The Ultimate Anaerobic Biodegradability of Municipal Sludge and FOG
The anaerobic biodegradability of three types of municipal sludge (primary, secondary, and dewatered secondary), as well as two types of partially dewatered (polymer dewatered and lime dewatered) fat, oil and grease (FOG) was assessed at 35°C using a previously digested anaerobic sludge as seed. Samples of these five components, as well as various combinations of the individual components were tested. Under batch conditions, the sludge initial loading was 3 kg VS/m3 and the highest FOG loading tested was 1.23 kg VS/m3. At the end of the 120 days incubation, the extent of the VS destruction was equal to 56.7, 23.3, 26.7, 70.7, and 78.3% and COD destruction was equal to 58.5, 26.3, 30.5, 70.8, and 82.2% for the primary, secondary, dewatered sludge and the polymer- and lime-dewatered FOG samples, respectively. The methane yield was 470, 179, and 247 mL methane @ STP/g sludge VS added for the primary, secondary, and dewatered sludge samples, respectively. In contrast, the methane yield for the two FOG samples was 993 and 878 mL methane @ STP/g FOG VS added for the polymer- and lime-dewaterd FOG samples, respectively. Primary sludge and FOG degradation occurred significantly faster than the degradation of dewatered sludge and TWAS. Following an initial period of 3 to 5 days, FOG degradation followed approximately first-order kinetics with a rate constant in the range of about 0.1 to 0.15. The remaining of the samples did not follow first-order kinetics, with their fist-order rate coefficients decreasing with digestion time. There were indications of increased degradation with increasing FOG loading of the previously digested sludge that was used as seed. The ultimate degradation of the various combinations could be predicted based on the ultimate degradation of the three sludge and two FOG tested components.
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Document Type: Research Article
Publication date: 2007-10-01
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