January 2007, Vol. 19, No.1


Distributed Wastewater Management Is Our Future

Todd Danielson

Water is a resource. Wastewater can be cleaned and then used to maintain stream base flows, irrigate lawns, recharge aquifers, serve as industrial feed waters, or do any number of things. Those of us in the water quality field have known this for some time.

We also know that humans have an impact on our ecosystems. For instance, interbasin transfers of water — pumping the water out of one watershed, supplying it to end users, and treating and discharging it in another watershed — affect the availability of water for consumptive use and for the environment.

As several seemingly unrelated factors, such as water scarcity and ecosystem impacts, are starting to align, there has been an important shift in our water management paradigm. This shift is toward holistic water management — integrating drinking water, stormwater, and wastewater management and considering all water as a resource. Distributed wastewater management is a valuable tool water professionals can use to address the wastewater component — and even part of the water component — of the holistic approach.

Distributed wastewater management is not tied to any specific form of wastewater treatment. Instead, it is a systems architecture that helps utilities determine how best to manage water, based on environmental risks, costs, and other desired outcomes. It is master planning an entire service district and determining if and where there should be a central collection system, cluster collection systems, individual onsite systems, satellite treatment facilities, and other infrastructure components.

This paradigm represents a departure from decentralized wastewater management, which was restrictive in scope. The “decentralized” terminology has polarized some professionals on both ends of the spectrum to believe “you are either with us or against us,” based on narrow allegiances to either big central facilities or individual onsite systems. The water quality field should not promote such divisiveness. Distributed wastewater management enables utilities to consider options other than the single, large gravity sewer and end-of-pipe treatment facility but does not suggest they must mothball their existing facilities and construct thousands of onsite and cluster systems.

The U.S. Environmental Protection Agency (EPA) has estimated that it will take $390 billion in the next 20 years to replace existing wastewater infrastructure and build new infrastructure to meet demand. This news is sobering. To best serve utilities, customers, and the public, engineers should be looking actively for ways to reduce this cost appropriately. Distributed wastewater management can help us accomplish this goal. Instead of limiting our options to expanding near-capacity collection and treatment systems or constructing additional pump stations and long force mains to connect remote development, we should be considering all treatment options.

With proper distributed wastewater management, onsite and cluster technologies can be considered comprehensively to determine if they can provide environmental benefits equal to or greater than constructing or upgrading conventional sewers and treatment plants for new development. Distributed wastewater management considers all available alternative solutions, including small, multiple systems that harness more of the environment’s assimilative capacity or provide opportunities for reuse, thereby reducing costs and increasing reliability. This approach can reduce reliance upon complex, high-maintenance technologies, which are subject to more catastrophic failures, power losses, and other service disruptions, while maximizing reuse potential. It also may help reduce large capital outlays through “just in time” capacity building, rather than through one-time capacity investment that may not be needed for years after construction, if at all.

Utilities can address localized pollution issues by constructing smaller, more targeted wastewater treatment and dispersal alternatives and reducing the length and costs and operational problems of pipelines, manholes, and lift stations. Without proper inspection and maintenance programs, collection systems can be significant sources of pollution. Fecal coliform counts in raw wastewater can easily be 1 × 106 to 1 × 107 per 100 mL, while treated effluent has counts in the 3 to 200 per 100 mL range. By the numbers, 3.8 L (1 gal) of raw wastewater leaking from a collection system has the same pollution load (as measured by fecal coliform count) as anywhere from 1900 L (500 gal) to 12,500 m3 (3.3 million gal) of effluent.

By constructing more treatment systems and distributing them more naturally across a service district, utilities can reduce the potential for catastrophic failure. There is a certain truism to the phrase, “Dilution is the solution to pollution.” Spreading out the point and nonpoint sources allows for more dilution and protection of the watershed.

The distributed approach also may help keep water in originating drainage basins of watersheds, thereby helping maintain groundwater levels and stream base flows. Protecting natural water balances becomes increasingly important as our population grows and more water is being withdrawn from water sources to satisfy consumption needs.

Distributed wastewater management is much more than solely the “package plant” solutions of the past 50 years. Most package plant facilities employ expensive conventional collection systems and high-maintenance activated sludge treatment, and discharge directly to surface waters. Utilities can benefit from implementing effluent, pressure, and vacuum sewers — which can be more cost-effective than conventional sewers in many applications — and more passive treatment facilities that discharge treated wastewater to the soil or reuse it.

The distributed management approach expands our wastewater toolbox by including many treatment and beneficial use options for consideration during planning, design, construction, operation, and upgrading of facilities. The approach allows for a mixture of solutions for any district or area. For instance, smaller, dispersed technologies may not be feasible in many urban areas because of population density and physical constraints. However, employing satellite facilities for suburban fringe areas in lieu of central facilities expansion might be economically appropriate in these mixed-density areas.

EPA considers a well-managed distributed treatment system to be a component of a sustainable wastewater infrastructure, with benefits equivalent to traditional conveyance and centralized treatment. As such, a distributed wastewater management approach simply is a pragmatic method that utilities should consider to best manage their water problems. A properly planned distributed wastewater management structure would allow for orderly and cost-effective migration among available technologies as conditions, such as population density, change within the wastewater management area.

Todd Danielson is manager of community systems at the Loudoun County Sanitation Authority (Leesburg, Va.) and a member of the Water Environment Federation (Alexandria, Va.) Small Communities Committee.

Todd Danielson is manager of community systems at the Loudoun County Sanitation Authority (Leesburg, Va.) and a member of the Water Environment Federation (Alexandria, Va.) Small Communities Committee.

Editor’s Note: What are your thoughts on distributed wastewater management? Write to us at magazine@wef.org. Starting with the February issue, WE&T will offer a regular column devoted to this topic.