Study On Dry Anaerobic Digestion Of Solid Phase Stuff Of Food Waste

Meticulous pretreatment is usually necessary in full scale anaerobic digestion plant for food waste treatment.The pretreatment processes generally include partition,grit removal,crushing,slurring,oil extraction by steam,and triple-phase separation of oil-liquid-solid.The solid phase derived from triple-phase separation is characterized with high content of total solid(TS),low p H and C/N,and especially,high content of volatile solid(VS)and volatile fatty acid(VFA),which is higher than that of raw refuse.However,few have reported for anaerobic digestion of such stuff.The anaerobic digestion of solid phase stuff of food waste(SPSFW)was researched in the present paper based on lab-scale and pilot-scale tests under mesophilic and thermophilic conditions.The gas production efficiency,treatment effect and factors influencing anaerobic digestion of SPSFW were researched.Co-anaerobic digestion of SPSFW with kitchen waste and water hyacinth was carried out on the problems of VFA accumulation in the anaerobic digestion system.This research attempts to provide technical support for the engineering application of SPSFW.The main research contents and results are as follows:(1)Lab-scale anaerobic digestion of SPSFW under mesophilic condition.The results showed that the maximum gas production rate of VS and methane content was 0.62 L/g VS and 60.3% respectively while OLR=2.5 g VS/(L·d).The system was sensitive to VFA and ammonia nitrogen.When VFA exceeded 4000 mg/L and ammonia nitrogen concentration was above 3200 mg/L,the gas production rate of VS decreased.(2)Lab-scale anaerobic digestion of SPSFW under thermophilic condition.The results indicated that the maximum volumetric gas production rate and gas production rate of VS were obtained while OLR=3.41 g VS/(L·d),which were 1.48 L/(L·d)and 0.45 L/g VS respectively.The maximum of gas production rate of VS appeared earlier than that of mesophilic conditions,and VFA concentration kept high.Under thermophilic conditions,with the increase of OLR,hydrogen nutrition mathanogenic bacteria such as Methanothermobacter and Methanoculleus became the dominant species,which resulted in the decrease of species diversity and capacity of gas production.(3)Pilot-scale anaerobic digestion of SPSFW under mesophilic condition.Under mesophilic condition(35±2 ?),pilot-scale experiments were carried out to study the impact of organic loading rate(OLR)on anaerobic digestion of the fine pretreated solid phase stuff of food waste using a 4 m3 full mixed reactor.The results show that the the system reached the optimum operating condition while OLR=4.77 kg VS/(m3·d),with which the maximum volumetric gas production rate was 2.56 m3/(m3·d)and maintained 1.95~2.10 m3/(m3·d),and the methane content of gas and the removal rate of total solid(TS)were above 60% and 93% respectively.In case of high OLR(5.97-6.86 kg VS/m3·d),VFA tended to accumulation while ammonia nitrogen concentration could remain stable relatively.The system was not sensitive to VFA accumulation when ammonia nitrogen concentration was less than 6000 mg/L,and the methane-producing rate of VS could remain 0.32 m3/kg VS.However,while ammonia nitrogen concentration rose to more than 6000 mg/L,the activity of methanogenic microorganisms was inhibited,and the system became sensitive to VFA.(4)Pilot-scale co-anaerobic digestion of SPSFW with kitchen waste under mesophilic condition.The results showed that co-anaerobic digeston of SPSFW with kitchen waste with a mixed ratio of 2:1 of mass obtained higher volumetric gas production rate and methane content than that of the same quantity feed with pure SPSFW.When the feed rate was 120 kg/d,the average volumetric gas production rate and methane content were 2.30 m3/(m3·d)and 63.8% respectively.Co-anaerobic digestion of SPSFW with kitchen waste can reduce the accumulation of VFA,enhance the acid buffering capacity of the system,and improve the operation capacity of SPSFW.(5)Lab scale co-anaerobic digestion of SPSFW with water hyacinth.The results showed that the optimum mass fraction of water hyacinth of mixed stuff was 5%,and the maximum volumetric gas production rate,methane-producting rate of VS and methane content were 1.58 L/(L·d),0.64 L/g VS and 59.6% respectively.Co-anaerobic digestion of SPSFW mixed with 5% water hyacinth could slightly improve the efficiency of gas production,but the methane content of biogas was slightly lower than that of pure SPSFW.Water hyacinth is a kind of good mixed fermentation substrate.Co-anaerobic digestion of SPSFW with water hyacinth for biogas production is feasible in engneering.