Determination of rate and order of denitrification of nitrified effluent using activated sludge

Civil Engineering Department, Indian Institute of Engineering Science of Technology, Shibpur, Howrah-711 103,

West Bengal, India

E-mail: debabrata@civil.iiests.ac.in

Manuscript received online 03 February 2019, accepted 25 March 2019

Denitrification studies of synthetic nitrified effluent were performed in laboratory scale batch activated sludge process to examine the effect of absence of organic carbon on denitrification. The orders of the reaction under two conditions of organic carbon content were determined and relevant rate constants were evaluated from the experimental data. During the study, maximum nitrate removal of 92% and 54% was achieved in case of denitrification using methanol and without using methanol respectively under a nitrate to biomass concentration ratio of 0.1. Zero order reaction kinetics was observed to be the best fit for all the studies. The maximum specific denitrification rates were observed to be 11.93±5.13 and 9.46±1.56 mg nitrate/g MLSS/h respectively in presence and absence of methanol. The maximum denitrification rate was attained, when methanol was added @ 1.9 times of nitrate concentration under a nitrate to biomass ratio of 0.2. In presence of sufficient biomass in a reactor, limited supply of readily available organic carbon facilitates endogenous metabolism and addition of external carbon may be reduced, thus economizing the process.