Sequential nitrification and denitrification in a divided cell attached growth bioelectrochemical reactor

A divided cell bioelectrochemical reactor comprised of two upflow submerged columns packed with Celite biocarrier was operated to generate oxic and anoxic compartments where the nitrified effluent from the first column was denitrified in the second for sequential nitrification-denitrification of a simulated waste-water. The experiments were carried out at current intensities of 0.5 mA/cm(2) and 1.0 mA/cm(2) over six phases. The wastewater pH decreased after contacting the oxic (nitrifying) compartment due to the acid equivalents produced electrolytically and during biological nitrification. The wastewater pH subsequently increased after contacting the anoxic (denitrifying) compartment due to the base equivalents produced electrolytically and the acid equivalents consumed during denitrification. At a current intensity of 0.5 mA/cm(2), up to 56% of the influent nitrogen was removed on average during Phases I to III prior to operating at a higher current density. The nitrogen removal efficiency dropped to 15% at a current density of 1.0 mA/cm2 because of the pH inhibition and excess gases produced in the nitrification column. The reactor system did not recover from the inhibition.