Use of domestic greywater for small-scale irrigation of food crops: Effects on plants and soil

Abstract

Disposal of greywater presents a problem in areas served with on-site sanitation or in areas with poor service provision. Such areas often also face challenges with respect to food security. Use of greywater for irrigation of food crops represents a possible beneficial use of greywater which can contribute to household food supply and to informal income generation. In this study, an above-ground crop (Swiss chard, Betavulgaris var. cicla) and a below-ground crop (carrot, Daucus carota) were irrigated in pots with mixed greywater sourced from households in an informal settlement. A simple form of sub-surface irrigation was used. Plant growth, crop yield, and levels of macro- and micronutrients in crops and soil were monitored through six growth cycles. Equivalent treatments, irrigated with either tap water or a hydroponic nutrient solution, were conducted for comparison. The same soil was used throughout to allow accumulation of greywater-derived substances in soil to be detected. The results indicated that: (i) irrigation with greywater increased plant growth and yield relative to crops irrigated with tap water only, although crops irrigated with hydroponic nutrient solution yielded the highest growth and yield; (ii) irrigation with greywater improved plant nutrient content relative to crops irrigated with tap water; (iii) soil irrigated with greywater showed increased electrical conductivity and increased concentrations of metals over time, coupled with an increase in sodium and metal concentrations in crops. Thus, provided precautions are taken with regard to salt and metal accumulation, greywater offers a potential source of water for household crop irrigation which additionally shows some fertiliser properties.