Membrane bioreactor for drinking water denitrification

Abstract

The aim of this study is to evaluate the performance of a membrane bioreactor with cell recycle to be used for drinking water denitrification, when operated with a high nitrate load (up to 7.68 kgNO₃ ⁻/m³ day) and low hydraulic retention time (down to 0.625 h). Nitrate and nitrite were always completely removed for all the operational conditions used. The effluent's nitrite concentration kept below 0.1 mg NO₂ ⁻/l with exception of a short period, during the reactor start-up, when it accumulates. The performance of the membrane bioreactor was also evaluated using a groundwater containing 148 mg NO₃ ⁻/l. Nitrate and nitrite concentration in the effluent were below the recommended values for drinking water when the reactor was controlled at pH 7.0. The membrane flux decreases during operation as a consequence of membrane fouling. The flux decrease was more severe during operation with synthetic medium than with contaminated groundwater due to the existence of molecular complexes in the synthetic broth. A backshock technique was used to reduce the surface fouling of the membrane. Combining this technique with the use of a reserve asymmetric structured membrane it was found that the membrane flux remains nearly unchanged.