Hassanpour Morteza, Cai Guiqin, Cooper Tal, Wang Qilin, O'Hara Ian M, Zhang Zhanying
Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, Brisbane, Queensland 4000, Australia; School of Mechanical, Medical and Process Engineering, Faculty of Engineering, Queensland University of Technology, Brisbane, Queensland 4000, Australia.
Centre for Agriculture and the Bioeconomy, Faculty of Science, Queensland University of Technology, Brisbane, Queensland 4000, Australia; School of Biology and Environmental Science, Faculty of Science, Queensland University of Technology, Brisbane, Queensland 4000, Australia.
Sci Total Environ. 2022 Nov 20;848:157727. doi: 10.1016/j.scitotenv.2022.157727. Epub 2022 Aug 2.
In this study, a FeCl-assisted hydrothermal treatment (HTT) process under mild conditions (90 °C-130 °C) was developed for deep dewatering of anaerobically digested sludge. HTT of sludge at 90 °C-130 °C with 4%-6% Fe ions loading based on total sludge solids followed by mechanical dewatering reduced sludge water content from 82% to 38%-53% and sludge weight by 62%-72%. The treatment increased the flowability of sludge through reduction of apparent viscosity and disintegration of colloidal forces between sludge particles. This study unveiled that FeCl-assisted HTT process had three mechanisms for improving sludge dewaterability and flowability. The treatment hydrolysed sludge flocs in the presence of Lewis acid FeCl and high temperature (90-130 °C). Fe ions also improved dewaterability through the formation of double electric layers and neutralisation of surface negative charges, leading to flocculation of sludge flocs. More importantly, the hydrolysed sludge components produced during HTT process acted as reducing agents and led to in-situ generation of iron oxyhydroxide nanoparticles through reduction-oxidation reactions, further enhancing flocculation/co-precipitation of sludge flocs. The treatment reduced EPS content and changed conformational structures of EPS proteins by breaking down hydrogen bond-maintaining α-helix which led to a loose EPS protein structure and enhanced hydrophobicity and flocculability. Furthermore, the FeCl-assisted treatment promoted immobilisation of the majority of heavy metals in the sludge matrix through co-precipitation/complexation reactions with iron species and organic/inorganic matters. This indicates that the FeCl-assisted treatment reduced direct toxicity/bioavailability of the majority of heavy metals and the treated sludge may be suitable for land application. Overall, this study provides new insights into mechanism of FeCl-assisted HTT process for dewaterability of anaerobically digested sludge and immobilisation of heavy metals.
在本研究中，开发了一种在温和条件（90℃-130℃）下的FeCl辅助水热处理（HTT）工艺，用于厌氧消化污泥的深度脱水。在90℃-130℃下对污泥进行HTT处理，铁离子负载量基于总污泥固体为4%-6%，随后进行机械脱水，污泥含水量从82%降至38%-53%，污泥重量减少62%-72%。该处理通过降低表观粘度和破坏污泥颗粒间的胶体力来提高污泥的流动性。本研究揭示，FeCl辅助HTT工艺有三种改善污泥脱水性能和流动性的机制。该处理在路易斯酸FeCl和高温（90-130℃）存在下使污泥絮体水解。铁离子还通过形成双电层和中和表面负电荷来改善脱水性能，导致污泥絮体絮凝。更重要的是，HTT过程中产生的水解污泥成分作为还原剂，通过氧化还原反应原位生成羟基氧化铁纳米颗粒，进一步增强污泥絮体的絮凝/共沉淀。该处理降低了胞外聚合物（EPS）含量，并通过破坏维持α-螺旋的氢键改变了EPS蛋白质的构象结构，导致EPS蛋白质结构松散，增强了疏水性和絮凝性。此外，FeCl辅助处理通过与铁物种以及有机/无机物质的共沉淀/络合反应促进了污泥基质中大多数重金属的固定。这表明FeCl辅助处理降低了大多数重金属的直接毒性/生物有效性，处理后的污泥可能适合土地应用。总体而言，本研究为FeCl辅助HTT工艺对厌氧消化污泥脱水性能和重金属固定的机制提供了新的见解。
