Water Technologies

We design Ultra Filtration plants for various applications like RO pre treatment, drinking water, ETP, STP and as per customised requirements.

What is Ultra Filtration?

Ultra filtration is a separation process using membranes with pore sizes in the range of 0.1 to 0.001 micron. Ultra Filtration removes high molecular-weight substances, colloidal materials, and organic and inorganic polymeric molecules. Low molecular-weight organics and ions such as sodium, calcium, magnesium chloride and sulfate are not removed. Because only high-molecular weight species are removed, the osmotic pressure differential across the membrane surface is negligible. Low applied pressures are therefore sufficient to achieve high flux rates from an ultrafiltration membrane. Flux of a membrane is defined as the amount of permeate produced per unit area of membrane surface per unit time. Generally flux is expressed as gallons per square foot per day (GFD) or as cubic meters per square meter per day.

Ultra Filtration membranes can have extremely high fluxes but in most practical applications the flux varies between 50 and 200 GFD at an operating pressure of about 50 psig, in contrast reverse osmosis membranes only produce between 10 to 30 GFD at 200 to 400 psig.

Ultra Filter VS. Conventional Filter:

Ultra Filtration like Reverse Osmosis is a cross-flow separation process. Here, the liquid stream to be treated (feed) flows tangentially along the membrane surface, thereby producing two streams. The stream of liquid that comes through the membrane is called permeate. The type and amount of species left in the permeate will depend on the characteristics of the membrane, the operating conditions, and the quality of feed. The other liquid stream is called concentrate and gets progressively concentrated in those species removed by the membrane. In cross-flow separation therefore, the membrane itself does not act as a collector of ions, molecules, or colloids but merely acts as a barrier to these species.

Conventional filters such as media filters or cartridge filters on the other hand only remove suspended solids by trapping them in the pores of the filter-media. These filters therefore act as depositories of suspended solids and have to be cleaned or replaced frequently. Conventional filters are used upstream from the membrane system to remove relatively large suspended solids and to let the membrane do the job of removing fine particles and dissolved solids. In ultra filtration, for many applications no prefilters are used and ultra filtration modules do concentration of all the suspended and emulsified materials.

FACTORS AFFECTING THE PERFORMANCE OF ULTRA FILTRATION:

There are several factors that can affect the performance of an ultra filtration system. A brief discussion is given below.

Flow Across the Membrane surface : The permeate rate increases with the flow velocity of the liquid across the membrane surface. Flow velocity is especially critical for liquids containing emulsions or suspensions. Higher flow also means higher energy consumption and larger capacity pumps. Increasing the flow velocity also reduces the fouling of the membrane surface. Generally an optimum flow velocity is arrived at by a compromise between the pump horsepower and increase in permeate rate.

Operating Pressure : Permeate rate is directly proportional to the applied pressure across the membrane surface. However, due to increased fouling and compaction the operating pressures rarely exceed 100 psig and are generally around 50 psig. In some of the capillary-type ultra filtration membrane modules, the operating pressures are even lower due to the physical strength limitation imposed by the membrane module.

Operating Temperature : Permeate rates increases with the increasing temperature. However, temperature generally is not a controlled variable. It is important to know the effect of temperature on membrane flux in order to distinguish between a drop in permeate due to a drop in temperature and the effect of other parameters.