Department of Chemical Engineering, Imperial College London, South Kensington, Exhibition Road, London SW7 2AZ, United Kingdom.
Efficiency Technologies, Bluecube House, Milton Keynes, Buckinghamshire MK12 5TS, United Kingdom.
Environ Sci Technol. 2021 Apr 20;55(8):5291-5300. doi: 10.1021/acs.est.0c03724. Epub 2021 Mar 16.
Sludge produced from wastewater treatment has little to no value and is typically treated through volume reduction techniques, such as dewatering, thickening, or digestion. However, these methods inherently increase heavy metal concentrations, which makes the sludge unsuitable for land spreading and difficult to dispose of, owing to strict legal requirements/regulations concerning these metals. We addressed this problem, for the first time, by using recyclable low-cost protic ionic liquids to complex these toxic metals through a chemical fractionation process. Sewage sludge samples collected from wastewater plants in the UK were heated with methylimidazolium chloride ([Hmim]Cl, triethylammonium hydrogen sulfate ([TEA][HSO]) and dimethylbutylammonium hydrogen sulfate ([DMBA][HSO]) under various operating temperatures, times and solids loadings to separate the sludge from its metal contaminants. Analysis of the residual solid product and metal-rich ionic liquid liquor using inductively coupled plasma-emission spectrometry showed that [Hmim]Cl extracted >90% of Cd, Ni, Zn, and Pb without altering the phosphorus content, while other toxic metals such as Cr, Cr and As were more readily removed (>80%) with [TEA][HSO]. We test the recyclability of [Hmim]Cl, showing insignificant efficiency losses over 6 cycles and discuss the possibilities of using electrochemical deposition to prevent the buildup of metal in the IL. This approach opens up new avenues for sewage sludge valorization, including potential applications in emulsion fuels or fertilizer development, accessed by techno-economic analysis.
从废水处理中产生的污泥几乎没有价值，通常通过减容技术进行处理，例如脱水、浓缩或消化。然而，这些方法本质上会增加重金属浓度，这使得污泥不适合土地施用，并且由于对这些金属的严格法律要求/规定，难以处置。我们首次通过使用可回收的低成本质子离子液体来解决这个问题，通过化学分馏过程来络合这些有毒金属。从英国废水厂收集的污水污泥样品在不同的操作温度、时间和固体重度下，用甲基咪唑啉氯化物 ([Hmim]Cl)、三乙铵硫酸氢盐 ([TEA][HSO]) 和二甲基丁基硫酸氢盐 ([DMBA][HSO]) 加热，以将污泥与其金属污染物分离。使用电感耦合等离子体发射光谱法对残余固体产物和富含金属的离子液体进行分析表明，[Hmim]Cl 可提取 >90%的 Cd、Ni、Zn 和 Pb，而不改变磷含量，而其他有毒金属，如 Cr、Cr 和 As 则更容易被去除 (>80%)，采用 [TEA][HSO]。我们测试了 [Hmim]Cl 的可回收性，在 6 个循环内效率损失不明显，并讨论了使用电化学沉积来防止 IL 中金属积累的可能性。这种方法为污水污泥的增值利用开辟了新途径，包括通过技术经济分析在乳液燃料或肥料开发中应用的可能性。
