Free Nitrous Acid Inhibition On Nitrous Oxide Reduction By A Denitrifying-enhanced Biological Phosphorus Removal Sludge

摘要

Nitrite has generally been recognized as an inhibitor of N_2O reduction during denitrif ication.This inhibitory effect is investigated under various pH conditions using a denitrifying-enhanced biological phosphorus removal (EBPR) sludge.The degree of inhibition was observed to correlate much more strongly with the free nitrous acid (FNA) concentration than with the nitrite concentration, suggesting that FNA, rather than nitrite, is likely the true inhibitor on N_2O reduction.Fifty percent inhibition was observed at an FNA concentration of 0.0007-0.001 mg HNO_2-N/L (equivalent to approximately 3-4 mg NO_2~- -N/L at pH 7), while complete inhibition occurred when the FNA concentration was greater than 0.004 mg HNO_2-N/L The results also suggest that the inhibition on N_2O reduction was not due to the electron competition between N_2O and NO_2~ reductases.The inhibition was found to be reversible, with the rate of recovery independent of the duration of the inhibition, but dependent on the concentration of FNA the biomass was exposed to during the inhibition period.A higher FNA concentration caused slower recovery.