Study On Enhancement Of Zero-Valent Iron/Biochar Coupling SO₄^2- Reduction For Anaerobic Treatment Of Wastewater Containing Antibiotics And Heavy Metals

The existence of antibiotics and heavy metals has harmful effects on anaerobic wastewater treatment systems,and even deteriorates their operational performance.In this study,a zero-valent iron/biochar coupling SO42-reduction enhanced anaerobic system was used to treat wastewater containing antibiotics and heavy metals,in order to provide a cost-effective technical support and theoretical reference for the treatment of wastewater containing antibiotics and heavy metals.Biochar was prepared from biochemical pressure filtration sludge and added to the anaerobic reactor together with zero-valent iron and SO42-as a coupling system.The system with zero-valent iron and SO42-,biochar and SO42-,and SO42-added were set,while the system without the above substances were used as the control.The enhancement effect of zero-valent iron/biochar coupling SO42-reduction on anaerobic treatment of wastewater containing antibiotics and heavy metals was studied.The results showed that the treatment effect and methanogenic activity of the coupling system were better than those of the other systems.The CODCr removal rate,CODCr degradation rate constant,antibiotic removal rate,gas production and coenzyme F420 content were 97.0%,0.2802 h-1,68.9%,695 m L/cycle and 0.019 μmol/g VSS,respectively.The addition of SO42-significantly increased the removal of heavy metals Zn and Cu in the anaerobic system from 81.7% to more than 99.3% and 88.2% to more than 99.4%,respectively.The analysis of the changes in the content of zinc,copper and sulfur in the sludge as well as XPS showed that zinc and copper ions were basically removed by reacting with H2 S generated by sulfate reduction in the system to produce sulfide precipitation.The results of the study on volatile fatty acids showed that the addition of zero-valent iron and biochar promoted the degradation of propionic acid and the production of acetic acid,and improved the utilization of acetic acid by methanogens.The sludge index of each system was investigated and the results showed that the coupling system had a more compact sludge structure and better flocculation performance.The strengthening mechanism of the coupling system was investigated from the microbial co-metabolism bacteria combined with electron transport.Metagomic sequencing results showed that the hydrolytic fermentation bacteria,hydrogen and acetic acid producing bacteria,methanogenic bacteria and sulfate reducing bacteria in the coupling system formed a more stable and balanced bacterial community structure,which enabled them to better adapt to the environment containing antibiotics and heavy metals.The study of intracellular electron transfer showed that the zero-valent iron/biochar could promote the process of electron transfer in the iron-sulfur center,complex I to coenzyme Q,and coenzyme Q to complex Ⅱ,and improved the ETS activity of sludge,and accelerated the enzymatic reaction of organic matter.The extracellular electron transfer was studied by electrochemical method,and the analysis indicated that the coupling system had higher specific capacitance and more redox active substances with stronger redox activity.Meanwhile,the solution resistance and charge transfer resistance in the system were smaller than other systems,the current value and conductivity were larger,and the electron transfer rate was significantly higher.Finally,the effect of antibiotic and heavy metal load shock on each system was studied,and it was found that the coupling system could maintain better operational performance with stronger resistance to load shock under load shock,and had better treatment effect on highly loaded antibiotic and heavy metal wastewater.