The Transition Stage in the Start-up of an Anaerobic Sludge Digester

The start up dynamics of a one-million and two-hundred-thousand liter anaerobic digester of municipal waste treatment sludge was studied. In the digester, mixing was accomplished by circulation of the produced biogas at a rate of 0.13 m3 per hour of the digester volume per hour. During the nine-month study, no serious phenomena of foaming, getting sour, temperature fall, etc. were observed despite the fact that there were problems including gas leakage, sludge leakage, heating system shortcomings and weak mixing system. In the process of digestion of a 3:1 mixture of primary and secondary sludge at a rate of 25 m3/day, 25˚C and a residence time of 48 days, volatile content removal was as high as 60%. The experimental data collected in this study was checked against a theoretical model already published in the literature and a good comparison was observed between the measured values and those calculated based on this model.