank cleaning tipping bucket: CSO Group Ltd GRP kiosks, FST scrapers & site-wide metalwork: Victoria Engineering 6mm bar screen, skip rails & trolleys: Graham Steelwork Engineering Potable & FE service water boosters: Dutypoint Ltd Lifting equipment: Columbus McKinnon Co Ltd Solar panels & EV charger: Solmatix Renewables Ltd [caption id="" align="alignnone" width="1200"] CAS basins in operation - Courtesy of NI Water[/caption] Solar It was recognised that a large area of land within the footprint of the existing WwTW site would be available for use following demolition of old structures. As a result, NI Water asked GEDA Construction and Water Solutions Ireland to investigate the feasibility of installing solar energy within the space available. Following a successful outcome of the feasibility study, it recommended that a 62Kw solar PV array would be installed in the free space which would provide renewable energy to run some of the WwTW operations and boost the sustainability of the site. A 22KW dual EV charger unit was also installed which is used by NI Water’s growing fleet of electric vans. Solmatix Renewables Ltd installed a ground-mounted solar PV panel system consisting of 164 solar panels within the footprint of the old works. New electrical invertors and controls housed within the new MCC kiosk were installed and cabled directly onto the new MCC. The solar system has been set up as zero export, meaning everything that is being generated on site, is used on site through the plant and other electrical equipment. The estimated payback period on NI Water’s £70k investment is 6.5 years (savings of £11,000/year on electricity costs at Ballygowan WwTW). [caption id="" align="alignnone" width="1200"] Solmatix Renewables Ltd solar farm - Courtesy of NI Water[/caption] Alkalinity A challenging issue encountered during the design and construction of the new works at Ballygowan WwTW was the high acidic nature of the incoming influent. During review of the design and aided by a sampling regime of the influent under varying flow conditions, it was determined the site required alkalinity dosing to allow the wastewater treatment process to provide adequate nitrification (in other words ammonia reduction) within the biological treatment to meet the 1mg/l ammonia discharge consent. This problem required NI Water and GEDA Construction to design, supply, install and commission a supplementary packaged chemical dosing system to increase the alkalinity levels and achieve a stable pH within the wastewater to safeguard optimum treatment. NI Water shared some past negative experiences encountered with similar alkalinity dosing plants which was invaluable to ensure that a well thought out, comprehensive solution was selected, which would deliver the requirements of supplementary dosing but reduce the ongoing operation and maintenance requirements encountered on other schemes for NI Water. The agreed solution was to provide a new proprietary sodium carbonate (powder) make up and dosing system, all housed within its own GRP kiosk and standalone control panel. Odour control Due to the proximity of nearby residential housing, the design and execution of odour containment and treatment was a major consideration for this project. Early odour models and specialist supplier engagement was imperative to ascertain the potential effects of odours. GEDA Construction provided a cost-effective, proven solution through a carbon filter plant dedicated for the inlet screening and grit removal works, and a second Mónashell Biofilter plant from Anua Clean Air UK was provided solely for the sludge treatment and storage tanks. Both systems, along with covering large areas of the works with solid top flooring, safeguard against the negative effect odours can cause. [caption id="" align="alignnone" width="1200"] Ballygowan WwTW nearing completion - Courtesy of NI Water[/caption] Collaboration and PR Collaboration was instilled throughout every aspect of the planning, design and construction phases for the new Ballygowan WwTW. NI Water and its project management team developed a proactive communication and PR strategy for project which included erection of storyboards; circulation of project brochure; issuing of regular updates to residents; briefings for elected representatives; circulation of press releases and a number of events and initiatives with the local residents’ association. A collaboration initiated with the local council also saw the creation of a small orchard by local children on an area of disused council land adjacent to the WwTW, which GEDA prepared for planting out. Outcome By working in partnership with each other, as well as myriad stakeholders, NI Water, Tetra Tech, GEDA Construction and the wider supply chain were able to successfully overcome difficult challenges to deliver a sustainable, state-of-the-art wastewater treatment solution, capable of meeting its stringent consent standard and serving the community for many years to come.