[Properties of Biochars Prepared from Different Crop Straws and Leaching Behavior of Heavy Metals].

In this study, rice straw, soybean straw, wheat straw, and corn straw were chosen as raw materials, and biochars were prepared through the pyrolysis method at 550℃ under oxygen-limited conditions to investigate the physicochemical properties of biochars derived from the straws, the migration and transformation characteristics of heavy metals (HMs) (Cr, Ni, Cu, As, Cd, and Pb) after pyrolysis, and their leaching behaviors in different leaching solutions. The results showed that the physicochemical properties and elemental composition of the biochars were basically consistent. However, compared with that of biochars derived from other straws, biochar derived from wheat straw had a higher ash content (22.48%) and H/C radio (0.06). Meanwhile, biochar derived from corn straw had a smaller micropore volume (0.006 cm3·g-1) and a correspondingly smaller specific surface area (110.120 m2·g-1), which was consistent with the SEM image. After pyrolysis, the content of HMs (except Cd) increased by 14.04% to 410.81%, especially that of Cu and As. However, the content of Cd in soybean straw and corn straw decreased by 20.49% and 8.20% after pyrolysis, respectively, due to the low boiling point of Cd. Furthermore, most of the HMs (except Cd and Pb) tended to transform from unstable (acid-soluble/exchangeable and reducible forms) to stable forms (oxidizable and residual forms), implying that pyrolysis facilitated the stabilization of the HMs. The HMs in biochar were not leached or were leached in small amounts in ultra-pure water and buffered salt solutions, as opposed to leaching in relatively larger amounts in acetic acid solution and humic acid solution. Cr and Ni showed low leaching capacity in all leaching solutions. Cu showed relatively high leaching capacity in acetic acid solution, with the leaching amount ranging from 2.601 mg·kg-1 to 4.224 mg·kg-1, and As showed a relatively high leaching capacity in humic acid solution, with the leaching amount ranging from 0.074 mg·kg-1to 0.166 mg·kg-1. After pyrolysis, the environmental quality index (PIi) and the Nemerow pollution index (NPI) values of various HMs increased by different degrees. However, the pollution of single HMs remained at a safe level, and the integrated pollution of biochars was at the level of "clean". Due to the significant increase in potential ecological risk factors (Er) of Ni, Cd, and Pb after pyrolysis, the potential ecological risk index (RI) of biochar derived from the rice straw increased slightly. However, the potential ecological risk indexes of biochars derived from other straws significantly decreased after pyrolysis, owing to the stabilization of HMs.

[Inhibition of methanogenium by erythromycin and its domestation].

Erythromycin is a kind of antibiotic drugs with certain biological toxicity. In order to investigate the inhibitory effect of erythromycin on methanogens and its acclimation capacity, Anaerobic Toxicity Assay (ATA) and continuous experiment were conducted in anaerobic bottles and the Up-flow Anaerobic Sludge Blanket Reactor (UASB), respectively, to determine the accumulated methane production, ratio of methane production rate, COD removal efficiency, and methane content. The results showed that the methane production ratio was reduced to 56.1% in the presence of 150 mg x L(-1) of erythromycin and it was reduced by 99% when the erythromycin reached 250 mg x L(-1), indicating that the activity was completely inhibited. Keeping the erythromycin at an concentration of 20 mg x L(-1) in the process of continuous operation for 60d, the COD removal efficiency and methane content reached up to 81.4% and 64.2%, respectively. The results suggested that erythromycin had an inhibitory effect on methane bacteria, and the half inhibitory concentration was 150 mg x L(-1) (IC50:150 mg x L(-1)). The COD removal efficiency and methane content were increased by 15.13% and 22.05%, respectively, after domestication for 60 d.