Anaerobic digestion as a means of energy regeneration in sewage purification plant "Città di Verona"

In the article we report the results achieved in energy recovery at Verona wastewater treatmont plant. Such recovery is obtained through sludge anaerobic digestion and use of biogas in a cogeneration station (two groups, 500 kW of electric power and 700 kw of thermic power each). In 1985 20 million cubic meters of sewage were processed, 10,000 tons of dewatered sludge 23% were obtained, producing 4,200-4,500 m^3/day of biogas with an average methane concentration of 70%, 7,200-7,500 kwh/day of electric energy were produced. Average specific biogas production was 17-22 l/people x day. These values allowed a saving of 45% in electric energy used by utilities of wastewater treatment plant in 1985. Each kwh produced costed L 18. Owing to the good results obtained in sludge processing, we are now considering the possibility to dispose of organic fraction of MSW through the same biologica process. Therefore it follows that reutilization of power within municipal service permits the best economic exploitation and a high profitability of investments.