You have probably heard about reverse osmosis as part of your science lecture in school. But what does it really mean? What is reverse osmosis? Well, for starters, it is a process that can help in removing inorganic solids or contaminants that already dissolved in a solution.
What happens is that the household water pressure thrusts the tap water through a semipermeable membrane. As a result, impurities or pollutants, like chloramine, fluoride, lead, detergents, sulfates, and nitrates are now removed from the water, giving you a safe and clean drinking water.
Reverse osmosis is also generally used for producing energy, treating waste water and recycling. So with this, it has become beneficial in dealing with water issues that have developed into pressing worldwide threats.
Currently, climate change has become a cause for unfortunate environmental effects like heavy flooding, droughts and rise and fall of sea levels. There is the risk of overpopulation as well, which can result in water being an ultimate environmental issue to emerge in the following years to come.
By looking at what reverse osmosis can do, it is not surprising that this procedure is among the mainly pursued solutions in the future.
Thus, it is only fitting to explain it in more details. For one, reverse osmosis simply means doing osmosis in reverse or the opposite way. Osmosis does not require any energy to work. So the opposite of this means you need to exert energy, especially to the more saline solutions.
As mentioned earlier, a semipermeable membrane exists that allows the passage of water molecules, except for most organics, bacteria, pyrogens and dissolved salts. There needs to be a strong energy or pressure to be applied in order to push the water through the membrane.
To add, the energy or the pressure must be greater than the osmotic pressure that is occurring naturally so that the contaminants are held back while pure water freely passes through.
There is also a similar membrane process to reverse osmosis (RO) called nanofiltration (NF). And actually, there are five membrane procedures all in all that are normally used in producing drinking water.
Aside from RO and NF, there are microfiltration (MF), ultrafiltration (UF) and electrodialysis/electrodialysis reversal (ED/EDR). The thing is all these five are categorized as membrane procedures.
However, applications and technologies are extremely diverse in some circumstances. Generally, three groups exist that cluster the related membrane procedures: RO and NF, MF and UF and ED/EDR.
In clustering the said membrane processes, there are four reasons that separate one group from another:
- Membrane type
- Method of removing contaminants
- Procedure driving force
- Main application
MF and UF
These two processes are pressure-driven that utilize microporous membranes in eliminating contaminants like microorganisms and turbidity. They use a sieving mechanism on the basis of size omission. Ions and other dissolved constituents are not part of what they can remove from water.
However, there are UF membranes in industrial applications that help isolate organic molecules with high molecular weight from solutions. The only concern is that these membranes can’t be used for treating municipal drinking water because they are not commercially available.
RO and NF
Just like the previous membrane processes, these two are also pressure-driven. The difference is that they use a semipermeable membrane to mainly aim at the removal of contaminants dissolved in water. That is, through a diffusion-controlled separation procedure.
When there is high pressure applied to the membrane’s feed side, the water gets pushed through the membrane surface’s molecular structure. The dissolved solids like solutes, on the other, are hugely rejected.
ED and EDR
If the two groups above are pressure-driven, this pair is electrochemical charge-driven. What happens is that dissolved ions get separated via ion permeable membranes with the help of an electrical potential gradient. The ion permeable membranes can selectively transfer ions with a positive or negative charge and eliminate ions with the opposite charge.
Moreover, unlike MF and UF, these two membrane processes have been used for treating municipal water and wastewater as well as for desalinating reclaimed and brackish water.
Truly, it is a happy fact that there are different ways that water can be purified so humans can safely consume it. Cancer patients, for one, are very fortunate that these filtrations have been invented because drinking reserve osmosis water can keep them safe, given that they have weakened immune systems. All in all, reverse osmosis is definitely a useful process for purifying water.