Hatchery to Achieve Low Phosphorous Effluent Limits

Owned and operated by the New Hampshire Fish and Game Department, the Powder Mill Fish Hatchery is the largest of six hatcheries in the state. As a result of cyanobacteria blooms in downstream impoundments of the Merrymeeting River, Powder Mill’s 2020 National Pollutant Discharge Elimination System permit imposed a lowest-in-the-nation monthly average total phosphorus effluent concentration limit of 12 µg/L. This requirement called for innovative approaches to treatment and facility upgrades.

We are leading these efforts using a highly technical team comprised of hatchery, wastewater and drinking water experts to assist in:

• Characterization of source water and effluent with respect to TP and phosphorus speciation
• Review of potential treatment alternatives and technology most suitable for a pilot study
• Design of bench testing and pilot study objectives, procedures and required analytical analysis 
• On-site operation of the chosen pilot units
• Interpretation of pilot results and determination of technological achievability

Due to the anticipated high cost of effluent treatment to reach the required permit limits, combined with the fact that this hatchery supplies roughly 30% of the state’s Brook, Rainbow and Brown trout, we are also performing condition assessment and evaluation of modernization alternatives for all six hatcheries in the state. Combined with a Statewide Stocking and Production Plan, our team will implement the most cost-effective approach to meet sport fish demands and TP effluent limits through a combination of expansions at other hatcheries, as well as implementation of modernized fish rearing facilities and effluent treatment at Powder Mill.

The pilot units that were selected for this bench-scale study included membrane ultrafiltration, ion exchange and adsorption. To our knowledge, these technologies have never been implemented to treat hatchery effluent. Cloth Media Disk Filter technology has also been tested on a bench-scale to determine if adequate filtration can be achieved in lieu of membranes.  

While the study is currently ongoing, modernization of the hatchery from raceways to circular tanks may allow the facility to roughly halve their water usage, opening the potential to explore a dilution factor to allowable effluent concentration limits. Circular tanks also allow for a continuous collection and removal of solids, which will reduce the amount of phosphorus released to the effluent. These improvements to fish rearing will dramatically lower the cost of a new effluent treatment system.