STABILIZATION AND DEWATERING OF WASTE-WATER USING HOLLOW-FIBER MEMBRANES

An experimental study for combined stabilization and dewatering of industrial wastewater was carried out by means of a microfiltration unit inside a bioreactor. The module type used was a hollow fiber membrane with a transport area of 0.3 m(2) and pore size of 0.1 mu m. The membrane material was polyethylene. Dewatering was accomplished by applying suction pressure across the membrane. Four suction pressures in short-term experiments with activated sludge from the Barceloneta Regional Wastewater Treatment Plant (BRWTP) were studied. The objective here was to determine the membrane hydraulic characteristics and the best conditions for stable, long-term operation. The experiments showed that the flux through the membrane decreases with vacuum pressures greater than 60 kPa owing to rapid clogging of the membrane micropores. Long-term experiments of 62 days duration were carried out with a pharmaceutical wastewater at a suction pressure of 20 kPa. Parameters measured included COD, MLSS, and MLVSS. The operation mode was intermittent with cycle time of 20 min: 4 min of suction followed by 16 min without suction, with average hydraulic retention time of 10.5 h. This mode of operation gave better and more stable results than continuous operation. The MLSS concentration inside the reactor increased throughout the operation, but was always under 40,000 mg/l, the limit for stable operation without sludge wastage. The average COD removal efficiency during the long-term experiments was 63%, with a maximum value of 86%.