Study On The Behavior Of Typical Antibiotics In The Aerobic Composting Process For Human Feces Disposal

The presence of antibiotics is an emerging concern in waste management strategies.Due to the low bioavailability and the high excretion rate of antibiotics,there is a great deal of residual antibiotics in human feces,which seriously threatens ecological environment and human health.Aerobic composting is widely applied in human feces treatment and reclamation.Aerobic composting is a feasible and effective approach to promote the removal of antibiotics,however,whether these antibiotics would affect the composting process is also increasingly attention.This study aims to maximize the environmental and health benefits and minimize the environmental load.We used source separation and aerobic composting technology to deal with human feces,and to explore the behavior characteristics of typical antibiotic residues in aerobic composting.In view of the limitations of the traditional analysis and treatment methods,such as high detection limits,low recoveries and long analysis time,the multi-residue analysis and the detection method of antibiotics in human feces and fecal composting samples were optimized.The aerobic composting experiments were carried out to study the main factors contributing to the decrease of extractable antibiotics during the aerobic composting process and to assess the impact of the composting temperature on these factors.At the same time,with tetracycline as an example,the effects of antibiotic residues in the feces on the composting process,enzyme activities and microbial community succession were researched.The results provided theoretical and application bases for enriching the aerobic composting process and strengthening the removal efficiency of antibiotic residues in the feces.The main work and achievementsare as follows:(1)By optimizing the conditions of sample pretreatment,solid phase extraction and liquid chromatography-tandem mass spectrometry(LC–MS/MS),a multi-residue analytical method for quantitative determination of different kinds of antibiotics in human feces and fecal composts was established.The extraction methods and filtration conditions were optimized in sample preparation and extraction.During solid phase extraction(SPE),the conditions of the solid phase extraction cartridge,flow rate and elution solvent were optimized.LC–MS/MS which had been validated and tested on human feces and compost samples was used to identify and quantify the antibiotics.The result shows that the method was able to simultaneously detect and quantify the antibiotics and has a good selectivity and sensitivity.During usage,the developed method significantly improved the recoveries for the target antibiotics,which were85.3%~98.4% in all sample matrices at three different levels.In addition,method quantification limits(MQL)for the four antibiotics in human feces and compost samples were 11.0~18.9 and 11.5~20.2 ?g/kg(DW),respectively.(2)The aerobic composting experiments were conducted under three different temperatures(55 ?C,35 ?C and uncontrolled temperature),with human feces as a compost material and sawdust as a microbial carrier.Attention was paid to the degradation characteristics of four typical antibiotics(i.e.tetracycline,chlortetracycline,sulfadiazine and ciprofloxacin)during aerobic composting of human feces.The objectives of the study were to clarify the main actions which contributed to the decrease of extractable antibiotics in the aerobic composting process,including hydrolysis(chemical degradation)of antibiotics only in moist environment,adsorption by sawdust particles and the microbiological action,and to assess the impact of the composting temperature on these actions.The result shows that the most effective removal of the four antibiotics was found in thermophilic composting at 55 ?C where all antibiotics were removed by more than 90%,whilst the chemical properties of antibiotics affect the removal efficiency of the antibiotics.The degradation of tetracycline and chlortetracycline was found to be more temperature-dependent than sulfadiazine and ciprofloxacin.It was revealed that the removal of tetracycline and chlortetracycline was mainly by hydrolysis in moist environment,whereas the removalof sulfadiazine and ciprofloxacin was mainly attributed to adsorption onto sawdust particles.The contribution of microbial action to antibiotic degradation is insignificant for most antibiotics except for ciprofloxacin which was degraded by up to 20% due to this factor.(3)The effects of antibiotics on aerobic composting are investigated by dosing of tetracycline(TC)in fresh human feces with sawdust as biomass carrier.At the TC dosages of 0,100,250 and 500 mg/kg,the process parameters such as temperature,pH,water-soluble carbon(WSC),germination index(GI),dehydrogenase activity(DHA)and urease activity were monitored in a 21-day composting process.Moreover,microbial community succession was examined by high-throughput 16 S rRNA gene sequencing.Findings indicate that with the increase of TC concentration,temperature increasing during aerobic composting was inhibited,pH was lowered,WSC residue was increased,GI was decreased,and the DHA and urease activity were also hindered.Furthermore,elevated TC caused significant changes in microbial community succession and reductions in the community diversity and abundance.Therefore,interference in microbial community structures and hindrance to biological activity are believed to be the main adverse effects of TC on the composting process and maturity of the composting products.