Study On Antibiotic-containing Wastewater By Spartina Alterniflora-based Biochar And Chlorella Enhanced SBR

In recent years,due to the widespread use of antibiotics in fields such as human health and animal husbandry,the exposure range and quantity of antibiotic residues in various environmental media such as soil and water have shown a significant growth trend.The potential ecological risk effects such as bioaccumulation,amplification effects,biological toxicity,and resistance gene transfer are of concern,In the latest‘List of Key Controlled New Pollutants（2023 Edition）’in China,antibiotics and 13 other environmental risk substances are included in the key control scope,and strict environmental risk control measures are implemented.In this context,the treatment of antibiotic containing wastewater has become a focus of attention in the field of wastewater pollution treatment.Sequential batch reactor（SBR）is one of the most widely used technologies in wastewater treatment,which has high removal efficiency for conventional pollutants.However,the traditional SBR system is not efficient in removing antibiotics,and further exploration is needed to enhance its antibiotic removal efficiency by coupling with other methods.Both biochar and microalgae have good organic pollutant removal capabilities and have broad application prospects in wastewater treatment.However,in the face of composite wastewater containing antibiotics in practice,the treatment effect of a single biochar or microalgae is not ideal,and it is necessary to further couple other processes to achieve efficient and synchronous removal of antibiotics and conventional pollutants.In this context,this study constructed two sets of SBR reactor systems,coupling traditional SBR with modified biochar and Chlorella,respectively,to explore the strengthening effect and mechanism of modified biochar and Chlorella on the treatment of antibiotic containing domestic wastewater in SBR reactor.In the activated carbon SBR reaction system,the malignant invasive species Spartina alterniflora was selected as the raw material to prepare magnetic modified biochar.After characterizing its physicochemical properties,it was added to the SBR reactor;The microalgae SBR reaction system was optimized by selecting Chlorella for cultivation,and then inoculated into the SBR photoreactor to construct an SBR microalgal-bacterial consortium.The effects of Spartina alterniflora modified biochar and Chlorella on the removal of conventional pollutants and the antibiotic moxifloxacin in the SBR reactor in the two experimental systems were explored respectively,and the effects of modified biochar and Chlorella on the changes of microbial community structure in the reactor were explored through the analysis of microbial diversity in the two experimental systems.The main research results of this paper are as follows:1.Magnetic modified biochar prepared from Spartina alterniflora was characterized by field emission scanning electron microscopy（SEM）.It was found that the surface of Spartina alterniflora modified biochar was rough,with many particles appearing,with a relatively dense distribution,and a lot of crystallized substances were formed.Through the Surface Area Porosity Analyzer,it was found that the BET specific surface area of modified biochar was 464.59 m²/g.The average pore size is 2.07 nm,between micropores and mesopores,with many adsorption sites.X-ray diffraction（XRD）analysis of the chemical composition of the modified biochar showed that Fe₃O₄ and K₂CO₃ had been widely attached to the surface of the biochar,and Fourier transform infrared spectroscopy（FTIR）could observe the characteristic absorption peaks of various oxygen-containing functional groups,such as O-H,C=O,C-C,and Fe-O.2.When the biological carbon reactor（MBC-SBR）was operated in the same environment as the conventional SBR for 60 days,the concentration of COD,ammonia nitrogen（NH₄⁺-N）,total nitrogen（TN）,total phosphorus（TP）,and antibiotics in the effluent of MBC-SBR was lower.Compared to the conventional SBR reactor,the removal rates of COD,NH₄⁺-N,TN,TP,and antibiotics in MBC-SBR were increased by 3.87%,3.31%,11.54%,26.08%,and 12.93%,respectively.Therefore,after adding biochar to conventional SBR,the removal effect of TN,TP,and antibiotics is particularly significant.Through metagenomic sequencing analysis,at the phylum level,the main bacteria in both groups of reactors were Proteobacteria,Actinobacteria,Candidatus＿Saccharibacteria,Nitrospirae,and Bacteroidetes.However,there were significant differences in relative abundance between the two groups,with abundance of 72.16%,5.55%,1.12%,and 3.08%in MBC-SBR,respectively;The abundance in conventional SBR is 60.93%,13.56%,6.39%,and 4.12%.At the genus level,the main genus of bacteria in the MBC-SBR experiment was Thauera in the early stage,and Aeromonas in the later stage;However,in the conventional SBR reactor,the main bacterial genus during the three stages is all Thauera,and there are significant differences between the two groups of reactors,which to some extent explains the difference in pollutant removal rates between the two.The resistance genes detected in the two sets of reactors were mainly ARO:3000501,ARO:3004480,ARO:3000410,ARO:3002971,and ARO:3002975,mainly tetracycline and quinolone resistance genes.However,the abundance of resistance genes in MBC-SBR was significantly lower than that in conventional SBR,indicating that the addition of biochar had a good inhibitory effect on antibiotic removal and transfer of resistance genes in SBR.3.After running the microalgae reactor（microalgal-bacterial consortium）and SBR under supplementary light conditions for 60 days,the bacteria algae symbiosis system showed good treatment effects for COD,NH₄⁺-N,TN,TP,and antibiotics.Compared to conventional SBR reactors,the removal rates of the Microalgal-bacterial consortium increased by 5.31%,2.80%,14.62%,18.40%and 16.4%,respectively,indicating that the addition of chlorella significantly enhanced the removal effect of TP and antibiotics in SBR.At the same time,in the Microalgal-bacterial consortium,the content of chlorophyll increased from 130.47 mg L^-1 to 345.72 mg L^-1,with an average increase of 5.98 mg L^-1/d,while the lipid content increased from 237.5 mg L^-1 to340 mg L^-1,with an average daily increase of 2.85 mg L^-1,indicating that the Microalgal-bacterial consortium has better pollutant removal ability and good oil production ability,and has broad application prospects in wastewater recycling.The analysis of microbial sequencing results shows that the dominant bacteria in the microalgal-bacterial consortium and conventional SBR have small differences at the phylum level,but significant differences at the class level.At the class level,the two sets of reactors are mainly Gammaproteobacteria,Bacteroidia,and Alphaproteobacteria.Compared to conventional SBR,the relative abundance of Gammaproteobacteria and Bacteroidia are 31.7%and 37.45%in the microalgal-bacterial consortium,respectively,significantly higher than 26.08%and 27.00%in conventional SBR.The correlation between environmental factors and the abundance of microbial phylum level in two sets of reactors was analyzed through RDA.The difference in contribution of RDA1 at the first coordinate was 55.49%,while the difference in contribution of RDA2 at the second coordinate was 20.17%,indicating a significant positive correlation between environmental factors and microorganisms（p=0.003）.In addition,the relative abundance of resistance genes in the microalgal-bacterial consortium is lower than that in conventional SBR,indicating that Chlorella also has a good inhibitory effect on the transfer of resistance genes in conventional SBR.In summary,compared to traditional SBR reactors,modified biochar SBR and microalgal-bacterial consortium SBR have significantly improved the removal efficiency of traditional pollutants and moxifloxacin.Spartina alterniflora modified biochar enhanced SBR reactor has better antibiotic removal effect.In addition,using malignant invasive species Spartina alterniflora as raw material to prepare biochar provides a new idea for the resource utilization of invasive species.In the chlorella enhanced SBR reactor,the microalgal-bacterial consortium has a significant enhancement in the removal of TP,and has a good fat production ability,which has a broad application prospect in wastewater recycling.