Quantifying biochar-induced greenhouse gases emission reduction effects in constructed wetlands and its heterogeneity: A multi-level meta-analysis.

Zero-waste biochar is an emerging tool for carbon neutralization, but the role of biochar in reducing greenhouse gases (GHGs) emissions from CWs were controversy and uncertainty. Yet, no previous study has integrated multiple research systems to quantitatively examine biochar-mediated GHGs emission reduction potential in CWs. Here we synthesized 114 studies to quantify biochar-induced declines ability of GHGs in the CWs by using the multi-level meta-analysis, reveal the variation of GHGs emission effect in different biochar-CWs and its response relationship with biochar, and identify the moderating variables that had a strong explanatory effect on the emission reduction effect of biochar. We showed that biochar remarkably affect CO2 mitigation (p < 0.05), but has insignificant and heterogeneous effects on CH4 and N2O. Pyrolysis time, influent dissolved oxygen (DO), influent NO3--N concentration, hydraulic retention time (HRT) and wetland type can significantly affect the effect of biochar on CH4 emission reduction. Particularly, the importance of HRT and wetland type was 0.89 and 0.85, respectively. Specially, the surface batch CWs modified by biochar could significantly promote the emission of CH4 (p < 0.001), and the effect size was up to 89.59. For N2O, biochar diameter, biochar addition ratio, influent COD/TN ratio, plant name, and removal efficiency of NO3--N/TN/COD were significant moderators. Among them, influent COD/TN ratio and plant name showed a stronger explanation. Planting Cyperus alternifolius L. significantly enhanced the N2O emission reduction capacity by biochar (p < 0.001), and effect size was as low as -24.32. 700-900 °C biochar can promote CH4 flux but inhibit N2O flux. This study provides an important theoretical basis and valuable strategic guidance for more accurate estimation and improvement of synergistic emission reduction benefits between CH4 and N2O of biochar in CWs.

Decontamination performance and cleaning characteristics of three common used paved permeable bricks.

To investigate the effectiveness of different permeable bricks on the pollutants from urban rainfall runoff, three common used bricks (ceramic brick, cement brick, and steel slag brick) were selected and applied to study their decontamination performance. The influencing factors such as rainfall intensity and contaminant concentrations were investigated. Then the ultrapure water was used to wash the permeable brick to research the pollution status and cleaning characteristics by monitoring the water quality of the rinsing water. Suspended solids (SS), chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), total phosphorus (TP), and heavy metals (Cu, Zn, Pb, and Cd) in the influent and effluent were measured. The results showed the following: (I) The upper layer of the brick may play a more critical role in purification process; the uniform and dense pore distribution of ceramic permeable brick was instrumental in the retention of particulates. (II) Contaminant concentration and rainfall intensity had a great influence on pollutants with lower removal rate and had little effect on pollutants with higher removal rate. (III) Non-sintered bricks containing a certain amount of cement increased the pH after filtration. (IV) The removal performance of permeable brick for dissolved pollutants such as COD, NH4-N, and TN was inferior to that for SS, TP, and heavy metals since the discrepancy in removal mechanism of pollutants. The study could offer a new perspective for the decontamination research of pervious bricks.