Study on Characteristics and Effecting Factors of Nitrification in Media-added Activated Sludge Process.

The characteristics and the effecting factors of the nitrification in the media-added activated sludge process (M-AS) were studied using pilot-plants. The hydrophilic gels and sponges were used as the adhesion media for microorganisms. The nitrification rate of the hydrophilic gels showed 60-109 g-N·m-3-media·h-1, and the concentration of the attached microorganisms on the media were 1,500-6,900 mg·l-1 as MLSS in the oxic reactor. Although the MLSS of the sponges was approximately equivalent to that of the hydrophilic gels, the nitrification rates of the sponges were lower than those of the hydrophilic gels because the principal place for the growth of the nitrifier was considered as the outer surface of the sponges. The media nitrification rate increased in proportion to the increase of the adhesion area of the added media. The DO dependency of the media nitrification was higher than that of the suspended activated sludge. The specific nitrification rate of the attached microorganisms showed 4-5 times higher than that of the suspended activated sludge. The authors considered that this was caused by the low BOD/NH3-N ratio of the oxic reactor influent.