(134f) Breakeven Costs of Distributed Advanced Technology Water Treatment Systems

This paper presents a financial analysis of the implementation of distributed technology systems to provide advanced treatment of water for direct human consumption. The degradation of water quality within a distribution network, a phenomenon that presents considerable financial and technical obstacles to the delivery of secure water supplies to end-point consumers, is one of several problematic issues that might well be addressed by distributed systems. The principal economic driver supporting implementation of such systems are the costs associated with upgrading large centralized treatment facilities and distribution networks to provide water of a quality that consistently meets increasingly stringent drinking water standards. The prime focus of the research described here is a comparison of centralized upgrade costs to those costs associated with implementation of the DOT-Net model for advanced drinking water treatment under various scenarios and technical conditions for different system sizes and populations. The approach described can be readily adapted to the scenario of partial centralized treatment, followed by optimized selection and placement of advanced treatment technologies to meet specific more stringent consumer water quality needs. While disinfection by-products (DBPs) comprise the specific water quality parameter selected for articulation of the comparative analysis, the general methodology described is applicable to most other water quality measures as well. Indeed, the approach is applicable in general to any scenario in which existing water quality is insufficient and advanced treatment processes must be selected and located in the most cost-effective manner.

The specific application of the model discussed here posits a water quality degradation inherent to the distribution network. This is a broad application of the model in that such degradation can be modeled either as ?sharp? (e.g. immediate degradation upon discharge to the distribution network), or ?progressive? (e.g. the leaching of pipe materials or formation of disinfection by-products (DBPs) in its spatial and temporal character. To provide an economic and technical framework, this paper addresses DBP formation within distribution systems as a representative water quality issue. In the paper we estimate disinfection by-product (DBP) formation within a distribution network, and then apply this cost estimate to calculate ?break-even? costs for alternative use of distributed water treatment technologies to meet DBP exposure limits.

Five main results can be drawn from this phase of our research. First, based on our model, more than half of a typical water utility service population receives water containing TTHM concentrations in excess of EPA regulatory limits. Because of the long detention time, for an average system the treated water TTHM precursor concentration must be reduced to approximately 0.076 mg/L. Second, break-even capital, operations and maintenance costs for a unit designed to treat 10 connections ranged from $US 260,000 to $US 45,000, with the greatest costs associated with the smallest utilities. Third, we found two primary factors which tend to influence break-even costs: economies of scale and proportion of residential connections. For the smallest water utilities, where break-even cost is highest, economies of scale dominates and so break-even cost reduces quickly as system size increases. As water utility size increases, the influence of economies of scale starts to become moderated by the reducing proportion of residential connections, causing the break-even point to reduce at an increasingly slower rate. Eventually, for a water utility service population of about 80,000 people, these two forces nearly balance and further increases in utility size result in fairly small reduction in break-even point. Fourth, we found very little difference in break-even costs for varying initial TTHM precursor concentration. Instead we found a fairly close balance between the cost of treating a more concentrated flow of TTHM precursor concentration and the number of residential connections impacted by excess DBP concentrations. Finally, our work highlights the balance between centralized and distributed treatment approaches and identifies the variables pushing towards each approach.

The water quality parameters and related details selected for this work reflect typical treatment parameters for the scenario of DBP treatment where water quality degradation occur primarily within the distribution network. It is important to recognize however that the approach employed is applicable to any scenario in which existing water quality is insufficient and advanced treatment processes must be selected and located in the most cost-effective manner.