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Membrane Chemical Cleaning

An Integral Part of Filtration

Membrane chemical cleaning for microfiltration (MF) and ultrafiltration (UF) in the water industry has significant impact on the filtration process. Effective cleaning can increase the flux and protect the membrane from fouling. Various cleaning chemicals can be used to remove fouling materials and to restore the flux.

CategoryTypical ChemicalsMajor Functions
Caustic Hydrolysis, solubilization NaOH
Oxidants/Disinfectants Oxidation, disinfection NaOCl, H2O2
Acids Solubilization Citric acid, HNO3
Surfactants Emulsifying, dispersion Surfactants, detergents
Table: Major categories of membrane cleaning chemicals

Caustic is generally used to clean membranes fouled by organic and microbial foulants. It basically hydrolyses and solubilizes the foulants. Hydrolyzing the foulants increases the solubility which prevents the membrane from getting clogged. Caustic works really well when combined with an oxidizing agent. Acids are primarily used for removing scales and metal dioxides from the fouling layer. Surfactants form micelles with fat, oil and proteins in water and help to clean the membrane fouled by the same. In addition, surfactants affect fouling dominated by the formation of biofilms.

Filtration Solutions, Inc.’s HP series membrane filters are made of polyacrylonitrile (PAN) polymer in both hollow fiber and sheet forms. This membrane is characterized by a pore size of 0.05 microns with an approximate molecular weight cut-off of 100K Dalton. These membranes are used for oil/water separation and suspended solids removal. To avoid fouling by free oils, the HP series membranes are engineered to be hydrophilic compared to other membranes which are oleophilic. These membranes are easily washed using a caustic solution. Other chemicals can also be used based on the requirements.

The SHP series membrane filters of Filtration Solutions, Inc. are made of chemically modified polyacrylonitrile (PAN) polymer in spiral-wound form. This membrane is characterized by a pore size of 0.01 microns with an approximate molecular weight cut-off of 20K – 50K Dalton. They are also used for oil/water separation. Cleaning is simple, like the HP series membrane filters.

Concentration, cleaning time, temperature and hydrodynamic conditions are important factors affecting cleaning efficiency. One important aspect is cleaning compatibility between the membrane media and cleaning chemicals. A membrane with a high chemical tolerance would allow greater freedom in selecting the composition and strength of cleaning solutions.