MEMBRANE BIOPROCESSES FOR THE DENITRIFICATION OF DRINKING-WATER SUPPLIES

A membrane bioreactor (MBR) system, consisting of a bioreactor coupled to a hollow fiber ultrafiltration membrane module, has been developed at the Centre International de Recherche sur l'Eau et l'Environnement (CIRSEE). This process combines the advantages of biological conversion of nitrate to nitrogen with that of hollow fiber ultrafiltration technology to produce high quality drinking water. The influence of several parameters, both biological and hydraulic, on the overall performance of the process has been investigated. With adequate membrane backwashing frequency and crossflow velocity, we were able to obtain, and to maintain for more than two months, a net permeate flow rate of over 100 1-hr-1-m-2. It has also been found that such a high permeate flow rate was not detrimental to the overall denitrification process, since permeate nitrate and nitrite concentration remained below 20 and 0.1 mg-l-1, respectively, for a nitrate volumetric loading rate of 2.8 kg-m-3-day-1 at a hydraulic retention time of either 60 or 30 minutes.