Removals Of Heavy Metals And Antibiotics By Using Raw And Modified Biochar And Applications In Anaerobic Digestion Processes

With the development of intensive and large-scale livestock and poultry breeding,the combined pollution of heavy metals and antibiotics in livestock and poultry waste has become a major environmental issue that needs to be addressed.As a highly phosphate esterified and aromatized environment-friendly adsorbent,biochar has been widely used in the treatment of heavy metals or antibiotic pollution in recent years.Anaerobic fermentation technology is a harmless and resource treatment technology for livestock and poultry manure.It is mainly applied to the removal of organic pollutants with high concentrations of nitrogen and phosphorus,but the application of heavy metals and antibiotics has not yet been reported.In this study,biochar was prepared from peanut hulls,sawdust,paper sludge,and new-type swine manure digestate,and modified biochar was prepared using modified hydrochloric acid,ammonia,and potassium permanganate.First,a series of adsorption tests were used to determine the biochar with the best comprehensive adsorption capacity and the interaction between the contaminants.Then,the anaerobic fermentation response surface test mediated by biochar was used to determine the optimal process conditions for anaerobic fermentation,combined with the removal rate of heavy metals/antibiotics during the fermentation process.Finally,an biochar-mediated anaerobic fermentation system with better methane yield and comprehensive removal rate of heavy metals/antibiotics was established.The main results were reported as follows:(1)Characterization results of biochar produced from peanut shells,sawdust,paper sludge and swine manure digestate showed that these raw had positive electronegativity(in p H=6 environment medium);The sawdust raw biochar and the peanut shell raw biochar were rich in microporous structure with average pore sizes of 2.527 and 2.291 nm,respectively.The ash content of paper sludge raw biochar was as high as 87.35%,and surface functional groups was abundant and the average pore size was the largest in all biochar.The yield of swine manure digestate raw biochar was as high as 62.44%,and it was rich in C-O and-OH functional groups.After modified by HCl,NH3·H2O and KMn O4,the specific surface area and total pore volume of swine manure digestate modified biochar significantly increased,and the number of C=O and-OH functional groups increased significantly.Except peanut shell biochar modified ammonia,the negative electrobiota of all modified biochars was changed to negative value.(2)Results of adsorption tests of biochar and its modified materials on heavy metals/antibiotics complex pollution showed that the biochars with the highest removal rates of Cu/Zn,As(Ⅲ)/SDM/ROX,and TYL were the paper sludge raw biochar,the swine manure digestate biochar modified with potassium permanganate,and the peanut shell biochar modified with hydrochloric acid,and the maximum removal rates of Zn,As(Ⅲ),SDM and TYL were 94.45%,80.89%,83.76% and 81.36%,respectively.From the total ranking of pollutant removal rates,it could be seen that the swine manure digestate biochar modified with potassium permanganate had the best comprehensive removal effect of heavy metals/antibiotics.(3)The experimental results of the interaction of heavy metals/antibiotic single or combined contamination showed that Cu,Zn and As(Ⅲ)exhibited antagonism in a single heavy metals pollution systems.SDM and TYL exhibited synergism in a single antibiotics pollution system.In the compound pollution system containing heavy metals and antibiotics,Cu,Zn and As(Ⅲ)exhibited promotion of TYL;the interaction between Zn/As(Ⅲ)and SDM showed antagonism,while Cu showed promotion;SDM/TYL showed a promoting effect on Cu and As(Ⅲ)but antagonism on Zn.(4)The results of swine manure anaerobic fermentation mediated sawdust raw biochar showed that the cumulative methane yield in the fermentation system with a TS of 8%,swine manure amount of 100%,and biochar amount of 4% was as high as 217.99 m L/(g VS).Response surface optimization design results showed that when the cumulative methane yield reached 247.20 m L/(g VS)(predicted value),the optimum process conditions for anaerobic fermentation were TS of 8.78%,swine manure amount of 94.54%,biochar amount of 5.49%,and the impact of these on cumulative methane yield from the largest to the smallest was: swine manure amount> TS> biochar amount.(5)Adsorption test results of different biochars on methane yield and heavy metal/antibiotic removal performance in the anaerobic fermentation system showed that adding paper sludge raw biochar could effectively relieve ammonia inhibition and increase methane production,the cumulative methane yield up to 146.98 m L/(g VS).The comprehensive removal effect of heavy metals/antibiotics compound pollution from swine manure digestate potassium permanganate-modified biochar and paper sludge raw biochar was better than the sawdust raw biochar,and had more prominent effects on the passivation of Cu and Zn/As,respectively.In general,the addition of paper sludge raw biochar can meet both the maximum methane yield requirements and the efficient removal of heavy metals/antibiotics.