Enhanced Co-digestion Of Sewage Sludge And Food Waste In Anaerobic Membrane Reactor By Therml Hydrolysis Pretreatment And Study On Molecular Metabolism Mechanism

Sewage sludge and food waste are typically perishable organic solid waste with large output,and it also have two-sided properities of resource recovery and pollution.If not handled properly,it is easy to cause serious harm,and is a major issue related to people’s livelihood.In this regard,sweage sludge mixed with food waste and thermal hydrolysis pretreatment strategy were applied to increase hydrosis rate,enhance methane yield and the degradation rate of organic solids.Three aspects in this research are included:（1）exploring the mechanism of hydrolysis pretreatment on the release of organic matter and the pathway of Maillard reaction;（2）investigating the possibilities for its comprehensive application,which coupled with a novel immersion anaerobic membrane bioreactor（AnMBR）;（3）elucidating the fate of dissolved organic matters（DOMs）in the TH-AnMBR system.The main research conclusions are as follows:（1）The solubility of sludge and food waste was significantly improved by Thermal hydrolysis（TH）pretreatment,and the highest average concentrations of SCOD（Soluble Chemical Oxygen Demand）and SPS（Soluble polysaccharide）reached6.35±0.09 and 1.64±0.06 g/L at 160℃-40 min,which were 1.87 and 2.56 times higher than those in the control group,respectively.SPN（Soluble Protein）and NH₄⁺-N（Ammonia nitrogen）concentrations increased with TH temperature.However,the rate of NH₄⁺-N increase even faster with temperature when over 180℃,indicating that proteins were solubilized largely by the reason of TH pretreatment,along with partial degradation.TD-EEM analysis confirmed that TH pretreatment promoted the dissolution of sludge and food waste,but also greatly promoted the increase of humic acid concentration and the occurrence of Maillard reaction.Synchronous and asynchronous map of FTIR can speculate on the possible occurrence of the Maillard reaction:mild hydrolysis of the proteamide band→-OH begins to participate in dehydration and condensation reactions→forming alkyl and ether bonds→polymerization is active,and C=O bands are produced in esters.FT-ICR MS analysis indicated that TH pretreatment improved the relative strength and chemical diversity of the matrix.However,high temperature TH can lead to the production of Mrps intermediates such as furan,pyrazine,pyridine,pyrimidine,pyrrole,piperidine,piperazine,thiazole,etc.,and may inhibit subsequent AD process in the presence of these intermediates.（2）The hybrid system of TH pretreatment and AnMBR mesophilic fermentation was successfully operated for 150 days,and the co-digestion performance of sludge and food waste under different TH pretreatment temperatures was monitored.Results show that the optimal performance was observed at 160℃-40 min.Under these conditions,the methane yield was as high as 111.9 m L/L_reactor/d,94%higher than that of the control(57.6 m L/L_reactor/d),and the transfer efficiency of COD to methane was 49.63%,23.84%higher than that of the original（25.79%）.More importantly,it also effectively avoided the deterioration of permeate quality induced by Maillard reaction and caramelization process,and the removal rates of COD,PN and PS were stable at 98.3±0.2%,97.8±0.7%and 99.0±0.5%,respectively.The microbial analysis indicated that TH pretreatment not only can enrich organic matter-degrading bacteria（i.e.,Chloroflexi,Bacteroidetes,Firmicutes,etc.）and methanogenic archaea（i.e.,Methanosaeta,Methanobacterium,and Candidatus＿methanofastidiosum etc.）,but also can promote synergies between different microorganisms（such as Anaerolineae and Methanosaeta etc.）.The whole operation process ensures high stability and low membrane fouling,and shows the high feasibility and broad prospects of TH pretreatment coupled AnMBR system.（3）This study provides new insights into the transition of key DOMs in TH pretreatment and AD processes.TH pretreatment increased the proportion of low and high molecular weight compounds,significantly improved the relative strength and chemical diversity of DOMs in the feed matrix,and reduced the relative strength and chemical diversity of DOMs in effluent.Most of the compounds introduced by 160℃-TH pretreatment are biodegradable in AD,which had low aromatic or polarity,and corresponding to protein/amino sugars and unsaturated hydrocarbon regions.Strong decomposition and Maillard reaction occurred in 200℃-TH pretreatment,and the compounds introduced with high hydrophobic and aromatic structure content（lower O/C and H/C values）had poor biodegradability,mainly CRAM.For homologous DOMs with the same KMD,compounds with lower NOSC,higher H/C,and lower O/C may be more biodegradable.Numerous heterocyclic substances are detected in the effluent（e.g.pyridine,piperazine,pyrimidine,etc.）,which may cause harm to the environment and should be fully considered before final disposal.