A comprehensive five-year plan is proposed for an innovative research project and a complementary educational program. The research is motivated by the large benefits in increased environmental and human health protection and cost savings, which may result from improvements to solids settling processes in biological wastewater treatment systems, and the observation that a fundamental yet potentially critical factor (density) affecting settling has been scarcely studied. Efficient biosolids settling is vital the provision of a clarified effluent and a concentrated solids stream for system recycling and wasting. The gravitational force that drives all settling processes is a function of buoyant density (the difference between liquid and solid densities). It is hypothesized that although biomass buoyant density can vary substantially, and that new, effective strategies can be developed to improve solids separation based on density optimization. This is based on observations that (1) high-density microbial storage product (MSP) concentrations vary in treatment systems, (2) MSP accumulation affects bacterial density, and (3) previous reports indicate systems selecting for MSP-accumulating organisms improve settling independently of filament control. Furthermore, MSPs, density, and settling were correlated as expected in preliminary experiments. Factors such as floc size and filament content clearly affect settling rates, and the current hypothesis suggests that biomass density may be an additional, fundamental, and previously neglected factor that should be considered in the analysis and control of biomass settling. A governing objective of this proposal is to produce and validate a model linking process parameters, density, and settling. This will require determination of the relationships between operational parameters and MSP accumulation (and other factors affecting density), between these factors and density, and between density and settleability.
The broader impacts of this work include increased protection of environmental and human health and costs saving through increased process performance; development of a better understanding MSPs, which are ubiquitous in natural and engineered systems but not always well-understood; improved understanding of biological phosphorus removal processes and aerobic MSP accumulation; increased representation of underrepresented groups in the sciences; improved high school curricula; and development of advanced laboratory and modeling skills in undergraduate and graduate students.
