Liquid Waste Treatment
The Waste Water Treatment Section comprises a team of 16 and is responsible for the operation of the Island’s public pumping stations and sewage treatment works.
Due to the topography of the Island, the sewerage system cannot depend on natural gravity alone in order to convey the sewage to the main treatment works, and a series of 107 pumping stations, strategically placed around the Island, is required to keep the sewage flowing towards the treatment works at Bellozanne. The pumps used are predominantly electrically driven submersible units which operate automatically in sumps located below ground.
The Bellozanne sewage treatment works is the main sewage works on the Island, with the only other treatment being undertaken by a small package treatment plant located at Bonne Nuit. The Bellozanne works treats a base population of 85,000 increased to 120,000 in the summer due to tourism. The works provides primary settlement, biological treatment by the activated sludge process and Ultra Violet disinfection prior to discharge to St Aubin’s Bay for flows up to a maximum of approximately 78,000 cubic metres per day. Flows in excess of this figure, which can add an extra 8,000 cubic metres per day, receive primary settlement and are then mixed with the fully treated effluent and given Ultra Violet disinfection before discharge.
The quality of the final effluent is required to meet the stringent EU standards for discharge into Bathing Waters, as laid down in the Discharge Certificate issued by the Environment Department.
The sludge produced is treated passing it through sludge thickeners, followed by anaerobic digestion. Historically, 25% of the treated sludge was disposed of by deep injection to agricultural land, with the remainder de-watered by centrifuge and then thermally dried before being co-incinerated with the municipal waste. From 2005 deep injection has been phased out, and the advanced treatment thermally dried product is now marketed and recycled back into the land bank.
The operation of the Sewage Treatment Works and all of the Island's pumping stations is monitored remotely by computer systems, and the information fed back to the central control room at Bellozanne which is manned 24 hours a day, every day of the year. This system gives early warning of any problems at any of the facilities, enables members of the Team to be dispatched day or night to resolve the problem, and hence prevent potential pollution incidents.
Click on the following link for a diagram of how the Sewage Treatment Works operates:
Recycling of waste water PDF
For a detailed explanation, click below:
Sewage Treatment Information PDF
