Bellozanne Sewage Treatment Works, Jersey

Sweco have worked with the States of Jersey for almost twenty years and since 2014 have partnered with the Department for Infrastructure (DfI) under their Technical Consultancy Framework. As part of this framework, Sweco are developing the design of the new Bellozanne Sewage Treatment Works (STW) prior to it being tendered as a Design and Build contract.

Key Facts

Client: States of Jersey
(Department for Infrastructure (DfI))
Location: Jersey
Fee Value: £500,000
Construction Value: £50m
Dates: 2010-2022

Background information


Over a five year period, Sweco supported DfI in preparing a Waste Water Strategy for Jersey. The strategy highlighted that due to outdated assets and a growing population, the existing Sewage Treatment Works (STW) at Bellozanne no longer met environmental standards. The only viable option in terms of meeting the current and future requirements being to replace the existing STW.

The replacement of the existing works is programmed to be completed in phases to ensure continuity of service. Accommodation and enabling works began in 2015 and will continue until the start of the STW construction in February 2018.

The estimated completion date for the STW is July 2022.

In preparing the Waste Water Strategy (WWS), Sweco analysed and identified how Jersey collects, treats and disposes of waste water at various facilities operated by DfI. This included:

  • A review of the condition and performance of all the existing assets
  • A review of current and future legislation and European directives
  • A reassessment of the location for the sewage treatment works
  • A review of the sewerage (collection) system
  • A review of future population growth and location of new housing developments and
  • A focus on actual environmental outcomes as opposed to arbitrary limits.

The existing STW at Bellozanne has been operational for over 50 years and has undergone several upgrades. In recent years, and despite significant maintenance, the plant has been inefficient and failed to meet the required nitrogen standards.


The proposed replacement of the existing works is based on carbonaceous removal to achieve a BOD/ SS standard for a connected population equivalent of 118,000, the 2035 design horizon. The proposed site layout makes provision for potential future secondary treatment upgrades such that the requirement for an additional ammonia standard or total nitrogen standard can be incorporated. The proposals also allow for a 20% increase in the flow and load.

The land available for the construction of the new STW is limited and Sweco are working with DfI on the following Accommodation Works projects to create space for the new STW:

  • Removal of the hillside (approximately 70,000m3 of rock);
  • Construction of a new Clinical Waste Incinerator (CWI) such that the existing installation can be demolished;
  • Demolition of the redundant digesters to allow construction of a new Tanker Import Facility;
  • Relocation of the Household Waste Recycling Centre (HRC)
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