Abstract
The simultaneous removal of carbon and nitrogen of the anaerobically pretreated distillery wastewater with nitrate, nitrite and ammonia addition was investigated in an expanded granule sludge bed (EGSB) reactor inoculated with methanogenic granule sludge. The experiment showed the COD removal efficiency decreased with the nitrogen loading increasing. Moreover, denitrifiers out-compete methanogens for the utilization of organics gradually, and COD removed by methanogenesis decreased to only 20% by measuring the amount of CH4 produced at low C/N ratios of 2, 3 and 4. Nitrate reduction to ammonium didn’t occur whatever the C/N ratio under anaerobic conditions. At high C/N ratios of 10 and 8, little total Kjeldahl nitrogen (TKN) was removed. However, 30%-50% of TKN entering the reactor was removed at lower C/N ratios of 2, 3 and 4 suggesting the removal of ammonium. At a lower C/N ratio of 2, the nitrite and the nitrate accumulation were observed and TKN removal decreased gradually due to their inhibition. The result suggested that the nitrate and ammonium simultaneous removal occurred through a coupling of nitrate reduction to nitrite by denitrification and then nitrite reduction to nitrogen gas by both denitrification and Anammox at a proper C/N ratio in an anaerobic EGSB reactor.
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