Experimental analysis and modeling of denitrification using electrocoagulation process

Abstract

Electrocoagulation (EC) has been studied to assess its applicability as a denitrification process for drinking water. The objective was to investigate the mechanisms of nitrate removal. Electrolysis has been driven in the discontinuous mode with aluminum electrodes, using a synthetic water representative of drinking water. The respective effects of mixing, initial nitrate concentration, current and initial pH have also been analyzed. Experimental results have shown that EC removes effectively the nitrate anions, following first-order kinetics. The rate of denitrification is proportional to current. The removal of nitrate anions results primarily from their electroreduction into ammonium, but total nitrogen decreases simultaneously in water and follows zero-order kinetics. Nitrogen mass balance has shown that the formation of N2 gas is negligible and that the secondary depollution mechanism is adsorption onto the flocs. Adsorption experiments on preformed flocs highlight a preferential adsorption of ammonium. A numerical model able to simulate nitrate removal has been established. The analysis of operating costs has shown, however, that EC is an expensive method, except for waters exhibiting very high nitrate contents. Consequently, EC should be preferentially used as a pretreatment step for biological denitrification when implemented to eliminate simultaneously other types of pollution.