Hydrogen peroxide levels in biochar-based bioretention cells with three environmental conditions and its potential risks

Recently, biochar with persistent free radicals has widely been applied to the removal of nutrient in bioretention cells. However, there is a lack of information on hydrogen peroxide (H2O2) levels in biochar-based bioretention cells with three environmental conditions and its potential risks. In this study, batch experiments were used to investigate H2O2 levels in biochar-based bioretention cells with different weight ratios of sand to biochar (S/B), hydraulic loading rate (HLR) and antecedent dry period (ADP). Potential risks of H2O2 on dominant community were also explored. Results showed that H2O2 levels in bioretention cells with 9:1, 8:2 and 7:3 of S/B were significantly high with the range from 0.024 to 0.044 mmol/L, and the production decreased with the increasing contents of biochar. Furthermore, H2O2 levels in three different heights of substrate layers and the bottom outlet enhanced with the rise of HLR, where the amplification of H2O2 in the middle layer was the largest, reaching 438.5% (ratio of H2O2 level at 2.0 m(3)/m(2)/d of HLR to the one at 0.4 m(3)/m(2)/d of HLR). In contrast, the long ADP was unfavorable to H2O2 levels in biochar-based bioretention cells. The production of H2O2 resulted in the change of dominant microflora (Bacteroidetes and Firmicutes), and the dosage of biochar could be the key. Altering these mentioned factors to achieve the regulation of microbial community structure in bioretention cells with biochar could be one of the promising approaches for the improvement of biological degradation function.