Standing on the grated aluminum catwalk over pools of churning sewage sludge at the Edgemont Ranch wastewater treatment facility, one experiences a level of cognitive dissonance. The brain tells the body to react with revolted disgust at the sight of thousands of gallons of human excrement.
But the olfactory signs just aren’t there.
A mild organic smell permeates the air, but the malodor one expects from sewage treatment is obtrusively absent.
“That’s a healthy sludge,” said Kurtis Martinez. “It’s because your bugs are working right. If your bugs are working right and your process is working right, you should not have a stink smell.”
Martinez is the assistant utilities manager at Edgemont Ranch Metropolitan District, the facilities provider for the 710-unit housing development located about 6 miles up Florida Road (County Road 240) northeast of Durango. He operates the development’s hybrid single-batch reactor wastewater system called BIOCOS. The $8.6 million system went online four months ago, and Martinez could not be happier.
Robert Ludwig is Edgemont’s utilities manager. And he’s extremely proud of the fact that the effluent discharged into the Florida River from his system is cleaner than the river itself.
Within the United States, the BIOCOS system is nothing short of novel. Only two others like it exist in the country. The system is a proprietary technology developed by World Water Works at University of Innsbruck in Austria to treat wastewater in mountain communities.
Most wastewater treatment systems rely, at least in-part, on bacteria to break down solids and digest organic material. However, temperature, oxygen content and the “appetite” of those bacteria all affect how effectively they are able to do their job.
Edgemont’s system is small. It occupies just 9,119 square feet of land, sitting several hundred feet off County Road 234. Water flows in from the development via a single pipe underneath ranch land. A screen filters out anything larger than 6 millimeters, such as toilet paper, and deposits it in a trash can. Water settles in a trough to separate grit, before it is pumped into the BIOCOS.
The system itself works inside a 5,000-square-foot concrete box containing six basins. The basins work in sets, operating simultaneously. They also serve as a backup for one another in case one should fail.
“There’s two of everything,” Martinez said. “When something breaks down, you got time to fix something while the other one works. Everything is redundant.”
The raw sewage is then pumped into the two aeration tanks. Those tanks are connected to two alternating sludge recycling and settling tanks. A unique air lift pulls the condensed layer of sludge from the bottom of those “Alt tanks” and uses centripetal force to separate the denser, better-settling bacteria from the smaller, less hungry bugs.
The hungriest of the bugs are pumped back into the aeration tanks, where they are mixed with incoming sewage to allow for a more rapid and effective breakdown of organic material. The smaller bugs are released into one of two sludge basins.
Recycling bugs with fresh sewage takes eight minutes. Then, water is transferred to the Alt basin, where air bubbles mix it for five minutes.
“We’re glorified bug farmers,” Martinez said.
Once mixing and aeration occurs, the basin settles for 62 minutes. Then, the cleanest layer of water, which is nearly clear, is decanted from the basin for 75 minutes. Although the total cycle time is 150 minutes, the parallel basins mean the system is constantly feeding sewage into the system via one side and discharging out of the other.
After decantation, the water runs through a UV light system, which renders any remaining bacteria unable to reproduce. Clean effluent then flows out a pipe and into the Florida River.
The sludge that is not recycled slowly accumulates. Martinez will eventually run it through a fan press, which will turn it into a caky topsoil-like material, which can be disposed of in a landfill or spread across grassland.
What is unique about Edgemont’s system is not so much the process of aerating bacteria to induce the breakdown of organic matter, but the efficiency of the process.
Before its installation, Edgemont’s sewage ran through a series of three lined sewage lagoons. The retention time of water in the lagoons was 70 to 90 days, compared to the seven-day retention time of the BIOCOS.
More importantly, the water discharged from the lagoons was unable to meet the Colorado Department of Public Health and Environment’s increasingly strict effluent standards.
“(Lagoons) do not treat water if they're under 4 degrees Celsius because all the bugs go to sleep,” Ludwig said. “And so we knew that we had been having nitrogen problems with our discharge.”
The district got a new wastewater discharge permit from the state in 2014 which outlined that effluent standards would tighten in 2020. The new standards meant that Martinez and Ludwig would have a limit on the ammonia levels in the effluent – levels they could not attain nine months out of the year.
“We decided that we didn’t want to throw a million dollars here to put a cover over (the lagoon) or a million dollars there to put a simple fix ... that cost a lot of money because we knew the bigger picture was that nobody’s going to be able to have a lagoon in this area anymore,” Martinez said.
And so, in October 2019, the men packed a bag for Austria.
“(Anecdotally), I think that in Europe, they’ll spend a little more on public works projects like water and wastewater treatment plants,” said Nick Marcotte, a process engineer with Element Engineering who worked with Edgemont to design the system. “They definitely have a different process about going about procuring them and building them.”
After settling on the BIOCOS system, Edgemont began the process of gaining CDPHE approval for the new system. Before they could do so, the new effluent limits kicked in, and the agency fined Edgemont $45,000.
But Ludwig and Martinez hardly seem bothered.
“We all want to go above and beyond to try and put out the best water that we can back into the river,” Martinez said.
To that end, Martinez and an engineer from World Water Works are constantly trying to tweak the system.
The productivity of the bugs is determined by temperature and availability of oxygen. Using a computer system which Martinez can control from his phone, the plant automatically turns oxygen blowers off and on to regulate productivity based on a certain metrics.
Perhaps the most novel aspect of the Edgemont system, however, is that metric itself. Probes in the basins can test for ammonia, nitrate and dissolved oxygen levels and Martinez can manually select which of those metrics the system uses to determine how much aeration is necessary.
“This DO (dissolved oxygen) probe on this side is actually controlling the blowers right now,” Martinez said, pointing to a device in one of the basins as he checked the system on his iPhone. “Once (the basin) drops to a 0.8 (parts per million)– we’re at a 1.5 right now – then the air is going to kick back on.”
According to Ludwig, no other plan in the country is capable of running off ammonia control, and very few can run off nitrate levels.
From nearly every perspective, the plant is an odorless success.
Not only is it energy efficient, but very little water is lost via evaporation, a significant issue for lagoons. The effluent it discharges into the Florida is clear, but more importantly, water quality testing affirms that it is in fact clean.
Total Inorganic Nitrogen, which includes nitrite, nitrate and ammonia, can cause the acidification of waterways and impair the survival and reproduction of aquatic life. It is one of the larger concerns for a high-elevation plant such as Edgemont.
Under Edgemont’s 2022 permit, the system’s effluent may contain up to 20 milligrams per liter of TIN; the day of the interview, the effluent contained 3.75 mg of TIN.
The system works so well that Ludwig says Edgemont has received significant interest from other districts seeking to improve.
“I think within the next couple of years, there will be many, many more (of these systems),” Marcotte said.
“It was weird how we got into this fairly elite group of turd-treaters,” Ludwig said. “... It’s definitely taken us out of our comfort zone to do this. But doing that has created some of the best treatment I’ve ever seen.”