Optimization of the Proportions of Kitchen Waste and Municipal Sludge in Anaerobic Co-Digestion

For acquiring the optimal proportions of kitchen waste and municipal sludge in anaerobic co-fermentation, this study firstly prepared the mixtures including kitchen waste and municipal sludge with different proportions (specifically, 1:0, 4:1, 3:2, 1:1, 2:3, 1:4 and 0:1), then performed sequencing-batch anaerobic fermentation at 37 degrees C and finally conducted anaerobic co-digestion. The main conclusions are described below: (1) The mixtures with different waste-to-sludge ratios had different C/N ratios and therefore imposed different effects on the growth and metabolism of microorganisms in the fermentation process. Both kitchen waste and municipal sludge were significantly inferior to the mixtures in methane-producing performance; (2) The mixture with a waste-to-sludge ratio of 4:1 produced most methane during the fermentation process, with a cumulative methane production of 3406.70 mL and a biodegradation rate of 67.40%; the anaerobic fermentation of sludge showed the least cumulative methane production (1598.08 mL). The cumulative methane productions from the anaerobic fermentation process of the mixtures with different waste-to-sludge ratios of 3:2, 1:0, 1:1, 2:3 and 1:4 were 3231.74 mL, 3029.76 mL, 2720.23 mL, 2520.94 and 1793.86 mL, respectively. Therefore, it can be easily found that the optimal ratio of organic kitchen waste to municipal sludge in anaerobic co-digestion was 4:1.