Comprehensive investigation and mechanisms of drilling waste sludge dewaterability by Fe(II)/persulfate pretreatment

Abstract The drilling waste sludge mainly sourced oil well cement slurry with fluid loss additives. The fluid loss additives make the drilling waste sludge has strong water holding capacity. The preliminary difficulty of reduction of drilling waste sludge was dewatering. Fe(Ⅱ)/persulfate pretreatment was reported to improve dewaterability and reduce organic matter in sludge. Herein, we systematically investigated Fe(Ⅱ)/persulfate pretreatment on improving the dewaterability of drilling waste sludge and revealed the involved mechanism. The experimental results showed the Fe(Ⅱ)/persulfate pretreatment decreased the water content (WC) and specific resistance to filtration (SRF) of sludge filter cake to 29.73% and 79.46% respectively with 16 mg/g DS (dry solid) Fe(Ⅱ) and 12 mg/g DS persulfate. In addition, the dewatering time was decreased by 80.38%. The correlation analysis results indicated that these characteristics interactions (sludge VSS solubilization, particle size, Zeta potential, viscosity and dewatering) significantly influenced the dewatering of drilling waste sludge. Mechanism investigation revealed that high VSS content in sludge had strong water affinity capacity and negative Zeta potential, which inhibited the dewaterability and aggregation. When Fe(Ⅱ)/persulfate pretreatment decomposed sludge flocs and oxidized organic matter, the bound water adsorbed was released. The cations of Fe2+ and Fe3+ compressed the double electric layer alleviating the electronegativity and aggregated the sludge particles. Consequently, the aggregated drilling waste sludge reinforced the hydrophobicity and porous structure, which availed to drain bound water out and improve the deep dewatering. This work provides possible strategy supports for drilling waste sludge dewatering in the future.