Recycling of sludge residue as a coagulant for phosphorus removal from aqueous solutions.

Phosphorus pollution poses a significant challenge in addressing water contamination. The coagulant is one of the effective methods to remove phosphorus from wastewater. Abundant Al and Fe oxides in sludge residue make it have great potential to synthesize water treatment coagulants. However, the utilization of sludge residue for preparation of coagulant was seldom investigated. In this study, we fabricated a novel coagulant, polyaluminum ferric chloride (SM-PAC), using sludge residue as a raw material through acid leaching and polymerization processes. Characterization results confirm that the parameters of SM-PAC meet the specifications outlined in the national standard (GB/T 22627-2022). We investigated the effects of pH, dosage, initial phosphorus concentration, and contact time on the removal efficiency of SM-PAC. As anticipated, the prepared SM-PAC exhibited a significant efficacy in removing phosphorus, meeting the discharge standards set for municipal sewage. Furthermore, the adsorption kinetics analysis suggests that the predominant mode of phosphorus adsorption on SM-PAC is chemical adsorption. Furthermore, the SM-PAC was employed in the actual wastewater treatment plant and exhibited excellent efficiency in phosphorus removal. The utilization of SM-PAC can not only effectively address the issue of sludge disposal but also achieve the goal of "treating waste with waste." It is expected that the proposed method of reusing sludge residue as a resource can provide a sustainable way to synthesize a coagulant for phosphorus removal.