Effect of copper sulfate addition on nitrousoxide emission in high speed denitrification process using macro-porous cellulose carrier

Nitrous oxide emission from the immobilized denitrification process was inv estigated under copper-added and copper-free conditions to realize high-spe ed denitriflcation with minimum nitrous oxide emission. Nitrous oxide emiss ion was found to be smaller in culture using immobilized cells acclimatized under copper-added condition. Transient phenomena of nitrous oxide emissio n, nitrate reduction and nitrite accumulation were then investigated in rep eated batch experiments by transferring immobilized cells acclimatized in c opper-free conditions into copper-added medium. Nitrous oxide emission obvi ously decreased, and maximum nitrous oxide concentration of seventh batch c ulture was about 1/40000 of that of first batch culture. Nitrate reduction gradually decreased from second batch to fourth batch culture and it turned to increase from fifth batch culture to seventh batch culture. At seventh batch culture, nitrate reduction rate was restored up to 80% of the initial speed. This repeated batch experiment clarified that nitrous oxide emissio n was repressed by copper sulfate addition. The effect of pH and temperatur e on nitrous oxide emission were also investigated in a continuous denitrif ication experiment under copper added conditions. Nitrous oxide emission wa s increased by lowering pH and lowering temperature. At optimum operating c ondition (pH8.0, 30 degreesC), nitrogen removal efficiency of 99.9%, nitrou s-oxide concentration in the emitted gas of 3.1ppm(v/v) and conversion rati o to nitrous oxide of 0.000316% were obtained when 280mg-Nl(-1) nitrate con taining medium was treated at 6 hours of hydraulic retention time.