Experimental study and mathematical modeling of enhanced biological phosphorus removal using glucose as the dominant substrate
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Two parallel sequential batch reactors (SBR) were set up and operated in order to investigate the metabolism of glucose in an enhanced biological phosphorus removal (EBPR) process, and compare the mechanisms of phosphorus removal when using either acetate or glucose as the dominant organic substrate. Initial results indicated that feeding glucose as the dominant substrate caused poor and unstable EBPR performance. After many variations, the operating procedures for the glucose system were modified to longer anaerobic reaction time, higher glucose concentration in the influent, and shorter aerobic reaction time with a limited DO level. It was also found important to control the pH level near neutral during the reaction. The application of these modified procedures successfully established a stable EBPR performance in the glucose system, which proves that short chain fatty acids (SCFAs) are not the only kind of substrates required for a successful EBPR process. Measurements of several important intracellular reserves and other compounds from the SBR experiments also revealed that in the glucose system, glycogen has a higher chance to replace the energy role of polyphosphate during the anaerobic reaction, hereby causing the breakdown of EBPR performance. Compared with the acetate system, it was found that during the anaerobic condition less PO4-P was released into the medium, a lower level of poly-β-hydroxyalkanoate (PHA) was accumulated, and the accumulated PHA was mainly in the form of 3-hydroxyvalerate (3-HV) rather than 3-hydroxybutyrate (3-HB) in the glucose system. Lactate was also found to be released into the medium during the anaerobic condition in the glucose system. Other experimental results indicated that the bacteria could potentially perform denitrification under anoxic conditions in the glucose system. Microorganism identifications indicated similar bacterial compositions with 'Aeromonas hydrophilia' as the predominant species in both EBPR systems. Applying fundamental biochemistry knowledge to the experimental results, a new biochemical model was hypothesized to explain the metabolism of an EBPR system using glucose as the single substrate. Based on this theoretical model, a mathematical model was developed which simulated successfully the dynamics of the key metabolic components in the EBPR system using glucose as the single substrate.