The Performance Of Agsbr For Swine Wastewater Treatment And Its Mechanism For Antibiotic Removal

At present,with the rapid economic growth and the improvement of living standards,people's demand for livestock and poultry products has gradually increased,and large-scale livestock and poultry farming has produced a large number of livestock and poultry wastewater.The wastewater contains high concentration of chemical oxygen demand?COD?,ammonia nitrogen?NH₄⁺-N?,total phosphorus?TP?and antibiotic contaminants.It discharges into the receiving water body will bring potential hazards to the ecological environment and human health.The existing treatment process has good removal effect on conventional organic matt er,however,the removal of ammonia nitrogen,phosphorus and antibiotics are still difficult.In view of the difficult removal of antibiotic organic matters in this kind of wastewater,it is imperative to develop efficient and economical water treatment technology.In this study,the aerobic granular sludge?AGS?combined with sequencing batch reactor?SBR?to form AGSBR was proposed to treat this kind of wastewater.The effect of decontamination in AGSBR and the performance of AGS were investigated.The mechanism of removal of tetracycline?TC?and oxytetracycline?OTC?by AGS were studied in depth.AGS was cultured simultaneously in membrane bioreactor?MBR?and SBR.The results showed that AGS obtained by SBR took shorter time,better morphology and settlement performance.Therefore,the mature AGS was domesticated and cultured by inoculating frozen storage granular sludge and common activated sludge in SBR,respectively.After 22 days of operation,the structure of AGS formed by domestication of frozen granular sludge was compact and its edge was smooth.The value of mixed liquid suspended solids?MLSS?exceeded 8 g/L,and the sludge volume index?SVI?reached 37 mL/g.The removal rates of COD,NH₄⁺-N and TP were all over 90%.The reactor inoculated with activated sludge operated for 54 days to obtain AGS in good shape.Compared with the former,its sludge performance and decontamination efficiency were lower.The results showed that the AGSBR can be started quickly by using frozen stored granular sludge as inoculated sludge.The AGSBR parameters were further optimized to achieve the goal of efficient treatment of livestock and poultry wastewater.When the shear stress was 1.86 cm/s,the removal rates of COD,NH₄⁺-N and TP by AGSBR process were 94.0%,79.0%and 90.0%respectively.AGS with the best morphology and performance can be obtained under this condition,its MLSS and SVI values were 6.0 g/L and 35.0 mL/g,respectively.Optimizing AGSBR under different influent C/N ratio.At this time,the concentration of influent pollutants was higher than that befor,when C/N ratio was 8,AGS with better morphology and performance was formed.Its MLSS and SVI values reached 6.0 g/L and 55.3 mL/g respectively.The removal rates of COD,NH₄⁺-N and TP were 96.0%,88.0%and 75.0%,respectively.At this time,the removal effect of nitrogen and phosphorus were poor,therefore the AGSBR was further optimized under different hydraulic retention time?HRT?conditions.When the HRT was 4 h,the AGS had better adaptability to wastewater.The removal rates of COD,NH₄⁺-N and TP by AGSBR process were 96.0%,93.2%and 89.3%respectively.The effluent concentration of pollutants reached the standard of"Discharge standard of pollutants forlivestock and poultry breeding".The settlement performance of AGS obtained at this time was good,and the MLSS and SVI values were 8 g/L and 44.5 mL/g,respectively.Using the optimized condition parameters,AGSBR was applied to treat simulated and actual swine wastewater,and its treatment efficiency and operation stability were investigated.The results showed that the AGSBR operated steadily in the treatment of simulated wastewater,however,the biomasses of AGS in two reactors were significantly different.MLSS in TC-containing and OTC-containing reactors were 5.8 g/L and 8.6 g/L,respectively.While there was little difference in the removal efficiency of pollutants,the removal efficiencies of COD,NH₄⁺-N and TP were over98%,87%,98%respectively,and the removal efficiencies of TC and OTC were 90%and 89%,respectively.The results showed that the resistant microorganisms in the two reactors were Proteobacteria,Bacteroidetes,Actinobacteria;?-proteobacteria,?-Proteobacteria,Actinobacteria;Comamonas,Ottowia,Fluviicola.In addition,using methanol,starch and sucrose as supplementary carbon sources for treatment the actual wastewater from pig farms with the AGSBR process.The results showed that the AGSBR process had the best treatment effect when sucrose was used as supplementary carbon source.The removal rates of COD,NH₄⁺-N and TP were96.83%,81.14%and 97.37%respectively.The effluent concentrations were lower than the limit value of"Discharge standard of pollutants forlivestock and poultry breeding"?GB/T18596-2001?.The removal rates of TC and OTC were 81.4%and80.7%respectively,and the AGS had good shape,its MLSS and SVI were 12.65 g/L and 29.23 mL/g,respectively.The adsorption and degradation kinetics of AGS on TC and OTC were studied in order to elucidate the removal mechanism.The results showed that the removal process of TC and OTC by AGS was dominated by adsorption in the early stage and degradation in the later stage.The highest contribution ratios of adsorption in AGS to TC and OTC before domestication were 0.70 and 0.72,while the highest contribution ratios of degradation in AGS to TC and OTC after domestication were 0.88 and 0.72.When the sludge concentration were 15 g/L and 10 g/L,the AGS had the best removal effect on TC and OTC,which was related to the competition between microorganisms.In addition,AGS had better mineralization of TC and OTC.Total organic carbon?TOC?removal rates of the two antibiotics were 71.8%and 70.9%,respectively.The intermediate products of TC and OTC were detected.22 intermediate products of TC and 13 intermediate products of OTC were found,and the degradation pathways of TC and OTC were speculated and analyzed.Finally,the differences of functional bacteria,functional genes and metabolic pathways in the degradation of TC and OTC by AGS were investigated by using macrogenome detection technology,and the mechanism of AGS degradation of target pollutants was revealed.During the degradation of TC by AGS,there were significant differences in microorganisms?P<0.05?,including Sphingopyxis,Ruminococcus,Fluviicola and so on,while in the degradation of OTC,there were significant differences in microorganisms including Leclercia,Haloferula,Sphingopyxis and so on.Polysaccharide lyases,auxiliary activities and glycosyl transferases play dehydrogenation,oxidation and glycosylation roles in the degradation of OTC.It is suggested that the degradation of TC and OTC by microorganisms in AGS not only have the same metabolic pathways,but also have their own special metabolic pathways,and the enzymes that play different roles in the same metabolic pathways were also different.Naphthalene 1,2-dioxygenase plays a key role in the degradation of aromatic intermediates of TC and OTC.Alcohol dehydrogenase plays an important role in the conversion of aliphatic alcohols,aromatic alcohols intermediates and corresponding aldehydes and ketones during the degradation of TC.Aldehyde reductase plays an important role in the conversion of aldehydes into alcohols during the degradation of OTC.The research results in this study will have important theoretical reference and guiding significance for AGSBR process to treat actual livestock and poultry wastewater to the efficient treatment of livestock and poultry wastewater.