Hybrid conditioning of ionic liquid coupling with H2SO4 to improve the dewatering performance of municipal sludge

Abstract

Municipal sludge generated from wastewater treatment plants can cause a serious environmental and economic burden. A novel hybrid conditioning strategy was developed to enhance the dewatering performance of sludge, employing 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C₄mim][CF₃SO₃]) treatment combined with H₂SO₄ acidification. Following conditioning, the capillary suction time ( ${\text{CST}}_{\text{normalized}}$ ), the specific resistance of filtration (SRF), and moisture content of the treated sludge were decreased to 1.99 ± 0.24 (s·L/g TSS), 1.33 ± 0.05 (10¹² m/kg), and 72.01 ± 0.94%, respectively. The results were superior to those achieved with sludge treated solely by H₂SO₄ acidification or [C₄mim][CF₃SO₃] alone. The biomacromolecules within the sludge flocs were dissolved by [C₄mim][CF₃SO₃], while simultaneously, the microorganisms were inactivated. Consequently, the colloidal-like structures of the sludge flocs were destroyed. Additionally, the ionizable functional groups of the biomacromolecules were instantly protonated by the introduced H⁺ ions, and their negative charges were neutralized during the H₂SO₄ acidification process. The presence of H⁺ ions promoted the weakening of electrostatic repulsion between the sludge flocs. As a result, an enhancement of sludge dewaterability was obtained after treatment with [C₄mim][CF₃SO₃] and H₂SO₄ acidification. The finding of the intensification mechanism of sludge dewaterability brought by hybrid treatment of acidification and [C₄mim][CF₃SO₃] provides novel insights into the field of sludge disposal.

Keywords: Acidification; Dewaterability; Hybrid conditioning; Ionic liquid; Municipal sludge.