Life Cycle Assessment of Decentralized Wastewater Systems and its Comparison to Centralized Wastewater systems

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Courtesy of Water Environment Federation (WEF)

 ABSTRACT

The typical process flow of collecting, treating, and disposing wastewater – identified as the centralized approach – consumes large quantities of energy while releasing environmental emissions. The traditional wastewater treatment plant design is developed on the premises of economies of scale, assuming unit costs to treat wastewater decrease as the plant capacity increases. However, this frame of thought is challenged when considering a decentralized approach to treatment. Decentralized wastewater systems focus on using several smaller treatment plants to treat the same amount of wastewater that enters single centralized systems. Recent research examined the environmental impact of centralized wastewater treatment processes by conducting life cycle assessments (LCAs). A LCA is an approach designed to
investigate a process, through determining the quantity of emissions released in the environment, evaluating the impact/effect of those emissions, and recommending improvements to reduce emissions released. Numerous studies have been published regarding the environmental impact of centralized wastewater systems; however no analogous research has been published that evaluates impact of emission releases on the environment due to decentralization. The goal of this study was to develop a detailed analysis of the economic and environmental impacts of decentralized wastewater systems. The LCA methodology was used to assist with an analogous comparison. A case study approach was taken, focusing on different life cycle phases of the infrastructure system. Final results illustrated that when attempting to determine which system has the lower impact to the environment, it truly depends on which actual impact is being considered. In simply examining greenhouse gases, carbon dioxide is almost two orders of magnitude higher with centralized systems, while the reverse is true when analyzing methane. The same “flip flop” can be said for the toxic releases as well as conventional air pollutants. Thus, one must be careful to ensure that generalizing sweeping statements are not made for either treatment system.

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