N. Bernet ( ) · F. Habouzit · R. Moletta Institut National de la Recherche Agronomique, Laboratoire de Biotechnologie de l’Environnement, Avenue des e´tangs, 11100 Narbonne, France. Fax: (33) 68 42 51 60 e-mail: bernet@ensam.inra.fr Appl Microbiol Biotechnol (1996) 46:92—97  Springer-Verlag 1996 ORIGINAL PAPER N. Bernet · F. Habouzit · R. Moletta Use of an industrial effluent as a carbon source for denitrification of a high-strength wastewater Received: 26 October 1995/Received revision: 15 February 1996/Accepted: 20 February 1996 Abstract Denitrification of a high-strength synthetic wastewater (150 g NO  l) was carried out using a wine distillery effluent as an example of an industrial carbon source (22.7 g chemical oxygen demand l). Two configurations were tested: one consisted of an acidogenesis reactor followed by a denitrifying reactor and the other was a single reactor directly fed with the raw effluents. In both cases, denitrification was achieved at a nitrate load of 9.54 g NO  l day (2.19 g N as NO  l day) with good specific reduc- tion rates: 32.6 mg and 35.2 mg N as NO  g volatile suspended solids h, calculated on a single day, for the two-step and the one-step process respectively. Dis- similatory nitrate reduction to ammonium did not occur, even in the one-step process. Introduction Biological denitrification is a convenient way to re- move nitrate from wastewaters. Nitrates are generally reduced to nitrogen gas by heterotrophic bacteria that need an organic carbon source as an electron donor for their respiration (Payne 1973). When the nitrate-con- taining wastewater does not comprise any available organic carbon, it is necessary to add an external carbon source to the effluent in order to achieve denit- rification. The carbon sources commonly used for de- nitrification of waters are methanol, ethanol or acetic acid. In the case of high-strength effluents, such as uranium refinery wastewaters containing up to 150 g NO  l, the use of these chemicals represents a criti- cal cost in the process. Indeed, according to the stoichiometry, denitrification of 1 g N as NO  (N- NO  ) needs 2.85 g chemical oxygen demand (COD); that is, almost 100 g COD for 1 l of a 150-g NO  l wastewater. The use of industrial carbon sources for denitrification has been reported previously (McCarty et al. 1969; Monteith et al. 1980; Skrinde and Bhagat 1982). The nature of the carbon source determines the route of nitrate reduction. Indeed, competition between denitrification and dissimilatory nitrate reduction to ammonium in media with low dissolved oxygen con- centrations seems to be largely controlled by the nature of the electron donor (Tiedje et al. 1982; Akunna et al. 1993). Therefore, the use of an industrial organic source as an electron donor for denitrification will have to be tested in order to prevent nitrate reduction to ammo- nia. Volatile fatty acids are known to be readily usable as carbon sources by the denitrifying bacteria (Gerber et al. 1987; Paul et al. 1989; Akunna et al. 1993; Fass et al. 1994; Eilersen et al. 1995). These volatile fatty acids can be produced from any effluent or solid waste containing organic matter, during the first steps of anaerobic digestion: hydrolysis and acidogenesis. In this work, wine distillery effluents were used as a carbon source for denitrification, either after a sepa- rate acidogenesis step to produce volatile fatty acids or in a single-step configuration at the risk of favouring nitrate reduction to ammonia. Indeed, in this last con- figuration the nature of the carbon compounds, such as glycerol, and the presence of fermenting bacteria could favour nitrate reduction to ammonia (Cole 1978; Tiedje 1988; Pohland 1992; Akunna et al. 1993). Materials and methods Experimental apparatus Figure 1 shows the two configurations studied. In both cases, bench-scale continuous-flow stirred reactors were used. Water