High-rate seawater denitrification utilizing a macro-porous cellulose carrier

Abstract

Continuous denitrification experiments were undertaken using marine denitrifying bacteria immobilized in a macro-porous cellulose carrier. The denitrifying capacity of this immobilized system was examined using an ejector-type bioreactor at pH 8.0, 30°C, under anaerobic conditions. In addition, the immobilized denitrifying bacteria were isolated and characterized. The results showed that complete denitrification will not occur unless (i) a phosphorus (g) per NO 3-N (g) ratio ( P NO 3-N ) of 0.029, (ii) 0.01% trace element solution (containing Fe, Mn, Mo, etc.) at 280 g/m 3 NO 3-N concentration and (iii) a methanol concentration at 30% more than the theoretical carbon concentration requirement are maintained. Copper enhanced nitrite reduction at an influent Cu (g) per influent NO 3-N (g) ratio ( Cu NO 3-N ) of 0.002. Based on these results, a feeding medium was formulated which not only reduced costs but, more importanly, allowed the maximum NO 3-N loading rate of 24.8 kg-N/m 3-carrier/d (at a NO 3-N influent concentration and hydraulic retention time of 500 g/m 3 and 5 h, respectively). This value is comparable to that of freshwater in which a macro-porous cellulose carrier was also employed, indicating the insensitivity of the immobilized denitrifying bacteria to salinity. The morphological and physiological characterisitics of the immobilized denitrifying bacteria showed similarities to Hyphomicrobium spp.