The economic and environmental costs of treating all wastewater at a centralized location can be a burden. At what point does decentralized treatment make more sense?
Decentralized wastewater treatment is certainly not new, but at the same time it has yet to be embraced as a popular alternative to centralized, big-plant operations. That soon may change, according to the president of Bio-Microbics, Bob Rebori, who admittedly has a vested interest in seeing it popularized (his company specializes in decentralized solutions). Rebori’s optimism is not unfounded, however, as an objective argument can certainly be made for the benefits, and even the inevitability, of wider-scale decentralization.
For his part, Rebori is not calling for a revolution. His experience — over 32 years in both large- and small-flow markets — leads him to favor the term “distributed” over “decentralized.” The latter, he reasons, suggests an “us-versus-them” dynamic, when in reality the proper treatment approach is purely circumstantial, dependent on location, economics, and objectives. From my conversation with Rebori, here are five reasons for a community or business to consider decentralized (AKA “distributed”) wastewater treatment.
On-site treatment and reuse makes sense on many levels, which is why it’s predicted to trend up in the coming years. Heavy water users can save money — and the environment — by closing the loop on the traditional treatment cycle, cutting out the central wastewater treatment plant (WWTP) while reducing environmental discharges. This lessens the burden on collection systems and limited-capacity WWTPs, while also increasing available water supply.
According to Rebori, Bio-Microbics’ BioBarrier® membrane bioreactor (MBR) technology is capable of removing 95 to 99.9 percent of contaminants from wastewater, and is the only onsite reuse system NSF/ANSI-certified for use in toilet-flushing (essentially meeting potable water standards). Typical commercial reuse applications are far less demanding, however; they include: landscape irrigation, makeup water for cooling towers, washdown water for floors and machinery, and concrete curing in hot, arid regions. Implementing reuse as part of building design can also earn points for water efficiency toward LEED certification from the U.S. Green Building Council or other green build programs.
Easy setup and operation is not only a convenience, it is often a necessity. Personnel in industrial/commercial settings likely have little to no experience with wastewater treatment equipment, and small, remote municipalities — the logical candidates for decentralized treatment — are often short-staffed.
The basic difference between centralized and decentralized collection and treatment, according to Rebori, is full-time control and operation versus the intermittent O&M required of decentralized systems. “The key for decentralized systems is to make them simple, low cost, and robust — simple to install, simple to maintain,” he said. “Many of our systems might only get a visit once or twice a year. Even our very large systems may only get visited once every three months.”
The lack of day-to-day oversight or testing may give some pause, but Rebori noted that minimal attention is the precise benefit of decentralized systems. Furthermore, it’s not as though the units are unchecked — Bio-Microbics products undergo ongoing third-party evaluation, in addition to spot testing in the field. The EPA has also affirmed the viability of decentralized systems through the Decentralized Memorandum of Understanding (MOU) Partnership.
From a regulatory standpoint, all 50 states adopt their own standards for decentralized treatment. In Rebori’s experience, standards are usually handled on a county-by-county basis, regulated through the health department rather than the state’s Department of Environmental Protection (DEP). Efficacy is proven through both third-party certifications and testing from regulators. “We give them our treatment equipment and it needs to operate for six or nine months, even a year, with absolutely no interference,” he said.
Nutrients in the environment create toxic algal blooms that are harmful to both fish and humans, resulting in strict state and federal regulations on WWTPs for effluent phosphorus and nitrogen. The algae problem continues, however, due to the nutrient loading of non-point sources such as agricultural runoff. The EPA has acknowledged this fact by endorsing a watershed approach to nutrient control, giving municipalities more flexibility in how they limit total maximum daily loads (TMDLs) — beyond what comes out of the plant itself. This means controlling nutrients at the (non-point) source.
Whereas a central treatment facility is largely helpless against downstream runoff, decentralized systems can treat high nutrient loads wherever they occur, before they reach the watershed. Whether it’s a farm or a collection of failing septic systems, Rebori argued that “decentralized treatment fits perfectly with the TMDL approach.”
“Would you want a beastly plant sticking up, above the ground, in your backyard?” asked Rebori. “You wouldn't want to see it. You wouldn't want to hear it. You certainly wouldn't want to smell it.”
Bio-Microbics’ units, engineered for a 25+-year lifespan, usually are housed almost entirely underground in locally acquired concrete, plastic, or fiberglass tanks. The only feature visible above ground is the blower(s), which can be installed up to 100 ft. away from the system. According to Rebori, the systems are odorless as well. “We design it so that it can be buried and still maintained,” he said. See the video below for a tutorial showing the installation and treatment process of Bio-Microbics' decentralized MBR.
Of course, it always comes down to economics. Installing pipes and pumps is expensive, and increasingly so for more remote areas. The economic argument supporting decentralized treatment is therefore closely tied to population density. “If there's not a great deal of density, the economics are a slam dunk for decentralized systems,” said Rebori. “Not just to install them, but to operate and maintain them for outlying areas.”
“When you treat and dispose of wastewater on-site, very often you don't need collection and pumps,” he continued. “It's not just another capital cost — it's another maintenance cost and power issue when you have a collection system.”
That’s not to say Rebori didn’t have an argument for well-populated, sewered areas. “If there's a great deal of density and you have high-strength dischargers, the economics make sense for pretreatment of waste, to knock it down,” he asserted.
While Rebori may indeed have a vested interest in the proliferation of “distributed” systems, he makes points worthy of consideration. Ultimately, it is a cost-per-unit calculation that needs to be resolved — the cost per property to handle wastewater, and/or the cost per milligram of nutrients removed. That calculation will be variable in each circumstance, but looking at the density and location of dischargers is a good place to start.
When it comes to smaller-scale economic discussion, Rebori shared with me how his company, Bio-Microbics, can deliver decentralized solutions cost effectively.
“We assemble and ship in high volume; we don't wait to get a purchase order to make something. The suggested retail price of our regular 9,000-GPD FAST® (fixed integrated treatment technology) wastewater treatment system, delivered to anywhere in the U.S. — not even a discounted price — is $25,000.
“We made it so that it's within reach of everyone. Think of it like the Ford Model A compared to the Model T — you had to make it in high volume and get the cost down so the lion’s share of the general public could afford to utilize it. That's what our challenge has been in decentralized treatment, and that's the reason why we do it the way we do.”