Temperature effects on biodrum nitrification

Abstract Filtration systems are required to maintain recirculated water quality, and are directly related to reliability and profitability in closed-cycle operations. Nitrifying biological filters (biofilters), a necessary component in closed-cycle filtration systems, use nitrifying bacteria to oxidize ammonia to nitrate through a two-step, temperature-related process known as nitrification. Unfortunately, biofilters are often inefficiently incorporated into filtration systems because quantitative design data for aquacultural applications are severely lacking. To assist in future biofilter design, biodrum (a biofilter type) performance was evaluated at controlled air and water temperatures (7°C to 35°C) by measuring influent and effluent ammonia, nitrite and nitrate concentrations. Other variables known to affect nitrification were controlled by delivering a synthetic, inorganic wastewater to two identical bench-scale biodrums in a one-pass arrangement. Flow rate was constant throughout the experimental trials (0·62 liters/min) and pH remained between 7·5 and 8·5. Influent ammonia concentration was maintained between 7·0 and 10·0 mg NH4+N per liter. Biodrum performance was found to be linearly related to temperature in this range (140–400 mg NH4+N oxidized per liter of filter per day, respectively).