By Mott MacDonald Bentley

Mott MacDonald Bentley were appointed to deliver a design and build project to upgrade several key assets at a United Utilities Treatment Works (WTW) to ensure compliance with performance recommendations and regulatory requirements. The upgrades will also reduce the average ‘unit cost to treat’ by maximising output from the WTW, making it the most cost-effective treatment works in the area.

The project involved the replacement of 147No. bell pressure filters constructed in the 1920s and 1950s with a new Rapid Gravity Filter (RGF) plant and associated clean backwash/air scour system and dirty backwash storage and treatment system, replacement of the existing flat bottomed Multiflo lamella clarifiers with new standard lamella clarifiers and upgrades to the pH correction system.

The project included extensive Electrical Instrumentation Control Automation (EICA) works with a number of challenges such as inter Programmable Logic Controller (PLC) communications between new Siemens and existing Rockwell PLCs, multiple buried services in the lamella compound area and the requirement for multiple cable diversions prior to construction of the RGF structure.

The lamella clarifier plant EICA works mainly comprised of an ‘Intelligent’ motor control center (MCC) with Siemens PLC and HMI, turbidity monitoring for 4No. lamella clarifiers, de-sludge pumps on the sludge outlets with pressure, flow and over-temperature protection, actuated valves and suspended solids monitors with air cleaning compressor panels, 4No. flocculation tanks with level probes, flowmeters, mixers, and actuated valves.

The RGF plant EICA works mainly comprised of an ‘Intelligent’ MCC with Siemens PLC and Supervisory Control and Data Acquisition (SCADA) Thin Client, 4No. RGF LCPs with Siemens PLCs, level, turbidity, differential pressure monitoring and actuated valves for 8No. RGFs, RGF inlet channel with turbidity, iron, aluminium, level, and flow monitoring, Duty/Assist/Standby backwash pumps with pump condition, flow, and pressure monitoring, and Duty/Standby blowers with pressure, temperature, and air flow monitoring.

The SCADA and network upgrade works comprised of 2No. SCADA racks with SCADA server, Network Attached Storage drive and Uninterruptible Power Supply, 9No. Fibre Optic Break Out Panels with 17No. network switches for connection to new equipment and existing site network switches.

Digital Delivery | Digital tools such as BIM360 and Autodesk Civil3D were utilised to aid design and construction stages which allowed for good collaboration between design and site teams as well as subcontractors. 3D model coordination for the RGF and lamella structures, pipework, cable routes and ducting was instrumental in reducing risk of clashes and associated delays in construction. The 3D model was also used to consider construction phasing and temporary installation requirements.

Electrical Safety | The decommissioned redundant plant consisted of 147No. bell pressure filters each with 4No. actuated valves and agitators, 4No. backwash pumps and associated actuated valves and instrumentation, 3No. filter backwash MCCs, 12No. local PLC panels, 14No. turbidity instrument boards and associated flow or pressure instrumentation.

With such a large amount of assets to decommission, it was vital that safe isolation procedures were employed. These procedures ensured we positively knew the cabling originated from the MCCs and helped us identify any unknown ‘rogue’ cables that were connected to the MCCs or ran through the MCCs from elsewhere.