Comparative study of greywater treatment using activated carbon and woodchip biochar for surfactant and organic matter removal

Greywater (GW) treatment is recognized as a more efficient alternative to blackwater treatment, particularly for reuse applications, due to its lower pathogen content and higher concentrations of chemical oxygen demand (COD) and surfactants. In this study, the adsorption performance of woodchip biochar (BC) and activated carbon (AC) was compared for the removal of COD, anionic surfactants (ASU), and non-ionic surfactants (NISU) from GW. Response Surface Methodology (RSM) was employed to optimize the removal efficiency of both organic matter and surfactants. AC demonstrated higher adsorption capacities for COD and ASU, with K_L = 0.007 L/mg and Qmax = 0.95 mg/g for COD, and K_L = 1.4 × 10⁴ L/mg and Qmax = 0.08 mg/g for ASU. In contrast, BC showed a significantly higher affinity for NISU, with K_L = 8.4 × 10³ L/mg and Qmax = 0.01 mg/g. Breakthrough curves and pseudo-first-order (PFO) kinetics provided insights into adsorption dynamics, with AC showing delayed breakthrough and greater longevity, while BC offered rapid adsorption and cost-effectiveness. The treated GW achieved substantial reductions in contaminant levels, with final COD and surfactant concentrations reduced to approximately 10 mg/L and 0.05 mg/L, respectively, meeting Italian and Australian regulatory standards. The study highlights the potential of woodchip BC as a cost-effective and sustainable alternative to AC, particularly for short-term adsorption applications, and offers valuable insights into the treatment of GW for reuse.