Background
A Combined Sewer Outfall (CSO) at Adlington, Lancashire released unscreened domestic sewage and trade effluent, diluted with rainwater into the River Douglas. To protect the environment from the adverse effects of waste water discharges, United Utilities are required to improve the sewerage systems and limit pollution from CSOs.
The Overall Objective
Civil engineering specialists, were contracted by a Water Company to build the new infrastructure offering sewerage system improvements and enhanced environmental protection. Part of the works involve secant piled walls augured deep into the ground and below the water table. Cementitious grout is placed to the base of each pile which displaces around 10m3 of water per pile at ground level. However, due to close contact with neat grout, the displaced water is highly alkaline and laden with soil particles.
Siltbuster Ltd were consulted at a very early stage and advised the Contractor the lowest risk water disposal route would be via the nearby waste water treatment works. The Contractor approached the Water Company and duly gained permission however, to protect the treatment works and minimise risk of pollution to the aquatic environment, strict constraints were placed upon the quality and volume of water to be accepted.
Solution
At the planning stages, Siltbuster assessed the water treatment challenge by considering the likely contaminants of concern, the anticipated daily volume which may be generated, and the strict quality criteria described in the Water Company’s waste water consent.
Siltbuster then designed a robust and practical water treatment solution using modular equipment from our substantial hire fleet. Firstly suspended solids loading is greatly reduced using a standard Siltbuster HB50 lamella clarifier to provide a low turbulence space and long residence time whereupon gravity can act upon the settling solids and allow them to be retained. Secondly, water is discharged to the Contractor’s holding tank, the purpose of which is two-fold:
- To attenuate the volume and control the discharge rate into the sewer, but also;
- To act as a treatment vessel for the neutralisation of base (alkaline pH) conditions using a Siltbuster pHD unit.
The battery powered Siltbuster pHD unit is located next to Contractor’s tank and uses a pH probe and diffuser plates, suspended in the tank, to continually monitor and neutralise alkaline conditions using carbon dioxide autonomously without operator supervision.
The combination of the two modular Siltbuster units has given the Contractor’s confidence to progress the works knowing the waste water treatment works and aquatic environment are protected. The water treatment element of the works commenced August 2021 and is anticipated to be complete by November 2021.
