Membrane Technology
Osmosis is a natural phenomenon, which is most evidently seen in transferring of water in trees from the leaves to the tree itself. It involves the passage of water from the section containing lower concentration of ionic substances to a higher concentration section when the two are separated by a semi-permeable membrane.

Membrane technology is applied to simultaneously concentrate, fractionate and purify any aqueous solution. The technology is based on a combination of sieving and sorption diffusion mechanisms. A membrane is the most important part of the technology as it selectively separates certain species in a fluid or medium-to-large sized dissolved molecules from the solution. Products with functional properties can be produced using this process, which are superior to products produced by conventional processes. The criterion for selecting a membrane is the size of the pores, which should be smaller than the size of the smallest particle in the feed stream that is to be retained by the membrane. Membranes have configurations such as

1. Spiral wound

2. Tubular

3. Hollow-fiber

4. Plate & frame

The different configurations are meant for different applications depending on factors like viscosity, concentration of suspended solids, particles, size, temperature etc. A comparison of different membranes has been provided below:

MEMBRANE CONFIGURATION COMPARISON TABLE

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Crossflow Filtration
A very simple process, where the pumping of the feed stream is done to self-clean the process from solutes & solids, that are swept away by the pressure of the concentrate stream which runs parallel to the surface of the membrane. The concentrated solution is recirculated more than once in order to deplete the feed fully. Depending upon the application & process requirement, either the permeate or the concentration or both may become the product.

Aqua Clear uses Spiral wound membrane technology. Spiral membranes are packaged in a host of ways. The spiral wound membrane element is constructed of one or more envelopes wound around a perforated central tube. In operation, the feed enters one end of the membrane element under required pressure. The permeate passes through the membrane element into the envelope & spiral inward to central tube for collection. The retained feed is called the concentrate and passes out of the downstream. More water passing through the membrane results in more concentration of solids. Spiral wound design offers the best all-around characteristic of high packing density and is rugged, which help in high-pressure operations. This makes the technology economical and it is one of the reasons why it is accepted worldwide.

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Reverse Osmosis
The most complex technique in membrane separation technology derives its name from 'Osmosis'. If a solution is separated from a solvent or two solutions of different concentrations are separated, the less-concentrated solution will flow towards the more concentrated one due to its natural instinct. This is known as 'Osmosis'. If hydraulic pressure is in excess than the natural osmotic pressure, its application on the concentrated solution will result in the reverse flow of the solution. This helps extracting pure solvent from the solution and the process is called 'Reverse Osmosis'.

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Nanofiltration
A cost-effective process it does not accept the divalent ions & low molecular weight organics. It allows maximum monovalent ions to pass through it. Nanofiltration membranes also remove 90% of feedwater's hardness ions, large colour molecules and double-charged scaling ions like calcium & magnesium ions. One very common application is the municipal drinking water plants. The process very effectively and efficiently concentrates either valuable or undesirable substances from a process stream. Nanofiltration requires half the pressure to treat a same amount of water, when compared to other techniques.

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Ultrafiltration
Ultrafiltration is a process where a low-pressure fractionation of selected components by size is done. The process is similar to Reverse Osmosis. The membrane depending on the molecular weight chosen, lets the dissolved salts & lower molecular weight materials to pass while it concentrates the high molecular weight species. Mostly, these membranes find applications in numerous industries for concentration & clarification of large process streams.

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Microfiltration
The process of Crossflow Microfiltration has the most open membrane and is generally used for separating suspended solids and macro-materials like Starch, Bacteria, Molds etc. It is a low pressure, energy-efficient process that dynamically separates micron size or smaller particles from the liquid or gaseous feed stream. The process has lower running costs as it operates at low transmembrane pressure. Microfiltration is a multi-stage operation with applications in effluent concentration, sterile filtration, wine clarification etc.

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