| Quinoline and indole are easily diffusible and highly toxic nitrogen heterocyclic compounds(NHCs),which have the risk of carcinogenic,teratogenic,and mutagenic to the human body.NHCs exist in industrial wastewater such as coking and coal pyrolysis.Due to the steric hindrance of its bicyclic fused structure,long photooxidation half-life,and high biological toxicity,the problems of ring cleavage rate limitation and high biological toxicity are commonly encountered in biodegradation.The C/N ratio of coking wastewater containing NHCs is high.When traditional biological processes are used,the carbon source in the denitrification stage is excessive,and the biodegradation efficiency is low.The potential of organic matter degradation is not fully utilized,and the current advanced treatment technology is expensive,making it difficult to remove NHCs harmlessly.The biological treatment of such industrial wastewater mostly uses biological and deep physicochemical units for treatment,which ultimately leads to high COD and total nitrogen concentrations in the effluent,making it difficult to remove NHCs innocuously.In this paper,the process theory of coupling SO4-· preoxidation with anaerobic biodegradation of NHCs is constructed,which based on the molecular double-ring condensed structure of NHCs and the characteristics of persulfate reduction products,and the anaerobic biological removal system of NHCs is enhanced by providing electron acceptor with persulfate preoxidation.With quinoline/indole with different heterocycle sizes and conglutination degrees as the research object,the effect of different persulfate excitation methods on quinoline/indole cleavage.To reveal the mechanism of NHCs ringopening/carbon nitrogen transformation and electron acceptor transfer;To establish the transport pathway between electron acceptor and donor of sulfate-reducing bacteria(SRB),heterotrophic denitrifying bacteria(hNRB)and anaerobic fermentation acidogenic bacteria(AFB),and explore the effects of residual oxides and pyrolysis products on the activity of typical functional microorganisms;Analyze the ecological network of microbial interaction and interaction of "SRB-hNRB-AFB" to strengthen anaerobic biological removal of NHCs,clarify the coupling mechanism of chemical oxidation and biodegradation,and provide a theoretical basis for promoting the treatment of refractory industrial organic wastewater.(1)In response to the issue of the fused heterocyclic structure and high biological toxicity of NHCs that are difficult to be degraded by microorganisms,ultrasound(US)enhanced sulfate radical(SO4-·)preoxidation technology was introduced to degrade NHCs.Adding 0.7 g/L ZVI and 2.4 mmol/LPS under initial pH values of 7 and 200 W ultrasound,the degradation rates of 1 mmol/L quinoline and indole reached 98.37%and 99.02%respectively after 21 minutes.Compared to individual ZVI and PS degradation,US increased the quinoline degradation rate from 93.21%to 98.37%,and increased the indole degradation rate from 94.42%to 99.02%.US could accelerate the stripping of ZVI oxide layer,increasing the ion iron concentration in the system by 27.64%,and promoting the decomposition of PS to produce SO4-·.The routes of quinoline preoxidation include hydroxylation,pyridine ring opening,benzene ring breaking,etc;The main products of indole preoxidation are indole ketone,indigo red,and 3-methylindole.Therefore,the SR-AOPs composed of US/ZVI/PS accelerated the process of quinoline/indole heterocycle cleavage,removed its rate limiting step,reduces the biological toxicity of NHCs,and produced intermediate products that can provide electron acceptors and donors for the biodegradation process,which was expected to promote subsequent biodegradation.(2)To solve the problem of high carbon to nitrogen ratio in the biodegradation process of NHCs,a study was proposed to use the intermediate product carbon source of NHCs degradation in(1)as the electron donor for SRB sulfate reduction and hNRB denitrification,and to use SO4-· preoxidation by-products as SRB electron acceptors for synergistic metabolism of different functional bacterial communities.Enrichment and cultivation of SRBhNRB-AFB microbiota were carried out in a sequencing batch bioreactor.After 60 days of operation,the removal rates of SO42-and NO3-reached 81.69%and 99.19%,respectively,and the removal rate of COD reached 97.16%.The average degradation rates of quinoline and indole in the reactor were 43.93%and 25.97%,respectively,and the flora was inhibited by the toxicity of NHCs.Bacteroidetes,Sulfurovum,Bacteroidetes,Pseudomonas,Longilinea,etc.were detected,forming SRB-hNRB-AFB Anaerobic organism synergetic metabolism system.(3)To solve the problem of low efficiency in the degradation and utilization of NHCs by the SRB-hNRB-AFB microbial community in the sequencing batch reactor and the low performance of synergistic removal of carbon,nitrogen,and sulfur under continuous flow operation,expanded granular sludge bed and double layer filter material bioretention tank were made.The enriched and expanded SRB-hNRB-AFB microbial community in the sequencing batch reactor was inoculated into these two reactors.The removal rates of SO42and NO3-by EGSB reached over 85.21%and 99.07%,respectively.The average degradation rates of quinoline and indole by EGSB were 60.93%and 45.59%,while those by bilayer bioretention tanks were 45.89%and 26.90%,respectively.The latter had a large fluctuation range of effluent concentration,loose sludge particles,and filter materials were prone to loss.Taking into account the degradation ability of NHCs,stability of system operation,and resistance to hydraulic shock load,EGSB has obvious advantages.Therefore,EGSB was selected to load SRB-hNRB-AFB for the next stage of research.(4)SR-AOPs coupled EGSB degradation process was constructed to couple the preoxidation and biodegradation mentioned above.The average degradation rate of quinoline by the coupled process reached 99.78%,which is 1.64 times and 2.27 times higher than that of the EGSB and anaerobic sequencing batch reactors alone,respectively.The average degradation rate of indole by the coupling system reached 96.62%;98.71%and 95.51%of sulfate and nitrate nitrogen were removed.The functional bacterial communities SRB,AFB,and hNRB,were highly enriched in the SR-AOPs EGSB system.The Mass balance calculation of medium carbon,nitrogen,and sulfur in the coupling system confirmed the feasibility of the coupling process for NHCs degradation.Compared with the traditional biodegradation method,it solves the problems of pyridine cyclization,toxicity inhibition,and high energy consumption of quinoline/indole refractory toxic organic compounds,and fully utilizes the carbon source in NHCs. |
