| Biochar has recently attracted a global concern, because it can improve soil textures, contribute positively to plant biomass and reduce environmental risk of organic pollutants and heavy metals when it is added into soil. Biochar can be simply made from many feedstocks. The high specific surface area, microposrosity, and charge characteristics make boichar to be a very efficient sorbent for a range of organic contaminants and heavy metals. Thus, it is expected that biochar has significant effects on the mitigation and bioavaiability of these pollutants.In this research, biochars were made from four different materials including rice, bean, wood chip, and pig manure. Each material was heated at four different temperatures including300℃,400℃,500℃and600℃. Totally, sixteen types of biochars were obtained. The objective of this research was:(1) to investigate PAHs and heavy metal concentrations in the different types of biochars;(2) to assess the potential risk of PAHs in biochars and heavy metal to human health;(3) to study the effect of biochar on the removal and plant uptake of PAHs and heavy metals in biochar-amended soil. The main results were as follows:(1) The PAHs concentrations (μg/kg) in rice, bean, wood chip and pig manure biaochars were in the range of332.1-6358.8,1345.2-4737.0,501.5-4216.4, and182.7-1010.5, respectively. Temperaure had great influences on PAHs levels in made biochars. Made at300℃, wood chip biochar had the highest PAHs concentrations. However, for biochars made at400℃and500℃, rice biochar had the highest PAHs concentrations. Made at600℃, bean biochar had the highest PAHs concentration. The trend of the PAHs concentrations in rice biochar, bean biochar and pig manure biaochar made from different temperatures were as follows:400℃>500℃>300℃>600℃. However, the PAHs concentration in wood chip biochar decreased as the temperature increased. PAHs with different-ring were descreased as the temperature increased, namely, two-ring>three-ring>four-ring>five-ring.(2) Biochar contained PAHs and thus had potential threat to local resident health. PAHs in R300, R400, R500, B300, B400, W300, W400and P300brought on high cancer possibility, especially B400and W300.(3) Biochars were heavily polluted by Cu, Zn, and Cd. For biochars made at the same temperature, concentration of heavy metals was hightest in pig mature biochar, while was lowest in wood chip biochar. For biochars made from the same feedstock, the concentration of heavy metal in biochars made in500℃or600℃was usually higher than that in biochar made in300℃or400℃.(4) Cadmium in biochars might had potential cancer threat to local resident health. Furthermore, human health threat of Cd was higher for pig mature biochar than other biochars.(5) Biochar played an important role in the removal and uptake of soil PAHs by ryegrass. Four soil treatments were obtained:blank (CK, no biochar addition), adding biochar (C), adding fertilizer (NP) and adding biochar and fertilizer both (CNP). Pot experiment was carried for the four soil treatments. Results showed that the loss of the PAHs was higher in soil amended with biochar than blank treatment. Fertilizer had great influences on the removal and uptake of PAHs by ryegrass. Total amounts of PAHs in the whole plants, or in the plant parts (root or shoot) were higher in soil with fertilizer than in soil without fertilizer.(6) Biochar played an important role in the uptake of heavy metals by ryegrass. There were no significant differences among the four soil treatments in total amounts of Cd, Ni, Cu and Cr in soil. However, total amounts of those metals in ryegrass were lower for the biochar treatment, i.e. CNP<NP; C<CK. This suggests that the sorption of Cd by biochar has reduced the plant uptake. |
PDF Full Text Request