Decentralized Sewer a Boon to Developers, Industry Professionals, and the Environment
Should you pipe your new commercial development into a municipal sewer, or should you have your engineer design a decentralized liquid-only wastewater treatment system instead?
It’s a big decision to make. It’s one that can shape the project’s financial, operational, and environmental outcomes.
For many residential and commercial developments, the most profitable wastewater solution is treating wastewater closer to where it’s generated.
Decentralized collection, treatment, and dispersal systems can reduce infrastructure costs, accelerate development timelines, unlock more buildable lots, and protect local water resources. That’s why developers, wastewater professionals, and the environment often emerge as the winners.
In the right circumstances, “small pipe” offers advantages that gravity sewer extensions simply can’t match.
The Developer
When a developer plans a sewer system, decentralization can improve project economics in several ways.
A decentralized system can increase the number of marketable lots by reducing the land area required for centralized infrastructure and making remote sites economically viable. It can unlock unusable sites, those that are too far from municipal sewer systems, and those where gravity sewer extensions are too costly. Infrastructure costs can be reduced, too, because decentralization can be a phased infrastructure investment.
Take, for instance, the case study of a luxury lakeside tract in Sunset Bay, Tennessee. The developers of a slow-build, 750-home subdivision needed a modular wastewater treatment system that could consistently meet the stringent nitrate requirements (20 mg/L) set by the Tennessee Department of Environment and Conservation.
Standard septic systems wouldn’t reliably meet the strict nitrate requirements, and many of the lots weren’t large enough to use an onsite advanced treatment system and drainfield. The nearest municipal treatment plant was 20 miles away, so connecting to that wasn’t an option either.
The developers, along with engineers from Environmental Systems Corporation and wastewater equipment manufacturer Orenco Systems, devised a solution: a liquid-only sewer system.
It included a collection tank at each lot, as well as a secondary treatment system, an AdvanTex® AX20, that produced effluent that met nitrate requirements. Following collection, the liquid traveled through small-diameter pipe to a drainfield dispersal system that served the entire subdivision. As designed, the system had a capacity of 165,000 gpd (625 kL/d) and was maintained by the local utility.
Sunset Bay’s wastewater treatment system resulted in strong project economics for the developers. Because the homeowners paid for their own primary and secondary treatment units, the developers only needed to fund installing the small-diameter collection lines, setting up the dispersal area, and handling any subsequent nutrient removal.
In addition, because permits for the on-lot primary and secondary treatment systems were approved as a standardized package, the time required for design/review/approval was much shorter. The authorities needed only to give their OK on the drainfield, not a centralized treatment system.
And because the system was engineered to treat wastewater closer to where it was generated, developers were able to avoid expensive sewer extensions, reduce earthwork requirements, and phase the infrastructure buildouts with demand.
The results—lower up-front capital expenses, improved project cash flow, and the potential to increase the number of marketable lots—all contributed directly to stronger project profitability.
The Dealer/Contractor/Servicer
For dealers, contractors, and service providers, decentralized systems create recurring opportunities that extend far beyond installation. Design support, start-up assistance, monitoring, maintenance, upgrades, and ongoing service contracts can provide long-term value throughout the life of the system.
A case study out of Grizzly Ranch, California, shows how dealer expertise can contribute to the right solution for the job, as well as long-term operation, maintenance, and infrastructure support opportunities.
The master-planned community in the Sierra Nevada foothills had problems collecting and treating its wastewater. On-lot grinder pumps there failed frequently and cost $3000 each to replace. Not only that, but the community’s wastewater had to be hauled away and treated elsewhere—a cost of up to $200,000 per year—because the sequencing batch reactor (SBR) had never been operational due to low flows in the slow-build development.
The general manager of Grizzly Ranch Community Services District (CSD) learned of liquid-only sewers from a neighboring CSD and discovered, after further research, that a similar collection system could be installed with Grizzly Ranch’s existing infrastructure.
After consulting with a group of wastewater professionals—including Pace Supply, a local Orenco Systems dealer—the Grizzly Ranch CSD board of directors decided that an AdvanTex AX-Max™ Treatment System fed by on-lot tanks fit the bill. It would provide immediate year-round treatment of inconsistent flows and be installed over time as the development built out.
So, with the plan approved, crews switched out grinder pumps for liquid-only sewer components at the existing home sites and installed two AX-Max treatment systems capable of treating up to 25,000 gallons per day in place of the unused SBR. The treatment train also included two 32,000-gallon tanks from the previous treatment system that were repurposed as pre-anoxic tanks. And, to finish it off, an Orenco Controls™ TCOM™ panel with touchscreen was installed to handle all the monitoring and controls.
Together, Grizzly Ranch CSD and Pace Supply solved a problem and came out as winners. Their work minimized the impact on the development’s infrastructure, shifted the working capital from repair to maintenance, and ensured the project would remain sustainable as the number of connections increased. The solution created long-term operation and infrastructure support opportunities for everyone involved.
The Environment
Environmental performance is another area where decentralized systems typically excel.
Installing onsite wastewater collection with decentralized treatment and dispersal is often less obtrusive than laying big concrete sewer pipes for a package plant. This is particularly true in areas with undulating landscapes, rocky soil, or shallow bedrock where directionally bored pipes leading to secondary treatment make more sense.
Primary and advanced secondary treatment units themselves can reduce nutrients, organic matter, and other pollutants before they reach groundwater. By treating wastewater close to where it’s generated, decentralized systems can help communities grow while protecting local water resources for future generations.
Dispersal of clean effluent into the soil itself benefits the environment, too. As area groundwater is withdrawn for residential, agricultural, municipal, industrial, and other uses, it must be recharged from the surface with treated stormwater and wastewater. Drainfield technology, including chambers and other surface-area multipliers, makes this possible without the need to haul and shovel heavy gravel.
Onsite collection and liquid-only sewering to secondary treatment is also a sustainable approach to wastewater management. As a development or small commercial property grows, the system grows.
For example, developers in a Jack’s Point, New Zealand, case study sought to build a residential community with 900 luxury homes. The location was just outside Queenstown, a resort community on the shores of Lake Wakatipu with a view of the snow-capped Southern Alps. Jack’s Point would include walking and biking paths, a golf course, and a clubhouse with a restaurant, pro shop, and offices.
Unfortunately, local sewer service was more than 5 miles (8 kilometers) away, and the municipal wastewater treatment plant would require an upgrade to accommodate the additional flow.
The developers needed an economically sustainable collection system that could handle variable terrain, followed by a reliable treatment system that would produce high-quality effluent and could be installed in stages, with minimal visual impact on the community.
Innoflow Technologies of New Zealand put forth a design-build-operate proposal that incorporated an Orenco liquid-only sewer, AdvanTex secondary wastewater treatment, and subsurface drip irrigation used to water nearby fields. After considering three package plant options and three reticulation options, the developer and governing body approved the plan.
The decentralized system was able to reduce nitrogen while minimizing visual impacts and supporting staged growth that respected the surrounding environment. The approach also eliminated dependence on costly offsite sewer expansion, allowed modular build-out, and recharged the area groundwater.
The Winners
For the right project, decentralized wastewater treatment creates value across the board. Developers gain flexibility and profitability. Dealers, contractors, and service providers gain long-term opportunities. Communities benefit from responsible environmental stewardship and sustainable growth.
One development decision. Three clear winners.