RO systems: Difference between revisions

[[category:equipment]][[category:water]]

A home RO water system is a convenient way to obtain pure water that can be adjusted to serve as the basis for any style of beer or wine. Reverse osmosis (RO) purification involves forcing [[water]] through a membrane using pressure, which removes minerals and other impurities.<ref>[https://www.dupont.com/water/technologies/reverse-osmosis-ro.html Reverse osmosis (RO).] DuPont website. Accessed October 2020.</ref> The pressure required for this process is usually applied via municipal water pressure or sometimes with a pump. RO is a type of crossflow filtration, having two output streams: one with the purified water and one that carries away the waste water containing a high concentration of minerals.<ref name=filmtec>[https://www.dupont.com/content/dam/dupont/amer/us/en/water-solutions/public/documents/en/45-D01504-en.pdf FilmTec™ reverse osmosis membranes technical manual.] Dupont website. Updated April 2020. Accessed October 2020.</ref> The system typically removes at least 90% of the dissolved solids.<ref>Kunze W.  Hendel O, ed. [[Library|''Technology Brewing & Malting.'']] 6th ed. VBL Berlin; 2019.</ref><ref name=hob>Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. [[Library|''Handbook of Brewing.'']] 3rd ed. CRC Press; 2017.</ref><ref name=water/><ref name=hbtrog/> However, as little as 20% of the feed water may be captured as filtered water in a home RO system (i.e. for every 1 gallon collected, 4 gallons go down the drain); this can be a concern in areas where water availability is limited and/or water disposal is problematic.<ref name=filmtec/><ref name=water/><ref name=bmp5>Eumann M, Schaeberle C. Water. In: Bamforth CW, ed. [[Library|''Brewing Materials and Processes: A Practical Approach to Beer Excellence.'']] Academic Press; 2016.</ref>

Terminology:<br/>

'''Permeate''' - The purified water that passes through the RO membrane.<br/>

'''Concentrate''' - The waste water that does not pass through the RO membrane. It contains relatively higher amounts of dissolved solids (e.g. salts).<br/>

'''Recovery rate''' - The percentage of permeate collected from the water entering the system.<br/>

'''Rejection rate''' - The percentage of dissolved solids removed by the filter.<br/>

'''Total dissolved solids (TDS)''' - The mineral content of the water, expressed as parts per million (ppm, which is effectively the same as mg/L).

==Best RO systems==

[[File:Star-6-16.png|left]] Editor's pick

# FilmTec™ RO membrane, 24–100 gpd

# TFC RO membrane, 100 gpd

# TFC RO membrane, 90 gpd

Summary of our selection criteria:

** No GAC or "combination" pre-filters

*No unnecessary stages like multiple carbon blocks or DI resin

*Flush valve (highly recommended)

*Pressure gauge (recommended)

*Clear standard housings (recommended)

Activated carbon removes many unwanted compounds from the water, but most importantly it [[chlorine removal|removes the chlorine]] that would otherwise harm the RO membrane.<ref name=filmtec/><ref name=specman/> Three forms of activated carbon filters are seen in water filtration systems: granulated activated carbon (GAC), carbon block, and catalytic carbon.<ref name=ndsu/>

GAC should be avoided as a pre-filter. A carbon block will typically offer much better performance at only very marginally increased cost.<ref name=cbtech>[https://www.carbonblocktech.com/carbon-filter-buyer-guide/ Carbon block filter buyer's guide.] Carbon Block Technology website. Accessed October 2020.</ref><ref name=hbtguide/><ref name=ndsu/><ref>[https://www.waterfiltershop.co.uk/blog/granular-activated-carbon-filters-vs-carbon-block-filters/ Granular activated carbon filters vs carbon block filters.] Water Filter Shop website. September 2016. Accessed October 2020.</ref><ref>[https://www.epicwaterfilters.com/blogs/news/carbon-block-water-filters-vs-granulated-active-carbon-water-filters Carbon block water filters vs granulated active carbon water filters - which is better?] Epic Water Filters website. December 2018. Accessed October 2020.</ref><ref>[https://rajahfiltertechnics.com/water-filtration/granular-activated-carbon-vs-activated-carbon-block-water-filters/ The difference between granular activated carbon and activated carbon block water filters.] Rajah Filter Technics website. Updated April 2018. Accessed October 2020.</ref>

Every RO system should contain a carbon block. Pore size typically ranges from 0.5 to 10 microns. Smaller pores remove chlorine and other compounds more effectively and provide greater protection to the RO membrane, with 0.5 micron being the most superior by far.<ref name=bhfaq/><ref>[https://spectrapure.com/collections/filters/products/0-5-micron-carbon-block-filter-10-inch-l-x-2-8-inch-dia-cf-0-5-10 0.5 micron carbon block filter 10".] SpectraPure website. Accessed October 2020.</ref> Carbon blocks are also sometimes rated by the volume of water that can pass through before they need to be replaced.<ref name=cbtech/> This can range from a few hundred gallons up to 20,000 gallons. Be wary if the filter doesn't specify this! Carbon blocks are not very effective at removing chloramine, especially filters with pores larger than 0.5 micron.

Many RO systems on the market contain multiple larger-pore carbon pre-filters +/- post-filters. They intend to trick you into thinking that the extra stages are better, but really they just want to sell you a more expensive system and more replacement filters. Just one quality (small-pore) carbon block is needed. Surface area of the carbon block increases exponentially with smaller pore size, so for example, in theory it would take '''a hundred''' 5 micron carbon filters to provide the same performance as a single 0.5 micron carbon filter!!

Catalytic carbon is an advanced activated-carbon product designed to remove chloramines. If there are chloramines in your water, a catalytic carbon filter stage must be used because chloramines will damage the RO membrane and potentially cause off-flavors in your brew (see [[Chlorine removal]]).<ref name=hbtrog>[https://www.homebrewtalk.com/threads/reverse-osmosis-guide.678265/ Reverse osmosis guide.] HomeBrewTalk website. 2012. Accessed October 2020.</ref><ref name=hbtguide/> Catalytic carbon also removes [[hydrogen sulfide]] gas, which produces the "rotten egg" smell in some well water and can impair RO membrane performance.<ref name=ndsu/><ref>[https://www.lenntech.com/Data-sheets/Filmtec-Water-Chemistry-Feedwater-L.pdf Water chemistry and pretreatment: treatment of feedwater containing hydrogen sulfide.] Dow Tech Manual excerpt. Accessed October 2020.</ref><ref>Boyle N, Ghiu S, Levitus N. [https://www.hazenandsawyer.com/publications/the-use-of-catalytic-gac-for-removal-of-hydrogen-sulfide-in-groundwater/ The use of catalytic GAC for removal of hydrogen sulfide in groundwater.] Hazen and Sawyer website. May 2016. Accessed October 2020.</ref>

The RO membrane removes dissolved minerals and other contaminants from the water.<ref name=bhfaq/> There are two types of RO membranes: thin film composite (TFC) and cellulose triacetate (CTA). TFC is preferred because it has a higher rejection rate and longer lifespan.<ref name=screwy>[https://www.thescrewybrewer.com/2014/07/pure-brewing-water-using-reverse-osmosis.html Pure brewing water using reverse osmosis.] The Screwy Brewer website. July 2014. Accessed October 2020.</ref><ref>[http://www.advancedwaterfilters.com/buying-guide-reverse-osmosis-systems/ Buying guide: reverse osmosis systems.] Advanced Water Filters website. Accessed October 2020.</ref><ref>Sagle A, Freeman B. [https://www.twdb.texas.gov/publications/reports/numbered_reports/doc/R363/C6.pdf Fundamentals of membranes for water treatment.] ''The future of desalination in Texas.'' 2004;2(363):137.</ref> FilmTec™ membranes for example are among the most reliable and consistent TFC elements in the industry.<ref name=ami/> Be wary when purchasing a system if it doesn't specify what type of membrane is included.

Home RO membranes have different production flow (flux) ratings that indicate how quickly purified water is produced, typically ranging from 24 to 100 gallons per day (gpd). Lower flux membranes have a higher rejection rate, and the lower flow rate also improves the effectiveness of the carbon filters due to longer contact time. For these reasons, it's best to choose the lowest flux membrane that can keep up with demand. Be aware that the actual performance of your system won't exactly match the manufacturer flux rating because your system will have different operating conditions from factory specification.<ref name=filmtec/><ref name=ami>[https://www.appliedmembranes.com/filmtec-membranes-residential-home-ro-membranes.html Dow FilmTec home RO membrane elements.] Applied Membranes Inc. website. Accessed September 2020.</ref>

A DI stage contains an ion exchange resin; it can be used to remove minerals that the RO membrane failed to reject. Systems with this stage are called "RODI". Very few people use a RODI system for brewing water because it's not worth the added expense and maintenance—the low amount of dissolved minerals remaining from a functional RO system will have no significant impact on the brewing process.<ref name=hbtguide/>

A carbon post-filter is often suggested to help to improve the taste of drinking water.<ref name=hbtguide/><ref>Woodard J. [https://www.freshwatersystems.com/blogs/blog/stages-of-reverse-osmosis-systems Stages of reverse osmosis systems.] Fresh Water Systems website. October 2017. Accessed October 2020.</ref> However, a high-quality carbon block pre-filter plus low-flux RO membrane combined with proper maintenance should allow the system to effectively remove basically all of the offensive volatile organic compounds. Therefore a carbon post-filter will be generally unnecessary on a quality system, even for drinking water. However, in-line GAC post-filters can easily be added or removed if needed based on your particular water and RO system. GAC is often used as a post-filter because high performance isn't needed at this stage, and also the contact time will be significantly longer compared to the pre-filter, which increases the effectiveness.

Single-use housings (e.g. {{amazon|B00IB14XDU|APEC Countertop system - Amazon}}) are another gimmick designed to increase price (and brand loyalty) with no added value for the customer. They're arguably no more convenient than standard filters and yet you will pay much more money for replacement filters and have fewer options for specifications. Even with disposable housings, the system still needs to be cleaned periodically.

A pressure gauge can still be installed even if you already purchased a system without one. Example: [https://www.buckeyehydro.com/pressure-gauges-1/ Buckeye Hydro pressure gauge kits]

A Total Dissolved Solids meter (which actually measures water conductivity and merely estimates TDS) is an essential tool for monitoring RO membrane performance. Some systems offer inline TDS monitoring for convenience, but using a handheld meter is also perfectly fine. See [[TDS testing]] for meter recommendations; they are inexpensive and very easy to use.

A flush valve temporarily allows a higher flow of water through the system to flush minerals and organic contaminants (including microbes) away from the RO membrane. Periodic flushing is important for proper system maintenance and longevity of the RO membrane (see the maintenance section below). Therefore a flush valve is highly recommended, either manual or automatic.

As the name implies, a manual flush valve must be opened and closed by hand whenever you need to flush the system. It's easy—just turn the valve 90°, but you need to remember to do it.

An automatic flush control system fully automates the flushing process. Depending on the product, it can flush the membrane for a short period at start-up, every hour during operation, and at shut-down.<ref name=screwy/> Keep in mind this device requires power to operate, unlike the rest of a basic RO system.

A flush valve can still be installed even if you already purchased a system without one. Example: [https://www.buckeyehydro.com/membrane-flush-kit/ Buckeye Hydro flush kits]

There are two different kinds of pumps that may be used in an RO system, each for a different purpose:

If your water line pressure is too low for the system to operate efficiently (i.e. under 40psi), then a "booster pump" should be used to increase the water pressure on the RO membrane. It should be added between the carbon block and the RO membrane, rather than before the entire system.<ref name=hbtrofs/> Also see the Optimization section below.

If you are using a pressurized storage tank, a permeate pump is highly recommended. This device helps pump the permeate into the tank and will dramatically improve system performance. It does not require electricity to operate since it utilizes the hydraulic power from the waste water.

Collection in an open (unpressurized) vessel simply requires placing the end of the permeate tubing into whatever vessel you want to fill with water, such as plastic water jugs. You will need to manually turn off water flow to the RO system when the vessel is full. The obvious major downside to this method is that the vessel will overflow if it runs for too long. A simple solution to avoid problems in that case is to place the collection vessel in a sink, in a tub, on the ground near a drain, or outside (weather permitting). Setting a timer is a good idea since it can predict when the vessel is full very accurately once you know the production speed of your system.

If you prefer to have the system shut-off automatically when the vessel is full, you can use a dedicated vessel with a float valve installed. The float valve will shut off the permeate flow when the water fills to the level set by the valve (similar to how a toilet tank works). In this setup, an automatic shut off valve (ASOV) is also needed to shut off the flow of water from the feed water supply line; otherwise water would continue to flow down the drain after filling stops.<ref name=bhfaq/><ref name=screwy/> Additionally, a check valve is needed to prevent backflow through the RO membrane.<ref name=buckeye>[https://www.buckeyehydro.com/content/3_Stage_RO_System.pdf Understanding and operating your new reverse osmosis system (premium series RO system instructions).] Buckeye Hydro website. Accessed October 2020.</ref> Keep in mind that tanks and plumbing in contact with the filtered water should be plastic (or lined with plastic) because the purified water is corrosive to metal.<ref name=water/> If metal must be used for the collection vessel, [[stainless steel]] is preferred.<ref>[https://www.homebrewtalk.com/threads/ro-systems-cost-effective.670740/ RO systems cost effective?] HomeBrewTalk website. 2019–2020. Accessed October 2020.</ref>

Here we have a few tips for installation.

Don't leave the system in direct sunlight. It may overheat or encourage algae growth (particularly in systems with clear housings).<ref name=specman/>

A more permanent solution is to use a "drain saddle". This simple device secures the concentrate tubing to a drain pipe below a sink, in which you have drilled a 1/4" hole.<ref name=buckeye/>

If you need/want to increase your line pressure, you can install a booster pump between the pre-filters and RO membrane. Example: [https://www.buckeyehydro.com/booster-pump-kits/ Aquatec 8800 booster pump from Buckeye Hydro]. If your water comes from a municipal source, another option is to increase the water pressure for the whole house. This is controlled by a pressure regulator on the water line coming into your house, which is simple to adjust.<ref>Becker N. [https://www.popularmechanics.com/home/how-to/a1053/4202333/ Homeowners clinic.] Popular Mechanics website. November 2006. Accessed October 2020.</ref><ref>[https://www.plumbingsupply.com/residential-water-pressure-explained.html Residential water pressure explained.] March 2017. Accessed October 2020.</ref> Be wary that excessively high pressure on the entire house can put extra strain on plumbing—consult a professional.

If more than 4 cups of concentrate are produced for one cup of permeate, then a tighter flow restrictor would be beneficial. The flow restrictor is inexpensive and easy to replace in most systems.<ref>[https://www.homebrewtalk.com/threads/ro-water-filter.646093/ RO water filter?] HomeBrewTalk website. 2018. Accessed October 2020.</ref> For systems with pressurized tanks, a permeate pump would greatly improve the recovery rate. Example: [https://www.buckeyehydro.com/aquatec-permeate-pump/ Aquatec permeate pump]

Other factors like water temperature and source water TDS can also affect performance, but aren't so easy to control.<ref name=filmtec/> For example, water temperature is one of the most important factors affecting performance.<ref name=hbtguide/> Colder water and/or lower water pressure will result in slower production and lower recovery rate. Buckeye Hydro has a [https://www.buckeyehydro.com/calculator/ calculator] to help predict the effects of various water temperature and pressure combinations. If your source water has very high TDS (lots of calcium in particular), a water softener may be something to consider to help improve performance and prolong the life of the RO membrane.

Regular maintenance will lower the operation cost, extend the life of the system, and ensure that it continues to produce high-quality water.

[https://www.bulkreefsupply.com/insta-test-free-total-chlorine-strips-lamotte.html.html LaMotte chlorine test strips] (free and total chlorine) - Bulk Reef Supply

The RO membrane is the most expensive part of the system. It must be replaced when the rejection rate begins to decrease, which usually corresponds to an increased TDS. For monitoring, a [[TDS testing|TDS meter]] should be used to compare the permeate TDA to the source water TDS.<ref name=hbtrofs/> Allow the system to run for several minutes before checking. See [[TDS testing]]. Be aware that membranes commonly produce purified water more slowly as their function declines.<ref name=bhfaq/> Also be aware that the TDS of the permeate tells you nothing about the condition of your pre-filters or when to change them.<ref name=hbtguide/> If the system is well-maintained and the pre-filters are consistently replaced on time, the RO membrane should last several years.<ref name=filmtec/><ref name=hbtrog/> New RO membranes must be flushed for at least 60 minutes to remove preservatives before using the product water. Don’t run flush water through other stages in your system.

Every RO system is under constant threat of excessive microbial growth and/or mineral concentrate forming a biofilm or mineral scale respectively.<ref name=flemming>Flemming HC. [https://www.researchgate.net/profile/Hans-Curt_Flemming/publication/289774253_Biofouling_on_Membranes_-_A_Short_Review/links/5779259108ae1b18a7e61f1a.pdf Reverse osmosis membrane biofouling.] ''Exp Therm Fluid Sci.'' 1997;14(4):382–391.</ref> Both of these can result in significantly decreased system performance (i.e. "fouling" of the membrane).

The simplest way to prevent RO membrane fouling is by regular use of a flush valve. Ideally it should be at least flushed every day, but at least once every 1–2 weeks may be acceptable in home systems.<ref>[https://www.homebrewtalk.com/threads/reverse-osmosis-equipment-advice.599894/ Reverse osmosis equipment advice.] HomeBrewTalk website. 2017. Accessed October 2020.</ref><ref name=hbtguide/><ref name=fws/> It should be flushed for around 15–30 seconds periodically during use and immediately after each use (ideally until concentrate TDS matches feed water TDS). Short flushing intervals are more effective than long flushing times—flushing for 30 seconds every 30 minutes is better than flushing for 60 seconds every 60 minutes.<ref name=filmtec/>

Along with regular use or flushing of the system to avoid stagnant water, it's generally recommended to wash and sanitize the entire system at least once per year.<ref name=water/><ref name=hbtguide/><ref name=hbtrofs/><ref name=fws>Woodard J. [https://www.freshwatersystems.com/blogs/blog/sanitize-water-filtration-systems-after-a-shutdown How to sanitize your water filtration systems after a shutdown.] Fresh Water Systems website. May 2020. Accessed October 2020.</ref><ref>[https://www.espwaterproducts.com/how-to-sanitize-a-reverse-osmosis-system/ How to sanitize a reverse osmosis (RO) system.] ESP Water Products website. Accessed October 2020.</ref><ref>Fitzgerald G. [https://www.best-osmosis-systems.com/ro-clean-sanitize/ How to sanitize a reverse osmosis system + RO tank cleaning guide.] BOS website. August 2020. Accessed October 2020.</ref> Cleaning may also be considered when the the system shows decreased flux or decreased rejection rate, rather than simply replacing the RO membrane.<ref>[https://www.lenntech.com/cleaning-ro-systems.htm Cleaning of a RO system.] Lenntech website. Accessed October 2020.</ref> Sanitation alone is not effective; the system must first be cleaned.<ref name=flemming/>

==See also==

*[[Chlorine removal]]

 

 

==References==