In west Wiltshire, close to the border with Somerset, the town of Bradford on Avon until 1876 was served in the form of sewers that ran from various locations directly into the River Avon. It was not until around 1907 that these discharges were connected to a purpose-built sewage treatment works, together with large earth-covered holding tanks next to the river, downstream from the town.

A new modern and larger sewage treatment works, operated by Wessex Water, was built later in the 20th century on the other side of the Kennet & Avon Canal.

Ferric dosing is deployed on the site for Phosphorous removal.

Existing Works & Project Objectives

The Bradford on Avon Ferric twin storage system was near to its end of service life and required replacement. As the replacement unit was to be positioned in the same location as the existing plant and Ross-Shire Engineering (RSE) were approached to provide a proposal for the replacement works.

Our proposal included for the design, supply, delivery, offloading, installation & commissioning of a replacement 18m3 compact dosing system.

The modular, built-offsite approach RSE proposed allowed the existing unit to continue dosing for as long as possible, resulting in lower intervention time and a lower cost as the requirement for temporary works was reduced to a much shorter period.

Access constraints onto site were an added challenge with a narrow bridge across the canal and a tree canopy immediately prior to the site entrance. Detailed design within BIM platform allowed accurate engineering to focus on meeting both access restrictions, whilst maintaining operational access and lifting requirements of the unit.

As a result of the constraints, the tanks were designed rectangular to provide the best utilisation of space within the new kiosk footprint.

Remedial civils works were carried out to provide additional ducts and access around the new Dosing Kiosk as the footprint increase to comply with current specifications and standards.

Temporary Dosing was deployed for the decommissioning and commissioning phase to allow the site to meet discharge consents whilst the unit was replaced.

The Project

RSE were engaged in late 2019 to provide a mechanical and electrical design & build package. The project was completed and handed over in early 2021 following lengthy delays due to the COVID-19 pandemic.

Prior to contract award, RSE worked collaboratively with the client to develop an agreeable solution to meet the site specific challenges faced. This results in the following scope of works:

A non-walk-in, self-bunded kiosk arrangement to house a fully off-site assembled solution. The kiosk offered was to be of a GRP construction. A key driver for the project was to ensure the system was able to be retrofitted into the same footprint available onsite to avoid increasing the civils scope of works and resulting in longer periods of temporary dosing.

The kiosk was to be provided with an integral base to provide a suitable design for single piece lifting and transportation. Several double access doors were provided for the MCC Control Section, Tanker Reception point, a pair of Duty/Standby Dosing Skids along with a bund access hatch. The roof was provided with an integral handrailing, anti-slip finish and two tank inspection hatches for infrequent maintenance access. A rain canopy was provided, to be finally assembled once the unit was safely offloaded.

All heating, lighting and ventilation were included during the build, with additional service connections provided for site interfaces such as trace heating and emergency washdown facilities.

The modular system incorporated an integral bund, with integrated bund leak detection, providing 110% capacity of the chemical storage tank’s total volume. Ultrasonic level instrumentation was also provided to monitor the level within each chemical storage tank, along with a Cat and Mouse visual indicator available at the Tanker Reception point with a local alarm and monitoring panel.

The two dosing skids each comprised of duty/standby dosing pumps per dosing stream, utilising the Watson Marlow Q Dos Universal+ range of digital peristaltic pumps.

RSE carried out the off-site Factory Acceptance Test and onsite installation of the GRP dosing kiosk, including two weatherproof point of application (POA) catchpots which were installed locally to each injection point over each process channel.

The project marked the first chemical dosing system RSE had supplied directly to Wessex Water, who contributed to a truly collaborative project, providing 360 degree involvement as part of an integrated, one-team delivery.

“The available area for the dosing system was quite restricted but RSE were able to provide a compact solution that met Wessex Waters design standards and requirements but not compromising on quality or performance,” said Matthew Ormerod, Project Manager, Wessex Water.


RSE are specialists in off-site construction methods for multiple water treatment equipment, including chemical dosing. The RSE group of companies allow us to provide specialist, high quality offerings in every area.

Our Chemical Dosing projects range from maintenance and repair, service & breakdown cover, product supply and full turn-key projects. We specialise in design, manufacture, installation and commissioning across the UK for water authorities, Tier 1 delivery partners and alternate sectors.

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