Supply Chain - Wastewater Treatment - Products & Services

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.

Leominster WwTW is a medium sized biofilter sludge works, treating a population equivalent of approximately 11,000. Welsh Water have invested £12.1m to deliver the process enhancements at the works as part of Welsh Waters’s commitment to deliver on improved water quality in the Wye River basin catchment. Other enhancement works were completed on existing sites including Eign, Rotherwas and Kingston & Madeley WwTWs. As part of the National Environmental Programme (NEP) commitments to meet the obligations of the Water Framework Directive in AMP7, new permit limits were put in place for 31 March 2025. The project exceeded this milestone by one year, achieving the tightened permit and Welsh Water’s annual commitment for river reach improvement. Existing works

In advance of the improvement scheme, the works comprised an inlet works, primary settlement tank (PST), seven mineral media biofilters, two humus settlement tanks (HSTs), ferric dosing, two storm tanks and sludge storage.

The works treated mainly domestic sewage from the catchment of Leominster, Herefordshire.

The planned improvement works

The upgraded Leominster WwTW is designed to cater for increased treatment flows equating to a design horizon population equivalent of 16,685 (46% growth) and a tightening of the phosphorus permit from 1mg/l to 0.5mg/l. The new works design included for the integration of the following process improvements into the existing treatment works infrastructure:

Four new tertiary nitrifying sand filters (including a tertiary lift pumping station and backwash returns system). New ferric sulphate dosing system for primary, secondary, and tertiary dosing points of application (including a new dosing equipment kiosk and safety shower). New sodium bicarbonate dosing system to supply additional alkalinity to the process for pH correction (including a chemical storage silo and dosing system). Inlet works refurbishment, upgrading the two existing escalator screens with two new 6mm screens, screenings trough, screenings transfer to two new compactors. New passive bypass screen with improved operation and maintenance access provision. New access platform around the screens to reduce the need for operator access into confined space areas. New potable water booster pumping station. New final effluent sampling system. New low voltage distribution board and inlet works MCC. New tertiary treatment MCC. Scope of works

As part of Welsh Water Capital Delivery Alliance (CDA), Morgan Sindall, in partnership with designers, Arcadis, was appointed as the main contractor by Welsh Water. The scope of works for the project included the investigation, assessment, design, procurement, construction, and commissioning of existing and new treatment facilities; thus providing capacity to treat increased sewage loadings to meet discharge permit standards agreed with the Environment Agency (EA).

[caption id="attachment_15336" align="alignnone" width="1200"] (top left) Construction of tertiary treatment system December 2022, (top right) construction of tertiary treatment system May 2023, (bottom left) Construction of tertiary treatment system July 2023, and (bottom right) Construction of tertiary treatment system November 2023 - Courtesy of Morgan Sindall Infrastructure[/caption] Innovative solution selection

Welsh Water, Arcadis and Morgan Sindall collaboratively assessed multiple options as part of the optioneering phase of the outline design, which included optioneering workshops for shortlisting, and risk and value assessments to select the most cost-effective solution based on whole life cost and risk. A schedule of innovative solutions included:

New nitrifying sand filter to combine the need for tertiary solids removal, to achieve the tightened phosphorus permit, and increase nitrification capacity to relieve pressure on the works to meet the existing ammonia permit.  Removed need for additional secondary treatment. Re-use of the inlet structure for the new 6mm screens, improving access and removing need to go in confined space during routine maintenance procedures. Re-use of the existing ferric sulphate storage tanks. Assessment of innovative alternative chemical to ferric sulphate (rare earth minerals). Use of BIM 3D modelling to ensure integration of mechanical design and location for the alkalinity silo and tertiary plant and avoid clashes with existing underground pipework. Gravity fed sampling system for final effluent monitoring. Design for Manufacture and Assembly (DfMA) MCC kiosk (used in the development of Welsh Water standard design). Re-assessed the need to refurbish existing sludge holding tanks through modification of sludge imports. Re-use of old Dortmund style rectangular/pyramidal standby PSTs. Re-purposing and re-establishment of area of works with abandoned process treatment assets– reducing the need for land purchase. Utilise existing static mixers on secondary ferric sulphate dosing. Ferric sulphate dosing flexibility (primary, secondary and tertiary). Project initiation and whole supply chain early engagement

The overall delivery programme for the treatment upgrade scheme at Leominster presented the Welsh Water CDA team a challenge to meet the NEP regulatory output dates for end of March 2025 and ODI date for 31 March 2024. To efficiently meet this milestone, the team developed a joint collaborative plan to work to with the key project stakeholders, including members from Welsh Water asset and operations teams and key supply chain members.

[caption id="attachment_15328" align="alignnone" width="1200"] Construction of tertiary treatment system February 2024 - Courtesy of Morgan Sindall Infrastructure[/caption]

The development of up-front outline design specifications and subsequent letting of Early Contractor Involvement (ECI) contracts with the supply chain allowed for all parties to truly work collaboratively in setting out and advancing the design strategy in an efficient manner. The ECI contracts enabled the supply chain and Arcadis to work together in an open and transparent manner through driving greater design efficiencies through sharing of ideas, skills, industry experiences, true value engineering opportunities, developing design and construction innovations, all resulting in a positive influence to the final scheme solution.

The successful working relationship was maintained through regular joint online progress meetings and workshops, where design efficiencies were discussed and implemented, and where any potential blockers were removed, to benefit design and construction. Other joint stakeholder meetings which assisted the advancement of the delivery programme included HAZOP’s, Access, Lifting and Maintenance (ALM) reviews, DSEAR meetings, referencing lesson learnt from previous schemes, progressing DfMA opportunities, production of outline commissioning plans early, and holding regular buildability review meetings as the design progressed. Having a common project management system, where all members of the joint delivery team shared information, was hugely beneficial, in addition to the open access to the scheme’s federated 3D BIM model.

Leominster WwTW: Supply chain - key participants Client: Welsh Water Principal contractor & civils: Morgan Sindall Infrastructure Designer & environmental consultants: Arcadis CFA piling rig: Foundation Piling Ltd Shaft installation: B&W Tunnelling Ltd Sheet piled interlocked cofferdam: Berryrange Ltd Mechanical installation: Industrial Pipework Services Ltd Electrical installation: PCS Ltd Earthing specialist subcontractor: BEST Services Ltd Tertiary nitrifying sand treatment: Brightwork BV Tertiary nitrifying sand treatment: Nijhuis Industries UK & Ireland Ferric dosing system: Colloide Alkalinity dosing system: Rospen Industries Ltd MCC & ICA controls: GPS Group Kiosks: Morgan Marine PLC network: Mitsubishi Below ground access chambers: Cubis Systems Pumps: Xylem Water Solutions Inlet screens and screening handling: SPIRAC Ltd Potable water booster system: Dutypoint Ltd Static mixer: Statiflo Ltd Temporary pump specialist: Hydrainer Pumps [caption id="attachment_15329" align="alignnone" width="1200"] Fully constructed tertiary treatment system integrated into existing treatment works - Courtesy of Morgan Sindall Infrastructure[/caption] Sustainable and efficient design and construction

The new tertiary treatment plant and associated pipework, utilities and control kiosks were installed in an area within the boundary of the existing treatment site, where disused sludge drying beds were previously located. Re-purposing this area led to a more sustainable solution as it avoided the associated expenditure, programme, and environmental requirements that land purchase would have involved.

Due to this area of the existing treatment site being near the final effluent pipework, it enabled the flow diversion to the new tertiary lift pumping station to be achieved via a short length of below ground gravity pipe at a shallow depth. This is also a more sustainable design as it avoided the increased excavation and carbon footprint requirements that additional manholes, longer/deeper pipe lengths and a pumped solution would have required.

Other examples included surveying existing duct runs and draw pits to review capacity and reuse, where possible, as well as refurbishing the existing ferric dosing system and containment bund, instead of installing new plant, thus providing efficiencies and cost savings to Welsh Water.

Another element of efficient design and construction was the civil bases associated with the three new MCC kiosks for the new plant and equipment being installed.

As the two larger kiosks were to be DfMA and hence delivered to site with the panels already installed within the kiosk, a support frame for the kiosk and floor was also provided. Due to the panels requiring man access below them for installation of cables, the support frame included for vertical legs and steps for access into the kiosk that was installed on a simple concrete flat slab with mesh reinforcement. This was a more sustainable solution as it minimised the excavation requirements and reduced the total volume of concrete and steel when compared with sitting the kiosk at ground level on a below ground concrete trench and base slab with more steel reinforcement. The solution led to a quicker installation and better from a Health & Safety perspective as the extent of confined space working was reduced due to the absence of a trench.

[caption id="attachment_15331" align="alignnone" width="1200"] Example of a Cubis Systems modular chamber and (inset) chamber being assembled at Leominster- Courtesy of Cubis Systems & Morgan Sindall[/caption] For the smaller alkalinity MCC kiosk (not DfMA), it was decided that the kiosk would sit at ground level but as it still required access under the panel for installation, a below ground trench was required. To make the construction process more efficient, the trench comprised of innovative and sustainable HDPE recycled plastic modular units from Cubis Systems, that were put together on site and built around with minimal concrete surround and base slab and backfill to support the kiosk. As well as the material of the modular solution being more sustainable, it also led to a reduced carbon footprint in delivery due to it being very light weight. This also made it a safer and quicker installation as the manual handling involved was minimal.

Cubis Systems products were also used for the draw pit construction where the rapid stack modular units were utilised to form the main structure saving man hours with additional safety benefits.

The existing layout of the inlet works presented increased risks to operations with the main components below ground level and within a confined space. The new design involved raising the working platform to ground level, around the new screens and creating a better working environment and removing the need for operations to enter the previous confined space areas.

Design efficiencies

Working together with Welsh Water and the framework MCC subcontractor (GPS Group), the team were instrumental in the development of the standardised design for manufacture and assembly (DfMA) design for MCC kiosks within the Welsh Water business. The Leominster team delivered this standard product in the form of a new low voltage distribution board kiosk and a new tertiary filter MCC kiosk at the site.

The DfMA GRP kiosks are mounted on a raised steel frame floor to support the MCC and the access covers while giving ample space beneath the structure for cable connections and testing.

This kiosk design reduced health and safety risks associated with installation and commissioning and led to considerable reduction in installation time on site, as the kiosks were delivered to site, off loaded, and fixed down, all within a few hours. [caption id="attachment_15332" align="alignnone" width="1200"] Installation of DfMA low voltage distribution board MCC kiosk - Courtesy of Morgan Sindall Infrastructure[/caption]

The early engagement, with the electrical installation subcontractor, PCS Ltd, through an agreed Early Contractor Involvement contract arrangement, ensured that cable design and routes were agreed early in the design, to the new plant and equipment.

The standard designs for lighting, junction boxes and emergency stops were used where possible. In addition, the Welsh Water Capital Delivery Alliance team worked collaboratively with PCS Ltd and BEST Services Ltd, an earthing specialist subcontractor, to fully understand the earthing requirements for the site. Regular design review meetings were held to develop a workable earthing design, considering the impact of this deliverable with numerous site constraints.

Conversion of the existing Siemens PLCs to remote I/O, allowed for integration of all existing signals into the new schemes Mitsubishi PLC network. This minimised the number of telemetry outstations on the site, bringing all control associated with these MCCs into the new PLC network.

Hydraulic integration of new process scope into existing works

The new project scope required integrated into the existing treatment works hydraulic design and included the incorporation of two new SPIRAC Ltd escalator screens and storm bypass static screen within the existing civil structure, and the installation of new flow control weirs into the existing biofilter and humus tank distribution chambers.

[caption id="attachment_15337" align="alignnone" width="1200"] New Fineguard inlet screens from SPIRAC Ltd with improved safe access for operators – Courtesy of Morgan Sindall Infrastructure[/caption]

The new weir design was needed to achieve an appropriate flow distribution across the two sets of existing biofilters and the three existing humus tanks. To ensure seamless integration and maintain safe flow throughout the facility during the implementation of these changes, a comprehensive hydraulic assessment was conducted to verify the incorporation of new process assets within the treatment stream without negatively impacting on the existing asset structures.

To maximise the reuse of the existing works pipeline infrastructure and flow hydraulics, the team positioned the new tertiary treatment filters within the site layout to optimise the existing final effluent pipework arrangement by rerouting the flows from the existing humus tanks to the new tertiary treatment lift pumping station and then reintegrated the treated effluent from the tertiary filters back, by gravity, into the existing pipework to the final effluent lift pump station.

This approach reduced costs and construction time for the delivery of the project, reduced the impact of maintaining the existing works operation during the construction period and removed the need to agree a new final effluent sampling point location with the Environment Agency.

Digital delivery

To maximise the understanding and detail of the existing site arrangement and optimise the design process, a point cloud survey was undertaken, and a 3D Revit model produced. Along with existing as built drawings, asset and topographical survey information and historical as built drawings, the 3D model was developed further and then used to produce and develop a 3D model of the design proposals.

[caption id="attachment_15334" align="alignnone" width="1200"] (top left) Federated 3D model capture of sampling kiosk with tertiary filters - Courtesy of Arcadis, (bottom left) as built sampling kiosk with tertiary filters - Courtesy of Morgan Sindall Infrastructure, (top right) Federated 3D model capture of lift pumping station with tertiary filters - Courtesy of Arcadis, and (bottom right) As built tertiary filter lift pumping station pipework with duplex filter and tertiary filters - Courtesy of Morgan Sindall Infrastructure[/caption]

The 3D model was federated to include all the different design models (including those by the design subcontractors) and then used in internal meetings to agree on design proposals, by being marked up for updating. The federated model was also used to avoid underground clashes with existing pipework and produced the 2D drawings that informed the pricing and construction of the proposals and was also instrumental in getting acceptance from the stakeholders when used in project gateway approvals, HAZOP and ALM meetings.

This digital strategy for the project led to significant efficiencies in design as the federated model that contained the developed design proposals was uploaded to a BIM Docs page for the project, where all design deliverables were also kept, reviewed, and issued to the key stakeholders via the workflows and transmittals tools. The whole project team (designers, subcontractors, suppliers, stakeholders) were able to easily access and view the pertinent design information and subsequently design reviews and project decisions could be made easily which was instrumental in fostering a collaborative approach on this project.

Engineering challenges

Groundwater: As part of the overall design, a 3m diameter and 6m deep tertiary lift pumping station, was designed to lift and transfer influent flows, intercepted and diverted from an existing 450mm diameter final effluent gravity pipe, to the four new tertiary sand nitrifying filters.

During ground investigative works, it was identified that there was a high-water table present that would make construction of the shaft difficult. To fully understand the impact, pump tests were carried out to quantitate the expected groundwater influx during excavation and allow Arcadis to prepare and submit applications for abstraction and discharge (A&D) licences from the EA.

[caption id="attachment_15344" align="alignnone" width="1200"] Lift pumping station - Courtesy of Morgan Sindall Infrastructure[/caption]

However, due to the lengthy time-frame expected to obtain EA approval for an A&D licences, the team needed to reconsider the construction methodology of the lift pumping station in order to meet the consented target date of 31 March 2024.

B&W Tunnelling Ltd, who had been appointed to undertake the original caisson installation, jointly developed a solution with Morgan Sindall that would enable the pumping station to be constructed without the need to abstract any significant amount of groundwater. The agreed method was to drive interlocked sheet piles around the perimeter of the planned structure to a depth at which it will cut off any groundwater. With the groundwater under control, the caisson could then be installed under ‘dry’ conditions.

A 4.8m x 4.8m cofferdam was installed using 12m long GU27N sheet piles to penetrate the underlying mudstone formation. During construction the piles were required to stand as cantilevers. The temporary sheet piles were used for the construction period only, and were extracted once the caisson was complete. The Berryrange Ltd cofferdam allowed for safe construction of the shaft/lift pumping station and ensured the project kept on programme.

Network Rail: The location of the new tertiary plant on the site was in close proximity to the busy railway line that runs from South Wales to North Wales and Manchester. Network Rail were consulted, and mitigation measures agreed to ensure the safest method of constructing the new asset was followed.

A basic asset protection agreement (BAPA) was approved, which enabled Network Rail to review the safety documentation of lift plans (tandem lift method), method statements and temporary works design ahead of the planned work to install the filter tanks, sodium bicarbonate storage silo and associated high level stairs and working platform structures.

An appointed Network Rail Supervisor attended site to oversee the construction operations, which included the safe operation of piling rigs, multiple cranes, concrete pumps and the safe use of excavators in the vicinity of the operational railway line. This process was undertaken for over 20 separate operations through the programme period, all of which were undertaken safely and successfully.

[caption id="attachment_15335" align="alignnone" width="1200"] Installation of tertiary sand filters adjacent to railway line under agreed BAPA procedures - Courtesy of Morgan Sindall Infrastructure[/caption] Health & Safety

As always, during wastewater upgrades or extensions, the challenge and onus on the team is to integrate the new plant and processes, safely and efficiently, into the existing treatment works infrastructure, while ensuring that the existing process is not impacted or interrupted.

To formalise these crucial planning activities, Welsh Water required Morgan Sindall to work to their Business Continuity Plan (BCP) process. This BCP process encompasses the development and joint agreement of a detailed activity plan, initially, between Morgan Sindall and Welsh Water local operations teams, followed by presentation of the safe systems of work to Welsh Water senior managers for their final acceptance and approval.

As the integration of the new assets were built in and around the existing works, construction activities were proactively reviewed and agreed with Welsh Water to ensure minimal disruption to the operational site during the periods when these improvement works were being conducted.

Instances where the BCP process was followed included:

When temporary over pumping was needed to construct two intercepting manholes on the existing final effluent gravity pipeline. During over pumping of incoming sewage from the inlet works structure and during the installation of the new screening units. During construction of two flow meters on the feed pipes to the two sets of existing biological filters During the power upgrade to site and transfer of mains control to the new LVDB MCC unit from the old. [caption id="attachment_15333" align="alignnone" width="1200"] Leominster WwTW: Tertiary sand filters - Courtesy of Morgan Sindall Infrastructure[/caption]

In the case of the installation of the biological filter feed flow meters, a gravity solution was selected due to the hydraulic sensitivity of the biofilters and fluctuating flowrates of the incoming wastewater with the weather. The construction required several shutdowns and temporary storage of incoming flows as well as the installation of a network of above ground pipelines with flow control valves and flow meters over a 200m distance across the operational site.

Enhancing communities

During summer 2023, the Leominster team approached the local country park to enquire if there was any community-based volunteering work that the team could assist with. The Park Ranger highlighted an area of which they were planning on creating a community garden.

The Morgan Sindall and Welsh Water team assisted the local country park rangers with clearing a large area of brash and vegetation at Queenswood Park to open the space up. In addition, the team assisted in providing a new stone footpath and bridge to enhance access for the public. Several bird boxes were installed to encourage and enhance local bird populations in the area.

Another example where the team have helped and supported the local community was through the provision of food parcels to the local Food Bank. Staff from Welsh Water, Morgan Sindall and the project supply chain, all donated food parcels to the local charity to distribute.

To encourage and assist with the development of future engineers, the team invited two Year 11 students to undertake work experience on the site for a week and hosted a new graduate on the site as part of the Year in Industry placement scheme.

To celebrate British Science week, the Herefordshire Women’s Institute attended site during construction. The Leominster Town Clerk and numerous local councillors were also invited to site to explain the environmental benefits of the new enhancement works to the existing treatment works.

[caption id="attachment_15338" align="alignnone" width="1200"] Fully constructed tertiary treatment system integrated into existing treatment works - Courtesy of Morgan Sindall Infrastructure[/caption] Programme

Scheduled collaborative planning was undertaken at the design stage with all project stakeholders ensuring key deliverables were targeted and met to enable start on site. The collaborative planning sessions were also carried through to the construction phase where the main project programme was developed with all disciplines and key supply chain partners to achieve the milestones set.

Coupled with the regular planning sessions weekly site progress meetings were undertaken with all parties ensuring everyone was aware of the planned and forthcoming works with progress monitored throughout.

The main construction programme consisted of separate civil working areas ensuring the foundations and main structures were in place before mechanical and electrical supply chain partners were integrated into the programme to work alongside each safely to optimise the working time of the programme.

All parties worked together on site successfully with a standard daily safety brief to everyone ensuring all individuals were aware of the planned activities.

Sewage from Hereford and the immediate environs is treated by two wastewater treatment works: Eign WwTW and Rotherwas WwTW. The population served is 156,000 (2019), with a predicted population of 177,000 by 2040. Both sites are located in Hereford, England and fall under the responsibility of Welsh Water, with final effluent being discharged to the River Wye. All incoming flows are screened and de-gritted at Eign. Subsequently the flows are split at 60% to 40% ratio between Rotherwas and Eign, respectively, to undergo further treatment. This case study is focused on the modification works undertaken at Rotherwas. It should be noted that the chemical dosing plants at Eign have also been refurbished/upgraded to optimise phosphorus removal performance on that site. Existing works & project need

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.

[caption id="attachment_15289" align="alignnone" width="1200"] Google Maps image showing the site locations[/caption] Overview of works undertaken

To meet the new consents the following works were required:

A new tertiary solids removal (TSR) plant along with new P removal chemical dosing systems. Full replacement of the P removal primary dosing system (PACL dose) due to the age of the asset. A tertiary dosing system (ferric sulphate dose) on the feed to the new TSR plant. An upgrade of the power supply at Rotherwas WwTW and the installation of a new HV substation.

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.

Interception chamber, sample chamber and outfall

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.

[caption id="attachment_15291" align="alignnone" width="1200"] Interception chamber - Courtesy of Morgan Sindall Infrastructure[/caption]

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.

Rotherwas WwTW: Supply chain - key participants Designer: Arup Main contractor: Morgan Sindall Infrastructure Shaft supplier/designer: B&W Tunnelling Ltd Structural slabs: Adfil Tertiary solids removal plant: Bluewater Bio Ltd Mechanical design/installation & steelwork: Industrial Pipework Services (IPS) Ltd TSR lift pumps: Xylem Water Solutions Dirty backwash return pumps: Mono Pumps Dirty backwash water tank: Goodwin Tanks Ltd Chemical dosing plant: Colloide LV installation: Protocol Control Systems (PCS) Ltd MCC supply/installation: General Panel Systems (GPS) 11kV supply/installation (including switchgear & transformers): Hornbill Engineering Ltd Pumping specialist: Hydrainer Pumps Valves: AVK UK Ltd Static mixer: Statiflo Ltd FE analysers: Partech Instruments Safety showers: Hughes Safety Showers [caption id="attachment_15286" align="alignnone" width="1200"] Tertiary dosing POA and bypass - Courtesy of Morgan Sindall Infrastructure[/caption] Lift pumping station

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.

A 1.5m deep by 1.2m wide collar was constructed to enable the installation of the 8.2m diameter wet well, which was constructed with precast concrete segments. The shaft segments were sunk approximately 8m below ground level and a 1.7m deep concrete plug was cast at the base of the shaft. During shaft construction, local ground dewatering was installed within the shaft. Groundwater was pumped into settlement tanks and then into recharging wells approximately 70m away. [caption id="attachment_15297" align="alignnone" width="1200"] External lift pumping station – Courtesy of Morgan Sindall Infrastructure and (right) Lift pumping station: Installed pumps during construction phase - Courtesy of Arup[/caption] Tertiary Solids Removal (TSR)

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:

First option: 4 (No.) 3.7m diameter, 8m long horizontal filters. Second option: 16 (No.) 2.8m diameter vertical filters.

The vertical filters option was selected due to the following:

This option could fit within the existing site boundary. Smaller backwash pumps were required. Smaller blowers were required. A reduced capacity dirty backwash tank was needed. A TSR treated clean water tank for backwash water was not required. There was reduced hydraulic impact on the works’ inlet receiving chamber (which was already hydraulically challenged). There was greater system redundancy to support operation and maintenance activities. [caption id="attachment_15279" align="alignnone" width="1200"] Bluewater Bio Ltd’s tertiary filters - Courtesy of Morgan Sindall Infrastructure[/caption]

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

Total suspended solids: 10 mg/l. BOD: 28 mg/l. Ammonia: 10.3 mg/l. Phosphorus: 0.32 mg/l.

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.

Dirty backwash & wastewater management

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.

[caption id="attachment_15284" align="alignnone" width="1034"] Dirty backwash tank and returns pumping station - Courtesy of Morgan Sindall Infrastructure[/caption]

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.

Chemical dosing

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.

[caption id="attachment_15290" align="alignnone" width="1200"] Tertiary dosing plant - Courtesy of Morgan Sindall Infrastructure[/caption] Construction & programme

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:

Running newly constructed part of site from 800kVA generators, to commission the new plant before it was transferred onto mains power. Replacement of existing 500kVA transformer with the whole site running on temporary power generation. Site investigation works for the existing rising main crossing which required over-pumping for the de-sludge pumping station.

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.

[caption id="attachment_15292" align="alignnone" width="1200"] (top left) HV switchgear kiosk, (top right) RMU kiosks, TSR secondary dosing kiosk & safety shower, and (bottom right) MCC kiosk - Courtesy of Morgan Sindall Infrastructure[/caption] Innovations

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.

[caption id="attachment_15281" align="alignnone" width="1200"] Rotherwas internal lift PS craning in of the baffle wall - Courtesy of Morgan Sindall Infrastructure[/caption]

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.

Project completion

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.

Monkmoor Sewage Treatment Works currently serves a catchment of 116,000 (PE) in Shrewsbury, which is expected to grow to 146,000 by 2033. The works is a conventional activated sludge plant (ASP) and treats a combination of domestic and trade waste, consisting of landfill leachate, wastewater from other traders, meat process wastewater and sludge imports. The existing site consists of an inlet works, four storm tanks, four primary settlement tanks, four ASP lanes, four final settlement tanks, and a sludge treatment facility, which digests indigenous and imported sludge from surrounding sites. Tightened permits

The table below shows the current and revised:

Current permit Revised permit BOD 25 mg/l BOD 25 mg/l SS 45 mg/l SS 45 mg/l NH3 10 mg/l NH3 10 mg/l P - P 1 mg/l Fe - Fe 4 mg/l

The solution to meet the tightened P permit was to provide a new chemical dosing facility and additional final effluent monitoring equipment. In order to meet the growth driver, Membrane Aerated Biofilm Reactor (MABR) units were to be installed into the existing anoxic zones.

The aim was also to reduce the mixed liquor concentration within the ASP, thereby reducing the load to the final settlement tanks, helping to counteract the additional solids produced by chemical dosing. Installing MABR also had a CAPEX and OPEX saving over building new ASP lanes. The total value of the project was £6.2m.

[caption id="attachment_14838" align="alignnone" width="1200"] (left) Google Maps image showing Monkmoor STW and (inset) the existing anoxic zone - Courtesy of Mott MacDonald Bentley[/caption] Chemical dosing and FE monitoring

Two 60m3 ferric sulphate storage tanks were installed to meet the new phosphorous consent. The dose location was at the top of the ASP feed screw pumps as this is a turbulent area.

Existing ducts were used to cross the road to avoid breakout of concrete. The tanks were placed in a bund and instead of a delivery lay-by, sleeping policemen were used to contain the drainage in the delivery area from the rest of the road. As traffic will be stopped during delivery, this separates the delivery personnel from the live traffic.

The drainage is designed to gravitate from the chemical dosing area to the settled sewage. This is beneficial as the alternative location, the inlet works, is well over 300m away. This prevented additional excavation and removed the need for an additional pump station.

In the existing final effluent chamber, new iron and phosphorus monitors were installed. The existing kiosk was replaced, and existing monitors were relocated to the new kiosk, which was placed on the opposite side of the chamber to the existing, which allowed reuse of existing cables.

[caption id="attachment_14840" align="alignnone" width="1200"] (left) MABR blower from Aerzen Machines and (right) two 60m3 ferric sulphate storage tanks installed in the chemical dosing area - Courtesy of Mott MacDonald Bentley[/caption] Introduction to Membrane Aerated Biofilm Reactor

The Membrane Aerated Biofilm Reactor (MABR) from OxyMem Ltd uses gas permeable polydimethylsiloxane (PDMS; also known as silicone) hollow fibre membranes, which supply oxygen for aerobic oxidation as well as providing a surface for the growth of the biofilm.

PDMS membranes are dense; meaning they have no pores. Process air is fed to the PDMS hollow fibres and the oxygen diffuses through the PDMS by molecular diffusion into the biofilm. This can simply be described as bubble-less aeration. The biofilm, which receives its oxygen directly from the surface on which it is growing, performs biological treatment for carbon and nitrogen removal, the two major pollutants in municipal wastewater.

Each OxyMem MABR module is made up of individual membrane fibres grouped together into bunches containing 550 fibres. A cassette is made up of 25 of these bunches, each potted into a PVC header. A number of cassettes are then placed into a module and connected to the inlet and outlet distribution manifolds.

As process air is fed to the module through the top distribution manifold, it travels through the fibres and is collected at the bottom manifold. The exhaust air collected is used to power two airlift pumps, so no moving parts or extra power is required. The airlift pumps ensure the zone below the modules is mixed and helps to ‘pull’ MLSS into each module. The MABR modules are designed with a top cowling that prevents bypass and ensures all the flow must travel vertically past an established biofilm on the network of high surface area membranes before it can exit the module and MABR zone.

Scouring the biofilm with air is essential to remove excess sludge and keep the biofilm thickness optimal during operation, maximising the MABR performance. Scouring is achieved using a dedicated scour blower, which supplies air through a distribution grid, installed at the bottom of the MABR modules, at a high flow rate in discontinuous mode. This grid is integrated within the module. [caption id="attachment_14826" align="alignnone" width="1200"] (left) MABR units being readied for crane lift and (right) lowering an MABR module into the support steelwork installed on the ASP anoxic zone - Courtesy of OxyMem Ltd[/caption]

The MABR system implemented at Monkmoor is an MABR integrated with activated sludge (called MABR-IFAS or Hybrid-MABR), where the modules are dropped into the existing ASP anoxic zone. There are several key benefits to using an MABR system:

Additional biological capacity. Minimal to zero additional footprint. No need to drain tanks (in most cases). Reduction of process spikes. Ease stress on existing assets. Low process emissions. Resilient process.

At Monkmoor, due to the growth driver, more ammonia needed to be removed from the ASP lanes. One option was to build more lanes, but the MABR solution allowed a retrofit of the existing tanks.

The requirement was that 162 kg N-NH4/d must be removed from the anoxic zones. Therefore, 48 (No.) OxyMem MABR units were installed; 12 per lane. The modules were grouped into banks of three; with each lane having four groups. Process air is supplied continuously to each module and the scour cycle operates periodically on each bank. To provide both process and scour air to the modules, four 15 kW blowers were installed. The process blowers were sized to provide 712 Nm3/hr of air and the scour blowers sized for 577 Nm3/hr of air.

MABR technology has previously been installed at Spernal STW but only ten OxyMem and five Veolia units had been installed as part of a trial. Monkmoor was the first large-scale installation of MABR within the UK.

[caption id="attachment_14839" align="alignnone" width="1200"] MABR installation - Courtesy of OxyMem Ltd[/caption] Monkmoor STW: Supply chain - key participants Client: Severn Trent Principal designer & contractor: Mott MacDonald Bentley MABR technology: OxyMem Ltd Mechanical installation: Alpha Plus Ltd Electrical installation: Lloyd Morris Electrical Ltd Chemical dosing: Colloide Quality monitoring: Servitech International Ltd MCC: CEMA Group Blowers: Aerzen Machines MCC kiosk: Dutypoint Ltd Design decisions

Throughout the design process, MMB liaised with the Severn Trent operations team, to ensure they were onboard with the new assets, helping to give the team confidence in the design.

The mechanical installation was completed by Alpha Plus Ltd, who worked with MMB to design and install the steelwork to support the modules, and the pipework connecting the modules to the blowers. The design of the steelwork required consideration of the interfacing with the existing walkways. The key benefit of the MABR solution is the modifications to the ASP enabled the whole install to be undertaken whilst keeping the existing process live. This was a key consideration when deciding how to support the modules.

The final design involved steelwork spanning across the existing anoxic zones and dropping down underneath the existing walkways, to be supported by the concrete walls of the ASP. Structural checks were completed to ensure the existing ASP walls were suitable.

[caption id="attachment_14827" align="alignnone" width="1200"] MABR support steelwork - Courtesy of OxyMem Ltd[/caption]

Access was required in order to make the connections for the process and scour air. There were many options considered in terms of how access should be provided. By holding a design sprint, it was decided that in order to avoid installing walkways over aerated water, the existing walkways would be used as the main access. Installing additional walkways would reduce the area in which MABR units could be installed and would provide an access platform that would require authorised entry only.

The modules were installed using a lifting frame that enabled installation without needing access to the top of the modules. The pipework was made using a man riding basket. After installation, limited access is required so a non-permanent, temporary access solution can be used. By considering the interfaces with the existing walkways and the access challenges they posed, it was possible to complete the installation without draining the lanes. The modules were lifted into the tank using a crane and the existing crane pads on site were reused for this.

Flexible hosing attached to the module, supplied by OxyMem Ltd, was attached using a camlock to the process and scour air manifolds. Banks of three modules were connected to these manifolds. The manifolds were connected to common pipe runs back to the duty/standby process and scour blowers. It was important to ensure the aeration pipework had falls to low points to enable condensate collection and drains. When designing the pipework and steelwork, consideration for operator access for maintenance was also a priority. For example, the existing mixers within the anoxic zones were retained and need still to be able to be lifted out for maintenance, the layout of the new process enabled this. The pipework was designed so that it creates a vertical gallery on the main ASP walkway, enabling access to both new and existing equipment.

[caption id="attachment_14822" align="alignnone" width="1200"] MABR module being lowered into place within a bespoke steelwork frame - Courtesy of OxyMem Ltd[/caption]

For the steelwork, there were three options; 316 stainless steel sections, a 316 stainless steel lattice or FBE coated mild steel. It was not possible to procure the stainless-steel section sizes required. A stainless-steel lattice would be more readily available than stainless steel sections. However, there would be an increased risk of ragging, a lot of welding required, and it would be difficult to keep in tolerance due to the tendency of stainless steel to warp/pull forwards following welding. Additionally, if there was any ragging, this could lead to the water becoming stagnant and therefore corrosive to the stainless steel. In the end, despite possible re-coating being required if cut or drilled, FBE coated mild steel was selected. This was because the section sizes were more readily available, pipe support attachments would be easier as they could be bolted onto the beam flange, there would be possible cost savings over stainless steel and there was no increased risk of corrosion.

In order to monitor the performance of the MABR units, DO, redox and pH meters were installed into the anoxic zone on one lane. Additionally, an ammonia monitor was installed on the ASP distribution chamber and at the end of one of the anoxic zones.

These monitors were designed to be moved between lanes in to enable a performance assessment of each lane if required. An additional off-gas pipe was added to the first bank of modules on each lane so that if required, in the future, additional monitoring of the off-gas could be completed to determine the potential of MABR units to remove NOx.

The MABR units were constructed off-site in OxyMem Ltd’s factory. On site, the top cowling was installed, and the units were lowered into the lanes.

Conclusions/summary

A successful large-scale installation of MABR was completed, along with chemical dosing and FE monitoring equipment. Data is still being collected to show the performance of the MABR units but initial results are showing that the units are meeting the required ammonia removal target. The biofilm grew quickly and the required removal was taking place within a month.

The issue: Energy efficiency has not been the focus so far

Operational efficiency and reliability should be priorities in wastewater treatment plants. Consequently, there has been a prominent focus on being more efficient and reducing carbon footprint. This WwTP treats wastewater for over eight million people. The company was working with three energy-intensive competitor blowers that no longer met today‘s standards, this is where AERZEN was consulted.

The solution: Turbo technology for efficient aeration

For this replacement a detailed calculation of profitability showed a potential energy saving. All three blower units were showing significant signs of wear. Therefore, instead of an extensive and costly refurbishment, it was decided that these old units should be replaced with three new efficient AERZEN Turbo Blowers.

AERZEN consulted with the company Air Technology to determine the current load requirement. A detailed profitability calculation indicated energy savings of over 20%. AERZEN supplied 3 Turbo G5plus blowers (3 x AT150 0.8S DN250), which modernised the plant as they replaced the competitor’s aging blowers that were consuming a lot of energy. While these works were going on, the client involved AERZEN Rental to avoid downtime, who supplied the end user with 2 BVO 55000 skid mounted assemblies. Type of technology Turbo blower Overpressure 1,000 mbar Version Positive pressure Conveying media Air, neutral gases Volumenstrom 360 to 8,400 m3h Conveying oil-free [caption id="attachment_8979" align="alignnone" width="1200"] Courtesy of AERZEN Machines[/caption] The result: Modern technology used to reduce CO2 emissions

The space-saving installation of the new turbo technology from the G5plus series enables an efficiency gain of approx. 21% for the aeration of wastewater tanks which ultimately leads to savings in operating costs.

Additionally, in comparison to the earlier ventilation systems, the noise emissions were significantly decreased.

Summary

This wastewater treatment facility can save over £21.000 by utilising state-of-the-art technology, the AERZEN Turbo G5plus blower. AERZEN had a 4-week lead time. The calculation assumes an amortisation period of about three years. The cost and energy savings coincide with the customer‘s desire to reduce their carbon footprint.

Ian Moore, Technical Director, Air Technology, commented:

"It’s looking like a really good installation, and it is much quieter and more efficient than the old system."

  For more information: AERZEN Machines | +44 (0)208 502 8100 | www.aerzen.com