Back in 2019, Natural England put out guidance in the Solent region, the European designated sites that are off the coast were failing under their legal requirements for the volume of total nitrogen added into the Solent.
As such any residential development cannot produce a net increase in nitrogen in to the Solent.
To ensure there is no net increase in nitrogen, developers must offset any nutrient addition with a nutrient reduction in the form of a credit scheme.
For example, a field of horses will produce less nitrogen than a pig farm, therefore removing a pig farm with give a developer credit. However, whilst this credit scheme allows developers to add nitrogen into the Solent, mitigating the amount produced is vital to ensure a net no increase occurs.
This "trade off" credit scheme has proved valuable and could even be used in other areas of the country. The Environmental Analyst recently published an article titles "Nitrate trading scheme could be adopted nationally"
Human waste is normally treated in a sewage treatment plant before being released into the environment. To put it simply, ammonia (coming from human urine), is broken down in a treatment plant and converted to Nitrates, then nitrites, and eventually nitrogen Gas. Each stage of the process is less harmful to the environment.
We often see Ammonia reduction levels being used to compare treatment plants, but rarely do we see total Nitrogen (sometimes abbreviated to TN, or Ntot).
Why? Because nitrates are generally less harmful than Ammonia. Therefore the nutrient quantity is less of a concern than the more harmful Ammonia.
Whilst less harmful than Ammonia, High levels of nutrients in a river can lead to something called “eutrophication” This is the name used for a situation where an ecosystem has an unnatural amount of nutrients. Upsetting the ecosystem in this way can cause blooms of algae which in tern can affect other plant life in the river.
"Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients. It has also been defined as "nutrient-induced increase in phytoplankton productivity"
https://en.wikipedia.org/wiki/Eutrophication
When it comes to choosing a sewage treatment plant. A system that has a designated “denitrifying” zone should be used, systems such as the solido smart will reduce total nitrogen by 83.1% this may not sound like a huge reduction when the treatment plant reduces Ammonia by 98%. However, it is still very high and will allow developers to work less hard to make the trade off. Whichever plant used, ensure the manufacturer has total nitrogen on their performance certificate, the percentage reduction is the key figure needed for Natural England.