Uptake Rate of Ammonia-nitrogen With SterileUlva sp. for Water Quality Control of Intensive Shrimp Culture Ponds in Developing Countries

Ammonia-nitrogen uptake by seaweed was modeled based on the concept of ammonia-nitrogen permeation through cell membrane, and the derived model of uptake rate was experimentally verified. In this study, sterile Ulva sp. was employed as seaweed to treat model culture solution, and the distribution equilibrium of the ammonia-nitrogen between the culture solution and cell inside was measured to obtain the equilibrium. For this measurement, the seaweed was pretreated before the uptake runs to inhibit the assimilation by methionine sulfoximine for removal of the assimilation effects on the uptake rate. The parameters of the distribution equilibrium and permeation rate of ammonia-nitrogen were measured. The pretreated seaweed could uptake ammonia-nitrogen and the ammonia-nitrogen permeated through the cell membrane from the culture solution into the cell according to the concentration gradient. The seaweed saturated with ammonia-nitrogen was immersed in the culture solution without ammonia-nitrogen and it could excrete ammonia-nitrogen once taken in. In both cases of the uptake and excretion, the systems attained equilibrium after around 6 hours. The ammonia-nitrogen concentration in the cell increased with the concentration in the culture solution at equilibrium. The flux of ammonia-nitrogen was almost proportional to the concentration difference, defined as that between the ammonia-nitrogen concentration in the cell and the hypothetical concentration of ammonia-nitrogen in the cell which is in equilibrium with the culture solution. The overall permeation coefficient was measured as 9.1 · 10 m h for both cases of uptake and excretion, and this relationship was valid when the concentration difference was large enough relative to the flux.