The roles of Rhodococcus ruber in denitrification with quinoline as the electron donor

Denitrification is an important step in domestic wastewater treatment, but providing bioavailable electron donors is an expense. However, some industrial wastewaters contain organic compounds that could be a no-cost or low-cost electron donor, because they otherwise must be treated separately. In this work, quinoline was used as an electron donor to drive denitrification through bioaugmentation with Rhodococcus ruber, which is able to biodegrade quinoline. When quinoline-acclimated biomass (QAB) was used for denitrification, addition of R. ruber accelerated biodegradation of quinoline and its first mono-oxygenation intermediate (2-hydroxyquinoline). Although R. ruber was not directly active in denitrification, its biodegradation of quinoline and 2-hydroxyquinoline supplied products that other bacteria used to respire nitrate. In contrast, glucose-acclimated biomass (GAB) could not achieve effective denitrification with quinoline, whether or not R. ruber was added. Analysis by high-throughout sequencing showed that genera Ignavibacterium, Ferruginibacter, Limnobacter, and Denitrosoma were important during quinoline biodegradation with denitrification by QAB. In summary, bioaugmented R. ruber and endogenous bacterial strains had complementary roles when biodegrading quinoline to enhance denitrification. The significance of this study is to enable the use of industrial wastewater to provide electron donor to drive denitrification.