The benefits of a POU/POE reverse osmosis (RO) system in a home or business are widely known among consumers today. With a population that is more focused on health and wellness than ever before, it has become easier to sell the benefits of an RO system to this type of consumer. Where difficulties arise, however, is with the health-conscious home- or business-owner who is also concerned with environmental health or cost effectiveness of a treatment system. This consumer will know that some RO systems can require a lot of energy and waste a significant amount of water in the long-term.
Fortunately, the newest low-energy (LE) and low-pressure (LP) membrane options for the residential and commercial sectors can alleviate some of these concerns. Customers can reduce their energy use and see a host of other benefits while still getting quality water for their home or business with today’s membrane technology. Experts in membrane and membrane system manufacturing put their fingers on the pulse of membrane technology’s constant evolution to tell us what dealers need to know now to please the modern end-customer.
The changing face of membrane technology
While the trends of demand in the water treatment industry may change on a day-to-day basis, it takes a lot longer for the technology to catch up. The highly complex development of membrane material dictates the efficiency of an entire POU/POE system. Nevertheless, experts have seen significant changes within the past five years.
“The biggest difference that we see in the residential market space in the last five years has been the advent and acceptance of a two leaf element,” says Chris Sacksteder, associate product director, reverse osmosis at Dow Water & Process Solutions. “The original RO elements had just one single leaf of membrane. The state-of-the-art right now is to have two leaves of membrane per element, which gives you a more efficient element, tends to lead to longer element life and we are able to get higher rejection, so higher contaminant removal.”
Membranes are measured by flow rate (gallons per day – gpd) and pressure (psi). The psi indicates the pressure that is necessary to achieve the flow rate associated with that particular membrane.
While flow rates for the residential market can range from 24 all the way up to 100 gpd, according to Sacksteder, the lowest membrane option available on the residential membrane market is 50 psi, according to Henry Avina, sales manager at AXEON Water Technologies. Other common test rates for membranes in the residential market are 60 or 65 psi.
Typical operating pressures for commercial membranes range from 225 to 150 or 100 psi, according to Avina, but the lowest on the market for the commercial sector, where LP and LE can make a significant impact, is 80 psi.
“I think it was a significant leap just going from 150 psi to 100 psi,” notes Avina. “When I had first started in water treatment 15 years ago the standard was 225 psi, then they came out with 150 psi commercial membrane, then from there it went down to the 100 psi and from there we developed the 80 psi membrane. So, there have been significant changes in just the 15 years I’ve been in water treatment; who knows what's next?”
The need-to-know basics
Although 50, 60 and 65 psi are the basic test standards for residential membranes today, those measurements do not determine the feed water pressure a system must be run with, according to Avina and Sacksteder.
The test psi indicates that to achieve the gallons per day the membrane is tested for, you need to use that specific pressure. Avina used the example of a 50 gpd membrane tested at 50 psi; to achieve 50 gpd, you should operate it at 50 psi. The membrane, however, will still perform at other pressures.
“Unfortunately, there's no industry standard on what the test pressure is to test the flow rate. And so…we use 50 psi, some competitors will use 60 or 65. [However,] when people compare flow rates, it's important for them to look at the test conditions that the flow rate is measured at,” advises Sacksteder.
Dealers must also be cognizant that LP and LE membranes are not suitable for all applications, although they are adequate for most.
“[Low-pressure and low-energy membranes] can change the water quality slightly,” explains Avina.
High rejection membranes that produce the best water quality, with 99 to 99.5 percent rejection of the total dissolved solids, operate at a high pressure of 225 psi. The applications for these membranes are few and far between, according to Avina, who referenced pharmaceutical manufacturing as an industry that might require the highest purity water. The standard low-energy membrane, however, produces anywhere from 98.5 to 99 percent rejection — a slight difference, but suitable for most applications.
What’s in it for the consumer?
There are many benefits of LP and LE membranes for both residential and commercial customers. First, there are the general benefits of any water filtration membrane technology, which includes getting higher purity water for drinking and cooking but also the convenience of having the system in the house or business and being able to stop buying bottled water or five gallon water cooler systems. According to the experts, undeveloped areas of the world see more benefits from LP and LE systems in the residential sector than countries like the U.S.
“In more developed areas like the United States [and] Western Europe, where we have good infrastructure, you'll typically have in a home a line pressure coming out of a faucet of 40, 50 or 60 psi. When you go to some lesser developed and more rural areas, the line pressure there could be as low as 15 or 20 psi. They don't have as much pressure to drive the water through the membrane [and] that's [why] they're looking for lower pressure and lower energy membranes,” adds Sacksteder.
“These systems go all over the world, and there are so many variables out there … you want to start out with the lowest energy membrane,” says Avina.
But there are also significant benefits to both the residential and commercial sectors in the U.S. In the residential space, since the feed pressure is usually a set number that is not adjustable, having the lowest possible pressure rating for a membrane can be beneficial with other variable factors — for example, temperature.
“Temperature greatly affects a membrane's ability to produce water. The typical standard for testing a membrane is 77º F, so when you say a membrane can produce 50 gallons per day at 50 psi that's with an assumption of the77º F water,” notes Avina. “If you end up with 50º F water, that actually cuts the membrane's ability to produce in half.”
With the lowest energy membrane, whatever your customer's home’s feed water pressure may be, the temperature will not impact the system’s production as much. So ultimately you’ll get a more productive system with a lower energy membrane, according to Avina.
In the commercial space, many businesses use booster pumps to achieve a certain feed water pressure. The low-pressure membranes require less energy because you can run the pump at a lower pressure; which in turn puts less pressure on the system and the piping, extending its life cycle, Avina explains.
“Basically, if you've got a membrane that requires lower pressures to operate, you can significantly reduce the size of the pump, which will draw less energy,” adds Avina.
A membrane that requires less pressure can produce more water with the same amount of pressure being applied and consumes less energy because you can use a smaller pump, Avina continues. This can affect the cost-per-gallon of water you’re producing, especially in commercial settings. In many commercial settings, according to Avina, the 80 psi membranes can even be run on feed water pressure, without any pump.
In summary, more water production, less energy output and lower costs of production are the three main benefits of LP and LE membranes.
New frontiers in membrane efficiency
Membrane technologies in development now are building on the two-leaf element design described by Sacksteder, which he believes can give some scaling resistance, leading to a longer element life and possibly higher recovery.
“That's important to homeowners because the higher the recovery, the less water they're paying for, the less water they're having to discharge and the more water they're actually getting to use in their drinking or cooking,” says Sacksteder. “Some of those advances we think will also increase the life of the element. So over the course of a 10 year system life, we may be able to cut the number of elements that are purchased and then thrown away in half to the homeowner. And, you look at it on a global scale, millions of elements are being thrown away every year, and if we can have some impact on reducing the number of elements that are thrown away every year we think that it would have a good sustainable impact.”
There is also a great demand for even lower energy and lower pressure membranes, and Avina predicts seeing a membrane rated as low as 60 psi for the commercial sector in the coming years.
While many of the newest LP and LE membrane technologies show the most dramatic benefits in the municipal and industrial sectors due to the scale of their water production needs, the commercial and residential customers can also benefit in many ways from the newest membranes by saving money and energy and increasing production.