Wastewater
Three Rivers Biosolids Facility
*Two 1.6 million-gallon post-tensioned anaerobic digesters with combined heat and power, thermal dryers and a Class A biosolids product, built on an operating treatment plant campus.
- Client
- Three Rivers Sanitary District
- Engineer
- Willamette Basin Engineers
- Location
- Eugene, OR
- Value
- $25M–$100M
- Delivery
- Progressive Design-Build
- Status
- Completed
- Completed
- 2021
Spec sheet
By the numbers
- Digesters
- Two 1.6 MG, post-tensioned concrete
- Digester height
- 62 ft sidewall, 78 ft dia.
- Biogas engines
- Two 1.1 MW CHP units
- Dryer capacity
- 8 dry tons per day
- Concrete placed
- 9,700 CY
- Contract value
- $58.9 million (GMP)
Story
Challenge, solution and outcome
Challenge
The district was sending 32,000 wet tons of biosolids per year to land application at rising cost, and had to meet a state mandate to produce a Class A product. The new facility had to tie into the existing plant sludge lines and gas system without upsetting the existing digesters.
Post-tensioning, digester gas handling and dryer equipment all carry long lead times and specialist installation requirements.
Solution
We contracted the post-tensioning specialist and the dryer manufacturer during design, then scheduled the work around their fabrication calendars. Digester walls were formed with a climbing system and stressed in three stages, with maturity sensors determining the stressing date.
The gas system was built under a hot-work permit program with continuous LEL monitoring, and every gas pipe was pressure-tested and pneumatically proved before purging. The district's operators were trained on a simulator that we set up two months before start-up.
Outcome
The facility produced its first Class A product 38 days ahead of the baseline schedule. The CHP units now cover about 62 percent of the plant's electrical load, and annual biosolids hauling fell by 71 percent.
The project closed with 0 lost-time incidents over 262,000 hours, and the digesters passed their water-tightness test with zero measurable loss.
Safety
Safety highlights
- 0 lost-time incidents over 262,000 work hours
- Digester gas hot-work permit program with continuous LEL monitoring
- Post-tensioning exclusion zones and stressing-operation checklists
- Climbing-form fall protection engineered for 62-foot walls
From the owner
“The digesters were the first thing in our history to hold water on the first test. The operations team still talks about how well the commissioning was run.”
Gallery
Project gallery
