Dynamics For Enhanced Methane Production During Co-digestion Of Sewage Sludge And Food Waste In Anaerobic Membrane Reactor (AnMBR)

Organic solid wastes such as sewage sludge（SS）and food waste（FW）are important by-products ofhuman production and life.They have the characteristics of miscellaneous composition,obvious regional differences,and high difficulty in treatment.Their harmless disposal and resource utilization are urgent.This thesis took SS and FW as the processing objects,and anaerobic membrane bioreactor（An MBR）as the core technology.Aiming at the problems of low organic carbon conversion rate,single digestion carbon-nitrogen ratio imbalance,and low energy conversion rate,SS and FW anaerobic methane conversion performance evaluation and metabolic mechanism research based on An MBR were developed systematacially.Analysis and optimization of organic loading rate（OLR）,temperature,solid retention time（SRT）,hydraulic retention time（HRT）and other operating parameters were done,in order to determine the best methane conversion conditions and membrane pollution control strategies,and promote the application of An MBR in SS,FW and other organic solid waste anaerobic methane conversion.Combining the research status and development of domestic and foreign SS and FW treatment technologies trends,analysis and comparison of the characteristics and technical advantages of different treatment technology modes in terms of organic degradation or conversion performance,energy and resource regeneration etc.were done.It can provide theoretical and data references for organic solid waste treatment and high-value conversion.The main research results are as follows:1)The study of plasma ozone pretreatment on sludge and food waste to strengthen sludgedissolution and anaerobic co-digestion was carried out.The effects of different dosage of ozone on sludge dissolution,and anaerobic co-digestion performance of sludge and food waste were explored.The response mechanism of microbial community under different dosage of ozone was compared and analyzed.The results showed that after ozone pretreatment,the microorganism cells dissolved and dissolved organic matter in the system was released.With the increase of ozone dosage,the concentration of volatile solids showed an upward trend,and reached the highest value of 7.08±0.25 g·L^-1when the ozone dosage was0.06 g O₃·g^-1TS.The increase of soluble organic matter also promoted hydrolysis and acidification,so the removal rate of total solid increased with the increase of ozone dosage.Dissolved chemical oxygen demand,soluble protein and soluble polysaccharide both increased and decreased during the experiment,which may be due to the joint process of sludge dissolving and organic fermentation in the system.According to the analysis of the influence of plasma ozone pretreatment on methane conversion,on the 40th day,the cumulative methane production rate reached the highest when the ozone dosage was 0.01 g O₃·g^-1TS,and its value was 75.86±2.94 m L·g^-1VS.The response mechanism of microbial community in this system was as follows:when ozone dosage was 0.02 g O₃·g^-1TS,microbial community richness and diversity were the highest.Under the ozone dosage of 0.02 and 0.04 g O₃·g^-1TS,ozone pretreatment had little effect on the hydrolysis and acidification process.However,under different ozone dosage,the hydrolysis and acidification processes in the system were stable.2)A study on the optimization of single digestion performance of submerged An MBR sludge wascarried out.Effect of four key operating parameters such as SRT,HRT,OLR and temperature on sludge anaerobic digestion performance on an An MBR were explored.Control efficiency of the membrane fouling in situ of different membrane fouling control methods were compared and analyzed.The results show that when the operating conditions are medium temperature,OLR<2.5 kg VS·m^-3·d^-1,and HRT<10 d,An MBR can operate stably under the condition of SRT>40 d to achieve high-efficiency biodegradation of sludge and methane conversion.In addition,membrane fouling,as the main factor affecting membrane filtration performance,can be controlled in situ by physical adsorption,solid-liquid fluidization and quorum quenching（QQ）,or through anti-fouling membrane materials,feed pretreatment,etc.to control ex-situ.However,how to further realize the high-efficiency carbon conversion and methane generation of SS in an An MBR,and effectively control or slow down membrane fouling,remained to be studied in depth.3)The performance of anaerobic co-digestion and metabolic mechanism of SS and FW based onsubmerged An MBR were studied.By tracking and analyzing the parameters such as organic matter degradation,CH₄production and microbial community change,the synergistic performance of co-digestion and metabolic mechanism were revealed.The results showed that the degradation rate of volatile solids（VS）was increased from 17.5%to 40.0%under the OLR of 0.59 to 0.64 kg·m^-3·d^-1.The COD removal efficiency reached 95.3%,the CH₄yield reached 78.7 m L·g^-1COD_added,and the CH₄content was about60%.Transmembrane pressure（TMP）and average membrane flux are maintained at-3.1～-2.7 k Pa and0.106 L·m^-2·h^-1,respectively.The membrane was polluted slightly.The results of 16S r RNA analysis showed that the main anaerobic digestion bacteria in an An MBR were Proteobacteria,Bacteroidetes and Cloacimonetes.The relative abundances were 36%,21%and 21%,respectively,before the feeding matrix was adjusted.Their relative abundances turned to be 26%,28%and 17%,respectively,after the feeding matrix was adjusted.The dominant methanogens are Methanosaeta and Methanolinea.The relative abundances were 0.4%and 0.1%,respectively,before the feeding matrix was adjusted.Their relative abundances turned to be 0.5%and 0.4%,respectively,after the feeding matrix was adjusted.Therefore,the anaerobic co-digestion of SS and FW based on submerged An MBR has the advantages of enhancing methane conversion and membrane fouling control,and is a technology with great application prospect for co-disposal and energy conversion of multi-source organic solid waste.4)By combining with the research status and development trend of treatment technology for SS andFW in the domestic and overseas,the characteristics and advantages of different technology modes（such as,An MBR,thermal treatment,anaerobic digestion and high-value product directional conversion）in resource conversion and energy regeneration were analyzed and compared.The results showed that in the thermal treatment technology,biochar was the main resource conversion form in hydrothermal and pyrolysis,syngas was the main form of gasification,and electric energy recovery was the main form of drying combustion,but the secondary emission of pollutants（NO_x,SO₂）is unavoidable.Biogas rich in methane could be recovered by anaerobic digestion,but the disposal of biogas residue,slurry and other by-products was still very challenging.While,An MBR had many advantages,such as long SRT,abundant biomass and good effluent quality,etc.,and had become a favored technical choice in the field of anaerobic digestion.In contrast,due to the complex structure and obvious regional characteristics of SS and FW,the directional transformation of high-value products had big differences in product types and quality.Combined with resource conversion,energy regeneration and environmental efficiency,it can be seen that anaerobic digestion and methane recovery of SS and FW with An MBR as the core is an economic,efficient,green and environmental protection technology mode.