China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai, 201306, China.
China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai, 201306, China; School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China.
J Environ Manage. 2023 Oct 15;344:118394. doi: 10.1016/j.jenvman.2023.118394. Epub 2023 Jun 22.
Large amounts of coastal silt produced annually is urgent to be treated with a feasible strategy. This study converted it into subgrade soil by cement solidification for resource utilization. Biochar was used as exogenous additive for enhancing compressive strength of the product, simultaneously achieving carbon sequestration. Three biochars derived from peanut shells (PSBC), cow dung (CDBC) and sewage sludge (SSBC) at 300 °C, 500 °C and 700 °C pyrolysis, were added into raw materials with 1%, 2% and 5%, respectively. All biochars significantly improved the compressive strength of the subgrade soil by 20-110%. Biochar catalyzed cement hydration reactions to produce more Ca(OH), CaCO and calcium silicate hydrates (C-S-H gel). The catalytic capacity of different biochars followed the order of SSBC > PSBC > CDBC. Addition of 2% SSBC500 induced the greatest increase in 28 d-strength from only 1.0 MPa-2.1 MPa, which was due to that 500 °C biochar had a suitable specific surface area and porosity. Biochar facilitated CO capture (absorption) during the hydration reactions at the initial 48 h with 55-70 mg g. The high alkalinity and water holding capacity of biochar contributed to the absorption of CO; the high content of minerals in SSBC compared to CDBC and PSBC promoted chemical conversion of CO to carbonate. Besides, the biochar itself as carbon rich material was encapsulated in the subgrade soil, which can be regarded as a long-term carbon sequestration strategy. Carbon budget analysis demonstrated that converting one ton dry silt into subgrade soil with addition of 2% biochar could increase CO sequestration from 11 kg to 36-94 kg. This study proposes a novel strategy of using biochar to strengthen the subgrade soil simultaneously achieve long-term carbon sequestration.
每年产生的大量滨海淤泥亟待采用可行的策略进行处理。本研究通过水泥固化将其转化为路基土，实现资源利用。生物炭可用作外源性添加剂，以提高产品的抗压强度，同时实现碳固存。将三种生物炭（花生壳生物炭 PSBC、牛粪生物炭 CDBC 和污水污泥生物炭 SSBC）分别在 300°C、500°C 和 700°C 下热解得到，添加到原材料中，添加比例分别为 1%、2%和 5%。所有生物炭均显著提高了路基土的抗压强度，提高幅度为 20-110%。生物炭催化水泥水化反应，生成更多的 Ca(OH)、CaCO 和硅酸钙水合物（C-S-H 凝胶）。不同生物炭的催化能力依次为 SSBC>PSBC>CDBC。添加 2% SSBC500 可使 28 天强度最大提高 2.1 MPa，仅为 1.0 MPa，这是因为 500°C 生物炭具有适宜的比表面积和孔隙率。生物炭在水化反应初期的 48 小时内促进 CO 的捕获（吸收），吸收量为 55-70mg/g。生物炭的高碱性和保水能力有助于 CO 的吸收；与 PSBC 和 CDBC 相比，SSBC 中的矿物质含量较高，促进了 CO 的化学转化为碳酸盐。此外，生物炭本身作为富含碳的物质被包裹在路基土中，这可以被视为一种长期的碳固存策略。碳预算分析表明，将一吨干淤泥转化为添加 2%生物炭的路基土，可以将 CO 的固存量从 11kg 增加到 36-94kg。本研究提出了一种利用生物炭增强路基土并同时实现长期碳固存的新策略。
