High nitrate removal from synthetic wastewater with the mixed bacterial culture Lucija Foglar a, * , Felicita Bris ˇki a , Laszlo Sipos b , Marija Vukovic ´ a a Division of Industrial Ecology, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulic ´ev trg 19, HR-10000 Zagreb, Croatia b Department of General and Inorganic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulic ´ev trg 19, HR-10000 Zagreb, Croatia Received in revised form 27 May 2004; accepted 2 September 2004 Abstract The applicability of the mixed bacterial culture, originated from two-stage anaerobic–aerobic industrial yeasts production waste- water treatment plant for high rate denitrification processes was investigated. After acclimation to nitrate, the dominant strains were Pseudomonas and Paracoccus sp. Complete denitrification with low accumulation of nitrite-N (0.1mg/l) was found in synthetic wastewater, obeying a zero-order reaction with respect to nitrate and a first-order reaction with respect to biomass concentration. Denitrification was then monitored in the continuous-flow stirred reactor at different hydraulic retention time, HRT (62–28h) in order to achieve the optimal HRT. Nitrate was completely removed during following 45days, at 25 °C with HRT, which we reduced from 62 to 28h. Yet still, at 28h HRT, high average specific denitrification rate of 142mg NO  3 -N=g VSS h was obtained. Ó 2004 Published by Elsevier Ltd. Keywords: Continuous flow denitrifying reactor; Denitrification; Kinetic model; Mixed bacterial culture; Nitrite accumulation 1. Introduction Nitrogen-containing compounds released into envi- ronment can create serious problems, such as eutrophi- cation of rivers, deterioration of water quality and potential hazard to human health, because nitrate in the gastrointestinal tract can be reduced to nitrite ions. In addition, nitrate and nitrite have the potential to form N-nitrous compounds, which are potent carcino- gens (Forman, 1991). Biological removal of nitrate is widely used in the treatment of domestic and complex industrial wastewaters (Delanghe et al., 1994; Lemmer et al., 1997; Sozen and Orhon, 1999; Kesseru ¨ et al., 2003; Dong and Tollner, 2003). Biological denitrifica- tion enables transformation of oxidized nitrogen com- pounds by a wide spectrum of heterotrophic bacteria into harmless nitrogen gas with the accompanying car- bon removal. Based on its price and availability, metha- nol is most commonly used as additional carbon source for bacterial denitrification (Wang et al., 1995). This process has been well studied, but biological denitrifica- tion of wastewater is usually slow and lasts several days. Thus, a high rate denitrification process is needed. Great efforts were made recently to slightly increase nitrate re- moval rate. In that respect, the adapted mixed bacterial cultures from various industrial wastewater treatment plants proved to be very useful. According to literature, 0960-8524/$ - see front matter Ó 2004 Published by Elsevier Ltd. doi:10.1016/j.biortech.2004.09.001 * Corresponding author. Tel.: +385 1 4597 270; fax: +385 1 4597 260. E-mail address: lfoglar@pierre.fkit.hr (L. Foglar). Bioresource Technology xxx (2004) xxx–xxx ARTICLE IN PRESS