School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, PR China.
Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
Chemosphere. 2016 Apr;149:263-71. doi: 10.1016/j.chemosphere.2016.01.060. Epub 2016 Feb 8.
Currently, sludge pyrolysis has been considered as a promising technology to solve disposal problem of municipal sewage sludge, recover sludge heating value, sequester carbon and replenish nutrients in farmland soils. The resultant sludge-derived biochar (SDBC) is potentially an excellent stabilizing agent for metal species. This study applied the SDBC into four soils that had been contaminated in field with cationic Pb(II) and Cd(II)/Ni(II), and anionic Cr(VI) and As(III), respectively. The performance of metal stabilization under various operational and environmental conditions was evaluated with acid batch extraction and column leaching tests. Results indicated the SDBC could effectively stabilize these metals, which was favored by elevated temperature and longer aging. Periodic temperature decrease from 45 to 4 °C resulted in the release of immobilized Cr(VI) and As(III) but not Pb(II). However, a longer aging time offset such metal remobilization. This was possibly because more Pb was strongly bound and even formed stable precipitates, as shown by XRD and sequential extraction results. With increasing time, Cr(VI) was sorbed and partly reduced to Cr(III), while immobilized As(III) was co-oxidized to As(V) as indicated by XPS spectra. Column tests revealed that adding SDBC as a separate layer was unfavorable because the concentrated Cd(II) and Ni(II) in localized positions increased the peak levels of metal release under continuous acid leaching. In contrast, uniformly mixed SDBC could effectively delay the metal breakthrough and reduce their released amounts. Yet, a long-term monitoring may be required for evaluating the potential leaching risks and bioavailability/toxicity of these immobilized and transformed species in the SDBC-amended soils.
目前，污泥热解已被认为是一种很有前途的技术，可以解决城市污水污泥的处理问题，回收污泥热值，固碳，并补充农田土壤中的养分。所得的污泥衍生生物炭（SDBC）很可能是一种极好的金属稳定剂。本研究将 SDBC 应用于分别受阳离子 Pb(II)、Cd(II)/Ni(II)，阴离子 Cr(VI)和 As(III)污染的四种土壤中。通过酸批式提取和柱浸出试验评价了各种操作和环境条件下的金属稳定性能。结果表明，SDBC 能有效地稳定这些金属，这一效果受到温度升高和老化时间延长的促进。从 45 到 4°C 的周期性温度下降导致固定化 Cr(VI)和 As(III)的释放，但不导致 Pb(II)的释放。然而，较长的老化时间可以抵消这种金属的再迁移。这可能是因为更多的 Pb 被强烈结合，甚至形成了稳定的沉淀物，这一点从 XRD 和顺序提取结果中可以看出。随着时间的推移，Cr(VI)被吸附并部分还原为 Cr(III)，同时固定化的 As(III)被共同氧化为 As(V)，这一点从 XPS 谱图中可以看出。柱试验表明，将 SDBC 作为单独的一层添加是不利的，因为局部位置的高浓度 Cd(II)和 Ni(II)会增加连续酸浸过程中金属释放的峰值水平。相比之下，均匀混合的 SDBC 可以有效地延迟金属突破，并减少其释放量。然而，可能需要进行长期监测，以评估 SDBC 改良土壤中这些固定化和转化物种的潜在浸出风险和生物利用度/毒性。
