Relationship between release of nitric oxide and CO2 and their dependence on oxidation reduction potential in wastewater treatment

Nitric oxide (NO) is an intermediate of denitrification process and can be produced by denitrifiers, nitrifiers and other bacteria. In our experiments we measured the dynamic flow of NO depending on oxidation reduction potent ial (ORP). Different ORP-ranges were related to various carbon loading stag es in the wastewater treatment pilot plant. Nitrification and denitrificati on were achieved by a sequence of aeration and non-aeration periods. Our me asurements show that different carbon loading conditions (low feed, balance d and overloaded conditions) did not change the range of the mixing ratio o f NO emissions when the aeration conditions like air-flow and temperature w ere kept constant. Minimum and maximum NO mixing ratios were 34.7 and 91.8 ppbv; 52.3 and 91.3 ppbv; 57.6 and 109 ppbv for low feed, balanced and over loaded conditions, respectively. The curve of the NO graph relied on nitrif ication/denitrification dynamics. The dependence of NO release on different ORP and CO2-release during the various conditions are shown. Longer aerati on times resulted in an increased release of gaseous NO. The net-release of NO g(-1) nitrogen removed was between 0.014% and 0.028%. The NO fluxes to the air were observed between 8.3 and 14.9 Mg m(-2)d(-1)NO. The major relea se occurred during high aeration periods whereas the concentration of disso lved [NOaq] in the wastewater was less than 0.05% of the gaseous release du e to very low solubility of the NO. (C) 2001 Elsevier Science Ltd. All righ ts reserved.