An evaluation of wastewater reuse benefits.

Abstract

The discharge of untreated domestic wastewater results in well-documented environmental health hazards. In many poor areas of the world the costs of constructing, operating, and maintaining mechanized wastewater treatment facilities is prohibitive. Given limited resources and competing demands, low-technology stabilization ponds have been suggested as an attractive means of reducing wastewater treatment cost. Another approach is to lower the net cost of treatment by reusing treated wastewater in ways that would generate revenue. Uncertainty exists about the conditions under which reuse is economically remunerative. Reuse projects usually focus on fresh water conservation or inexpensive disposal sites. Little analysis, however, has been done on the economics of wastewater reuse projects for revenue generation. The purpose of this study was to develop and illustrate a method for evaluating net benefits which might be derived from two reuse applications: aquaculture and irrigation. It presents a framework for identifying and estimating the costs and the monetary returns of such projects, and the criteria for deciding among desirable reuse alternative, which application is economically desirable. This includes the cost of treatment necessary to avoid health hazards from improper use of wastewater. The benefits of protecting health by treating wastewater are assumed to be achieved by meeting wastewater reuse standards. The methodology was applied to alternative projects in an Egyptian community with a population of about 60,000, using stabilization ponds which meet World Health Organization standards for wastewater reuse. The analysis utilized site-specific inputs which were adapted from data of Egyptian and Israeli origin, and research findings from the Suez Station in Egypt. The reuse applications were aquaculture (raising tilapia), irrigation of wheat and maize, and combinations of aquaculture and irrigation. Estimates were made of the costs and revenues of each. The sensitivity of conclusions to possible variations in criteria (net present value, internal rate of return, and benefit-cost ratio), and to assumptions about prices, yields, and interest rates were analyzed. The critical uncertainty in this study is the community acceptance of fish cultured in wastewater for human consumption. If fish are accepted, aquaculture would provide higher profits than irrigation. If the fish are not accepted they can be used for animal feed. In this case, the price of fish is very low and irrigation will be preferred. Applications based on mixed proportions of aquaculture and irrigation are never the most profitable. This study indicates that wastewater reuse could lower the net cost of wastewater treatment with the consequent public health benefits. The applied methodology provides a systematic procedure for determining the profitability of proposed reuse projects, and for estimating which option is economically preferable.