Effect of Free Nitrous Acid Pretreatment on Fermentation and Anaerobic Digestion

Free nitrous acid (FNA) was applied to thickened waste activated sludge (TWAS) and the pretreatment’s effect on anaerobic digestion and fermentation was evaluated. Different concentrations of the chemical were assessed using semi-continuous flow digesters at solids retention time of 1, 2, 3 and 20 days. FNA pretreatment was able to improve fermentation after 1-day SRT to the same levels as 2-day SRT without pretreatment. 0.7 mg N/L FNA applied to TWAS yielded 30% increase in methane production and 23% VS destruction compared to the control. The results showed that application of FNA to TWAS can be utilized to reduce fermentation period in a 2-stage anaerobic digestion process and improve methane production.