Effect of domestic greywater reuse for irrigation on soil physical and chemical characteristics and tomatoes growth.
From Firenze University Press Journal: Journal of Agriculture and Environment for International Development
Guillaume Nyagatare, University of Rwanda, College of Agriculture Animal sciences and Veterinary Medicine
Christian Shingiro, University of Rwanda, College of Agriculture Animal sciences and Veterinary Medicine
Claire Nyiranziringirimana, University of Rwanda, College of Agriculture Animal sciences and Veterinary Medicine
Most of the world’s food supply comes from agriculture which depends on water, whether from rain, irrigation or a combination of the two (Pescod, 1992). Agricultural water reuse practices vary significantly around the world, ranging from the use of untreated wastewater in regions where wastewater treatment is limited, to the use of highly treated recycled water in the more developed regions. In either case, both food and non-food crops are commonly irrigated. Across all contexts, water scarcity is the common motivation for agricultural reuse (Sheikh et al., 2018). Rwanda, like other countries in the world, is experiencing the effects of climate change manifested through variability and irregularity in rainfall patterns, thus, increasing competition for water resources in allocation, access and management. Agriculture which is the backbone and key component of Rwanda’s economy is constantly competing with domestic, industrial, and environmental uses for a scarce water supply (World Bank Group, 2021).
Yet water supply for small-scale farmers and pastoralists, who constitute the major work force in Rwandan agriculture, is an imperative toward achieving food security (Food and Agriculture Organization, 2019). Accelerating changes in land use, urbanisation, and industrialisation are aggravating competition for a scare resource. Devising more effective methods of water management is therefore increasingly imposing itself as a civilisational emergency for Rwanda, and indeed for the whole planet. The treatment and reuse of wastewater is one of the best options for water conservation available to communities located in arid and semi-arid regions. The potential for wastewater reuse is not only limited to large-scale projects supplied by community wastewater treatment facilities but is also available to individual homeowners (World Health Organization, 2006b). In dry seasons of Rwanda, agriculture is only possible trough irrigation practice. The irrigation water for extensive land or small-scale farming in marshland comes from surface water such as rivers and lakes. However, irrigation of hillside rural households’ vegetable/kitchen gardens, which constitute important complements to healthy nutrition and food security in Rwanda, can hardly rely on surface water due to insufficient uphill water redistribution capacity. Thus, uphill the risk of dry-seasons starvation is real. Nonetheless, risk-averse, and household-chores-bound female household members are reluctant to irrigate their land with grey water, fearing harm to their soil, crops, and household.
Yet, generally in Rwanda bathing and laundry activities produce each approximately 10 L of grey water daily per person (Matto & Jainer, 2019). In that context, a family of five persons produces approximately 100 L of grey water daily which could be equal to 3m3 per month per household and 36m3 per annum per household. And this does not include grey water produced in schools and universities, prisons, hotels, and many places receiving many people (Matto & Jainer, 2019; Boulware, n.d.). With grey water recycling, it is possible to reduce the amounts of freshwater consumption as well as wastewater production, in addition to reducing water bills. Unlike rainwater harvesting, grey water recycling is not dependent on season or variability of rainfall and as such is a continuous and a reliable water resource. Grey water has a relatively low nutrient and pathogenic content and therefore it can be easily treated to a high quality using simple technologies (Erwin, 2005). If the grey water is used as an additional water source, an increased supply for irrigation water can be ensured, which will in turn lead to an increase in agricultural productivity and contribute to food security. However, there are several problems related to reuse of untreated grey water. In fact, laundry grey water consists of an aqueous solution of suspended solids (dirt and lint), organic material, oil, grease, and sodium, nitrates and phosphates from detergent (Eriksson et al., 2002). The risk associated with careless use of grey water in irrigation includes soil pollution and degradation through clogging, dispersion and salinization; water bodies’ eutrophication and pollution and spreading of diseases due to the exposure to micro-organisms in the water (World Health Organization, 2006a). Therefore, reused grey water must also be of satisfactory bio-physico-chemical quality. Safe reuse of grey water implies understanding the risks and benefits associated with grey water reuse and the development of local low-cost technologies for the ecycling and mitigation of the risks of, and amplification of the benefits of, grey water reuse for the benefit of low-income rural communities.
The overall objective of this study was therefore to contribute to a systematic investigation into ways to promote grey water reuse in Rwandan agriculture. Results were expected to strengthen the body of evidence needed to develop a safe scheme for grey water recycling and reuse in Rwanda. The specific objective of this study was to compare the effect of three different grey water-reuse treatments (laundry grey water (T1), grey water mixed with tap water at 1:1 ratio (T2), alternation of grey water and tap water (T3) with tap water only as a control (T0), on: Some selected physical properties: hydraulic conductivity, aggregate stability, porosity, and bulk density; and some chemical properties: pH, Electrical Conductivity (EC), Sodium Adsorption Ration (SAR) and nutrients concentrations of a sandy loam Ustox (USDA Soil taxonomy) located in the Eastern province of Rwanda, Kayonza district, Mwiri sector. The yield of tomatoes (Lycopersicon Esculentum) grown in the same location and soil as indicated above.
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