| Anaerobic digestion is a promising method for treatment and utilization of municipal organic waste.However,anaerobic digestion of mixed collected municipal organic waste often enconters large digestion volume and mechanical troubles due to the significant content of non-biodegradable impurities.Anaerobic digestion of source-sorted municipal organic waste faces with problems such as unbalanced nutrients,low biogas productivity and unstable operation because the biodegradability of substrates varies greatly.These problems severely limited the application of anaerobic digestion in the field of municipal solid organic waste treatment.In order to address the issues above,this research proposed extrustion,co-digestion and pretreatment strategies for improving the anaerobic digestion performance of organic waste.The procedure parameters of extrusion,mixing ratio,low-temperature alkali and hydrothermal pretreatment were investigated,and the enhancement mechanisms were explored.The main research contents and conclusions are shown as following:(1)The effectiveness of extrusion technology for organic fraction separation from mixed collected municipal solid waste was examined and its enhancement effect on anaerobic digestion of food waste was investigated.The results showed that extruded OFMSW had high methane yields(334?430 mL/g VS),and it was very stable during the 220-day operation with no VFAs accumulation;addition of extruded OFMSW in digester of food waste that already lost its stability due to VFAs accumulation successfully decreased the VFAs from 3139 mg/L to 48 mg/L,and the methane productivity restored to 2558 mL/L/day;Although they had similar compositions and characteristics,the contents of trace metals(Fe,Co,Ni,Mo)in extruded OFMSW were 5?150 times of those in food waste.The trace metals were proved to play important role in maintaining the stability of anaerobic digestion system.(2)Co-digestion strategy was proposed for co-treatment of source-sorted municipal organic wastes(sewage sludge,food waste and yard waste)and the interactive effects among co-susbtrates were investigated.The results showed that addition of SS significantly improved the stability of anaerobic digestion of FW.Sole anaerobic digestion of YW had low methane yield(196?199 mL/L/day),while co-digestion with SS or FW effectively enhanced the methane yield(596?1696 mL/L/day);Synergetic enhancement was observed in co-digestion of YW and FW,with the CPI of 1.19 at mixing ratio of 1:1(F W:YW).qPCR results indicated that co-digestion of SS with FW or YW significantly improved the abundance of archaea from 6.9×108 copies/mL and 4.8×105 copies/mL to 6.7×1010 copies/mL and 6.7×1010 copies/mL,and its ratio from 0.4%and 1.7%to 17.1%and 12.7%,respectively,indicating more balanced mirobial community structures and improved synergistic metabolic performance.(3)Given the slow biodegradation rate of yard waste in anaerobic digestion system,low-temperature alkali pretreatment was adopted for improving its performance.The results showed that the hydrolysis rate of YW after pretreatment was improved by 1.58 times,and the methane yields in batch experiments increased by 11.5?34.5%.These results could be ascribed to the decreased crystallinity(1.5?26.8%)and removal of lignin.The effectiveness of alkali pretreatment was also proved in semi-continuous anaerobic digestion experiment.The methane yield was improved by 78.5%with alkali pretreatment,and the methane content increased from 56.1%to 65.1%.Alkali pretreatment was favorable for growth of Bacteroidetes and Clostridia,and the total abundance of them was much higher than those in untreated trail(69.5%vs 51.3%),indicating higher ability to metabolize complex substrates.Alkali pretreatment did not change the methanogensis pathway and the dominated archeae(Methanosaeta,92.4%).(4)At the background of the plastic limit order and the generation of waste bio-based plastic,anaerobic biodegradation behavior of PLA plastic was investigated and the influence of hydrothermal pretreament on its biodegradation was evaluated.The results showed that PLA plastic was slowly biodegraded at mesophilic condition(k<0.001 day-1),with final methane yields of 3 7?51 mL/g VS after 146 days incubation.In thermophilic digester,399?443 mL CH4/g VS of PLA plastic was obtained after 146 days incubation,which were close to the theoretical methane potential(TMP)of PLA,but the effective digestion time was long(96?135 days).Although bacteria of Thermacetogenium(27.4%),Acetomicrobium(18.3%)and Defluviitoga(17.8%)and archaea of hydrogenotrophic Methanothermobacte(80.1%)in thermophilic digester could convert waste PLA plastic into methane,the efficiency was low.Hydrothermal pretreament significantly improved the hydrolysis rate to 0.111 day-1 and methane yield to 1590%with a shorter degradation time(13?30 days).LC-QEMS analysis results revealed that cleavage of ester bond in PLA chain was the main mechanism during its hydothermal pretreatment for enhancing the methanization. |
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