Performance and kinetic evaluations of a novel bioreactor system in the low-oxygen/low-fluid shear reaction environments
Biotreatment is one of the most cost-effective means to reduce the organic and nutrient contents of liquid waste streams prior to their final discharges to the environment. Despite the fact that numerous bioreactor configurations and system schemes are currently available for a wide variety of environmental applications, it remains a major challenge to design a bioreactor system that is capable of offering effective and integrated functions of biodegradation, biomass-liquid separation, and biomass retention. For many environmental applications, the bioreactors are required to operate under low-substrate concentration conditions in order to meet stringent discharge requirements and as a result, both biodegradation rates and bioreactor biomass holdup are inevitably low. Auxiliary means are often used in conjunction with the bioreactors to rectify the problems. For instance, gravity clarifiers are incorporated as an integral part in the conventional activated sludge systems (suspended-growth systems) to capture and recycle the biomass as well as to produce low-SS (SS: suspended solids) effluent streams. On the other hand, small, fluidized media particles are used in biofluidized bed reactors (attached-growth systems) to form biofilm communities that effectively immobilize and retain the bacterial cells. In many cases, secondary clarifiers are not required to produce low-SS effluent streams. A novel bioreactor system, which combines desired characteristics of both suspended-growth and attached-growth systems, has been developed at the University of Pennsylvania. An upflow bioreactor is utilized to grow and maintain the biomass communities with the desired properties. In-situ, submerged-bubble oxygenation is replaced to eliminate intensive gas effervescence in the bioreactor to create a quiescent hydrodynamic environment that enables effective gravitational separation of bacterial cells from the axial liquid flow. The axial liquid flow, in turn, permits the formation of a biomass matrix, which can be described as continuous, interlocking, mat-like architecture, and loosely-structure with large void spaces. An external oxygenator, which is coupled to the upflow bioreactor, is employed to provide oxygenation and mixing of both feed and bioreactor effluent streams. A fully aerated stream, which is diverted from the oxygenator vessel, is used as the vehicle for the delivery of oxygen, substrates, and nutrients into the biomass matrix to sustain and control the desired biodegradation reactions. The chemoautotrophic biomass matrix performing the autotrophic nitrification and denitrification (AND) reactions and a heterotrophic biomass matrix responsible for the combined carbon and nitrogen (C/N) removal are grown and maintained to test the effectiveness of the bioreactor system. At a specific substrate loading rate, oxygen influx is employed as main experimental variable to control the extents of reactions to be achieved as well as to manipulate the reaction pathways to be maintained. (Abstract shortened by UMI.)
Chemical engineering|Environmental engineering|Sanitation
Nootong, Kasidit, "Performance and kinetic evaluations of a novel bioreactor system in the low-oxygen/low-fluid shear reaction environments" (2006). Dissertations available from ProQuest. AAI3225514.