In Activated sludge process we have both heterotroph and autotroph.
It is for sure possible. In municipal activated sludge systems most systems today are one-sludge types which can both nitrify and denitrify. Many sludge bacteria which can reduce nitrate can also reduce oxygen depending on availability.
Thanks..@Henrik Andersen
In denitrification NO2- act as electron accepter but if you put denitrifying bacteria in one sludge system then it can also use DO as electron accepter . So then how denitrifying bacteria will choose whether to take DO or NO2- .
if you have any journal related to this query please send it.
The denitrifying bacteria reduce nitrate (NO3-). Bacteria that can reduce both oxygen and nitrate use oxygen if it is available since it gives most energy and nitrate then the oxygen isn't present.
In the sewage treatment plant you need to make a section with aeration in order to create conditions there ammonia can be oxidized to nitrate and another zone without oxygen for the denitrification.
In sewage treatment this is text book material so I don't know any papers on it.
To complete Henrik's answer, this is because denitrifying bacteria prefer oxygen that you need to have an anoxic zone or an anoxic period if you operate in a single tank system.
Aerobic denitrifiers can present under either aerobic or anaerobic conditions. They can use oxygen and nitrate as terminal electron acceptors simultaneously under limited oxygen conditions.
Yes of course denitrifyng bacteria growth under aerobic and anoxic conditions, it is well explain and describe in the large litterature dealing with nitrification-denitrication processes.
Besides biological and kinetic considerations, in practice denitrification may occur in aerobic systems when oxygen does not reach heterotrophic bacteria and if biodegradable carbon is available. This may happen in the following cases:
a) in aeration basins with low dissolved oxygen concentration which cannot diffuse to the interior of thick sludge flocks;
b) in poorly mixed aeration basins, where anoxic zones may be present (e.g.: in corners)
c) in the interior of biofilms, either biofilters, MBBRs or IFAS (hybrid systems that combine MBBR with suspended biomass).
In submerged biofilters without backwashing, I measured denitrification rates related to DO in the bulk liquid as vD = 1.82 exp(-0,14*DO) in gNO3-N/m^2/d where DO is the dissolved oxygen concentration in mg/L.
The reference is
Canziani R., Vismara R., Basilico D., Zinni L. (1999). Nitrogen removal in fixed-bed submerged biofilters without back-washing, Water Science and Technology, vol. 40, n. 5-6, pp.145-152
Denitrification in the presence of dissolved oxygen also occurs in attached growth systems, for example in biofilters. This is because at the part of the biofilm superfical dissolved oxygen is completely consumed, whereas in the nitrate is reduced by bacteria in the deepest part of the biofilm.
The following article describes the effect of dissolved oxygen in the denitrification process.
Gomez, M. A., et al. (2002), Effect of dissolved oxygen concentration on nitrate removal from groundwater using a denitrifying submerged filter, Journal of Hazardous Materials, 90(3), 267-278.
Dear Behera,
Some the activated sludge organisms are obligate aerob, they can not tolerate absence of oxygen. Some of denitrification organisms are facultative anaerob. It means that they can obtain energy in anaerobic conditions. However they grow better in aerobic conditions. Because they can obtain more energy than that they do in anaerobic conditions. therfore they abort the denitrification in aerobic conditions.
Yes; pls. see D Bilanovic, P Battistoni, F Cecchi, P Pavan, J Mata-Alvarez (1999) Denitrification under high nitrate concentration and alternating anoxic conditions. Water Research, V.33, Issue 15, Pages 3311-3320
As with any other metabolic group, there is a whole range of responses of denitrifyers in the presence of oxygen from Thiomicrospira denitrificans (which cannot tolerate any O2) to many others that continue to denitrify at air saturation. Reports of aerobic denitrification started about 10 years after the first recognition of denitrification at the end of the 19th century, and continued regularly throughout the 20th century. Some were clearly due to anaerobic microsites and inefficient mixing, but mass specs and 15N compounds have been used to confirm the existence of aerobic denitrification. Many of these bugs are also heterotrophic nitrfyers, and the mechanism may serve as a way of preventing NOx accumulation.
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