NITRIFICATION PERFORMANCE OF MARINE NITRIFIERS IMMOBILIZED IN POLYESTER-POROUS AND MACRO-POROUS CELLULOSE CARRIERS

To determine the best type of carrier for marine nitrification, the ma cro-porous cellulose and polyester carriers were compared in continuou s nitrification experiments using a 15.7 dm(3) airlift-type bioreactor . Employing a feeding medium containing only ammonium chloride (as sub strate) and sodium bicarbonate (as carbon source), ammonium loading ra tes of 2.6 and 0.65 kg-N/m(3)-carrier/d were obtained for polyester an d cellulose carriers, respectively. The addition of a trace element so lution (TE) resulted in a further increase of ammonium loading rates t o 5.20 and 1.62 kg-N/m(3)-carrier/d, for the polyester and cellulose c arriers, respectively. Nitrite oxidation became a rate-limiting step u nless a minimum influent of inorganic carbon (g)/influent NH4-N (g) ra tios of 1.2 and 5.0, and 0.02% TE at 50 and 40 g/m(3) NH4-N concentrat ion were maintained for the polyester and cellulose carriers, respecti vely. These differences in nitrification capacity and nutrient require ments are due to differences in the physico-chemical properties of the carriers. Measurement of the effectiveness factor showed that in cell ulose carriers, the diffusion of oxygen was limited. In addition, prec ipitation, which is common with seawater, occurred inside the cellulos e carriers after approximately five months of continuous experimental runs. The precipitates further limited oxygen and other nutrients' tra nsfer, and also caused inefficient circulation of the heavier cellulos e carriers. Morphological observations show that the ammonia and nitri te oxidizers are Nitrosomonas marina and Nitrospina sp., respectively.