Effects of Transition to Water-Efficient Solutions on Existing Centralized Sewer Systems—An Integrated Biophysical Modeling Approach

Abstract

Technical alternatives offering high water efficiency are being developed to complement existing centralized water and wastewater conveyance and treatment systems. Understanding of the negative effects wide-spread implementation of such alternative systems may have on existing systems is still limited, despite the importance of this inevitable transition. In this study, we present a novel approach to systematically identify these negative impacts. A comprehensive model integrating transport and transformation processes in sewer pipes was set up and simulated for various transition scenarios. A significant finding of this research is that reduced flows and increased chemical oxygen demand (COD) concentrations result in the accumulation of sediments and sulphides in sewer pipes. For the examined sewer system, when reducing the total daily flow by 50%, 30% of the pipes were found to accumulate sediments, and 30% of the pipes experienced effects due to the presence of sulphides in different states depending on the wastewater temperature. It was found that an optimal spatial distribution of these water-efficient solutions will most likely require compromises between sediment and sulphide accumulation. The product of two design parameters, diameter and bed slope, was found to be a suitable predictor of the potential of a pipe to accumulate sediments. This research provides novel approaches to assessing the feasibility of transition to solutions offering higher water efficiency. The results indicate where the most affected points in the systems are expected to occur and might help in preparing an experimental approach to assess such negative effects, increasing urban water management efficiency.