Water Scarcity and the Potential Role of Distributed Wastewater Management
Abstract:This abstract summarizes current perspectives on the inclusion of distributed wastewater management in wastewater facilities planning, specifically in the context of water scarcity and supply augmentation needs. The US faces significant pressures on water supply: Regulatory regimes, inter-state conflicts, climate change, population growth in arid and drought-prone areas, water laws and litigation, surges in energy costs to move water through engineered supply systems, intrusion into groundwater supplies, and in some areas the virtual disappearance of surface waters from lack of recharge. Within facilities and watershed planning, distributed wastewater management is an approach to addressing water scarcity that can support sufficient groundwater recharge and base flows in stressed watersheds, reduce the length of hydrologic cycles, create more reuse opportunities, contribute to watershed and ecosystem restoration, and reduce mass balance-related water shortages and ecosystem problems where water export diminishes available supply.
Watershed-based approaches to scarcity often have the effect of focusing or resizing engineering and management strategies on maintaining ecological and system health within natural, hydrogeographic boundaries. In stormwater management, there is increased emphasis on green infrastructure with an approach that can be characterized, if glibly, as “it's the recharge, stupid.” Infiltration, street edge alternatives, green roofs, green solutions for CSOs, permeable pavement, and efforts such as Chicago's and Milwaukee's to replace parking lots and alleys with permeable pavement, represent efforts to re-infiltrate water as close to where rain falls as possible. The focus is on naturalized treatment first, bolstered and implemented with engineering or 'grey' solutions.
Wastewater treatment today, for its part, is following a similar path that might best be characterized by the old solid waste slogan of “reduce, reuse, recycle.” Increasingly prevalent are improved wastewater treatment technologies with ever smaller footprints; more water reclamation and recycling, especially in California and Florida; dual-plumbed neighborhoods; and co-generation, even as public funding and support for new sewer projects, even in highgrowth areas, has dissipated.
With severe and accelerating constraints and pressures on U.S. water supplies, which by 2050 will need to serve 100 million more Americans concentrated mainly in existing and often watershort metropolitan areas including greater Atlanta, Los Angeles and Phoenix, water supply augmentation will need the flexible, green approaches now being deployed on the water “disposal” side - watershed management, green infrastructure in stormwater and flood control recycling and reuse in wastewater engineering, and distributed wastewater management. This amounts, in effect, to a call for deploying new and expanded concepts of water re-use as part of water supply.
In treating wastewater as a resource rather than a waste product to be moved away, distributed wastewater management represents an important tool for dealing with water scarcity through its core principle: to manage water at the optimal distance from the source that supports healthy watershed hydrology, livable communities, and sustainable water budgets. Principally thought of as the management of on-site or soil-based wastewater treatment systems, “distributed wastewater management” is a catch-all phrase for incorporating properly managed small-scale and soil-discharging wastewater treatment systems into the overall wastewater facilities planning approach. Since EPA's 1997 response to congress, which declared properly managed septic systems to be a permanent part of the nation's wastewater infrastructure, the focus has expanded from individual septic systems to centralized, professional management of systems ranging in size from individual households to entire districts within a metropolitan area. Distributed approaches have gained ground as a flexible and often more affordable approach to providing sound wastewater treatment in growth areas; a realistic way to improve environmental quality and public health in un-sewered rural areas; and a way of characterizing innovative engineering approaches that re-use or re-distribute wastewater for new purposes, even the midst of metropolitan areas and settlements.
The paradigm of distributed management as it pertains to water supply applies, principally, to urbanized and urbanizing areas. Rural areas rely on on-site or small-scale community systems as a matter of necessity, not engineering optimization. What faces the urbanizing and urban areas now is a simultaneous problem of supply limitations and demand growth, where the old engineering choice – septic or sewer, or septic until sewer – has to be re-thought to cope with the limitations on natural systems and the continued growth of the nation's urban and urbanized settlements. This is in evidence at all scales: The macro or basin scale, of gradually phasing out ocean wastewater outfalls, cross-basin transfers, and extractive water supply approaches that result in negative water budgets and depleted surface and ground waters; the mid-scale of utilities and providers, adopting principles of managing multiple sizes and types of community wastewater treatment to reduce hydrologic disruption and augment supply, embracing the principles of watershed hydrology, livable communities, and recharging surface and ground water resources; and the micro or site scale, by introducing technologies to increase infiltration, conservation and re-use on individual sites, lightening the hydrologic footprint of human settlements.
Within the public-health based model of US regulations, however, re-use is and always has been problematic. Recent papers at WEF and in other forums have documented the host of other barriers and limitations on plant- and soil-based treatment of water in human settlements, whether “waste” or “storm,” such as stormwater design criteria, antiquated zoning regulations and UIC permitting processes. Wastewater is, of course, the trickier of the two to “re-use,” in the context of supply augmentation. US regulations on re-use stem from an effort to limit exposure to various constituents, chiefly pathogens; the path of least resistance for water supply is to derive “clean” water from surface or groundwater sources, instead of running the regulatory and public perception gauntlet of directly re-using treated “waste” water. Groundwater infiltration, as an interim step in water re-use, reduces many of the public health-based concerns and is of course the accepted medium of treatment between a household septic system's leach field and individual drinking wells nearby. However, groundwater injections have their own regulatory constraints, many of which work against the concept of augmenting water supplies with re-infiltrated wastewater.
And yet, in many arid parts of the US, wastewater re-use and distributed management are gaining use and acceptance in the context of augmenting potable water supply, as well as other uses in protecting aquifers from intrusion, restoring surface water ecosystems, and meeting needs for industrial and agricultural users. Distributed wastewater management approaches, which can keep wastewater within its watershed of origin, are being promoted as a way to reduce the energy and financial demands of cross-basin transfers – and as a remedy in regions and watersheds where surface waters are depleted by the combination of groundwater withdrawals, impervious cover, and sewers to ocean outfalls.
Several emerging cases illustrate the potential role of distributed management in augmenting water supply. At the mid- or utility scale, the Northeastern Illinois Regional Water Supply Study, led by the Chicago Metropolitan Planning Agency (CMAP), presents an interesting example of the next frontier in water supply and management for large metro areas. Under its Lake Michigan allocation, Chicago “loses” the treated water that is discharged into the Chicago River and downstream by the Metropolitan Water Reclamation District of Greater Chicago. The City also “loses” any rainfall that is moved out of the Lake Michigan watershed by engineered stormwater conveyances and impervious cover.
The need for supply augmentation is focusing, to date, on the creative use of the City's existing Lake Michigan allocation. The City's effective supply is reduced by the discharge of treated wastewater from the Chicago Metro Water Reclamation District into the Chicago River and downstream, and also by stormwater conveyances that export rainfall out of the narrow Lake Michigan watershed. Ironically, the combined impact of engineered systems and wastewater discharge means that Chicago has more useable water in drought conditions than in a heavy rainfall year. Thus, one of the most powerful supply augmentation tactics within Chicago's regulatory framework is to export as little water as possible into the Chicago River and to reinfiltrate as much as possible into the Lake Michigan watershed, through stormwater infiltration or, conceptually, land application of wastewater. Chicago's aggressive and ambitious efforts to increase stormwater infiltration are well-known; what remains to be seen is if, when, and under what circumstances the City may turn to wastewater re-use or land application as another method of supply augmentation.
At the site or neighborhood scale, the Solaire was the first water reuse project in New York City's Battery Park City area and it represents a way to take stormwater and wastewater out of the central conveyance systems or grid, and use both to offset a project's water supply and wastewater disposal needs. Now seven similar projects in Manhattan have followed suit in part thanks to water reuse incentives created by the NYC DEP. The Solaire and similar water re-use projects represent a distributed systems approach at the site scale, and an important alternative for minimizing or mitigating water balance impacts in urban and suburban areas. As applications and uses continue to expand, new technology will expanding beyond the current uses of toilet flushing, cooling towers, laundry and irrigation but also notes that the water demand considerations and supply options are entirely site-specific, requiring individual design – rather than standard engineering connections – at each site, and within each regulatory context. Also, it is important to note that the capital spent on these distributed water reuse systems defers or replaces the future capital spending that is required on both the water supply and wastewater disposal systems.
Thought leaders in engineering also are addressing the need to incorporate distributed options into wastewater facilities planning, especially in a water-scarce world. At the NOWRA-IWA Conference in 2007, Paul Brown of Camp Dresser McKee presented his view as a water resources planner and thought leader in the field. Brown made six recommendations: First, to call a “truce” between the promoters and engineers of conventional large-scale and distributed small-scale systems; second, to better articulate the paradigm of distributed or integrated wastewater management, especially in terms of water supply; third, to create safe havens for innovation in the field; fourth, to develop better system modeling tools that capture more of the benefits of a whole-systems or integrated approach; fifth, to create a robust system of monitoring and data collection, to feel comfortable that those people and systems “off the grid” of conventional wastewater or water supply can stay off safely; and sixth, to empower individuals to shift the perspective beyond the exposure or public health regulatory model, recognizing that health and property are without value if the Earth is not healthy.
But if much has been done to articulate the paradigm of integrated management and sustainability, and if there is great confidence in the ability to develop the technology and engineering to create healthier ecosystems and watersheds, there is little beyond a set of demonstration cases. This approach to wastewater in a water supply context is not being applied widely. The concepts are compelling, but what is next? What holds back engineers, municipalities, water districts, and regulators from turning to these systems and approaches? With some clear benefits in a drought and climate-challenged environment, what blocks these agencies from deploying soil-based wastewater dispersal, groundwater recharge, building recycling systems, and on-site or highly localized treatment?
Practitioners in this field are being asked to help define the tipping point: With the potential upsides becoming better known, at what point will we use distributed wastewater for supply on a regular basis? What, in other words, is the 4.00 gas in the use of distributed wastewater for supply augmentation, and what conditions might precipitate that point? What is being missed in terms of research, regulatory reform, engineering practice or technology that could make this breakthrough come more broadly, and with greater beneficial effect for people, utilities and ecosystems?
Engaging professionals from water reuse, disinfection, policy, utility management and other complimentary disciplines is crucial to this discussion. Moving from case study to general practice takes time and collaboration. The participation and support of colleagues is welcomed.
Document Type: Research Article
Publication date: 2008-01-01
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