Purification Efficiency And Mechanism Of Antibiotic Wastewater By Microcosm Of Algae-bacterial Symbiosis

To kill bacteria or inhibit the growth and reproduction of microorganisms,antibiotics are widely used in many fields of human life as a kind of medicine.However,the majority of antibiotics are not digested by organisms.Therefore,they discharged directly into surface water,causing not only organic pollution of aquatic environment,but also inducing resistance genes in environmental microorganisms,which then spread among bacterial groups via gene horizontal transfer,posing a major threat to public health and safety.At the same time,antibiotic wastewater also contains a large number of conventional pollutants.The efficient and simultaneous removal of antibiotics and conventional pollutants is a challenge for antibiotic wastewater treatment technology.Constructed wetlands（CWs）,as a new ecological treatment technology,have been proved to take a great potential for the removal of antibiotics in recent years.The substrate and microorganisms in CWs can purify antibiotic wastewater through adsorption and biological metabolism.In addition,As a potential biological resource,microalgae has the ability to purify antibiotics.To improve the efficiency of antibiotic wastewater purification,9 types of microcosm were set up in this study,which were composed of microalgae,sediment microorganisms and gravel substrate.They are Algae microcosm（A）,Algae-Gravel microcosm（AG）,EOM microcosm（E）,Light microcosm（L）,Dark microcosm（D）,Sedimentmicrocosm（S）,Sediment-Gravelmicrocosm（SG）,Algae-bacterial-Sediment microcosm（AS）and Algae-bacterial-Sediment-Gravel microcosm（ASG）,respectively.The study investigated the purification ability and mechanism of different types of microcosms for a representative class of antibiotics,β-Lactam antibiotics（β-Lactams）wastewater,clarified the type of microcosms with optimal purification efficiency,and provided theoretical foundation basis for efficient treatment of antibiotic wastewater.The main substrate conclusions are as follows:（1）Microalgae converted organics,nitrogen,and phosphorus nutrients into algal cells via their own metabolism,thereby purifying antibiotic wastewater.Furthermore,EOM effectively adsorbed pollutants such as antibiotics and pollutants also been removed by photolysis and hydrolysis.In comparison to other microcosms,AG had the best antibiotic removal effect,with a removal rate of 98.84%.Antibiotics had shown strong toxicity to microalgae and inhibited their growth activity and algal production.Gravel removed pollutants such as antibiotics via adsorption and interception,as well as mitigated the negative effects of antibiotics on microalgae survival and growth.（2）The sediment microorganisms effectively purified antibiotic wastewater.The addition of gravel significantly enhanced the purification ability（P<0.05）.The final comprehensive score of S and SG in antibiotic wastewater treatment was 0.7626 and0.8248,respectively.The relative abundance of microorganisms interacted with the removal rates of pollutants.Antibiotics had a screening effect on the microbial community structure.It promoted the growth of resistant microorganisms while inhibiting or killing the sensitive microbial community,resulting in changes in the microbial community structure and a decrease in richness and diversity in the systems.Gravel protected the diversity of microbial community structure to a certain extent by providing growth medium and removing pollutants.（3）Antibiotic wastewater removal capacity was AG>A>L>ASG>E>AS>D>SG>S,and the removal rate was 98.84>98.76>97.97>92.4>91.59>90.75>80.3>79.55>75.69.By comparison,apart from the lower purification efficiency of antibiotics compared to AS,the algae-bacteria symbiotic microcosm（ASG）combined with gravel has the highest removal rate of other conventional pollutants.According to the weighting method,the comprehensive scores are:0.8717>0.8477>0.8248>0.8215>0.7626>0.7460>0.6602>0.5571>0.4441,respectively.The treatment capacity is shown as follows:ASG>AS>SG>AG>S>A>L>E>D,ASG provided the most extensive antibiotic wastewater treatment potential.（4）In the algae-bacteria system,algae and microorganisms promoted each other’s growth through behaviors such as nutrient exchange.Microorganisms decomposed organic matter through respiration to provide CO₂for microalgae and microalgae absorbed and utilized through photosynthesis to release O₂and extracellular metabolites for use by microorganisms.The interaction of the two promoted the growth of microalgae and the preservation of microbial community structure,as well as the reduction of pollutants in wastewater.The presence of gravel provided a growth medium for organisms and removed pollutants through adsorption and sedimentation to help organisms resist adverse living conditions.