Microbiological assessment of food crops irrigated with domestic greywater

Abstract

Two of the challenges facing Africa in the 21stcentury are effective use of restricted water resources and ensuring food security. The eThekwini Municipality is not exempt from these challenges and is investigating ways in which they can be addressed in the local context. One of the aims of national government has been to ensure the supply of clean drinking water and suitable sanitation to every household. As part of its efforts in this regard, eThekwini Municipality has introduced a multi-tiered water supply programme ranging from full-pressure water systems and flush toilets to stand pipes and dry toilets. In the dry sanitation systems, there is no real provision for the disposal of domestic greywater and, bearing in mind that South Africa is a water scarce country, the municipality is investigating ways of using this water as a resource rather than viewing it as a waste. A preliminary trial was set up in 2003 using this water to irrigate vegetables to be used for home consumption. The microbiological safety of this practice needed to be examined to ensure that it would indeed help to uplift communities by the provision of healthy food as well as provide an ecologically sound use and reuse of available water. The initial proposal was to investigate total coliforms, E. coli and Enterococcus as the normal faecal indicators for health purposes as well as Staphylococcus as a human skin surface micro-organism and coliphage as a viral indicator. The first controlled field trial was put in at the test site at the University of KwaZulu-Natal in 2005 using several crop types and three irrigation regimes. The vegetable samples were examined both internally and externally for the selected micro-organisms. It was found that very few E. coli were detected and in later crops the micro-organism list was expanded and further identification of the total coliform organisms detected is being addressed. This paper presents the results from the analyses to date.