| Monosodium glutamate wastewater with high sulfate,high ammonia nitrogen and high organic matter is a typical industrial wastewater.However,due to the inhibitory effect of ammonia nitrogen and sulfate on anaerobic digestion and the complex relationship between ammonia nitrogen and sulfate,it has been difficult to treat this type of industrial wastewater.In view of the difficult treatment of industrial wastewater with high sulfate,high ammonia nitrogen and high organic matter,taking simulated monosodium glutamate wastewater as the object,this study investigated the long-term operation performance changes of two UASB reactors under different influent conditions,combined with sludge characteristics and microbial community changes,summarized the metabolic path and microbial community changes,To explore the influence of different ammonia nitrogen concentration and different COD/SO42-ratio on the long-term operation performance of anaerobic digestion and analyze the inhibition reasons,so as to provide a theoretical basis for the actual treatment of typical industrial wastewater with high sulfate,high ammonia nitrogen and high organic matter.The main conclusions are as follows:(1)Two UASB reactors were continuously operated for 270 days under the condition of HRT=6 h.UASB reactor 1(F1)and UASB reactor 2(F2)can be divided into three stages according to different inlet water quality conditions.In the three research stages of F1,the influent ammonia nitrogen and sulfate concentrations are kept at 500 mg/L,and the influent COD concentration is gradually reduced(2000 mg/L,1000 mg/L,500 mg/L).During the three research stages of F2,influent COD concentration was kept constant at 2000 mg/L,and influent ammonia nitrogen and sulfate concentrations were gradually increased(500 mg/L,1000 mg/L,2000 mg/L).The long-term operation performance results of F1 show that there is only slight inhibition in F1-Ⅰ and F1-Ⅱ experimental stages,but obvious inhibition in F1-Ⅲexperimental stage,which is manifested as:gas production decreases,methane proportion in gas production component decreases from 80%to 60%,and COD removal rate decreases significantly(from 93%to 67%).The analysis shows that the low COD/SO42-value(COD/SO42-=1)is the main reason for the inhibition.The long-term operation results of F2 showed that only slight inhibition existed in F2-Ⅰ and F2-Ⅱ experimental stages,and significant inhibition appeared in F2-Ⅲ experimental stage,which were as follows:Gas production decreased from 16 mL/d to 2 mL/d,methane concentration decreased from 83%to 53%,and COD removal rate decreased significantly from 93%to 46%.The analysis shows that low COD/SO42-value(COD/SO42-=1)and inhibition of ammonia nitrogen toxicity are the main reasons for the performance decline.In addition,in F1-Ⅲ and F2-Ⅲ experimental stages,the proportion of nitrogen in the gas producing components increased significantly,indicating the emergence of nitrogen removal path.(2)When the ratio of COD/SO42-is greater than or equal to 2,the metabolic pathway of anaerobic digestion is dominated by acetic acid and butyric acid as intermediates.SRB mainly uses propionic acid and valerate acid as substrates for sulfate reduction,and hardly uses acetic acid for sulfate reduction.In the F1-Ⅲ experimental stage,the reduction of COD/SO42-ratio will further increase the types of sulfate metabolizing substrates,enrich the metabolic pathway of sulfate reduction,and the activity of using acetic acid to metabolize sulfate is significantly strengthened,which indicates that the competition between SRB and MPA and acetic acid is one of the reasons for the performance decline.In addition,with the decrease of COD/SO42-ratio,abundant substrate metabolic types of SRB lead to the metabolic pathway transformation to incomplete metabolism,which is also an important reason for the degradation of the operation performance of the reactor.In F2-Ⅲ,that is,when ammonia nitrogen concentration is equal to 2000 mg/L and COD/SO42-ratio is equal to 1,the ability of MPA to produce methane directly from acetic acid and methanol is obviously inhibited,while the SMA value of butyric acid is higher,indicating that the metabolic pathway activity of butyric acid is better,which may be related to the electron transport of methane production.(3)From the perspective of microorganisms,in F1,with the decrease of influent COD concentration,the abundance ratio of Synergistota gradually decreases,and that of Chloroflexi and Desulfobacterota gradually increases.This means that the sulfur autotrophic denitrification pathway appears and the sulfate reduction reaction is enhanced.Methanosaeta has a dominant abundance in the three stages of F1,indicating that the methane-producing pathway is still dominated by acetic acid metabolism.Methanbacterium has significantly increased its abundance in the stages of F1-Ⅲ,indicating that the methane-producing pathway using H2 and CO2 metabolism has begun to strengthen.In F2,with the increase of influent ammonia nitrogen and sulfate concentration,the abundance ratio of Synergistota increased first and then decreased,while that of Firmicutes increased significantly,which may be related to Firmicutes’ relatively high toxicity tolerance to ammonia nitrogen.The abundance of Methanosaeta in the three stages of F2 accounts for more than 90%,indicating that the metabolic path of methanogenesis is still dominated by acetic acid metabolism.Considering the serious accumulation of acetic acid during F2-III operation,it is indicated that SRB and MPA competing substrate(acetic acid)are not the main reason for the decrease of methanogenesis,but the more reason is that the toxicity of ammonia nitrogen leads to the decrease of methanogenesis performance. |
