| Pyridine,as a typical hazardous and recalcitrant contaminant with its toxic,teratogenic and carcinogenic properties,was widely used in chemical industries,leading to severe environmental pollution.Anaerobic and aerobic bioprocesses have been recognized as relatively economical and environmentally friendly methods for treating industrial wastewater,as compared to various physicochemical methods.Nonetheless,owing to the structural stability and volatile property of pyridine,traditional anaerobic and aerobic biological treatments were faced with low efficiency and air pollution risks respectively.Therefore,to fundamentally solve the problems of volatilization of pollutants and high cost under traditional bubble aeration,it is necessary to develop a novel oxygen supply strategy to replace traditional bubble aeration.In this study,an algal-bacterial symbiosis system that could utilize light energy to produce oxygen coupled with the aerobic degradation of pyridine was developed,and a dynamic membrane photobioreactor（DMPBR）was designed and operated.The stability of pyridine degradation by the algal-bacterial system was verified in the DMPBR.According to the determined intermediate products,the mechanism of pyridine degradation by the algal-bacterial system was proposed;An external-loop split-type dynamic membrane photobioreactor（ESDMPBR）was proposed for treating high-strength pyridine wastewater,resulting in improved photosynthetic oxygenation and mitigated membrane fouling;An algal-bacterial sludge system（ABS）was rapidly developed by inoculation of algal-bacterial consortia,and the simultaneous pyridine degradation and nitrogen removal could be realized.Furthermore,metatranscriptional analysis and the key enzymatic activity assays were performed to reveal and verify the proposed microbial metabolic mechanism and the fate of nitrogen involved in the simultaneous pyridine biodegradation and nitrogen removal.Aerobic pyridine biodegradation,which has been proven to be efficient,was often limited by serious air pollution caused by high pyridine volatilization under traditional bubble aeration.In this study,a feasible oxygen supply strategy was developed through the coupling of an alga namely Chlorella sorokiniana FACHB-275 into the aerobic biodegradation system inoculated with a pyridine-degrading bacterium namely Paracoccus sp.NJUST47.The results indicated that dissolved oxygen（DO）concentration in this algal-bacterial symbiotic system could reach as high as 7.3±0.4 mg·L-1 under light.Pyridine could be completely removed at initial concentration of 125 mg·L-1 within 108 h in Chlorella-Paracoccus coupled system,while pyridine removal in Chlorella-only system was negligible and pyridine removal efficiency in Paracoccus-only system was as low as 38.2±1.3%.Mutualistic symbiosis between Chlorella and Paracoccus,including utilization of NH4+released from pyridine biodegradation by Chlorella and utilization of O2 produced through photo-oxygenation by Paracoccus,led to the accelerated growth of both Chlorella and Paracoccus.Furthermore,the favorable long-term operational stability of Chlorella-Paracoccus coupled system was verified in a DMPBR.Moreover,based on the identified intermediates,possible pyridine biodegradation mechanism involved in Chlorella-Paracoccus coupled system was proposed.In order to avoid pyridine volatilization in the conventional aerobic system based on bubble aeration,an algal-bacterial symbiotic system based on photosynthetic oxygenation was developed.Nonetheless,pyridine at high concentration would inhibit algal growth and photosynthetic activity,and thus decrease oxygen production efficiency.An external-loop split-type dynamic membrane photobioreactor system was proposed for treating high-strength pyridine wastewater,which consisted of a pyridine degrading reactor(R1-1),and an algal-bacterial dynamic membrane bioreactor(R1-2)for the photosynthetic oxygenation.The results showed that pyridine could be effectively removed at the influent concentration as high as 500mg·L-1 at the hydraulic retention time of 48 h.Preferable algal growth and photosynthetic activity were retained in R1-2,with Fv/Fm maintained at 0.502±0.013 at the influent pyridine concentration of 500 mg·L-1.The decreased reactive oxygen species and malondialdehyde level as well as the relatively low catalase and superoxide dismutase activities also revealed the alleviation of oxidative stress in algae.The mitigated membrane fouling was due to reduced protein/polysaccharide ratio in the extracellular polymeric substances in the mixed liquor and fouling layer in R1-2.Rhodobacter and Rhodococcus were the dominant genus in R1-1 and R1-2,and Chlorella was enriched in R1-2,responsible for pyridine degradation and oxygen production.Algal-bacterial symbiotic system has been suggested for wastewater treatment with no bubble aeration.In this study,an algal-bacterial sludge system（ABS）was rapidly developed by inoculation of algal-bacterial consortia and continuously operated for 72 days to achieve simultaneous pyridine biodegradation and biological nitrogen removal.As high as 150 mg·L-1pyridine could be thoroughly removed in the ABS system at hydraulic residence time（HRT）of48 h,while TN removal efficiency could be maintained at 80%approximately.Furthermore,comprehensive bioprocesses in ABS system mainly including photosynthesis,pyridine biodegradation,assimilation of carbon and nitrogen,and nitrification-denitrification were revealed at metabolic and transcriptional levels.Especially,nitrification-denitrification was verified as a crucial process for nitrogen removal(accounting for 79.3%of TN removal at 180μmol·m-2·s-1)and denitrification could also participate in the biodegradation of pyridine and its intermediates in ABS system.Emissions of ABS system mainly consisted of algal-bacterial biomass,O2 and N2 without the requirement of additional carbon and nitrogen source.In addition,the micro-environment with DO and pH gradients of algal-bacterial floc was suggested for simultaneous aerobic and anoxic bioprocesses. |
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