Total Solids (TS) were determined by drying the samples at 105°C to constant weight; Volatile Solids (VS) were determined by combustion of the dried samples to constant weight at 620°C. Chemical oxygen demand (COD) and ammonia-nitrogen (NH3-N) analyses were conducted according to the German standard method for the examination of water, waste water and sludge (Frachgruppe Wasserchemie, 1985). The total nitrogen (Kj.-N) concentration was determined using a semi-automatic Kjeldahl method. Volatile Fatty Acids (VFA) and gas analyses were carried out using gas chromatography, pH measurements were done with conventional glass electrodes.