Remediation of Flow-Through Trout Raceway Effluent via Aquaponics

Abstract

Production and nutrient removal were assessed for three vegetable crops (kohlrabi, lettuce, and Swiss chard) and two edible flowers (calendula and nasturtium) grown entirely on effluent from a flow-through trout raceway. Soluble nutrient concentrations in the effluent averaged 0.56 and 0.19 mg/L for total nitrogen and soluble reactive phosphate, respectively. Seeds were sown into Styrofoam trays filled with vermiculite and placed directly into the plant growing channels. Lettuce was harvested at 6, 9, and 12 weeks for a total mean harvest biomass of 4.5 kg/m². Kohlrabi and Swiss chard were harvested at 12 weeks, with a mean harvest biomass of 15.4 and 7.5 kg/m², respectively. Harvest biomass of kohlrabi was significantly greater than that of lettuce or Swiss chard. Nasturtium flowers were harvested at 9 and 12 weeks, while calendula did not begin to produce flowers until 12 weeks. There were no significant differences in percent removal of total ammonia nitrogen (TAN), nitrate, or phosphate at 6 weeks. However, at 9 weeks, kohlrabi, Swiss chard, and nasturtium removed significantly more TAN and nitrate than lettuce and calendula. Total ammonia nitrogen removal decreased at 12 weeks while nitrate removal increased for kohlrabi, Swiss chard, and calendula. Phosphate removal was low for all cultivars and may be the result of high phosphate concentrations in the source water. Careful crop selection will be necessary to maximize the benefits of aquaponics as crops varied in growth rates, overall nutrient removal capacity, and timing of nutrient removal.

Received May 17, 2016; accepted July 3, 2016 Published online November 18, 2016

Acknowledgments

This experiment was funded under U.S. Department of Agriculture Special Grant Agreement 2008-34601-19205. The authors would like to thank Tom Vowls for his assistance on this project.