Effect of Flow Rate Increase on the Performance of a Pilot-Scale Biological Nutrient Removal Reactor

Abstract

Nutrient removal in two identical pilot-scale reactors is assessed at influent flow rates of 3, 45, and 6 L/min. The bacteria community structure of nitrifiers and denitrifiers and the protein:polysaccharide ratio (PN/PS) in extracellular polymeric substances (EPS) are monitored at each flow rate. Except for the chemical oxygen demand (COD), the reactor performance in terms of ammonia and phosphorous removal begins to deteriorate at the 45 L/min influent flow rate. Nitrobacter are more dominant than are nitrite-oxidizing bacteria (NOB). The PN/PS ratio in sludge EPS significantly decreases as the solids retention time (SRT) decreases from 9.3 to 2.2 days. The PN/PS ratio temporarily increases in response to an increase in flow rate before normalizing to a steadier value.