NITRIFICATION KINETICS OF A TRICKLING BIO-FILTER WITH STYROFOAM BEAD MEDIA IN SEAWATER AT DIFFERENT WATER TEMPERATURES

Jeonghwan Park*1, Pyong-Kih Kim2, and Seongdeok Park2
 
 *1Department of Aquaculture and Fisheries, University of Arkansas at Pine Bluff,
Pine Bluff, AR, USA 71601, parkje@uapb.edu ; 2Department of Marine Bio-Science, Gangwon Provincial College, Gangneung, 210-804, South Korea

Since recirculating aquaculture systems (RAS) reuse culture water with a series of water treatment devices, maintaining appropriate water conditions is critical to successful operation. Nitrogen compounds such as ammonia and nitrite are major concerns in RASs and converted to nitrate by nitrification, which is a two-step microbial oxidation process. Nitrification rate is determined by the enzyme activity of nitrification bacteria. Major influence factors to the activity are dissolved oxygen (DO) and substrate concentrations. When DO requirements are met, substrate concentrations are the next limiting factor to nitrification rate. Nitrification rate (R, g․day-1) can be expressed with the Michaelis-Menton equation derived from rates of chemical reactions catalyzed by enzymes, incorporating the substrate concentration (S, g․m-3), the maximum conversion rate (Rm, g․day-1), and the half saturation constant (Ks, g․m-3) as follows: R = Rm [S/(Ks+S)]. The effect of water temperature on nitrification is also critical for bio-filter design and operation, since water temperature primarily affects the enzyme activity of nitrification bacteria. The purpose of this study was to evaluate nitrification characteristics of a trickling bio-filter using cost-effective bio-media in simulated marine culture tanks (30 psu) at varying temperatures.

Three experimental systems were installed, consisting of a trickling bio-filter (1.5 m tall x 0.2 m diameter) and a culture tank (1 m x 1 m x 1 m). Bio-media were low density Styrofoam beads (2 mm diameter) and each bio-filter was filled with 10 L of bio-media. Daily turnover rate was set at 24 times. Artificial nutrients were continuously dosed at a rate of 440 mg TAN/m2-day-1 for 11 months (at 25 C) to each tank prior to experiments. Once bio-filters were fully conditioned, nitrification rates were repeatedly measured for 10 days (5 times/day) at each combination of TAN loading rates (55, 110, 220, and 440 mg TAN․m-2 surface area․day-1) and water temperatures (15, 20, and 25 C).

Based on measured data, nitrification kinetics were evaluated using the Michaelis-Menton equation (Table 1).