Regardless of whether it is in the eyes of a company or an individual, waste is never well perceived. In the different industrial environments, several types of resources are used and these represent important costs. This is why it is sometimes beneficial to invest in infrastructure that allows the reduction of costs associated with the use of different resources used in your processes.

In short, the purpose of this article is to present a technique for treating the concentrate from a reverse osmosis process in order to allow for maximum reuse.

Water is scarce and expensive resource

Although very efficient, Reverse Osmosis systems require a very large quantity of water to supply the users' needs. Typically, reverse osmosis systems offer a 75/25 ratio, which means that 75% of the incoming water can be used while the remaining 25% is the concentrate and is sent to the drain. These ratios can be adjusted depending on the water and contaminants. For example, if the feed water is very clean, the ratio can be adjusted to decrease water losses, 80/20 for example. On the other hand, if the water contains a high concentration of silica, the ratio may need to be adjusted to decrease the concentration of the concentrate to avoid membrane fouling (60/40).

The water waste generated by these permeate/concentrate ratios is immense and it is no understatement to say that water is a limited and important resource. Not to mention that its use can sometimes represent exorbitant costs. Depending on your location, water costs vary greatly.

For example, in Toronto in 2022, when you use less than 1,099,850 gallons, the cost is $0.01994045/gal. Above that, the cost per gallon is $0.01395781. To highlight what these costs represent, let's imagine this situation.

Your company has a reverse osmosis system with a flow rate of 80 gallons per minute (gpm) with a 80/20 ratio. This means that the system spends 20 gallons per minute to provide the 80 usable gallons. Operating 8 hours a day, 5 days a week year-round. That's an annual total of 12,480,000 gallons of water used by your reverse osmosis system alone. In cost, this represents a grand total of $180,773.48 annually.

Optimized Use of Your Water

In an effort to reduce water consumption and save money, and as mentioned above, the permeate/concentrate ratio can be adjusted under certain conditions. However, this is not always possible. Since in the above situation, the rejection rate is already very low, it would be difficult to decrease waste even further.

To put this in perspective, the losses associated with the 80/20 ratios in the current situation represent approximately 2.5 million gallons of water over a one-year period. Using the lowest cost, this represents an annual loss of approximately $35,000.

With the objective of reducing these relatively important financial losses, at Durpro, we propose an alternative solution allowing to recover up to 25% of concentrate.

• Before going any further, although 25% may seem low, in the situation used, it represents some 625,000 gallons of water or nearly $9,000 annually.

In short, one of the solutions offering an interesting return on investment consists of adding a second, smaller reverse osmosis unit that allows the reuse of a fraction of the concentrate that would normally have been rejected. In addition to offering an interesting return on investment, the addition of a second reverse osmosis reduces water waste.

This diagram represents, in a very simplified way, the principle of adding a second reverse osmosis system in order to reduce water losses.

An ecological return on investment

Using the above example of an 80 gpm reverse osmosis system, the addition of a second 20 gpm reverse osmosis system would allow the reuse of 25% of the concentrate from the first osmosis system.

Therefore, by saving 625,000 gallons of water per year, without taking into account future increases in the cost of water, and by installing a 20 gpm reverse osmosis system, estimated at +/- $50,000 with annual operating costs approaching $1,000, here is an approximation of the investments versus the expenses associated with the addition of this type of system.

Even if this table is very simple and these are only estimates, in a situation exactly like the one described above, the return on investment would be in about 6 years.

A beneficial addition

Obviously, the above estimates only reflect the situation described above. It is therefore important to note that the variations in return on investment can be major. The changes can come from the fact that the GPM produced is not the same, the variable cost for the use of the water or the type of contaminants in the water.

• To learn more about the factors that can affect the acquisition and operational costs of an industrial water treatment system, we invite you to visit this article.

Although the costs associated with the installation of a second reverse osmosis system can vary greatly, in Canada, the return on investment caused by the addition of this type of system is generally advantageous since the use of water in the industrial sector can represent significant costs. Not to mention the various advantages that companies with ecological practices have (corporate image, social value, environmental awareness, etc.).