Paper Mill Sludge Derived Biochar and Magnetic Biochar for simultaneous removal of COD and TDS from dye wastewater

Abstract

Dye wastewater, characterized by high chemical oxygen demand (COD) and total dissolved solids (TDS), poses significant environmental challenges. Despite the abundance of paper mill sludge, the existing literature provides limited evidence of its use as biochar for simultaneous COD and TDS removal in real-world effluent. This study addresses this gap by transforming PMS into biochar and magnetic biochar, and systematically evaluating their performance in removing COD and TDS from actual dye effluent. Biochar was synthesized via slow pyrolysis at 500°C (10 °C min⁻¹ heating rate, 1 h residence time), and magnetic biochar was produced by subsequent magnetization. Both adsorbents were characterized using proximate analysis, iodine number (IN), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) to establish their properties as novel adsorbents. Batch adsorption experiments evaluated the effects of pH, adsorbent dosage, and contact time. Results indicated that magnetic biochar outperformed biochar under all tested conditions. Under optimized operating conditions of pH 3, adsorbent dosage of 2.0 g/50 mL, and contact time of 180 min, biochar achieved COD and TDS removal efficiencies of 78% and 71%, respectively.

In contrast, magnetic biochar achieved 86% COD removal and 91% TDS removal. The superior performance of magnetic biochar is attributed to modifications in surface characteristics and increase active adsorption sites. Overall, this study demonstrates, for the first time, the effective and sustainable application of PMS-derived biochar and magnetic biochar for the simultaneous removal of COD and TDS from real dye wastewater, providing a viable pathway for the valorization of industrial waste.