[Effects of Hematite and Biochar Addition on Wastewater Treatment Efficiency, Greenhouse Gas Emission, and Microbial Community in Subsurface Flow Constructed Wetland].

The type and structure of the substrate in constructed wetland affects the diversity and abundance of microorganisms, thereby influencing the effect of sewage treatment. In this study, four groups of wetlands were constructed in the greenhouse:blank-constructed wetland (CW0), hematite-constructed wetland (CW1), biochar-constructed wetland (CW2), and hematite+biochar-constructed wetland (CW3), to study the differences in sewage treatment effects, greenhouse gas emissions, and microbial community structures of constructed wetland systems under different filler substrates. The results showed that the addition of hematite or biochar increased the COD removal rate of -0.12% to 1.7%. The addition of biochar increased the removal rate of NH4+-N by 22.48% and NO3--N by 6.82% and reduced the emission flux of CH4 by 83.91% and N2O by 30.81%. The addition of hematite reduced the removal rate of NH4+-N by 1.12%, increased the removal rate of NO3--N by 3.98%, and reduced the emission flux of CH4 by 33.29% and N2O by 25.2%. Adding biochar or hematite increased the relative abundances of Actinobacteria and Proteobacteria, which was beneficial to the removal of COD. The Ace, Chao, Sobs, and Shannon indexes in the substrate treated with biochar were the largest, and the Simpson index was the smallest. The treatment with hematite was the opposite, indicating that the richness and diversity of microbial communities in the treatment system with biochar was the largest. Adding hematite reduced the richness and diversity of the microbial community in the constructed wetland system. Adding biochar or hematite increased the relative abundances of Dechloromonas, Thaurea, Saccharimonadales, and other denitrifying bacteria, which was beneficial to wetland denitrification. The addition of biochar increased the abundances of nosZ, nirS, and nirK functional genes, which were conducive to the occurrence of denitrification. The addition of biochar increased the abundances of pmoA functional genes, reduced the abundance of mcrA functional genes, and inhibited the production of CH4. It also increased the abundance of methanotrophic bacteria and promoted the occurrence of the CH4 oxidation process. Although the addition of hematite increased the abundance of mcrA functional genes, Fe3+ competed with methanogens for electron donors and inhibited the production of CH4.

[Effects of Plastic Film Mulching and Biochar Application on N2O Emission from a Vegetable Field].

The aim of this research was to examine the effects of biochar addition (B0:0 t·hm-2, B20:20 t·hm-2, and B40:40 t·hm-2) and mulching (FM:film and NM:no film) on vegetables. The impact of N2O emissions in the field was based on the pepper-radish rotation vegetable field system on the farm of Southwest University, using static dark box/gas chromatography to conduct in-situ observations in the field for one year. In this experiment, a total of six treatments were set up, namely NMB0 (CK) and FMB0, NMB20 and FMB20, and NMB40 and FMB40. The results showed that FM significantly increased the content of ammonium and nitrate nitrogen in the pepper season soil (P<0.05) but had no significant effect on soil environmental factors in the radish season. Compared with that of NM, the pepper season FM increased the N2O emissions of the B0, B20, and B40 treatments by 52.87%, 52.97%, and 52.49% (P<0.05), respectively, but the radish season FM had no significant effect on N2O emissions. Biochar had no significant effect on soil environmental factors in the pepper and radish seasons. The addition of biochar in the radish season reduced N2O emissions by 28.76%-67.88% (P<0.01), and the addition of biochar in the pepper season had no significant effect on N2O emissions. Compared with that of NM, under different biochar levels, FM increased the yield of pepper by 15.85%-161.32% and increased the yield of radish by 43.97%-75.80%. Biochar significantly increased the yield of peppers and had no significant effect on the yield of radishes. Regardless of whether the film was covered or not, when the amount of biochar added was 20 t·hm-2, the yields of pepper and radish were the highest. The analysis of N2O emission intensity revealed that FM in the pepper season significantly reduced N2O emission intensity, whereas in the radish season FM and biochar significantly reduced N2O emission intensity, and both planting seasons reached the lowest N2O emission intensity under the FMB20 treatment. Therefore, mulching and applying 20 t·hm-2 biochar were the best farmland management measures for the pepper season and radish season, which could achieve high yields and the lowest N2O emissions, accomplishing a win-win for economic and environmental benefits.