Nitrification Kinetics and Simultaneous Removal of Biomass and Phosphorus in Rotating Biological Contactors

Abstract

This paper presents some important aspects of the Rotating Biological Contactor. (1) Steady-state biofilm kinetics and its application to the design of an RBC aiming at nitrification : Using the proposed kinetics in which the flux of rate-limiting substrate is expressed as a function of the bulk substrate concentration, liquid boundary layer thickness, liquid film thickness, and molecular diffusion coefficient and intrinsic reaction rate of the substrate, the relationship between the bulk ammonia concentration and ammonia flux was predicted at various sizes and rotating speeds of disk. Experimental verification of the predicted results was also made. A new disk media, i.e., reticulated media with surface protrusions,was proposed to promote the external diffusion of soluble substrates to the biofilm, and to reduce the disk weight. (2) Simultaneous removal of the detached biomass and precipitated phosphorous in a two-storey RBC:A two-storey RBC, whose upper and lower parts function as the RBC trough and storage space of the detached biomass, was operated in a four-staged unit. Experimental investigation showed that the phosphorus precipitated by aluminium was adsorbed to the biofilm, and settled into the lower part as the detached biomass. The removal efficiency of the detached biomass was very high resulting in an effluent suspended solids concentration of about 10 ppm.

Control of heterotrophic layer formation on nitrifying biofilms in a biofilm airlift suspension reactor

“…Biofilm models predict that in general, fast growing organisms are located at the outside, while the slow growing organisms can be found at the inside of biofilms (Reichert, 1994;Wanner and Rei-chert, 1996). This phenomenon has been experimentally verified in aerobic biofilms: fast growing heterotrophic organisms are located at the outside, whereas slower growing nitrifying organisms can be found at the inside (Okabe et al, 1995;Okabe et al, 1996;Tijhuis et al, 1996;Watanabe et al, 1990). A similar structural organization has been observed in anaerobic, methanogenic granules and sulfate reducing granules as well (MacLeod et al, 1990;Ramos et al, 1994;van Houten et al, 1995).…”