Studies On The Removal Performance Of Organic Pollutants In Semi-coking Wastewater And The Biotransformation Characteristics Of Quinoline Organic Compounds

Semi-coking industry is an emerging and important part in coal-based energy and chemical industry.Semi-coking wastewater has complex quality,with various types and high concentration of organic pollutants mainly including phenol,naphthalene,phenanthrene,quinoline,pyrene,benzo[a]pyrene.These substances have poor biodegradability and great harm,which not only have a serious inhibitory effect on microorganisms,but also brings huge hidden dangers to human health and ecological environment.At present,there are many practical problems in the biochemical treatment system of semi-coking wastewater,which seriously affect sustainable and healthy development of coal chemical industry.For example,the sewage biochemical treatment system always operates unstably and the effluent is difficult to reach the standard.In view of the specific problems existing in the harmless treatment of semi-coking wastewater,on the premise of systematically analyzing the removal rules of different organic pollutants in each treatment unit duringn the process of semi-coking wastewater treatment,the efficient biological transformation of the typical nitrogen-containing heterocyclines quinoline in wastewater was emphatically studied in this study.On that basis,a biodegradation system of quinoline immobilized cells was constructed to effectively remove quinoline organic compounds from wastewater.The main research results are described as follows:(1)The removal characteristics of organic pollutants in different treatment units of semi-coking wastewater"physicochemical-biochemical"combined treatment process(raw sewage,total phenol extraction,ammonia nitrogen stripping,anaerobic treatment,aerobic treatment,coagulating sedimentation effluent)were quantitatively analyzed.The total concentration of 37 kinds of harmful organic pollutants quality detected in raw semi-coking wastewater including phenols,polycyclic aromatic hydrocarbons,benzene,quinoline,indoles,pyridines,anilines,hydrocarbons and furans was 4580.0 mg/L.(2)Different organics exhibtied varying removal effects in each treatment.Total of37 organics was effectively removed in the extraction stage,with a removal rate of82.72%.The benzene,phenol,pyridine and aniline compounds in wastewater were mainly removed via anaerobic and aerobic biodegradation,with a removal rate of78.07%.The effluent of the biochemical treatment unit still included residual quinoline and polycyclic aromatic hydrocarbons,with a total concentration of 203.8 mg/L.Through coagulation and precipitation,the COD concentration in the effluent was168±39 mg/L,the effuclent showed certain biological toxicity.(3)Aiming at the problem that nitrogen-containing heterocyclines in semi-coking wastewater are hardly effecitively removed,three dominant strains that can use quinoline as the only carbon source and nitrogen source were screened?identified and named as Bacillus sp.LH-1,Ochrobactrum sp.WC and Sphingobacterium sp.LX.Their tolerance to quinoline reached 600 mg/L.After induction,the degradation rates of quinoline by Bacillus sp.,Ochrobactrum sp.and Sphingobacterium sp.reached 23.696mg/(L·h),37.312 mg/(L·h)and 27.137 mg/(L·h),respectivley,which were 10-20 times higher than the values without induction.(4)The biological metabolism of quinoline were studied.In the process of quinoline were degraded by Ochrobactrum sp.WC bacteria,N was released so as to generate NH₄⁺-N and constitute cell material.Through detection,the degradation products included 2-hydroxyquinoline and 8-hydroxycoumarin.It is speculated that the degradation pathway is dominated by 8-hydroxycoumarin pathway,and intracellular enzyme was the main factor.Simultaneous addition of formic acid(0.1 mmol/L)and molybdenum ion(0.05 mmol/L)to the quinoline degradation system can significantly induce the enzyme activity and accelerate the metabolism of quinoline.The biodegradation effects of the three species of bacteria in the mixture of 1:1:1 were better than that of the pure bacteria.After the culturing for 6 hours under optimal conditions,the removal rate of the mixed bacteria to 300 mg/L quinoline reached 99.27%.(5)A novel ZnO NPs/PVA sponge composite immobilized carrier was prepared and a biodegradation system of quinoline was constructed.The analysis results showed that the degradation performance of the immobilized cells was significantly increased compared with that of the free cells.At an initial concentration of 500 mg/L,the quinoline degradation rate constant reached 0.4590 h^-1.After 30 times of reuse,the quinoline degradation rate of immobilized bacteria remained above 99.32%within 7hours,with good mechanical tolerance.(6)The quinoline degrading bacteria were mixed and immobilized with the polycyclic aromatic hydrocarbons(PAHs)degrading bacteria,and the immobilized cells were used for the deep treatment of coagulating sedimentation effluent in the combined treatment process of semi-coking wastewater.The results showed that the effluent COD was significantly reduced from 168 mg/L to 56 mg/L,and the aromatic organic compounds were effectively degraded,and the effluent could meet the discharge standards.