Inhibitory Effect Of Antibiotics And Heavy Metals On Anaerobic Digestion Of Piggery Wastewater And Its Control Strategy

Anaerobic biological treatment(anaerobic digestion) is widely used in piggery wastewater treatment process, however, antibiotics and heavy metals as special contaminants in this kind of wastewater have self-inhibition effect on the biotreatment technology. To find the law of the inhibitory effect of antibiotics and heavy metals on anaerobic biological treatment the photobacteria toxicity test and anaerobic digestion inhibition test were adopted. The rule of the individual inhibition, the joint inhibition, and the accumulative inhibition of antibiotics and heavy metals were studied through statistical methods. "Identification-Removal" control strategy was proposed to eliminate the inhibitory effect on anaerobic biological treatment. The main results are as follows:(1) Study on the general toxicity of piggery wastewater. The results showed that the toxicity of piggery wastewater was in equivalent to 18.2mg/L of mercury chloride. The piggery wastewater has strong self-inhibition on anaerobic digestion. The contribution percentages of antibiotics and heavy metals to the general toxicity of piggery wastewater were separately 31% and 23%.(2) Study on the inhibitory effect of antibiotics. The results of photobacteria toxicity test showed that the order of antibiotics toxicity was aureomycin > florfenicol > amoxicillin) sulfamethazine, of which the IC₅₀ value were 1.17mg/L, 15.45mg/L, 78.62mg/L, and 83.00mg/L, respectively. The different levels of antibiotics had inhibitory effects on relative light illumination intensity of photobacteria and the inhibitory ratio of illuminatioin intensity was 12.1%～79.5%. The joint toxicity of four kinds of antibiotics was antagonistic or additive. Results of anaerobic digestion experiments indicated that the order of inhibory effect was the same as the result of photobacteria experiments and aureomycin was the strongest in the four kinds of antibiotics. The results of sensitive step test showed that hydrolysis fermentation and hydrogen-production acetogenisis were the rate-limiting steps in the inhibition of aureomycin or amoxicillin.(3) Study on the inhibitory effect of heavy metals. The results of photobacteria toxicity test indicated that the order of heavy metals toxicity was Cu (â…¡),Zn (â…¡),Cr (â…¢), of which the IC₅₀ value were 0.68mg/L, 1.18mg/L, and 11.32mg/L, respectively. The different levels of heavy metals had inhibitory effects on relative light illumination intensity of photobacteria and the inhibitory ratio of illuminatioin intensity was 41.4%～93.0%. The joint toxicity of three kinds of heavy metals was antagonistic or additive. Results of anaerobic digestion experiments indicated that the order of inhibory effect was the same as the result of photobacteria experiments. The inhibitory effect of Cu (â…¡) was the strongest in the three kinds of the factors and the inhibitory effect of Zn (â…¡) was highly accumulative. The results of sensitive step test showed that hydrolysis fermentation and hydrogen-production acetogenisis were the rate-limiting steps in the inhibition of heavy metals.(4) Study on the joint inhibitory effect of antibiotic and heavy metals. The results of photobacteria toxicity test and anaerobic digestion test indicated that the different levels of antibiotic and heavy metals had inhibitory effects on relative illumination intensity and anaerobic digestion. The inhibitory ratio of illuminatioin intensity and accumulative methane production were 44.0%～100.0% and 27.88%～83.65%, respectively. The interaction between aureomycin and Cu (â…¡) was antagonistic and was of additive effect between aureomycin and Zn(â…¡).(5) The "Identification and Removal" control strategy was proposed for anaerobic digestion of piggery wastewater. The results showed that Aureomycin, Cu (â…¡) and Zn (â…¡) were significant factors, the inhibitory concentration of which were 8.0mg/L, 1.0mg/L and 1.2mg/L, respectively. The effectiveness and stability of anaerobic digestion was increased significantly after piggery wastewater was pretreated. The "Identification-Removal" control strategy can be used as a guide to the engineering practice.