Flexible modular plant will expand as new homes and businesses are built

The new town of Ebbsfleet is one of the most important developments in the south of England, with plans to build 15,000 new homes for a planned population of 40,000. Part of the development is the build of a wastewater treatment plant for Castle Hill, Kent – the first phase of the Government’s new garden city to be built at Ebbsfleet Valley.

Multi-utility provider Metropolitan was awarded the contract to deliver services for the 1,500-home Castle Hill development by Landsec. The agreement includes installation of a new onsite wastewater treatment works for 4,000 population equivalent (PE).

Metropolitan appointed Alpheus, a specialist in water and wastewater asset management and design, to provide the plant. Working in partnership with Alpheus to deliver a flexible system to serve the homes, businesses and amenities currently under construction.  The new wastewater treatment works is being built in two stages with the supply of 16 above ground Hybrid-SAF -  Submerged Aerated Filter package treatment units along with primary lamella clarifier units, final settlement tanks, blowers and the airlines.

Prestigious development

Technical director Andrew Baird said: “It is a very prestigious project – particularly as it involves the creation of Ebbsfleet new town.

“We have been discussing plans with Alpheus for three years to ensure the new plant will meet the requirements of the first inhabitants of Castle Hill. Given the long-term vision for the development, it is important that the plant optimises the footprint available and is flexible to accommodate a growing population.”

At present, effluent from the homes and commercial properties in the Castle Hill development is collected in a storage tank and transported away by tanker. However the town, which is 17 minutes away from central London by high-speed rail and situated on the High Speed 1 service to continental Europe, is set for rapid expansion.

Two-stage build

The first stage of the new treatment works which will serve 2,000 PE has been completed and comprises one primary lamella clarifier, eight Hybrid-SAF units connected in series and the final settlement tank. The second stage, on which work is expected to begin next year, will expand the plant to serve 4,000 PE.

Andrew Baird explains: “The existing storage tank is adequate to serve the homes constructed during phase one of the Castle Hill development. We plan to move on to stage two, to be built alongside stage one, which will comprise a primary lamella clarifier, sludge storage tanks, eight additional Hybrid-SAF units and an additional final settlement tank.”



The area has protected groundwater so the Environment Agency stipulated that the new treatment plant had to be installed above ground.  The plant will release wastewater treated to the high standard required by the Environment Agency into the Thames Estuary.

The project’s quick turnaround will keep costs down for the customer as minimal civil engineering is required for installation on-site.

In the future it may be decided to connect the Castle Hill development to mains sewerage, but at present none nearby have sufficient capacity. The modular configuration of the package plant has been designed to be highly flexible and will serve the town as it expands.

Easy installation

The company has a long standing relationship with contractor Alpheus and has worked closely with them to design a plant which can serve the new city well.

Metropolitan Director, John Marsh said “Metropolitan has worked with Landsec to provide a multi-utility solution for the site and the provision of all its essential connection requirements.  Finding a cost effective solution for the treatment of wastewater has led Metropolitan to install the onsite Hybrid-SAF plant – which meets the entire needs of the Castle Hill development and will be delivered on time and to budget.”

Declan Maguire Operations Director of Alpheus, said, “We are delighted to be involved in such a significant project, which draws on Alpheus’ expertise in design and build projects. The modular design of the Ebbsfleet plant means it can be built in two stages, which will provide the necessary wastewater treatment as new homes are built and the garden city expands."

“The first phase is due to finish in the autumn. We hope to be involved in future developments at Ebbsfleet.”