Anaerobic Co-Digestion Of Antibiotics And Heavy Metals Contained Swine Manure And Straw

The agriculture and graziery industry in China has been developing rapidly in recent years.However,according to official data of government about 1.04 billion tons of waste straw and 3.8 billion tons of manure was dumped every year.Agricultural waste settlement has become a big challenge in China.Anaerobic co-digestion technology can both promote the methane yield and solve the problem of imbalance of carbon and nitrogen ratio in anaerobic monodigestion,which is considered as an effective way to managing agricultural waste.However,antibiotics and heavy metals in pig manure not only affect the anaerobic process,but also restrict the safe use of anaerobic biogas slurry.Therefore,it is very important to optimize anaerobic co-digestion conditions of pig manure and straw and investigate the effects of antibiotics and heavy metals in manures during anaerobic digestion process.In this study,sucrose nutrient solution is firstly used to start the semi-continuous stirred tank reactor.Pig manure and straw were used to acclimate mesophilic and thermophilic semi-continuous stirred tank reactor to stable operation.The optimal inoculation rate and substrate carbon/nitrogen ratio in anaerobic co-digestion were optimized by using the sludge from semi-continuous reactors.The study of copper and zinc's effects on anaerobic co-digestion and their morphological changes were conducted in mesophilic and thermophilic condition.The effects of norfloxacin and sulfamethoxazole on anaerobic digestion and their degradation were also determined in this study.16S rDNA Amplicon sequencing technology were used to analyze the microbial community changes.Two sets of anaerobic reactors operateed in mesophilic and thermophilic condition was started up by gradually increasing the TS load of feeding.When the two reactors were operating under the TS load at 63.35±2.84g/L,the daily biogas yield of mesophilic and thermophilic reactor is 4204.75±1817.39mL and 5802.29±1136.04mL,respectively.The higher biogas yield of thermophilic reactor is attributed to higher VS degradation ability for substrates in thermophilic condition.The batch experimental results showed that the anti-acidification ability of thermophilic anaerobic digestion system was stronger under the same inoculation rate or load rate.The unacidication limit of inoculation rate under mesophilic and thermophilic anaerobic co-digestion was 0.6 and 0.2 respectively?based on TS ratio?.Mesophilic and thermophilic anaerobic digestion reached maximum methane yield when the substrate carbon/nitrogen ration at 20:1 and 35:1 respectively,and the corresponding methane yield was 148.38ml/gVS and 221.22ml/gVS,respectively.Under the 50mg/L initial antibiotic dosage,the degradation half-life of norfloxacin and sulfamethoxazole in mesophilic anaerobic co-digestion was 19.47d and 0.81d,respectively.In thermophilic anaerobic co-digestion,the half-life is shortened to 5.70d and 0.30d.It was also discovered that the anaerobic digestion process is beneficial to the stabilization of copper and zinc.At the end of 60 days anaerobic digestion,the proportion of biounavailable copper and zinc in mesophilic anaerobic sludge was 86%and 25%respectively,while the number in thermophilic anaerobic sludge increased to 94%and43%respectively.The residual antibiotics ans heavy metals in pig manure did not reduce the anaerobic methanogenic activity.On the contrary,the addition of Cu²⁺,Zn²⁺,norfloxacin and sulfamethoxazole in pig manure could promote the methane yield in both mesophilic and thermophilic anaerobic co-digestion to some extent.Under mesophilic condition,Cu²⁺,Zn²⁺and sulfamethoxazole have obvious promoting effect on methanogenesis,and norfloxacin has certain inhibiting effect.Under thermophilic condition,Cu²⁺,Zn²⁺,norfloxacin and sulfamethoxazole all increased methanogenesis to some extent.16S rDNA Amplicon sequencing result indicated that the increase of relative abundance of methanogens like Methanosarcina and Methanoculleus is the reason for the increase of methane yield.However,from the perspective of safety for returning manure to the field,the control of residual pollutants still needs to be strengthened.