Investigation of Oxygen half saturation coefficients for nitrification
Open AccessThe major objective of this research was to investigate the oxygen half saturation coefficients for nitrifying autotrophic bacteria in a mixed culture system and in an individual system for Ammonium oxidizing bacteria (AOB) and Nitrite oxidizing bacteria (NOB), respectively. The oxygen half saturation coefficient for mixed system (KO,AUT), the oxygen half saturation coefficient for AOB (KO,AOB)and the oxygen half saturation coefficient for NOB (KO,NOB ) at different mixed liquor suspended solids ( MLSS) concentrations in the temperature range of 13.2 to 23.8 ºC was investigated in this research work. Three different MLSS concentrations in the range of 2000 mg/L, 3000 mg/L and 4000 mg/L were used. It was observed that increasing solids concentration increased Oxygen uptake rate (OUR) and resulted in decreasing KO,AUT, KO,AOB, and KO,NOB. All studies were conducted at Blue Plains Advanced Wastewater Treatment Plant (AWTP). Two different methods; the Declining Dissolved Oxygen (DDO) method and the Batch Constant Dissolved Oxygen (BCDO) method were used to investigate the oxygen half saturation coefficient for nitrifying autotrophs.The KO,AUT was evaluated with ammonium chloride only as a substrate, and ammonium chloride and 3 mg/L sodium nitrite as substrate. It was observed that the addition of sodium nitrite resulted in decreasing oxygen uptake rate (OUR) and in increasing oxygen half saturation constant (KO). The KO,AUT evaluated with ammonium chloride as a substrate was in the range of 0.14 to 0.37 mg/L, while the KO,AUT with ammonium chloride and sodium nitrite as substrate was in the range of 0.20 to 0.42 mg/L. For both conditions, the KO,AUT increased with decreasing temperature and increasing OUR. The higher values of KO,AUT in the second case showed that the presence of nitrite even in small quantity of 3 mg/l, could have a significant effect on KO,AUT. It may have slowed down the AOB's activities, decreased OUR, and resulted in increasing KO,AUT.The KO,AOB was investigated using sodium azide as an inhibitor to inhibit the NOBs from mixed culture system. The KO,AOB was observed in the range of 0.50 to 1.1 mg/L, which increased with increasing temperature and decreasing OUR. Comparatively higher values of KO,AOB was observed in this research which might be one of the effects of using an inhibitor. The 24 µM sodium azide used to inhibit NOBs from mixed system may have also slowed down the AOB activities and resulted in increased KO, AOB. The KO,NOB was determined with sodium nitrite as a substrate for two different situations. First, it was determined by aerating the mixed liquor sample to consume all ammonium- nitrogen , and in the second situation; Allylthiourea (ATU) was used to inhibit AOBs from the mixed culture system. It was observed that ATU resulted in decreasing OUR and increasing KO slightly. In the first case, the KO, NOB ranged between 0.09 to 0.21 mg/L, while in the second case, using ATU as inhibitor, the KO,NOB ranged from 0.14 to 0.26 mg/L. The measured KO,NOB increased with decreasing temperature and decreasing OUR as well. This investigation showed that 12 mg/L ATU used to inhibit AOBs from mixed culture system, had very little effect on OUR and KO,NOB, indicating negligible effect on NOBs. In the BCDO method, the KO, AOB and the KO, NOB were evaluated. The KO found for both AOB and NOB were smaller than KO found by DDO method. The KO,AOB and KO,NOB determined by BCDO method were very close to each other. The range of KO,AOB was between 0.08 to 0.11 mg/L, whereas KO,NOB was between 0.09 to 0.13 mg/L.
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