The reuse of greywater (GW) is an attractive addition to water management options. One of the major concerns limiting GW reuse is the possible presence of harmful microorganisms. In addition to total coliform organisms, enteric organisms (Salmonella, Shigella and poliovirus Type
1 Cryptosporidium, Giardia) and opportunistic pathogens ( Staphylococcus aureus and Pseudomonas aeruginosa) may be present in GW. Recently, researchers at Ben Gurion University have developed a new small-scale, decentralized greywater treatment system, the Recycling Vertical
Flow Constructed Wetland. The population dynamics of E. coli, Staph. aureus and Ps. aeruginosa in three different synthetic GWs formulated to reflect the variable composition of domestic GW were examined in this treatment system. E. coli, Staph. aureus, and Ps. spp. were
present in samples from all of the systems at the beginning of each treatment cycle. Control studies indicated that the concentration of E. coli changed by less than 2% in untreated samples of GW over 3 days. In the RVFCW, E. coli was reduced to concentrations below detection
(<1 CFU (100ml)−1 ) at the end of the treatment cycle. (2–3 d) and therefore, consistently resulted in E. coli levels that meet the USEPA standards for water reuse (USEPA, 2004) Removal of Staph aureus varied depending on the formulation of GW while
there was no significant change in the number of Ps. spp. in any of the GW formulations. Thus, both of these opportunistic pathogens could be found in treated effluent in the absence of E. coli. These results underscore the need for extensive microbiological monitoring of greywater
systems as well as the need for the development of greywater specific standards.
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