| WAS is produced with sewage treatment in sewage treatment plants,and contain a lot of harmful substances that can enter the environment with common treatment methods such as dumping and landfilling,which poses great threat to people’s health.Biochar,an environment-friendly adsorbent,has a high specific surface area and carbon content.It is mainly derived from agricultural waste such as plant or animal manure and produced by pyrolysis under low-temperature in hypoxic or anaerobic conditions.In recent years,the application of biochar in anaerobic digestion has attracted attention.However,the effect mechanism of biochar on WAS anaerobic digestion is still unclear.Firstly,this study used batch experiment to study the effect of different types of biochar on the gas production capacity of WAS anaerobic digestion,and screened out the best biochar.Then we used continuous experiment to study the influence of different content of biochar on the WAS anaerobic digestion process and gas production characteristics.Finally,combined with analysis of3D-EEM,FT-IR and EPS in the sludge,the mechanism of the impact of biochar addition on the WAS anaerobic digestion system was revealed.It is expected to provide theoretical guidance for the practical application of WAS anaerobic digestion.The main conclusions inferred from this study were as follows:（1）In batch experiments,the cumulative methane production accelerated by adding biochar were 16.2%（pig manure biochar）,10.14%（wheat straw biochar）,6.49%（sawdust biochar）and 31.84%（walnut charcoal biochar）.Different types of biochar promote the degradation of EPS by increasing the conversion of LEPS to SEPS,and increasing the proportion of polysaccharides,and ultimately improve the methanation rate.By characterizing biochar,it was found that the large specific surface area and porous structure of biochar provided a good living environment for microorganisms.In addition,biochar itself is alkaline,which was suitable for the survival of methanogens.（2）In continuous experiments,when the concentration of pig manure biochar was 5g/L,The promotion rate of methane yield is 6.67%and the biodegradation rate of SDBS in the WAS is increased by 1.85%.When the concentration of pig manure biochar was increased to 8g/L,it inhibited the rate of methanogenesis by 10.00%,and inhibited the activity of hydrogen-and-acetic producing bacteria.High-concentration biochar（10g/L and 20g/L）had an inhibitory effect on the hydrolysis,acidification and methanation in the anaerobic digestion process.When the biochar concentration were 8-20g/L,the SDBS biodegradation rate were decreased by 2.96%～7.69%compared with none addition,which was due to the inhibition of microorganisms at higher biochar concentration（8-20g/L）.The addition of biochar promoted the transfer of residual SDBS from the liquid phase to the solid phase.（3）When the concentration of pig manure biochar was 5g/L,the hydrolysis of EPS was promoted by promoting the conversion of TEPS and LEPS to SEPS,which ultimately promoted the rates of hydrolysis,acidification,acetic acidation and methanation in the anaerobic digestion of WAS.When the concentration of pig manure biochar was increased to 8g/L,the microorganisms protect themselves from toxicity by secreting bound EPS.When the concentration of pig manure biochar was20g/L,the reactor can operate stably at a lower methane production rate(0.21L?g VS-1),which indicated that the higher concentration biochar caused"Steady state"to the anaerobic digestion of WAS.It may be due to the microorganism had produced adaptive domestication under the long-term operation and secreted EPS to avoid toxic damage and maintain the"inhibitory stable"state. |
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