Department of Chemistry, Umeå University, SE-90187 Umeå, Sweden; Industrial Doctoral School, Umeå University, SE-90187 Umeå, Sweden.
Department of Chemistry, Umeå University, SE-90187 Umeå, Sweden.
Waste Manag. 2022 Sep;151:60-69. doi: 10.1016/j.wasman.2022.07.023. Epub 2022 Aug 1.
Hydrothermal carbonization (HTC) is a treatment technique with great potential for sanitizing digested sewage sludge (SS) and converting it into valuable products. In particular, phosphorus (P) recovery from hydrothermally carbonized SS has attracted special attention in recent years. This work aims to examine the leaching efficiency of P and the consequent release of metals and heavy metals from SS hydrochars (at 180, 215 and 250 °C) using organic acids (oxalate and citrate) over a range of pH values (0-4) and extraction times (5 min-24 h). Both organic acids triggered P extraction efficiencies exceeding 75 % at the lowest pH, but only oxalate reached a nearly complete P release from hydrochars at pH > 0 and for all carbonization temperatures. Low HTC temperature (180 °C) and short extraction time (5 min) were the optimal conditions treatment for P recovery when reacted in oxalate solutions of maximal pH buffering capacity (pH = 1.4). However, oxalate leaching also transferred metals/heavy metals into the P-leachate, with the exception of Ca being retained in the solid residue from HTC as Ca-oxalate precipitate. Different characterization methods confirmed the presence of this precipitate, and provided information about the surface and morphological changes of the SS hydrochars following acid treatment. The results suggest that HTC not only a promising technique to sanitize and reduce the volume of SS, but also an efficient means for P recovery using oxalic acid, thus contributing to the circular economy of P.
水热碳化（HTC）是一种具有很大潜力的处理技术，可以对消化后的污水污泥（SS）进行消毒，并将其转化为有价值的产品。特别是，近年来从水热碳化 SS 中回收磷（P）引起了特别关注。本工作旨在研究使用有机酸（草酸盐和柠檬酸盐）在 pH 值（0-4）和提取时间（5 分钟-24 小时）范围内从 SS 水热炭（在 180、215 和 250°C 下）浸出 P 的效率，以及随后释放的金属和重金属。两种有机酸在最低 pH 值下均引发了超过 75%的 P 提取效率，但只有草酸盐在 pH>0 且所有碳化温度下均能从水热炭中几乎完全释放 P。低 HTC 温度（180°C）和短提取时间（5 分钟）是在草酸盐溶液具有最大 pH 缓冲能力（pH=1.4）时，用 oxalate 溶液反应进行 P 回收的最佳条件。然而，草酸盐浸出也将金属/重金属转移到 P 浸出液中，除了 Ca 作为 Ca-草酸盐沉淀保留在 HTC 的固体残渣中。不同的表征方法证实了这种沉淀的存在，并提供了关于酸处理后 SS 水热炭表面和形态变化的信息。结果表明，HTC 不仅是一种对 SS 进行消毒和减少体积的有前途的技术，而且是使用草酸回收 P 的有效方法，从而有助于 P 的循环经济。
