Alkaline chemical membrane cleaning

The overall lifespan of a membrane is governed by the membrane chemical resistance and its antifouling property. Common membrane-cleaning processes employ acidic and alkaline solutions for removing salt precipitates and organic foulants, respectively, to recover the membrane permeability and other performances, which are important to minimize the energy consumption and operating costs (Li and... 

Table 4 summarizes the efficiency of membrane filtration as preliminary treatment in the hybrid process to obtain regenerated water for industrial reuse. Working with the adequate cleaning cycle to avoid fouling and to keep a constant flux (10 1 min ) important reduction in suspended solids (90%) and turbidity (60%) of the wastewaters is achieved but there is no significant reduction of other chemical or physical parameters, e.g., conductivity, alkalinity or TDS, or inactivation of E. coli. 

Membranes are made from different materials. Cellulose nitrate ultrafiltration membranes are of limited chemical and thermal compatibility and with imprecise cut-off. The membranes from polyvinylidene fluoride, polyaciyloiutrile or polysulphone possess good chemical compatibility are more stable over a very wide pH range and ate easy to clean. Problems with membrane fouling can usually be overcome by trcatment of the membranes with detergents, proteases or with acid or alkaline solutions. 

The systems also allow cleaning with strong alkaline or acid chemicals, also oxydants as H2O2 and NaOCl which in some cases is necessary to keep the membranes sufficiently clean in the long run. 

Cleaning of the membrane was performed with 0.3 wt% nitric acid at 45 °C and the alkaline detergent Ultrasil 11 at 0.25 wt% and 55 °C. The membrane flux did not always fully recover after each chemical cleaning. A 200 mg/L CI2 solution administered as sodium hypochlorite (NaOCl) would, however, restore the original flux. 

Cleaning with chemical agents can be used. They need to be compatible with the membrane to avoid damaging the membrane structure. Some common cleaning agents are acids (strong or weak), caustic (NaOH), detergents (alkaline, non-ionic), enzymes, complexers, and disinfectants. 

Batch times can range from 12 to 22 hours depending on the desired final concentration and the required number of diafiltration volumes. At the end of a batch run, membranes are chemically cleaned. Cleaning may take up to 3 hours and involve the use of an alkaline or acidic solution, or both, with a final sanitization step (e.g., 200 ppm NaOCI solution, a dilute solution of sodium bisulphite or a bactericide/fungicide). In some cases, steam sterilization may be performed at the end of each run especially when using inorganic membrane filters. 

Fuel cells as clean and efficient energy devices convert chemical energy in a fuel directly into electricity via electrochemical reactions. Several types of fuel cells, such as phosphoric acid (PAFC), proton exchange membrane (PEMFC), molten carbonate (MCFC), solid oxide (SOFC), and alkaline fuel cells (AFCs), have been... 

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