Effects And Mechanisms Of NOR On Biological Phosphorus Removal And SCFA Production From Waste Activated Sludge Anaerobic Fermentation And Its Regulation

Antibiotics have played a major role in the treatment of human diseases,greatly improving the survival rate of human beings.However,in recent years,antibiotics have been intensively used for a long time in many fields such as medicine,aquaculture and agriculture,a large part of which cannot be completely absorbed and utilized?about 25%⁷5%of antibiotics cannot be metabolized?,causing continuous release into the environment.Therefore,the problem of antibiotic contamination is getting worse.Due to the exogenous characteristics,it was reported the normal metabolism and growth of organisms would be interfered under the exposure to antibiotics,causing toxic effects.The wastewater treatment plant?WWTP?is the last barrier for pollutants to enter into the water environment,thus it is considered as the main hotspot for the released antibiotics as a summary point of various sewage.At present,activated sludge microorganisms play a major role in the wastewater biological treatment,making important contribution to the removal of easily degradable organic matter,nitrogen and phosphorus.Traditional WWTP usually do not have a special process to effectively treat or degrade antibiotics.Therefore,the presence of antibiotics may have a potential effect on the stable operation of wastewater biological treatment.In addition,due to the strong adsorption and the relatively long sludge retention time of the activated sludge,antibiotics are often enriched and concentrated in the sludge during the wastewater biological treatment.Therefore,antibiotics may also have a potential impact on subsequent sludge treatment.Norfloxacin?NOR?,a representative third-generation fluoroquinolone antibiotic,has strong broad-spectrum antibacterial activity,low toxicity and high clinical efficacy and has been widely used in recent years.It was reported that there was trace amount of NOR in the wastewater and wastewater activated sludge,but the behavior of NOR on the physical-chemical properties of activated sludge and nutrient removal efficiency during the wastewater biological treatment as well as subsequent sludge resourceful utilization has not been investigated.The aims of this work was therefore to investigate the behavior of the physicochemical properties of activated sludge and phosphorus removal efficiency after long-term exposure as well as SCFA production of sludge anaerobic fermentation in the presence of NOR,and to reveal the potential effect and functional mechanisms of NOR on wastewater enhanced biological phosphorus removal and the anaerobic fermentation of sludge resourceful utilization.Firstly,this paper investigated the effect of long-term exposure to NOR on the physicochemical properties of activated sludge.The main factors of sludge extracellular polymer,sludge surface charge,relative hydrophobicity,bioflocculation,sludge sedimentation and dehydration were investigated before and after NOR exposure.The experimental results showed that lower concentration of NOR?10?g/L?had no significant effect on LB-EPS after long-term exposure.Long-term exposures of 100 and 500?g/LNOR promote the secretion of proteins and polysaccharides in LB-EPS,increasing their content.However,it has no effect on TB-EPS.Long-term exposure to different concentrations of NOR had no significant effect on the relative hydrophobicity and surface charge of the activated sludge.Higher concentrations of NOR?100 and 500?g/L?have an adverse effect on the flocculation capacity of activated sludge,and the adverse effects were particularly noticeable after long-term exposure with a NOR concentration of 500?g/L,and the effluent turbidity was significantly increased.After long-term exposure to higher concentrations of NOR?100 and 500?g/L?,the settleability and dewaterability of sludge has significantly deteriorated.The reason might be that the increase of LB-EPS content resulted in the increase of the interstitial water between sludge flocs,hindering the compression of the sludge flocs and the separation from the water.Based on the above research,the long-term effects of NOR on enhanced biological phosphorus removal were investigated simultaneously.The changes of biological phosphorus removal efficiency,intracellular polymer conversion,key enzyme activities of phosphorus removal and microbial community structures after long-term exposure to NOR were mainly investigated.The results showed that long-term exposure to low concentrations of NOR?10ug/L?has no significant effect on phosphorus removal efficiency.The long-term exposure of100 ug/L NOR resulted in a slight decrease in phosphorus removal efficiency to 94.41±1.59%.However,when the concentration of NOR was increased to 500 ug/L,the phosphorus removal efficiency decreased from 97.96±0.85%to 82.33±3.07%,indicating that the long-term exposure of 500 ug/LNOR have an significant adverse effect on the removal of phosphorus.The mechanism analysis showed that the presence of NOR not only inhibited the release of phosphorus and the consumption of acetic acid in the anaerobic stage,but also negatively affected the absorption of phosphorus in the aerobic stage,resulting in the increase of the phosphorus content in the effluent.In addition,the activity of key enzymes for phosphorus removal?exo-polyphosphate hydrolase?PPX?and polyphosphate kinase?PPK??were significantly inhibited in the presence of NOR.Moreover,the relative abundance of Candidatus_Accumulibacter in the biological phosphorus removal system were respectively decreased to 6.07%in the presence of NOR whereas the relative abundance of Candidatus_Competibacter and Defluviicoccus were increased to 8.38%and 5.18%,respectively.The NOR adsorbed by activated sludge would enter the stage of subsequent sludge resource utilizationwith the sludge discharge.Therefore,this study further investigated the effect of NOR on the short-chain fatty acid?SCFA?production from sludge anaerobic fermentation.Under initial pH 10 conditions,the effect of different concentrations of NOR?0,10,100,500 mg/kg TSS?on the SCFA production,each process of anaerobic fermentation?solubilization,hydrolysis,acidogenesis and methanogenesis?and microbial community were detailedly investigated.The experimental results showed that when the NOR concentration was increased from 0 to 500 mg/kg TSS,the corresponding maximum SCFA yield decreases from 91.25±4.11 to 79.92±3.20 mg COD/g VSS.There was no significant difference in the proportion of each SCFA in total SCFA production.It was found that the presence of higher concentration of NOR?500 mg/kg TSS?had no significant effect on sludge solubilization and the hydrolysis of macromolecular organic compared with the control.However,higher concentration of NOR?500 mg/kg TSS?caused slightly inhibitions to acidogenesis and methanogenesis.Microbial analysis revealed that higher concentration of NOR?500 mg/kg TSS?significantly decreased the relative abundance of microorganisms Hyphomicrobium,Caldisericum and Gammaproteobacteria associated with hydrolysis,SCFA production and SCFA consumption,respectively.In addition,NOR could be partially degraded during the anaerobic fermentation of sludge.In the 10 mg NOR/kg TSS reactor,the total NOR concentration decreased significantly from 0.196±0.011 mg/L to 0.159±0.009 mg/L,the removal rate was about 18.87%.In the 500 mg NOR/kg TSS reactor,the removal rate was only 4.32%.Finally,this study investigated the feasibility of using potassium ferrate to alleviate or eliminate the effect of NOR on the SCFA production from anaerobic fermentation of sludge.It was found that there was no difference in the maximum SCFA production from anaerobic fermentation in the presence of different NOR concentrations after pretreatment of 0.12 g/g TSS potassium ferrate.By measuring the concentration of NOR,it was found that the potassium ferrate enhanced the degradation of NOR,thus mitigating the inhibitory effect of NOR on the SCFA production from anaerobic fermentation of sludge.The total NOR concentration on the 10 day of fermentation decreased to 0.012±0.002 mg/L in the 10 mg NOR/kg TSS reactor after pretreatment of 0.12 g/g TSS potassium ferrate.The removal rate is about 93.78%.In the 500 mg NOR/kg TSS reactor,the removal rate was approximately68.32%.Meanwhile,it was found that a large amount of·OH,·O₂-and ¹O₂ can be produced.In addition,potassium ferrate could enhance the degradation of humic acids in the excess sludge,its content decreased to 781±43 mg/L after 48 h of fermentation.Moreover,the species and total detection frequency of other recalcitrant organics,which were hardly degraded in ordinary anaerobic condition,also decreased remarkably,reducing the environmental risks.The proportion of biodegradable parts in the released organic matter and the bioavailability of organic matter were also increased.It was estimated that the potassium ferrate supported method may save?$186,000 per year in a wastewater treatment plant?Q=10⁵ m³/day?compared with conventional wastewater treatment models.The effects of NOR on the wastewater enhanced biological phosphorus removal and anaerobic fermentation of sludge resourceful utilization were conducted via physicochemical properties of activated sludge,phosphorus removal efficiency and SCFA production from anaerobic fermentation.Meanwhile,the variation of NOR was also investigated.In addition,it is also proposed that potassium ferrate pretreatment could be used as a mean to regulate the negative effect of NOR on the SCFA production of sludge anaerobic fermentation.Furthermore,the results obtained in this work could provide some scientific insights and references for the regulation of wastewater treatment and sludge treatment.