Experimental Study On Single-phase Reactor Of Anaerobic Digestion For Food Wastes

Nowadays a large amount of food wastes are produced in China, which has notable characteristics of high contents of organic matters, moisture and grease. How to dispose food wastes properly has becoming a significant and urgent problem. Anaerobic digestion is considered to be an effective approach to resource recovery of organic wastes including food wastes. In order to realize the characteristics of anaerobic digestion for food wastes deeply, provide reference information for practical engineering in Chongqing, promote its application and industrialization, the single-phase reactor of anaerobic digestion was adoped. The start-up and opration process of mesophilic wet digestion for food wastes were studied and the important parameters, including organic load, pH value, VFA, alkalinity and ammonia nitrogen and so on, were involved. The main results were listed as follows:①Study on semi-batch start-up of single-phase anaerobic digestion reactor for food wastes. The result shows that initial volume load of 1.0kgVS/m~3·d and loading at a gradually increasing rate of 0.5kgVS/m~3·d per step is a proper way to achieve the goal, which also demands effective anaerobic inoculation sludges and relative high rate of inoculation. During the start-up process, the peak value of biogas yield reached 4.63L/L·d and the content of methane stabilized around 50%. The pH value kept in the suitable range of anaerobic digestion almost. The highest value of COD reached 21380mg/L, while the moisture content decreased gradually. The concentration of ammonia and kjeldahl nitrogen increased during the process with the ammonia peak value of 1560.70mg/L. In the late phase of start-up, the capacity of biogas yield dropped and organic matters tended to be accumulated. Anaerobic digestion system resumed gradually after the pause of feeding.②Study on continuous experiment of single-phase anaerobic digestion reactor for food wastes. While the volume load ranged from 2.5 to 4.0kgVS/(m~3·d), the peak value of daily biogas yield reached 114.7L/d (corresponding to load of 3.5 kgVS/ (m~3·d)); pH value ranged from 7.41 to 7.79; ammonia, kjeldahl nitrogen and moisture content increased step by step. During the phase of volume load of 4.5kgVS/(m~3·d), the expansion of materials and large amount of bubble emerged. The biogas yield falled acutely and biogas yield per uint mass of food wastes dropped to 84.9L/kg. The pH value was 6.68 but dropped continuously and there was possibility of ammonia inhibition. The biogas yield during continuous experiment was 0.91L/gVS, and 117.90L/kg equivalent, with methane yield of 77.38LCH4/kg.③The effect of grease on test result of solid and moisture content was studied by contrast test. The result shows that exact test of grease content is supposed to adopt method without removal of grease (methodⅠ) , while that of solid and moisture content can adopt method with removal of grease (methodⅡ) respectively. The method without removal of grease (methodⅠ) is proposed to get relative exact result of solid and moisture content considering easy and feasible operation.④The paper studied the influencing factors and representations of acidification in anaerobic digestion system. The strong anti-acidification capacity was related to the reasonable operation mode and the feed of materials with high nitrogen. During a majority of reaction time, pH value stabilized in a proper range, with alkalinity higher than 2000mg/L and VFA below 3000mg/L. In the late phase of semi-batch start-up and continuous experiment, VFA cumulated in some extent. Representatively, during the volume load of 4.5kgVS/(m~3·d), VFA reached 9359.2mg/L and alkalinity dropped to 4222.7mg/L.⑤The test result of VFA and ratio of VFA/BA are suggested to be the discriminant index of anti-acidification capacity. WhenVFA/BA<0.4 , it is considered that the system has enough buffering capacity; When VFA/BA= 0 .4～0 .8, it is considered that the system has limited buffering capacity; When VFA/BA>0.8 or VFA>3000mg/L , it is considered that the system has little buffering capacity and VFA tended to be cumulated, when monitoring and control measures should be adoped in time. It is considered that the anaerobic digestion system resumes and can be fed again when VFA/BA<0.4 and the ratio stabilizes.