METHANE AS CARBON SOURCE AND ENERGY FOR BIOLOGICAL WASTE WATER DENITRIFICATION

Abstract

In Mexico, waste water treatment does not focus in the elimination of nutrients (nitrogen and phosphorous). Nevertheless, Mexican legislation, NOM-001-ECOL-1996 establishes maximum permissible limits of 40 total nitrogen mg/l for water discharged into receiving bodies (Diario Oficial de la Federación, 1997). In order to overcome this requirement, it is necessary to develop biological processes for nutrient removal. In the last 30 years, a limited number of works has been published where it is considered to use the methane as carbon source and energy in the biological denitrification. The reported works defer in their results leaving a filed for developing research studies on this subject, methane being the main by-product of anaerobic digestion. Biogas is an attractive option of cheap substrate capable of achieving reasonable rates of nitrate removal. In this study, methane was used as energy and  carbon source for biological denitrification under anoxicconditions. During 152 days, a reactor with capacity of 2.5L was fed with synthetic (denitrifying) water and a concentration of 35 mg/l of N-NO3-. Pure methane (99.0%) was introduced to the system until reaching a partial pressure of 4.41lb/in2. Although the obtained denitrifying activity is low, 14.6g N-NO3-/g SSV*d (0.61g N-NO3-/g SSV*h) it may be concluded that it is feasible to use methane as carbon source and energy for wastewater desnitrification.

Key Words: Anoxic, denitrification, methane, nitrate, wastewater treatment.