Denitrification under high nitrate concentration and alternating anoxic conditions

Denitrification under high nitrate concentration was studied in a fed-batch mode. Methanol, sodium acetate and effluent from anaerobic digesters (AD) were compared as the carbon sources. An alternating oxy-anoxy regime (10 mi n aeration over a period of 110 min) seems to promote the establishment of denitrifying bio-flocks of good settling characteristics. The bio-flocks pr oduced in an anoxic reactor were of inferior settling characteristics. Bio- flocks at concentrations of 4 to 5 g VSS/l denitrify efficiently on all thr ee carbon sources tested. A maximum nitrate removal rate was found to be 0. 486 g NO3--N/(g VSS day). Nitrite accumulated initially but its concentrati on decreased with time and eventually reached zero when acetate or AD efflu ent were used as the carbon source. (C) 1999 Elsevier Science Ltd. All righ ts reserved.