Achieving Ultra-low Effluent Inorganic Nitrogen and Total Suspended Solids Concentrations Using BAF Technology at Extremely Short HRTs in Cold Climate

The paper presents results from years-long plant operation or the performance testing at three complete nitrogen removal Biological Active Filters (BAFs) plants in the U.S.A. which was conducted to investigate the ability of BAF processes with extremely short hydraulic retention times (HRTs) in cold climates (≤10 °C) to remove ammonia and total nitrogen (TN), the effect of process designs and operations on meeting extremely low effluent TN concentrations, and reliability of performance. The paper also reports the ability of BAFs achieving low effluent TSS concentrations at short HRTs. Last but not least, the paper summarizes the evolving understanding of the possible mass transfer mechanisms across transfer layer and within the biofilm which could lead to achieve ultra-low substrate concentrations in bulk liquid when the mass transfer across the mass transfer layer and within biofilm becomes limiting factor due to low substrate concentrations in bulk liquid.