Supply Chain - Water Treatment - Precast Concrete Structures

The Argyll SCADA (Supervisory Control & Data Acquisition) Project consists of control system replacement at four water treatment works in the Argyll & Bute region of Scotland:  Inverary, Dhu Loch, Campbeltown and Kilchrenan. The project need was to address hardware obsolescence issues which presented Scottish Water with an unacceptable risk to continuity of supply. This case study focuses on one of the four projects, Inveraray Water Treatment Works, located on the western shore of Loch Fyne in Argyll & Bute.

Background to Inveraray WTW

Inveraray WTW treats raw water abstracted from Stellaire Ban Loch, which is supplemented from Loch Righeachan. Final water gravitates to supply the town of Inveraray and is also pumped to a nearby service reservoir. The works is a conventional two stage facility employing aluminium sulphate coagulation, dissolved air flotation, primary rapid gravity filtration and secondary pressure filtration. The existing control system had reached the end of its serviceable life and was no longer supported by the manufacturer, presenting an unacceptable risk to continuity of supply from the WTW. To address this risk, Scottish Water initiated a project to replace the existing control system for the works.

Inveraray WTW existing works process and control system overview

ESD was appointed as Principal Contractor to deliver the project. The initial focus was on appointing the right team to deliver the project. A Project Manager was appointed who had extensive experience in the EICA commissioning of critical water treatment works. A Design Lead was appointed who had 30 years’ experience in the manufacture, design and specification of MCC and Control System projects. A Principal Process Engineer who specialises in water treatment was assigned to review the documenting of the existing process control requirements. Experienced EICA Commissioning Engineers were consulted and appointed with the knowledge that the method of migration, testing and commissioning were a key focus. BGEN Ltd, as a Client Framework MCC/SI specialist, were appointed as the System Integrator Sub-contractor and awarded a contract to support the design of the project.

Project Challenges

The principal challenges were:

• Lack of existing information – limited drawings with no record of change in 30 years and initially no annotated programmable logic controller (PLC) software available.
• Loss of experienced control engineers who could have provided support to the project.
• Limited number of industry engineers with necessary experience.
• Remote location of each site, with plant shutdowns constrained.
• Operational constraints meaning work on two plants simultaneously was not possible.
• Special considerations to be made for seasonal changes in demand, making sure the plant was running efficiently and coping with the necessary requirements of both high and low demand periods during the summer and winter.

Project Planning

Leveraging the experience within the project team, the Project Manager and Design Lead worked with Scottish Water stakeholders to agree the deliverables required and methodology. Contrary to other projects on the client’s Investment Programme, it was agreed there were two key deliverables that were required ahead of agreeing a Target Price for the Project. Firstly, a Programmable Logic Controller Migration Strategy document was produced by the subcontractor. BGEN Ltd had extensive experience in the development of this document, and specific experience in the migration of PLCs on live process plants. This document detailed all permanent and temporary equipment required to replace the Control System on site. A Functional Design Specification (FDS) was the second key document. Previous project experience in utilising an FDS as a test document was recognised and, in order to capture existing functionality, ESD adopted a “bottom-up” approach to its development.  Site surveys and interviews with site operations were undertaken to validate and update existing P&IDs which were 30 years old. These were then used as a basis to develop a Control Philosophy and FDS with Operations. BGEN Ltd and ESD worked together to develop the FDS against the minimal information available from the existing ICA installation – i.e. unannotated PLC software, SCADA mimics, wiring and site inspections. As the Argyll project developed, parallel surveys and FDS development at another ESD site identified more annotation on similarly structured PLC software which allowed previously unknown functionality to be identified and captured in an updated FDS. Once these outputs had been completed, the team worked with Client Technical Assurance to quantify risk and opportunity on the remaining unknowns. This in turn allowed ESD to agree a final version of an FDS & Migration Strategy with all parties prior to Factory Acceptance Testing (FAT). Having both key documents produced to detail allowed ESD to firm the scope with all parties and mitigate commercial risk.

Factory testing

With the FDS agreed and developed to a Software Design Specification by BGEN Ltd, full and comprehensive Factory Acceptance Testing of the software was undertaken at BGEN’s workshop facilities at Penketh. Drawing on previous industry experience and feedback from a variety of system integrators and water industry ICA Commissioning Engineers, a fully robust and complete Factory Test was critical to the success of on-site commissioning. It is more efficient and economical to correct errors prior to the connection of equipment to live process plant and equipment. The Client FAT was signed off to the satisfaction of all parties. [caption id="attachment_18607" align="alignnone" width="1200"] Dirty washwater tank - Courtesy of ESD[/caption]

Implementation

The replacement process at Inveraray was carried out over the following stages:

1. Installation
2. Soak testing: In this stage, the plant processes are fully operational utilising the hybrid control for a timed period of 'soak' testing. This ensured the plant can be successfully operated under the new PLC and SCADA control. It also provided an opportunity for site operators to gain early familiarisation and training with the new Siemens SCADA system, preparing to take over once the replacement works are complete.
3. I/O (input/output) migration: After confirming through 'soak' testing that the plant was successfully running with the new control system, the final stage involved replacing the existing PLC I/O with the new Siemens I/O.  This stage was irreversible and only began once the new system was proven to be fully operational.

The I/O migration involved systematically isolating plant areas, disconnecting the field wiring from the existing PLC I/O modules and reconnecting it to the new Siemens I/O modules. The main concern during this process was minimising any disruption to plant operation.

Digital I/O was migrated, module by module, using new intermediate socket-to-terminal boards, making sure all the associated I/O of the new PLC was wired correctly on the new terminal boards which then have their sockets connected to the existing plugs wired to the existing field terminals. The existing field terminal wiring thus remained undisturbed. This digital I/O migration strategy was utilised due to very congested cable trunking in the rear sections of the MCC. Rewiring this section for the new I/O would have risked disturbing existing terminal connections, jeopardizing plant operations. Such disturbances are common during rewiring and can usually cause significant delays and disruptions. This technique, successfully used at Tobermory WTW, avoided unnecessary disturbance of existing field terminals.

Analogue I/O for each module was migrated signal by signal using existing field terminals and without congested cable trunking which were disconnected from the existing PLC modules and reconnected to the  Siemens PLC modules by rewiring.

[caption id="attachment_18606" align="alignnone" width="1200"] The sludge building - Courtesy of ESD[/caption] Project summary & innovations The Argyll SCADA project was identified as a high risk project due to the critical nature of the process and the absence of any information that would have helped define the scope and the basis of the design. With all but one of the four projects handed over, the management of the process and commercial risk in delivering the project has been deemed a success for Scottish Water and its customer base. Impactful decisions that supported the success of the projects:

• Resourcing key personnel with ICA, Process and Project Management experience in delivering PLC / SCADA replacement projects.
• Identifying the key risks prior to defining scope, including extensive, intrusive surveys to review and consolidate software condition and existing drawings and documentation.
• Regular and positive collaboration with the Client, agreeing the required process control with Site Operations and Client Technical Assurance to produce a documented Migration Strategy.
• Consideration on whether a document FDS was required prior to contract award for a more accurate Target Price.
• Validation and survey of existing field devices to provide I/O from existing drives, valves and instrumentation.
• Implementation of hybrid control prior to physical migration of I/O, providing further certainty on the new software configuration.
• Archiving of existing process control outputs for review, to consider rationalisation of the process – this was useful in the Argyll SCADA project as retuning process control resulted in an estimated 30% saving of operational costs.

Argyll WTW SCADA Project: Supply Chain - key participants  

• Principal designer & contractor: ESD
  • Binnies
  • Galliford Try
  • MWH Treatment
• Systems integrator, electrical installer & telemetry contractor: BGEN Ltd
• Client: Scottish Water

Located 5 miles south of Chelmsford, Hanningfield Water Treatment Works (WTW) is the largest works operated by Essex & Suffolk Water (ESW). The WTW, which has a peak output of 220 MLD, draws water from the 26,000 ML Hanningfield Reservoir to supply a large part of south Essex. The washwater system is over 50 years old and required upgrading and refurbishment. This case study follows on from the paper in 2022 and details the progress of the main construction activities through to completion.

Existing works

The treatment process comprises pre-ozone, pulsator clarifiers, rapid gravity filters (RGFs), main ozone, granular activated carbon (GAC) and chlorine disinfection. Dirty backwash water from the RGFs and GAC discharges by gravity to two settlement tanks. Supernatant from the settlement tanks was pumped to Hanningfield Reservoir. Settled material was transferred to sludge tanks for onward pumping to the Whitelillies Reed Beds facility, which provides low energy sludge treatment and supplements the diverse ecosystem that Essex & Suffolk Water has nurtured over many years.

Project need

The original washwater system installed in the early 1970s was at risk of contravening its consented discharge parameters. This was due to increases in treatment works capacity and changing influent water quality to the treatment works, largely due to the algal load from the Hanningfield Reservoir. Operational practices to cope with filter-blinding algal events required increasingly frequent washing to maintain the production capacity of the works. The increased washwater production during the algal bloom period further exacerbated plant reliability by affecting the articulating floating arm draw-offs and pump performance of the system. Essex & Suffolk Water commissioned Stantec UK to carry out concept and definition studies, details of which were presented in a case study in the 2022 edition of UK Water Projects and on WaterProjectsOnline. A summary of the solution which was described in detail in the previous article are included in the following synopsis. [caption id="" align="alignnone" width="1200"] New pumping station layout 3D model - Courtesy of TES Group[/caption]

The solution

The existing washwater tanks operate with continuous inlet flow and draw-off by periods of supernatant pumping (via floating arm draw-offs) and subsequent periods of settled material pumping. New consent parameters of 50 mg/l suspended solids and 30 mg/l Fe now apply, including the caveat that no chemicals will be added to aid settlement. To achieve these new consent requirements, extensive lab and full scale in situ tests using the existing washwater settlement tanks were undertaken to ensure a good understanding of the existing washwater production and the time needed for natural settlement to occur. The concept design also considered the storage of GAC-conditioning water following a GAC delivery, where the fine particles would not generally be suitable for return directly to the reservoir. This led to the solution identified being a total of an additional two settlement tanks (three is the minimum number required to deal with the peak flow from filter backwash). While concept design identified that a new pumping station will be required to house the supernatant pumps serving all four tanks, detail hydraulic analysis carried out as part of the detailed definition identified that the separate settled washwater pumps would be installed in the new and the existing pumping stations to keep suction line as short as possible. [caption id="" align="alignnone" width="1200"] Refurbished pumping station: (left) 3D model - Courtesy of TES Group and (right) pumping station layout - Courtesy of Essex & Suffolk Water[/caption]

Contracts awarded

For operational and hydraulic reasons, the new works needs to be located close to the existing washwater tanks. The only land that was available was on a small hillock. An enabling works contract was awarded in 2017 to prepare the working platform for the new works. The enabling works involved earthworks, haul road, service protection bridges and exploratory investigations of the buried services in the area. Following the completion of the enabling works, the competitive tender for the main works was won by a bid submitted jointly by Farrans Construction and TES Group. Both companies have a good track record in the UK water industry and have relevant experience in delivery of Essex & Suffolk capital projects, Farrans with their civil engineering expertise and TES on the MEICA works.

Hanningfield WTW: Washwater Tanks Phase 2: Supply chain - key participants

• Designer/main contractor: Farrans TES JV
• Process design: Stantec UK
• MEICA design: TES Group
• Cost management: Turner & Townsend
• Civil design: Pell Frischmann
• Earthworks/groundworks: RB McGeary Contracts Ltd
• CFA & sheet piling: Murphy Group
• Reinforced concrete/formwork: Murform Ltd
• Superstructure steelwork: AC Bacon Engineering
• Washwater pumps: SPP Pumps Ltd
• Flow Control: Hydro International
• Penstocks: Ham Baker Group
• Valves: Glenfield Invicta
• Pipework & access platforms: Franklyn Yates Engineering
• MCCs: TES Power
• System integration: OCE Systems
• Transformer/RMU: Schneider Electric
• Flow meters/instruments: Siemens
• Pressure instruments: IFM Electronic
• Cranes & lifting: ABUS Crane Systems Ltd
• Photovoltaic system: Solar UK Ltd
• Fire alarms/security: Openview Security Solutions Ltd
• Lightning protection: Bacon Group
• Flow controls: Auma Actuators

COVID-19

Shortly after contract award in early 2020, COVID-19 was declared a global pandemic. The construction industry was then given government guidance to carry on operating, and Site Operating Procedures (SOP) were issued by the Construction Leadership Council. Additional welfare facilities and safe working practices based on the SOP were put in place to protect the workforce and to minimise the risk of spread of infection. The original works programme was extended to allow for an initial postponement of the works start date, and for reduced productivity caused by the social distancing requirement. [caption id="" align="alignnone" width="1200"] 3D model of the whole works - Courtesy of TES Group[/caption]

Civil construction

The main civil works involved constructing a new pumping station and two new settlement tanks, both requiring deep excavations to create the formation of their reinforced concrete bases. Given that most of the excavation would be in the London Clay formation it was decided that the use of battered excavations across the site would provide the most cost-effective solution. But due to the proximity of several critical assets; (i) the existing washwater tanks and pumping station (ii) the existing haul road and (iii) live site services (11kV ring main, fibre optic cable, sludge pipeline, and the supernatant pipeline), it was necessary to use sheet piles in the space available to ensure the workings were safe and retained. Ground piles were used to ensure the tanks did not settle or have any impact on ground heave. This was followed by large reinforced concrete bases and walls to form the washwater tanks. The pumping station foundation and surrounding walls were all reinforced concrete and installed to a depth below ground of approximately 5m. The new pumping station is approximately 27m long by 12m and 8m tall and has a steel superstructure construction with metal cladding. There was an array of on-site pipeline work within Farrans’ scope. The first phase of pipework was to divert a number of live mains which were one of first construction activities on site prior to the earthworks. The detailed services information collected by ESW under the enabling works contract proved to be extremely useful for planning these diversions. Farrans had to install line valves and trust blocks to isolate the sections, and the work was staged to keep the duration and number of planned outages down to the minimum. A detailed method statement was submitted to ESW for review during the planning of these diversion works. The bulk of the new pipework constructed was laid to connect the new and existing structures at significant depth, up to 7m below ground. Due to the limited space availability, open dig was often not an option, so trench boxes had to be used. In addition, the planning of the excavation work had to take account of the many existing buried services, particularly in the area adjacent to the existing structures, to ensure that they are not impacted upon. [caption id="" align="alignnone" width="1200"] (left) Concrete pour for pumping station base and (right) the pumping station superstructure and tank bases construction - Courtesy of Farrans Construction[/caption]

MEICA design & installation

TES used Autodesk Revit to undertake the detailed 3D design for the project, utilising point cloud laser scans of the existing plant and tanks enabling the development of a detailed and accurate model of the future completed works. The new structures and associated mechanical and electrical equipment for both pumping stations were modelled and coordinated with various discipline models using the BIM360 Design Collaboration and Revit. This therefore ensured all teams were working with the latest data and model throughout the project, thus producing a true 3D vision of the planned completed works. A new 500kVa 11000/415v transformer and RMU connected to the existing site-wide HV ring main network was required to power the new pumping station. The site management team, HV specialist subcontractors and senior authorised persons worked closely to ensure the safety of personnel and reduce risk or damage to the existing power network. RAMS for identification, cable isolation, spiking procedures, and jointing work were reviewed in line with all relevant safety procedures and regulations before transfer of control was approved and works could commence. A detailed complete electrical design was developed in-house using various electrical packages to include AutoCAD, EPLAN, Amtech & Relux, which proved invaluable at time of installation and testing. [caption id="" align="alignnone" width="1200"] Installed new pumps and gantry crane - Courtesy of Essex & Suffok Water[/caption]

Refurbishment of existing assets

Upon the completion, commissioning and 28-day trial of the new pumping station and new tanks, the dirty washwater from the treatment works was diverted to the new pumping station and tanks. This allowed the second phase of the work programme to proceed which was to refurbish the existing washwater pumping station and two settlement tanks. All the existing pumps and pipework were removed from the pumping station and new settled washwater pumps and pipework installed. The new arrangement has significantly improved the access for operational staff because it is less congested now that the supernatant pumps are re-located to the new pumping station. The two existing concrete settlement tanks, which have been in service for around 50 years, are still structurally sound but required surface cracking and joint repairs. The contractor detected asbestos containing materials in the existing joint filler, so the repair was changed to using over-banding in preference to be disturbing the existing joint fillers.

Commissioning

TES developed a commissioning plan with the purpose to assure that the electrical systems were safe, reliable, perform within manufacturer tolerances, were installed in accordance with the design specifications, and conformed to ESW standards. ESW engineering and operations teams were consulted throughout the various stages of the plan development. Progress, control, and operational commissioning was undertaken using the industry standard level 1,2 & 3 testing documentation, therefore providing client confidence, and fulfilling end user operational requirements and quality. ESW operation and maintenance personal were trained, and specific routine maintenance tasks were demonstrated. [caption id="" align="alignnone" width="1200"] New tanks during commissioning - Courtesy of Essex & Suffolk Water[/caption]

Environment

Considerations were given to the high ecological sensitivity of the site throughout the project, particularly related to the presence of a large numbers of reptiles. Vegetation management and reptile relocation were part of the enabling works. As areas of the construction site are handed back, these areas have been restored to grassland. To maximise the potential for biodiversity, suitable seed mixes of native grass and wildflowers have been sown. On sloped areas the diversity of plant species leads to greater soil stability as well as promoting pollinators. Following on from the reptile relocation works, a large hibernaculum site has been constructed within the restored grassland area. The residents of the nearest villages were kept informed via letter drop on the progress of the project and how traffic and noise are to be mitigated. The final landscape works will involve tree and shrub planting to screen out visual impact on the nearest neighbour.

Summary

At the time of writing (August 2023) the Hanningfield Washwater Project has started final reliability trials. The project team has worked collaboratively to deliver a high-quality product meeting the required standards in a safe manner while protecting the environment having overcome the severe challenge of COVID-19.

Littlehempston is a large complex potable water treatment works located near Totnes, South Devon, which has multiple river and reservoir sources. It supplies circa 78,000 properties to an area that includes Torbay, Newton Abbot and Kingsbridge. The original treatment works comprises flat bottom clarifiers (FBC) and rapid gravity filters (RGF), with an additional process stream added later, utilising dissolved oxygen flotation (DAF) and additional RGFs. The current £14.4 million, 2-year project involves intercepting the flows where the two treatment streams join and passing through a new granular activated carbon (GAC) process and ultraviolet (UV) treatment to the improve drinking water quality.

Project drivers

South West Water’s objective to employ granular activated carbon (GAC) has been to address the following:

• Ensure compliance with pesticide standards.
• Target a 25% reduction in total trihalomethanes (TTHMs)  in the final water leaving the treatment works.
• Target a reduction in average levels of TTHMs to less than the screening value of 50 µg/l.
• No detections of methyl-isoborneol (MIB) greater then 5 ng/l in final water and target a long-term reduction in taste and odour customer contacts.

At the scoping stage, Galliford Try and Arcadis worked closely with South West Water to establish the most cost-efficient solution when considering both operational costs (OPEX) and capital expenditure (CAPEX) to ensure South West Water achieved the best whole life costs. [caption id="" align="alignnone" width="1200"] 21m diameter dirty back wash tank - Courtesy of Galliford Try[/caption]

Project scope

The project solution includes a new GAC treatment process. Six reinforced concrete contactors, were constructed in situ, and housed within a steel clad, portal frame building. ODEX piles were used to support the structure due to the encountered ground conditions. The new primary disinfection is to be via ultraviolet (UV) disinfection. The UV building containing the reactors is an in situ concrete structure, supporting a GRP (glass fibre reinforced plastics) kiosk. This kiosk also houses the new control panels for the GAC and UV processes being installed. Two new precast tanks are being installed, providing dual use as combined interstage pumping and clean backwash water storage. An off-site fabricated, precast solution was used which provided significant programme advantages, and reduced the health and safety risks. A four-pump arrangement provides duty/standby interstage pumping, clean backwash feed and a common standby which can support both interstage or backwash pumping as required. The duty pressure and flow characteristics of both systems was optimised to allow the same pump to be selected for both operations. This provides South West Water improved flexibility and resilience for future operation and maintenance. [caption id="" align="alignnone" width="1200"] Below ground large diameter pipework required to be installed around existing structures and services - Courtesy of Galliford Try[/caption] A further tank will be used for the collection of GAC backwash and rinse. The GAC backwash water is not being combined with the existing site waste and supernatant system, and instead will be returned via new pumps directly to the inlet works. Appropriate sampling is being installed to confirm it is of suitable quality to return and can be diverted into the existing wash water system if required. This sustainability driven solution improves the efficiency of the plant, reducing pressure on incoming water resources whilst avoiding discharges to the environment. During the outline design phase, an existing redundant structure on site was identified as being suitable for use as a collection tank for GAC regeneration wastewater. Re-using this structure provides improved value for money, whilst reducing the carbon consumption and the environmental impact of constructing a new concrete structure, as per the original concept. The re-purposing works will require some minor inlet and outlet pipework modifications, installation of new pumps and removing of the redundant equipment.

Littlehempston WTW: Supply chain - key participants

• Delivery contractor: Galliford Try
• Design: Arcadis Consulting (UK) Ltd
• Piling: Roger Bullivant Ltd
• Reinforced concrete works: D Wall Construction Services Ltd
• Precast concrete tanks: A-Consult Ltd
• Steel frame building: Hewaswater Engineering Ltd
• Reinforcement: Hy-ten Ltd
• Aggregates & concrete: E & JW Glendinning Ltd
• Plant hire: Plantforce Rentals Ltd
• Ultraviolet reactors: Trojan Technologies
• Underfloor drains & launders: Xylem Water Solutions
• Underfloor drains & launders installation: Western Carbons Ltd
• Stainless steel pipework & galvanised mild steel structures: Alpha Plus Ltd
• Pipework: Freeflow Pipesystems Ltd
• Ductile pipework: Electrosteel Castings (UK) Ltd
• Flow control: Affco Flow Control UK Ltd
• GRP kiosk: Pro-Tect GRP Enclosures Ltd

[caption id="" align="alignnone" width="1200"] FRC construction of GAC cells - Courtesy of Galliford Try[/caption]

Project challenges

As part of the scheme the site team have had to make pipework modifications to intercept flows between the existing RGF filters and primary contact tank. To achieve this, a series of seven independent site shutdowns were carried out weekly to facilitate the modifications needed. This area, affectionately known as the 'bear pit', required detailed planning to develop a suitable solution. The final arrangement includes branch connections to allow the existing flow paths to be kept on-line, the installation of new pipework, refurbishment of redundant pipework, temporary cross-connections to allow commissioning flows to be circulated, and also includes a new static mixer for the relocated dosing point for chlorine and orthophosphoric acid. The challenges were amplified further by the limited access to the area, meaning that pipework had to be fabricated in small sections that could be safely lifted in. A point-cloud survey of the original pipework was integrated into the BIM model which allowed the concept development. Exact measurements were then verified manually on site before fabrication. A 4D approach was implemented during the design development which allowed for the different phases to be visualised and support the buildability and planning discussions between the project delivery team, and South West Water operations. Access to site is also incredibly challenging, as the rural Devon location is only accessible with heavy goods vehicles (HGVS) via a narrow single-track road with infrequent passing places for HGVs for approximately 5 miles. This impacted multiple design and construction decisions, limiting the size of rebar, pipework, precast units and various types of plant and machinery that could be used such as piling rigs, excavators and cranes. The site team arranged suitable locations to hold vehicles allowing all HGVs movements to be managed through the narrow lanes. Surrounding business were updated weekly on HGV movements and in return made the site traffic management team aware of their movement so that they could also be coordinated. [caption id="" align="alignnone" width="1200"] GAC building pipework gallery - Courtesy of Galliford Try[/caption]

Carbon savings and in-house capability

Local resources and materials were used where possible including subcontractors which as a result provided a boost to the local economy during the construction phase. Where local suppliers were not available, Galliford Try endeavoured to use off site build solutions where possible to minimise commuting. The following in-house resources were utilised:

• Management.
• Electrical design.
• Process control.
• Commissioning.
• Workforce to undertake the following:
  • Establish and demobilise site.
  • Civils groundworks.
  • Hard and soft landscaping.
  • MECIA works.

Stakeholder management

At pre-construction phase, all third-party stakeholders were identified and entered onto a management plan. Galliford Try’s Customer Liaison Officer contacted all stakeholders prior to commencement to provide them with the appropriate project contacts should they have questions, queries, or complaints and to establish their requirements and desires throughout the construction phase of the works. As part of the management plan all communications where complaints or agreements are made are formally recorded, resolved, and closed out. [caption id="" align="alignnone" width="1200"] GAC & UV buildings with interconnecting pipework - Courtesy of Galliford Try[/caption]

Noteworthy

This job was aided by the useful wealth of archived drawings and pictures stored by South West Water on site. The documents gave Galliford Try a useful insight into the history of the water treatment site and proved to be invaluable in the process of locating services. Notably, Galliford Try discovered these documents were stored in a cold-war era bunker making the exercise of ploughing through documents not your average day on site!

Summary

Collaboration between client, contractor, designer and the wider supply chain has been a key factor in resolving significant challenges including establishing pipe routes for large diameter interconnecting pipework, suitable crane platforms for inaccessible areas of the existing operational site and the pipework modifications required during works shutdowns in the 'bear pit'. [caption id="" align="alignnone" width="1200"] Fit out of the contactor gallery prior to the erection of the steel clad portal frame building - Courtesy of Galliford Try[/caption] Currently (May 2023) all the structures are nearing completion, mechanical installations are well advanced with electrical fit outs to commence late summer 2023. Large diameter site-wide interconnecting pipework is currently being laid, with the vast majority programmed to be completed during the summer and early autumn months of 2023 to take advantage of more favourable ground conditions. Process Commissioning is to commence in late 2023 and is scheduled to be completed well in advance of the Drinking Water Inspectorate (DWI) Compliance Date 31 March 2025.

Lee Road Water Treatment Plant (WTP) provides approximately 70% of Cork City’s total treated water supply. Water is taken from the River Lee, treated and then pumped to reservoirs in the north-west of the city through a system of rising mains. Water is distributed to consumers throughout the city via a network of gravity distribution mains. The treatment of drinking water began at this site in 1879, and whilst there have been several upgrades throughout its lifespan, none have been completed since the 1950s. This treatment plant upgrade is the first major investment in over 60 years and will support continued population growth and economic development in the city. The upgraded treatment facilities have safeguarded the water supply for Cork City and the works have enabled the supply to be removed from the Environmental Protection Agency’s (EPA) Remedial Action List.

Undertakings

Murphy Ireland are one of eight contractors that have been on the Uisce Éireann framework to deliver major non-infrastructure projects since 2017. Murphy was awarded the €40m Lee Road WTP contract via competitive tender in 2019 and was required to complete these key works by July 2022, while the existing plant remained in full operation. Uisce Éireann issued a high-level outline design brief with Murphy responsible for completing the full detailed design. A significant amount of optioneering, value engineering and constructability reviews were undertaken. The end solution offered better value for money and Murphy was appointed Project Supervisor Design Process (PSDP), equivalent to Principal Designer under CDM regulation, and Project Supervisor Construction Stage (PSCS), equivalent to Principal Contractor, for the duration of the project. [caption id="" align="alignnone" width="1200"] Lamella plate sedimentation tanks - Courtesy of Murphy Ireland[/caption]

Scope of works

The upgraded facility designed and delivered by Murphy included:

• Reconfigured raw water intake inclusive of a raw water band screen and bypass arrangements.
• Coagulation, flocculation, and clarification system.
• Six rapid gravity filters utilising Xylem Water Solutions' Leopold underdrain filters.
• Chemical and UV disinfection.
• Installation of pH correction facility via dosing sodium hydroxide.
• Washwater and sludge handling facilities, incorporating a sludge plate press.
• New treated water pumping station and refurbishment of existing pumping station, complete with high efficiency frequency inverters and motors.
• EICA infrastructure including PLCs, communication links and SCADA system.
• Prevention measures to protect the works from flooding during extreme weather events.
• Full Murphy managed operation and maintenance of the facility for 12-months.

Construction challenges

All process wastewater is collected and treated, ensuring it is suitable for discharge to the adjacent river Lee within the specified discharge standards. During construction, Murphy encountered and resolved a number of construction challenges due to the high-water table on the site adjacent to the river Lee. This led to challenging working conditions. Murphy addressed this issue by installing deep sheet pile cofferdams to lower gravel beds and installed a ringed dewatering system to manage groundwater. The site was raised following construction of tank structures to provide a new ground level 2m above previous levels. [caption id="" align="alignnone" width="1200"] Overview of site showing the build complexity - Courtesy of Murphy Ireland[/caption] Another key challenge on this project was keeping the existing plant operational for the entire construction phase to its full capacity. It was essential that the works were carried out with no interference to the existing water treatment process. Working within a city presented several logistical constraints including constrained and restricted site access. Therefore considerate, efficient, and well-planned logistics plans and methodology were integral to minimising disruption for the locality and the smooth running of the construction works. Construction Site Traffic Management (CSTM) was meticulously managed and ensured no interference with the existing plant operations. Staged infill operations were undertaken to minimise this disruption. Significant off-site construction was undertaken in addition to rigorous off-site factory testing, resulting in a reduced number of construction defects and a smooth and efficient commissioning process. The commissioning plan was developed throughout the life cycle of the works and signed off by the client three months ahead of planned commissioning. This gave enough time for all parties to be briefed and understand commissioning requirements, durations, key activity outputs and agree standards to be reached. [caption id="" align="alignnone" width="1200"] UV disinfection - Courtesy of Murphy Ireland[/caption]

Lee Road WTP - Supply chain - key participants

• Principal contractor: Murphy Ireland
• Process/MEICA design & systems integrators: Murphy Process Engineering
• Civil design: Finbarr Gannon Ltd
• Electrical design: Seamus Byrne Electrical Ltd
• Groundwater dewatering: WJGL Ltd
• Groundwater monitoring: Priority Geotechnical Ltd
• Formwork: Hickey Formwork ltd
• Precast concrete tanks: Shay Murtagh Precast
• Sheet piling: Ward Piling
• Steel reinforcement: James’s Street Steel Manufacturing Ltd
• Tower crane hire: Mantis Cranes
• Security fencing: Irish Fencing Services
• General & specialist fabrication: Russell Metal Fabrication Ltd
• Gantry crane: Ballinphellic Engineering
• PLCs & MCCs: Omron CPU35/ASC
• Intake band screens: Beaudrey
• Process pipework: Freeflow Pipesystems UK
• Process pipework: Superior Pipeline Products Ltd
• Sludge plate press: Micronics UK Ltd
• Pumps: Celeros UK
• Flow controls: Rotork
• Inverters & motors: ABB
• Valves: Talis
• Leopold underdrain filters: Xylem Water Solutions
• Air compressors: Atlas Copco Ltd
• UV disinfection: Hanovia
• Chemical dosing: Colberge Water Systems
• Bulk chemical storage tanks: SILOTANK
• Bulk chemical storage tanks: Phaser Limited
• Surge vessels & walkways/access systems: Murphy Design

Protection of assets

Situated beside the River Lee, the existing water treatment plant experienced significant flooding in the past and was at the end of its useful lifetime. The design solution delivered a state-of-the-art treatment facility whilst raising the site by 2m to protect against future flooding during extreme weather events. For instance, the existing ground consisted of porous gravel beds that facilitated easy passage of groundwater. Careful dewatering design ensured good management of resulting groundwater flows. [caption id="" align="alignnone" width="1200"] UV-treated water - Courtesy of Murphy Ireland[/caption]

Achieving a successful delivery

Collaborative working was central to Murphy’s approach, and in conjunction with Uisce Éireann, continual updating of the three week look ahead and the Master Information Delivery Plan (MIDP), ensured effective planning and minimised unforeseen events. Murphy’s in-house expertise designed and delivered the project with strict adherence to Uisce Éireann Asset standards, and provided mechanical, electrical, instrumentation and control automation (MEICA), and civil services, including in-house process design, piling, and structural steel design and fabrication. Mid-programme planning changes were introduced to help achieve an improvement to the delivery programme. The original plan for the project was to reuse the existing sedimentation tanks, however Murphy suggested building entirely new ones as this would provide a better overall product, improving programme, in addition to improving the whole-life cost and de-risking the supply concerns for the locality. The upgrade works on Lee Road WTP will also reduce the energy consumption and running costs by more than 40%. Sustainability, as on all Murphy projects, was a key part of the strategy at Lee Road. Various measures were put in place to protect local wildlife such as bats and otters, in addition to ensuring, waste material was reused where possible. [caption id="" align="alignnone" width="1200"] Alum bulk storage - Courtesy of Murphy Ireland[/caption]

Meeting Uisce Éireann’s customers’ needs

Independent testing of raw water, treated water, sludge parameters, noise, and other parameters were undertaken during the Performance period to confirm compliance with EU Drinking Water Regulations. Murphy provided leadership for the following:

• Uisce Éireann have an ongoing water network upgrade programme around Cork City and Murphy supported Uisce Éireann’s needs to managing reservoir demands, alter final chlorine residual and optimising final water pH.
• Leading demonstrations of shutdown controls, water despatch control and interlocks with service reservoirs during EPA audits.
• Working collaboratively to commission an automated coagulation control system, which optimises use of aluminium sulphate coagulant, yet reacts quickly and efficiently to changing raw water characteristics such as colour, turbidity and UVT.
• Holding regular operational team meetings to agree the O&M programme approach.
• A three-year spares assessment vetted by the client to reach collective agreement.

[caption id="" align="alignnone" width="1200"] Rising main pressure vessel - Courtesy of Murphy Ireland[/caption]

Working throughout the pandemic

With the project being delivered during the Covid-19 pandemic, multiple different challenges presented themselves. For example, throughout the start of the project at peak periods there could be upwards of 80 people working on site at any one time. However, following the onset of Covid-19, Murphy had to adapt the working practices, incorporating social distancing measures, rotas for breaks and shift start and completion patterns. Despite working throughout the Covid-19 pandemic and with the variety of risks, the safety record from the project was exemplary. Across two years of works the team had zero lost time incidents. Lee Road was selected for an external ISO Quality audit by Lloyds Accreditation and passed with distinction.

Community liaison

School visits during the operation phase continued to form a part our interaction with local groups and community, dovetailing with Cork City Council’s adjacent visitor centre which highlights the history of waterworks at Lee Road since the 1850s. During the construction phase local labour was utilised along with local suppliers. During Covid while many other workers in the city were furloughed, construction works continued at Lee Road which was deemed an essential construction project. The design processes included regular HAZOPs workshops to include at least 20 people from the client ranging from plant operators to statutory body representatives. [caption id="" align="alignnone" width="1200"] Final pumping - Courtesy of Murphy Ireland[/caption]

Conclusion

Following commissioning, which took place throughout the first half of 2022, water went into supply in July 2022, and Cork now has a new, secure, modern, state-of-the-art water treatment facility that will serve the community for years to come. The flooding risk that pertained has now been removed and the new works at Lee Road is fully integrated with the City and County water reservoir storage system, offering huge flexibility in clean water provision.

Water companies are facing ever tightening standards, including the treatment of micro-pollutants to almost non-detectable levels in drinking water, very low levels of phosphorus discharge from wastewater treatment, and the requirement to drastically reducing storm overflow spills. The proprietary silicon carbide (SiC) membrane and module is an innovative technology that provides some unique advantages for potable water, wastewater and CSO applications, and helps water companies increase their treatment capacities, reduce costs and reduce their carbon footprint; major drivers for the industry when selecting key process technologies.

Silicon carbide (SiC) ceramic membranes

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

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

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

[caption id="attachment_18309" align="alignnone" width="1200"] Cembrane SiC membranes, modules, stacks & towers - Courtesy of Enpure Ltd[/caption]

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

• Increased flow: Get up to five times more flow out of existing rapid gravity filters (RGFs) by using Silicon carbide ceramic membranes.
• Low carbon footprint: SiC can be installed in existing tanks available on site, reducing the need to build new concrete structures.
• Consistent water quality: The SiC membranes consistently produce water that meets and exceeds regulatory standards independent of feed water quality.
• Durability & reliability: After multiple years of operation, the SiC membranes show no signs of degradation and no decline of the membrane permeability, vastly improving whole-life cost.
• Operational efficiency: Low maintenance and remote monitoring capabilities minimise operational costs and staffing requirements.
• 25-year whole-life cost: The whole life cost is estimated to be significantly improved compared to the traditional alternative.

[caption id="attachment_18308" align="alignnone" width="1200"] Applications of Cembrane SiC membranes - Courtesy of Enpure Ltd[/caption]

Cembrane

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

Case Study: Gothenburg Water Treatment Plant (Sweden)

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

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

[caption id="attachment_18311" align="alignnone" width="1200"] (left) Installation of Cembrane SiC stack, (top right) Cembrane SiC stack from above, and (bottom right) SiC membranes have sprinkler cleaning option - Courtesy of Enpure Ltd[/caption]

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

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

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

• • Flows: 50% increase from 3,500m³/day to 5,200m³/day.
  • Manganese: <0.02 mg/l (target <0.05 mg/l).
  • Iron: Non-detectable (target <0.05 mg/l).
  • Turbidity: <0.1 NTU (target <1 NTU).
  • Recovery rate improvement: from 80% to 99%.

Conclusion

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

This project was commissioned by UK Water Industry Research (UKWIR), as part of their efforts to address one of the 12 Big Questions the UK Water Industry is facing, “How do we achieve 100% compliance with drinking water standards (at point of use) by 2050?”. Today, no more than 10% of the total incoming flows to water treatment works (WTWs) can be made up of treated recovered process water streams (e.g. centrate/filtrate from sludge processing units, filter backwash, membrane concentrate/reject, etc.). One of the main concerning issues prohibiting the higher ratios of recovered process water/raw water mixing as an input to WTWs, is the risks associated with contaminants such as Cryptosporidium, viruses and microplastics which may be present at elevated concentrations in the recovered process water streams. The goal of this project is to facilitate maximising the safe recycling of recovered process water streams at WTWs, through identifying and recommending the adoption of optimum methods of treatment and monitoring, as well as proposing methods of risk mitigation for the above-specified contaminants. [caption id="" align="alignnone" width="1200"] Recovered process water recycling at WTWs - Courtesy of WSP[/caption]

Approach

From a long-list of 24 solid-liquid separation technologies (Figure 3.1), the ones deemed most suitable, both technically and commercially, for the removal of Cryptosporidium, viruses and microplastics from recovered process water streams were shortlisted under eight process groups:

1. Coagulation/flocculation.
2. Sedimentation.
3. Depth filtration.
4. Slow sand filtration.
5. Surface filtration.
6. Membrane separation (MF and UF).
7. Adsorption (GAC and PAC).
8. Microfluidic separation.

Detailed technical and commercial information for each process group was obtained from academic literature, case studies and vendor profiles. In addition to provision of performance data, an overview of waste by-products of each technology was given and CAPEX/OPEX calculations were undertaken. This information was integrated with findings from an expert workshop with attendees from academia, industry, and regulators to feed into the development of a cost-quality model. This was to support the water industry in the selection of the most appropriate recovered process water treatment processes, based on the characteristics of the incoming recovered process water streams and the resilience of the existing treatment processes on-site. [caption id="" align="alignnone" width="1200"] Technology appraisal: long list of solid-liquid separation technologies - Courtesy of WSP[/caption]

Project outputs

Treatment technology selection: With regards to coagulation and flocculation, the use of conventional aluminium and ferric based coagulants is still dominant in the water industry. However, emerging technologies such as electro-coagulation and natural-substance coagulation can offer more sustainable and environmentally friendly options. Coagulation is not a solid removal treatment on its own and would require to be coupled with other technologies such as sedimentation, filtration and/or membrane separation to achieve high solid removal efficiencies. The three main methods of sedimentation include horizontal flow, up-flow solid contact, and tilted plate (lamella) separators. While low in CAPEX and frequently used in the water industry, the horizontal flow systems require large footprint, and are prone to flow turbulence, short circuiting, and sludge re-suspension. These construction and operational issues can be significantly minimised when using compact tilted plate separators, although it comes at the cost of a higher CAPEX. [caption id="" align="alignnone" width="1200"] Coagulation/flocculation and sedimentation process groups - schematics from (Gandiwa, 2020) (watertectonics.com, 2022) (van Djik, 2007)[/caption] Among seven different types of depth filtration analysed in this study, the down-flow systems with continuous backwash showed the highest removal efficiency. Moreover, newly developed activated glass media was suggested to be more efficient at removing particles of 15 µm and smaller, compared to the conventional sand media. Therefore, upon more trials, these emerging media may be proven to be more suitable for the removal of viruses and Cryptosporidium from recovered process water streams. Slow sand filtration has 20-50 times smaller flux than depth filtration, and thus it requires much larger footprint. Nevertheless, the free-gravitational operation of the system and no backwash requirements are among the key advantages of slow sand filters. These systems are not very efficient for total suspended solids (TSS)/turbidity removal (~90%), but highly effective for Cryptosporidium (up to 3 log) and viruses (1 – 4 log). Surface filters offer higher efficiency than depth filtration with respect to TSS/turbidity. The backwash is also more efficient (2-5% of effluent) compared to depth filters (4-8% of effluent). However, sensitivity to influent quality (i.e. best at TSS< 20 mg/l) makes surface filters less suitable for recovered process water treatment compared to depth filters. Among different types of surface filtration methods analysed in this study, the bag filter offered the widest range of pore size (2-75 µm), and thus its design deemed to be easier to be tuned according to the specific contaminants in the recovered process water streams. [caption id="" align="alignnone" width="1200"] Depth filtration, slow sand filtration and surface filtration process groups – schematics from (Bielefeldt, 2011) (Metcalf & Eddy, 2014) (Eliquo Hydrok, 2020) (Rosedale Products, 2015) (mena-water.com, 2022)[/caption] Sedimentation, slow sand filtration, depth and surface filtration were in the same order of magnitude in terms of both CAPEX and OPEX. Conventional sedimentation (i.e. horizontal flow) and slow sand filtration offer the lowest overall cost and the simplest operation. Nevertheless, where space is a major constraint, the addition of lamella plates to the conventional sedimentation tanks, and/or the use of higher rate depth or surface filtration, instead of slow sand filtration can offer footprint efficiency at a slightly higher CAPEX. The OPEX of solid-liquid separation technologies would increase when they are paired with coagulation/flocculation processes. The addition of coagulation/flocculation can significantly boost the performance of some technologies (i.e. sedimentation, slow sand filtration, depth filtration and surface filtration), but is less beneficial for other technologies (i.e. MF/UF and microfluidic systems). Microfiltration (MF) and ultrafiltration (UF) offer modular and high efficiency solutions for fine solids removal, specifically with regards to viruses (up to 7 log removal) and Cryptosporidium (up to 6 log removal). Still, their sensitivity to fouling, scaling and large solid blockage (i.e. pre-treatment requirements) and high TOTEX are among the main considerations of applying these technologies. Among the different types of MF and UF configurations reviewed, hollow fibres offer better flux to volume (i.e. economy of scale) due to their high surface to volume ratio. Spiral wound types are also compact, but their resistance to positive hydraulic pressure make them more suitable for nano filtration (NF) and reverse osmosis (RO). In terms of material, emerging metallic membranes have been shown to be mechanically robust and efficient for the removal of fine particles, such as Cryptosporidium (5.1-5.4 log removal). Yet, further trials are needed before adapting these membrane types in a large scale in the water industry. The small footprint, modularity, and scalability of membrane technologies make them a suitable choice for small WTWs, where having a compact design is a priority. Moreover, MF/UF offer effective removal efficiencies (i.e. up to 7 log removal for viruses, up to 6 log removal for Cryptosporidium) for where a high degree of purification is necessary. Still, for larger WTWs and/or where lower ratio of recovered process water recycling is required, MF/UF membranes do not offer an economically feasible option. The high cost of membranes makes MF/UF technologies 10 – 15 times more expensive in terms of CAPEX than other technologies, while the high cost of pumping energy (0.2-0.3 kWh/m³) make the OPEX of MF/UF systems 2-15 times higher than other solid-liquid separation techniques, except microfluidic devices. Activated carbon adsorption (GAC/PAC) is not an efficient method of solid separation. However, it can offer effective polishing (as post-treatment) for other technologies to minimise the taste and odour issues in the recycled recovered process water. Among different configurations, the up-flow GAC columns offer higher efficiencies as they promote a greater surface contact between the granules and the effluent. The disadvantage of the up-flow systems is the higher OPEX associated with pumping and the risk of media loss into the final effluent. The costs of GAC are very similar to that of depth filtration, unless considering the assets and energy required for media regeneration, which would make the costs 2-5 times higher than that of depth filtration. Inertial focusing (IF) microfluidics are among the emerging and rapidly growing methods of solid removal from water systems, working based on the selective separation of microparticles through variously sized microchannels. Separation efficiencies up to 96% for Cryptosporidium and 99% for microplastics have been achieved in the lab-scale. Microfluidic separation is a chemical-free and easily scalable process, with an in-built ability of waste streams segregation and collection. However, sensitivity to blockage (i.e. requiring significant pre-treatment) and the low level of technology readiness (lab tested with drinking water and Cryptosporidium, scaled up for other applications), are some of the main challenges for the full adoption of this technology in the water industry. [caption id="" align="alignnone" width="1200"] MF/RO membrane separation, GAC/PAC adsorption, and microfluidic separation processes – Schematics from: (PCI Membranes, 2021) (Applied Membranes Inc, 2021) (reverseomosis4operators.com, 2021) (Balster, 2013) (ElgaLab, 2021) (Jimenez & Bridle, 2016) (Tang, 2020) (Miller, 2016)[/caption] Cost estimations for inertial focusing microfluidics were provided by a UK-based vendor, extrapolating figures from previous smaller scale installations. The estimations suggest the lowest CAPEX among all processes (~3.4 £/m³), owing it to the significant advancements in the material and manufacturing methods (e.g. 3D printing, laser cutting, etc.) in the recent years. The OPEX however, is still the highest among all processes, about 2-10 times higher than MF/UF membranes, and 10-100 times higher than other separation processes. The high OPEX of microfluidics is due to the cost of pumping fluids through small micro channels. It is clear that significant reduction in pumping energy is necessary for microfluidic devices to be introduced as competitive solid-liquid separation technology in the water industry. For the liquid waste (i.e. backwash from filtration and/or retentate/concentrate from the membrane systems) recycling to the head of the works, or mixing with the untreated process water, are key possibilities. However, further intermediary treatment (e.g. clarification) may be required depending on the quality of the liquid waste. [caption id="" align="alignnone" width="1200"] Treatment technology comparison overview - Courtesy of WSP[/caption] Cost-quality model: In order to assist water companies in the UK and the Republic of Ireland to compare and select the most appropriate recovered process water treatment processes, based on the characteristics of the incoming recovered process water streams, as well the resilience state of the existing treatment processes on each particular site, a quantitative cost-quality model was developed. The model generates as an output the following key analytics:

• Treatment process scenarios to choose from based on the provided recovered process water types and characteristics.
• CAPEX, OPEX and TOTEX estimations (-10% to +20% error margin).
• Operational daily energy cost (kWh range).
• Operational daily carbon footprint (kg CO₂ range).
• Recovered process water volume for any given treatment scenario.
• Estimated efficiency of removal for Cryptosporidium, viruses and microplastics.

[caption id="" align="alignnone" width="1200"] Model output example: scenario-based treatment technology & configuration comparison - Courtesy of WSP[/caption] Monitoring method selection: The main methods of detection and monitoring of microplastics, Cryptosporidium and viruses were grouped and reviewed under three main tiers, based on the methods ease of use/time to result, and the accuracy/quality of the results from each method. [caption id="" align="alignnone" width="1200"] Key methods of detection & monitoring - Courtesy of WSP[/caption] Selection of monitoring methods should consider that recovered process water streams are likely to be relatively highly contaminated so any method should perform well under such conditions. Additionally, a review of particle counters noted that for particle counting there was good correlation between particle counts and oocyst numbers after coagulation/sedimentation treatments and slow sand filtration, but not after membrane filtration methods. Hence, it is important that the choice of monitoring method should consider the treatment methods used. [caption id="" align="alignnone" width="1200"] Detection and monitoring method selection - Courtesy of WSP[/caption]

Operational risk control

A wide variety of potential risks related to the safe return of recovered process water, with a particular focus on the three target contaminants, were identified. However, weighting of the risks was considered challenging due to the variation between the different contaminations (e.g. acute versus chronic risks) and the broad nature of the contaminant classes, particularly viruses and microplastics. In general, the lack of knowledge/evidence was identified as being a high risk, especially in terms of microplastics behaviour/impacts, monitoring methods, the possibility of resistant strain selection through recovered process water return, and emerging contaminants. This latter factor and the difficulty of determining risk levels were the main regulatory risks. Regular reviews of reports, such as the Badenoch and Bouchier reports, were deemed necessary to keep up with scientific advances and emerging contaminants. Commercial risks were to reputation and the associated cost, with operational factors like balancing flows, monitoring and contingency plans being of medium risk. Digital twinning can be used to model the impact of recovered process water return scenarios for individual WTWs, though water companies should consider the wider company perspective. From the Expert Workshop the availability, approval and adoption of new treatment process was considered low risk though there were concerns about cost/space and the impact on existing processes when returning to head of the works. When evaluating the proposed technologies in this project, a variety of disadvantages, in categories of cost, space, performance, regulation and waste were identified for each technology, with no technology being clearly superior or worse to others. The monitoring techniques were deemed essential by the Expert Workshop to the successful safe return of recovered process water, with more evidence required to assess different sensors and monitoring approaches, particularly in the more contaminated recovered process water streams, and to determine trigger levels for action. Turbidity was seen as a reasonable indicator of risk for Cryptosporidium, and more work is needed to determine methods and surrogate/indicator parameter correlations for viruses and microplastics. Monitoring should also be applied to source waters to identify potential for catchment management approaches as well as enable dynamic management of ratios of recovered process water return based on input water qualities.

Conclusions

The aim of this study was to facilitate maximising the safe recycling of recovered process water at WTWs, while minimising the risk of outbreaks and health issues concerning Cryptosporidium, viruses and microplastics. This goal was achieved through delivering:

• A detailed review of the best available techniques (BAT) to detect, monitor and remove the above-mentioned contaminants from recovered process water streams.
• A gap analysis of the expert reports by Badenoch and Bouchier to highlight monitoring, treatment and control advancements made since 1998.
• Expert recommendations for systematic minimisation of operational and control risks associated with the safe recycling of recovered process water at WTWs.
• A cost-quality model, to assist water companies with treatment technology comparison and selection for recovered process water treatment and recycling.

For the full project details and its outputs please visit UKWIR website at: https://ukwir.org/maximising-the-safe-return-of-recovered-process-water

Project stakeholders

• Client: UK Water Industry Research (UKWIR)
• Contractor: WSP
• Collaborator: Dr Helen Bridle, Heriot-Watt University
• Project Director: Elena Gil Aunon, WSP
• Technical Lead: Dr Payam Malek, WSP
• Project Manager: Barrie Holden, UKWIR

Project Steering Group

• Affinity Water
• Anglian Water
• Irish Water
• Northern Ireland Water
• Northumbrian Water
• Scottish Water
• South East Water
• United Utilities
• Welsh Water
• Yorkshire Water