Removal of total organic carbon and calcium ions from leachate membrane concentrate through polyferric sulfate coagulation enhanced with biochar

Abstract

With the development of industrialization and urbanization processes, a large amount of leachate membrane concentrate (LMC) with poor biodegradability, high organic pollutants and salt content has been generated. Previous studies often struggled to balance treatment effectiveness with operational costs or caused secondary pollution. In this study, polyferric sulfate (PFS) was selected for the coagulation treatment of LMC with Box-Behnken Design (BBD) experiments as optimization and then enhanced with wheat dust biochar (WDB) to solve the above problems. The optimized conditions were a pH of 5.9, a PFS dosage of 4.8 g/L, a water temperature of 19.9 °C, a rapid stirring speed of 400 rpm, and a slow stirring time of 15 min, achieving a total organic carbon (TOC) removal rate of 75.20 % with corresponding reductions in other pollutant indicators. When biochar was added, the TOC, ammonium nitrogen (NH₄⁺-N) and Ca²⁺ removal rates increased to 81.36 %, 82.85 % and 90.23 %, respectively. The chroma and turbidity were also significantly reduced. Moreover, adding biochar increased the sedimentation rate to 3.75 times the original rate, reduced sludge volume and improved water yield, leading to cost savings. Overall, this method is simple to operate and environmentally friendly, offering both effective treatment and economic benefits and holding practical significance for engineering applications and resource recovery.