Study On The Effect Of Magnetic Biochar On Anaerobic Digestion Of Sewage Sludge And Microbial Community

With the continuous progress of urbanization in China,the output of municipal sewage increases year by year.In the process of sewage treatment,urban sewage treatment plants continuously adsorb harmful substances such as pathogens and organic pollutants,and eventually accumulate into the sewage sludge,which seriously threatens the health of ecological environment.As a relatively mature and widely used technology,anaerobic digestion can effectively realize the recycling,stabilization,harmless and reduction of sewage sludge.However,due to the low degradation rate of organic matter,limited hydrolysis and acidification,and slow interspecific hydrogen transfer（IHT）efficiency,the biogas production capacity of traditional sewage sludge anaerobic digestion was“rate-limited”.In order to break through the bottleneck of“speed limiting”,under the principle of“treating waste with another waste”,this study prepared magnetic biochar using oil tea shell as raw material,and added it into sewage sludge anaerobic digestion system in a certain proportion.From the perspective of gas production performance and microbial community diversity,the influence mechanism of magnetic biochar as an additive on biogas production process was analyzed.The specific conclusions of this study were as follows:（1）Scanning electron microscopy showed that the magnetic biochar showed a denser pore structure than the raw biochar.In the process of magnetization modification,the specific surface area and pore volume of biochar decreased,which may be due to iron oxide crystals blocking the original pores of biochar.X-ray diffraction results showed that the main components of biochar changed from amorphous carbon to magnetic iron oxide and iron after magnetized modification.At the same time,the increase of oxygen-containing functional groups in biochar is beneficial to strengthen the electron transport process.（2）The addition of magnetic biochar can better promote the anaerobic digestion of sewage sludge biogas production performance.When the dosage was 40 mg/g TS,the promotion effect was the strongest,and the cumulative biogas production was 439.71m L/g VS_added,which was increased by 42.21%compared with the blank group(309.20m L/g VS_added).At the same time,when the magnetic biochar dosage reached 80 mg/g TS,the biogas production performance of sewage sludge anaerobic digestion was inhibited.（3）During the whole anaerobic digestion period,the p H of all units was maintained between 6.93 and 7.46,with no significant acid accumulation.The addition of magnetic biochar promoted the hydrolysis process of sewage sludge anaerobic digestion,and the degradation rates of total solids（TS）and volatile solids（VS）reached 28.99%～46.13%and 49.42%～63.81%,respectively.The removal rates of dissolved chemical oxygen demand（s COD）,soluble protein and soluble polysaccharide were also increased in different degrees.The concentration of volatile short-chain fatty acids（VFAs）in each plant increased first and then decreased,and the main metabolites were acetic acid.In addition,the trace of the form of iron in the system found that the concentration of soluble Fe³⁺was much lower than that of soluble Fe²⁺because soluble Fe³⁺was continuously reduced to Fe²⁺as an electron donor.（4）16S rRNA amplified sequencing technology revealed the effects of magnetic biochar addition on microbial community diversity in sewage sludge.The results show that magnetic biochar can effectively promote biogas production because of its enrichment of Methanosaeta,Methanobacterium,Methanosarcina and other methanogenic archaea.