Study On The Behavior Mechanism Of Biochar Enhanced Co-digestion Of Food Waste And Sludge

Anaerobic digestion is more and more widely used to treat food waste and sludge due to its advantages of balanced C/N ratio,dilution of toxic substances and efficient recovery of methane.Compared with the medium temperature anaerobic digestion system can reduce the volatile solids and inactivate the pathogens in the system.The anaerobic digestion system has the advantages of high methane production and more thorough degradation of organic matter.However,when the temperature increased,the hydrolysis rate also became faster,and it was easier to cause the imbalance of the formation and degradation of organic acids under high organic loading,which resulted in the accumulation of VFAs.Therefore,how to effectively promote the degradation of VFAs and improve the anti-shock ability of the system against the decrease of pH value is the key to realize the efficient and stable operation of co-digestion technology of food waste and sludge.Traditionally,hydrogen/formic acid as the electronic medium of the syntrophic oxidation process is often the rate-limiting step of methane production process.This study investigated the effect of biochar on the anaerobic digestion process under different loads,analyzed the efficiency changes of biochar during long-term of digestion system,observed the change of EPS of different VFAs under the action of biochar and in digestion system.The characteristics of microbial loading were analyzed and the promotion mechanism of methane production by syntrophic oxidation was concluded as follows:?1?The delay time t₀ and methane production rate R_max increased linearly with the increase of load under different loads.The delay time without biochar can reach up to18.6d while the addition of biochar keeps it at about 2d and R_max also increases by 1.86times.When the 4500mg-COD/L was exceeded,the R_max of the digestion system was limited,but the experimental group was not affected by load,but the biochar addition group was not affected by the load.This is due to the fact that the basic functional groups of biochar neutralize the organic acids produced by hydrolytic acidification under high load and effectively prevent the rapid decline of pH value at the initial stage of the reaction so as to improve the anti-buffer ability of the system.?2?Through three-cycle co-digestion experiments under the action of biochar,it was found that the R_max of the system without biochar was 7.25mL/d,17.58mL/d and22.61mL/d in three cycles,and the addition of biochar was effective.R_max was increased to 15.29 mL/d,31.79 mL/d,and 41.87 mL/d.Although the rate of R_maxax growth in the same digestion system has slowed down in the third cycle,the addition of biochar obviously favors the increase of R_max in the system for a long time?3?Through the degradation kinetics of a single VFA,it can be seen that the addition of biochar effectively shortens the conversion of butyric acid to acetic acid and also promotes the conversion of acetic acid to methane.The analysis of the microbial population of the co-digestion system confirms that the biochar can increase the system.The richness of interspecies oxidation of methanogenic archaea?such as Methanosaeta and Methanosarcina increased from 41.1%to 59.7%?,The inhibition experiment of interspecific H₂ transfer indirectly showed that biochar mainly promoted the direct interspecies electron transfer between bacteria and methanogens attached to porous biochars.