Nutrient Neutrality: Tackling Nitrate & Phosphate Pollution

19 April 2024 by CSG

Nitrate and phosphate pollution is on the rise in the UK and Ireland. These chemicals are all around us – both naturally occurring and man-made. They are essential to plant and animal life and the world would be a very desolate place without them.

In this blog, we want to introduce readers to the problem of nutrient pollution. We will also let them know the role that their septic system can play and explain mitigation strategies that have been introduced to help curb the issue.

Nitrate and phosphate pollution

Nitrates and phosphates are essential for the growth of both plants and animals. Human activity has altered their natural cycles. There are two primary ways that excess nutrients enter our environment and waterways:

  • Agricultural Runoff: The fertilisers farmers use are often high in phosphate and nitrates. These can be carried by rainwater into streams and rivers where they will accumulate.
  • Wastewater Discharge: Septic tanks, sewage treatment plants and sewage treatment works also release phosphates and nitrates into the environment from human excrement.

Modern farming and food production techniques have resulted in our food containing high levels of these nutrients. Detergents and cleaning products in the home can also contain phosphorus. This can lead to additional nutrient pollution. Phosphate is also used in drinking water treatment to control lead levels.

Phosphates and Nitrates are used in fertilisers, which help farmers to produce more crops. This helps to make food cheap and abundant. However, these nitrates can enter drinking water as a result of runoff or leakage from fertilised soil, sewage and septic systems. Excess nitrate in drinking water is a potential health concern and high levels threaten water supplies. A growing body of literature also indicates potential associations between nitrate/nitrite exposure and health effects such as increased heart rate, nausea, headaches, and abdominal cramps.

The effects of these chemicals are being seen around the UK. For example, not a single river in England is in good overall health. This can be seen in our state of UK rivers chart below:

State of UK rivers - Ecological, chemical and overall health

If excess phosphate or nitrogen enters a waterway, a process called eutrophication can occur. This process will reduce river biodiversity and could eventually kill all plants and animals that live in the water.

It starts with algae feeding on the excess nutrients in the water resulting in rapid growth. Soon a layer of algae will cover the surface water and prevent sunlight from reaching the water below.

The lack of sunlight causes aquatic plants to die off, leading dissolved oxygen levels in the water to drop. This reduces the number of fish and crustaceans the waterbody can support. Finally, once the algae have used up all the nutrient reserves, they also die, leaving behind uninhabitable water and habitat loss. The wider eco-system is also impacted such as when species of birds like herons can no longer have access to their food source.

what is eutrophication due to nitrate and phosphate pollution from septic systems

What is Nutrient Neutrality?

Nutrient neutrality is a term used in the construction industry and is a means of ensuring that a plan or project does not add to existing nutrient burdens. This means there is no net increase in nutrients because of the plan or project. The UK government has determined that numerous water-based sites of Special Scientific Interest (SSSIs) and Ramsars (wetlands of international importance) across the UK are showing excess levels of nutrients – such as nitrates and phosphates.

These sites are a range of rivers and coastal areas where the presence of excess nutrients increases the risk of Eutrophication. A full list of the catchments can be found here. In some of these areas, housing development has slowed down due to the lack of availability of schemes to offset the additional nutrients.

Housing development in these catchments can add to the nutrient load because of the additional nitrate and phosphate pollution arising from their wastewater.

Nutrient Neutrality is a concept which ensures that new housing developments or site upgrades don’t increase the levels of phosphate and nitrates entering vulnerable watercourses or catchment areas. This approach was outlined by Natural England in March 2022. When nutrient neutrality is needed, mitigation measures are applied before the development. This is to avoid impacts in the areas of development, rather than compensating for the impacts after they have occurred.

Developers must calculate the additional nutrient load arising from their project and then arrange to mitigate this before any new properties can be occupied.

Nutrient mitigation schemes can include:

  • Nature-based solutions, such as wetland creation
  • Taking farmland out of production
  • Upgrading septic tanks with package treatment plants that remove more of the nitrates and phosphates

What is the role that septic tanks play?

Septic tanks are a common feature in many residential areas, particularly in rural locations. These tanks might seem like an unlikely contributor to nutrient pollution. However, these decentralized wastewater treatment systems can play a significant role in releasing nitrate and phosphate pollution into the environment. In areas where septic tanks are prevalent, the discharge of effluent into the soil can result in nutrient leaching into groundwater. Ultimately, it will find its way into rivers, lakes, and other water bodies.

Septic tanks were designed to treat organic matter. In the UK climate, they primarily act as a settlement tank, with most of the wastewater being released into the environment carrying with it high levels of nutrients. The sludge is then emptied on a regular basis.

Package sewage treatment plants: the environmentally sound way forward?

Sewage treatment plants are more sophisticated wastewater treatment systems. In some cases, they come with a phosphate dosing system. The system utilises ferric chloride to precipitate out phosphate as ferric phosphate. This method reduces the amount of phosphate released to the environment by over 90%!

Sewage treatment plants can also perform biological removal of phosphorus. The process uses microorganisms to convert phosphates into less toxic forms such as phosphorus minerals. This process occurs in nature in wetlands and rivers. GRAF, a major manufacturer of package treatment plants, claims that their system’s biological phosphorous removal is up to 80.2%. However, a Natural England report from 2016 suggests that the biological process can be less efficient than chemical forms of removal.

Modern sewage treatment plants, for instance, SBRs (sequencing batch reactors) can remove up to 87% of nitrates from household wastewater if well-operated and serviced.

How can you help reduce nutrient pollution?

If you own a property with on-site treatment, one way you can help combat nutrient pollution is by using eco-friendly cleaning products in moderation. These eco-friendly products tend to contain lower levels of phosphate and break down safely in the environment.

You can also ensure proper operation and maintenance, such as annual emptying and servicing where appropriate. Always operate your system in line with the manufacturer’s instructions and be very careful about what products go down the drain.

But the biggest impact could be made by replacing your old septic tank with a modern package treatment plant built with nitrate and phosphate removal capabilities. If you need more information, contact us today by clicking here or give us a call on 0800 011 6600.