Wastewater Treatment Plant is Moving Missoula Toward Carbon-Neutral Future

The Missoula Wastewater Treatment Plant is an example of how the Food-Energy-Water Nexus objectives are put into action.

On a brisk day in early October, as the leaves in Missoula change to orange and gold and fresh snow accumulates in the surrounding mountains, trainees in the UM BRIDGES program set out to explore an unexpected site integral to reducing the city’s carbon footprint– Missoula’s Wastewater Treatment Plant. The Missoula Conservation & Climate Action Plan (CCAP) established a target of carbon neutrality by 2025. Some of the steps to meeting this goal are; reduction of green house gasses; reduction of building operating costs; and promoting public and environmental health. The Missoula Wastewater Treatment Plant is Missoula’s largest consumer of energy, giving it the greatest potential for helping meet these goals.

Trainees arrived at the plant, cold but excited, and were greeted warmly by Gene Connell. Mr. Connell has worked at the plant for 27 years and currently serves as the Facility Superintendent. Mr. Connell guided the trainees through the plant, and in the process, revealed the facility’s many innovative systems for resource reclamation. Throughout the tour, trainees were immersed in a range of Food-Energy-Water Nexus interactions and saw strategies developed by the treatment plant and the city of Missoula to provide services that benefit the community. Trainees witnessed the evolution of methods, from the original processes dating back to 1962 when the facility first began treatment, to its current, state-of-the-art processes.

The Missoula sewage system transports about 7.5 million gallons of water to the wastewater plant every day. Even with this impressive intake, the plant is only at 62.5% of its potential capacity. The plant is designed for a total capacity up to 12 million gallons, leaving room for the city’s water use to increase over time.

At the plant, water moves through a series of different stages of treatment, starting at the “headworks” building. Here larger solids like gravel and garbage are mechanically removed through a screening process, separated from the rest of the wastewater, and sent to a landfill. The importance of this initial stage cannot be understated, as it protects the operation of downstream equipment and enhances the efficiency of the overall treatment process.

During normal operation, the headworks uses two pumps, which can move up to 8 million gallons of wastewater a day, with another pump always in reserve in case of maintenance or mechanical failure. Almost all operations in the plant have a backup, to ensure that the system can continue running if one part breaks or malfunctions. Redundancy is important because, as Gene jokingly indicates, working on headworks is “like fixing an airplane in midair.” The plant must maintain processing even when sections are being repaired, in order to continuously process waste and protect public health.

Trainees watching the first step of treatment– removal of garbage and gravel from the incoming wastewater.
Gene explains the role of the heat exchangers on the buildings. Warm air being released from the headworks building runs through a heat exchanger, where heat is recovered and returned to the building rather than being released into the air.

From headworks, water moves on to a primary clarifier. Here, remaining solids, which are mostly organic, are able to accumulate as sludge at the bottom of the clarifier tanks via sedimentation, and as suspended scum at the surface. This process removes about 50% of organic solids, which may later be used for compost. Before primary clarifiers were implemented in 1962, sewage went straight to the Clark Fork River!

Secondary treatments utilize microbial processes to further break down waste products. Naturally occurring bacteria are cultivated in controlled bioreactors, designed to create the most productive environment for bacteria that will consume undesirable nutrients in the wastewater. One of the main goals of wastewater treatment plants is to reduce the concentration of nitrogen and phosphorus in water before it is released back into the environment, as too much of either compound could lead to unhealthy algae blooms. Through aerobic processes (which involve oxygen) and anaerobic processes (which occur without oxygen), bacteria substantially decrease water phosphorus levels, from approximately 4-5 ppm to 0.5ppm.

As an added bonus, Missoula’s plant takes advantage of these processes by capturing the byproduct methane, a known greenhouse gas. Rather than releasing this gas into the atmosphere, the plant uses 100% of the methane released to power the plant’s systems. Overall, energy from this methane helps account for 20% of the plant’s energy needs, which is very beneficial as the Wastewater Treatment Plant is Missoula’s largest municipal power consumer. The plant maintains approximately 90% efficiency from methane use, coupled with its heat exchanger systems.

The plant took another step forward when it switched from using chlorine and sodium hypochlorite to disinfect water, to ultraviolet (UV) radiation for disinfection. This method exposes wastewater to UV light, destroying potentially harmful viruses and bacteria, preventing their replication and reproduction. Chlorine and sodium hypochlorite are still used at many other wastewater treatment facilities, and while they work well against most pathogens, they are not effective against all the types that UV light can eliminate. Additionally, UV disinfection does not produce harmful byproducts and is not toxic to the environment. This makes the process safer, not just for those who would handle the chemicals, but also for the community and the environment.

Mr. Connell explains the benefits of ultraviolet disinfection compared to its predecessors, chlorine and sodium hypochlorite.

After the water is treated so that it will not cause any environmental or health issues, it is released back into the Clark Fork River, but the organic material removed from the water during the process is not wasted. In addition to treating wastewater, the Missoula Wastewater Treatment Plant has several side gigs. It manages a revenue generating compost program and an innovative Hybrid Poplar Tree Plantation.

The treated biosolids from the plant are used to create a Class A EPA compost, which can be used for mine reclamation purposes, landscaping, and agriculture. It takes 30 days to produce this high-quality compost, after which it can be sold at a profit to Superfund mining reclamation projects as well as the local community. In 2016, the City of Missoula bought EKO Compost, located adjacent to the plant. This purchase gave them more freedom to invest in better equipment and increase compost odor control.

A tractor moves loads of compost to smaller piles to be properly aerated before it will be ready to be sold to the public.

Just beyond this composting facility is a sea of green for as far as the eye can see. This sea is made up of 70,000 hybrid poplar trees arranged in neat rows covering over 160 acres. The trees, all sterile clones of each other, have grown rapidly since they were planted in 2014. This relationship is beneficial for both the trees and the city. Around 1 to 1.5 million gallons of treated water are diverted from the wastewater plant to irrigate these trees, and in the process, the trees help take up additional nitrogen and phosphorus nutrients. Originally, the trees were expected to be harvested for biomass power production. The University of Montana had intended to build a biomass power plant, but when that idea was put on hold, the plantation was unable to find another buyer. Alternatively, after 12 years, these trees could be harvested and sold for timber, but similarly, a suitable buyer has yet to be found. At the moment, the fate of the poplar plantation is uncertain. However, the city of Missoula wants to continue to use the land, water, and nutrients being produced by the plant to grow some type of crop, which will produce additional revenue for the city.

Six-year-old poplar trees, part of the Hybrid Poplar Tree Project, grow in neat rows along the Clark Fork River.

The Missoula Wastewater Treatment Plant is an example of how the Food-Energy-Water Nexus objectives are put into action. The plant considers the river throughout the treatment process by recycling waste products to power the facility, producing compost for restoration and agricultural use, or supplying water and nutrients to the poplar plantation for potential future use in energy or timber production. These are all impressive innovations, yet the plant is always looking forward. Mr. Connell spoke about possible options for reducing emissions, such as converting all bulbs in the plant to LED and finding solutions to become more energy independent.

Missoula is a community known for its strong environmental awareness, and Missoula’s citizens and government are constantly striving toward increased sustainability. This is shown in our dedication to reaching carbon neutrality by 2025. There is no one single solution to eliminating Missoula’s carbon emissions. Diverse strategies and solutions will need to be considered to achieve this goal, but the Missoula Wastewater Treatment Plant is taking a leading role in bringing the city closer to a carbon neutral future.

BRIDGES Trainee volunteers with Watershed Education Network

In August, when the dog days of summer were still in full swing, 3rd-5th grade students were scooping up minnows from a rapidly desiccating stream and releasing them back into Rattlesnake creek – a feat they called “Mission fish-possible.” As part of Watershed Education Network (WEN)’s Rattlesnake Creek Explorers Bilingual Camp hosted by Missoula International School, these students had been learning that healthy fish habitat is cold — and decided to take action!

With a background and interest in environmental education, Ada Smith, BRIDGES trainee and PhD candidate in Society & Conservation, has been both teaching and learning as a volunteer for WEN this year. WEN’s mission is to foster knowledge, appreciation and awareness of watershed health through science and outreach.

Ada’s experience working with WEN has been testament to the power of experiential learning. She witnessed the campers’ curiosity about river ecosystems and aquatic life grow as they spent time with feet and hands in the water. During another program called “Fish Week” in May, 7th grade students learned to cast rods, ID aquatic macro-invertebrates, and key in to their senses to learn about the river ecosystems right in their backyard. Here’s to learning-by-doing and growing the next generation of Montana watershed stewards!