Antonio Faggianoa, Maria Ricciardia, Oriana Mottab, Antonino Fiorentinoc, Antonio Protoa

aDepartment of Chemistry and Biology “Adolfo Zambelli”, University of Salerno, via Giovanni Paolo II 132, 84084 Fisciano, SA, Italy;
bDepartment of Medicine Surgery and Dentistry “Scuola Medica Salernitana”, University of Salerno, via S. Allende 1, 84081 Baronissi, SA, Italy
cDepartment of Chemistry, University of Milan, Via Golgi 19, 20133 Milan, Italy

This study compares the performance of activated carbon (AC) and woodchip-derived biochar (BC) in greywater (GW) treatment, focusing on the removal of chemical oxygen demand (COD), anionic surfactants (ASU), and non-ionic surfactants (NISU). GW, a significant component of domestic wastewater, contains high levels of organic pollutants and surfactants that can pose environmental risks if not treated effectively [1, 2]. Adsorption experiments were conducted to assess the performance of AC and BC, using Response Surface Methodology (RSM) to optimize the removal efficiency, coupled with breakthrough curves and isotherm modelling to understand adsorption dynamics better. The breakthrough curves indicated that AC provided a longer adsorption duration for COD and ASU, with delayed saturation compared to BC, which demonstrated faster contaminant removal but reached breakthrough earlier. Adsorption kinetics followed pseudo-first-order models, with AC reaching maximum adsorption capacities of 0.95 mg/g for COD and 0.08 mg/g for ASU. In contrast, BC displayed a significantly higher affinity for NISU, with a Langmuir constant (KL) of 8.4 × 103 L/mg, making it particularly effective for removing non-ionic surfactants. 

Isotherm analysis confirmed that monolayer adsorption was predominant for both adsorbents, with the Langmuir model providing the best fit for COD and surfactant removal. AC demonstrated a slightly higher adsorption capacity for COD, whereas BC showed a distinct advantage for NISU. This suggests that the choice between AC and BC should depend on the specific contaminants in the GW. Treated GW achieved COD concentrations reduced to approximately 10 mg/L and surfactant levels around 0.05 mg/L, meeting stringent reuse standards in Italy and Australia. Although AC offered greater long-term adsorption performance, BC emerged as a cost-effective and environmentally sustainable alternative for shorter-term applications. Its rapid adsorption rates, combined with lower environmental impact and production from renewable biomass, position BC as a promising solution for GW treatment, particularly in contexts where cost efficiency and sustainability are prioritized. These findings suggest that integrating biochar into GW treatment systems offers a viable, eco-friendly alternative to activated carbon, especially for applications focused on non-potable water reuse.

Keywords:  Greywater treatment; biochar adsorption; surfactant removal; sustainable water reuse

References

1. Faggiano, A., Ricciardi M., et al., Separation and Purification Technology 2025, 356, 129861. DOI: 10.1016/j.seppur.2024.129861. 

2. Quispe, J. I. B., Campos, L. C., et al., Journal of Water Process Engineering 2022, 48, 102908. DOI: 10.1016/j.jwpe.2022.102908.