The anaerobic decomposition of the primary and secondary sludge takes place in the three digesters. In one of the digesters, anaerobic decomposition of the hygienised liquid waste takes place. The total volume of the digesters is seven thousand two hundred cubic metres.
Over a period of thirty days, at a temperature of approximately thirty-nine degrees Celsius, anaerobic conversion of the organic matter to biogas takes place. The first stage involves acid hydrolysis, where organic matter decomposes into short-chain fatty acids. The methanogenic phase then follows in which methanogenic bacteria convert the fatty acids into biogas.
The biogas is stored in the gas storage tank, while the digested sludge undergoes mechanically thickening on a centrifuge until the content of dry matter reaches approximately thirty percent. Thickened sludge is stored at the disposal site ready for final disposal. Pumps then transfer the centrate to a storage tank where it undergoes deammonification.
BIOGAS is mixture of approximately sixty-five percent of methane, thirty-four percent of carbon dioxide and one percent of other gases. After digestion, the Biogas passes from the gas storage tank through a column containing activated carbon, which removes impurities such as organic silicon compounds, solvents and sulphide to a generator to produce electricity. The electrical energy produced covers over ninety percent of the treatment plant's energy needs as well as providing all the heat energy required by the treatment processes. Any excess electricity produced goes back into the electrical grid, while flares dispose of any excess biogas.
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