Electric energy from wastewater sludge and foodstuff waste

The pollution of our living waters cause a considerable environmental problem all around the world. The main sources of pollution are the industry, agriculture and population. For the purpose of protecting our living waters, the primarily applied technology is wastewater treatment, whose main goal is to prevent the arrival of polluting matters in the environment. Wastewater treatment is a high energy need process, however, through the practical utilization of organic matters harmful for the environment, a very important produce, renewable energy can be produced. The method through which waste is removed, degraded and then reused and finally produce renewable energy is nothing else but anaerobe treatment. Biogas can be produced from the joint anaerobe fermentation of the high organic matter content sludge produced as a product of wastewater treatment and of the matters originating from urban and industrial organic waste, whose utilization considerably contribute to the lowering of the costs of wastewater treatment processes. The role of this efficient, cost saving and environment friendly technology has increased, since the removal of harmful matters at low costs becomes an ever more important issue in the programs of the governments of the various countries.
At the South-Pest Wastewater Treatment Plant, for the purpose of producing biogas, solid and liquid organic waste is managed together with sludge originating from wastewater treatment. As a first step, we execute the degrading of organic matters in thermophilic anaerobic fermentors (operating temperature 55°C, useful volume: 2,000 m3), then in mesophilic anaerobic fermentors (operating temperature 35°C, useful volume: 3x2,600 m3), which is a quite complicated process based on the symbiotic relation of numerous strains. Hydrolytic bacteria degrade the big molecule organic compounds with their extracellular enzymes, as a result of which short carbon chain fatty acids, carbon dioxide and hydrogen gas are produced. After that, a second group of bacteria transforms the short carbon chain fatty acids into organic acids, mainly into acetous acid. Further carbon dioxide and hydrogen gas is produced during this process. Finally methanogenes produce biogas from acetous acid and hydrogen, the methane content of which exceeds 60%. At the South-Pest Wastewater Treatment Plant, the energy content of the biogas produced as described above is transformed into electric energy by two gas engine-generators (their electric performance is 494 kW and 836 kW respectively). The produced electric energy covers 90% of the plants electric needs and 100% of its thermal needs.