| China has an annual pig slaughter about 660 million,and about 20 million pigs will be dead based on a typical mortality rate at 3%.Large number of dead pigs could cause serious environmental pollution if they are not properly managed.Pyrolysis is a new technology for the safe treatment of the dead animals.Biochar derived from dead pigs is rich in phosphorus,calcium and other minerals,which makes it a good candidate for alternative fertilizer as well as for remediation of soils contaminated with heavy metals.However,there is little information on the efficacy of using pig biochar as an alternative phosphorus fertilizer,and the effect of pig biochar on heavy metal bioavailability in contaminated soils.In the current study,raw pig biochar was produced from dead pigs through pyrolysis at 650 o C.The acidulated biochar was obtained after mixing pig biochar in nitric acid(65~68%).An incubation experiment was carried out to investigate the effect of addition of raw and acidulated pig biochar on P transformation in soil.The results were compared with the treatments of single superphosphate and calcium magnesium phosphate,the two common commercial phosphorus fertilizers.In addition,an incubation experiment was conducted to explore the effect of addition of raw and acidulated pig biochars on the bioavailability of heavy metals in a soil contaminated with Pb and Zn.The results were compared with the treatments of activated carbon and bamboo biochar.The main results are as following.1.Concentration of most P fractions increased in the biochar and fertilizer treatments.Compared to the control,the acidulated biochar treatment was more effective than the pig biochar in improving the proportions of the soil labile and moderately labile phosphorus,whereas there were no significant differences in these P proportions between the acidulated biochar and the fertilizer treatments.Concentrations of Na HCO3-Pi and Na OH-Pi in the acidulated pig biochar-treated soil were approximately 4.5 and 3.0 times,and the concentrations of Dil.HCl-Pi,Conc.HCl-Pi and Residual-P were 3.5,1.2 and 1.2 times of those in the control soil,respectively.Compared to control,percentage of the labile P pools significantly increased in all biochar and fertilizer treatments,but there were no significant differences among the biochar and fertilizer treatments.In comparison with the control,the moderately labile P pools in the biochar and fertilizer treatments increased by 36.2 to 77.2%,with the following orders,the acidulated pig biochar > superphosphate > calcium magnesium phosphate > pig biochar.The percentage of stable P pools reduced with the addition of the amendments,and the proportion of the stable P pools was negatively correlated(P<0.01)with the proportion of the labile and moderately labile P pools.2.Soil p H increased significantly(P<0.05)with the addition of raw pig biochar,activated carbon and bamboo biochar.Compared to the untreated control,the pig biochar treatment increased soil p H by1.2 units.The acidulated pig biochar treatment significantly(P<0.05)increased the soil cation exchange capacity(CEC)by 11.3%,whereas the other treatments had no significant effect on soil CEC.In addition,the concentration of available P in soil increased significantly after biochar and activatedcarbon addition,and concentration of the soil available P in the acidulated pig biochar treatment was 3.4,94.4 and 86.2 times of that in the raw pig biochar,activated carbon and bamboo biochar treatments,respectively.Compared to the control,the concentration of extractable Zn significantly decreased in the biochar and activated carbon treatments,and the reductions were by 49.9%,34.6%,20.2% and 8.0% in the raw pig biochar,bamboo biochar,activated carbon and acidulated pig biochar treatments,respectively.The application of raw and acidulated pig biochars resulted in the reduction of soil extractable Pb by 31.1% and 60.4%,respectively.In conclusion,both pig biochar and acidulated pig biochar treatments significantly increased the concentrations of different soil P fractions,and the acidulated treatment was more effective than the pig biochar treatment.The raw pig biochar treatment was more effective in reducing the bioavailability of Pb and Zn in soil. |
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