An Exploration Of The Effect And Mechanism Of Co-addition Of Cerium Chloride And Biochar On Anaerobic Fermentation Of Biogas

China is a large producer of organic solid waste.Organic solid waste is a dislocation resource.If the treatment is unreasonable,it will cause environmental pollution and waste of resources.Methane is a kind of high-value clean energy,which can be obtained from anaerobic digestion of organic solid wastes.However,due to the differences of physical and chemical properties of organic solid wastes from different sources,,the anaerobic reactor may be difficult to proceed smoothly because of the difficult degradation,easy acidification and low production efficiency of the substrate in practical application.In order to effectively increase methane production and make the anaerobic digestion proceed smoothly,the effect of adding biochar and cerium chloride on methane production by anaerobic digestion were systematically studied under the pretreatment condition of composting on fermentation substrate.Based on this,the enhanced anaerobic digestion process for methane production with cerium chloride modified biochar was optimized.In addition,biogas residue containing carbon and Ce³⁺,as a by-product of anaerobic digestion,was used for resource utilization.By preparing biogas residue biochar（BSB）,the process of enhancing methane production from anaerobic digestion with adding BSB was studied.The main results were as follows:（1）The effects of biochar and Ce³⁺co-addition on anaerobic digestion of mushroom bran were investigated under the condition of composting pretreatment.The gas production results showed that CP could shorten the lag phase of reaction,then biochar+Ce³⁺further synergistically enhanced CH₄ production.The cumulative CH₄ yield of the biochar+Ce³⁺group reached 69.69 m L/g VS,which was 22.3%,4.4%,16.2%,17.1%,and 5.7%higher than the production rates of CK,CK-char,DF,DF-char,and DF-Ce,respectively.The high-throughput sequencing analysis revealed that CP increased bacterial richness and diversity,and the co-addition of biochar+Ce³⁺was beneficial to the growth of Syntrophomonadaceae,Anaerolineaceae and Ruminococcaceae species.Hence,following composting pretreatment（CP）,biochar and Ce³⁺worked synergistically to increase CH₄production.（2）The results of enhancing anaerobic digestion of biogas with adding cerium chloride modified biochar showed that:（1）Generally speaking,the enhancement effect of cerium chloride modified biochar without Na OH activation is basically better than that of activated biochar with Na OH.The results indicated that the modified biochar that was not activated by Na OH was more beneficial to enhancment of methane production of anaerobic digestion.（2）When the concentration of Ce³⁺in the biochar modified by cerium chloride was 0.3μmo L/L,the cumulative biogas production and methane production were 302.33 m L/g VS and 139.18 m L/g VS,respectively,which increased by 19.65%and25.85%compared with the control group,respectively.The above results showed that the best Ce³⁺dosage for preparing cerium chloride modified biochar was 0.3μmo L/L.（3）Adding biochar modified by cerium chloride prepared at 500℃,adopting inoculum（1）,the cumulative gas production of biogas and methane reached 280.05 m L/g VS and 134.63 m L/g VS,respectively,which increased by 13.68%and 14.35%compared with the control group,respectively.This result showed that 500℃was the best pyrolysis temperature of the biochar modified by cerium chloride.（4）When the treatment group（adding biochar modified by rare earth cerium prepared at 500℃）adopted inoculum（2）,the cumulative biogas production was slightly higher than that of the other groups,and also increased by 4.1%compared with the control group,but it was significantly lower than that of the adopted inoculum（1）.This indicated that the enhancement of anaerobic digestion by adding biochar modified by cerium chloride was not only affected by its own characteristics,but also by different inoculums.（3）Biochar from biogas residue was applied to anaerobic digestion,and two inoculants were used for comparison.The results showed that when adding inoculum（1）,the biochar from biogas residue prepared at 400℃had the best enhancement effect on anaerobic digestion.The cumulative biogas production and the cumulative methane production reached 448.33 m L/g VS and 204.47 m L/g VS,respectively.Compared with the control group,they increased by 24.81%and 24.31%,respectively.When adding inoculum（2）,the biochar from biogas residue prepared at 550℃had the best enhancement effect on anaerobic digestion.The cumulative biogas production and the cumulative methane production reached 313.69 m L/g VS and 136.76 m L/g VS,respectively,which increased by13.34%and 13.22%,respectively,compared with the control group.It indicated that the biogas residue,a by-product of anaerobic digestion,can still be charred again to effectively improve the methane production,and the inoculum will also have an impact on the enhancement of anaerobic digestion by biochar from biogas residue.However,under different inoculation conditions,the optimal pyrolysis temperature of biochar was different,and the specific reasons still needed to be further explored.（4）The characterization analysis results of biochar from biogas residue showed that,with the increase of pyrolysis temperature,the pores of 2-5 nm were more,the specific surface area was larger.However,the results of biogas and methane production showed that the enhancement effect of methane production was not increased with increasing temperature,which indicated that the specific surface area was not the most important factor affecting the gas production efficiency.Furthermore,the biogas residue biochar prepared at 400-600℃had relatively abundant functional groups,and the absorption peak intensity at the wave number of 2360 cm^-1was the largest.