Groundwater water treatment for iron and manganese reduction and fish rearing studies applied to the design of the Ruth Burnett Sport Fish Hatchery, Fairbanks, Alaska

Studies at the Fairbanks Experimental Fish Hatchery (FEFH) were conducted to investigate the operational characteristics of media filtration groundwater treatment for iron and manganese reduction, water reuse and recirculation technologies for fish rearing, and conditions of fish gill tissue during rearing. Results were used to aid in the design and planned operation of the Ruth Burnett Sport Fish Hatchery (RBSFH), currently under construction in Fairbanks, Alaska. Under a two-stage filtration scenario, with hydraulic loading rates of 0.39 and 0.43 cm/s for Stages 1 and 2, respectively, manganese dioxide media filtration typically removed dissolved iron from 5 to 6.5 mg/L down to 0.1 mg/L or less, and allowed for suitable fish rearing and health (based on gill condition) in treated groundwater. Poor water quality from filter equipment malfunction or improper operation typically manifested tissue damage (epithelial lifting, hypertrophy, degeneration, and in some cases iron adhesion) observed in fish gills. Design refinements from initial use, including changes in hydraulic loading rates and transition from single-stage to two-stage filtration, were required for long-term use of media filtration and were included in the design of the future hatchery. Dissolved manganese removal from groundwater (from 0.7 to <0.05 mg/L) was also implemented by continuous low-level potassium permanganate addition. Small-scale flow-through, fully recirculating, and partial reuse rearing systems were used to mimic planned future fish production, and resulted in 97% or greater survival and adequate growth (average specific growth rate between 1 and 2%) and health of rainbow trout during most rearing trials.