Water purifying methods RO UV UF

Reverse osmosis Ultraviolet Ultrafiltration

Introduction of the different purifying methods

The three major principles for water purification are RO (reverse osmosis), UV (ultra violet) and UF (ultra filtration). Often those acronyms are used in the products name to show which method is used for the water purification. Some water purifier also use multiple techniques. The water is not only purified by the particular module but there are also other filters, like sand or carbon, deployed.

There are significant differences between RO, UV and UF which can be seen in a short overview in the following table:

RO UV UF
Requires electricity Requires electricity Does not require electricity
More than half of the run through water is wasted No water is wasted Amount of wasted water is 5%
Maintenance costs are quite high Annual replacement of lamp and filters Minimal maintenance
Germs can be carried over. Not all UV systems may kill e-coli, bacteria and viruses Seperates physically bacteria and viruses, but doesnt remove them
The shelf life can be reduced due to collodial impurities
Ideal for surface water ormunicipal water

Reverse osmosis water purifier

How do RO water purifier work?

RO water purifier system

RO stands for reverse osmosis. Often you can hear or read something like aro water purifier or aro water filter. This is just a false pronunciation, we explained it earlier what the abbreviation means. The water scarcity is the very important reality of modern living thanks to the increasing population, growing industrialization, expanding agriculture and rising standards of living have pushed up the demand for water. Efforts have been made to collect water by building dams and reservoirs and creating ground water structures such as wells, while water is a renewable resource, but also a finite resource. The total quantity of water available on the globe is the same as it was two thousand years ago. To cope up with the demands of fresh water it has become inevitable to recycle the water by one of the many water purification methods available in the current scenario and while we still research to develop better methods. Currently we use methods like RO (Reverse Osmosis), Ultrafiltration, Filtration, UV irradiation, Organic absorption, Deionization, Distillation to name a few. Reverse Osmosis is one of the very popular methods in India for the purification of water. It is a process in which dissolved inorganic solids such as, salts are removed from water by passing it through a semi permeable membrane under pressure. It will reduce a pretty wide spectrum of contaminants such as dissolved salts, Lead, Mercury, Calcium, Iron, Asbestos and Cysts. It works well with less turbid water.

History

In 1959, two researchers Sidney Loeb and Srinivasa Sourirajan at ULCA succeeded in producing a functional synthetic RO membrane from cellulose acetate polymer. They demonstrated that high solute water was pressure forced through the engineered membrane which acted as a filter that allowed only water molecules to pass through while rejecting the excess and huge salts particles. Fresh water that was filtered was drinkable water and the membrane was actually durable and could operate under normal water pressure and operating conditions. This was how this new technology called Reverse Osmosis(RO) came into existence.

Advantages of RO

  • The RO treated water is pure and tastes better than municipal water is because the RO system removes about 98% of chemicals from the tap water which has taste and smell of chlorine.
  • With the removal of lead, mercury, chlorine, asbestos and other 2100 well known toxins, RO system significantly reduces the risk of illness and diseases.It removes most of the contaminants like arsenic, lead, copper, lead, municipal additive like fluoride. It also removes most of the germs.
  • The water that you get from RO system hydrates your body at a faster pace.
  • The best part about RO system is that all the pollutants are not collected but directly flushed down the drain.The RO system is best for areas having hard water which is less turbid.

Disdvantages of RO

  • Minerals like iron, magnesium, calcium and sodium are larger in size than water molecules, the semi-permeable prevents them from passing on to the other side thus rendering water de-mineralised which is good for the health and it might leave water very tasteless.The healthy minerals which are removed along with the process will turn water acidic and drinking it will not help maintain the ideal slightly alkaline pH of blood.
  • The RO membrane fails to remove any dissolved salts ions or particles that are smaller in size as compared to water molecules. Volatile organic chemicals (VOCs) such as chlorine, chloramines, pharmaceuticals etc are not removed in this process.
  • It is expensive to use an RO water purifier as it runs on electricity which is important to build the water pressure required for reverse osmosis.
  • It requires regular cleaning and maintaining.
  • There is a lot of water wasted during the process of purification. Approximately for one gallon of water almost three gallons are wasted.

Solutions to the disadvantages : The water wastage is a problem in most RO systems still but some of them have come with storage solution which stores the water collected after the process and used for cleaning and other purposes. The RO process has been improved over the years and have come come up with this 5 stage purification method which takes care of the residual problems. Also a system is in place to preserve the natural and require minerals like calcium, magnesium, sodium etc.

Ultraviolet water purifier

How do UV water purifier work?

UV water purifier system

UV-C (100-280nm) is the short length electromagnetic rays which are used in the process of water purification for the last 25 years or so for its germicidal properties. It is easy,clean,safe methods of ensuring that water is bacteria free. UV-C rays (photons) penetrate microorganisms and becomes absorbed by the DNA of the pathogen in the water being treated. The DNA is altered in such a way that the pathogen cannot reproduce and is essentially killed and cannot cause infection. This process of DNA modification is called inactivation. Process is simple but effective, destroying 99.99% harmful organisms without adding any chemicals to the water. It is important to filter the water before applying the UV radiation to it, the dirt and debris which makes the water turbid will interfere with the mechanism of UV-C.

Advantages of UV

  • There is no addition of harmful chemicals like chlorine, so there is no risk of overdose or the danger of the byproducts of the chemical used. This also makes it very environmental friendly.
  • UV does not change the taste, odour or colour of the water.
  • Unlike chlorine, UV systems are effective against both Cryptosporidium and Giardia.
  • More effective against viruses than chlorine.
  • There is no waste of water in the process of UV purification.
  • UV systems are capable of treating variable amounts of water with minimal amount of space with the only maintenance being an annual lamp and filter replacements.
  • It is an immediate process and so need to hold tanks or long retention of water.
  • It is compatible with most other water purifications processes like RO, UF etc.

Disdvantages of UV

  • This methods will not work in turbid water. The suspended particles will shield the organisms from the radiation, a pre-filtration process is there for required if the water is turbid.
  • ron, calcium or manganese, if present in water will cause the staining around the bulb sleeve and will interfere with its efficacy and therefore the water softening will be require in these cases.
  • Humic and fumic acids as well as tannins will reduce the amount of UV energy available to penetrate through the water to affect the genetic material or DNA of the molecule.
  • Temperature is an important determining factor. The optimal operating temperature of the UV lamp must be near 40 degrees C or 104 degrees F. UV levels will fluctuate with excessively high or low temperature levels.
  • There is no residual treatment unlike chlorine where it stays in water and continues to disinfect the water, where as the UV is in the water only during the contact time.

In a typical operation, water enters the inlet of a UV lamp and flows through the annular space between the quartz sleeve (which contains the germicidal lamp) and the outside chamber wall. The irradiated water leaves through the outlet nozzle. Several design features are combined to determine the dosage delivered: 1. Wavelength output of the lamp. 2. Length of the lamp - when the lamp is mounted parallel to the direction of water flow, the exposure time is proportional to the length of the lamp. 3. Design water flow rate - exposure time is inversely related to the linear flow rate. 4. Diameter of the purification chamber - since the water itself absorbs UV energy, the delivered dosage diminishes logarithmically with the distance from the lamp. In a typical operation, water enters the inlet of a UV lamp and flows through the annular space between the quartz sleeve (which contains the germicidal lamp) and the outside chamber wall. The irradiated water leaves through the outlet nozzle. Features to look for: 1. Expandable system - parts should be as uniform and as interchangeable as possible to permit easy expansion later. 2. Sight port - enables visual monitoring of lamp operation; also permits later adaptation to electronic monitor device using the same port. 3. Single lamp per chamber - provides greater safety through more accurate monitoring than does a multi-lamp /single-chamber system. 4. Quartz protection sleeve - cold water moving past an unshielded lamp will reduce the lamp temperature and the radiation yield. A protective quartz sleeve will allow the higher lamp temperature required for optimum output of 2537 Å radiation. 5. Mechanical wiper - for cleaning the sleeve surface without shutdown or disassembly of the unit. 6. Optional accessories - Flow controls, UV light bulb monitor, electronic water shut-off valves and alarms, should be available to provide fail-safe operation without operator attendance. A single lamp purifier can be designed to handle any flow rate up to approximately 2400 gallons per hour (gph). By multiplying purifier units, in series and in parallel, higher flow rates can be achieved.

Ultrafiltration water purifier

How do UV water purifier work?

UF water purifier system

The pollution of fresh surface water and the increasing demands with regard to health and the quality of our water magnify the availability problem and hence water purification and recycling will play a key role in the future of our planet's health and prosperity. Need of the hour is developing economical, easy to use and robust technologies to recycle the fresh water. Ultrafiltration/Membrane filtration is one of the most promising technologies that has emerged in the past decade covering all these requirements. It is usually abbreviated as "UF". In this technology, a membrane with pore size between 1-100nm is used to separate suspended solids, colloids, bacteria and viruses.

DIFFERENCE BETWEEN RO AND UF:

RO requires electricity to create pressure, where as ultrafiltration can work well with normal tap water pressure or minimum pressure. RO is suitable to remove the dissolved salts where as UF can not remove the dissolved salts.

Advantages of UF

  • No need for chemicals (coagulants, flocculates, disinfectants, pH adjustment etc)
  • -Will provide purification even in case of absences of electricity.
  • -Exclusive UF water purifiers are very compact and very mobile.
  • -Good and constant quality of the treated water in terms of particle and microbial removal.

Disadvantages of UF

  • Ultra- Filtration simply cannot eliminate any dissolved inorganic substances from drinking water.
  • To maintain a significant pressure movement, frequent cleaning is necessary.
  • Effective when preceded by carbon adsorption or when coupled with other purification strategies like RO and UV methods.

Solutions to the disadvantages : The water wastage is a problem in most RO systems still but some of them have come with storage solution which stores the water collected after the process and used for cleaning and other purposes. The RO process has been improved over the years and have come come up with this 5 stage purification method which takes care of the residual problems. Also a system is in place to preserve the natural and require minerals like calcium, magnesium, sodium etc.

Introduction of the different purifying methods

Due to the pros and cons of Ro, Uv and UF there are water purifying system on the market which combine succesful the different technologies. How can I know as a customer which product besides capacity, price, design fits for me. RO systems work fine when the water consumption of a household/company is high. expensive, maintenance for chaging filters, a hole must be drilled into the wall because they are countertops, slow flow rate removes contaminants, filters are long lasting, coffee tastes good how it works: has multiple filters plus the ro membrane