Effects Of MnO_x-loaded Biochar On Heavy Metals In Livestock And Poultry Manure

Food safety has always been a hot topic.People are gradually aware of the seriousness of food safety issues and low-polluting organic food becomes more popular today.However,heavy metals pollution problem in the livestock manure used to foster organic plant causes the limited application of animal excrement as agricultural fertilizer.Biochar is a new environmental multifunctional material,which can effectively adsorb heavy metals and organic pollutants,and has great potential in improving soil fertility,reducing greenhouse gas emissions and environmental restoration.In this study,biochar was prepared from rice straw and then modified with Potassium Permanganate to improve the adsorption effect of heavy metal ions by modified MnOx-loaded rice straw biochar(MRBC).Batch sorption experiments showed that contact time,initial concentrations of Cu2+ and Zn2+,the dosage and initial solution pH affected the removal of the heavy metals.The biochars before and after modification were characterized with Elemental composition,Scan electronic microscope(SEM)and Fourier transform infrared spectroscopy(FTIR)to explore the adsorption mechanism of Cu2+ and Zn2+.And pot experiment was used to study the effect of 50%MRBC on heavy metals contaminated soil remediation and bio-availability of heavy metals.These results provided the theoretical basis for reducing organic manure heavy metal pollution and promoting organic manure resource utilization.The main conclusions of this work were as follows:(1)Rice straw were used to produce biochar at pyrolysis temperature of 600℃ for 3 h.Then MnOx-loaded biochar was prepared with Potassium Permanganate(KMnO4).Results suggested that the higher KMnO4 concentration was,the better removal effects of Cu2+ and Zn2+ were.It should be attributed to manganese oxide group present on biochar surface,which will increase adsorption sites for metal ions.The removal rates of Cu2+ and Zn2+ by 50%MRBC were 4 times that by RBC.The sorption kinetics was fitted to the pseudo-second-order kinetics model and the sorption equilibrium was reached after 240 min.The sorption isotherm conformed to the Langmuir model and the maximum sorption capacity of Cu2+ and Zn2+ reached 107.53 and 96.15 mg·g-1,respectively.The adsorption optimum pH ranged from 4.0 to 6.0 and the optimum carbon dosage was 3 g·L-1.(2)50%MRBC surface was loaded with MnOx,and the sorption mechanism was speculated as follows:1)surface complexation between abundant oxygen-containing functional groups and heavy metal ions;2)The ion exchanges between inorganic mineral elements(K+,Na+,Mg2+,etc)and metal ions in aqueous solutions;and 3)the cationic-π effect between metal ions and the C-O-C group formed by pyrolysis of cellulose and hemicellulose in straw.(3)The application of modified biochar(50%MRBC)in pig manure contaminated soil could decrease heavy metal contents and reduce the bioavailability of heavy metals.The soil pH and organic matter content increased after the application of modified biochar.With the the proportion of modified biochar addition increased(1%,2.5%and 5%),the removal efficiency of heavy metals in pig manure organic fertilizer increased.The Cu reduction rate in soil reached 20.6%,28.2%and 42.1%,respectively.And the reduction rates of Zn were 15.3%,23.7%and 31.8%,respectively.As the proportion of MnOx-biochar increased,the exchangeable cooper,carbonate-bound cooper and Fe-Mn oxide bound cooper transferred to organic cooper and residual cooper.Similarly,the residual zinc content increased while exchangeable zinc,carbonate-bound zinc and Fe-Mn oxide bound zinc content all significantly reduced.In particular,the organic bound zinc content kept stable.(4)Applying pig manure organic manure could increase plant height,root length and fresh weight.The contents of Cu and Zn in the aboveground part were higher than that in the underground parts of rape.The contents of Cu and Zn in the aboveground and underground parts of rape treated with 5%biochar varied significantly(P<0.05)and the passivation effect of Cu was better than that of Zn.