抄録
Nitrification characteristics of immobilized microorganisms and suspended sludge in a nitrified liquor recycling process were examined through plant operation tests using synthetic and real municipal wastewaters. Influence of factors was evaluated on nitrification performance of a nitrification tank using pellets with immobilized microorganisms, and contributions to overall nitrification of the tank were estimated on pellets and suspended sludge respectively from nitrification activities based on respiration rates. It was confirmed that the nitrification rate of the nitrification tank sensitively depended on the DO concentration in the tank and followed the Monod equation. As the half saturation constant for DO concentration in the equation, a value of around 9mg/l was obtained, which was higher than reported values of 0.5 to 2 mg/l for suspended sludge. The nitrification activity of pellets decreased to a great extent due to limitations by low NH4-N concentrations (Ne) of less than around 0.3 mg/l in the nitrification tank, and shared the contribution ratio to overall nitrification of the tank with suspended sludge almost evenly. While, the nitrification activity of pellets increased significantly to cover nearly 90% of overall nitrification when Ne exceeded 0.3 mg/l at low water temperatures or high nitrogen loading rates. It is concluded from these results that monitoring and control of DO and NH4-N concentrations are important in operating the nitrification tank using pellets.
