Molasses fermentation to produce low-cost carbon source for denitrification

Abstract

In the present work, the fermentation of molasses using Saccharomyces cerevisiae was optimized in terms of denitrification efficiency, using the relative total nitrogen (TN) removal ratio and the C/N consumption ratio as the indicators. The denitrification efficiency in different wastewater was also measured in the presence of different carbon sources for denitrification, that is, fermentation broth, unfermented molasses, sodium acetate, ethanol and methanol. The results indicated that the optimal fermentation conditions were as follows: pH = 4.0; temperature, 33 °C; dilution rate, 0.15 h−1; sugar concentration, 13%; ammonium chloride concentration, 0.5 g/L; and air-flow rate in the reactor, 0.1 vvm for 30 min every 12 h. The relative TN removal ratio with the fermentation broth was 39% higher than that with unfermented molasses. However, the denitrification efficiency of the fermentation broth varied between landfill leachate, herbicide wastewater and brewing wastewater. The relative TN removal ratio was significantly higher only in the brewing wastewater, and the C/N consumption ratio was also significantly lower than that with methanol, ethanol and molasses. These results showed that the use of molasses fermentation broth as the carbon source for denitrification has advantages for specific sewage regarding effectiveness. The raw material cost of the fermentation broth was ca. 30% lower than sodium acetate. The results also suggested that the bacterial community structure had a significant impact on the denitrification efficiency of the fermentation broth.