How are biosolids processed?

The Biosolids Lifecycle

Advanced Anaerobic Digestion

Anaerobic digestion is the process by which microorganisms break down biodegradable material (in this case sewage sludge) in the absence of oxygen. By controlling the process, two useful products are obtained: biogas and residual digestate (a nutrient-rich fertiliser). Biogas, which contains a mix of methane and carbon dioxide, can used directly to produce electricity and heat or purified for injection into the gas network.

Advanced Anaerobic Digestion (AAD) processes have been developed to add even greater performance to the digestion process, as well as reducing the overall mass of solids. For sewage sludge, conventional anaerobic digestion will destroy 30 to 40% of the organics present, whereas advanced anaerobic digestion may achieve 60% or more.

Gas to Grid

Biogas consists of methane, carbon dioxide, and traces of other ‘contaminant’ gases. The methane part of the gas is cleaned to remove impurities and propane is then added so that it matches the consistency of the public gas network. The gas can then be injected into the gas distribution network.

‘Power from Poo’ Initiative

NWL are the first water company in the country to use all of the sewage sludge to produce gas and electricity. They have 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.

Power from Poo - Advanced Anaerobic Digestion at Howdon

Video used in a display at Tyneside Discovery Museum about Howdon Sewage Treatment Works and Advanced Anaerobic Digestion Centre. This is a very simple and straightforward explanation of the treatment process for sewage, both effluent and sludge.

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