Demetallization of Sewage Sludge Using Low-Cost Ionic Liquids

Abstract

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 4 ]) and dimethylbutylammonium hydrogen sulfate ([DMBA][HSO 4 ]) 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 II , Ni II , Zn II , and Pb II without altering the phosphorus content, while other toxic metals such as Cr III , Cr VI and As III were more readily removed (>80%) with [TEA][HSO 4 ]. 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.

Moving towards Biofuels and High-Value Products through Phytoremediation and Biocatalytic Processes

“…The ionoSolv process conducted on the biomass (1 h at 150 • C,) allowed the obtainment of a clean pulp rich in cellulose, with the removal of hemicelluloses and 60% of lignin. Furthermore, the described methods also caused the electrodeposition of metals, resulting in total Pb extraction (99.3%) and a recovery of between 96 and 98% of Cd, Cu and Zn, thanks to the action of the ionic liquid as a metal dissolving agent [121].…”

Combining phytoremediation and biorefinery: Metal extraction from lead contaminated Miscanthus during pretreatment using the ionoSolv process

“…29 Moreover, ionic liquids have a wide electrochemical window, which makes them very attractive solvents for the electrodeposition and recovery of metals from ionic liquid liquors. [30][31][32] Here, we show that ionic liquid pretreatment is a formidable tool to integrate phytoremediation and biorefining into valuable and clean (metal free) chemicals and energy while using a solvent stream that can be recycled and used for the recovery of the metals via electrodeposition.…”

1-Butyl-3-methylimidazolium Chloride Affects Anaerobic Digestion through Altering Organics Transformation, Cell Viability, and Microbial Community

“…Ionic liquids (ILs), a large class of salts with negligible vapor pressures, high thermal, and brilliant solvation potential in both water and lipids (amphiphilic), have been considered the next generation “environmentally benign” solvents and widely used in various industrial processes such as cellulose processing, electrolytes in batteries and supercapacitors, corrosion protection, and even sludge demetallization and dehydration. − According to the reports from Global Market Insights, the IL market size surpassed USD 1.4 billion in 2020 and is likely to grow at a compound annual growth rate of 18.4% by 2027 (). The increased application of ILs inevitably results in their environmental occurrence.…”