Study On Dry Anaerobic Digestion Of Food Waste

Food waste in big cities has become an important problem of the construction of Ecological Civilization City due to its great quantity, high content of moisture, organic matters and grease. Among the many food waste treatment proceedings, dry anaerobic digestion is considered to be an effective approach to resource recovery of food waste with the advantage of a higher resource recycle rate and less secondary pollution. To study the start-up process and the effect of different inoculate rate on anaerobic digestion of food waste, a sequencing batch dry anaerobic reactor was designed and fabricated, using complex microorganisms as inoculated bacteria. The main conclusion are as follows:(1)Fed-batch method was used in the start-up test. The volume load gradually increased to make the microorganisms grows under mild environment with low organic load. Daily gas production increases along with the volume load. The peak was 5340mL on 38th, and the methane content was around 55% (V/V). VFA increased rapidly at the beginning stage, then became stable around 2500mg/L. Total alkalinity rose constantly, and the maximum was 7033mg/L. The high total alkalinity ensured the reactor a strong buffering capacity, which made the pH stabilize at 6.8-7.5 except drop to 6.5 at the beginning. Providing a suitable environment for the growth of methanogenic bacteria. The ammonia concentration increased from 450mg/L to 1161mg/L, and no ammonia poisoning came out.. The number of methanogenic bacteria in the reactor gradually increased from 1.15×104·g-1 at the beginning to 4.5×106·g-1.(2)Five reactors numbered Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ are set up with 1kg domesticated mature food waste as inoculum, and 2kg、2.5kg、3kg、3.5kg、4kg fresh food waste added correspondingly to study the effect of inoculate rate on gas producing efficiency. The total gas production of reactor III is 58810mL, and methane production is 26150mL, the biogas yield and methane yield of per unit mass of VS are 0.380L/g and 0.195L/kg respectively. There are two gas peaks of anaerobic digestion of food waste:peak of carbon dioxide and peak of methane. The increase in feed quantity can increase the maximum of the peak of methane and pull off the time of peak of methane. But when the feed quantity was too large, acidification came out, which made the peak of methane small or even disappear. Feed quantity has a significantly influence on VFA concentration., The maximum of VFA concentration of Reactor Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ　were 4380mg/L,4500mg/L,5160mg/L, 8820mg/L,11580mg/L. Total alkalinity and feeding amount have no significant relationship. The minimum pH value has an inverse correlation with feed quantity. The minimum of pH of reactor Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ、were 6.7,6.8,6.4,5.7,5.3. The maximum of ammonia nitrogen concentration of reactor Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ　were 1443mg/L,1499 mg/L,1443 mg/L,1387 mg/L,1317 mg/L. There were no ammonia poisoning occurring.