Summary:

The article presents the analysis of operation of sewage sludge co-fermentation with waste fats coming from de-fattening process of industrial sewage generated in fat production facilities. Within the period of two years (2008-2009) analyses of the co-fermentation process efficiency have been carried out measured by the volume of generated biogas as well as the analysis of influence of the amount of waste fat used on the sewage sludge and waste fat mixture fermentation process. The average volume proportion between the fermented sludge and waste fat was 10:1. The maximum ratio was 4:1 (fat constituted 25% of batch). Depending on the amount of dosed fat the biogas fermentation was increased even by 80% in comparison to the case where only sewage sludge was fermented. During the examination period 107 m3 of biogas in average have been additionally achieved, for each 1 Mg of fat added into the fermentation chambers. Such volume of biogas allows for generation of additional 180kW of electric energy and approx. 2,8 KW of heat energy recovered from exhaust fumes. It was agreed that the increase of generated biogas volume depends not only on the ratio of dosed waste fat but also on its characteristics. It was observed that in case of dosing fat in which organic matters biodegradation processes had been already started the volume of biogas was increased. It demonstrates that such mixture of sludge and fat was more acceptable for methane bacteria responsible for fermentation process effectiveness. Sludge after fermentation is characterized by stable parameters: pH 7,0-7,4, basicity 72-99 val∙m-3. During co-fermentation process the mineralization degree of fermented sludge decreases from 40% to 33% which can be taken as negative aspect of this process. A two-year operation of this installation proved that waste fat co-fermentation is very effective in biogas production which in effect provides higher cost-effectiveness of this process. Loading chambers even with big portions of fat did not interfere the sewage sludge fermentation.