Enhanced backwash

A typical UF pilot plant has been used in this study. Examples of application for these membranes can be found in the literature [40, 58]. The UF unit woks in deadend mode (2.5 m h ) and it can be operated in filtration, backwash and chemically enhanced backwash (CEB) modes as described in the literature for similar UF systems [40]. The specifications of the hollow fiber UF modules and the operating conditions are summarized in Table 5. 

Chemical enhanced backwashes (CEB) are also used to minimize the cleaning frequency of hollow fiber membranes. Chemical enhanced backwashes include the use of chemicals, such as hypochlorite, acid, and caustic in relatively high doses, to affect a mini chemical clean of the membranes without a full membrane cleaning. Concentrations of up to 1000 ppm acid, 500 ppm caustic, and 1000 ppm hypochlorite are typically used in a CEB. 

A.2 Enhanced Backwash In an enhanced backwash, a low dose of oxidant/ disinfectant is automatically injected into the permeate during a backwash (with permeate) in order to enhance the efficiency of cleaning. While a normal backwash (with permeate) is very short (ca. 15-30 s) and is performed automatically (every 15-45 min), an enhanced backwash usually takes long (i.e., approx 10-15 min), and the frequency is usually every 4-6 h. 

The enhanced backwash comprises three steps first, a backwash with permeate (approx 30 s) to remove accumulated particles from the hollow fiber. Second, a short soak (10-15 min) with alow dose of oxidant/disinfectant to remove adsorbed foulants fiom the membrane, and finally another short backwash (with permeate) to remove the chemicals from the systems. 

Cieaning Maintenance cleaning by backwash or chemically enhanced backwash is an option for contained and submerged modules and easier for hollow fibers. Clean-in-place may be easier for contained systems and smaller volumes of chemicals may be required. 

Visvanathan C, Ben Aim R. Enhancing electrofiltration with the aid of an electro-osmotic backwashing arrangement. Eil. 

Scouring with air enhances separation of the collected particles from the filter medium. When a filter is taken out of service for backwashing, it is first drained to a level about 100 mm above the top of the bed. Blowing with air for a few minutes releases the filtered particles from the grains of filter medium. The backwash fluid then performs more efficiently. The drain-scour-backwash cycle takes 10-15 min. It is fairly common practice to repeat this cycle once or twice. This technique improves results, and its fioquency can be increased if filter performance is deteriorating. Even when used infrequently, this procedure should be included in the plant operating manual and built into the control program to afford the operator easy access. 

Dead end filtration operation mode was used, and the installation was continuously running 24 h daily. The membrane flux was 60 L/(m h) and filtration cycle was 30 min, and the backwash time was set up at 1 min. To inhibit the growth of bacteria on the surface, membrane was immersed with 10 mg/L of NaClO solution for 5 min every 8 h. When the membrane flux reduced or transmembrane pressure (TMP) increased significantly, the backwash flow was increased to enhance washing. The quality of membrane inflow and effluent were examined and monitored during the experiment. 

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