A Feasibility Analysis Methodology for Decentralized Wastewater Systems – Energy-Efficiency and Cost Kartiki S. Naik 1* and Michael K. Stenstrom 2 ABSTRACT: Centralized wastewater treatment, widely practiced in developed areas, involves transporting wastewater from large urban areas to a large capacity plant using a single network of sewers, whereas decentralization is the concept of wastewater collection, treatment and reuse at or near its point of generation. Smaller decentralized plants can achieve extensive reclamation and wastewater management with energy-efficient reclaimed water pumping, modu- larized expansion and lower capital investment. We devised a methodology to preliminarily assess these alternatives using local constraints and conducted a feasibility analysis for each option. It addressed various scenarios using the pump-back energy consump- tion, sewer and treatment plant construction and capacity expansion cost. We demonstrated this methodology by applying it to the Hollywood vicinity (California). In this study, the decentralized configuration was more economical and energy-efficient than the centralized system. The pump-back energy consumption was about 50% of the aeration energy consumption for the centralized option. Water Environ. Res., 88, 201 (2016). KEYWORDS: decentralization, reclamation, reuse, wastewater, energy, pumping, collection, satellite treatment, feasibility, cost. doi:10.2175/106143016X14504669767337 Introduction Centralized wastewater treatment consists of a large treatment plant connected to an elaborate wastewater collec- tion system. Wastewater collection, treatment and reuse at or near its point of generation is called decentralized wastewater treatment (Tchobanoglous and Crites, 1998). Decentralized configurations generally use shorter collection networks of relatively smaller size. Such systems are sometimes used to relieve sewers leading to larger central treatment plants. For example, in the City of Los Angeles, the D.C. Tillman and Glendale wastewater treatment plants, located upstream of the Hyperion treatment plant avoided overloading trunk sewers and provided reclaimed water near potential users (City of Los Angeles, 2013). With increasing need for reclamation, it is necessary to have a simple system not only to reclaim the wastewater but also to convey it to the respective area for reuse. Since reclaimed pipelines generally flow in the opposite direction of sewers, they usually need to gain some elevation in their course. Reducing the length of the pipeline is the principle solution to minimize pumping energy consumption. Centralized plants generally cannot be located close to all the potential reclaimed water users. It is especially difficult to establish such a large treatment facility in any residential neighborhood. Thus, for centralized plants, returning recycled water can require tremendous energy due to pumping. Adapting the design of large centralized treatment plants to local reclamation needs to reduce pumping cost can be difficult. Decentralized treatment systems have a smaller scale, thus simplifying modification required to meet local needs. With smaller collection-reclamation loops, decen- tralized wastewater treatment systems can reduce pump-back energy consumption. Decentralization is also an alternative to the expensive construction of larger trunk sewers to convey the added flow of newly developed or growing areas. With smaller sewers and treatment plants, these systems can also provide wastewater treatment and collection access to remote communities. Many developing regions do not have access to wastewater collection and treatment rendering them susceptible to disease outbreaks. Satellite or decentralized treatment systems can be an excellent solution to reduce public health risk. Both treatment concepts have pros and cons; for instance, large treatment plants have more economy of scale. Satellite treatment plants are usually assumed to be limited to primitive treatment systems such as septic tanks, in turn difficult to optimize for energy and cost. (Massoud et al., 2008) But to take advantage of improved public health, energy-efficient reclamation and conveyance, and modular expansion, it is necessary to devise an optimization algorithm to obtain a customizable, cost-effective, energy-efficient wastewater collection and treatment configuration for such regions. This study involves optimizing sewer networks and decen- tralized treatment plant locations in an urban area to minimize pump-back energy consumption for recycled water. We computed pump-back energy consumption as a fraction of treatment and aeration energy for a hypothetical but realistic example (Hollywood). We optimized the decentralized waste- water collection and treatment configuration for Hollywood for minimum energy consumption and cost. 1* Graduate student at UCLA at time of writing, Dept. of Civil and Environmental Engineering, University of California, Los Angeles; email: knaik@ucla.edu. 2 Dept. of Civil and Environmental Engineering, University of California, Los Angeles March 2016 201