Supply Chain - Wastewater Treatment - Tertiary Treatment

Once the expansion is completed, Newthorpe flows and Heanor flows will have separate preliminary and primary treatment streams, before combining in the secondary treatment stage.

Flows from the Newthorpe catchment will arrive at the existing inlet works. This area will stay as per the current arrangement and only the mechanical equipment will be upgraded. The flows are lifted using Archimedes screw pumps to a raised inlet works structure.

This structure holds the fine screens, which are designed to capture at least 80% of all the solids above 6mm. After the screens, a detritor will settle all grit and inorganics such as sand; removing them from the process stream to avoid damage to the mechanical equipment.

The wastewater from the catchment then flows to the primary treatment area, where the first physical separation of particles using gravity to settle the fines at the bottom of the two existing primary settlement tanks is carried out.

The effluent from the primary settlement tanks, that is currently connected to a secondary treatment consisting of trickling filters and hummus tanks, will now be diverted to the new works’ expansion.

Flows from the Heanor catchment area that arrive at Heanor will be pumped 2.5km to a newly build inlet works at Newthorpe. Similar to the existing inlet works, the new inlet works will feature 2D 6mm screens provided by Longwood Engineering Company Ltd and a 4.5m detritor provided by Tuke & Bell Ltd.

After the detritor, the flows merge, without having been settled, with the Newthorpe flows. Keeping the Heanor flows unsettled is key to provide the right load for the process to work.

The main biological treatment happens in this secondary stage, where the aim is to reduce to the consented levels certain parameters such as Phosphorus, ammonia, iron and suspended solids. The process selected for Newthorpe is an enhanced bio phosphorus removal process in a modified University of Cape Town (UCT) configuration.

The first stage in the process is the anaerobic zone, where the polyphosphate-accumulating organisms (PAOs) thrive in an environment with no oxygen nor nitrogen introduced. In this stage, the PAOs accumulate volatile fat acids which will help them being biologically competitive in the aerobic phase of the treatment.

The next stage is the anoxic zone, where recirculated active sludge (RAS) from the secondary settlement process is introduced.

This RAS recirculates the bacteria through the system as well as introduces nitrogen oxides which have been created in the aerobic section by the oxidation of ammonia (NH4). In this anoxic zone, the nitrogen oxides are transformed into nitrogen gas which escapes to the atmosphere.

The third stage of the process is the aerobic zone in which air is introduced. Under these conditions, three main processes concur:

The final stage of the secondary treatment is the secondary sedimentation on the final settlement tanks, where the rich-P sludge is removed from the system and either recirculated to the anoxic zone; or thickened and wasted to produce other products such as gas and cake on sludge digestion processes.

The final stage of the process aims to further reduce the P levels in the effluent by capturing non-organic phosphorus.

Ferric sulphate is dosed upstream of the tertiary solids removal unit to cluster the particles into larger floccules that are then removed by a physical filtration system. The system selected in Newthorpe is FilterClear (mixed media filtration), designed and manufactured by Bluewater Bio Ltd. Once commissioned it will be the largest FilterClear system in wastewater treatment.

MMB and Severn Trent will be working together during the commissioning of the plant to understand the emissions of greenhouse gases in sewage treatment works and how to optimise the plan to reduce them. Instrumentation to measure NO and N2O will be installed on the ASP.

Nitrous oxide is produced during the biological removal of ammonia in nitrifying ASPs. Monitoring nitrous oxide emissions (along with nitrite) during commissioning at Newthorpe will not only provide STW with a baseline process emissions factor (EF) for the site but also with valuable insights into the mechanisms resulting in nitrous oxide production.

At Heanor, the main structure, which is the new transfer and storm pumping station structure, is currently in its final stages.

The site will be operational in its final configuration by December 2024 to meet the regulatory requirements.

The 2.5km 450mm dual rising main connecting Heanor STW to Newthorpe STW is now completed by with only the pressure testing and its final connection to Newthorpe STW pending. The rising main will be ready to transfer flows in October 2024, to aid with the EBPR maturation process ahead of the regulatory commitment.

The route of the rising main crossed several historical mine sites. MMB’s geotechnical team conducted an investigation to understand the status and position of the mine entries and any other mine-related features along the route. Additionally, a watching brief was in place to quickly identify any non-natural ground features.

Thanks to this effort all the risks were mitigated, and the rising main was safely constructed by Johnston Trenchless Solutions.

At Newthorpe, all major civil structures are completed, and on the site, a major operation of backfilling, electrical and mechanical installation is currently ongoing.

In 2024, the Newthorpe STW expansion project has been awarded two Green Apple Awards in the categories of Building & Construction and Sustainable Water Management. The project also won the first Ground Engineering Awards for MMB for the UK Project with a Geotechnical Value of between £500k and £1m.

Newthorpe STW and Heanor Milnhay STW have been merged in one of the major AMP7 Severn Trent projects, with Mott MacDonald Bentley as principal designer and contractor. The expansion to Newthorpe STW will be one of the largest enhanced bio-phosphorus treatment sites in the region covering a population equivalent of 100,000 and will achieve a tightened permit of 0.2 mg/l, whilst minimising the use of chemicals to remove phosphorus.

The project is currently on track to achieve the biological maturation of the EBPR by its regulatory date in December 2024.

Yeovil WRC in Somerset is a large treatment works owned by Wessex Water, serving a population equivalent (PE) over 75,000 (including trade discharge). The existing treatment processes comprised:

To meet tightened consent requirements, a major upgrade was required during AMP7; comprising tertiary MBBR plant and a tertiary solids removal (TSR) plant.

The TSR plant with chemical dosing is required to achieve the total phosphorus (TP) consent of 0.5 mg/l. On a whole life cost basis, taking into account process reliability, delivery programme, power demands, chemical consumption and maintenance requirements, FilterClear from Bluewater Bio Ltd was identified as the preferred solution, and the contract was awarded in May 2022.

FilterClear is a true depth filtration technology, with 900 mm of filtration bed depth. The influent is pumped to the top of the filter and flows through four layers of media: anthracite, silica, alumina and magnetite, which have decreasing particle size and increasing density. This configuration provides an equivalent of 4-stage filtration in a single vessel, allowing the filter to operate at a much higher filtration rate (up to 35m3/h) and achieve a better effluent quality than conventional sand filters; coupled with its much smaller footprint. FilterClear is a powerful tool in a designer’s armoury.

The key benefit of depth filtration is to enable the solids to be removed progressively through the entire depth of the 4-layer filter bed, extending the run-time and reducing backwash frequencies. The backwash can be controlled by timer or pressure. After backwash, the media will settle back to the original layers thanks to the carefully selected density and particle sizes of the four media types.

FilterClear has an average operating pressure of 0.4 bar, offering a low energy demand and a low operational carbon footprint.

Experience across the many FilterClear plants installed to date has highlighted the low cost of ownership, particularly with respect to operation and maintenance. The plants are fully automated and typically require just one annual service (less on sites with activated sludge upstream). There is no routine requirement for replacement parts or filtration cloths and the FilterClear plants require only a top-up of anthracite every few years.

Furthermore, all media layers are naturally-occurring minerals, thereby not introducing any microplastics or fibres into the treated effluent or dirty backwash water.

For chemical P removal, good coagulation and flocculation are critical. Many TSR technologies need purpose-built coagulation and flocculation tanks with mechanical mixing, and some will also require polymer dosing.

By comparison, FilterClear only requires coagulant dosing for P removal; no polymer or ballast material is required. This is because large flocs are not essential for depth filtration. Chemical dosing can be added directly upstream of the FilterClear plant via an inline static mixer, and flocculation will occur in the headspace inside the filter vessel, above the media bed, removing the need for mechanical mixing or a flocculation tank, thereby simplifying the asset and reducing associated costs.

The absence of a separate flocculation tank further minimises the FilterClear footprint, makes the solution simpler to build and operate and eliminates the associated operational and maintenance tasks. It also eliminates the need for an overflow from the flocculation tank which, having been dosed with coagulant, represents a compliance risk.

The key elements of the FilterClear plant at Yeovil WRC are:

The FilterClear plant design has taken into account the following:

Thanks to the high filtration rate, the FilterClear plant has a smaller footprint in comparison to conventional filters. The compact nature of the FilterClear plant makes it ideal for the very congested site at Yeovil. At the time of writing (July 2024), the FilterClear plant has been installed and is currently being commissioned.

Most TSR plant suppliers prefer to offer an effluent total suspended solids (TSS) guarantee as a surrogate to a TP guarantee. However, water companies have realised that, at low concentrations, there is a very poor correlation between the TSS and TP concentrations thereby introducing compliance risk.

As the developer and owner of the technology, Bluewater Bio Ltd has a deep understanding of both the process and phosphorus removal, and accordingly are able to provide a TP guarantee. This offers the client and their contractor the simplest and clearest assurance of meeting the final effluent permit as well as being contractually most straightforward. FilterClear performance has been tested and proven at over 50 sites across most UK water companies, all reliably achieving the respective permit requirements for both TP and iron. Knowing that more stringent TP permits will be imposed in AMP8, Wessex Water carried out long-term trials to push the performance limits at several sites with impressive results.

‘Site A’ is a typical small trickling filter site. In AMP7, a FilterClear plant was installed to meet a new 0.5 mg/l TP permit. The trial demonstrated that the plant achieved an average TP below 0.07 mg/l, with a 95%ile iron concentration of 0.27 mg/l. This performance has been achieved with an overall ferric dose of just 15 mg/l (including 1st point and 2nd point dosing) with simple flow-proportional dosing control, and despite some unrelated control issues during the trial. The long-term trials have demonstrated that FilterClear plants can reliably achieve a TP permit of 0.1 mg/l, making the solution future-proof. This offers the client a means of reducing WLC whilst adding future certainty.

Increasingly, clients and their tier one partners are looking to minimise site construction activities and durations. FilterClear plants are designed to allow off-site assembly and testing, then delivery to site as a package plant. Where possible, the complete filter gallery, including backwash pumps, blowers, actuated valves, instruments and controls are skid-mounted and transported fully assembled. Site activities are then limited to coupling the filter vessels, adding the media and commissioning. This DfMA approach ensures both quality and safety are well controlled and ultimately delivers a better solution in a shorter time at a lower overall cost.

Health and safety is an integral part of the design process, ensuring that all equipment is safe to install, operate and maintain. Filtration and backwash of the FilterClear plant is fully automated, with minimum operational input. The filters are enclosed, with no moving parts or serviceable components within the vessels and need minimal operator intervention. Due to the enclosed, fully automated design, risk of operator exposure to wastewater or chemicals is minimised. Furthermore, all machinery is at ground level for easy access.

Throughout the project, the design teams worked closely with Wessex Water on the ALM assessment to ensure that the plant is operator-friendly. Particular attention was paid to eliminating hazards during operation and maintenance.

Innovation plays a critical role in the water industry’s ability to adapt to climate change, population growth and new and emerging pollutants. Bluewater Bio continue to develop and enhance technologies so that they excel in performance, value, reliability and sustainability.

In 2024 Bluewater Bio Ltd received a King’s Award for Enterprise in the Innovation category for its FilterClear technology. The award was granted on a recommendation by the Prime Minister and approved by His Majesty The King and is the most prestigious award for a UK business. This award is further recognition that FilterClear has become the preferred choice for clients.

With AMP8 on the way, over 900 sites will be on the national P removal programme and FilterClear will play a major part in delivering a successful outcome.

Flows received at Rotherwas are split between four primary settlement tanks (PSTs). A portion of the effluent from the PSTs is pretreated by a high-rate filter (HRF) to lower biological load and then mixed with the rest of settled flow before passing to 18 biological filter beds. The effluent from the biological filters is dosed with poly aluminium chloride and flows into four humus tanks. Effluent from the humus tanks flows to the works outfall for discharge into the River Wye.

Due to the requirement for a new tighter discharge limit for phosphorus, reducing the total standard from 1 mg/l to 0.4 mg/l, Welsh Water was required to undertake modifications to both sites.

To meet the new consents the following works were required:

The proposal also required an interception chamber located on the existing final effluent pipework, downstream of the humus settlement tanks, to divert flows to the new lift pumping station and further pass them onto the new TSR plant, incorporating 16 vertical (2.8m diameter) pressure filters.

The pumped feed to the new TSR will be dosed with ferric sulphate. Treated flows from the TSR will then gravitate via a drop chamber to the existing final effluent sample chamber and outfall to the river. The TSR plant will also incorporate a dirty backwash tank and pump return system, that will pass filter backwash returns to the works reception chamber.

A new outfall interception chamber was installed on the existing live final effluent pipework (1m diameter and approximately 4m deep), between the existing humus tanks and sample chamber.

The interception chamber facilitates diversion of humus tank effluent to the new lift PS, which feeds the new TSR plant; it also provides an emergency overflow to bypass the lift pumping station. The emergency overflow incorporates an actuated overflow weir which operates automatically to prevent back flooding of the existing humus settlement tanks under certain high river level conditions. The chamber is a 4m diameter structure, 4m deep.

Due to the chamber being built over the live pipework, a Business Continuity Plan had to be in force during construction. This meant that 24/7 over-pumping was in place to pump the pass forward flow of 574 l/s, as required. Construction of the chamber required a cofferdam, which was sunk using a Movax (vibrating hammer attached to 32T machine). The final effluent pipe was carefully exposed, then cut using wire rope.

New sample chamber level instruments and duty/standby progressive cavity sample pumps complete with necessary pipework and pressure instruments were installed by the existing sample chamber. The pumps provide a continuous flow for the new final effluent sample instruments installed within the existing sample kiosk: pH, total suspended solids, ortho-phosphate, soluble iron and soluble aluminium.

A tertiary solids removal lift pumping station was required to provide the motive pressure and flow for the TSR filtration process. The selected TSR technology consists of multi-media pressure filters in above-ground vessels. The pumping station consists of a wet well with three variable speed submersible pumps (duty/assist/standby) to provide the maximum flow rate (574 l/s) required for the new TSR plant. The pumps are controlled by variable speed drives to cater for the fouling of the multimedia pressure filters during operation.

Level instrumentation for controlling the lift pumps was submerged pressure transducers, as the works suffer from severe foaming during certain periods, and this allows for continued effective control as the ultrasonic signals would be lost during these events.

Several options were considered for the tertiary treatment stage; all of which achieved the necessary solids removal and P performance.

They were assessed against a number of criteria and the FilterClear process from Bluewater Bio Ltd was selected. It should be noted that a major constraint was space on site, and the Bluewater Bio plant’s low footprint meant that it could be located within the existing site boundary, avoiding use of the neighbouring field which is prone to flooding.

There were two options for the Bluewater Bio Ltd package:

The vertical filters option was selected due to the following:

The filters were specified to achieve the following process performance at the 95-percentile limit:

The treated effluent from the TSR plant will pass by gravity directly to the existing sample chamber and outfall. An energy dissipation drop chamber was also installed to receive the treated effluent from the TSR; this aided the hydraulics and allowed a controlled flow to the downstream existing sample chamber.

Bluewater Bio Ltd confirmed that there was no need for a clean water storage tank for backwash purposes as there was sufficient water volumes within the TSR filter system. Therefore, backwash water is taken directly off the filter outlet manifold and pumped through the filters via backwash pumps. Air scouring is also carried out as part of the backwash process. Filters are called to wash on pressure differentials across the filter bed and/or timed intervals.

The dirty backwash waters from the filters are conveyed to the dirty backwash water storage tank. This storage tank is 7.7m internal diameter by 9.9m high and has a suitable operating volume of 412m3.

This volume allows for effective metering/smooth delivery of the dirty washwater back to the head of the works at the inlet receiving chamber. This is important as the instantaneous backwash pump flow rate is too high to be accepted by the works.

The captured dirty backwash water in the storage tank is returned via three variable speed progressive cavity pumps operating in a duty/assist/standby mode. The need for progressive cavity type pumps was driven by the required operating envelope for effective flow rate returns. The flow and volume of the backwash water return is monitored and recorded via an electromagnetic flow meter which will be used as part of the M-Certed site flow monitoring.

The backwash return flow rate range is 30 l/s to 89 l/s depending on levels within the storage tank.

A gravity return feature has also been installed as a bypass around the backwash return pumps, which can be used as an alternative when operating conditions allow.

To ensure the effective removal of phosphorus in the treatment process, two new chemical dosing systems were installed. The first provides primary dosing (PACL dose) upstream of the PSTs and includes a single storage tank of 62m3 and a dosing kiosk housing duty/standby pumps.

The second chemical plant provides tertiary dosing (ferric sulphate dose) directly into a static mixer on the TSR rising main, which feeds the TSR filters; it also includes a single storage tank of 57m3 and a dosing kiosk housing duty/standby pumps.

There were several significant construction challenges experienced on site. The major one was the limited space available within the construction area. This led to a potential congested working area with up to 50 personnel on site at the same time, working in close proximity to one another. This required the construction programme to be carefully planned and coordinated to ensure that the works were constructed safely, with relevant segregation, and to ensure the protection of the work force at all times.

Another challenge was ensuring the treatment works were running effectively at all times and maintaining compliance as to no cause detriment to the existing process. To enable the treatment works to remain operational during the construction of the new assets especially the interception chamber, which was constructed over the existing live final effluent pipe, several Business Continuity Plans (BCPs) were compiled and agreed with the client and operations collaboratively.

Significant over-pumping (up to 600 l/s) needed to be in place for approximately 10 weeks, requiring 24/7 operation with duty and standby pumps, pump-men attendance, and on call to ensure that there was no risk of breaching the EA discharge permit.

Several major BCPs were required for the following works:

A number of smaller BCPs were also in place for the EICA works, including power and signal cable installation.

The planning of the construction works was crucial, as the 18-month programme was extremely tight. This meant that there was little float during the construction period.

There were several innovations on this project covering different aspects including operation, Health & Safety/CDM, environmental and TOTEX savings. Two of these innovations are outlined below.

Lift pumping station baffle wall: The design called for the 2.5m high and 5.6m wide baffle within the 8m deep 8.2m diameter wet well; the baffle invert had to be installed 1m above finished floor level, supported off the side benching. The original design intent was for the baffle to be a stainless steel plate; however, this became cost prohibitive, resulting in a change to a concrete structure, which would be cast in situ.

However, to maximise best Health & Safety practices, it was proposed to construct the baffle wall as a precast element on site, at ground level. The precast wall weighed approximately 11 tonnes and was installed within the pumping station using a 200T crane. This greatly reduced the Health & Safety risks (limiting confined space working) and allowed for better quality control of the shuttering frame. Off-line construction also offered a safe working area for the shuttering team, steelwork fixers and better access for the concrete pour. There was a remaining risk associated with lifting a large element into position within the wet well.

To overcome this, an enhanced lifting arrangement was developed which involved the local reinforcement of the baffle alongside special fixings (lifting eyes) which could be removed upon completion. The benching concrete also had to be evenly poured around the wall to ensure its stability in the temporary case.

Clean water tank for TSR backwash process: The initial proposal was to construct a 226m3 clean water storage tank for the backwash process. However, this was associated with significant cost and there was insufficient space on the site for this to be located. The team challenged the requirement for this tank and, with the support of Bluewater Bio Ltd and Welsh Water’s Operations team, a risk-based analysis was carried out which concluded that the tank was not required. This was due to the sufficient storage in the filter system, ensuring effective backwash under all operating conditions.

Welsh Water have invested £30m at Eign and Rotherwas WwTWs. These phosphorous removal schemes are part of a programme of upgrades to existing wastewater treatment works that will improve water quality in the rivers. Lessons learnt from these schemes have been used by Arup and Morgan Sindall and shared with the Welsh Water Capital Delivery Alliance partners to improve scheme delivery of other rural wastewater treatment works.

Early contractor engagement with mechanical subcontractors, chemical dosing suppliers, and DfMA MCC suppliers, helped achieve significant design and construction efficiencies.

Eign and Rotherwas WwTWs were completed in line with achieving the new tighter P permit by the end of March 2024.

The capital scheme at Southern Water’s Horsham New WwTW will deliver an upgrade to the treatment facilities at the site to cater for the significant growth forecast within the Horsham catchment and surrounding areas over the next ten years, together with an improvement in the Total Phosphate final effluent emission standard, tightening from 1 mg/l to 0.25 mg/l.

These improvements to the site’s treatment processes have been designed for a 2035 population equivalent of 93,345, representing a 15% increase since 2020. There are no proposed increases to the permitted dry weather flow or permitted flow to full treatment as part of the scheme.

As well as the WFD quality driver, the project also encompasses an element of capital maintenance to be delivered by 31 March 2025, as follows:

The third and final project driver, also to be delivered by 31 March 2025, is the need to ensure the upgraded Horsham New WwTW has sufficient hydraulic and process treatment capacity to allow for the 15.5% increase in expected growth in the local population up to 2035.

Ferric dosing

Alkalinity dosing

Tertiary Treatment

Inlet screens

Storm pumping

Re-configurate secondary treatment stage

New Moving Bed Biofilm Reactor (MBBR) nitrification process stage

Upgrade site HV infrastructure

Upgrade site standby power infrastructure

Site SCADA & telemetry upgrade

Sludge treatment

The replacement of the existing 40 year old inlet screens was always going to be a significant milestone for the project and a very challenging operation. Before the new screens could be installed, which are needed to remove a vast amount of solid matter from the treatment process, the existing inlet channels were widened in places using a wire saw to provide additional room for the inclined toe of the new screens. The existing screens were electronically isolated and disconnected, along with an existing spiral conveyor, before being mechanically disconnected and removed.

This complex activity required specialist support from supply chain partners John F Hunt, FSD and R&B Engineering, to ensure a safe and successful operation.

Manufactured by FSM Frankenburger in Germany on behalf of M&N Electrical & Mechanical (Hydro International Ltd’s UK Wastewater Services division), the new state of the art inlet screens measure 12.8m in length and are among the largest Alpha Beta Escalator Screens not only in the UK, but in Europe. Accordingly, their installation required close collaboration between CMDP JV, Southern Water and all relevant supply chain partners.

With just over 10mm tolerance on either side, the new screens were successfully slotted into position within their concrete inlet channels. Pipework and cabling were installed before commissioning was completed.

As part of the project scope for the WFD quality driver, the tertiary treatment process has been enhanced by extending the existing deep bed sand filter. This has involved the construction of three extra cells, to complement the four cells already in situ.

Due to the ground conditions in this area of the site, piling was required to ensure the structural validity of the new cells, with a significant amount of temporary works required. At the time of writing (July 2024), the internal pipework has been completed and walkway platforms are in the process of being installed, with external pipework scheduled for completion at a later date.

The addition of a new moving bed biofilm reactor (MBBR) nitrification process stage to the treatment process is a key element of the project, with the installation of two new reactors undertaken by Veolia Water Technologies. As part of the scope for the project’s growth driver, the new MBBR process introduces fixed film controllable biological treatment to the works’ capabilities.

Prior to the installation of the new MBBR reactors, a substantial amount of piling was required to ensure the stability of the ground in the area where they are now situated. Work is now underway to install the underground feed pipe that will serve the new reactors.

The scope for the project’s quality driver includes an enhancement to the works’ alkalinity dosing capability, with a new 80m3 bulk storage facility comprising of two 40m3 tanks in a common bund and two-point dosing facility at the carbonaceous filter’s distribution chamber and the humus tanks effluent chamber. This element of the project was led by MEICA specialist Bridges Ltd.

When the new tanks were being installed at the bottom of a sloped area of the site, concerns emerged around the stability of this a bank in the immediate vicinity. As a result, a decision was taken to sheet pile the bank, thus ensuring its stability.

The base of the area housing the new dosing equipment was also piled, prior to a concrete slab being poured. The existing dosing capability will remain in operation until the upgrade goes live, at which point it will be decommissioned.

A ‘self-delivery’ approach to construction was adopted, with CMDP JV directly contracting the various specialist sub-contractors required to deliver the project.

Through careful management by the site team, this approach has resulted in significant cost savings, through a reduction in the amount of non-productive time spent on site by the supply chain. This has been particularly beneficial due to the number of unchartered services unearthed on site that would have otherwise resulted in time delays.

A self-delivery approach has also allowed further savings through the avoidance of mark-up of goods and services that would have been imposed had CMDP handed control of management of the wider supply chain to a third party. This has also allowed CMDP to prioritise the use of local suppliers wherever possible.

A significant challenge throughout the lifespan of the project has been the excess of buried and unchartered services on site. To control the high risks of excavation works, since the start of construction CMDP JV has issued a total of 182 “permits to dig”, with no service strikes recorded at the time of writing.

Another significant health and safety challenge faced by the project has been the fact that Horsham New WwTW serves as a Sussex area hub for four other Southern Water “Tier One” suppliers, resulting in a large amount of vehicle traffic on a constrained site.

Recognising that, proactive communication with all internal stakeholders has paid dividends, reducing delays to the project and disruption to other users of the site.

The project involves a combination of environmental mitigation and improvement, with landscaping and habitat enhancements on-site ensuring an overall 9% gain in biodiversity within the boundaries of the works.

To minimise any detrimental noise impact resulting from the operation of the upgraded works, the three blowers from Aerzen Machines that form part of the new MBBRs will have acoustic barriers installed. These barriers will ensure that any noise from the blowers, which form part of the process air system, will not impact the residential properties located closest to the works.

An opportunity to further minimise the environmental impact of the project has been possible through the use of local suppliers, as detailed further in the ‘Social Value’ section below.

In line with the commitment shared by both Southern Water and CMDP to ensure a positive impact upon the communities they operate within, the efforts of the site team at Horsham New WwTW were recognised with a national award.

The Considerate Constructors Scheme (CCS) National Site Awards are one of the most prestigious accolades in the sector, highlighting those sites that have made the greatest contribution towards improving the image of construction. At a ceremony held in London, CMDP JV Construction Manager Garry Burgess was presented with a Bronze Award to recognise the efforts of the Horsham New team in terms of creating value in the local community and being respectful to the public, the workforce and the environment.

A customer-centric approach and focus on protecting and improving the environment has proved very successful for this project, with the site team achieving a top score of 45/45 (ranked as excellent) for three consecutive assessment visits.

With very few homes or businesses in the immediate vicinity of the works, the construction phase of the project has had negligible impact on the local community.

However, with the importance of ‘Social Value’ growing rapidly within the water industry, and Southern Water aspiring with the help and support of CMDP JV to improve the communities in which it operates, the project team partnered with Horsham District Council’s voluntary sector support team.

This has led to project staff regularly taking time away from the scheme to support local organisations in need of volunteers to help worthy causes in and around the town; ensuring the project delivers a long-term positive impact on the local community and wider area.

This approach has helped to make the project an exemplar for both companies in terms of the creation of long-term social value and furthers Southern Water goal of being a local company that cares.

As well as partnering, efforts have been prioritised in areas where a genuine need exists within the local community, and where the project team could employ their skills most effectively. The Social Value portal’s ‘Themes, Outcomes, Measures (TOM)’ system was used to measure and report the value of the wealth of social value activity undertaken by the project team, which includes:

Use of the ‘Themes, Outcomes, Measures’ system allows the project team to track success and ensure momentum, which in term will help to set a benchmark for the social value element of future projects.

With strong relationships established with a wide range of local organisations and key stakeholders, the figures listed above will continue to grow as the project progresses towards its scheduled completion in 2025.

The complex upgrade of Horsham New WwTW involved the installation of a range of new hi-tech machinery; including two of the largest Alpha Beta Escalator Inlet Screens in Europe.

CMDP JV’s self-delivery approach has provided added flexibility and numerous benefits, and a keen focus on social value will ensure a long-lasting positive impact beyond the scope of the project itself.

Once complete, the upgraded works will be equipped to cater for the significant growth forecast within the Horsham catchment and surrounding areas over the next ten years. It will increase the quality of the treated water being returned to the River Arun and ensure Southern Water fulfils its regulatory requirements.

The technical solutions considered during design included increasing the storm tank capacity and the hydraulic capacity of the wastewater treatment works (WwTW) to reduce the intermittent storm discharges, with UV irradiation or membranes being considered to achieve the disinfection requirements.

Details of the five sites are as follows:

The project drivers required a reduction of spill frequency at storm overflows for all the catchments that discharge into Southampton Shellfish Water. This impacted five separate wastewater treatment works catchments.

Early in the design, the Southern Water (SW) project team identified an efficiency opportunity of combining the FFT U_IMP5 (increase in flow to full treatment) Driver with the Shellfish Driver, which had a significant impact on reducing the volume of the storm storage tanks. SW held regular meetings and agreed the approach with the Environment Agency (EA) including alignment of Regulatory output dates to the end of the AMP period.

The assessment of storm storage is based on the agglomeration approach outlined in the EA PR19 shellfish guidance and methodology. The definition of a significant spill was agreed with the EA at the conceptual stage of the scheme. This assessment treated all the discharges as a single agglomeration.

In summary, the integrated combined driver approach provided the following benefits:

To develop the solutions required at each wastewater treatment works, the sewer network performance for the five catchments was designed using a 10-year rainfall dataset. The observed spill frequencies across the catchment had to be agglomerated to ensure that 10 significant spills or less per year was achieved over a long-term (10 year) average.

This meant the modelling was more complex and took a lot longer than a usual model build and verification exercise because of the need to assess all five catchments together.

Following subject matter guidance from across the industry, the project team used an innovative approach of using an extended rainfall series duration and a single rain gauge. In addition, the team targeted the storage volumes at sites where there was available capacity to arrive at the most efficient storage volumes that were significantly lower than the original estimates, all while complying with good industry practice. In summary, this included:

The project team considered the best location for increasing the capacity of storm storage considering the cost/benefit for reducing significant storm spills. For example, at Millbrook WwTW redundant storm tanks were utilised that provided a volume of 3,140m3. The increase in volume at Millbrook enabled the storage volumes to be optimised across the agglomeration of sites with volumes being offset against other more constrained sites.

The initial significant storm volumes at Woolston were extremely challenging given the location of the site within an urban environment and lack of available space. The project team identified an opportunity of increasing the FFT at Woolston, which provided a significant reduction in storage. The scope involved utilising hydraulic headroom within the works, and through the installation of additional MBR capacity and associated pump upgrades, enabled a 20% increase in FFT at Woolston WwTW (427 l/s to 534 l/s).

The programme to deliver the increase in FFT at Woolston was short and provided an early reduction in E. coli concentration discharging to the Solent. This early delivery reduced 20% of the total E. coli concentration across the agglomeration of sites and was fundamental in agreeing new regulatory dates for the SW_ND (storm storage) drivers. The combination of the integrated driver approach to reducing spills, the innovative modelling and optimisation of assets reduced storage volumes by circa 46,000m3.

The final volumes are as shown in Table 2:

In response to a number of drivers, the EA has recently revised its approach to design and permitting of UV irradiation systems for the disinfection of final effluent. The aim is to move away from the use of generic assumptions, to follow international best practise with an approach which employs the use of a site-specific data in conjunction with performance validated UV irradiation equipment. This revised approach enables development of a significantly better understanding of performance and limitations on a site-specific basis.

Understanding the variation and impact of key wastewater characteristics on parameters such as UV transmittance and the UV dose-response relationship enables selection of a representative design envelope and minimum target UV dose. This enables the capital solution to be optimised, minimises power usage, operational costs and carbon impact while securing environmental performance.

The steps undertaken for the development of the design parameters and permit conditions for the UV irradiation systems at Slowhill and Millbrook WwTWs can be summarised as follows:

The new UV irradiation systems have been in operation at both sites since Autumn 2023 and are consistently achieving concentrations of E. coli in the final effluent discharges that will maintain the concentration at the Shellfish Water Boundary below the post PR19 target value of 5 cfu/100ml as a geomean.

Due to the limited availability of operational land in Woolston, the new storm shaft is being constructed beneath a car park and green area own by Southampton City Council (SCC), the area also had a Multi-Use Games Area (MUGA). The project team and the representatives of the Council engaged in extensive discussions prior to submission of the planning application which ensured a positive outcome for both parties.

From those conversations the project team learnt that the Council had worked to create a low nutrient coastal grass environment in the zone affected by the project. The topsoil had been amended and sown with the current species in previous seasons. Therefore, the agreed approach was to retain the topsoil stored on site and reinstate it at the end of the project, enabling the green area to grow and cover the old disused carpark.

The first activity after site mobilisation was relocating the reptiles that naturally inhabit coastal grass biomes. All areas with long grass that were part of the construction compound had the grass cut in two passes to encourage reptiles to move to nearby unaffected zones. Additionally, the top 100mm of soil was hand excavated with an ecologist carefully moving those reptiles still on site.

SW, working closely with the local Council, has ensured that the pre-existing facilities not only are kept despite the new structures being built, but that they are also improved. The number of parking bays and EV charging points will be maintained with improved access arrangements to avoid unwanted camping vans. The MUGA will be improved so the excessive slope that the old court had is removed and the pedestrian access to an adjacent park is protected with bollards, as previously vans used to park using part of the footpath.

The storm tank at Millbrook WwTW and the increase in flow to treatment at Woolston WwTW were both commissioned in July 2022 while the projects to install UV irradiation at Slowhill and Millbrook WwTWs were commissioned in Autumn 2023. In combination, these improvements represent a reduction of 72,500 cfu/s of E. coli being discharged to the Southampton Shellfish Waters, which is more than 60% of the total E. coli concentration reduction when all the projects are completed.

Results from sampling carried out after commissioning have demonstrated that both UV irradiation systems at Slowhill and Millbrook have reliably achieved the target efficacy, with concentrations of E. coli in the effluent post disinfection regularly below 200 cfu/100ml. Additionally, concentrations of E. coli in the final effluent discharge from Woolston have been consistently below 35 cfu/100ml since July 2019, following commissioning of the MBR.

The next key milestones are 31 December 2024, when the new storm tank at Ashlett Creek WwTW will be commissioned, and 31 March 2025, when all the remaining storage and increase in flow to treatment drivers will be completed.

FilterClear is a true depth filtration technology, with 900 mm of filtration bed depth. The influent is pumped to the top of the filter and flows through four layers of media: anthracite, silica, alumina and magnetite, which have decreasing particle size and increasing density. This configuration provides an equivalent of 4-stage filtration in a single vessel, allowing the filter to operate at a much higher filtration rate (up to 35m3/h) and achieve a better effluent quality than conventional sand filters; coupled with its much smaller footprint. FilterClear is a powerful tool in a designer’s armoury.

The key benefit of depth filtration is to enable the solids to be removed progressively through the entire depth of the 4-layer filter bed, extending the run-time and reducing backwash frequencies. The backwash can be controlled by timer or pressure. After backwash, the media will settle back to the original layers thanks to the carefully selected density and particle sizes of the four media types.

FilterClear has an average operating pressure of 0.4 bar, offering a low energy demand and a low operational carbon footprint.

Experience across the many FilterClear plants installed to date has highlighted the low cost of ownership, particularly with respect to operation and maintenance. The plants are fully automated and typically require just one annual service (less on sites with activated sludge upstream). There is no routine requirement for replacement parts or filtration cloths and the FilterClear plants require only a top-up of anthracite every few years.

Furthermore, all media layers are naturally-occurring minerals, thereby not introducing any microplastics or fibres into the treated effluent or dirty backwash water.

For chemical P removal, good coagulation and flocculation are critical. Many TSR technologies need purpose-built coagulation and flocculation tanks with mechanical mixing, and some will also require polymer dosing.

By comparison, FilterClear only requires coagulant dosing for P removal; no polymer or ballast material is required. This is because large flocs are not essential for depth filtration. Chemical dosing can be added directly upstream of the FilterClear plant via an inline static mixer, and flocculation will occur in the headspace inside the filter vessel, above the media bed, removing the need for mechanical mixing or a flocculation tank, thereby simplifying the asset and reducing associated costs.

The absence of a separate flocculation tank further minimises the FilterClear footprint, makes the solution simpler to build and operate and eliminates the associated operational and maintenance tasks. It also eliminates the need for an overflow from the flocculation tank which, having been dosed with coagulant, represents a compliance risk.

Increasingly, clients and their tier one partners are looking to minimise site construction activities and durations. FilterClear plants are designed to allow off-site assembly and testing, then delivery to site as a package plant. Where possible, the complete filter gallery, including backwash pumps, blowers, actuated valves, instruments and controls are skid-mounted and transported fully assembled. Site activities are then limited to coupling the filter vessels, adding the media and commissioning. This DfMA approach ensures both quality and safety are well controlled and ultimately delivers a better solution in a shorter time at a lower overall cost.

Health and safety is an integral part of the design process, ensuring that all equipment is safe to install, operate and maintain. Filtration and backwash of the FilterClear plant is fully automated, with minimum operational input. The filters are enclosed, with no moving parts or serviceable components within the vessels and need minimal operator intervention. Due to the enclosed, fully automated design, risk of operator exposure to wastewater or chemicals is minimised. Furthermore, all machinery is at ground level for easy access.

Most TSR plant suppliers prefer to offer an effluent total suspended solids (TSS) guarantee as a surrogate to a TP guarantee. However, water companies have realised that, at low concentrations, there is a very poor correlation between the TSS and TP concentrations thereby introducing compliance risk.

As the developer and owner of the technology, Bluewater Bio Ltd has a deep understanding of both the process and phosphorus removal, and accordingly are able to provide a TP guarantee. This offers the client and their contractor the simplest and clearest assurance of meeting the final effluent permit as well as being contractually most straightforward. FilterClear performance has been tested and proven at over 50 sites across most UK water companies, all reliably achieving the respective permit requirements for both TP and iron. Knowing that more stringent TP permits will be imposed in AMP8, Wessex Water carried out long-term trials to push the performance limits at several sites with impressive results.

‘Site A’ is a typical small trickling filter site. In AMP7, a FilterClear plant was installed to meet a new 0.5 mg/l TP permit. The trial demonstrated that the plant achieved an average TP below 0.07 mg/l, with a 95%ile iron concentration of 0.27 mg/l. This performance has been achieved with an overall ferric dose of just 15 mg/l (including 1st point and 2nd point dosing) with simple flow-proportional dosing control, and despite some unrelated control issues during the trial. The long-term trials have demonstrated that FilterClear plants can reliably achieve a TP permit of 0.1 mg/l, making the solution future-proof. This offers the client a means of reducing WLC whilst adding future certainty.

During AMP7, Wessex Water installed 14 FilterClear plants across its region for phosphorus removal, ranging from small sites less than 4,000 population to large sites over 75,000 population. Yeovil Pen Mill Wastewater Recycling Centre (WRC) is the largest site among these.

Yeovil WRC in Somerset is a large treatment works owned by Wessex Water, serving a population equivalent (PE) over 75,000 (including trade discharge). The existing treatment processes comprised:

To meet tightened consent requirements, a major upgrade was required during AMP7; comprising tertiary MBBR plant and a tertiary solids removal (TSR) plant.

The TSR plant with chemical dosing is required to achieve the total phosphorus (TP) consent of 0.5 mg/l. On a whole life cost basis, taking into account process reliability, delivery programme, power demands, chemical consumption and maintenance requirements, FilterClear from Bluewater Bio Ltd was identified as the preferred solution, and the contract was awarded in May 2022.

The key elements of the FilterClear plant at Yeovil WRC are:

The FilterClear plant design has taken into account the following:

Thanks to the high filtration rate, the FilterClear plant has a smaller footprint in comparison to conventional filters. The compact nature of the FilterClear plant makes it ideal for the very congested site at Yeovil. At the time of writing (July 2024), the FilterClear plant has been installed and is currently being commissioned.

Throughout the project, the design teams worked closely with Wessex Water on the ALM assessment to ensure that the plant is operator-friendly. Particular attention was paid to eliminating hazards during operation and maintenance.

Innovation plays a critical role in the water industry’s ability to adapt to climate change, population growth and new and emerging pollutants. Bluewater Bio Ltd continue to develop and enhance technologies so that they excel in performance, value, reliability and sustainability.

In 2024 Bluewater Bio Ltd received a King’s Award for Enterprise in the Innovation category for its FilterClear technology. The award was granted on a recommendation by the Prime Minister and approved by His Majesty The King and is the most prestigious award for a UK business. This award is further recognition that FilterClear has become the preferred choice for clients.

With AMP8 on the way, over 900 sites will be on the national P removal programme and FilterClear will play a major part in delivering a successful outcome.

Winchester House, 259-269 Old Marylebone Road, London NW1 5RA

| 020 7908 9500 | bluewaterbio.com |

The assertion of uneconomic viability is becoming harder to argue as more sites are having ever tightening consents applied to them, meaning that the offsetting of better performance from larger sites is being negated, and these smaller sites are having to be upgraded to meet the consents and catchment area water quality targets.

The AquaPyr filter from ACWA Services has been designed to negate these CAPEX upgrade costs and issues as far as possible but still deliver a cost-effective, robust solution in providing tertiary solids removal for remote rural treatment works ensuring discharge consents are met.

Traditional cloth media filters typically generate between 2% and 5% of forward flow volumes as backwash water according to manufacturers data. However, these figures are based on higher flow works and do not scale downward when applied to smaller WwTPs.  It is not uncommon to have 15 to 20% of the forward flow utilised as backwash water and returned to the plant in smaller works or applications with higher TSS, such as filtration of chemically dosed feed for reduction of Total P. These high levels of backwash water being returned to the head of works can cause potential ‘flooding’ of the works as many are already close to their hydraulic capacity, resulting in the need for the construction of backwash balance tanks to control this additional flow being added to the works.

Low flow sites pose additional problems for traditional backwash cloth filters, as often flows are insufficient to generate the required waters for backwashing at low flow rates, such as summer months, when the need for chemical dosing for phosphorus removal is likely to be at its greatest with the resulting increase in solids that need to be removed prior to final discharge. This can result in maintenance issues for the filters or the need to build baffle tanks to hold sufficient water for the backwashing requirements during periods of low flow, again increasing CAPEX in the building of these and OPEX of the solutions with increased pumping requirements.

The ACWA AquaPyr filter is an innovative fully contained, deep pile cloth media filter that generates minimal waste during the filter cleaning process. This is possible as unlike traditional TSR filters, the AquaPyr filter uses a patented air driven cleaning process in place of water for backwashing the filter, thus eliminating the need to store water for backwashing and then attenuating used backwash water for return to the front of the works. Typical waste volumes per clean are between 4 litres and 50 litres depending on the size of the unit, and remain <0.25% of forward flow.

This resulting waste is of a relatively high solids concentration, as much as 2% dry solids (DS), meaning that this could be discharged to the sludge or humus tanks rather than returning to the head of works and putting extra loading stress on the works.

The AquaPyr filter comes in a range of sizes meaning treatment volumes of a single unit range from 0 to 2000m3/day dependent on the solids loading applied to the filter. Multiple units can be used in parallel to increase these volumes and provide duty standby resilience as required.

The units are fully self contained and all the pumps, drives and vacuum motors required for the operation of the unit are fitted internally. With a footprint range of 750mm x 710mm for a Model 25 up to 1960mm x 1770mm for a Model 440, the units have a uniquely small footprint for their treatment capacity.

The units low power draw and power requirements, ranging from 11 Amps for a Model 25 to 40 Amps for the Model 440 mean that all units are single phase, with the Models 25 and 65 actually being able to be used on a domestic three pin plug. AquaPyr filters consume little power; across all models power consumption averages in the range of 7 to 10 kWh/1000m3 of feed.

AquaPyr’s compact filter size, robustness and low operational costs led to Silver Lake, a small rural community in Indiana, choosing to use the technology on their unmanned sites. The Silver Lake WwTW is an activated sludge works with a design flow of 1.6 l/s.

The effluent entering the filter had 10 mg/l total suspended solids and a BOD of 10 mg/l. The requirement was for <=0.5mg/l Total P.

Two ACWA AquaPyr Model 25 units were chosen in a duty/assist configuration, and working at a hydraulic loading rate of 12 LPM/ m2 average daily flow which was 2 x peak and a solids loading rate of 0.05 kg/m2 daily average.

The resulting effluent quality after the filters was a Total P of <0.25 mg/l, BOD of 5 mg/l and TSS of <5 mg/l. The graph below shows the results of a 12 month period.

The ACWA AquaPyr Ultra Low Waste Filter has proven itself to be a robust cost effective solution in industrial and municipal waste water solutions. The total cost effectiveness of the AquaPyr filter, when compared with traditional cloth filters, further increases when looked at from a project cost basis due to the reduced civils works generally required for the installation and overall scheme requirements for the AquaPyr filter.

The ACWA AquaPyr Ultra Low Waste Filter is an innovative technology providing a solution for small and low flow water treatment works, where filter waste management and the hydraulic capacity of the existing works might make the use of a traditional tertiary solids removal process inappropriate or cost prohibitive due to the civils works and costs associated with their installation.

Silicon carbide ceramic membranes are submerged ultrafiltration flat-plate membranes with a pore size of 0.1 microns. They act as a physical barrier that blocks solids and pathogens, allowing clean water to pass through. The filtration process involves applying a slight vacuum to the membrane surface, pulling water through the membrane while contaminants are retained. After diamond, silicon carbide is the hardest material known to man.

One of the key advantages of SiC membranes, compared to any other organic or alumina ceramic membrane, is their natural hydrophilicity, which attracts water while repelling organic foulants. This reduces membrane fouling, improving filtration efficiency and reducing cleaning requirement. The system uses periodic back pulse washing and air scouring to dislodge accumulated solids, ensuring extended filtration cycle between chemical in place cleaning.

The SiC membranes are also chemically inert, sustaining pH between 2 to 13 and can act as a strong oxidising compound, such as ozone. They are also mechanically robust making them resistant to harsh mechanical and chemical cleanings.

Key benefits brought by the adoption of the Silicon carbide ceramic membranes are:

Cembrane SiC membranes have been installed in over 250 facilities worldwide. The innovative technology provides several advantages against more commonly used organic and inorganic membranes including market-leading flux rates, longevity, robustness and ease of operation. The membranes are manufactured in Denmark and the USA, and have been utilised in more than 70 countries to providing safe drinking water and wastewater treatment.

The Gothenburg Municipal WTP faced challenges reducing manganese levels to comply with regulatory limit of 0.05 mg/l. The plant used a conventional treatment process for treating borehole water by dosing potassium permanganate (KMnO4) to precipitate iron and manganese, followed by sand filtration. While this method effectively removed iron, it struggled to consistently reduce manganese to the required level resulting in non-compliant water.

Additionally, the plant needed to increase its capacity by 50% from 3,500m³/day to 5,200m³/day to meet growing demand. This had to be achieved within the existing filter footprint of 15m2, due to land ownership issues. An upgrade of the existing traditional green sand filters with KMnO4 dosing would have required 42m2 to achieve these requirements, whilst the SiC membrane alternative only required 15m2 and was therefore selected for pilot trials.

Performance confirmed by successful pilot trials: To assess the SiC membranes’ performance, the customer conducted a two-month pilot test between 2015 and 2016. The test evaluated the system’s ability to remove iron and manganese, as well as its durability and maintenance needs. The results were highly positive; manganese concentrations were consistently reduced to below 0.02 mg/l and turbidity was also reduced to less than 0.1 NTU (significantly below the target of 1 NTU). Following the successful pilot, the municipality decided to fully implement the SiC membrane system.

Eighty SiC membrane modules were installed in two filtration tanks, enabling the plant to treat up to 5,200m3/day within the 15m2 footprint. The membranes are installed within modules, each containing 42 flat sheet membranes, providing a total membrane surface area of 6.85m2 per module. These membrane modules are stacked in towers, with up to 15 modules per tower. Each tower includes a top permeate module, which collects the filtered water, and a bottom diffuser module, which distributes air for cleaning purposes. For Gothenburg, eight towers comprising ten filtration modules were installed in two of the existing filter structures.

Conclusions: Three years after installation, the SiC membrane system has continued to perform exceptionally well. A full inspection revealed no signs of decline in membrane permeability or structural damage, and the plant consistently delivers high-quality drinking water with the following parameters being achieved:

Conclusion

Cembrane SiC membranes give water companies the opportunity to expand and improve their treatment facilities at low additional cost and carbon footprint. Cembrane and Enpure are both part of SKion Water, who have a diverse portfolio of innovative companies providing technologies for water and wastewater treatment to municipal and industrial sectors. Enpure Ltd will deliver Cembrane SiC membranes throughout the UK.