Use of waste water for aquaculture: an experimental field study at a sewage-treatment plant, Egypt

The primary and secondary treated waste effluents were successfully used to grow the Nile tilapia Oreochromis niloticus (L.). The growth rate of fish reared in treated waste water was significantly higher than that of fish reared in the natural habitat. Bacterial loads in fish organs were higher in the gills followed by the intestine and the skin and finally the edible muscles. The total aerobic bacterial count was very low (9.3 × 10² g^?1) in the edible muscles of fish grown in secondary-treated effluent and complied with the WHO guidelines (less than 10⁵ g^?1). Salmonella, Shigella and Staphylococcus were completely absent in all fish samples examined. The highest concentrations of heavy metals were found in liver tissues, followed by intestine and gills and then the muscles. Accumulation levels were within the acceptable limits when compared to the international legal standards for hazardous elements in fish and fishery products. In conclusion, chemical and bacterial analyses indicated that there is no evidence of any public health hazard associated with treated waste water reuse in aquaculture. However, the risks, if any, to the fish growers, processors and consumers should be evaluated, specially that related to viral pathogens.