Supply Chain - Health & Safety - Confined Spaces

Weather has a major impact on raw water quality. Typically, rainfall increases flow in the river and, with it, turbidity. Colour, an indicator of natural organic matter, reduces in wet weather and increases in drier spells. Climate change has increased the intensity of rainfall, and this reduces the pH of the river water, making control of coagulation, which depends on colour, turbidity and pH, more difficult.

Higher turbidity during storm conditions requires a higher coagulant dose, and this further depresses the pH. This issue has, on several occasions, resulted in a shut-down of the works which struggled to meet treated water quality goals. Southern Water notified the DWI of this process issue and were issued with an improvement notice which required a long-term solution to be implemented by 28 February 2025.

Southern Water engaged Trant Engineering to develop and implement a solution. Trant had a dedicated team at Sandown working on other schemes and had good working relationships with the Southern Water Project Team and Operations. This meant that they already had a good understanding of the problem and were able quickly to propose a solution consisting of chemical storage, pH control and a caustic soda dosing system together with all the associated piling, reinforced concrete plinths, paths, slabs and buried service ducts.

The proposed process solution treated chlorinated process water through dosing with sodium hydroxide within carrier water immediately prior to entering the contact tank. A measured dose is applied to the process, calculated by measuring pH and flow. The dose is then adjusted as required through a process feedback loop to maintain a required target pH set point.

Because of space constraints, the incoming raw water mains had to be diverted. The dosing system required a pH analyser/controller mounted on a backboard with process instrumentation, pressure sensors, level controllers and automatic valves. Carrier water pumps and a water softener completed the dosing package with an adjacent dosing control panel with PLC and HMI.

There were several key challenges. Highly limited space available for the equipment required, extensive buried services, and challenging project delivery timescales to meet the regulatory outputs. Working closely with Southern Water and the established delivery partners Atkins Realis, Chemidose and F W Marsh, Trant’s team was able to complete the necessary Design, HAZOP and ALM process early in 2024.

The design was prepared with programme constraints heavily in focus and incorporated an off-site ready built kiosk with integral floor. This enabled the full kiosk fitout to be undertaken in parallel with the civils work on site and resulted in significant programme improvement. The dosing system was fully FAT tested offsite at Chemidose’s premises.

Space was tight to fit the kiosk on site, and tight within the kiosk to fit the process equipment needed whilst maintaining good access. A collaborative design process and a great team enabled this to be achieved within the constraints. Challenges were encountered on the civils design including unmapped significant pipework and unfavourable geotechnical conditions in the only viable location for the kiosk. The team moved quickly to resolve solutions which required a piled foundation to address the ground conditions and avoid loading the unmapped pipework whilst diversion was resolved.

The civil works and on-site preparatory M&E works were completed in parallel with the dosing kiosk fitout. This combined with the level of offsite fitout and testing substantially minimised the on-site installation period. The dosing kiosk was delivered to site as the civil works were completed, and a limited period of M&E works were required to connect into the existing site process.

Within four weeks of the kiosk delivery, commissioning was able to commence. A successful commissioning period allowed project works to enter active service several weeks ahead of the DWI regulatory date for installation. The project achieved full formal handover well ahead of the DWI regulatory date for commissioning.

By close cooperation throughout the supply chain, commissioning was able to commence within four weeks of the kiosk delivery. Being familiar with the site, Trant’s Instrumentation, Control & Automation (ICA) team was able quickly to integrate the new controls, and the new works was in service and formally handed over several weeks ahead of the DWI regulatory date for installation.

The solution deployment has been successful in addressing the problem of low pH causing a need to shut down the works during periods of heavy rainfall and this success has been welcomed by all parties.

Due to the scheduling and repetition of work being undertaken within the four-project portfolio, there was a strategic approach to the appointment of specific sub-contractors to maximise programme benefits and acceleration across the projects.

The primary area that was focused upon was the supply of chemical dosing kiosks with a DfMA approach and the mechanical and electrical installation services.

The Thorne STW scheme has a quality driver to reduce phosphorus concentrations in the final effluent to 2.0 mg/l without exceeding iron concentrations of 4 mg/l.

The new ferric sulphate dosing unit will run automatically, and the operator will only be required to ensure that there is a constant supply of chemicals.

A new liquid polymer plant will be installed to replace the existing powder polymer system which feeds the existing gravity belt thickener. To facilitate the replacement a temporary containerised rig was installed and commissioned prior to the removal of the existing plant which removed the existing H&S risk associated with powdered polymer.

The scope also included a full clean up of the existing polymer plant to help facilitate the safe installation and construction works.

The Aldwarke STW P scheme project has a quality driver to reduce phosphorus concentrations in the final effluent to 0.7 mg/l without exceeding iron concentrations of 4 mg/l (2.5 mg/l Al).

The proposed solution is to chemically remove the phosphorus with a primary and secondary ferric sulphate dose upstream of the primary settlement tanks and upstream of FSTs 1-4 respectively.

A new standard ferric dosing kiosk was provided with two dosing pumps and two 10m3 storage tanks complete with a remote fill point panel and remote wash system installed as a single DfMA off-site fabricated kiosk. This feeds two duty/standby POAs at the inlet works facilitated by a newly installed air mixing system as well as two duty/standby POAs at the RAS distribution chamber.

The FST A & B scum removal boxes were also replaced as well as isolation penstock installation. The existing scum pump was replaced and new MLSS probes were installed on the ASP outlet channels.

At Lundwood STW the quality driver is to reduce phosphorus concentrations in the final effluent to 2.0 mg/l without exceeding iron concentrations of 4.0 mg/l.

The solution was to convert the existing secondary treatment activated sludge plant (ASP) to a RAS anoxic configuration. This process will change the existing ASP into an enhanced biological phosphorus removal (EBPR) plant. To limit recycling of phosphorus from the dewatering process back into the EBPR plant, the project will provide ferric sulphate for P removal and caustic soda dosing to the settled sewage to mitigate against the impact of ferric sulphate dosing on the final effluent alkalinity.

Standard 7.5m3 ferric sulphate and sodium hydroxide (caustic) storage tanks and dosing kiosks were to be delivered and installed in a single DfMA off-site fabricated SR4 rated kiosk (due to site security classification). Both chemicals are pumped to their designated POAs and dosed into the PST distribution channel via a bespoke designed V-notch brackets positioned above the top water level of the channel, with the mixing in the channel facilitated by air-mixing provided by newly installed blowers.

The project benefited from carbon savings and construction efficiencies by reviewing the original proposed site location and relocating it to an area which eliminated the demolition of existing assets.

The driver at Castleford is to reduce phosphorous concentrations in the final effluent to 2.0 mg/l without exceeding iron concentrations of 4.0 mg/l.

The proposed solution is to chemically remove the phosphorus by dosing ferric sulphate dose upstream of the final settlement tanks.

The primary ferric sulphate dosing system includes constructing foundations and support structures, installing a 7.5m3 storage tank with duty/standby dosing pumps, and integrating with the existing SCADA and telemetry systems. Civil works required modifications to access pathways and safety installations. Electrical installation works ensured the new plant was fully integrated into the existing works control systems.

The POAs dosed into a splitter box upstream of the final settlement tanks which ensured even distribution of ferric sulphate within the FST distribution chamber.

In order to best meet the needs of the four sites, the design team needed to develop the most efficient and effective solutions for each individual site and application. A collaborative multidisciplinary approach was taken to produce each solution whilst looking for the efficiencies in the standard elements of the portfolio.

The team engaged with Yorkshire Water in weekly collaborative planning meetings to review design; technical challenges and construction programme together with reviewing project Risk & Value (R&V). By adopting this collaborative approach, we achieved design and delivery consistency while utilising standard solutions delivered by a design team comprising of civil, mechanical, electrical, and process engineers.

At the time of writing (July 2024) the projects are progressing well:

Thorne STW: As the first project in the portfolio and therefore the most advanced, Thorne STW has progressed through to commissioning and the Glanua Group team are preparing to bring the plant online.

Aldwarke STW: Significant progress has been made with the completion of the civil works and installation of the ferric dosing kiosk. The delivery team have now moved on to completing the mechanical and electrical installation. This has included the potable water connections, installation of the secondary dosing lines to kiosk dosing rigs. The team has also installed three VSDs to provide a more flexible control of the replaced ram pumps and the blowers have been installed to facilitate air mixing at the point of application.

Lundwood STW: The civil works are complete and kiosks have been installed on site. We we have also progressed with the mechanical and electrical installation works including the installation of the point of application units as well as air mixing pipework. The electrical installation has progressed and cables are being pulled to allow for the second phase of installation prior to commencement of commissioning.

Castleford STW: The civil works are progressing in line with the programme and this includes the demolition of the roadway prior to piling and kiosk base construction, as well as the integration of the drainage and commencement of roadway reinstatement to form the chemical delivery bunded area.

The primary Common Data Environment (CDE) and information delivery platform used programme is Autodesk’s BIM360 software. Utilising this, Glanua Group has been able to control the flow and dispersal of information throughout the project and delivery teams, enabling the information management workflow process and review to align with the ISO 9001 Quality Management Process.

The information management platform allows us to control how and when the various projects teams see and receive information ensuring the right information is delivered in the most efficient and effective way. This collaborative approach has ensured the right information is received at the right time.

Multiple digital tools were utilised to facilitate the safe design and construction process, this includes the Autodesk Revit suite for the civil structures and all mechanical and electrical equipment which was all modelled in 3D with subsequent sheets produced to facilitate a review and approval process as well as provide construction coordination, assessment, and as-built markups where required. Glanua Group utilised reality capture technology to establish baseline data and monitor progress against this.

Through the asset function of BIM360 Glanua Group has been able to replicate the client’s asset data requirements to collate data prior to submission on to their asset management database.

Within this function the procurement and construction/installation status could be tracked whilst assigning supplier and design information in preparation for the O&M and H&S file information.

Whilst significant progress has been made of all four projects, there is a number of key elements still need completing, a lot of work has been undertaken to help meet the project’s completion dates including completion of civil works, mechanical and electrical installation and wet and dry commissioning.