Molecular-based analysis and monitoring of microbial groups in activated sludge to advance the knowledge of biological processes in wastewater treatment

Wastewater treatment has often depended on the activated sludge process to remove chemical or biochemical oxygen demand, nitrogen, and/or phosphorus from influent wastes. Treatment efficiency is dependent on microorganisms that are responsible for the oxidation of different substrates in these waters. Currently, biomass estimations at the full-scale level are based on suspended solids concentrations of the mixed liquor in the activated sludge process. This research was conducted under the hypothesis that the substitution of biomass represented as suspended solids for microbial quantities enumerated using molecular methodologies will advance the knowledge of biological processes in wastewater treatment. The primary objective was to determine relationships between bacterial abundance and physicochemical parameters that improve the treatment efficiency of activated sludge. DNA amplification technologies allow direct quantification of bacteria, which is the basis for population assessment in this research.;Data collection consisted of physicochemical and biological analysis of activated sludge in a full-scale wastewater treatment plant. A number of treatment quality parameters were related to the abundance of total bacteria, ammonia oxidizing bacteria (AOB), and nitrite oxidizing bacteria (NOB) in a partially nitrifying wastewater treatment plant. This research has identified temperature and dissolved oxygen as key factors in the mechanisms for substrate competition between bacterial groups and demonstrated the improved microbial characterization of activate sludge is beneficial to wastewater treatment operations, especially under oxygen limited conditions. Furthermore, the removal of biochemical oxygen demand was highly influenced by the major oxygen consumers in the activated sludge, namely heterotrophic bacteria and AOB. The refinement of existing protocols, especially in the calculation of microbial kinetic parameters using specific biomass instead of a suspended solids estimate, is novel.;This research has improved the understanding of the complex relationships between different microbial groups within activated sludge. AOB were negatively correlated with biochemical oxygen demand, therefore treatment quality can be optimized by monitoring these organisms. Substitution of suspended solids for AOB biomass resulted in accurate calculations of nitrifying kinetics under oxygen limited conditions and can be obtained more rapidly than conventional methods. Furthermore, insights into the interrelationships within NOB have been gained for substrate competition and variations in both environmental and plant operating parameters. Nitrospira was determined to be the predominant NOB and was more efficient than Nitrobacter in a partially nitrifying environment. Ecophysiological factors were reaffirmed as the major source of population influence between total, ammonia oxidizing, and nitrite oxidizing bacteria in a full-scale wastewater treatment plant. Quantitative analysis of these populations elucidated operational adjustments that can be used to modify cell abundance and impact treatment efficiency.