Supply Chain - Wastewater Treatment - Nature Based Solutions

Sleaford is a small market town in the North Kesteven district of Lincolnshire. The town is situated on the edge of the fenlands, 11 miles from Grantham and 17 miles south of Lincoln. Sleaford Water Recycling Centre is located just off the A17, north-east of the town. Anglian Water was required to meet a new full flow to treatment (FFT) obligation that the current system could not achieve, as it did not possess adequate hydraulic and biological treatment capacity or volume to comply with the new, higher FFT requirements. As a result, Anglian Water instructed the @one Alliance to put a solution in place to meet the new regulation which had an obligation date of March 2025. Solution

The first proposed solution was to optimise the existing site with the introduction of an additional intermittently-used side stream, to achieve the increase flow from 119.5 l/s (10,327m3/d) to 160.2 l/s (13,845m3/d).

However, this solution was based on the PST/FST/sand filter which upon investigation, would have resulted in excessive costs and, due to the lack of space on site, would have been difficult to construct.

The Anglian Water @one Alliance was tasked with proposing a solution to meet the financial and operational requirements. As part of a ROV5 (risk | opportunity | value) meeting, the team decided on the reed bed solution. This solution included the removal of standby generators by utilising the new aerated reed beds to provide 4 hours of treatment capacity in case of power failure and the use of a pumping station. The scheme also including re-purposing the existing storm tank to remove the need for a new piled final settlement tank (FST), which resulted in the re-use of the current scraper bridge and its internals were maintained. The solution of the side-stream process of a primary sedimentation tank (PST) and aerated reed beds to treat the additional flow was taken forward as the DM1 strategy.

This solution at the design stage was adapted to deliver a new above-ground storm tank together with an additional side-stream process comprising a primary settlement tank and aerated reed beds in order to treat the additional FFT requirements of 40.7 l/s, plus return flows from the existing site, resulting in a total additional treatment of 55 l/s through the new side stream process.

This system will help the treatment works build resilience to extreme weather caused by climate change and will protect the local environment by helping reduce the use of storm overflows. The reed beds put in place will also use plants to naturally clean wastewater to help the environment.

[caption id="attachment_13912" align="alignnone" width="1200"] Above-ground tricking filter - Courtesy of @one Alliance[/caption] New storm tank

By excavating and balancing the drainage and inlet connection pipework, an octagonal base was constructed and Hayes GFS Ltd installed a new 6m diameter storm tank.

Flow control

As part of the solution, the @one Alliance needed to interconnect with the existing works and the current flow control. The team utilised 150mm electromagnetic flow meters capable of 55 l/s located at the inlet works and 250/150mm pipework to connect to the inlet works. Adding supporting steelwork, local isolators and junction boxes were used to receive the power and signalling from the flow meter’s transmitter. This was then able to be connected to the aerated reed bed MCC from Paktronic Engineering Company Ltd.

Converting the existing storm tank to a PST

Early in the design phase it was realised that by converting the existing storm tank into the new primary settlement tank there would be a reduction in costs, programme time and the carbon impact.

This could be achieved by installing 250/150mm stainless steel pipework from the inlet works to the existing PST inlet chamber (former storm tank) above the ground. The new PST was completed with supporting auto-desludge pump skid, motor and 10m of pipe sitting on a 6m x 6m x 0.25m concrete slab.

Aerated reed bed

The team managed to refurbish the existing tertiary treatment reed beds and install three duty/duty/standby blowers. The reed beds were fully cleared of all prior material, with new liners installed followed by new gravel and aeration pipework to promote reed bed growth.

By casting the new outlet wall in concrete and separating the FE chamber and the reed beds, the team managed to reshape the existing bases of the beds. By installing new weir plates, the reed beds could be fed from the humus tank outlet. By connecting the new PST to the reed beds with DN250 DI pipework 150m long with a range of buried sections we managed to connect the process up. A dry riser connection was provided for clean down abilities for Anglian Water in the future.

On completion of the construction phase, the team ensured weekly visual inspections of the reed beds and the water levels, then adjusted the control arm as necessary. They also ensured weeds were removed weekly whilst checking the blower intake filter, oil levels and blower belt guard to ensure the resource was in full working condition.

Moving forward, the team completed three monthly inspections of the valves’ flow to the directed reed beds to check that the outlet distribution ports were not blocked. This ensured an even spread of flow to the reed bed surface. This was checked by looking at the flow being collected in the level control chamber as this will give an indication if there are any blockages into the collection pipework.

[caption id="attachment_13911" align="alignnone" width="1200"] (top left) Preparing the reed beds, (top right) aeration pipework for the reed bed, (bottom left) the reeds, prior to planting, and (bottom right) reed bed planting - Courtesy of @one Alliance[/caption] Sleaford WRC: Supply chain - key participants Design & project delivery: @one Alliance Civil engineering works: Bell Formwork Services Ltd Mechanical & electrical installation: Glasswell & Last Reed beds: ARM Ltd MCC kiosk: Morgan Marine MCC panels: Paktronic Engineering Company Ltd Storm tank: Hayes GFS Ltd Challenges

Due to the residual impact of Covid-19 on the global supply chain in the summer of 2022, there was a 6-month delay in electronic hardware being delivered to site, despite this infrastructure being procured in advance. There were also delays with the civil engineering due to the congestion of existing services around the inlet works.

Conclusion

By re-purpose existing Anglian Water assets, the @one Alliance reduced the overall cost of the scheme, reduced carbon emissions and made the best use of limited space on site. This new aerated system will use the reeds to clean wastewater by utilising micro-organisms in the reed beds that break down, digest and clean the water so it can be safely returned to the natural environment; reducing the need for chemical dosing. Planning and design of this £4.1m project started in December 2021 and construction completed in March 2023.

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.

Dearne Reach is a 4.3-hectare Integrated Constructed Wetland (ICW) in Clayton West, Huddersfield, designed to enhance water quality along 4km of the River Dearne. Delivered by Mott MacDonald Bentley on behalf of Yorkshire Water, this ICW will reduce levels of un-ionised ammonia and improve storm flow treatment in line with the salmonid fundamental intermittent standards. To deliver this nature-based solution, Mott MacDonald Bentley excavated 13 wetland cells covering over 44,000m2 (equivalent of 7 football pitches!), creating space to house more than 350,000 wetland plants. Project background

As an alternative to the traditional grey infrastructure solution, which initially would have entailed 7,000m3 of additional storm storage and a 4.5km diversion of final effluent to a lower river reach, the Dearne Reach ICW offers a sustainable approach to pollution mitigation. Funded by Yorkshire Water as part of their capital delivery programme, it is currently the largest ICW developed in the UK to improve water quality while increasing storm storage resilience.

Aligning with Yorkshire Water’s WFD drivers and net zero ambitions, this project pioneers an ICW tailored for intermittent storm overflows, distinguishing itself from conventional ICWs that require constant inflow. Its innovative design ensures effective management of stormwater variability and will contribute to driving continuous innovation in nature-based solutions across the water industry.

[caption id="attachment_25943" align="alignnone" width="1200"] Construction of the first cells - Courtesy of MMB[/caption] Integrated constructed wetlands

Constructed wetlands are engineered ecosystems that harness natural processes to treat wastewater, stormwater, and industrial effluents. Sometimes described as ‘nature’s kidneys’ because of their ability to filter and clean wastewater by mimicking natural wetlands, these systems use porous media beds and emergent plants to remove contaminants through physical, chemical, and biological mechanisms.

Various treatment wetland types exist, including free water surface wetlands - also known as integrated constructed wetlands (ICWs).

ICWs allow water to flow above the soil through aquatic plants, enabling the removal of suspended solids, nutrients, and pathogens. These passive systems, closely resembling natural wetlands, rely on processes such as adsorption, precipitation, sedimentation, and filtration to improve water quality.

[caption id="attachment_25944" align="alignnone" width="1200"] Cell construction - Courtesy of MMB[/caption] Advantages for Dearne Reach

The ICW at Dearne Reach offers numerous advantages:

Water quality improvement: Effective removal of nutrients, heavy metals, pathogens, and organic pollutants. Carbon sequestration: Capturing carbon within plant biomass and soil, contributing to achieving net zero goals. Biodiversity enhancement: Providing habitats for birds and other wildlife, supporting ecological balance. Community benefits: Creating green spaces for public enjoyment and research opportunities. Versatility: Adapting to varying wastewater loads and flows, making it highly efficient at stormwater management. Low operational costs: Passive systems with minimal maintenance and no chemical requirements over decades, unlike conventional treatment plants. Plantings

At Dearne Reach, 52 different species of plants have been designed to sit in 13 adjacent cells in which over 350,000 plants adsorb nutrients from storm overflow discharges and wastewater flowing out of the Clayton West Wastewater Treatment Works.  These have been specifically selected for the treatment capacity, and alongside the enhancement of existing hedgerows across the site, has enabled a staggering 38% biodiversity net gain in terrestrial habitats.

[caption id="attachment_25945" align="alignnone" width="1200"] Liner installation - Courtesy of MMB[/caption] Variable stormwater discharges

The project introduced an ICW specifically designed to treat intermittent storm overflows. Unlike traditional ICWs, which are effective only with constant inflow, this innovative design can handle the variability and unpredictability of stormwater discharges. The wetland is divided into multiple cells, each optimised for maximum retention time and pollutant removal.

Advanced hydraulic controls and computational fluid dynamics (CFD) simulations were employed to model and optimise the flow through the wetland, ensuring effective treatment of fluctuating volumes and pollutant loads.

Pumping station & rising main

A new wetland pumping station has been designed to raise up to 350 l/s of flows from Clayton West WwTW to the ICW through a new rising main constructed using HDD trenchless methods. Once the water reaches the head of the wetlands, the entire system is passively flowing through two precast concrete distribution chamber structures and fourteen 1.4m wide cascades to transfer the water through each of the 13 cells.

Harnessing solar power

The innovative design harnesses solar power to operate a level sensor and flow meter chamber to successfully manage stormwater variability whilst achieving a passive system ICW with no additional power requirements. The introduction of the solar panels mean that the flow monitoring chamber could be installed to provide future quantity and quality monitoring data, which can be shared to support the evidence base of these emerging infrastructures.

As the largest ICW developed in the UK, its unique design and successful results will contribute to driving continuous innovation in nature-based solutions for storm management across the water industry. It stands as an excellent example of the power of collaboration between civil engineering and nature-based solutions to mitigate the impacts of climate change and promoting sustainable development.

[caption id="attachment_25941" align="alignnone" width="1200"] All cells constructed - Courtesy of MMB[/caption] Collaborative approach

To successfully design and build a wetland on the scale of Dearne Reach it was clear from the project outset that a collaborative design approach would be key to both a successful programme and commercial output. Therefore, collaboration between the design team, digital delivery team and geotechnical experts was fundamental. The challenges facing the site included, high shallow perched groundwater, sandy, gravelly clay requiring high degrees of compaction, and a requirement for over 13,000m3 of material for topsoil reuse. Alongside construction on a complex site within a coal mining legacy area, with archaeological potential and intersecting with a public right of way.

Dearne Reach ICW: Supply chain: key participants Principal designer & contractor: Mott MacDonald Bentley Outline design: Stantec UK Pressure testing: Ant Hire Groundworks: Lowthers Groundwater treatment: Siltbuster Ltd HDD rising main: Joseph Gallagher Ltd Liner suppliers: SIG Construction Accessories Precast structures: Craven Concrete Ltd Headwalls: Althon Ltd Treatment works package: HB Tunnelling Electrical package: Circle Control & Design Systems Ltd MCC installation: Technical Control Systems Ltd Communications instruments: Churchill Controls Ltd Wetland plant suppliers: Salix River and Wetland Services Grass & flower seed: Hurrells & Mclean Seeds Ltd Erosion protection: Geogrow Gate valves: Affco Flow Control (UK) Ltd Actuators: Glenfield Invicta Ltd Instrumentation: Marlec Instrumentation: IFM Electronic Ltd Flow meter: SIRIS Environmental Pipework: Aquaspira Ltd [caption id="attachment_25946" align="alignnone" width="1200"] Planting completed in all the cells - Courtesy of MMB[/caption] HDPE pipework & couplers: Westwood Pipelines Ltd HDPE pipework & couplers: Radius Systems DI pipework: George Green (Keighley) Ltd DI pipework: Electrosteel Castings (UK) Ltd DI pipework: UTS Engineering Ltd Metalwork: Fabtek Duct pits: Advanced Infrastructure Systems Pipe supports: Midland Fixings Ltd Drainage pipework: Wolseley UK ltd Drainage pipework: Myers Building Supplies Drainage pipework: Keyline Civils Specialist Ltd Pumps: Xylem Water Solutions Lifting gantry: Peter Cassidy (Leeds) Ltd Welfare cabins: Nixon Hire | Wernick Group Bolt-sets: BAPP Industrial Supplies Bolt-sets: VULCAN Industrial Fasteners RoadCem access roads: DNS Aggregates: Hague Plant ltd Concrete: Heidelberg Materials Plant hire: Lynch Plant Hire Plant hire: Grantham Industries Ltd Plant hire: Flannery Plant Hire (Oval) Ltd [caption id="attachment_25937" align="alignnone" width="1200"] Filling the first cells with water - Courtesy of MMB[/caption] Construction achievements

During construction, several notable achievements were made:

Groundwater management: As a result of high groundwater levels on the site, the system hydraulics were analysed, and cell height adjusted. This optimised the cut-fill balance and ensured no material import would be required to construct the embankments, ultimately preserving resources and reducing material waste whilst ensuring there would be no flotation risk

Bypass pipework reductions: Through the development of robust future access and maintenance plans, an opportunity was realised to eliminate unnecessary bypass pipework infrastructure. Initially, this had been proposed to allow each cell to be isolated for future maintenance. The removal of this pipework scope significantly reduced the carbon footprint and project costs.   

Sustainable lining solution: As the existing ground did not have a suitable impermeability to protect the underlying groundwater, the ICW had to be lined. To avoid the use of extensive plastic on site, a geosynthetic clay liner was used to create a self-sealing, resilient hydraulic barrier while minimising environmental impact.

Archaeological and geological integrity: The team ensured the coal mining legacy areas remained undisturbed, with archaeological trenching conducted site-wide to ensure any potential pre medieval features were not disturbed during construction.

RoadCem technology for sustainable access: Traditional concrete access roads were replaced with Roadcem soil stabilisation technology to reduce the required material import and associated carbon footprint with use of extensive artificial concrete.

Biodiversity commitment: 350,000 locally sourced plants were installed, arranged in seven planting zones, achieving a 38% biodiversity net gain in terrestrial habitats.

Public right of way enhancements: Social value was equally important to the project and the team collaborated with the local council to enhance the public right of way, improving accessibility with a wheelchair-friendly, 2m-wide footpath along the perimeter of the ICW, featuring timber fencing for optimal wetland viewing points to support community health and well-being.   

Carbon savings: The project has achieved a 60% reduction in embodied carbon and 40% reduction in operational carbon across its lifecycle – delivering a more environmentally friendly solution in comparison to the original grey infrastructure solution.

[caption id="attachment_25940" align="alignnone" width="1200"] Fully planted wetland - Courtesy of MMB[/caption] Innovative digital construction

From the outset, early collaboration with Mott MacDonald Bentley’s digital delivery team identified an opportunity to pilot the use of intelligent plant machinery, alongside a ‘Smart Construction Dashboard’ during the build.

Prior to mobilisation on site, the model and delivery programme was shared for upload into the Smart Construction/Earthbrain software. These platforms initially use Artificial Intelligence to generate an efficient delivery output, detailing size, type and number of machines required. They also generate a powerful earth shifting model, highlighting the most efficient distribution workflow for the cut/fill material to travel and be placed.

This was most useful to compare the tendered assumptions and check for any oversights in the planning phases. This approach improved accuracy, efficiency, and most importantly, improved health and safety standards on site. This marked a first-of-its-kind trial for deploying intelligent plant in the construction of a nature-based solution.

The site team reported significant benefits, particularly given the scale of the excavation, such as:

Model-driven excavation optimised material use, eliminating unnecessary cutting/filling and promoting a right-first-time methodology. Automated systems reduced manual surveying and minimised plant-people interaction, ensuring safer site operations. Precision excavation reduced material waste while moving 65,000m3 (117,000 tonnes) of soil, limiting reliance on imported fill. [caption id="attachment_25939" align="alignnone" width="1200"] Wetland plants developing - Courtesy of MMB[/caption] Successes & summary

The Dearne Reach ICW Project exemplifies sustainable development by delivering a low-carbon stormwater management solution. Leveraging natural processes such as sedimentation, filtration, and biological uptake, the wetland effectively removes pollutants and reduces the ammonia levels in stormwater in line with the salmonid fundamental intermittent standards. This enhances water quality and strengthens local biodiversity, aligning with global climate adaptation efforts.

The project’s innovative approach to managing stormwater discharges aligns with Yorkshire Water’s efforts to mitigate and adapt to the effects of climate change. It stands as an excellent example of the power of collaboration between civil engineering and nature-based solutions to mitigate the impacts of climate change and promoting sustainable development.

This first-of-its-kind trial has set a new benchmark for future wetland and nature-based solution projects across the water industry, with lessons learned shared to inspire continuous innovation in sustainable construction.

A mine water treatment scheme was implemented at Vivian (Six Bells) by the Coal Authority as an environmental service under its national remediation programme in 2006. Vivian (Six Bells) is located in South Wales, approximately 20km north of Cardiff next to the village of Abertillery. A mine water discharge from the Vivian Shaft was discovered in 1998, causing a significant impact to the Ebbw Fach. The scheme, with a new abstraction borehole, was implemented to treat the mine water and decrease the impact on the Ebbw Fach. The scheme was initially built and commissioned in 2006 with two settlement lagoons, a reed bed and a sludge drying bed to treat the mine water passively. The additional features, which include a cascade and a hydrogen peroxide dosing plant, were built in 2012 to achieve sufficient oxygenation, effective iron removal and to abate the release of hydrogen sulphide (H2S) into the environment. Existing works Six Bells Mine Water Treatment Scheme (MWTS) is operated by Severn Trent Services on behalf of the Coal Authority. The existing works treats 60 l/s of mine water that is dosed with hydrogen peroxide solution, injected to provide oxidation of ferrous iron. This water is then transferred to two setting lagoons via a cascade structure. There are two parallel lagoons and the combined discharge of these two lagoons is transferred to a reedbed, at the bottom of the site, before being discharged into a local river. Six Bells was flagged as an ‘amber’ MWTS in the Coal Authority’s Risk Register due to number of health and safety issues with the condition of cascade. Due to the limitations that the existing inlet and outlet structures put on treatment effectiveness, the site was chemically dosed to aid water treatment, with the chemical dosing facility in need of refurbishment in the coming years. The objective of the project was to improve the efficiency of the treatment plant and Health & Safety standards. The Coal Authority employed JN Bentley as framework partner to design and build the refurbishment works. How it works Water is pumped from the borehole. Air mixes with the mine water as it falls down the cascade steps, which causes the iron to oxidise and form particles. The water moves slowly through the lagoons. Large iron oxide particles fall out of solution and settle in the bottom of the lagoon. The water transfers to a reedbed which acts as an additional filtering layer. Periodically the iron sludge is removed from the lagoons and taken to the drying bed, to remove excess water so it is easier to store or move. Water is discharged into Ebbw Fach. [caption id="" align="alignnone" width="1200"] Sludge drying bed and reedbed - Courtesy of JBA Bentley[/caption] Objectives of the works The scheme proposal was to improve the efficiency of the treatment plant and the Health & Safety standards, by ensuring the works have a suitable and sufficient design; by achieving an efficiency enhancement in the treatment process, the lagoons and reedbeds performance shall improve. A new cascade structure will improve management of the flows as well as improve the operation and maintenance abilities of the operator. Enhancing the access and egress of the lagoons and reedbeds, the risk to operators’ Health & Safety were also set to be reduced. The effluent discharge quality during the refurbishment works was to remain within the permitted discharge consent limits that are stipulated by Natural Resources Wales (NRW). With the treatment works operating more efficiently, the chemical usage was to be reduced by the relocation of the dosing points due to the modified lagoon inlet pipework. The proposed refurbishment works would improve both the operation and environmental impacts of the site, improve the treatment capability, and prevent mine water pollution. The Coal Authority’s innovations team are researching new ways of reusing the ochre to minimise waste and cost. Possible uses found to date include ground remediation projects, within water treatment systems and as a pigment in paints Permits, consents & licenses To facilitate installation of works at Six Bells the following permits, consents, licenses and restrictions were applied for and approved by the respective consenting authority prior to commencement of the work. Consent to discharge: Working under the client’s existing consent to discharge permit. Blaenau Gwent County Council General Permitted Development. De-sludging Throughout the design and construction stage, the final operability of the scheme was continually reviewed, and standard construction details modified to suit. When in operation the lagoons need to be regularly de-sludged, which has historically been undertaken with extensive pumping and with considerable resource. This scheme’s levels were designed to facilitate a permanent gravity piped solution from the lagoons to a new sludge drying bed. This will both reduce operational costs and aid operation during the scheme’s life. [caption id="" align="alignnone" width="1200"] Reedbed inlet channel - Courtesy of JBA Bentley[/caption] Cascades The cascade requires periodic maintenance to prevent the buildup of ochre on the steps. Therefore, the cascades were split into two sections with access steps in the middle to facilitate maintenance. The standard precast solution was modified to extend the width of the cascade. This posed several construction challenges due to the weight of units to be installed, which were exacerbated by the lifting restrictions from the site boundary constraints. Working collaboratively with the designers, construction team and Craven Concrete (the precast concrete supplier), the inlet and outlet units were divided into sections with a maximum weight of 4.5t, so each one could be lifted and installed with an excavator. Six Bells Mine Water Treatment Scheme Refurbishment: Supply chain - key participants Client & principal designer: The Coal Authority Principal contractor: JN Bentley Detailed design of earthworks, cascades, lagoons, pipework, MEICA infrastructure and environmental ecologist support: JBA Consulting Precast concrete channels: Craven Concrete Ltd Concrete kerb - HGV & HB: Marshalls Geomembrane lining: Celtic Lining Ltd Pipework: Scott Parnell Sludge drying bed drainage: Keyline Civils Specialist Aluminium fixings: Celtic lining Ltd Fencing: Travis Perkins Carbon reduction In line with JBA Bentley’s carbon reduction policy, carbon tracking was undertaken throughout the design and build process. By targeting a reduction in concrete and minor modifications to standard details a total saving of 22% reduction in capital carbon was achieved from the outline design stage. Several changes are highlighted below: Reduction in the levels of the cascade. This has allowed for the edge of the cascade to get closer to an existing path behind Lagoon 1 and therefore not requiring two separate smaller paths next to each other at different levels. Concrete was saved by reducing the weir length from 8m to 6m. Cascade dosing was removed from the scope. GRP steps. Concrete retaining wall, saved 63T of concrete, replaced with above ground blockwork. Removal of top launder channel drainage pipework and valves by client. Outlet pipework length reduced by client. [caption id="" align="alignnone" width="1200"] Total embodied carbon footprint comparison - Courtesy of JBA Bentley[/caption] Summary The improvement works to the lagoon has enhanced the even flow distribution and eliminated the risk of short-circuiting of the flow. The entire available area of the lagoon can now be used for treatment. The additional treatment capabilities will likely reduce the chemical consumption for treatment works, saving money on hydrogen peroxide and increased maintenance costs. The works undertaken to the sludge drying bay prevents the mine water leachate to ground and allow polluted water collection in the chamber for recirculation to the lagoons and treatment prior to discharge. The new cascade offers better operational and maintenance capabilities. Finally, the works allow the Coal Authority and their operational contractors to maintain the scheme within the discharge consent limits. The biggest benefit to the community that the project has brought about is the scheme prevents untreated mine water entering groundwater resources.

Due to an upcoming reduction in the permitted phosphorus discharge levels introduced under the Water Industry National Environment Programme (WINEP), and the existing aluminium permit on-site, an upgrade was required at Wilmington STW to ensure that the Environment Agency consent permit was achieved. This required the installation of an additional process within the boundaries of the existing sewage treatment works.  Galliford Try achieved this by implementing a new, low carbon phosphorus removal process. Process selection and scope of works

For some time, South West Water had been looking for alternatives to chemical dosing to meet the new phosphorus targets. ARM Ltd (specialists in wastewater treatment using constructed wetlands, reed beds and natural wastewater solutions) had been promoting its ARMPhos™ technology, and Wilmington STW was just the right size and location for trialling the UK’s first full-scale reactive media reed bed. South West Water’s board approved Galliford Try to work with ARM Ltd to carry out this innovative solution.

The main interventions delivered by Galliford Try to make these improvements under the WINEP programme were as follows:

20m3 storm tank with return pumping station. 6m3 media bed feed batch tank and pumping station. ARMPhos™ media bed for P removal to meet the new phosphorus permit of 2.5 mg/l. Auto de-sludging for the site. The addition of recirculation and washwater systems. [caption id="attachment_11379" align="alignnone" width="1200"] (left) Levelling media layers and (right) ARMPhos™ media filter feed pump station - Courtesy of Galliford Try[/caption] Wilimington STW: Supply chain - key participants

Galliford Try provided a complete design and build package, acting as lead designer for process, civils and MEICA, and principal contractor for the construction and commissioning of the new treatment works, using in-house skilled labour.

Main designer & contractor: Galliford Try Reed bed designer & contractor: ARM Ltd Civils design: Eastwood & Partners Temporary works: D Wall Construction Services Piling: Saxton Drilling Ltd MCC & software: Galliford Try Kiosk: GR PRO Precision Manufacturing Flow meter: Siemens Pumps: Xylem Water Solutions Ductile iron pipework: Saint Gobain PAM UK Lagging/trace heating: Jade Insulation ARMPhos™ filter

ARM Ltd was contracted by South West Water to design and construct an ARMPhos™ reactive media bed to remove phosphate discharged from the wastewater treatment system, the use of which was the first in the UK for reducing phosphate levels to meet the new Environment Agency consent targets.

The ARMPhos™ reactive media bed operates downstream of the existing works as a tertiary process and reduces phosphate via chemical reaction with the ARMPhos™ media layer. The system operates on a 40% bypass philosophy (40% treated through the bed and 60% by-passed), with flows being re-mixed in the level control chamber.

As part of the design considerations the media filter bed outer perimeter banks were raised by 930mm to form a flood protection bund around the perimeter of the filter in order to mitigate/reduce flood risk.

ARMPhos™ Phosphorus Removal System overview

The reactive media, based on apatite, offers two modes of action; an initial adsorption/crystallisation phase of phosphate onto the apatite, which stimulates the second phase of crystallisation of complex calcium/phosphate out of solution onto the adsorbed crystals.

The adsorption phase is driven by attraction of phosphate ions to the naturally occurring cations, principally aluminium and iron, occurring within the apatite. These bind the phosphate to the apatite until all the binding sites become saturated. The loading rate up to saturation is understood and depending on the P loading rate and volume of media it can take several years before this stage is complete. The bound phosphate subsequently crystallises which seeds the second mechanism which is the crystallisation of calcium/phosphate complexes which form naturally in solution. There is some overlap of these two mechanisms. The adsorption phase is finite, but the crystallisation phase goes on indefinitely and system performance is ultimately limited by the reduction in hydraulic conductivity of the media.

At this point refurbishment is required though this may occur 10-15 years after commissioning if the system is designed and installed correctly and loads remain within design parameters. Traditional reactive media P removal solutions using slag or other naturally occurring minerals generally only display the adsorption step.

[caption id="attachment_11380" align="alignnone" width="1200"] Media filter feed pump station and filter bed - Courtesy of Galliford Try[/caption] Carbon savings

This nature-based solution has an extremely low carbon footprint. The process is passive, and apart from pumped flow to the bed it consumes no other power. Apart from changes of the depleted media (currently estimated every 10 to 15 years) the process has a very low carbon footprint. The process also benefits from further carbon reductions compared to other phosphorus removal processes as it requires no regular deliveries of chemicals or produces any sludge for export.

Galliford Try also reduced its carbon footprint during construction, as all excavated material generated was re-used on site in the construction of the filter. This not only reduced carbon associated with the export of spoil, but also vastly reduced the quantity of imported material required, including concrete.

As can be seen in the desktop study below, the reactive media bed process can provide significant reductions in operating carbon when compared to other P-removal options.

Phosphorus removal options Chemical dosing Chemical dosing & TSR ARMPhos™ Power (kgCO2e/yr) 196 1327 544 0.233 kgCO2e/yr (UK Government GHG Conversion Factors for Company Reporting 2021) Additional sludge transport 582 582 0 0.96 kgCO2e/yr for HGVs, 80km round trip (GHG Conversion Factors for Company Reporting 2021) Chemical transport 1635 1635 0 0.96 kgCO2e/yr for HGVs, 800km round trip, 4 deliveries/year plus proportion of bulk delivery Chemical manufacture 1716 1716 0 Total additional operating carbon  4129 kgCO2e/yr 5260 kgCO2e/yr 544 kgCO2e/yr Green Apple Award

Galliford Try competed against more than 800 other nominations in the International Green Apple Awards and won a gold International Green Apple Environment Award. They were presented with their trophy and certificate at the Houses of Parliament in November 2023. As a result of this success, Galliford Try have been invited to accept Green World Ambassador status and have their winning paper published in The Green Book (the leading international work of reference on environmental best practice) so that others around the world can follow their lead and learn from their achievement.

The judges said:

“Galliford Try and ARM developed an innovative, UK-first technology to reduce phosphorus discharge levels. This was installed at an existing sewage treatment plant. Achieving exceptional phosphorus removal and ecological enhancement, it’s now being considered for larger-scale applications, reducing chemical usage, costs, and carbon emissions”.

This will also entitle Galliford Try to represent their country in the Green World Environment Awards that are held in a different country every year. The Green Apple Awards are run by The Green Organisation; an international, independent, non-profit, non-political environment group that began in 1994 to recognise, reward and promote environmental best practice around the world.

[caption id="attachment_11378" align="alignnone" width="1200"] (left & middle) Processed media and (right) final effluent samples: pre and post passing through media filter bed - Courtesy of Galliford Try[/caption] Summary

This innovative scheme provided the Galliford Try Team with many challenges in design and delivery as described above. However, by November 2022 the plant was in the final stages of process commissioning, and initial survey data undertaken by South West Water-appointed Nijhuis Aquatic, show significant reduction of Total P ensuring the site easily meets the new consent limits. All subsequent testing in 2023 showed the ARMPhos™ bed continued to significantly reduce the phosphorus levels pre and post bed.

Due to the success of the project, this technology is now being used at Lamerton STW where construction commenced 2024. This works will treat a greater flow from the installation installed at Wilmington STW. The use of this technology removed the requirement for any additional chemical-based treatments. This reduces not only day-to-day operator interventions but also removes the constant costs and carbon impact of maintaining a chemical style treatment process.

This solution achieves the phosphorus permit without risking the aluminium permit and reduces reliance on poly-aluminium chloride and ferric; both of which are hazardous materials due to acidity and which require storage and handling. They pose a serious risk to aquatic life if they enter waterways directly or via surface water drains. It is also safer for operators as there is no requirement for them to handle chemicals.

With this being an installation of a naturally based reed bed, this also provided an ecological enhancement to the existing site environment and its surroundings. The technology also enabled the total carbon to be reduced in comparison to traditional phosphorus removal methods, this allowed Galliford Try to reduce the total carbon by 52%. The use of this system also allowed Galliford Try to reduce their operational maintenance hours as well as achieving a low visual impact.

The completed project helped to reduce phosphorus discharge into the local river, whilst not having any detrimental effect on alkalinity levels or increases in aluminium content, which would be commonly found in traditional methods of removal.

Lamerton is a village with a population of just over 800 people, located 3 miles north-west of the town of Tavistock in west Devon. Due to the reduction in permitted phosphorus discharge levels introduced under the Water Industry National Environment Programme (WINEP) and the existing aluminium permit on site, an upgrade was required at Lamerton STW to ensure the permitted Environment Agency consent permit was achieved. This required the installation of an new low-carbon phosphorus removal process within the boundaries of the existing sewage treatment works. Background

Working with ARM Ltd (specialists in wastewater treatment using constructed wetlands, reed beds and natural wastewater solutions), South West Water and Galliford Try successfully trialled the UK’s first full-scale reactive media reed bed at Wilmington STW.

Due to its success at Wilmington, ARMPhos™ technology will also be used at Lamerton STW; treating flows 23% higher than at Wilmington (FFT Wilmington: 3.8 l/s | FFT Lamerton: 4.7 l/s).

Project scope

To meet the improvements required under the WINEP, Galliford Try undertook the following:

17m x 17m media bed and associated pumping station with associated pipework and control instrumentation. ARMPhos™ media bed for phosphorus removal to meet the new phosphorus permit of 2.5 mg/l. [caption id="attachment_14737" align="alignnone" width="1200"] Phosphate removal process added to the works as a new tertiary treatment process - Courtesy of Galliford Try[/caption] ARMPhos™ filter

ARM Ltd was contracted by South West Water to design and construct an ARMPhos™ reactive media bed to remove phosphate discharged from the wastewater treatment system; the use of which was the first in the UK for reducing phosphate levels to meet the new Environment Agency consent targets.

The ARMPhos™ reactive media bed operates downstream of the existing works as a tertiary process, and reduces phosphate via chemical reaction with the ARMPhos™ media layer. The system operates on a 40% bypass philosophy (40% treated through the bed and 60% by-passed) with flows being re-mixed in the level control chamber.

As part of the design considerations, the media filter bed outer perimeter banks were raised to mitigate/reduce flood risk i.e. the existing ground level was raised by 930mm to form a flood protection bund around the perimeter of the filter.

ARMPhos™ phosphorus removal system overview

The reactive media, based on apatite, offers two modes of action; an initial adsorption/crystallisation phase of phosphate onto the apatite, which stimulates the second phase of crystallisation of complexed calcium/phosphate out of solution onto the adsorbed crystals. The adsorption phase is driven by attraction of phosphate ions to the naturally occurring cations; principally aluminium and iron, occurring within the apatite. These bind the phosphate to the apatite until all the binding sites become saturated.

The loading rate up to saturation depends on the phosphorus loading rate and volume of media, and it can take several years before this stage is complete. The bound phosphate subsequently crystallises, which seeds the second mechanism which is the crystallisation of calcium/phosphate complexes which form naturally in solution. There is some overlap of these two mechanisms.

The adsorption phase is finite, but the crystallisation phase goes on indefinitely and system performance is ultimately limited by the reduction in hydraulic conductivity of the media.

At this point, refurbishment is required though this may occur 10-15 years after commissioning if the system is designed and installed correctly and loads remain within the design parameters. Traditional reactive media phosphorus removal solutions using slag or other naturally occurring minerals generally only display the adsorption step.

[caption id="attachment_14736" align="alignnone" width="1200"] Reactive media bed in operation - Courtesy of Galliford Try[/caption] Lamerton STW: Supply chain - key participants

Galliford Try provided a complete design and build package in the delivery of this scheme and collaborated closely with ARM Ltd, who were the client-nominated reactive media filter bed process sub-contractor. Galliford Try also acted as principal contractor for the scheme and undertook construction and commissioning using in-house skilled labour.

Principal designer & contractor: Galliford Try Detail design: WSP Process contractor (reactive media bed): ARM Ltd Temporary works: MGF Ltd Formwork subcontractor: D Wall Construction Services Pump supplier: Xylem Water Solutions Kiosks: Quinshield Ltd Control panel & automation: Galliford Try Flow controls: AFFCO Flow Control (UK) Ltd Carbon savings

This nature-based solution has an extremely low carbon footprint. The process is passive i.e. apart from pumped flow to the bed, it consumes no other power. Apart from changes of the depleted media, (currently estimated every 10 to 15 years) the process has a very low carbon footprint.

The process also benefits from further carbon reductions compared to other phosphorus removal processes as it requires no regular deliveries of chemicals or produces any sludge for export. Galliford Try also reduced their carbon footprint during construction, as all excavated material generated was re-used on site in the construction of the filter. This not only reduced carbon associated with the export of spoil but also vastly reduced the quantity of imported material required including concrete.

The implementation of ARMPhos™ reactive media bed technology resulted in a significant reduction in operational carbon emissions, with an estimated operational CO2e reduction of ≈90% and total CO2e reduction of ≈38% (embodied plus operational CO2e) over 20 year period, when compared to phosphorus removal using a typical chemical dosing solution.

Summary

The use of this technology removed the requirement for any additional chemical-based treatments. This reduces not only day-to-day operator interventions but also removes the constant costs and carbon impact of maintaining a chemical-style treatment process.

[caption id="attachment_14738" align="alignnone" width="1200"] Final effluent post reactive media bed - Courtesy of Galliford Try[/caption]

This solution achieves the phosphorus permit without risking the aluminium permit and reduces reliance on polyaluminium chloride and ferric; both of which are hazardous materials due to acidity and which require special storage and handling. They pose a serious risk to aquatic life if they enter waterways directly or via surface water drains. It is also safer for operators as there is no requirement for them to handle chemicals.

With this being an installation of a naturally-based reed bed technology, this provided an ecological enhancement to the existing site environment and its surroundings. It also enabled the total carbon to be reduced in comparison to traditional P removal methods; allowing Galliford Try to reduce the total carbon by 52%. The use of this system also reduced Galliford Try’s operational maintenance hours as well as achieving a low visual impact.

The completed project helped to reduce phosphorus discharge into the local river, whilst not having any detrimental effect on alkalinity levels or increases in aluminium content, which would be commonly found in traditional methods of removal.