Denitrification of Drinking Water Using Biofilms Formed by Paracoccus denitrificans and Microbial Adhesion

A pure culture of Paracoccus denitrificans was used to denitrify drinking water in a fixed-biofilm reactor to avoid the release of unidentified and potentially hazardous bacteria or their metabolites. Four types of synthetic biofilm carriers were tested. Adsorption of cells and the formation of a bacterial film on these surfaces correlated with surface hydrophobicity as determined by a phenanthrene adhesion test. Colonization by P. denitrificans cells reached 4.2 × 10⁵ colony-forming units (CFU)/cm ² after 20 days of biofilm formation. To reduce the start-up period, biofilms were formed in enriched medium. Colonization was 1.8 × 10 ⁷ CFU/cm² after 7 days of biofilm formation. The ratio of the cell concentrations in the carrier material and in the water was 1.29 for net carrier. An artificial bacterial biofilm was made by immobilizing cells in calcium alginate gel attached to the surface of carrier. Cell immobilization did not prevent the release or growth of bacterial cells in the water phase and did not increase the denitrification rate. The optimal way of denitrifying drinking water by pure culture of P. denitrificans involved preliminary natural biofilm formation in rich medium.