Enhanced Anaerobic Degradation Of Nitrogen Heterocyclic Compounds By Carrier Coupled With Co-metabolism Substance

There are many kinds of toxic and refractory organic compounds in coal pyrolysis wastewater.Nitrogen heterocyclic compounds(NHCs)are typical organic pollutants with high concentration and high toxicity in coal pyrolysis wastewater.They have obvious biological toxicity inhibition effect on the growth and metabolism of microorganism in sludge,which seriously affects the treatment effect and stability of the biochemical treatment unit of coal pyrolysis wastewater.In the treatment of high concentration,toxic and refractory organic compounds,anaerobic process has some advantages.Exploring efficient and feasible enhanced anaerobic technology,so as to achieve the effective removal of NHCs,has become a necessary condition to ensure the high efficiency and stability of biochemical treatment unit in the treatment of coal pyrolysis wastewater.This subject takes the enhanced anaerobic degradation of NHCs in coal pyrolysis wastewater as the main line.Polyurethane(PU)carriers,Fe₃O₄@PU and Fe₃O₄@PU coupling sodium citrate are used as the enhanced means of anaerobic system.Under the enhanced anaerobic conditions,the degradation efficiency and degradation mechanism of NHCs were explored.Furthermore,the influence of different enhanced methods on the community structure of anaerobic microorganisms was further investigated,and the functional bacteria genus involved in the degradation process of NHCs was explored.This subject can provide theoretical basis and technical support for solving the problem in the treatment of coal pyrolysis wastewater.When the concentration of quinoline,pyridine and indole was 100 mg/L,the degradation ratios of NHCs in different anaerobic devices showed great differences.PU carrier has more advantages than powdered activated carbon(PAC)in enhancing the degradation of quinoline,pyridine and indole.Due to the addition of PU,the degradation ratio of pyridine was 50.33%in the anaerobic device,which was much higher than 10.99%in the control group.The addition of PU could improve the flocculation ability of anaerobic sludge and lay a solid foundation for the efficient degradation of pollutants.Acinetobacter,Comamonas,Levinea,Longilinea and Desulfomicrobium enriched on PU were the main functional bacteria to degrade NHCs.Due to the enhancement of Fe₃O₄@PU,the concentration of quinoline,pyridine and indole in the anaerobic bottle could be degraded from 101.14±1.33mg/L to 3.03±0.45 mg/L,from 101.13±1.24 mg/L to 10.99±0.89 mg/L and from100.28±1.21 mg/L to 0.30±0.17 mg/L.The corresponding removal ratios were97.00%,89.13%and 99.70%,respectively.The initial Fe content on the surface of Fe₃O₄@PU was 14.25%,and the Fe content was still 3.70%after 160 days of operation,which fully shows that the prepared carrier has good service durability.The anaerobic degradation of NHCs was firstly the hydrogenation reduction reaction on the nitrogen heterocyclic,in which the carbon-nitrogen double bond was reduced to the carbon-nitrogen single bond.Then the resulting carbon-nitrogen single bond was broken,and the nitrogen heterocycles were opened.Then the amino group on the benzene ring was broken,and the generated NH₃-N was released into the solution,resulting in the increase of NH₃-N concentration.Then the benzene ring was opened,and eventually the short chain olefin was formed.In the reaction,the increased value of NH₃-N concentration can indirectly reflect the degree of anaerobic hydrolysis of NHCs.The addition of Fe₃O₄@PU not only increased the hydrogenation and methylation rates of NHCs,but also increased the ring-opening rates of nitrogen heterocycles,benzene rings and the conversion rates of macromolecules to small molecules.The presence of Fe₃O₄can realize the rapid electron transfer and avoid the excessive accumulation of electrons in the degradation process of NHCs.At the same time,the addition of Fe₃O₄@PU can further enhance the detoxification effect of anaerobic microorganisms on NHCs.Under the effect of Fe₃O₄@PU,a large number of dominant bacteria were enriched in the anaerobic bottle.Moreover,the dominant bacteria were dispersed in a more comprehensive and balanced way,which was more favorable for the anaerobic bottle to adapt to the change of conditions.When the dosage was suitable,sodium citrate,chlorella,spirulina and sodium carboxymethyl cellulose(CMC)could enhance the anaerobic degradation of quinoline and indole.The degradation ratios of quinoline and indole in each bottle increased gradually when the concentration of co-metabolism substance increased from 50?g/L to 300?g/L.The addition of sodium citrate,chlorella,spirulina and CMC promoted the richness and diversity of bacterial community structure,and benefited the enrichment of some functional genera(Levilinea and Longilinea)responsible for the degradation of quinoline and indole.In enhanced anaerobic degradation of NHCs wastewater with these co-metabolic substances,acetic acid metabolism was the most dominant methane-producing mode,with a small amount of formic acid methanogenesis.The degradation efficiency of quinoline and indole was higher in the coupling process with sodium citrate and Fe₃O₄@PU.In the coupling process,the addition of Fe₃O₄@PU greatly promoted the effective enrichment of functional bacteria such as Giesbergeria,Acinetobacter and Aminicenantes.At the same time,the addition of sodium citrate provided a carbon source for functional bacteria,which was conducive to the enrichment and proliferation of these functional bacteria.Under the action of functional bacteria,the typical pollutants in coal pyrolysis wastewater successively underwent a series of reactions,such as hydrogenation reduction,ring opening by nitrogen heterocycle cracking,amino breaking,ring opening by benzene ring cracking and short chain olefin formation.In the treatment of simulated coal pyrolysis wastewater,Fe₃O₄@PU coupled with sodium citrate process had high removal effect on pollutants.The removal ratios of COD,total phenols,quinoline,pyridine and indole were 65.78%,65.22%,99.91%,85.23%and 99.95%,respectively.Fe₃O₄@PU coupled with sodium citrate process showed a good effect on the treatment of phenols and NHCs in coal pyrolysis wastewater.