DISTRIBUTED WASTEWATER MANAGEMENT FOR SMALL NORTH CAROLINA COMMUNITIES Victor D’Amato, PE, Tetra Tech, Inc., PO Box 14409, Research Triangle Park, NC 27709. (919) 485-2070. [email protected] ABSTRACT Distributed wastewater management relies on the optimum combination of decentralized and centralized system components for addressing the wastewater management of a service area. Many rural and exurban North Carolina communities rely on individual subsurface soil absorption systems (septic systems) for the bulk of their wastewater treatment needs. These septic systems have sometimes been implicated as reasons for water quality degradation and a historical lack of proactive management has sometimes resulted in system malfunctions, creating financial hardships – as well as potential health hazards – for homeowners. A distributed approach to wastewater management looks at the full complement of options for serving a community. In many small communities, lot density is not sufficient to make centralized sewering financially feasible. This presentation will report on the results of several recent studies looking at the use of decentralized alternatives where more traditional centralized service options were considered. These decentralized alternatives include cluster systems with advanced treatment, enhanced management of individual system and traditional water/sewer utility managed systems. The results of a recent Water Environment Research Foundation project that evaluated 20 case studies will be presented along with a more local example where a small disadvantaged community in Northeastern North Carolina is pursuing affordable decentralized systems for meeting the needs of their residents. Keywords: wastewater, decentralized, distributed, small community, water reuse. INTRODUCTION The manner in which the collection, treatment, and product management components of a wastewater system are arranged within a given service area is sometimes called the system architecture. System architecture has a profound but largely overlooked impact on system performance across a range metrics of importance to small communities, including capital and recurring monetary costs. Traditional system architectures, particularly in urban and suburban areas, rely on expansive wastewater collection and conveyance systems feeding a centralized treatment facility. Alternative architectures are developing for more efficient and effective wastewater management. These architectures combine traditional centralized and new uses of decentralized system infrastructure in an approach termed distributed management. Distributed water infrastructure systems are emerging in rural, suburban, and urban communities across the United States and abroad. Communities are recognizing that these strategies—which integrate water management at the individual site scale, to residential neighborhoods and small communities, to an entire watershed or region—are more efficient and effective across a triple bottom line of environmental, social, and economic considerations. The research project, When to Consider Distributed Systems in an Urban and Suburban Context, analyzed 20 case studies where distributed approaches are being used to provide integrated water services across a range of community-specific situations and management frameworks in the United States and Australia. This project was sponsored by the Water Environment Research Foundation (WERF) and the National Decentralized Wastewater Resource Capacity Development Project (NDWRCDP) to help planners, utility managers, engineers, developers, regulators and other decision-makers determine whether they should consider using a distributed approach in areas where users might normally be served by centralized systems. DISTRIBUTED WASTEWATER MANAGEMENT Distributed Wastewater Management for Small North Carolina Communities Managed distributed infrastructure incorporates both decentralized and centralized elements to most efficiently provide water-related services to users. The concept of distributed infrastructure as a key element of sustainable water management has been embraced in the stormwater sector, where control – and often beneficial reuse – are implemented close to the source using low impact design principles and various best management practices. For wastewater systems, distributed management uses smaller-scale systems within more centralized management frameworks. This involves integrating a range of system scales from onsite or onlot to cluster to regional to centralized (Figure 1). Figure 1. Distributed Wastewater Management Continuum. An obvious advantage of decentralization is the proximity of systems to wastewater sources and reuse areas (Figure 2) which minimizes or precludes energy inputs for conveyance. Distributed management has particular advantages for small communities in North Carolina, where more densely developed “main street” and crossroads areas lend themselves well to large cluster and semi-centralized systems while less dense areas can rely on small clusters and managed individual onsite systems. Benefits of distributed wastewater management include affordability and the ability to phase in system capacity as funding becomes available, the potential for water reuse and resource recovery, and energy efficiency. Figure 2. Distributed Management Versus Traditional Sewer Extension. Infrastructure Funding Traditional infrastructure projects are often characterized by large sunk costs. The financing and debt service associated with these projects can be crippling to communities, particularly if projected revenues are not realized, because, for example, an economic downturn slows or stops growth. The use of a distributed infrastructure approach, by contrast, allows for a variety of adaptive funding approaches, such as systems funded by developers that then turn them over to a utility for operation. Underserved communities can phase the installation of systems, prioritizing the areas of greatest need as grant funding or slowly developing revenue streams become available. Rapidly growing communities can increase treatment capacity by adding treatment modules to existing systems or new cluster systems as demand increases. State and federal clean water funding specifically Distributed Wastewater Management for Small North Carolina Communities recognizes and includes decentralized wastewater systems in the 20% Green Project Reserve which is set aside for environmentally superior projects. Resource Recovery Source control – for example, the separate management of graywater, blackwater, and even yellow-water or urine – is more viable at decentralized scales, helps conserve energy associated with treatment, and facilitates resource recovery and reuse. Distributed approaches help leverage the connections and synergies between land use and water management and to close the loop on waste-related resource cycles. Rural communities can use one of their greatest resources – land – for wastewater treatment, rather than costly mechanical treatment plants. Doing so recharges aquifers rather than discharging to surface waters and helps restore the natural water cycle and heal degraded hydrologic function. Recycling nutrients in wastes can support agriculture and food production while recovering energy from waste helps offset imported sources. Efficiency Distributed systems can provide great efficiency advantages over traditional approaches. First and foremost - treatment closer to the source and/or reuse area requires less energy for conveyance. Properly implemented, decentralized reuse technologies can be very efficient as well. Table 1 provides power requirements for common unit processes used in decentralized wastewater treatment and reuse systems. Table 2 presents operational power requirements for various types of decentralized reuse systems based on the data in Table 1. The model decentralized systems range from standard aquifer recharge systems to advanced attached growth-disinfection systems capable of meeting stringent effluent quality requirements for unrestricted reuses. These power requirements compare favorably with power requirements for traditional centralized systems. For comparison, energy requirements for wastewater collection, treatment and discharge/recycling in California have been estimated to range from 1,500 to 5,800 kWh/MG treated (CEC, 2005). The model decentralized systems benefit from relatively short conveyance distances, requiring little or no energy, along with low-energy treatment systems; for example, highly effective recirculating filters and soil dispersal systems generally require no forced aeration to effectively treat regular-strength wastewater to reclaimed water quality. Embedded and secondary energy impacts of decentralized reclamation and reuse approaches, while highly context specific, are believed to have significant advantages over centralized approaches, although no robust evaluations have yet been conducted to our knowledge. Table 1. Electrical Energy Demand for Unit Processes in 5,000 Gallon per Day Decentralized Reuse Systems (does not include energy requirements for maintenance activities or incidentals, e.g., lighting). Unit Process Power Units Notes Gravity Sewer 0.0 kWh/d Septic Tank 0.0 kWh/d Does not include periodic solids removal Pump Stations 1.0 kWh/d 1 hp pump on 1 hr/d, 100 gpm @ 30' TDH (60% efficiency) Filter Pumps 1.6 kWh/d 1/2-hp recirc. pump on 4 hr/d, 60 gpm @ 20' TDH (60% efficiency) Recirculating Filter 0.0 kWh/d Passive aeration; all energy associated