Biological Denitrification- reduction of nitrates, nitrites dissolved in water to molecular nitrogen. Which electron donor (ethanol or methanol) would be more suitable if only nitrite or nitric oxide is present on the system?
We studied the denitritation of a high-strength nitrite wastewater in a sequencing batch reactor using different organic carbon sources: ethanol, acid-fermented primary sludge centrate, acid-fermented secondary sludge centrate, glycerol and landfill leachate. The best results were obtained with glycerol. This paper can be found at Chemical Engineering Journal 172 (2011) 994– 998.
We don't have results for nitrite with methanol. In a previous work with nitrate denitrification, byproducts with methanol and ethanol were compared, showing 6 times higher rate for the ethanol byproduct, Water Research 37 (2003) 4211–4221.
Methanol rate was lower and also the adaptation time of the sludge was higher.
Thank you so much for the answer Dr. Baeza. However, I would like to know why the COD/N ratios vary with different carbon sources for nitrite denitrification? If we keep same COD concentration using different carbon sources, wouldn't they provide samilar nitrite reduction rates?
There are several reasons for the different COD/N ratios obtained. Landfill leachate ratio of 8.8 can be explained by the low biodegradability of the COD present in this wastewater. The glycerol COD/N ratio of 3.8 is similar to other results of the literature. It may be due to the fermentation process of glycerol to VFA that can be produced, leading to COD losses. The metabolic route for the degradation of each compound can give different yield for denitrifiers. I would recommend an experimental determination of this ratio if possible. These results are for only denitrifying systems. If the ratio is evaluated for a typical anoxic/aerobic WWTP part of the COD is lost by direct aerobic oxidation due to oxygen recycling, and hence the COD/N ratios can be much higher.
Compared to methanol, ethanol is more readily available carbon source for denitrification and it gives better performance in denitrification. However ethanol is expensive than methanol.
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