Water Resources Research Act Program

Details for Project ID 2019MT155B

Optimization of two-stage solids and nutrient removal wetland treatment system operating at a fish hatchery in a cold climate

Institute: Montana
Year Established: 2019 Start Date: 2019-05-31 End Date: 2020-05-30
Total Federal Funds: $2,000 Total Non-Federal Funds: $880

Principal Investigators: Luke Thompson

Abstract: The Ennis National Fish Hatchery (ENFH), located outside of Ennis, MT at an elevation of 5500 feet is a brood stock station, providing fish eggs to other hatcheries in the US. Brood fish live in 36 raceways, concrete channels that are 70 feet long and 8 feet wide. A flow of 20 MGD supplied from a nearby spring is split between raceways in a single pass before returning to Blain Springs Creek. Each raceway contains a grated tailbox at the outlet that serves to settle solid fish waste and unconsumed food particles. In the past, raceway solids were cleaned once a week and this solids load was discharged directly to Blain Spring Creek. In 2013 the Montana Department of Environmental Quality requested that the U.S. Fish and Wildlife Service mitigate the ENFH’s impact on Blain Springs Creek and by extension the Madison River. In 2014, a joint project between the U.S. Fish and Wildlife Service and Montana State University Bozeman was initiated to utilize a novel two-stage vertical flow wetland treatment system to reduce the environmental impact of the hatchery operations. Treatment wetlands (TW) are an accepted treatment alternative for domestic and industrial wastewater streams. TW mimic biogeochemical processes found in the natural environment to reduce contaminant concentrations in polluted water. These natural characteristics along with low operation and capital costs make TW an environmentally friendly and sustainable wastewater treatment option (1). TW are a popular treatment alternative in France where almost 3000 TW systems are treating municipal waste streams (2). TW have also been used to treat aquaculture waste streams (3,4,5). Both subsurface and surface flow wetlands have been considered for aquaculture applications (3,5) and at the ENFH a subsurface vertical flow (VFTW) system is employed. In a VF system, wastewater is dosed onto the surface of the wetland on which solid organic matter is filtered by porous gravel media and its degradation products are further remediated as the flow passes through the gravel media. Aquaculture waste streams are typically characterized by the total suspended solids (TSS), biological oxygen demand (BOD), total nitrogen (TN), and total phosphorous (TP) (6). The broodfish at ENFH are fed more than 36 tons of food per year. The solids retention system in the raceways settle out fish waste and unconsumed fish food into the tailboxes at the downstream side of each raceway. The solids are then pumped from each tailbox to the VFTW system. The VFTW at the fish hatchery has three stages of treatment: solids removal, nitrogen removal, and phosphorous removal (Figure 1). Effluent pumped from the raceways is collected in a solids retention tank. The solids retention tank then doses five aerobic solids treatment wetland cells where the collected solids are filtered and aerobically degraded. Nitrogen in the effluent from the solids cells is primarily nitrate and travels to a recycling tank that doses five anaerobic nutrient treatment cells where denitrification takes place. The effluent from the nutrient cells can be recycled back to the nutrient cells to enhance nitrogen and organic carbon removal. After a minimum of one pass through the nutrient cells flow diverts to the effluent tank. Flow from the effluent tank continues to phosphorous treatment gravel media beds. From the phosphorous beds, flow then deposits into a rapid infiltration bed near the creek. The overall nutrient and solids loading onto the wetland is an unknown variable because inconsistent operation of the pump vacuum system causes fluctuating flows and solids concentrations during the cleaning cycle and because solids accumulation rates vary in each raceway due to different fish sizes and breeding cycles. Gaining an understanding of the loading on the TW will allow further assessment and improvement of the system’s efficacy.