Cess & Septic Waste Treatment Processes

Our facilities and processes at our wastewater treatment works at Howdon are industry leading in their sustainability and eco-friendly approach.

Backed up by a network of satellite centres designed to reduce transportation costs, our treatment centres at Bran Sands and Howdon generate their own energy by converting the sludge from waste water into energy rich biogas. The solid waste that is left over after treatment is used on agricultural land as fertiliser, which is the Best Practicable Environmental Option and is supported by the UK government.

The ‘Power from poo’ production at Howdon, more formally known as Thermal Hydrolysis Advanced Anaerobic Digestion (AAD), started in 2012 with the company generating electricity. Three years later, this was followed by the production of gas for the National Grid, meaning customers were now cooking on poo too.

The Howdon plant is the company’s largest sewage treatment works and treats up to 12,000 litres of wastewater from customer homes and businesses every second. Its £8 million gas to grid plant is the biggest of its kind in the industry.

The industry-leading ‘Power from poo’ process has transformed sewage sludge from being a waste product that needed a lot of energy to clean up before it could return to the natural environment, into a fuel being used to produce green energy. The innovative process is cutting the company’s annual operating costs of around £9 million and delivering a significant cut of more than 20% in the company’s carbon footprint.

The Thermal Hydrolysis AAD process involves pre-treating the leftover sludge and heating it in something similar to a giant pressure cooker to around 165 degrees Celsius under six bar of pressure. This process destroys any pathogens and breaks down the cell structure, which is then fed to billions of bacteria in giant digester tanks, making it easier for them to eat.

As the bacteria eat the sewage sludge, they release biogas (methane and CO2), which is similar to a person burping and letting off wind. These gases are collected in huge 11-metre diameter sized golf ball-like biogas storage bags, before being fed into a high pressure water wash gas clean up system where the methane and CO2 are separated.

The gas to grid process has a higher financial return than electricity generation and was introduced as it is more efficient than CHP electricity production due to the amount of heat energy losses from the gas engines while creating electricity.


Septic/Cess Waste – Sustainability and Environmental Impact Statement

In March 2020, the Environment Agency published their strategy for safe and sustainable sludge use. In it, the Agency reiterated their position that the most sustainable option for treated sewage sludge is to recycle it to agricultural land as a fertiliser. It provides beneficial amounts of organic matter and nutrients to the soil. This also fits into the government’s strategy as set out in Defra’s 25 year environment plan.

At the same time, the EA also wishes to end the practice of spreading untreated septic tank sludge to land. Although the water industry voluntarily ceased spreading any untreated waste several years ago, it is still possible to spread septic tank waste under the Sludge Regulations. The new strategy will bring an end to this regulatory regime and all treatment and spreading will be brought into line with the Environmental Permitting Regulations.

The safest and most economical way of treating septic, cess and toilet waste is to import it into a regulated sewage treatment works such as Howdon or Bran Sands. Here, it will get treated along with the sewage and sludge on site, to not only provide a fertiliser for agricultural land but also to generate biogas which then gets send to the national gas grid for use in domestic properties.


for more information on how we make power from poo visithttps://www.nwl.co.uk/services/business/nwgrow/

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