A Gram-negative-staining, short-rod-shaped, floc-forming bacterium, designated strain RB3-7(T), was isolated from a laboratory-scale activated sludge system treating coke plant effluent. Comparative analysis of the 16S rRNA gene sequence demonstrated that the novel isolate was distantly related (≤ 95.8 % similarity) to Ottowia thiooxydans K11(T) within the family Comamonadaceae. Strain RB3-7(T) was catalase- and oxidase-positive and non-motile. The predominant fatty acids were C₁₆:₀, cyclo C₁₇:₀, C₁₈:₁ω7c and C₁₆:₁ω7c, and the major respiratory quinone was Q-8. The G+C content of the genomic DNA of strain RB3-7(T) was 68.5 mol%. On the basis of phenotypic, chemotaxonomic and molecular data, strain RB3-7(T) is considered to represent a novel species of the genus Ottowia, for which the name Ottowia pentelensis sp. nov. is proposed. The type strain is RB3-7(T) ( = DSM 21699(T) = NCAIM B 02336(T)).