Efficiency of multi-layer greywater and rainwater treatment for sustainable water management through water reuse in irrigation

The integrated management of greywater and collected rainwater for water reuse is a sustainable approach to reducing stress on freshwater sources and addressing water scarcity. This study proposes using treated greywater and rainwater for agricultural and landscape irrigation and evaluates the compliance of reclaimed water with European Union standards. Accordingly, an aerobic membrane bioreactor (MBR) was used to treat greywater, while a cross-flow flat sheet ultrafiltration (UF) system was employed for the treatment of collected rainwater. Treated greywater and treated rainwater were mixed in a 25:75 volumetric ratio and subjected to ultraviolet (UV) disinfection to produce reclaimed water. In greywater treatment, the MBR achieved removal efficiencies of 65.5 ± 4.3 % for chemical oxygen demand (COD), 62.5 ± 2.9 % for soluble COD, 47.8 ± 1.9 % for total nitrogen, and 47.2 ± 6.1 % for total phosphorus. Turbidity was reduced from 36.6 ± 8.0 NTU to 0.77 ± 0.10 NTU. Similarly, the UF system effectively reduced the turbidity of collected rainwater from 6.33 ± 0.64 NTU to 0.39 ± 0.09 NTU. Both treatment systems produced coliform-free effluents, with no detection of fecal coliform or Escherichia coli . Despite this outcome, the UV disinfection system played a critical role in ensuring the reclaimed water was free of pathogenic microorganisms. Thus, the effluents from the MBR and UF systems were treated with UV disinfection as a final quality assurance step. The results demonstrated that the proposed treatment configuration is applicable at the tested mixing ratio. The study also highlights the need to investigate different mixing ratios and alternative greywater and rainwater sources, as these factors influence influent characteristics and reclaimed water quality.