Faecal indicator organisms in the Renoster Spruit system of the Modder-Riet River catchment and implications for human users of the water

Abstract

The impact of a variety of urban discharges from Bloemfontein on the numbers of microbiological faecal indicator organisms in the water of the Renoster Spruit subcatchment was investigated using E. coli, C. perfringens and somatic coliphages as microbial indicators. The no-observed-adverse-effect-levels for the occurrence of these organisms in water intended for domestic purposes, for full-body contact recreation as well as irrigation of crops that may be eaten raw, were exceeded. The results indicated that the faecally polluted urban runoff, in combination with inadequately treated wastewater effluents, overcame the assimilation capacity of the Renoster Spruit in the immediate vicinity of the city to such an extent that it posed a possible risk of infection to potential water users for considerable distances downstream from the urban area. The high levels of faecal indicators in the Renoster Spruit diminished to such an extent downstream that the receiving Modder River, directly downstream from the confluence with the Renoster Spruit, posed an infection risk for domestic users only but not for recreational users of the water. Water at this point could also be used to irrigate crops eaten raw.


WaterSA Vol.28(2) 2002: 227-234