Membrane Water Filtration Plant

Water purification is the process of removing unwanted chemicals and materials. Water purification reduces the concentration of suspended particles, bacteria and parasites in water. Membrane water filtration system is used for water treatment including desalination of sea water and brackish water. It uses a semipermeable membrane for removing suspended and dissolved solids from water. Membrane technologies are considered alternatives to normal water treatment.

Types of Membrane Water Filtration

• There are two types of membrane separation processes--pressure-driven and electrically driven. In pressure driven process hydraulic pressure is used to force water molecules through the membrane. The impurities are retained in the feed water which becomes the rejected water. The water that passes through the membrane is recovered as pure water. In the electrically driven process, electric current is used to move ions across the membrane leaving the purified water behind. The ions are collected in the concentrate stream for disposal.

Membranes in Membrane Filtration Plants

• Polymeric materials, including cellulose polymers form the principle constituents in membranes used in membrane filtration plants. Cellulose polymer's widespread use is aided by their easy availability and cost-effectiveness. However, membranes composed of ceramics and metal oxides are not uncommon. The more recent development in membrane manufacturing is the addition of thin composite polyamide film (e.g., nylon). Polyamide films are characterized by the ability to withstand great physical force, but they are costlier than cellulose polymers.

Parts of Membrane Filtration System

• A typical filtration system consists of pre-treatment, pumping, cartridge, filtration, membranes and post-treatment. Pre-treatment removes suspended solids that can damage the membrane. Pumping increases the pressure to achieve the operating level which helps to maintain required velocity across the membranes. The membrane manufacturer always provides a cartridge filter for the removal of particles of size 5 microns and above. Membranes are hydraulically connected in series or parallel formation, depending upon quality of feed water and quality of water required. Post-treatment includes degasifier for the elimination of hydrogen sulfide and carbon dioxide.

Maintenance of Membrane Systems

• The life of a membrane ranges from three to five years, depending on its usage. The membrane gets rotten due to salts such as barium sulphate, strontium sulphate or calcium sulphate, which can be prevented by using certain inhibitors. The fouling of a membrane also occurs due to organic materials, which can be avoided by following proper pre-treatment process. The filtration process generates waste material which has to be disposed of in a proper manner. The disposal options include sanitary sewer, land application or deep well injection.

Advantages of Membrane System

• Membrane water filtration systems have enabled considerable reduction in the amount of chemicals required for treatment. Moreover, they require less space and less manpower. They also eliminate viruses and bacteria. Membrane filtration systems have a low system cost.