Modular wastewater treatment nutrient neutrality

With a nutrient neutral approach to new property developments expected to become more widespread across England, increasing numbers of developers are giving closer consideration to modular wastewater treatment, writes Andrew Baird.

Solutions for water’s biggest challenges

Nutrient neutral planning requirements put in place in parts of England to protect sensitive waters and marine life continues to pose a conundrum for many property developers.

The concept of nutrient neutrality emerged in June 2019, when government advisor Natural England advised local authorities with protected waters to only grant planning permission to new property developments proven to be nutrient neutral.

"Nutrient neutrality ensures new developments used for housing, mixed use and tourism do not increase the nutrient burden of nearby protected waters."

The guidance applies to areas with surface waters that are impacted by high levels of the contaminants, primarily phosphate and nitrate. These can be present in treated wastewater that is discharged to watercourses in the final stage of the recycling process.

The contaminants, often referred to as “nutrients”, can lead to increased growth of algae, which can have a detrimental impact on water environments and ecosystems. Nutrient neutrality ensures new developments used for housing, mixed use and tourism do not increase the nutrient burden of nearby protected waters.

In the affected regions, developers must prove their schemes would be neutral by demonstrating in planning applications how they would remove or offset the full amount of nutrients anticipated.

Modular, onsite wastewater treatment

The issue of nutrient neutrality is not going to go away. While Natural England’s initial guidance focused on several planning authorities in Hampshire, it now applies to selected authorities in Kent and Somerset, with more expected.

For properties that are not on mains drainage, onsite wastewater treatment can be a significant part of the neutrality equation. As an example, we continue to see an increase for our packaged wastewater treatment plants, which can remove up to 65 per cent of nutrients found in wastewater. By comparison, installation of a septic tank would have no positive impact on levels.

Packaged plants are pre-manufactured, custom systems that can be installed on most commercial and residential sites and can treat wastewater flows from just one property, up to a population of 30,000 people.

Modular units can be installed in a tight footprint and once they are up-and-running, visual impact, energy consumption and maintenance requirements are low.

Research into low-impact solutions

While onsite treatment is effective in removing a significant amount, developers must accept that there is no technology suitable for domestic use that would remove 100 per cent of containments.

Nutrient neutrality can only be achieved through a combination of measures and in most cases offsetting – removing nutrients elsewhere in the catchment - will have to be considered, which local planners can advise on.

Our research and development team, with support from Portsmouth University, is looking at further low-impact ways to remove more than 65 per cent of nutrients. The aim is to reduce levels for our utility, commercial and domestic customers, without the use of chemicals.

“We are trialling the use of UV light in treatment units to create a suitable environment for the growth of algae, which removes phosphorous.”

Technology being researched includes absorbent beads made from zeolite, a natural occurring mineral which will safely remove phosphorous. Elsewhere, we are trialling the use of ultraviolet light in treatment units to create a suitable environment for the growth of algae, which itself removes phosphorous. This can be retained in the sludge produced for removal by the waste carrier.

We are also working on solutions to support water companies with their own large-scale, stringent targets for nutrient removal.

While the issue of nutrient neutrality is complex and the guidance under constant review, some effective mitigation schemes have taken place to the benefit and relief of developers, and we are confident of technological advancements emerging soon.

- Andrew Baird is the technical director at water recycling specialist WPL.