Study On Enhanced Removal Of Quinolones And Sulfonamides By The A~2/MBBR Process

Antibiotics is a kind of typical emerging contaminants.Due to the continuous importation into the environment,it has seriously been threatens to the safety of ecological environment and human health in recent years.In order to effectively reply environmental damage caused by antibiotics and other ECs,China included them in the List of ECs Strengthen Control（2021 edition）.The municipal wastewater treatment plants is one of the main sources of antibiotic pollution.Therefore,improving the antibiotics removal efficiency of WWTP have important practical significance for effective prevention antibiotic pollution and reducing their risks to the ecological environment.The anaerobic/anoxic/aerobic（A²/O）process has been widely used to treat urban wastewater.However,there are two key contradictions in meeting the removal of antibiotic.For example:1)A high sludge reflux ratio is required for high bioconcentration,but high reflux ratio of sludge will lead to excessive nitrate and dissolved oxygen in anaerobic zone and anoxic zone,which weakens the removal effect of pollutants such as antibiotics.2)The removal of pollutants is adversely affected because microorganisms with long generations（e.g.,nitrifying bacteria）and short generations（e.g.,phosphate-accumulating organisms）cannot dominantly coexist.Moving bed biofilm reactor（MBBR）is double sludge system with high biological concentration,and biofilm has the conditions for microbial enrichment.So MBBR as an optimization strategy for secondary biochemical treatment of A²/O may compensate for the above deficiencies and improve the removal effect of antibiotics.In this study,the A²/MBBR process was investigated to enhance the removal of quinolones and sulfonamides antibiotics from actual wastewater.The crucial conclusions obtained were as follows.（1）The removal mechanism by the A²/O process was clarified.Biosorption and biodegradation had an effect on removal of ofloxacin（OFL）,and the former was slightly larger.For sulfamethoxazole（SMX）,biotransformation played a dominant role,and adsorption was almost negligible.In addition,biological decomposition of OFL and SMX was mainly accomplished in the oxic tank,it was key that enhanceing the biodegradation at this stage to improve the antibiotc removal efficiency of the A²/O process.（2）The biodegradation of OFL and SMX by MBBR followed the pseudo-first-order kinetic model,and the TSS normalized degradation rate constants was 0.003±0.0005 L·（g·h）^-1and0.012±0.0025 L·（g·h）^-1,respectively.The biodegradation of SMX by MBBR is mainly throμgh acetylation and hydroxylation at 17 N,hydroxylation at 4C and bond breaking at 7S-10N and 10N-13C.The transformation products mainly included N-acetyl sulfamethoxazole,N-hydrocarbyl sulfamethoxazole,4-hydrocarbyl sulfamethoxazole and 3-amino-5-methyl isooxazole,etc.（3）The effluent quality and stability of the A²/MBBR process were better than that of A²/O process when exposed to norfloxacin（NOR）.The protein and polysaccharide content in EPS extracted from biofilm were promoted by MBBR.And,MBBR promoted the accumulation and enrichment of microorganisms that can degrade antibiotics,which provided a microguarantee for A²/MBBR process to have good tolerance to antibiotics.（4）The enhancement effect of MBBR is mainly reflected in biodegradation.The actual wastewater verification study showed that the removal rates of OFL and SMX by A²/MBBR process was 30.0%and 53.3%,respectively,which was 12.3%and 24.7%higher than that of A²/O process,respectively.Meanwhile,the biodegradation of OFL and SMX was 13.9%and52.4%,respectively,which increased by 7.7%and 26.7%,respectively.（5）High-throμghput sequencing analysis showed that MBBR realized the coexistence of microorganisms with different generations as dominant species.The relative abundance of Acinetobacter,Pseudomonas,Aeromonas,Dokdonella and Nitrospira in biofilms were significantly more abundant than that in sludge,indicating that MBBR was conducive to the accumulation and enrichment of these bacteria.The degradation effect of OFL and SMX process was promoted by the A²/MBBR process.