Analysis of grey-water used for irrigating vegetables and possible effects on soils in the vicinity of Umtata Dam, Eastern Cape

Ll Mzini,K Winter

doi:10.4314/wsa.v41i1.14

Abstract

In the search for alternative and reliable water sources to irrigate vegetables for backyard gardens, an experimental field was set up in the vicinity of the Umtata Dam, north-west of the town of Umtata, to test grey-water quality and its effects on soil nutrient content following 4 successive growing seasons. Samples of grey-water that were generated from informal housing adjacent to the Umtata Dam were collected from kitchen and bath tubs/washing basins. These samples were analysed before being used for irrigating vegetable crops. The results showed that grey-water quality was efit for purposef for irrigating edible vegetable plants. Although the average Na+ (16 mg/.) and Cl- (15 mg/.) ions were significantly higher (p = 0.05) for grey-water than other treatments, both were below the limit of 100 mg/. set in the South African Water Quality Guidelines. The concentrations of nutrients and heavy metals found in the grey-water samples were significantly lower compared to the World Health Organization guidelines for the safe use of grey-water and within the target water quality range (TWQR) prescribed by South African guidelines for irrigation water. However, the study strongly recommends that grey-water be diluted in order to lower the salt content and to improve the irrigation water quality. Results from an analysis of soil samples showed no significant differences in pH as a result of applying grey-water throughout the soil profile of up to 90 cm depth. Na content of the soil irrigated with grey-water was not significantly different than that of plots where diluted grey-water and potable water were used. Therefore, the grey-water used in this study does not appear to cause an accumulation of salts and heavy metals in soil, in the short term. Keywords : grey-water, vegetables, soil, heavy metals, pH

Highlights

The use of untreated domestic grey-water for irrigating crops in small home gardens has several advantages (Holtzhausen, 2005; Al-Zu’bi and Al-Mohamadi, 2008)
There were significantly higher values for Cl, electrical conductivity (EC), HCO3, Na+, sodium adsorption ratio (SAR) and total dissolved solids (TDS) when grey-water was used in the experiment (p>0.05), and significantly higher CaCO3 hardness of the potable water
Grey-water contained elevated concentrations of Na+ (15 mg/l) and Cl- (16 mg/l) ions this was below the limit of 100 mg/l given in the South African Water Quality Guidelines (Fatoki et al, 2002)

Summary

Introduction

The use of untreated domestic grey-water for irrigating crops in small home gardens has several advantages (Holtzhausen, 2005; Al-Zu’bi and Al-Mohamadi, 2008). In the study by Rusan et al (2007), the accumulation of pollutants was due to grey-water irrigation, soil pH was not affected Despite these reports on the accumulation of heavy metals and elevation of pH and EC, some findings suggest that it does not pose any risks to the health of soils (Faruqui and Al-Jayyousi, 2002; Pinto et al, 2010). Sharvelle and co-workers (2012) investigated the effect of grey-water irrigation over the long term (more than 5 years) on landscapes, and observed accumulation of salts in soils which posed a risk to leach down to the water table. Sharvelle and co-workers suggested that with a sound grey-water management system, the contamination of the water table could be minimised

Methods

Results

Conclusion