Distribution of Nitrosomonas europaea and Paracoccus denitrificans immobilized in tubular polymeric gel for nitrogen removal

Abstract

To improve the cooperative removal of nitrogen by Nitrosomonas europaea and Paracoccus denitrificans, we controlled their distribution in a tubular gel. When ethanol was supplied inside the tubular gel as an electron donor, their distributions overlapped in the external region of the gel. By changing the electron donor from ethanol to gaseous hydrogen, the distribution of P. denitrificans shifted to the inside of the tube and was separated from that of N. europaea. The separation resulted in an increase of the oxidation rate of ammonia by 25%.

FIG. 1

Schematic diagram of a batch system with a tubular gel. Artificial wastewater (200 ml) containing 100 mg of N/liter (as ammonia or nitrate) was treated. The wastewater was agitated by stirring (100 rpm) at 30°C. Hydrogen gas serving as an electron donor for denitrification flowed through the lumen of the tube (360 ml/h).

FIG. 2

Time-dependent changes of the nitrogen concentration in wastewater containing ammonia (A) or nitrate (B) during the first batch experiment. Data are expressed as means ± standard deviations (SD) (n = 4).

FIG. 3

Fluorescence photomicrographs of N. europaea (A and B) and P. denitrificans (C and D) in regions of a tubular gel cut in cross section. Panels A and C show the external surface of the tubular gel, whereas panels B and D show the internal surface. The corresponding areas within the tubular gel are illustrated in the center diagram.

FIG. 4

Distributions of N. europaea and P. denitrificans within a tubular gel. The solid and dotted curves show the relative biomasses of N. europaea and P. denitrificans, respectively. These curves were determined by analysis of the images in Fig. 3A and D.