School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
Civil and Environmental Engineering Department, Stanford University, Stanford CA 94305, USA.
Environ Pollut. 2019 Nov;254(Pt B):113114. doi: 10.1016/j.envpol.2019.113114. Epub 2019 Aug 28.
Biochar as a porous carbon material could be used for improving soil physical and chemical properties, while insufficient attention has been paid to potential risks induced by infiltration of heavy metals in the runoff water flowing through biochar-amended soil. Four different soil-biochar matrices with same volumes were constructed including soil alone (M1), biochar alone (M2), soil-biochar layering (M3) and soil-biochar mixing (M4). Leaching experiments were conducted with Pb, Cu, and Zn contaminated runoff water. Results showed that biochar amendment greatly improved the water permeation, and the infiltration rates in M2, M3, and M4 were 2.85-23.0 mm min, being much higher than those in M1 (1.33-4.05 mm min), though the rates decreased as the leaching volumes increased. However, biochar induced more Pb, Cu, and Zn infiltrated through soil-biochar matrix. After 350-L leaching, M1 retained about 95% Pb, 90% Cu, and 36% Zn, while M2 only retained 4.80% Pb, 17.4% Cu, and 4.01% Zn; about 30% Pb, 80% Cu, and 15% Zn were retained in M3 and M4. Notably, Zn was trapped first and then re-leached into the filtrate, which resulted in a much higher effluent Zn than the influent Zn at the later stage. However, the unit weight of biochar showed a higher capacity for retaining heavy metals compared to per unit of soil. Under the dynamic water flow, all benefits and disadvantages induced by biochar were weakened with its physical disintegration. Biochar as soil amendment can enhance plant growth via ameliorating soil structure, while it would pose risks to environment because of large penetration of heavy metals. If biochar was compacted to form a denser physical structure, perhaps more heavy metals could be retained.
生物炭作为一种多孔碳材料，可用于改善土壤的物理和化学性质，但人们对重金属在径流水中渗透通过生物炭改良土壤所带来的潜在风险关注不足。本研究构建了包括土壤单独（M1）、生物炭单独（M2）、土壤-生物炭分层（M3）和土壤-生物炭混合（M4）在内的 4 种不同的土壤-生物炭基质，采用受 Pb、Cu 和 Zn 污染的径流进行淋滤实验。结果表明，生物炭改良极大地提高了水的渗透性，M2、M3 和 M4 的渗透速率分别为 2.85-23.0mm/min，明显高于 M1（1.33-4.05mm/min），但随着淋滤体积的增加，渗透速率降低。然而，生物炭诱导更多的 Pb、Cu 和 Zn 渗透通过土壤-生物炭基质。在 350L 淋滤后，M1 保留了约 95%的 Pb、90%的 Cu 和 36%的 Zn，而 M2 仅保留了 4.80%的 Pb、17.4%的 Cu 和 4.01%的 Zn；M3 和 M4 保留了约 30%的 Pb、80%的 Cu 和 15%的 Zn。值得注意的是，Zn 首先被截留，然后在后期重新释放到滤液中，导致滤液中 Zn 的含量比进水高得多。然而，与单位土壤相比，生物炭的单位重量表现出更高的重金属保留能力。在动态水流下，生物炭的所有优缺点都随着其物理解体而减弱。生物炭作为土壤改良剂可以通过改善土壤结构来促进植物生长，但由于重金属的大量渗透，它会对环境造成风险。如果生物炭被压实形成更致密的物理结构，可能会保留更多的重金属。
