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Development of microbial fatty and analysis as a monitoring tool for biological wastewater treatment systems Son, Kwang Soo

Abstract

The development of culture-independent methods for the identification of microbial community has opened a new era of study into real microbial populations and their dynamics. Although many attempts have been made to link such dynamics to system performance, few have been successful. In this research, a microbial fatty acid analysis technique was developed and evaluated for the detection of changes in microbial community populations associated with system performance. For the evaluation, three phases of experiments were executed. In Chapter 2, operating parameters such as pH, organic loading and chlorine addition, were varied in two identical laboratory-scale conventional activated sludge systems. Daily and cumulative similarity indices based on microbial fatty acid analysis were used to express the stability of microbial community populations in the systems. It was found that microbial compositions changed daily even under constant operating conditions and that the rate of change increased under dynamic operating conditions. The analyses of microbial fatty acids (MFA) also conveyed additional information: i f they are routinely executed as a monitoring tool for biological wastewater treatment systems, MFA analyses could be used for the calculation of biomass concentrations in a wastewater treatment system. The total fatty acid concentrations were estimated to be about 6.1% of the biomass concentration, measured as mixed liquor volatile suspended solids concentrations in this research. In Chapter 3, the new monitoring technique developed in Chapter 2, was applied to bioreactors with real municipal wastewater. The experiments demonstrated that the MFA analysis technique was also applicable to the reactors fed with real municipal wastewater. From the results, it was found that changes in operating factors such as pH, DO, chlorine addition impacted more significantly on the microbial community population and system performance in real municipal wastewater and the monitoring method developed was also applicable to a system subject to more dynamic operating conditions, suggesting that that this technique could be used for pilot-scale or full-scale wastewater treatment monitoring. The MFA monitoring technique was also evaluated using a lab-scale simplified University of Cape Town (UCT) reactor, to determine whether the technique was applicable for detecting a trend in a microbial population of an EBPR process (phosphorus-accumulating organism (PAO) dominant microbial population) toward a glycogen-accumulating organism (GAO) dominant microbial community structure. In order to convert a PAO-dominant microbial population to a GAO-dominant structure, several methods were tried: namely, low phosphate to carbon ratio (P/C) feed, high-temperature operating conditions (25°C and 30°C), and a mixed glucose and acetate feed. Among the three trials, only the glucose and acetate feed effectively converted the EBPR system to a GAO-dominant structure. The MFA technique clearly showed the transition from a PAO-dominant microbial population to a GAO-dominant one, through an increase in shift rates of microbial community structure. Similarity indices (daily and cumulative) based on microbial fatty acid analysis were used to estimate the shift rates of microbial community structures in the system. The experimental results demonstrated that the new monitoring technique could be a useful tool for preventing EBPR deterioration by monitoring the change in microbial population from PAO dominance to GAO dominance in EBPR. These experimental results showed that the MFA analysis technique with a simple similarity index calculation could be a useful tool to monitor changes in microbial community populations, which might be applied to advanced biological wastewater treatment system design and operation.

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