Investigation of the flow dynamics of a Vertical Bioreactor using the Residence Time Distribution

In the wastewater industry, conventional activated sludge processes are still the dominant technology. This process relies on large concrete tanks with poor mixing profiles, due to their rectangular cross-section.

Hitherto, Water Engineering has failed to see the relevance of vertical bioreactors. The STAR (Simultaneous Treatment of Ammonia and Phosphorous Removal) is a vertical bioreactor with three stages for the elimination of biological nutrient removal in wastewater. The STAR vertical bioreactor is capable of delivering high quality effluent within a significantly reduced footprint.

In this study, the mixing and fluid flow through the reactor is investigated using residence time distribution tests. A single pulse of conductive tracer is introduced into the first stage of the reactor. Conductivity sensors were used to measure tracer concentration at the exit of each stage. This conductive tracer represents a non-reactive component introduced into the process flow. Data generated from this experiment found evidence of a bypass rate of 7.5% of the feed rate. The data were compared with two theoretical models: The ideal Continuous Stirred Tank Reactor and the Generalized Nth CSTR in series model and found to approximate the residence time distribution.