Experimental Research On The Separation Of Oily Wastewater By The Modified α-Al₂O₃ Microfiltration Membrane With Nano ZrO₂ Coating

Membrane technology is one of the good-prospective technologies in the 21st centenary, which accelerates the development of the burgeoning industries and improves the living conditions. To our country, membrane technology has an important strategic effect on emission controlling of waste residues and wastewater re-resourced. Wastewater containing oil is the main part of the wastewater, which has the most serious destroy to the living conditions. It must be treated until it meets the emission standard. The traditional wastewater treatment methods could not separate completely the oil from the stable oil/water emulsions. However, membrane technology can do it. The problem to be solved for the membrane technology is the membrane fouling, which weaken seriously the separating performance. To decrease the fouling, commercial Al₂O₃ microfiltration membrane is modified with nano ZrO₂ coating, which increases the hydrophilic character of the membrane surface and decreases the adsorption of oil droplets. In this work, the preparation and the optimal operation parameter of the modified membrane are studied to obtain the good performance.Theα-Al₂O₃ microfiltration membrane was modified by in-situ hydrolyzation method, the effect of the different pore size and modification of coating material on membrane permeability. The result show selecting the better hydrophilic character of 0.2μm ZrO₂ microfiltration membrane as main research.To further explore the effect of different ZrCl4 modified concentration on the structure of the nano coating andα-Al₂O₃ micro-membrane permeability.The results show that the optimal precursor is 6 g/L ZrCl4 ethanol solution. Under this condition, the nano coating with the thickness of 14 nm distributes evenly on the alumina grains'surface which forms the membrane pore wall. The water flux of the modified membrane increases 32% than the unmodified one. Using 1 g/L oily wastewater as feed, the permeating flux of the modified membrane is 300 L/m2·h, which increases 30% than that of the unmodified membrane. The oil rejection is as high as 99.9%.Therefore, the modified membrane with nano zirconia coating prepared by in-situ hydrolysis can effective reduce the membrane fouling. The modified membrane treats stably and effectively the oily wastewater.The optimal operation parameters of the modified membrane to treat the oily wastewater are researched. The results show that the trans-membrane pressure should be in the range of 2.2 MPa 2.6 MPa. The optimal velocity of the feed is 5 m/s. Too high or too low velocity are harmful for the permeating flux. However, the feed velocity has less effect on the oil rejection. Increasing the temperature of the feed contributes to the permeating flux. However, the temperature loses its action on the flux if the temperature is over 45℃. Therefore, the optimal temperature range is 30⁴0℃. The permeating flux decreases obviously with the increase of the oil concentration in the feed if the oil concentration is under 5 g/L. In all the condition, the oil rejection is no lower than 99.8%. The appropriate interval of the backflushing is 10 min.The recovery of the fouling membrane can be obtained by the thermal treatment, ultrasonic assisted washing. The best way of them is the thermal treatment in which the fouling is calcined to remove the foulant. The permeating flux is recovered 80-90% of the initial flux of the virgin membrane.