| Coking wastewater is a characteristic organic wastewater produced in the process of coal coking,which has the characteristics of high COD concentration and biodegradation.At present,the coking wastewater is mainly treated by biological treatment process.The effect of anaerobic biological treatment has been poor.In the early,the previous research results show that there were obstacles in the process of anaerobic treatment of coking wastewater,which made it difficult for the system to complete the process of methane production.However,the characteristics of the inhibition stage and the mechanism of the inhibition are not clear.In view of this,this study,based on the spatial separation of hydrolytic acidification bacteria and methanogenic archaea,constructed a two-phase anaerobic bioreactor for the separation of hydrolytic acidification phase and methanogenic phase.The performance of anaerobic treatment of coking wastewater under different conditions was investigated.Combined with the characteristics of sludge and the analysis of microbial community structure,the inhibition stage of anaerobic treatment of coking wastewater was clarified and its inhibition mechanism was explored.The main research conclusions are as follows:(1)Through the experimental study on the performance of the two-phase anaerobic reactor for the treatment of coking wastewater,it was found that: When the influent COD concentration increased from 500mg/L to 1000mg/L,the VFA of hydrolytic acidification phase decreased from 119.73mg/L to 61.61mg/L,and methane production of methanogenic phase decreased from 124 m L/d to 69 m L/d.Acid protease activity decreased from 6.562 nmol/min/g fresh weight to 3.280nmol/min/g fresh weight.The activity of acetic acid kinase decreased from 0.289umol/min/g fresh weight to 0.0214umol/min/g fresh weight.This indicates that the coking wastewater can not produce methane normally and hydrolytic acidification phase was inhibited.(2)When the HRT of the system increased from 16h to 24h and 48h,the VFA of hydrolytic acidification phase decreased to 43.44mg/L and 31.41mg/L continuously,indicating that the accumulation of VFA in hydrolytic acidification phase has not been improved.By comparing the characteristics of water in and out of hydrolytic acidification phase,it was found that the small molecular weight phenols were effectively degraded.However,the increment of sulfide and ammonia nitrogen in hydrolytic acidification phase decreased continuously,suggesting that nitrogen-heterocyclic organic compounds and thiocyclic organic compounds had not been hydrolyzed effectively.These results indicate that the low accumulation of VFA in the hydrolytic acidification phase of coking wastewater is not caused by the slow degradation rate of organic matter.(3)The preliminary analysis of organic matter composition in the sludge phase showed that there were more and more kinds of macromolecular organic matter containing nitrogen,sulfur and other groups in the sludge phase,and the structure became more and more complex.This indicates that a large amount of organic substances adsorbed in the sludge phase inhibit the activity of hydrolytic acidifying bacteria,resulting in the prolonged HRT of the system and the failure to effectively improve the accumulation of VFA in the hydrolytic acidification phase.In addition,these types of organic matter also absorbed by sludge in the methanogenic phase in the process of extending HRT,which lead to the inhibition of methanogenic bacteria activity,so that the generation of methane gas could not be detected in the system.(4)The analysis of microbial community structure showed that the total abundance of acetogenic bacteria Bacteroidota,Proteobacteria and Firmicutes in the phylum level of hydrolytic acidification phase decreased from 77.10% to 64.63%.Actinobacteriota and Bacteroidota produced propionic acid,which decreased from48.43% to 11.75%,and both of them were inhibited by the toxicity of organic matter adsorbed by sludge.This resulted in a decrease in the yield of acetic acid and propionic acid in hydrolytic acidification phase.At the genus level of hydrolytic acidification phase,Ottowia,Comamonas and Pseudomonas could degrade phenols and nitrogen-heterocyclic organics,which only existed in the environment of coking wastewater,and the total abundance decreased from 13.14% to 2.38%,resulting in the ineffective degradation of nitrogen and sulfur containing organics.(5)At the genus level of methanogenic phase,Methanosaeta and Methanosarcina are acetic acid-trophic methanogens.The total abundance was77.74% at the initial phase,and it was less than 40% after the introduction of coking wastewater.Methanobacterium and Methanolinea are hydrogen-trophic methanogens.The total abundance increased(44.81%-74.14%)after the introduction of coking wastewater,which was greater than the abundance of acetic acid-trophic methanogens.The decrease of acetic acid production in hydrolytic acidification phase resulted in the predominance of hydrogen-trophic methanogens. |
