The anaerobic decomposition of the primary and secondary sludge takes place in three digesters, while the anaerobic decomposition of the hygienised liquid waste takes place in one digester. The total volume of the digesters is 7,200 hundred cubic metres.
In the digesters, the anaerobic conversion of organic matter to biogas takes place over a period of 30 days at a temperature of approximately 39 degrees Celsius. The first stage involves acid hydrolysis, during which organic matter decomposes into short-chain fatty acids. Then follows the methanogenic phase in which methanogenic bacteria convert the fatty acids into biogas.
The resulting biogas is stored in the gasholder while the digested sludge undergoes mechanical thickening in a centrifuge until the content of dry matter reaches approximately 30 percent. The thickened sludge is stored at the disposal site ready for final disposal. The water or centrate, the product of centrifugation, is then pumped into a storage tank where it undergoes deammonification.
BIOGAS is a mixture of approximately 65 percent of methane, 34 percent of carbon dioxide and 1 percent of other gases. After digestion, the biogas passes from the gasholder through a column containing activated carbon, which removes impurities, such as organic silicon compounds, solvents and sulphide. The biogas is used to fuel biogas engines to produce electricity. The electrical energy produced covers over 90 percent of the treatment plant's energy needs and provides all the heat energy required by the wastewater treatment processes. Any excess electricity produced goes back into the electrical grid, while flares dispose of any excess biogas.
For more information click "Technological Data"