Study On Self-cleaning Mechanism Of BDD/Ti Composite Membrane Module

Oily wastewater is a kind of water pollution source. Membrane separationtechnology is an ideal means of oily wastewater treatment for its low operationpressure, no phase change, less energy consumption, wide applicable range, highseparation efficiency. But the membrane fouling restricts its wide application. In theprocess of water treatment, the pollutants in the water attach to the membranesurface and holes, then the membrane resistance increases, and the membrane flux isreduced. It seriously affects the efficiency of wastewater treatment.To improve anti-pollution capability of the traditional membrane materials，andconsidering the incomparable electrochemical advantages of boron-doped diamondfilm (BDD) electrode,chemical gaseous phase deposition method was adopted forconducting the surface modification of boron-doped diamond film to the traditionalmetal titanium(Ti) membrane, a new composite membrane material was preparedwhich couples the membrane separation techniques with electrochemicalself-cleaning techniques. An electrochemical workstation was used to analyze theelectrochemical behaviors of composite material in detail by taking oily wastewateras the processing object. Results show that potential window of composite materialis broad and background current is low，the selecting working potential of electrodeis higher than oxygen evolution potential， composite material can decomposite oilywastewater efficiently. Electrochemical self-cleaning membrane module is designed.It is proved that this new diamond composite membrane can improve the pollutionresistance and separation effect, prolongs the service life obviously.The BDD film was deposited on porous titanium substrate using hot filamentchemical vapor deposition (HFCVD) system. H2flux was240sccm. C flux was70sccm. The reaction chamber pressure was3.5-4KPa.The substrate temperature was800℃.The grow time was6h. To prevent deformation and crack of the compositemembrane, substrate was annealed for10minutes under the723K, and the coolingtime of the sample was extended to five hours to release the stress in the film slowly.Cyclic voltammetry was used to test electrochemical properties of BDD/Ticomposite membrane. The composite film has nearly4v potential window. The oildroplets can be oxidated directly, or oxidated indirectly by the strongoxidizing· OH.Self-designed membrane module is used to treat oily wastewater. Because theelectrocatalytic effect can inhibit the growth of the gel layer, relative flux remains at74%, and COD removal rate can reach73.2%, far higher than titanium membraneand the composite membrane without electrocatalytic effect.Operating parameters is very important for the affect the performance ofcomponents. As a result of the side reaction, influence of electrocatalytic voltage tothe membrane flux and removal rate of COD is not very obvious. When theoperating pressure rises, the membrane flux rises first, then falls fast, finally whenthe membrane fouling is balanced with the electrocatalytic effect, the flux comes tobe stable. The COD removal rate with the increase of pressure drops first then rises. High concentration waste water inhibits the self-cleaning effect, and the membraneflux will fall.