You've probably heard of osmosis and reverse osmosis . Natural or forward osmosis is the type that commonly occurs in nature, primarily influenced by the presence of semipermeable membranes in cells. Whether in plant roots or human body cells, this phenomenon is essential for life. In fact, all cell membranes in biological organisms are semipermeable, allowing water to flow and maintaining a balance of certain nutrients. Beyond its natural function, the principles of osmosis are also applied in water purification technology using reverse osmosis, such as seawater desalination. In this article, we'll explain both concepts in detail.
What is osmosis and reverse osmosis?
When we have two solutions with different salt concentrations separated by a semipermeable membrane, a natural process tends to occur: water flows from the side with a lower salt concentration to the side with a higher concentration. This phenomenon is known as osmosis. The process continues until the concentrations on both sides are equal.
The human body, composed largely of water, naturally experiences osmosis as an integral part of many biological functions, from nutrient distribution to waste removal.
However, when it comes to desalinating water, such as seawater, this natural process is not useful, since we require reverse flow; that is, pure water must flow from the side with the higher salt concentration to the side with the lower concentration. For this, we need a process known as reverse osmosis , which requires the use of pressure to counteract the natural flow so that pure water passes through the semipermeable membrane, leaving behind the salts and other impurities.
This process is crucial today as it is used to produce drinking water from non-potable sources, and its best-known application is the desalination of seawater.
How does reverse osmosis work and what is its importance?
Reverse osmosis is based on reversing the natural osmotic process by applying pressure. Imagine a semipermeable membrane that separates a solution with a high concentration of salts from one with a low concentration. The objective of reverse osmosis is to allow water to pass from the solution with a high concentration of salts to the one with a lower concentration, generating cleaner water. To achieve this, we need a pressure that counteracts the natural osmotic pressure.
This process allows the removal of not only salts, but also other impurities, such as dissolved particles, heavy metals and bacteria, making water a purer product. It is relevant in many areas, but without a doubt, one of its greatest applications is the desalination of seawater to obtain drinking water in different parts of the world.
Reverse osmosis and water rejection
One of the main drawbacks of reverse osmosis is a phenomenon called water rejection . This refers to the fact that not all the water processed through the semipermeable membrane becomes clean water, as some of the water is discarded along with the impurities retained on the concentrating side of the membrane. Reverse osmosis membranes are designed to continuously clean themselves while operating, thus preventing them from becoming saturated with contaminants and suspended particles. However, this means that a considerable portion of the water, up to 60%, may be discarded as reject water, depending on the quality of the equipment and the type of water being treated.
In some advanced equipment, the ratio between product water (clean water) and reject water is more favourable, reaching 50%. Even so, the sustainability of this process remains a major challenge, especially in places where access to water is limited.
Furthermore, reverse osmosis membranes do not have an indefinite lifespan. Depending on the water quality and maintenance performed, a membrane can last between 3-5 years, although in domestic applications the period can be reduced to between 2-3 years. To prolong their lifespan, periodic maintenance is necessary, which usually involves cleaning with specialized chemicals to remove the buildup of dissolved solids that, over time, can clog the membrane.
How can the performance of reverse osmosis equipment be improved?
The good performance of reverse osmosis equipment depends on several key factors:
- Performing a correct pretreatment of the water before it comes into contact with the membrane. This involves removing as much suspended solids, impurities and other contaminants as possible. This can be achieved by installing sediment and activated carbon filters.
- Use of antifouling to prevent the accumulation of low-solubility salts such as calcium and magnesium, which can form deposits on the membrane surface.
- Realization of periodic cleanings of the membranes to maintain their optimal performance. Depending on the type of water to be treated, it will be necessary to use specific chemicals to descale or remove organic waste.
Preventive maintenance is crucial to avoid a significant reduction in equipment performance over time. Otherwise, reduced efficiency can translate into higher energy consumption and lower volumes of filtered water.
Osmosis filters in homes and their usefulness
Reverse osmosis filters are not exclusive to large-scale industrial or desalination applications. They are also available for use in homes, where they are used to purify water and improve its taste, especially in areas where water is hard or has a high chlorine content.
Using a reverse osmosis filter at home can remove both dissolved solids and organic impurities, significantly improving the quality of drinking water. However, many people opt for cheaper and more accessible solutions such as filter pitchers that use activated carbon filters to reduce these elements.
While a reverse osmosis filter can be a significant investment, for many people, simply letting the water sit for a while to allow some of the chlorine to evaporate is enough to significantly improve the taste of the water.
Ultimately, reverse osmosis is a highly efficient process for improving water quality. From industrial applications to domestic solutions, its versatility and ability to remove a wide range of contaminants make it an indispensable technology in water treatment globally.