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UK Housing Development

Nutrient neutrality and beyond: could private sewerage systems offer quick wins for removing nutrients from the environment?

04 Sep 2023


In the UK, the government has announced plans to scrap water pollution restrictions for new housing developments, known as the nutrient neutrality requirement. However, the planned changes do not negate the need for quick-to-implement catchment-scale nutrient mitigation solutions. As part of their plans to reduce nutrient loading by 2030, sewerage operators could be implementing nature-based solutions and other alternatives, which also have wider environmental and societal benefits. 

Mitigating nutrients now and beyond 

Until the details of an action plan have been unveiled by the Government and the amendments have had Royal Assent, there still exists a need to consider the impact of development on habitat sites. Going forward, the Levelling Up and Regeneration Bill (LURB) states that sewerage operators will need to enhance their treatment capabilities by 2030. This means that a lapse of up to seven years of nutrient mitigation options is likely with the need to continue to restore sites to favourable conditions during that period. As the UK Government stated in a press release on reducing pollution in 2022: “Nutrient pollution is an urgent problem for freshwater habitats and estuaries which provide a home to wetland birds, fish and insects. Increased levels of nutrients like nitrogen and phosphorus can speed up the growth of certain plants, disrupting natural processes and devastating wildlife.” 

So whether or not nutrient neutrality is the way to tackle it, the nutrient issue needs to be fixed. 

Some quick wins: what’s not to like 

Upgrading private sewerage systems (typically on-site wastewater treatment systems, such as septic tanks and package treatment plants located in areas not served by mains sewerage) offers an opportunity to remove 95% of the nutrients currently being discharged from a system.  

Replacing such an ageing septic tank, that often discharges a significant amount of nutrients, with a modern system, certified to the highest treatment standard, provides immediate nutrient mitigation unlocking nutrient mitigation credits in the short term, and providing catchment scale nutrient mitigation over the longer term. 

A practical solution to identifying private sewerage systems where upgrades could provide the biggest catchment benefits  

Upgrading the top ‘at risk’ package treatment plants (i.e. those with over 100 Kg/year) as shown in the example catchment map below could remove over 300 kg of phosphorus per year 

So upgrading systems on behalf of the current operator (usually operated by homeowners, communities and businesses) seems like a win-win catchment management approach to nutrient management. The problem is not so much ambition to do this as identifying those that could provide the most benefit in the optimal location. 

To help identification, Ricardo has developed an in-house model (outputs as shown in the map above)  which maps key opportunities areas for implementing all private sewerage systems upgrade suitability based on a range of criteria, related to the: 

  • Position in the catchment and hydrological connectivity, as this impacts the areas served by mitigation and lag time between implementation and full effect 
  • System functionality, as the removal technology will affect the performance 
  • Effluent quantity, as the more flow, the higher the nutrient load.

The model can help identify opportunities for nutrient management based on nutrient load reductions and the location within a catchment. It quantifies the catchment nutrient benefits provided by different package treatment plants, plus wider environmental benefits. 

Once a suitable system is identified the feasibility of the upgrade can be assessed by considering a new package treatment removal capability.  

From site selection to solution: 

Ricardo can provide services from initial site selection to effective mitigation including facilitating discussions with relevant stakeholders including landowners, regulators, water companies, local authorities and developers to achieve collaborative nutrient reduction.  As such we can:  

  • Identify optimal mitigation solution.  
  • Contact the operators and facilitate discussions about entering an agreement. 
  • Take water quality samples from the system and quantify the associated nutrient load. 
  • Review and advise on replacement systems
  • Produce technical documentation as evidence for mitigation.

The benefits 

Once a new package treatment plant is installed, the impacts are almost immediate as the wastewater discharge will have a significantly lower nutrient load. The real-time nutrient removal rates can be monitored to verify the mitigation.   

A part of a wider catchment management programme this approach can be really powerful in helping to rapidly and cost-effectively reduce nutrient loading to reservoirs and rivers for any organisation with the ambition or legal duty to lower the nutrient concentrations in the environment.  

Ready to reap the benefits? We can help you now! Contact us to speak to one of our water experts: info@ricardo.com