Abstract
In this experiment the effects of nitrate and nitrite on the anaerobic digestion process were studied, focusing on the relationship between methanogenesis and denitrification. The seed sludge used for these batch experiments was maintained for more than 5 months. The substrate used for the experiments was skim milk which did not contain nitrate or nitrite. The inhibitory effects of nitrate and nitrite on the methanogenic reaction, using acetic acid as the sole substrate, were approximately the same. The maximum methane production potentials decreased as the COD/N ratio decreased. Methanogenesis did not occur when the COD/N ratio of substrate was lower than 4.6. The conversion rate from nitrate to nitrogen, with acetate as the sole organic source was at its maximum when the COD/N ratio was 15. The conversion rates from both nitrate and nitrite to nitrogen, with glucose as the sole organic source, were at their maximum when the COD/N ratios were 15 and 6, respectively.
