Effect of pyrolysis temperature on characteristics, chemical speciation and environmental risk of Cr, Mn, Cu, and Zn in biochars derived from pig manure.

The comprehensive analysis of environmental risk for heavy metals in pig manure was essential for optimization of pyrolysis conditions and scientific utilization of pig manure biochars as soil amendment. However, in previous studies, the selected pyrolysis temperature points were limited and temperature interval was large, it's was difficult to accurately verify the effect of pyrolysis temperature on chemical speciation and environmental risk of heavy metals. Therefore, in this study, pig manure was pyrolyzed at 300-700 °C with a small interval of 50 °C to study the effect of pyrolysis temperature on characteristics and environmental risk of Cr, Mn, Cu and Zn in pig manure biochar. Results indicated that the characteristics of biochars (>500 °C) were relatively stable. The biochar obtained at 700 °C exhibited the largest surface area (8.28 m2 g-1) and pore volume (25.17 m3 kg-1), secondly is the biochar derived at 500 °C. The total percentages of exchangeable and acid fraction and reducible fraction decreased from 16.98% to 9.43% for Cr, 85.60% to 65.55% for Mn, 57.26% to 10.61% for Cu, 37.90% to 13.78% for Zn, respectively, suggesting that exchangeable and acid fraction and reducible fraction of Cr, Mn, Cu and Zn in pig manure were transformed into oxidizable and residual fractions after pyrolysis. The leaching rates, risk assessment code and potential ecological risk index values significantly decreased after pyrolysis and presented lower value at 500 and 700 °C. Biochars derived at 300-700 °C conditions posed no phytotoxicity with germination index >80%. Correlation analyses revealed that larger surface area, pore volume and pH values of biochars may help to immobilize heavy metals and reduce bioavailability. These findings demonstrated that bioavailability and toxicity of Cr, Mn, Cu and Zn in pig manure biochar were greatly reduced after pyrolysis and the optimum temperature was 500 °C considering energy cost.

Shen X ，Zeng J ，Zhang D ，Wang F ，Li Y ，Yi W ... -  《-》

Contrasting effects of composting and pyrolysis on bioavailability and speciation of Cu and Zn in pig manure.

The intensive and unregulated application of feed additives to commercial pig foods has resulted in high levels of Cu and Zn in pig manure. The aim of this study was to assess the impacts of composting and pyrolysis processes on the bioavailability and chemical speciation of Cu and Zn in pig manure products by single and sequential extractions, and to compare metal bioavailability in composts and biochar-amended soils in incubation experiments. Composting and pyrolysis processes can convert exchangeable and carbonate-bound Cu and Zn to organic matter and residual fractions, and significantly reduce the potential availability of metals in composts and biochars. The DTPA-Cu and Zn concentrations in soils amended with biochar BC700 were lower than in composts and soils amended with biochar BC400. It is suggested that 700 °C is the preferred pyrolysis temperature for the conversion of pig manure contaminated with heavy metals to biochar, in order to minimize environmental pollution.

Meng J ，Wang L ，Zhong L ，Liu X ，Brookes PC ，Xu J ，Chen H ... -  《-》

Changes in heavy metal bioavailability and speciation from a Pb-Zn mining soil amended with biochars from co-pyrolysis of rice straw and swine manure.

Biochar has been utilized as a good amendment to immobilize heavy metals in contaminated soils. However, the effectiveness of biochar in metal immobilization depends on biochar properties and metal species. In this study, the biochars produced from co-pyrolysis of rice straw with swine manure at 400°C were investigated to evaluate their effects on bioavailability and chemical speciation of four heavy metals (Cd, Cu, Pb and Zn) in a Pb-Zn contaminated soil through incubation experiment. Results showed that co-pyrolysis process significantly change the yield, ash content, pH, and electrical conductivity (EC) of the blended biochars compared with the single straw/manure biochar. The addition of these biochars significantly increased the soil pH, EC, and dissolved organic carbon (DOC) concentrations. The addition of biochars at a rate of 3% significantly reduced the CaCl2-extractable metal concentrations in the order of Pb>Cu>Zn>Cd. The exchangeable heavy metals decreased in all the biochar-amended soils whereas the carbonate-bound metal speciation increased. The increase in soil pH and the decrease in the CaCl2 extractable metals indicated that these amendments can directly transform the highly availability metal speciation to the stable speciation in soils. In conclusion, biochar derived from co-pyrolysis of rice straw with swine manure at a mass ratio of 3:1 could most effectively immobilize the heavy metals in the soil.

Meng J ，Tao M ，Wang L ，Liu X ，Xu J ... -  《-》

Chemical speciation and risk assessment of Cu and Zn in biochars derived from co-pyrolysis of pig manure with rice straw.

Pig manure has been utilized as a good feedstock to produce biochar. However, the pig manure-derived biochar from intensive pig cultivation contains high levels of total and bioavailable heavy metals. In this study, the co-pyrolysis of pig manure with other biomass (e.g. rice straw) at 300-700 °C was investigated to solve the above-mentioned topic. The ammonium acetate (CH3COONH4), Tessier sequential extraction procedure and hydrogen peroxide were adopted to evaluate the bioavailability, chemical speciation, and potential risk of Cu and Zn in the biochars. Results showed that the addition of rice straw significantly reduced the concentrations of total, exchangeable and carbonate-associated Cu and Zn in the biochars compared to the single pig manure biochars. Co-pyrolysis of pig manure with rice straw at a mass ratio of 1:3 and at 600 °C could be most effective to reduce the concentrations of CH3COONH4-extractable and potential released Cu and Zn in the biochars. In conclusion, the co-pyrolysis process is a feasible management for the safe disposal of metal-polluted pig manure in an attempt to reduce the bioavailability and potential risk of heavy metals at relatively high pyrolysis temperatures.

Meng J ，Liang S ，Tao M ，Liu X ，Brookes PC ，Xu J ... -  《-》

Influence of pyrolysis temperature on the properties and environmental safety of heavy metals in chicken manure-derived biochars.

Bai T ，Qu W ，Yan Y ，Ma K ，Xu Y ，Zhou X ，Chen Y ，Xu Y ... -  《-》