Electro-osmotic treatment of dredged sludge using lignosulfonate as additive

Abstract

Electro-osmosis (EO) has been widely recognized as a promising technique for the treatment of dredged sludge. However, EO alone often fails to deliver satisfactory results. A more effective approach involves its integration with stabilizing additives. In this study, an eco-friendly polymer stabilizer, lignosulfonate (LS), was incorporated into EO to evaluate their combined effects on the geotechnical behavior of sludge. Two common forms of LS—sodium lignosulfonate (LSS) and calcium lignosulfonate (LSC)—were applied at concentrations of 3 %, 6 %, 12 %, and 20 %. The results showed that the introduction of LS-derived ions (Na⁺ or Ca²⁺) markedly increased soil electrical conductivity, whereas excessive dosages reduced electro-osmotic permeability. LSS-treated soils exhibited higher conductivity than those treated with LSC, owing to the greater mobility of Na⁺ compared with Ca²⁺ under EO. Scanning electron microscopy confirmed that LS promoted soil particle aggregation and improved cohesion. X-ray diffraction indicated little change in the primary mineral composition of sludge, while X-ray fluorescence revealed that LS combined with iron electrodes significantly altered sulfur and iron contents. Overall, the synergistic use of EO and LS improved electrical conduction and enhanced soil microstructure, although its influence on permeability was limited. Mechanistically, soluble salts from LS reduced the zeta potential and electro-osmotic permeability, while the hydrophilic groups of dissolved LS formed a stable adsorption film between soil particles and pore water, further decreasing electro-osmotic permeability.