There are advantages and disadvantages in every technology.
CASE STUDY: NEW DELHI.
The area where I stay in New Delhi,India, the ground water is contaminated because of Dirty Yamuna River flowing nearby. And there is no piped water from Govt. The only option for drinking is Domestic RO (10 LPH) at home or the 20 liter JAR supplied by PRIVATE water companies. And for all other purposes ,people are installing water softener in the bore well water..If they dont use water softener,then the domestic RO membrane gets damaged and is to be changed twice a year.
RO is the only technology which can remove Bacteria, Iron, fluoride, Arsenic and other chemical contaminants. Arsenic and other heavy metals in well water is one of the most dangerous aspects of drinking well water. So you should have a fail safe water purifier system for Arsenic by installing a Point of Use - RO water purifier in the kitchen where water for drinking and cooking is taken.Reverse Osmosis is though expensive, is available as domestic filter. Once the membrane is clogged, it cant filter water anymore, so you always get pure water. This is not so with any other technology.
What is the desirable quality of drinking water?
As per the Bureau of Indian Standards, the desirable quality of drinking water is that which has TDS (Total Dissolved Salts) content of 500 ppm or less (ppm stands for parts of the salt present in a million parts of water). Where water of this quality is not easily available, the compromise level is water having upto 2000 ppm.
It is to be borne in mind that in some places, iron salts may be present and if the content of iron salts is more than the permissible 0.4ppm, even if the total salt content is less than the desired level, the iron salts will have to be removed before drinking that water. There are also some pockets West Bengal and U.P. where the water contains Arsenic. This is poisonous and so here also the same rule applies. In some pockets again, fluoride salts may be present which affect the bones if that water is drunk. Using this water for non-potable purposes is however not harmful.
Another point to be remembered is that water with very low salt content is not very palatable and therefore where the total salt content is less than 500, reducing it to 10 or 20 by RO is not only meaningless from the point of view of wastage of water but also from the cost and loss of palatability aspects. In cases where the salt content is not much higher than 2000 ppm, a simpler route would be to harvest rainwater which will dilute the salts and bring it within potable limits progressively.
What is the Reverse Osmosis (RO) Process?
Reverse Osmosis (RO) technology has been used for years in various industries to separate dissolved solids from water by forcing the water through a semi-permeable membrane. RO is also commonly used to purify drinking water and desalinate seawater to yield potable water. The water and other molecules with lower molecular weight (specific weight of molecules allowed to pass through is dependent on the selected membrane) pass through the micropores in the membrane, yielding a purified water stream called the permeate. Larger molecules are retained by the membrane as well as a portion of the water that does not pass through the membrane. This concentrated stream is called the concentrate or RO reject.
While RO is an effective method for handling wastewater, what to do with the concentrate or reject water (typically as much as 20-40% of the RO feed water volume) can be an issue. Specifically, the high salinity in RO reject / RO concentrate can make it prohibitive for discharge to a local sewer facility. Hauling the wastewater to a treatment facility can also be prohibitively expensive.
What can we do with the RO reject water?
In RO systems of small capacity suitable for domestic purposes, the rejected component may be as high as 40%. The process therefore is a wasteful one with much of the water having to be thrown away.
Diverting large volumes of this highly salty water into the sewage line could result in acting against the smooth movement of its contents. The reject will not be tolerated by normal garden plants. It will form deposits on the floor and sanitary ware. It is also not advisable to divert it to the septic tank.
If the water subjected to RO has less than 1000 ppm say, then the salt content in the reject water will not be much and it can be used for gardening or flushing. But the point is that this water need not be subjected to RO at all in the first place.
In Industries, we treat RO Reject by Solar evaporation or Forced evaporation.
evaporation is a time-tested methodology for reducing the water portion of water-based waste.
Typical RO reject / RO concentrate TDS concentrations are often in the range of 30,000 – 50,000 mg/liter. The salts in solution can range from highly soluble sodium and potassium salts to less soluble or reverse soluble calcium and barium salts.
