Fenton degradation of biologically pre-treated pulp and paper effluent using zero-valent iron from commercial steel wool

Abstract The production of pulp and paper (P&P) is a significant industrial sector that heavily relies on fresh water, generating effluents with flow rates, which in the new plants reach around 3,000 m 3 /h. Traditionally, P&P effluents are treated through biological processes such as activated sludge and aerated lagoons, effectively removing biochemical oxygen demand (BOD) and colour, complying with environmental standards. However, increasing water scarcity driven by climate change necessitates reassessing production rates to conserve water quality and volume while maintaining compliance. This study explores enhancements in effluent treatment by integrating an advanced oxidation step after conventional biological treatment. Specifically, the study evaluates and compares the efficiency of: (i) the conventional Fenton reaction with soluble iron salts, (ii) conventional coagulation, and (iii) a Fenton process using zero-valent iron (ZVI) from commercial steel wool, operating at near-neutral pH (5.5–7.5). Batch experiments were performed using jar tests with industrial effluent samples from a bleached Kraft pulp mill. The analyses included dissolved organic carbon (DOC), BOD, chemical oxygen demand (COD), lignin (measured at 280 nm absorbance), and true colour, with characterizations of steel wool via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) before and after treatment. Results indicated that the ZVI-steel wool/H 2 O 2 Fenton process achieved superior removal rates of lignin and recalcitrant compounds, with average removals of 57.1 % COD, 67.2 % BOD, 90.5 % colour, and 83.4 % lignin compounds. Notably, treatment at pH 7.5 exhibited efficiencies comparable to pH 5.5, allowing lower chemical costs by eliminating the need for acid and alkali for pH adjustments before and after the Fenton step. These findings suggest the ZVI-steel wool/H 2 O 2 process as a viable polishing step for treating effluents from P&P plants, contributing to better sustainability by reducing the need for additional chemicals for pH adjustment, and increasing the quality of effluents for discharge and reuse.