Darigold is one of North America’s largest dairy co-ops. Farmer-owned since 1918, Darigold represents over 500 family farms across the Northwest. It produces milk, sour cream, and cottage cheese.
The Darigold plant in Boise, Idaho, USA, was preparing to install a cottage cheese production line that would increase its wastewater flow as well as change the organic load. Nearly fifteen years earlier, ADI Systems had designed and built an ADI-BVF® reactor to pretreat Darigold’s wastewater, which significantly reduced direct discharge surcharge fees. Darigold realized a quick payback on that investment and experienced first-hand the effectiveness of ADI Systems’ treatment technology. Because of this positive experience, Darigold looked to ADI Systems again to help upgrade its wastewater treatment system.
As part of the expansion, ADI Systems designed, supplied, and installed a new 1.7 MG (6,400 m3) BVF® reactor to operate in parallel with Darigold’s existing BVF reactor. The project included tank internals, a recycle pumping system, a geomembrane tank cover for odor control, and interconnecting piping to the existing BVF reactor and activated sludge system.
Additionally, ADI Systems upgraded the biogas transmission system, aeration system, and control programming in order to accommodate the increases in hydraulic and organic load sent to the treatment system.
Darigold’s newly expanded treatment system was designed to treat wastewater with a flow of 217,000 gpd (820 m3/d) and chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS) concentrations of 13,000 mg/l, 8,000 mg/l, and 1,000 mg/l, respectively.
Darigold proceeded with its cottage cheese production line, as planned. The treatment system produces no foul odors, which is important because the plant is located in a well-developed area in Boise.
The long retention time associated with the BVF reactors ensures that fat, oil, and grease (FOG) in the raw wastewater and waste activated sludge from the downstream aerobic polishing system are properly digested. This reduces the need for waste sludge handling and disposal.
The upgraded wastewater treatment plant continues to provide Darigold with a robust, resilient treatment system that requires little energy to operate, thereby minimizing overall operating costs.