Ensuring nutrient neutrality to unlock development

With the country's watercourses among the worst in Europe, Natural England is applying principles to reduce pollution – but these have become a barrier to developers. How can a balance be struck?


  • Steve Warner FRICS

20 June 2023

River Thames with fields

Building control surveyors yet to deal with Natural England's requirement for nutrient neutrality on developments should get ready for the long haul – and for conditional approvals to become the norm.

Of the 355 local authorities in England and Wales, only 74 are currently required to achieve nutrient neutrality by UK government policy; among them, these authorities cover catchment areas such as the Norfolk Broads, the rivers Avon, Eden, Meese and Stour, plus coastal areas such as the Camel estuary in Cornwall, the Solent and the Deben estuary in Suffolk. There are, of course, others.

However, the extent of the requirement is currently under review by the government. It is surprising that more areas are not included, given that only 14% of rivers in England and Wales achieve what the European Environment Agency deems to be good ecological status.

Principles seek to prevent pollution

The primary causes of our failing watercourses and bodies of water are agriculture, effluent from wastewater treatment works and diffuse pollution.

New development can also add to the load on wastewater plants and to the local environment where no mains sewerage is available. Excess nitrogen and phosphorous that runs off from such development is causing eutrophication, that is the accelerated growth of certain unwanted types of algae that stifle aquatic habitats.

Natural England has therefore introduced the nutrient neutrality policy to lessen the impact of development in areas of outstanding natural beauty, wetlands, special areas of conservation, special protection areas, and sites protected under the Ramsar Convention. The principles behind the policy aim to allow development to proceed without causing further deterioration.

Each catchment area has been allocated £100,000 from central government to help the relevant local authorities and agencies such as the Environment Agency (EA) and Natural England fund the additional workload created by this policy.

The Levelling Up and Regeneration Bill, currently going through Parliament, sets the standards for water utility companies' discharge rates of nitrates and phosphates to watercourses, with a substantial reduction to be achieved by 2030.

It is these companies that will need to spearhead any attack against eutrophication and, with luck, allow the resumption of work on 120,000 dwellings that are stalled while developers seek to achieve nutrient neutrality.

Once utility company treatment works have been improved to meet the 2030 targets and the levels for nitrates and phosphates can be accurately predicted, planners and developers will be able to calculate the level of mitigation they need to provide.

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Developers have range of mitigation options

In most cases where development cannot be connected to mains drainage it can incorporate a wastewater treatment plant to deal with any sewage. In these cases, a form of mitigation is likely. One acceptable method of mitigation is to upgrade older septic tanks in the local area to more efficient treatment plants.

An alternative mitigation measure, albeit not an easy or straightforward one, is to create wetlands. The efficiency of phosphate and nitrate extraction will depend on the plants grown there, among other factors.

During the winter months, growth – and, therefore, uptake of phosphate and nitrates – will also be reduced. As such, there may be a need for large areas to be planted, to allow for dormant periods in winter. This could mean substantial wetlands are required instead of one wastewater treatment plant.

Uptake of phosphates and nitrates could be as low as 40%, but without adequate amounts of these nutrients there will be no growth at all. Willow, which could be harvested for biomass-fired boilers, is one of the preferred plants, while others include iris or reeds. These plants are all known for their uptake of nitrates and phosphates, but should be chosen for their suitability in the local climate.

The use of pocket orchards is a further alternative, with cherries comprising about 4% phosphorous. Apples are seen as an easier fruit to harvest and sell, but only contain around 1% phosphorus. 

It is important in either case that the fruit is harvested, so it does not degrade back into the ground and put back the chemicals it has removed. Trees will be planted in the predicted area of any wastewater plume in the land.

It is also possible to purchase credits to ensure nutrient neutrality. While this may be the easiest form of mitigation available, it does nothing to reduce the issue at source. It is more like a tax, with the money paid by developers used to create wetlands in another part of the county.

Administrative wrangles need resolution

However, the application of nutrient neutrality principles is complicated by the legislative situation.

Section 125 of the Building Act 1984 requires any development to connect to a public sewer if there is one within 30m, whereas under the principles any housing development is assessed differently. Each dwelling represents 30m; for example, ten dwellings at 30m each equals 300m. Hence, if there is a public sewer within 300m then the site must be connected.

But which takes precedence – the act or the policy? Should the act be amended to reflect the new principles? And who will enforce this – planners or building control surveyors?

Another difference between the act and the principles is that under the latter, if the rural development falls in a site of special scientific interest, then a permit to discharge a wastewater treatment plant is compulsory. It also requires any discharge to be at least 100m from any neighbouring outlet, and an increased distance of 40m from any watercourse.

Anyone needing a permit to discharge from the EA is likely to be waiting a long time. Currently it is taking an average of 114 days for new applications to be laid before an officer, and it will then take between three and four months more to determine. So, it is not unusual for more than a year to go by when obtaining a permit.

Another complication is that the EA will ask for both building control and planning approval, neither of which can be given without the permit. Building control surveyors will only be able to offer a conditional approval or rejection if waiting for the EA.

'The application of nutrient neutrality principles is complicated by the legislative situation'

Way forward for neutrality policy still unclear

Wastewater treatment plant manufacturers have been striving to solve the issue of nitrates and phosphates for the past 20 years. Many European countries are leading the way, with Norway developing binders such as Filtralite; once this product is full of nitrates and phosphates it can be replaced, and the removed chemicals used for fertiliser.

Although Natural England would allow the use of such binders, a developer would have to demonstrate a robust monitoring and testing regime to ensure the system stays in balance.

Other wastewater treatment plants are using enhanced technology, such as growing algae that soak up the nutrients, producing fewer phosphates and nitrates in the final effluent.

But it remains to be seen whether the use of reedbeds and pocket orchards becomes the norm in rural locations. And will their construction form part of the building control process, or will it be left to planners?

'Wastewater treatment plant manufacturers have been striving to solve the issue of nitrates and phosphates for the past 20 years'


Steve Warner FRICS is an associate at Assent Building Control
Contact Steve: Email

Related competencies include: Construction technology and environmental services, Contaminated land

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