High-strength wastewater

Bozeman, Montana, USA

Key facts

Key Facts
  • Technology: VF wetland with recycle and partial saturation
  • Challenge addressed: Cold-climate wastewater treatment for a ski resort in the mountains
  • Main innovation: Seasonal operation, recirculation for increased nutrient removal from high-strength wastewater

Environmental &
Socio-economic impacts

Water demand within the city is predicted to exceed supply by 2040 and thus innovative solutions for reuse are necessary. The Montana State University Bozeman (MSU) is at the forefront of NBSWT technology transfer, adaptation, and implementation in cold-climate regions in the United States, and the City Bozeman profits directly from the knowledge transfer.

Main Activities

Three full ski seasons of water quality monitoring data have been collected since the inception of the project.  The pilot treats up to 6 m3 d-1 of wastewater collected from the base area lodges at the ski resort.  The wastewater is generated primarily from latrines and kitchens and the goal of the system is to remove total organic carbon and total nitrogen before discharging into a drain field.

The effluent from the second stage has been reintroduced into the system at a 2:1 volume-to-volume ratio (recycle to influent), to promote total nitrogen removal. In addition to water quality monitoring, sampling for microbial abundance and diversity at various points within the system and sampling of greenhouse gas emissions were conducted. Microbial community dynamics were assessed over time and metagenomics analyses are being conducted to understand the stability of the community during rest periods.  Emissions of CO2, CH4 and N2O were measured from randomly selected locations in both stages, either at short time intervals or with continuous monitoring over several days.

Results

Throughout the seasons, overall COD removal was >95%, TN removal was >70%, and ammonia removal was >97%.  The removal efficiencies for COD, TN, and ammonia decreased only minimally when total flow was increased from 4 m3 d-1 to 6 m3 d-1 during the 22 – 23 season. During the 2023-24 season, COD loading rates to the first stage were consistent with the previous year at an average of 111 g/m2/day and system-wide COD removal was consistent at 95%. The total nitrogen loading onto the first stage was also similar to the previous season at an average of 36 g N/m2/day.

Results of the microbial DNA analysis indicate that the TW performance was complemented by high relative abundances of psychrophilic bacteria that are adapted to low temperatures. Spatial differences across stages indicated that the first and second stages supported distinct microbial communities, which agrees with water quality changes across the stages.

From the 2022 GHG study, emissions of CH4 and N2O were significantly higher in the first stage compared to the second stage of the TW. The emission factors for N2O and CH4 were similar to similarly operated TW systems and on the low end of most other treatment processes.

A survey was conducted with the stakeholders of the pilot.  The co-benefits that respondents would most like to see monitored included: 1) Reduction of energy demand; 2) Providing carbon storage/sequestration 3) facilitating environmental education and 4) increasing aesthetic value.  Responses did not comment on as many disadvantages and suggested that most can be mitigated.

Impact generated

The success of the pilot system has prompted Bridger Bowl to install a full-scale treatment wetland to remediate all wastewater generated from the base area ski lodges.  As a result of the wastewater treatment and other measures, Bridger Bowl has been recognized as a leader in sustainability among non-profit organizations. The organization has won multiple awards, including the Regional Pollution Prevention Recognition Award from the Environmental Protection Agency.  Educational placards about the treatment wetlands are available for patrons of the ski area to read when they visit.

Due to the success of the system, the City of Bozeman and Montana’s Department of Environmental Quality are sponsoring three additional pilots at the City’s municipal wastewater treatment plant. The pilots will demonstrate the potential to treat wastewater with treatment wetlands in the cold winter climate of rural Montana. They include a French vertical flow pilot for raw wastewater treatment, a recirculating vertical flow system for total nitrogen removal, and a tertiary vertical flow pilot for removal of low nutrient concentrations in the wastewater treatment plant effluent.

Organizations involved

INRAE
INRAE
INRAE