A novel slow release approach to bioaugment more effectively activated sludge systems

The survival and activity of microbial degradative inoculants in bioreactors is critical to obtain successful biodegradation of non- or slowly degradable pollutants. Achieving this in industrial wastewater reactors is technically challenging. We evaluated a strategy to obtain complete and stable bioaugmentation of activated sludge, used to treat a 3-chloroaniline (3-CA) contaminated wastewater in a lab-scale Semi-Continuous Activated Sludge system. A 3-CA metabolizing bacterium, Comamonas testosteroni strain 12, was mixed with molten agar and encapsulated in open ended silicon tubes. The tubes containing the immobilized bacteria represented about 1% of the volume of the mixed liquor. The bioaugmentation activity of a reactor containing the immobilized cells was compared with a reactor with suspended I2gfp cells. From day 25-30 after inoculation, the reactor with only suspended cells failed to degrade 3-CA completely, due to a decrease in specific metabolic activity. In the reactors with immobilized cells however, 3-CA continued to be removed. A mass balance indicated that ca. 10% of the degradation activity was due to the immobilized cells. Slow release of the growing embedded cells from the agar into the activated sludge medium, resulting in a higher number of active 3-CA degrading 12 cells, was responsible for ca. 90% of the degradation. Our results demonstrate that this simple immobilization procedure was effective to maintain a 3-CA degrading population within the activated sludge community