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, and in some cases up to 100%.<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).

[[File:RO-filtration.png]]

[[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)

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!!

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/><ref>[https://www.homebrewtalk.com/threads/my-ro-system.666033/ My RO system.] HomeBrewTalk website. 2019. Accessed October 2020.</ref>

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 combined with a low-flux RO membrane along 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 performance. GAC is acceptable as a post-filter because high performance isn't needed at this stage, and also the contact time in a post-filter is significantly longer compared to a pre-filter, which increases the effectiveness.

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 increases the longevity of the RO membrane and can improve system performance (see the maintenance section below). Therefore a flush valve is recommended to ultimately reduce maintenance costs, either manual or automatic. However, it is an optional component and a system will certainly function without regular flushing.

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.

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

The simplest way to prevent RO membrane fouling (thereby significantly prolonging the lifespan of the RO membrane) is by regular use of a flush valve.<ref>[https://www.marinedepot.com/aquarium-reverse-osmosis/upgrades-and-add-ons/flush-valves Flush valves for RO systems.] Marine Depot website. Accessed 2020.</ref><ref>[https://www.bulkreefsupply.com/membrane-flush-valve.html Reverse osmosis membrane flush valve.] Bulk Reef Supply website. Accessed 2020.</ref><ref>[http://www.purewateroccasional.net/hwautoflush.html How reverse osmosis flush valves work.] Pure Water Gazette How It Works Series website. Accessed 2020.</ref><ref>[https://www.purewaterproducts.com/img/docs/manuals/FLEXEON-210-LT-SERIES-USERS-MANUAL.pdf Reverse osmosis user's manual.] Pure Water Products. 2012.</ref><ref>[https://www.yourhealthywatersource.com/product-page/ro-membrane-flush-valve-john-guest-mur-lok-fittings RO membrane flush valve (John Guest/Mur-Lok Fittings).] Jett Water Systems website. Accessed 2020.</ref><ref>[https://www.condair.com.ar/m/0/2594385-a-ro-u-installation-manual.pdf Reverse osmosis system | Installation, operation, and maintenance manual.] Conair. 2018.</ref> 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/> Note that flushing can cause a small spike in TDS of the permeate if it continues to flow (depending on your water pressure). It's best for the flush water to also bypass the DI stage, if present.