A survey of the microbial quality of wastewaters in Ismailia, Egypt and the implications for wastewater reuse

Abstract

The occurrence of parasite ova, cysts and faecal coliforms in urban wastewater and their removal was determined after sewage treatment in gravel bed hydroponic (GBH) constructed wetlands receiving conventionally treated wastewater at Abu Attwa, Ismailia. Samples of raw wastewater and GBH influent and effluents were examined for eggs of intestinal helminths over two months in 1995. All raw wastewater samples were found to be positive for Ascaris lumbricoides but eggs of Hymenolepis spp, Trichuris spp, Ancylostoma duodenale and Toxocara spp were also detected in raw and conventionally treated wastewaters. In Ismailia, the concentration of eggs of human intestinal helminths in raw wastewater ranged from 6–42/L. In the influent to the GBH beds, the concentration of helminth eggs was reduced and ranged from 0–11/L; eggs of Ascaris were found in 28% of the samples. No helminth eggs were recovered from GBH treated effluents. Cysts of protozoa and faecal coliform bacteria were also removed by GBH beds to some degree. Raw wastewater contained cysts of the protozoa, Entamoeba coli, E. histolytica and Giardia spp. Although the density and diversity of species was reduced after treatment in the GBH beds, some amoebic cysts were found in the effluents. Faecal coliform removal averaged 2–3 logs during sewage treatment in GBH beds but effluents did not satisfy WHO guidelines for unrestricted irrigation. This survey indicates that GBH beds have the capacity to remove pathogens from wastewaters. Improvement in wastewater quality after GBH treatment satisfied WHO microbiological quality guidelines for restricted irrigation. With a retention time of 6h, GBH constructed wetlands have practical applications for wastewater treatment for safe reuse in Egypt.