Phosphate-rich municipal wastewater treatment using magnetite nanoparticles dispersed oakwood biochar-assisted pretreatment followed by air-gap membrane distillation

Vollständiger Abstract

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An integrated approach combining Fe 3 O 4 nanoparticle-loaded biochar-assisted pretreatment and air-gap membrane desalination (AGMD) was investigated for treating phosphate-rich wastewater. This study addresses key limitations of conventional coagulants, such as residual chemical load and limited removal efficiency. Fe 3 O 4 nanoparticles were co-precipitated on oakwood biochar (Fe 3 O 4 /BC). The Fe 3 O 4 /BC composite acts as a coagulant that can be rapidly separated under an applied magnetic field. This study systematically evaluated the pretreatment performance for turbidity and phosphate removal in phosphate-rich wastewater. A 94% phosphate and 77% turbidity reduction was obtained with a 2.5 g L -1 Fe 3 O 4 /BC dosage. In parallel, hydrophilic polyethersulfone (PES) and hydrophobic polytetrafluoroethylene (PTFE) membrane configurations were tested in AGMD with and without Fe 3 O 4 /BC-assisted pretreatment. The AGMD permeate flux, overall energy efficiency, and membrane fouling were compared in PES/AGMD, PT + PES/AGMD, PTFE/AGMD, and PT + PTFE/AGMD processes. A 21 times greater initial flux was obtained with the PES membrane in AGMD at 70 °C and 27.3 °C hot feed and coolant temperatures than with the PTFE membrane. However, higher flux reduction and higher salt deposition were observed on the hydrophilic PES membrane without pretreatment. The energy consumption for the PES/AGMD, PT + PES/AGMD, PTFE/AGMD, and PT + PTFE/AGMD processes were 1.516, 1.492, 4.559, and 4.245 kWh L -1 , respectively. Overall, the Fe 3 O 4 /BC-assisted pretreatment combined with AGMD presents a promising strategy for phosphate-rich municipal wastewater treatment. This enables effective contaminant removal while protecting membrane performance and reducing operational costs. Further work will focus on the reusability of Fe 3 O 4 /BC as a coagulant, long-term membrane performance, and pilot-scale validation.