BARC develops unique water purifier
The Desalination Division of Bhabha Atomic Research Centre is engaged in development and deployment of various types of membranes and other processes for a wide range of water-related applications such as sea and brackish water desalination, effluent treatment and recycle, and water reuse. BARC has put up several big and small plants for such purposes in different parts of the country. It also provides consultancy services to several agencies in this regard.
Recently, the division developed an ultrafiltration membrane based device for online purification of domestic water. According to BARC, this device is an efficient and economical alternative to various other commercially available water purification devices. During the last one year, BARC has transferred the knowhow of this technology to 10 private parties for commercialisation on non-exclusive basis through its Technology Transfer & Collaboration Division (TT&CD).
Ultraviolet (UV) devices work on the principle that most of the microorganisms are sensitive to UV-radiation and have a critical dose, above which they become inactive. The main limitation of this device is that it is electrically operated and does not remove any other contaminants. Inactivated, dead and decayed bacteria are always present in purified water. Efficiency of UV device is adversely affected if proper flow of inlet water is not maintained and appropriate pre-filtration system is not employed. The device is expensive and needs frequent servicing from technicians. A major part of the country lacks continuous electric supply and hence this device cannot be effectively used during non-availability of power.
Devices employing chemical addition are based on release of certain chemicals like chlorine, iodine or silver for destroying bacteria to give safe water. Their efficiency of destroying bacteria is always questionable due to poor residence time, and they also change the taste of water.
As far as membrane processes are concerned, reverse osmosis (RO) membrane devices can be used to remove virtually all kinds of contaminants, including salinity. This device is more suitable for industrial or community scale and too expensive for domestic purposes because it works with electrically operated pump generating 5-10 bars pressure. This device is not suitable for water containing low salinity (TDS) as in Mumbai, as it will remove many essential minerals from water.
Devices based on ultrafiltration membrane can physically remove bacteria, suspended solids and high molecular weight organics without the use of electricity, at tap water pressure, mainly by sieving (size-exclusion) mechanism. The useful life of this membrane device depends on configuration of the membrane. Most of the existing membrane devices employ UF membrane in either spiral, capillary or hollow fibre form. A drawback with these configurations is that they cannot be completely cleaned physically and due to deposition of suspended solids, their output keeps on decreasing with time. The on-line domestic water purifier developed at BARC's Desalination Division is based on this ultrafiltration membrane in cylindrical configuration, which is free from these limitations.
The ultrafiltration membrane device for domestic water purification has the following advantages over various other devices:
* The device is very effective. It almost completely filters out bacteria and turbidity, producing crystal clear water.
* The device is very compact and portable. It can be easily installed and needs no electricity or addition of any chemical.
* The device physically filters out bacteria. There will not be any dead or decayed bodies of bacteria in purified water unlike ultraviolet or chemical addition devices.
* Due to candle like cylindrical configuration of ultrafiltration membrane, they can be easily cleaned and reused number of times unlike ultrafiltration membrane of hollow fibre, capillary or spiral configuration which cannot be cleaned completely and has to be replaced after some time.
* The operational cost of device is almost negligible. It is almost maintenance free except occasional cleaning of membrane surface.
* Polysulfone, the material of preference for making ultrafiltration membranes, has excellent stability with respect to residual chlorine acids and alkalis.
* No additional column of activated charcoal is required.
* Not a single drop of water is wasted.
