Treatment of wastewater by ultrafiltration

During the last few years there has been a continuous and important growth in water consumption and consequently a strong increase of the domestic and industrial wastewater potential sources of environmental problems. Reclamation of wastewater is thus becoming a major goal in several countries where there is water scarcity. Thus we tested an a lab scale a combination of sand filtration and UF producing a clear disinfected water which could be reused. A tubular inorganic membrane CARBOSEP with 50,000 Da MWCO was used for this study. At a cross flow velocity of 4 m/s the polarization phenomena were limited leading to a maximum value of about 100 1/h.m(2) for a transmembrane pressure of 1 bar. With an increase of the cross flow velocity up to 6-7 m/s, the relation between the filtrate flux and the transmembrane pressure becomes nearly linear: in these conditions, in a range of transmembrane pressure 0.5-2 bar, the filtrate flux is only 15% lower than the pure water flux, proving a very low level of fouling. The removal efficiency of organics and suspended solids (including bacteria) was very good: 1) low values of COD (12 mg/l) BOD (5 mg/l) and absence of indicators of fecal contamination are the main characteristics of the treated water; 2) it can be concluded from these tests that the combination sand filtration/UF is efficient and that a cut-off of 50 Kda is a good choice.