Supply Chain - Renewables & Energy Management - Photo Voltaic Systems

Located in Leeds, Knostrop WwTW serves a population equivalent (PE) of approximately 990,00 while Blackburn Meadows WwTW serves a PE of approximately 500,000 in Sheffield. Both wastewater treatment works are owned and operated by Yorkshire Water and have undergone major development over recent years. The Green Gas Solutions Team at SGN Commercial Services is now underway delivering two large new gas to grid (G2G) installations that will give Yorkshire Water their first biomethane G2G capacity, maximising both green energy generation and fossil carbon abatement potential from their existing anaerobic digestion processes. Commercial details

The projects are being delivered by the Green Gas Solutions Team at SGN Commercial Services via a Design /Build /Finance /Operate /Maintain (DBFOM) model. In this novel model, Yorkshire Water retain control of process volumes, despite the gas to grid plants being owned and operated by SGN Commercial Services.

The biomethane produced will be shipped by Centrica Energy on behalf of Yorkshire Water. SGN Commercial Services will be paid a monthly service charge to cover capital repayment and O&M services for the duration of the project terms. SGN’s performance commitment is on the gas to grid plants availability, with gain/pain share against the contract availability target.

This model ensures that the parties are in control of the aspect that they are best at, and crucially, correctly motivated to perform optimally. Another great feature of this model provides Yorkshire Water with the option to either sell the green gas certificates associated with their biomethane or retain and retire them to offset their own greenhouse gas emissions.

[caption id="attachment_24444" align="alignnone" width="1200"] Commercial model schematic[/caption] Project scope & solutions

Both project sites currently have anaerobic digestion (AD) plants that process sewage sludge to make it safe for onward applications. The AD process also yields biogas as the organic matter in the sewage sludge is broken down by a carefully controlled culture of bacteria.

For decades, this biogas has been combusted in reciprocating engines to drive generators to produce green electricity. However, as the UK electricity grid decarbonises, the option to clean up this biogas and inject it into the gas grid represents far more benefit from a fossil carbon abatement perspective. The new gas to grid plants at Knostrop and Blackburn Meadows will do just that; removing impurities and biogenic CO2 from the biogas to leave pure methane that can be injected into the local gas network.

The gas to grid plants at both Blackburn Meadows and Knostrop STWs have been sized to take into account biogas production volume forecasts, as the local populations of Sheffield and Leeds continue to grow. The raw biogas capacities are 1,300 Nm3/h and 2,900 m3/h respectively.

Given that biogas from sewage sludge AD is typically about 60% methane, this means that around 800 Nm3/h and 1,800 Nm3/h of product biomethane respectively will be available for grid injection. A membrane upgrading process technology (to clean up the biogas and separate the methane for grid injection) will be deployed for both projects. This technology uses selective membranes to achieve this separation and has become the favoured option in recent years. [caption id="attachment_24445" align="alignnone" width="1200"] Blackburn Meadows G2G schematic - Courtesy of DMT Environmental[/caption]

The product gas is >99% methane, and this is passed forward to the grid entry unit for metering and analysis ahead of grid injection. It is at this stage that a small quantity of propane must be added to ensure the calorific value (CV) of the biomethane being exported is equal to that of the gas network.

The waste stream of biogenic CO2 will initially be vented, although plans are already being developed to add CO2 capture facilities that will provide the possibility of a carbon negative process. On both projects, the membrane plants are from DMT Environmental Technology, and the grid entry units are of SGN Commercial Services’ own design and are being built in partnership with Bohr Engineering.

In both cases, the existing AD and hence G2G plants are located in the middle of the wider Yorkshire Water sites. In both cases therefore, SGN CS are laying new pipelines to convey the product biomethane out of the site to connect to the local gas network.

Blackburn Meadows: In the case of Blackburn Meadows, the export pipeline will connect to a Cadent medium pressure system. As the biogas upgrading process operates at pressures above that in the Cadent MP system, the pressures can simply be regulated down to suit. Knostrop: For Knostrop, the best connection option is onto a Northern Gas Networks high pressure system. As the residual biomethane pressure off the back of the upgrading process is below that in the HP system, a further lift compressor installation will be required. In order to reduce the quantity of high-pressure pipework, the project team located the lift compressor compound in a separate compound on the boundary of the Yorkshire Water site. Knostrop & Blackburn Meadows G2G Projects: Supply chain - key participants Principal designer & contractor: SGN Commercial Services Planning & permitting: AtkinsRéalis Ground remediation: Hague Civils: Carter Taylor Civil Engineering Limited Export pipeline: Fox Hill Projects Biogas pipeline & ducting: Advance Engineering Biogas upgrade unit supplier: DMT Environmental Compressor equipment: Adicomp Grid entry unit supplier: Bohr Ltd Flow controls: AFFCO Flow Control (UK) Ltd [caption id="attachment_24453" align="alignnone" width="1200"] (left) Blackburn Meadows pipeline materials, (top right) export pipeline trenching and (bottom right) butt fusion welding - Courtesy of SGN Commercial Services[/caption] Implementation phase progress (as of June 2025)

Having progressed design to a suitable point, and in their capacity as the asset owner and site operator, SGN Commercial Services was required to submit a planning permission for both projects. Planning permission was successfully obtained in the latter part of 2024 and detailed design, allowing procurement to commence. SGN worked closely with the supply chain to optimise package plant designs to ensure safe and reliable operation.

The Blackburn Meadows project is slightly ahead of Knostrop in programme terms, with the compound area now cleared and ready for civils and, at the time of writing (June 2025), the cross-site biomethane export pipeline is being laid. The pipeline between the G2G plant and the site boundary is well underway but work to date on this element has not been without its challenges. Wastewater treatment works are notorious for a congestion of buried services and redundant underground structures. These challenges have tested the skills and experience of the project team, but a route has now been successfully mapped.

The project team has visited the supplier’s manufacturing facilities to view progress and witness factory performance tests. The majority of the mechanical G2G equipment is made in mainland Europe; which helps with the projects’ embodied carbon credentials.

The containerised/modular nature of G2G equipment facilitates extensive factory testing. This, in turn, minimises costly and potentially more hazardous site works conditions. The increased plant capacity and high-pressure connection introduce additional technical challenges for the Knostrop project, but the design is substantially complete, and the majority of plant is now on order.

On both projects, the compound areas are leased from Yorkshire Water for the duration of the term. At Knostrop, the opportunity is being taken to include offices and stores to facilitate the level of planned and reactive maintenance that will be required to uphold (and hopefully exceed) the contract availability commitments.

[caption id="attachment_24451" align="alignnone" width="1200"] Membrane unit factory visits - Courtesy of SGN Commercial Services[/caption] Outcomes and onward opportunities

The Blackburn Meadows G2G Plant is due to start commissioning at the end of 2025, with commercial operation expected early in 2026. Knostrop will be following on shortly after. Once complete, the two projects will allow Yorkshire Water to cumulatively generate 225 MWh of green gas per year. That’s enough to heat 20,000 UK homes, offsetting the release of 44,000 tonnes of fossil CO2.

Should SGN Commercial Services subsequently be appointed to deliver the aforementioned CO2 capture feature at both sites, Yorkshire Water could generate as much as 15,000 tonnes per year of biogenic CO2. This biogenic CO2 has value as an industrial product, offsetting the use of fossil derived industrial CO2.

More tantalisingly however, this biogenic CO2 could potentially be sequestered into permanent storage. If this were the case, Yorkshire Water would be taking CO2 out of the atmosphere and locking it away, allowing them to claim and/or sell carbon removal credits. The market value for these credits is still an emerging picture but they are likely to be extremely lucrative.

Another exciting prospect that is currently being investigated is the option to trim the amount of propane being added to the biomethane as it is injected into the grid. Using a concept solution that SGN Commercial Services developed for the SGN network, this trim is achieved by assessing the instantaneous ratio of network flow and export flow. Not only could this trim save biomethane producers a significant amount of money, but it would also further enhance the fossil carbon abatement impact of the project(s).

With the Knostrop and Blackburn Meadows Gas to Grid projects progressing well, Yorkshire Water are looking at further anaerobic digestion sites across their estate where G2G could bring environmental and commercial enhancements.

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

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

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

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

The scope of works for the upgraded facility included:

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

A description of these key features follows.

New inlet works

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

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

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

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

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

Biological treatment processes

The secondary treatment stage for Boherbue includes the following:

Two anaerobic selector tanks with three separate selector cell volumes. Two 624m3 aeration tanks with 109m3 of anoxic volume each for denitrification. Settlement provided by two 5m diameter/3.5m side wall depth secondary settlement tanks. [caption id="attachment_16524" align="alignnone" width="1200"] Secondary aeration treatment - Courtesy of Glanua[/caption]

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

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

Tertiary solids removal systems

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

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

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

Sludge drying reed beds

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

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

Reduction of carbon footprint of the plant by approximately 45 T over a 10-year period. Carbon capture via natural plant growth. Up to 25% organic matter removal due to mineralisation. Dewatering process completed with zero energy consumption. At full design loads, the SDRBs will remove over 49 (No.) 20,000 litre tankers from the road per annum. [caption id="attachment_16533" align="alignnone" width="1200"] Sludge drying reed beds to process wastewater sludge naturally - Courtesy of Glanua[/caption]

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

Solar technology

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

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

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

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

Boherbue WwTP: Supply chain - key participants Precast concrete: Glanua Group Designers: Jennings O’Donovan & Partners Designers: Construct Engineering Precast concrete: Shay Murtagh Precast Precast concrete: Carlow Tanks Precast concrete: FLI Precast Solutions Precast concrete: Tracey Concrete PLCs & automation: UMAC Systems Inlet screens: Definitive Ecology Tertiary solids removal cloth filters: Eliquo Hydrok Ltd Aeration blowers: Kaeser Kompressoren Aeration diffusers: Xylem Water Solutions Solar panels: The Low Carbon Energy Company Ltd CWF Storm Flush system: Eliquo Hydrok Ltd Steel modular buildings: Shanette [caption id="attachment_16530" align="alignnone" width="1200"] (left) Precast concrete aeration tanks reduced construction time and safety risks and (right) view of final clarifiers and cloth filters - Courtesy of Glanua[/caption] Innovative construction methods

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Finham STW, situated near Coventry in the West Midlands, is Severn Trent’s fifth largest wastewater treatment works and treats over 115 megalitres of effluent a day from half a million people. The works processes indigenous sludge on site as well as accepting exports from local, satellite sites, producing final effluent, ‘cake’ and biogas as outputs. The two separate elements at Finham comprised a Thermal Hydrolysis Plant (THP) and a Gas to Grid (G2G) project, which were delivered as a single advanced digestion scheme. Sludge is anaerobically digested to produce biogas which, prior to the advanced digestion scheme, powered two, 60-cylinder, combined heat and power (CHP) engines providing recirculated heat for digestion and electricity for the works. Following a competitive tender, the design and build contract for the purpose-built, brand-new, advanced digestion scheme was awarded to Costain by Severn Trent in 2019, with construction starting on site in early 2020. Overview - Gas to Grid Project The gas to grid (G2G) phase of works refines biogas from the digesters through a biogas upgrade unit (BUU) and blends it with propane to ensure the correct calorific value for export to the national gas grid. This phase was complete first with a sectional completion date of March 2021, determined by the Ofgem industrial Renewable Heat Incentive (RHI) scheme deadline. The first export of biogas to the Cadent Gas Network was successfully delivered by the key milestone and ensured that Severn Trent secured RHI-funded unit rate for its gas export. [caption id="" align="alignnone" width="1200"] Gas to grid process diagram - Courtesy of Costain[/caption] Overview - Thermal Hydrolysis Plant The thermal hydrolysis plant (THP) phase of the project was around 75% of the total value of the scheme and constructed alongside the G2G initially, before continuing to completion once the G2G section was handed over. The process utilises a Cambi Ltd designed THP which uses steam from two-gas boilers to hydrolyse sludge produced by the primary settlement tanks (PSTs), activated sludge plant (ASP) and imported sludge from regional sewage works around the midlands. This process increases the gas yield of the sludge when digested to increase G2G throughput. Process commissioning started in January 2022 and contractual completion was in July 2022. [caption id="" align="alignnone" width="1200"] Thermal hydrolysis plant process diagram - Courtesy of Costain[/caption] Gas to Grid Project Digesters, boosters and gas holder Biogas is produced by sludge digesting in 8 (No.) digesters on site. The pressure is regulated in each digester with a ‘floating roof’ which rises and falls with the volume of gas present. The project saw 6 (No.) boosters installed, 3 (No.) 1000m3/hr boosters to transfer the biogas from the digesters into the gas holder between 15-25mBar and 3 (No.) to provide a biogas feed to the boilers. A 2700m3 inflatable gas holder was constructed on a 400t concrete suspended slab to store biogas and provide the BUU with a consistent flow and pressure of gas. BUU, GEU and ROV The biogas upgrade unit (BUU) uses membrane technology to refine the biogas and export it to the grid. The BUU was procured from Italy and required careful management to navigate the international challenges posed by COVID-19 and Brexit. The BUU has a throughput flow rate of 720m3/h to 1800m3/hr. The upgraded gas is then sent through the grid entry unit (GEU) which monitors the characteristics of the gas and rejects non-compliant gas. The compliant gas is then exported to the gas grid through the remote operated valve (ROV) kiosk which is operated by the gas utility, Cadent, down 800m of newly laid medium pressure gas main in the highway which was installed using horizontal directional drilling (HDD) to minimise impact to the public. [caption id="" align="alignnone" width="1200"] (left) Inflated gas holder and (right) biogas upgrade unit and carbon storage silos - Courtesy of Costain[/caption] Thermal Hydrolysis Plant Sludge The THP process uses a blended mixture of sludge from surplus activated sludge (SAS) from the aeration settlement plant (ASP), primary sludge from the primary settlement tanks (PSTs) and liquid imports from satellite sewage works. Sludge ‘cake’ is also imported into the new THP cake bunker where it feeds directly into the THP silos. The blended sludge is transferred by progressive cavity pumps via 2 (No.) duty/duty 220m long buried sludge mains. Screening The transferred sludge is screened through 3 (No.) Huber Technology Strainpresses with 6mm screens that capture and remove solids in the sludge to prevent wear and tear damage to the THP process. Screenings are dropped from the elevated platform into 2 (No.) roll-on-roll-off skips ready for incineration off site. The elevated strain presses were craned onto the steel frame which was assembled in 3 days. The screened sludge in then moved into two, 1200m3 buffer tanks that keep the sludge moving to prevent settlement before it is dewatered. [caption id="" align="alignnone" width="1200"] (left) Sludge transfer pumps and (right) elevated strain press in front of the buffer tanks - Courtesy of Costain[/caption] Dewatering The screened sludge is dewatered from approximately 3% to 20% dry solids for transfer to the THP feed silos. 3 (No.) centrifuges work in a duty/duty/standby arrangement and backwash with final effluent (FE) as required. THP & boilers The cake is diluted with FE to 16% dry solids and fed into one of the 2 (No.) THP streams which process up to a maximum of 60 tonnes of dry solids per day (tds/day) per stream. The sludge is heated to around 95°C in pulper to become ‘homogenised’. This sludge is then pumped sequentially through each of the streams 4 (No.) reactors for batch treatment. Steam from the boilers is used to heat the sludge between 50-180°C where it is held at 6-bar pressure to undergo pasteurising hydrolysis for around 30-45 minutes. After hydrolysis, sludge is passed into the flash tank, where the pressure and temperature of the hydrolysed sludge are decreased by flashing steam back to the pulper. The flashtank provides the necessary thermal buffer capacity to release the excess energy contained in the sludge before entering the downstream pumps. The process kills all pathogens and, in turn, increases the potential gas yield of the sludge. 2 (No.) boilers, procured from Italy, produce 192°C steam from potable water, operate at 12bar and can run on either natural gas imported from the grid or biogas produced from the gas to grid plant. 2 (No.) CHP engines are situated locally to the boilers and the exhaust gas heat is recovered by boilers to optimise performance, these CHP engines can also run on either natural or biogas. The boilers are operated by BOAS accredited operators who were transitioned across from Costain to Severn Trent upon handover. The warm hydrolysed sludge is then blended with UV FE to reduce the temperature to around 42°C where it is fed back into the digesters via a bank of 8 (No.) sludge return pipes traversing 500m across the site footprint. [caption id="" align="alignnone" width="1200"] (top left) Centrifuges, (top right) THP silos, (bottom left) the boiler and (bottom right) the boiler house - Courtesy of Costain[/caption] UV treatment and sludge cake A UV plant was constructed to ensure no pathogens were introduced to the sludge post-THP which would normally be present in non-UV treated FE. This ensures that the biosolids product produced by the works is ‘enhanced’ quality and can be sold to farmers to fertilise fields growing a wider range of crops than those which can have ‘standard’ biosolids. A pair of Bollfilters with 25µm strainers from Bollfilter UK Ltd screen the FE prior to UV treatment to ensure that stringent disinfection standards are achieved and to prevent particulates damage to the plant. Other THP highlights The THP installation also included a polymer dosing plant, FE and potable break tanks, odour control unit, deep drainage and centrate pump stations with 700m of buried return pipework to head of works, a new FE pump station and a 1200m3 cake bunker. [caption id="" align="alignnone" width="1200"] THP reactors - Courtesy of Costain[/caption] Finham STW Advanced Digestion Plant: Supply chain - key participants Design & build: Costain Geotechnical investigation: Geotechnics Ltd Digester to G2G pipework: Alpha Plus Ltd Gas import/export pipe: Morland Utilities Ltd Mechanical installation: HL Engineering Contractors Ltd FE pump station: Arthur Civil Engineering Ltd G2G mechanical installation: Field System Design Ltd Pre-THP mechanical installation: Balmoral Ltd LV electrical installation: AVRS Systems Roads: Hercules Site Services Groundworks & FRC: Costain Trace heating & lagging: Thermal Design Ltd Thermal hydrolysis plant (THP): Cambi Ltd Biogas upgrade unit: Air Liquide UK Ltd Odour control unit: Air-Water Treatments Ltd Bollfilters: Bollfilter UK Ltd Gas holder: Power Plastics Ltd Centrifuges: Alfa Laval Ltd Buffer tanks: Balmoral Tanks Ltd MCCs, controls, switchboards etc: CEMA Ltd CTM imported cake reception silos & hoppers: CTM Systems Ltd GRP kiosks: Industrial GRP Ltd UV pathogen control: Lintott Control Systems Ltd Lightning protection & earthing: Omega Red Group Grid entry unit (GEU): Orbital Gas Systems Polymer storage & anti-foam dosing: Richard Alan Engineering Ltd Indigenous sludge screens: Huber Technology Indigenous buffer tanks air mixing: Stem Drive Ltd Lifting equipment: T Allen Engineering Services Ltd Steam boilers: Thorne Industrial Boiler Services Flare & G2G boosters: Uniflare Ltd Boiler & THP operational support: PBJ Engineering Services Ltd Construction The vast proportion of the civil installation was self-delivered, this allowed for flexibility in the installation programme to align with constantly changing delivery and subcontract dates affected by COVID-19 and material shortages. The delivery team consisted of over 100 operatives at its peak, covering a range of trades. The construction phase included the installation of over 3.4km of buried drainage, 3 (No.) cofferdams and over 200 crane lifts. The mechanical plant was largely designed for manufacture and assembly (DfMA) off site and was able to be delivered, lifted in and installed in a relativity short period of time. One of the highlights was the installation of the 175 tonne THP which was installed in 10 working days. [caption id="" align="alignnone" width="1200"] (left) Cake bunker cofferdam and (right) cake bunker - Courtesy of Costain[/caption] Health & safety The safe delivery of the project was extremely successful and managing the interface between multiple contractors working in a small footprint was priority throughout. The delivery and commissioning phase saw over 490,000 hours worked with a AFR (Accident Frequency Rate per 100,000 hours worked) of 0.00. A total of 2,315 different people contributed to the scheme and over 3,200 hazard and safety observations were raised. The design team were proactive in holding hazard and operability (HAZOP) reviews with the client from the outset of the project, using the integrated 3D design model to identify potential challenges in a virtual environment prior to construction. Due to the volatile nature of substances on site, stringent safety measures were adopted in line with the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). Procedures put in place during G2G commissioning and handover benefitted from cross-sector learning and Costain specialists from the Energy sector helped shape the measures put implemented. [caption id="" align="alignnone" width="1200"] CHP engines- Courtesy of Costain[/caption] Commissioning and handover Commissioning of the G2G took place in 2021 with the first export to the grid in March 2021 before the Government’s commercial RHI deadline. The gas quality standard is set by the end user, Cadent, who dictate a specific calorific value that the gas must be for export. This is monitored by the grid entry unit (GEU) which recirculates non-compliant gas back to the gas holder to be refined further. This refining process was complex and required close collaboration between the client and contractor. The gas to grid achieved sectional handover to the client first and was taken over whilst construction continued the THP. The THP was commissioned in 2022 and required complex commissioning to convert the digesters from conventional sludge to hydrolysed sludge. This was done in a phased approached, whilst closely monitoring the biology of the digesters, over the course of 3½ months. The health of the digesters directly impacts the sludge feed rate through continued monitoring of several factors including % dry solids, pH, ammonia content etc. Biodiversity Planning conditions set out a requirement to create a mitigation area to enable net gain in biodiversity on the Finham site. The client’s solution was to establish a wildflower meadow at least equal in area to the new hardstanding constructed to promote a thriving insect and wildlife environment. Whilst Severn Trent were considering the logistics and cost of how to fulfil the planning requirements, Costain’s self-delivery team were busy excavating over 15,000 tonnes of muck for the THP build. [caption id="" align="alignnone" width="1200"] Muck shift in progress - Courtesy of Costain[/caption] Costain worked collaboratively with Severn Trent to draft plans for the reuse of the muck in the proposed BIA and began the process of sampling and testing the muck. A comprehensive Materials Management Plan approved under the CL:AIRE regulations was produced detailing the proposal. Upon approval from all parties, the muck shift operation began. Costain operated three 30 tonne articulated dumpers (ADTs) to transport the muck across the site. Each dumper averaged 25 trips per day and the full operation was completed in just a little under two weeks. The overall benefits were: 15,000t of waste product eliminated. No requirement for Severn Trent to import material. Net saving after labour and plant costs. Reduced carbon emissions by 76.2 tonnes. Reduced road traffic by up to 1000 lorry journeys. Site participation in World Environment Day. Contractor/client collaboration and mutual benefit. Long lasting environmental legacy. [caption id="" align="alignnone" width="1200"] Finham THP & G2G - Courtesy of Costain[/caption] Project awards The advanced digestion project has been nominated for several construction awards including the Constructing Excellence Sustainability Award, the Pipeline Industries Guild Award, and was successful in winning the NEC Sustainability & Climate Resilience of the Year award 2021. Department for Business, Energy & Industrial Strategy (BEIS) also visited the project during its construction to showcase the Government’s investment in domestic, renewable energy generation.

Key information Commissioned: 2023 Turbine Type: Vertical 4 Jet Pelton Power: 867 kW Head: 149 metres Flow: 708 l/s   Gilkes Scope of supply 650mm Vertical 4 Jet Pelton Turbine Synchronous Generator, 950kVA, 480V, 720rpm Hydraulic Control Module Main Inlet Valve – DN400 PN25 Butterfly Valve Electrical Package Installation & Commissioning   Ground breaking on the Sherard Hydroelectric Facility started in 2021, with a purpose-built powerhouse at the Sherard Water Treatment Plant, west of the City of Cheyenne in Wyoming, USA. The Turbine is powered by raw water pressure that flows from Cheyenne’s water supply coming into the plant. The energy is primarily used to power the treatment plant, which typically consumes 200 to 400 kilowatts, any remaining power will be sold back to the grid.     Gilkes designed and built the 867kW Vertical Four Jet Pelton turbine for the project. During the turbine selection process Gilkes engineers originally offered two alternative machines, a horizontal twin jet machine and the vertical shaft four jet unit which the customer selected. The selected machine was a slightly lower cost option with higher annual energy production.   The customer had specified that an impulse turbine should be used even though the head was less than 500 ft (152m) because of the ability of impulse turbines to minimise surge effects when the flow is altered. A Francis turbine would produce less energy because of the range of flows and would cause dangerous pressures if the unit tripped.   The plant is a typical energy recovery scheme. Untreated drinking water from the City of Cheyenne reservoirs is collected and passed at flows of up to 25 cfs (0.7 m³/s) through 15 miles of pipeline to the Sherard Water Treatment Plant where it is treated and distributed around the city. Between 1975 when the WTP was first built and the commissioning of the turbine in 2023, the city had used pressure reducing valves (PRVs) to remove the excess water pressure. This was effectively wasting over 800 kW of power and over 4 GWh of energy every year.    

The Pattack hydro project is the largest storage project to be built in the Scottish highlands in recent years, and is the third scheme that Gilkes have been supplied equipment to on the Ardverikie estate. Previous schemes were in 1935 and 1986.

The project has a new mass concrete dam utilising 3,300m3 of concrete. It has created a new small lochan by impounding 196,000m3 of stored water, which is delivered to the turbine via a 6,500m penstock pipe.

Due to the storage element of this scheme Francis turbines were selected as the most suitable, achieving a peak efficiency of over 92%. The Gilkes designed control system employs sophisticated programming and algorithms, fine-tuned on site by Gilkes commissioning team, to maximise the storage potential of the site.

SCOPE OF SUPPLY: Full water to wire package including: 2 x Gilkes Francis Turbines 2 x 1000rpm Synchronous Generators 2 x Main inlet valves (Hydraulic weight to close butterfly valve) Control Panels Hydraulic Control Modules Installation Commissioning

The small footprint of the Francis turbines, and by close co-operation with the civils designers, enabled the powerhouse size to be minimised and also partially buried. This minimises any visual impact in this beautiful area.

The Ardverikie estate, on the shores of Loch Laggan, is a popular film location and has made appearances in several films and TV series.

Key statistics: Turbine 1 Turbine type: Francis Mechanical power: 3068kW Electrical power: 2995kW Net head: 142 Flow: 2390 Runner diamater: 625 Speed: 1000 Key statistics: Turbine 2 Turbine type: Francis Mechanical power: 2053kW Electrical power: 1995kW Net head: 152 Flow: 1525 Runner diameter: 525 Speed: 1000   For more information: Gilbert Gilkes & Gordon | +44 (0)1539 720028 | www.gilkes.com  

Bryn Cowlyd Water Treatment Works is in the county of Conwy in Wales and is fed from Llyn Cowlyd, which is the deepest lake in north Wales. The new WTW was commissioned in 2019 and is Welsh Waters flagship Works. Gilkes were approached by Skanska Construction for the detailed design, manufacture, testing and installation, commissioning and training of an energy recovery turbine suitable for flow control at the inlet to the works and to generate renewable energy which would contribute to the on site load required to operate the water treatment works. Welsh Water, Skanska and Gilkes worked together to determine the most suitable turbine and generator. With a net head close to 200m and a flow rate of around 323l/sec the hydrology was suited a Pelton turbine. After monitoring the expected variations, a 750mm single jet Pelton turbine was selected for efficiency and maximum annual energy production. [caption id="" align="alignnone" width="1200"] Bryn Cowlyd WTW single jet Pelton installation[/caption] It was an interesting project for Gilkes, as this was the first water treatment works where the entire project was done under BIM (Building Information Management) meaning a full 3D walk though of the treatment stages, energy recovery turbine and final treatment was available during the design stage and also for hazard awareness. Although the turbine could have been offered in a compact, Streamline format, the machine was offered in a more heavily built design to ensure that noise from the turbine was kept to a minimum. Gilkes are proud to have supplied further equipment for use on Welsh Water sites, having delivered three machines over the last 10 years. [caption id="" align="alignnone" width="1200"] Bryn Cowlyd WTW single jet Pelton installation[/caption] KEY STATISTICS Turbine Type: Single Jet Pelton Power: 575kW Head: 217 m Flow: 323 l/s Runner Dia: 750 mm Speed: 750 rpm SCOPE OF SUPPLY Reducing spool & inlet pipework Single Jet Pelton turbine Induction generator Turbine control & switchgear panels Operation & maintenance manuals Installation & commissioning Operator training Ongoing service & maintenance     For more information: Gilbert Gilkes & Gordon | +44 (0)1539 720028 | www.gilkes.com