The effects of nitrite on integrated process of denitrification with anaerobic acidification were conducted in a batch reactor using cassava stillage (CS) as substrate. The results showed that the final volatile fatty acids(VFA) production of anaerobic reactor was similar for with and without adding nitrate (600 mg·L-1 )

but severe inhibiton of acidogenesis took place after adding the same amount of nitrite and the final VFA production was only 1.8% of that of the blank reactor. The decrease of anaerobic acid production in the nitrate reduction process was mainly due to the presence of nitrite. A small amount of nitrite could strongly suppress anaerobic acidogenesis

and the effects of nitrite on VFA composition was n-butyric>propionic>acetic acid. With decrease of ratio

nitrite reduction rate decreased from 74.9% to 22.2%

and was suppressed almost completely (>90%) at the concentration free nitrous acid (FNA) above 0.05 mg·L-1. Furthermore

with increase of ratio the proportion of denitrification decrease gradually in nitrite reduction

while dissimilatory nitrate reduction to ammonium (DNRA) process became dominant gradually.