Nutrient neutrality mitigation project partners the National Rivers Consortium (NRC) and RSK Biocensus to generate nutrient credits through septic tank upgrades, aiming to unlock housing development while protecting river ecology.
The initiative applies Conservation Covenants under the Environment Act 2021, with RSK Biocensus acting as a Defra-designated Responsible Body to secure long-term monitoring and enforcement of mitigation measures.
Nutrient neutrality mitigation project uses septic tank upgrades to generate credits
Nutrient neutrality has affected housing development across 27 catchments in England, where additional nutrient loading from new residential schemes must be mitigated before planning approval can proceed. The scheme focuses on replacing older septic tanks with high-efficiency package treatment plants (PTPs), generating measurable reductions in total phosphorus and nitrogen.
The nutrient reduction at each site is calculated using the Natural England nutrient budget calculator or relevant regional tools. Credits are quantified as the mass of phosphorus and nitrogen removed per year and can be sold directly to developers operating within affected catchments.
The National Rivers Consortium, which works alongside Natural England and the Environment Agency, is responsible for identifying and upgrading eligible septic systems. Ongoing monitoring and servicing of installed treatment plants is undertaken in coordination with RSK Biocensus as the Responsible Body.
Conservation Covenants provide enforcement certainty
Conservation Covenants, introduced under the Environment Act 2021, create legally binding agreements on land to secure environmental outcomes in perpetuity. As a Secretary of State appointed Responsible Body, RSK Biocensus holds and enforces these agreements, providing local planning authorities with assurance over cross-boundary monitoring and enforcement.
The project has already been rolled out in Kent and Norfolk under strategic mitigation contracts. According to the partners, contracts currently cover 450kg/year and 500kg/year of phosphorus mitigation respectively. To date, 268 package treatment plants have been installed, generating 336kg/year of total phosphorus reduction and 2,892kg/year of total nitrogen reduction.
Nutrient neutrality requirements aim to reduce pollution pressures in sensitive river catchments, particularly where wastewater discharges contribute to ecological decline. Developers operating in affected areas must demonstrate that additional nutrient loading from new overnight accommodation is offset through approved mitigation mechanisms.
For further coverage on nutrient neutrality and river protection policy, visit our Rivers section.
