| With the process of urbanization in my country,the amount of domestic sewage discharged and treated is increasing,which is also accompanied by the production of a large amount of sewage sludge(SS).Anaerobic digestion technology can realize the stabilization and reduction of sludge as well as the recovery and utilization of energy.Due to the shortcomings of SS in my country,such as low C/N ratio and low hydrolysis efficiency,the efficiency of methane production in anaerobic digestion of the surplus sludge is low.Food waste(FW)contains a large number of easily biodegradable substances,which makes the anaerobic digestion system easy to acidify.The combined anaerobic digestion of SS and FW has a better C/N ratio,which can improve the methane production rate and system stability.However,due to the variable nature of municipal organic waste,the combined anaerobic digestion of SS and FW may also appear acid inhibition phenomenon because the optimal mixing ratio is difficult to determine.A large number of studies have shown that biochar can improve the efficiency and stability of anaerobic digestion system.However,different biochar have different effects on anaerobic digestion system,and the mechanism of biochar improving digestion efficiency is uncertain.Plant wastes are one of the main raw materials for biochar preparation.And shrimp shell is one of the common FW in daily life.It contains a lot of crude fat,crude protein,calcium protein,polysaccharide and so on,which is an ideal material for preparing carbon materials.In this study,plant biochar and animal biochar were prepared from pine sawdust and shrimp shell,respectively.The effects of biochar on the combined anaerobic digestion of SS and FW under different acid inhibition conditions and the potential mechanism were studied.And the effects of pine sawdust biochar(PB)and shrimp shell biochar(SB)on each stage of anaerobic digestion were studied using dextran as a single substrate.In this study,pine sawdust and shrimp shells were used as raw materials to prepare biochar.The preparation conditions are as follows:the temperature rise rate is 15°C/min from room temperature to 600°C,and nitrogen is used as a protective gas for cracking at600°C for 2 hours.BET specific surface area of PB and SB were 32.6 m~2/g and 303.8m~2/g respectively,and electrical conductivity were 0.62μS/cm and 3.33μS/cm respectively.The p H values of PB and SB are 7.42 and 9.90,respectively.Both biochar contained abundant alkali metals(Na,K),alkaline earth metals(Ca,Mg)and alkaline functional groups.The two biochar had good buffering ability to typical volatile fatty acids(VFA),and the SB had stronger buffering ability to acid than PB.Then,PB and SB were added to the combined anaerobic digestion system of SS and FW in different acid-inhibited environments at a dosage of 1.5 g/g·VS(25 g/L)to investigate the effects of biochar on the anaerobic digestion system.The results showed that when the ratio of volatile solids(VS)of SS to FW was 1:1(group A),the cumulative specific methane production of blank group(A0),group with PB(A1)and group with SB(A2)were 302.0 mL/g·VS,303.9 mL/g·VS and 308.9 mL/g·VS,respectively.When the ratio of VS of SS to FW was 1:2(group B),the cumulative specific methane production of blank group(B0),group with PB(B1)and group with SB(B2)were 247.9 mL/g·VS,280.9 mL/g·VS and 280.0 mL/g·VS,respectively.The addition of PB and SB shortened the lag period of group A from 10.2 days(A0)to 6.3 days(A1)and 3.5 days(A2)respectively,and the lag period of group B from 12.1 days(B0)to 10.8 days(B1)and 4.6days(B2)respectively.The methane content in each reactor increased to different degrees,from 59.95%(A0)to 57.23%(A1)and 66.26%(A2),and from 55.19%(B0)to 60.94%(B1)and 61.14%(B2).The buffer capacity of biochar alleviates the acid inhibition in the system.The minimum p H value of group A was increased from 5.7(A0)to 5.9(A1)and6.6(A2),and the minimum p H value of group B was increased from 5.3(B0)to 5.6(B1)and 6.3(B2).The p H recovery was accelerated and the stability of the system was improved.In addition,the addition of biochar accelerated the degradation of VFA.The total VFA concentration of A0,A1 and A2 reactors decreased below 200 mg/L on the36th,30th and 18th day,respectively.Until the end of the experiment,there were 867.5mg/L,225.1 mg/L and 33.0 mg/L of VFA in the reactors B0,B1 and B2,respectively.Analysis of the microbial community structure found that the addition of biochar changed the microbial community.By analyzing the microbial community,it was found that the addition of biochar changed the microbial community.The difference of microbial communities between SB groups(A2,B2)and blank groups(A0,B0)was significantly greater than that between PB groups(A1,B1).The enrichment of Synergistota,Methanosaeta and Methanosarcina was observed in shrimp shell biochar(A2 and B2),suggesting that direct interspecific electron transfer may have occurred.Finally,using dextran as a single substrate,the effects of PB(25 g/L)and SB(25g/L)on each stage of anaerobic digestion were investigated.The results showed that the addition of PB and SB increased the biogas yield and methane yield in the anaerobic digestion of dextran.Compared with the blank group,the biogas production of the PB group and the SB group increased by 55.6%and 21.0%,respectively,and the methane production increased by 15.3 times and 17.3 times,respectively.PB had a certain inhibitory effect on the hydrolysis and acidification process of dextran anaerobic digestion,but promoted the methane production process.SB had a certain inhibitory effect on the hydrolysis process of dextran,but promoted the acidification and methanogenesis.The methanogenic efficiency in methanogenic stage of the PB group and the SB group were 8.8 and 7.9 times that of the blank group,respectively.In the methanogenic stage,the presence of Synergistota and the enrichment of Methanosarcina in the reactor added with biochar may stimulate the occurrence of direct interspecific electron transfer,so as to improve the methanogenic performance. |
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