My alarm goes off. I drag myself out of bed, stumble into the kitchen, and put the kettle on for coffee. I pour a cup through the filter, and drink most of that first cup while throwing my lunch together, when, like clockwork, this routine is interrupted by an urgent need to poop. Like most of us, I flush the toilet without giving the smallest thought to where it goes once I say goodbye to what I ate the day before. And although this waste quickly disappears for me, the question lingers: where did it go?
On a bright, crisp September morning, our cohort of 12 new graduate students piled into vans destined for Missoula’s wastewater treatment facility. Our interests are varied and our disciplines diverse, but we are tied by a common desire to network outside of our immediate fields of study to address problems that intersect food, water, and energy systems. With this in mind, we set out to learn about the local challenge of managing the wastewater of Missoula and innovative ways to reclaim our waste into useful products.
When a toilet flush arrives at Missoula’s wastewater treatment facility, it is by all accounts contaminated. Dirty dishwater, laundry drainage, unwanted chemicals, and all other waste liquids come together to create a foul concoction that any person with eyes or a nose would instantly recognize. As it flows through the facility, a series of physical and biochemical processes transform this mixture back into water that is considered clean enough by society to be piped into the Clark Fork. But how does this change actually occur and what exactly is being removed from the water?
The first stop is a building called the headworks, where large solids such as toilet paper and sand are filtered out and compacted for easy disposal. This building is potentially the smelliest step of the treatment process, but since remodeling in 2011 the smell has been reduced to a vaguely unpleasant odor instead of an overpowering stench.
After traveling through the headworks, the water flows into one of several settling tanks to undergo primary treatment. During primary treatment a long arm skims the surface to catch floating materials, such as oils. Under the surface an extension of the arm scrapes the cone-shaped bottom to remove solids. Many of us were surprised that the stench wasn’t stronger, as the tanks housed what is still essentially raw sewage. “Most of the water people use is from the sink or shower, most of it isn’t from the toilet.” Gene, the Superintendent of MWTF reminded us. “I can tell apart the urine and laundry detergent.”
Primary treatment tank with visible surface skimmer.
It is relatively simple to remove physical pollutants, but the majority of time at a treatment plant is spent extracting dissolved nutrients from the water during secondary treatment -also known as the activated sludge process. Nitrogen and phosphorus are the primary targets, as they lead to ugly and often dangerous algal blooms and alter any ecosystem they enter. Western Montana rivers such as Missoula’s Clark Fork naturally tend to be low in nutrients, making them more vulnerable to excessive dumping. The facility uses natural bacteria communities that grow in the water to transform the nitrogen or phosphorus into a gas or solid for easy removal. This elegant solution simply requires the facility operators to provide ideal living conditions for helpful bacteria to thrive. The water is passed between a deep tank in which there is no oxygen present and a tank with aerators continually adding oxygen to the water, looking like the dirtiest hot tub you ever saw. The anoxic environment favors bacteria that convert nitrates (the primary nitrogen pollutant) into inert nitrogen gas and the aerated tank favors bacteria that uptake and remove phosphorus from the water.
This aerated tank provides an excellent environment for phosphorus loving bacteria.
Staring into the brown viscous water undergoing the “activated sludge” process, I think back to that post-coffee flush, and the fate of the caffeine that passes through me. And then, about other drugs and medications, like ibuprofen, antidepressants, hormones from birth control, and illegal drugs coming from 72,000 people. Most chemicals and metabolites in prescription and illicit drugs persist in the aquatic environment and remain bioactive even after passing through our bodies, which means that they can affect the critters living in lakes, ponds and rivers when they end up there. Luckily, the microorganisms in that thick brown water are hard at work, breaking down many of the contaminants, with around an 85% reduction of 55 identified contaminants in one study1. Other studies have shown that the combination of activated sludge and UV light break down some of the contaminants that have been identified, but other chemicals persist through these processes2, and are introduced into rivers when the treated waters are discharged. Advanced technologies to remove more of the chemicals are continuing to emerge, but they lag behind the introduction of new and increasing amount of chemicals coming from our homes. In Missoula, we benefit from the large size of the Clark Fork River, which means that even for the contaminants that make it through the waste water treatment facility, dilution will greatly reduce the load of chemicals that enter the river ecosystem. Even so, keeping in mind that what goes into our bodies and down our drains can end up in our rivers might help us reduce those pollutants before they even have the chance to enter the pipes.
After making its way through primary and secondary treatment, water at most treatment plants is returned to nearby rivers, streams, or lakes. At the Missoula Water Treatment Facility, six million gallons follow this path, but one million gallons of treated water per day meet a more lucrative fate. Traveling a few hundred yards, treated water is pumped to Missoula’s own hybrid poplar tree farm. Four years ago, in collaboration with the Clark Fork Coalition and Watershed Restoration, the city of Missoula planted 90,000 hybrid poplar trees on leased farmland next to the treatment facility. These trees were planted with the intent that they might absorb a portion of the still nutrient rich treated water. In one growing season these trees take up 8,700 pounds of nitrogen and 660 pounds of phosphorus from water that would otherwise end up in the Clark Fork River. Having expanded beyond their original count of 90,000 trees and with intentions of planting new poplar forest nearby, Missoula’s Poplar Farm is a true success story in environmental remediation and restoration.
A very small part of that original flush likely ends up as treated bio-solids that go into making compost. After nutrients are removed during secondary treatment, and the extracted water is sent off to the poplars, the resulting biosolids, or “sludge”, is combined with green waste from the public and waste from lumber mills. All of this organic matter is gathered into large piles to go through an aerobic composting process, where microorganisms break down the organic matter in the presence of ample oxygen. In this case, that is supplied through aeration pipes that provide air flow and encourage temperature regulation (the pile can heat up to 160 degrees!). The result is a rich compost that is available for public and private purchase. Originally started as the private enterprise EKO Compost, the City of Missoula purchased the operation in 2016. It now operates as Garden City Compost and it is an example of another step to attempt to close the loop on waste treatment and recovery.
After twelve hours, 1/7th of my morning’s flush has met the roots of poplars, a tiny portion has begun to turn into dirt that will grow new plants in someone’s garden, and the rest reentered the watershed via the river. Eventually this water will settle back down into the groundwater to be pumped up again, perhaps for agriculture, perhaps into roots of local foliage, or perhaps to your house or school as you prepare your morning coffee.
1Kasprzyk-Hordern, Barbara, Richard M. Dinsdale, and Alan J. Guwy. “The removal of pharmaceuticals, personal care products, endocrine disruptors and illicit drugs during wastewater treatment and its impact on the quality of receiving waters.” Water research 43.2 (2009): 363-380.
2Zupanc, Mojca, Tina Kosjek, Martin Petkovšek, Matevž Dular, Boris Kompare, Brane Širok, Željko Blažeka, and Ester Heath. “Removal of pharmaceuticals from wastewater by biological processes, hydrodynamic cavitation and UV treatment.” Ultrasonics sonochemistry 20.4 (2013): 1104-1112.