Irrigation System Design

Abstract Managed aquifer recharge (MAR) systems such as riverbank iltration and soil-aquifer treatment all involve the use of natural subsurface systems to improve the quality of recharged water (i.e., surface water, storm water, reclaimed water) before reuse (e.g. planned potable reuse). During MAR, water is either iniltrated via basins, subsurface injected or abstracted from wells adjacent to rivers. MAR systems represent an attractive option for augmenting and improving groundwater quality as well as for environmental management purposes. However, reuse systems designed for applications that involve human contact should include redundant barriers for pathogens that cause waterborne diseases. This case covers key aspects of a case study on virus removal at three full-scale MAR systems located in different regions of the United States (Arizona, Colorado, and California). MAR projects may be economically viable for developing countries; however, sustainable management is relevant to successfully maintain the attributes necessary for potable and non-potable water reuse. Keywords: management, aquifer, recharge, removal, viruses

Introduction With increasing global population, the gap between the supply and demand for water is widening and is reaching such alarming levels that in some parts of the world it is posing a threat to human existence. Scientists around the globe are working on new ways of conserving water. It is an opportune time, to refocus on one of the ways to recycle water—through the reuse of urban wastewater, for irrigation and other purposes. This could release clean water for use in other sectors that need fresh water and provide water to sectors that can utilize wastewater e.g., for irrigation and other ecosystem services. In general, wastewater comprises liquid wastes generated by households, industry, commercial sources, as a result of daily usage, production, and consumption activities. Municipal treatment facilities are designed to treat raw wastewater to produce a liquid effluent of suitable quality that can be disposed to the natural surface waters with minimum impact on human health or the environment. The disposal of wastewater is a major problem faced by municipalities, particularly in the case of large metropolitan areas, with limited space for land[1]based treatment and disposal. On the other hand, wastewater is also a resource that can be applied for productive uses since wastewater contains nutrients that have the potential for use in agriculture, aquaculture, and other activities. In both developed and developing countries, the most prevalent practice is the application of municipal wastewater (both treated and untreated) to land. In developed countries where environmental standards are applied, much of the wastewater is treated prior to use for irrigation of fodder, fiber, and seed crops and, to a limited extent, for the irrigation of orchards, vineyards, and other crops. Other important uses of wastewater include, recharge of groundwater, landscaping (golf courses, freeways, playgrounds, schoolyards, and parks), industry, construction, dust control, wildlife habitat improvement and aquaculture. In developing countries, though standards are set, these are not always strictly adhered to. Wastewater, in its untreated form, is widely used for agriculture and aquaculture and has been the practice for centuries in countries such as China, India and Mexico. Thus, wastewater can be considered as both a resource and a problem. Wastewater and its nutrient content can be used extensively for irrigation and other ecosystem services. Its reuse can deliver positive benefits to the farming community, society, and municipalities. However, wastewater reuse also exacts negative externality effects on humans and ecological systems, which need to be identified and assessed. Before one can endorse wastewater irrigation as a means of increasing water supply for agriculture, a thorough analysis must be undertaken from an economic perspective as well. In this regard the comprehensive costs and benefits of such wastewater reuse should be evaluated. Conventional cost benefit analysis quite often fails to quantify and monetize externalities associated with wastewater reuse. Hence, environmental valuation techniques and other related tools should be employed to guide decision-making. Moreover, the economic effects of wastewater irrigation need to be evaluated not only from the social, economic, and ecological standpoint, but also from the sustainable development perspective. Pakistan is a case which illustrates this problem. Both treated and untreated municipal wastewater in the vicinity of large cities like Faisalabad is used for vegetable production. But, how safe is this practice? How does one tradeoff between the obvious benefits of this use and the costs associated with it?