Rethink-Reverse-Osmosis

At WQA Aquatech 2014 in Orlando, two good friends of mine received well-deserved awards for their long-time selfless service to the water treatment industry. Chubb Michaud and Robert Slovak have given much to our ever-improving industry and while listening to Robert’s acceptance speech, I began to think about how far residential reverse osmosis drinking water purification has come in the last thirty years and how we can save the planet by installing Reverse Osmosis purifiers.

 

History

While small-scale reverse osmosis purifiers had been available since the 1960’s, Robert and his brother introduced affordable “fresh-squeezed” reverse osmosis water to residential consumers in the United States during the “Me!” era of the 1980’s. During that decade, regular Gasoline cost about a dollar per gallon, and few people gave any thought to how important it would be to provide affordable purified water to all homes.

The first residential reverse osmosis systems leveraged proven membrane separation technology that had already been used in industrial and military applications. The axial-wound CTA (Cellulose Tri-Acetate) membrane allowed for a compact form-factor. An automatic shut-off valve reduced waste, and a hydro-pneumatic storage tank allowed for simple storage and re-pressurization of purified water. The average system produced a whopping 17 gallons per day, at an average recovery rate of about 10 percent.

Competition quickly spurred innovation, and many enhancements to the art trickled into the marketplace, such as Thin Film Composite (TFC) membranes, quick-change filter housings, and water-on-water tanks.

Now, as we approach the middle of the second decade of the 21st century; the global water “crisis” is well underway with no conceivable end in sight. Whether you choose a pragmatic or emotional view of water scarcity, a clear conclusion is that we must be more careful in preserving precious clean water resources.

 

Technology

I’d be remiss if we didn’t take a moment to discuss how a typical residential undercounter reverse osmosis system operates.

The raw water is passed through multiple filtration stages. The filtration stages will typically include gross particulate filtration, activated carbon absorption/adsorption, and fine particle filtration. The goal is to reduce oxidants and also particulates larger than 5 micron in size to protect the membrane. A current trend among high-efficiency RO designs is to Prefilter using an Ultrafilter that protects from submicron solids as well as microorganisms that could foul the membrane.

After Prefiltration, the water is forced against a semi-permeable membrane, where impurities as small as 0.0001 micron in diameter are rejected and flushed to drain as part of the cross-flow effect that helps to keep the membrane pores clean. A drain restrictor controls the exact flow rate at which cleaning water is discharged. This discharge rate affects the rate of pure water production, as well as the projected longevity of the membrane. Smaller drain orifice sizes result in higher concentrate pressure. The higher the influent water pressure, the higher the rate of permeate flux through the membrane. If pressure is raised by restricting the discharge rate below manufacturer’s recommendations, the membrane can foul and fail prematurely.  Adding an influent pressure boosting pump is a standard technique for safely raising the rate of purified water production.

Naturally, since the water is being forced through extremely tiny pores, there is a significant loss of flow and pressure across the membrane, so the permeate water usually needs to be stored and re-pressurized before use.  Storage can be either pressurized, or atmospheric. Atmospheric storage tanks have a greater potential for microbiological contamination, so appropriate precautions should be taken to keep the water clean and safe.

Most good Reverse Osmosis systems will also include post-storage filtration to further “polish” the water and remove potential tastes and odors from storage. The final polishing filters are usually a cheap-effective granular activated carbon cartridge that has a long working lifespan and is economical to replace.

 

Waste?

Many well-meaning environmental activists denigrate Reverse Osmosis systems as “wasteful”, since water is used to clean the membrane/s and then discharged to drain. Because of this misinformation, some plumbers and dealers refuse to install them, for fear of contributing further to the rampant wastefulness that is endemic in the United States.

I don’t like the negative description of drain concentrate water as “waste water”, since it really is not. It is far better to discharge water through an efficient RO, than frequently replacing membranes with their associated production footprint.

Saying that a Reverse Osmosis purifier wastes water is akin to saying that an apple tree dropping its unpicked over ripe fruit is wasteful. The over ripe fruit returns nutrients to the earth and feeds the tree, which then grows more fruit. Discharge water from an RO is not “lost forever”, and will return through the household drainage system to a municipal plant, or back to the earth in an off-grid application. We can’t be blind to the “opportunity cost” of the purified water though, since it has to be pumped, stored, treated and distributed before it enters the RO appliance.

Since the discharge from a reverse osmosis processor is sanitary potable water (This is not considered wastewater, as it is never in contact with soils, dirt, or biological contaminants, it is merely concentrated clean water), the opportunity cost of the reverse osmosis discharge can be recovered through the use of some simple techniques:

-Car Washing –RO discharge can be stored and used to wash cars without feeling guilty about wasting water. Naturally, this water has an elevated level of Total Dissolved Solids (TDS), so it should be wiped dry by hand.

-Greywater – RO discharge can be routed to the household Greywater processor where it can be stored, pressurized and reused for toilet flushing and other code-approved Greywater applications.

-Surface Watering – If the local climate permits, the RO discharge can be routed directly to the garden with the use of an appropriate air gap. Many dealers will simply pipe the RO discharge into the home’s existing rainwater harvesting system with excellent results.

 

Innovation requires imagination

A lot of dealers that I coach are particularly innovative in the things that they add to their RO installations:

Alkalinity and ORP Changing Filters – Exotic media cartridges can be added to purified water systems that raise alkalinity and develop a negative ORP in the water. While you may or may not agree with the suggested health-benefits of these products, your client might want it and you should be able to help them.

Flavor – Flavor concentrates adding cartridges are available in certain markets that can add a variety of fruit flavors to purified water.

pH Neutralizers – When routing RO water to icemakers, hot water dispensers, and beverage makers, one runs the risk of exposing the metallic surfaces to water that could be corrosive. A simple solution is to introduce alkalinity with a food-grade neutralizer cartridge.

Multiple-use applications – Homeowners will often want to use their centralized RO processor for more than just drinking water and ice. A common application is to manifold and separate the drinking fixtures from an aquarium filler that is polished with a mixed-bed deionizer cartridge.

Water features – Many homes include water features, and waterfall-style humidifiers. These are inevitably problematic when fed with hard water, and even soft water. Reverse Osmosis water is becoming the water of choice for these fixtures.

Rethink RO

Don’t shy away from recommending reverse osmosis purification systems for your clients, it is still the most economical purification technology out there. In this new millennium, cities have less resources and employees available to clean the water that they provide, and we are continually being informed about a multitude of synthetic and organic emerging contaminants that are in aquifers and rivers. These emerging contaminants are usually most economically removed by a properly designed Reverse Osmosis System. Your clients deserve the best water at the very best price.