Ammonia Production and Removal in Recirculating Refrigerated Lobster (Homarus americanus) Impoundments

Abstract

This project was undertaken to determine the ammonia production by American lobsters (Homarus americanus) in commercial impoundments and to investigate practical ammonia removal methods. Emphasis was placed upon development of engineering design values for full scale operation designs. Major potential problems in operation of the ammonia removal methods of air stripping and Chondrus crispus nitrogen uptake were evaluated. Lobster ammonia production, for water temperatures from 5°C to 15°C and at lobster storage densities of 35 - 70 g/L, was established and approximated by two time dependent equations. They are: 0.16T o o Constant rate= 7.4e (+10% for 5 C-15 C); Initial rate= 25.0eO.llT (~20% for s 0 c-1s 0 c). The time until constant rate varied from three days at 15°C to sixteen days at 5°C. Air stripping for desorption was found to be ineffective as a commercial method for ammonia removal from impoundment waters. The use of macroalgae (Chondrus crispus) proved to be very successful as a remover of ammonia and nitrates from the culture waters. A biomass ratio of 7 - 8 1, lobsters to Chondrus crispus, was experimentally determined. This is approximately sixty per cent of the theoretical maximum. PH levels did not increase above pH 8.5 and were always within acceptable limits. The Chondrus crispus removed nitrogen in both ammonium and nitrate forms, therefore, reducing the total nitrogen levels within the recirculating system. The system was shown to be sensitive to major temperature shocks. Filtering was found not to reduce the ammonia buildup during the four week periods of water recycling. Water clarity and reduced fouling were noted with the use of filtering. The use of Chondrus crispus as an ammonia stripper is considered a successful and practical method for commercial lobster impoundment operators to control ammonia and nitrate buildup.