Effects of the activity of heterotrophs on nitrification in a suspended-growth reactor

• Published in: Water research (Oxford) 1990, Vol.24 (3), p.289-296
• Main Authors: Hanaki, Keisuke, Wantawin, Chalermraj, Ohgaki, Shinichiro
• Format: Article
• Language: English
• Subjects: ammonia; ammonia assimilation; ammonia oxidizers; Biological and medical sciences; Biological treatment of waters; Biotechnology; Environment and pollution; Fundamental and applied biological sciences. Psychology; heterotrophs; Industrial applications and implications. Economical aspects; inhibition; kinetics; nitrification; nitrite oxidizers; nitrogen removal; organic loading
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/0043-1354(90)90003-O

Ammonia (80 mg l −1 as N), with various concentrations of glucose, was continuously fed to laboratory scale reactors at 25°C to examine the effect of the activity of heterotrophs on nitrification. The assimilation of ammonia by heterotrophs happened in preference to nitrification, and reduced the available ammonia for nitrification. Glucose addition of 160, 500 or 1000 mg l −1 (as COD) decreased ammonia removal and ammonia oxidation to nitrite, and elevated the effluent ammonia concentration. The results clearly indicate that the addition of organic matter, which provokes the growth of heterotrophs, inhibits ammonia oxidation. Determination of the biomass index with batch experiments enabled estimation of kinetic constants for ammonia oxidizers ( μ m = 0.66 d −1, K = 1.0 mg l −1) and for nitrite oxidizers ( μ m = 0.58 d −1, K = 0.35 mg l −1) when no glucose was added. The addition of glucose to the reactor resulted in a high K (7.2 mg l −1 when 1000 mg l −1 of COD was added) whereas μ m was unchanged in the ammonia oxidation. It is suggested that inhibition takes place by decreasing the affinity between the ammonia oxidizers and ammonia. Experiments using acetate showed that toxic effect by organic matter is unlikely. One hypothesis is that transportation of ammonia from bulk water to the cell of the ammonia oxidizer is hindered by the presence of the crowded cells of the heterotrophs. Nitrite oxidation was not directly affected by organic loading.