Removal of chemical and microbiological contaminants from domestic greywater using a recycled vertical flow bioreactor (RVFB)

Abstract

Reuse of domestic greywater (GW) for non-potable purposes is emerging as an important approach to the management and conservation of water resources, particularly in rural and developing areas where small-scale decentralized treatments are suited. Recently, researchers at Ben-Gurion University (Israel) have developed a modular system – the recycled vertical flow bioreactor (RVFB) – for the removal of chemical contaminants from GW. We report on the removal of chemical contaminants, indicator organisms, and opportunistic pathogens from GW using this system. Synthetic GW, enriched with wastes from a dining hall, was added to experimental RVFB systems. The greywater was recirculated for 2–3 days at which time half of the water was removed from each system and replaced with fresh synthetic GW. Removal of chemical and microbiological contaminants was determined by comparing influent to effluent samples obtained after 8 and 72 h treatment in the systems. GW treatment using the RVFB system reduced effluent concentrations for NO 3-N, total ammonia nitrogen, NO 2-N, total suspended solids, boron, and anionic surfactants to below the levels considered acceptable for either recreation or irrigation. Reduction in chemical contaminants was associated with a significant increase in the number of both heterotrophic bacteria and surfactant-degrading bacteria within the RVFB. Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa were present at the beginning of each treatment cycle. Treatment using the RVFB system resulted in final E. coli concentrations that met the USEPA water quality criteria for recreational water. Viable S. aureus and P. aeruginosa were consistently present in samples obtained at the end of the 72 h treatment period. The survival of these non-enteric opportunistic pathogens underscores the need for the consideration of additional indicator organisms to monitor and assure the safe reuse of GW.