Towards low energy greywater treatment of surfactants and pathogens

Greywater reuse in households and off-grid applications is growing in response to water scarcity. Effective treatment technologies must balance water quality, efficiency, and low energy or chemical inputs. This study presents a low-energy, non-biological greywater treatment system using foam fractionation and in situ electrochlorination, leveraging ambient chloride in greywater. Designed for handwashing stations and household reuse, the system treats up to 450 L day^- 1 using < 1 kWh day^- 1 of energy with no chemical dosing. Among six screened physical-chemical processes, foam fractionation was the only method achieving > 80% COD removal with high water recovery. Smaller diffuser pore sizes and lower air flowrates improved COD removal by increasing bubble surface area, though at the cost of water recovery. Pulsed aeration improved water recovery by ~ 20% with minimal COD performance loss. Surfactant behavior, correlated with the critical micelle concentration (CMC), strongly influenced foam stability and COD removal. Both free and combined chlorine residuals were successfully generated via in situ electrochlorination, using only the chloride ions naturally present in greywater. In situ electrochlorination following foam treatment generated up to 0.53 mg L^- 1 of residual chlorine. Foam fractionation with small-pore diffusers removed surfactants and other compounds that inhibit chlorine generation, such as CAPB, SDS, and anions, improving disinfection outcomes. The system achieved > 70% COD removal and > 80% water recovery. This integrated, chemical-free system provides a promising solution for decentralized greywater reuse. With further optimization, it may consistently achieve < 50 mg L^- 1 COD and adequate disinfection, supporting sustainable hygiene in low-resource settings.

The online version contains supplementary material available at 10.1007/s43832-025-00295-x.