EVALUATION OF AUTOTROPHIC DENITRIFICATION AND HETEROTROPHIC NITRIFICATION IN SIMULTANEOUS BIOLOGICAL NUTRIENT REMOVAL SYSTEMS

Simultaneous biological nutrient removal (SBNR) is the occurrence of significant biological nutrient removal in biological wastewater treatment systems where defined anaerobic and anoxic zones do not exist. There is growing evidence that significant SBNR can occur in many systems, including those already configured for BNR. SBNR offers several potential advantages, but they cannot be fully realized until the mechanisms responsible for SBNR are better understood. Consequently, a research program has been initiated. The basic hypothesis of this research program is that three mechanisms might be responsible for SBNR: reactor macro-environment, floc micro-environment, and novel microorganisms.The research reported in this paper is focused on evaluation of the importance of novel microorganisms for nitrogen removal. A procedure was been developed as a screening tool to determine the relative significance of the activities of microorganisms capable of autotrophic denitrification and heterotrophic nitrification-aerobic denitrification in biological nutrient removal systems. Previously the nutrient removal capabilities of seven full-scale closed loop bioreactors known as Orbal™ oxidation ditches were evaluated. Data abd microbiological observations suggested that SBNR occurs in these systems(Daigger and Littleton, 2000). Three of the plants studied in the previous research were studied in this research. The results indicated that novel microorganisms were not substantial contributors to SBNR in the plants studied. They also demonstrated that the developed procedures are readily applicable to determine the activities of novel nitrogen removing microorganisms in systems accomplishing SBNR.