Effects And Mechanisms Of Tetracycline On Anaerobic Biological Treatment Performance For Livestock Wastewater

In the process of livestock breeding,a large number of antibiotics are added to livestock and poultry breeding feed to control the occurrence of bacterial disease,accelerate the growth of livestock and poultry and improve economic benefits of breeding.However,antibiotics added into feed could not be completely absorbed by livestock and poultry and released by their original forms and metabolites into environment through their urine and feces,resulting in a wide variety of antibiotics existed in livestock wastewater.Anaerobic biological treatment is one of the mainstream methods for livestock wastewater treatment due to its characteristics.In this study,tetracyclines commonly found in livestock wastewater were selected.The effects and mechanisms of tetracycline on the anaerobic biological treatment performance of livestock wastewater were explored through the combinations of semicontinuous experiments and batch experiments.It is expected to provide a guidance for operations and applications of anaerobic biological treatment for livestock wastewater containing antibiotics.The main findings are as follows:1)Low-dosage tetracycline promoted anaerobic biological treatment performance of livestock wastewater.Continuous additions of tetracycline in Livestock wastewater exerted inhibitory effect on anaerobic biological treatment.The inhibitory effect followed the "dose-response" effect,which was that the inhibitory effect was positively correlated with the tetracycline concentrations.After continuous additions of 54-day 4mg/L tetracycline and 49-day 8 mg/L tetracycline,daily methane production was decreased by 73.28%.2)After long-term exposure to tetracycline,tetracycline had inhibitory effects on hydrolysis,acidogenesis,acetogenesis and methanogenesis during anaerobic biological treatment of livestock wastewater,and its inhibition rates were 39.64%,39.25%,14.91%,and 97.58%,respectively.Tetracycline inhibited methanogenesis more seriously.3)Initial 30-day exposures to tetracycline could stimulate the activities of anaerobic microorganisms.ATP contents in anaerobic microorganisms and the key enzyme activities involved in anaerobic treatment were improved.After continuous 45-day additions of tetracycline,the activities of the microorganism were inhibited.From the perspective of enzymes,tetracycline had higher inhibition of coenzyme F420 related to methanogenesis,and its activity was reduced by 66%.4)Tetracycline stimulated the secretions of polysaccharide contents in extracellular polymeric substances,which affected the mass transfer efficiencies among anaerobic microorganisms to inhibit anaerobic biological treatment performance.In addition,tetracycline caused the liberations of lactate dehydrogenase of anaerobic microorganisms,cell structure destroying,and even the death of microorganisms.