Bioaugmentation of a structural extracellular polymeric substances (EPS) producer to improve activated sludge bioflocculation: lessons learned

Abstract

Structural extracellular polymeric substances (EPS) contribute to the bioflocculation performance of activated sludge systems. This research investigates the potential of bioaugmentation of a structural EPS producer, Azoarcus communis, as a bioflocculation improvement or remediation approach. An antibiotic-resistant and fluorescent protein-producing mutant was constructed to monitor the survival, persistence, and location of the augmented strain in the membrane bioreactor. Preliminary batch tests against a kaolin clay model system and deflocculated sludge revealed the flocculation potential of this strain. Morphological image analysis and fluorescence microscopy suggest that most of the bacteria augmented in suspension were initially attached to the sludge flocs with, however, only a limited fraction getting incorporated within the activated sludge floc biomass. This limited bioaugmentation prevented assessing its impact on bioflocculation and might be explained by metazoan and protozoan grazing, together with competition with indigenous organisms and sub-optimal growth conditions in the reactor for the engineered strain. HIGHLIGHTS The structural EPS producer Azoarcus is bioaugmented to enhance sludge bioflocculation.; Augmentation with an antibiotic-resistant and fluorescent mutant strain ensures proper enumeration and localization.; Azoarcus initially attached to sludge flocs but long-term persistence was limited.; An MBR setup avoids initial washout but grazing by metazoa and protozoa remains a problem.;

Keywords

• amyloid adhesins
• biological wastewater treatment
• flocculation activity
• fluorescent protein