金霉素浓度对鸡粪中温厌氧消化特性及抗生素降解的影响

Effect of chlortetracycline concentration on mesophilic anaerobic digestion characteristics and antibiotic degradation of chicken manure

针对抗生素污染对鸡粪厌氧消化影响不明的问题,该文利用批次试验探究了不同质量浓度金霉素(chlortetracycline,CTC)(4~200 mg/L)对鸡粪中温厌氧消化过程、产气效率及抗生素降解的影响。结果表明,低浓度的CTC(质量浓度≤20 mg/L)促进了鸡粪中温厌氧消化作用,其对累积水解、酸化、乙酸化及甲烷化的最大促进率较对照(质量浓度0mg/L)分别提高了12.69%,11.55%,11.31%和9.82%,厌氧消化有效降解了鸡粪中的CTC,降解率为59.87%~71.95%,这是因为厌氧污泥胞外聚合物(extracellular polymeric substances,EPS)由结合态(松散结合态(loosely bound EPS,LB-EPS)和紧密结合态(tightly bound EPS,TB-EPS))转化为黏液态(slime EPS,S-EPS)促进了水解作用,另外,CTC降解提供的碳源进一步促进了甲烷的生成。高浓度CTC(质量浓度≥60mg/L)抑制了鸡粪中温厌氧消化作用,且抑制率随CTC质量浓度的增大而升高,对累积水解、酸化、乙酸化及甲烷化的最大抑制率分别为16.48%,18.54%,18.96%和19.94%,CTC的降解率为43.4%~51.44%;在此条件下污泥EPS较对照提高了13.81%~39.23%,其中EPS蛋白浓度由943.01 mg/L增加为1 083.69~1 338.20 mg/L。中温条件下CTC对鸡粪厌氧消化抑制阈值为22.16 mg/L。消化结束后,沼液和沼渣中的CTC分别占总量的0.46%~3.13%和96.87%~99.54%,表明CTC绝大部分残留在沼渣中,存在较大环境风险,所以应对沼渣进一步无害化处理后才可还田使用。

Anaerobic digestion is a promising robust technology,which can not only reduce pollution of chicken manure but also produce energy,especially mesophilic anaerobic digestion of chicken manure has been widely used due to energy saving and long-term stability.In recent years,excess amount of antibiotics has been used in raising broilers to promote fast growth and prevent from diseases.The antibiotics residues problem in China rising day by day as compared to other countries,of which tetracycline antibiotic residues has been considered dangerous for living organisms.In China,it is reported that chlortetracycline residues especially in chicken manure was 563.8 mg/kg.Although,the toxicity threshold of antibiotics in soil regulated by Veterinary International Conference on Harmonization is 100μg/kg,it has been found that,the chlortetracycline residues more than 50%of the soil sample in China has been found higher than the threshold.Anaerobic digestion technology plays an important role in degrading antibiotics resides,this process not only wasaffected by the antibiotics concentration and category,but also more importantly by substrate category.Chicken manure has greatly potential to produce higher biogas production per organic matter than swine and cattle manure,but the effect of chlortetracycline contamination on biogas production of mesophilic anaerobic digestion of that is still unclear,removal of chlortetracycline during anaerobic digestion of chicken manure also unknown.The effect of chlortetracycline on hydrolysis,acidogenesis,acetogenesis and methanogenesis during anaerobic digestion of chicken manure has not been deeply studied yet.Therefore,this study aimed to explore the effects of antibiotics on mesophilic anaerobic digestion of chicken manure.Influence of a wide range of chlortetracycline concentrations(4-200 mg/L CTC)on anaerobic digestion of chicken manure were investigated by batch experiments.The obtained results indicated that mesophilic methane production was increased when CTC concentration was less than 20 mg/L.More specifically,the ultimate increase rates of hydrolysis,acidogenesis,acetogenesis and methanogenesis for methane production were 12.69%,11.55%,11.31%and 9.82%,respectively.Indeed,the removal efficiency of CTC was increased from 59.87%to 71.95%.Further analysis showed that methane production was increased as a result of the transformation of extracellular polymer substances(EPS)from bound EPS(LB-EPS and TB-EPS)to slime EPS(S-EPS),which promoted the hydrolysis,In addition,the degradation of CTC produced the carbon sources for microorganisms.However,mesophilic methane production was inhibited when CTC concentration was higher than 60 mg/L.Moreover,the inhibition rate was increased with raising CTC concentration,among them the inhibitory effect of 200 mg/L CTC concentration was the strongest than others,the largest inhibition rate of 200 mg/L CTC concentration for hydrolysis,acidogenesis,acetogenesis and methanogenesis was 16.48%,18.54%,18.96%and 19.94%,respectively,and the removal efficiency of CTC reduced up to 43.4%-51.44%.EPS increased by 13.81%-39.23%compared with control,of which the concentration of EPS protein increased from 943.01 mg/L to 1 083.69-1 338.20 mg/L,it is assumed that bacterial resistance for CTC was increased by stimulating EPS secretion.Analysis of the distribution of residual CTC within the digester indicted that 0.46%-3.13%of CTC was existed in liquid digester,while 96.87%-99.54%of CTC was found in solid digester,which posed a significant threat to the environment.Further safe treatment was needed before solid digester used as organic fertilizer into field.