RO systems
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Reverse osmosis (RO) purification involves forcing water through a semi-permeable membrane to remove minerals and other impurities.[1] Water moving across the membrane from high salt concentration to low concentration is the reverse of natural osmosis. To achieve this, pressure must be applied, usually 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.[2] An RO system typically removes at least 90% of the dissolved solids.[3][4][5][6] Usually only around 20% of the feed water is captured as filtered water in a home RO system (i.e. for every 1 gallon collected, 4 gallons go down the drain); this may be a concern in areas there water availability is limited and/or disposal is problematic or expensive.[5][7]
Terminology:
Permeate - The purified water that passes through the RO membrane.
Concentrate - The waste water that does not pass through the RO membrane. It contains relatively higher amounts of dissolved solids (e.g. salts).
Recovery rate - The percentage of permeate collected from the water entering the system.
Rejection rate - The percentage of dissolved solids removed by the filter.
Total dissolved solids (TDS) - The mineral content of the water, expressed as parts per million (ppm, which is effectively the same as mg/L).
Products
Below we compare RO systems without water storage tanks. All systems include tubing, housing wrench, and drain saddle (attaches the waste water tubing to a sink drain pipe).
| Product | Stages | Features |
|---|---|---|
Buckeye Hydro Premium RO System |
|
Includes:
Many options and other accessories are also available. |
| Buckeye Hydro Value RO System |
|
Includes:
|
| Bulk Reef Supply RO System |
|
Includes:
|
| APEC RO-CTOP Countertop (Amazon) |
|
Includes:
|
It is also possible to build a RO system from scratch if you want to go through the effort of sourcing all the parts for it and assembling it yourself. Most of the above suppliers sell the parts, and you could save some money this way. Housings and filters come in standard sizes.
...
- https://spectrapure.com/ (and here - affiliate)
- http://www.premierwatersystems.net/
- https://airwaterice.com/
- https://www.uswatersystems.com/
- https://www.marinedepot.com/aquafx-dolphin-reverse-osmosis-system-100-gpd - affiliate
System components
Filters
The typical RO system first passes water through a particle filter and then through a carbon filter before the RO membrane. These pre-filters help remove organics, chlorine, and chloramines, which would otherwise harm the RO membrane.[4] Therefore a typical RO system treating chlorinated water contains a default configuration of 3 stages:[8]
- Sediment filter
- Carbon block
- RO membrane
Sediment filters remove particulates from the water, which prolongs the life of other filters. Sediment filters come in a variety of pore sizes rated in microns. The smaller the pore size, the more effective they are at removing particulates. 5 micron is about the largest pore size that should be used.[6]
Sediment Filter reduces sand, silt, sediment and rust that affect the taste and appearance of the water.[9]
Carbon block filters mainly serve to remove chlorine from the water, which prolongs the life of the RO membrane. However, carbon blocks are not very effective at removing chloramine. If there is a lot of chloramine in the water, an additional carbon filter designed specifically for chloramine removal may be necessary.[6][8]
Carbon Block filters reduce chlorine, taste and odor problems, particulate matter, and a wide range of contaminants of health concern -- cysts (cryptosporidium and giardia), VOCs (pesticides, herbicides, and chemicals), certain endocrine disrupters, Trihalomethanes (cancer-causing disinfection by-products), heavy metals (lead, mercury), turbidity, MTBE, Chloramines and asbestos[9]
FYI, granular activated carbon (GAC) should be avoided as a pre-filter. A carbon block will typically offer much better performance at only very marginally increased cost.[8]
Also FYI, the sediment filter and carbon block do very little to remove dissolved solids, so they do not affect the TDS significantly.[10]
The RO membrane is the workhorse of the system; it removes the dissolved minerals and other contaminants from the water.[10] There are two types of common RO membranes: thin film composite (TFC) and cellulose triacetate. TFC has a higher rejection rate. Filters have different production flow ratings, e.g. 75 gallons per day (284 liters per day). Higher production rated membranes have a slightly lower rejection rate. For this reason, it's best to size your system as small as possible while being able to keep up with demand. Keep in mind that unless the working conditions of your system are the same as the manufacturer specifications, the actual production speed will be lower than the stated production rating. The two most important factors affecting production speed are water pressure and water temperature. For example, FilmTec™ membranes are specified at 77°F (25°C) and 50 psi.[8][11] Colder water and/or lower water pressure will result in slower production. There's a calculator here (Buckeye Hydro) to help predict the effects of these factors.
Thin Film Composite (TFC) membrane is made of a a synthetic material, and requires chlorine to be removed before the water enters the membrane. Chlorine will cause irreversible damage to a thin film membrane element and for this reason, carbon filters are used as pre-treatment in all residential reverse osmosis systems using TFC membranes. A Thin film membrane has a higher rejection rate (95-98%) and longer life than the CTA membrane.[9]
If you want to make water on brew day, you could go for a fast membrane like a 100 gpd element. In most cases you'll get about 3 gallons per hour from that membrane.[12]
A deionization (DI) stage can be used to completely remove all minerals from the water. This technically isn't a filter, but rather it works by utilizing ion exchange resins for both anions and cations. Very few people use a DI stage for brewing because it's not worth the added expense.[8]
A taste and odor filter after the RO stage may be helpful if you have a pressurized storage tank.[8]
To-do: Filter housings
Bells and whistles
- Pressure gauges
- Inline TDS meters
- Pumps
Tanks and plumbing in contact with the filtered water should be plastic because the purified water is highly corrosive.[5] If metal must be used, stainless steel is preferred. This includes any pump fittings that will be in contact with the water for extended periods.[13]
Tri-color Pressure Gauge lets you know when the sediment and carbon block filters need to be changed. By reading the pressure differential between the local source supply line and the output of the filter media this gauge indicates when the filter cartridges need replacing.[9]
Float Valve monitors the water level in an RO reservoir to automatically shut off the RO water feed to prevent overfilling. It works in the same way your auto sparge arm works in a mash lauter tun. Once the RO water feed has been shutoff the automatic flush control will run for about 30 seconds before shutting off the local water supply.[9]
Automatic Flush Control system (AFC) is used to periodically rinse the accumulated impurities and concentrated waste water from the surface of the RO membrane to help increase the life of the membrane. The AFC will flush the membrane for a short period at start-up, every hour during operation, and at shut-down.[9]
Auto Shut Off valve stops the flow of water from the local water supply line when the output of RO water is stopped, this saves a lot of water.[9]
- Pressure gauge should be added after the pre-filters.[12]
- Booster pump should be added between the carbon block and the RO membrane, rather than before the entire system.[12]
Collection and storage
The RO membrane cartridge has a housing with a small outflow orifice to limit the waste flow and create a high pressure on the membrane. The pure water that is forced through the membrane is then collected in a separate vessel.[5]
To-do: Open vessels vs pressurized vessels
To-do: Float valves
A 14 gallon pressure tank is appropriate if you want to store 6 to 8 gallons of RO water.[12]
A few things to consider regarding pressurized storage tanks:[8]
- The price and physical size of the tank.
- The water from a full tank is less pure than the water straight from the RO membrane.
- A pressure tank decreases the recovery rate.
- A pressure tank decreases the production speed.
To-do: Drainage
Installation
To-do: Source water plumbing
If you have a water softener, it's best to install the RO system after the softener. In other words, feed the softened water into the RO system. This improves performance.[12]
Measuring and adjusting recovery rate
A simple way to determine system performance is by measuring (not estimating), the ratio of permeate to concentrate: Line up 6 to 8 identical cups in front of your RO system outputs (Solo cups work great). With your waste water tube in one hand, and your RO water tube in the other, determine how many cups are filled with concentrate in the time it takes to fill one with permeate. If it's more than 4, then a tighter flow restrictor would be beneficial. Fortunately, the flow restrictor is inexpensive and easy to switch in most systems (e.g. Buckeye Hydro).[14]
Maintenance
Regular maintenance will extend the life of your system and ensure that it continues to produce high quality water.
Replacing filters
Replacing pre-filters regularly is necessary to protect the more expensive RO membrane. Fortunately, filter and housing sizes are standardized. Nearly all residential RO systems are designed to utilize 2.5 inch diameter x 10 inch length filters.[10]
Sediment filters should generally be replaced every 6 months, or according to the product specifications. However, the actual lifespan varies depending on the source water quality and how often the system is being used. If you would rather be more precise about when to replace it, use a pressure gauge after the pre-filters. When the pressure begins to decrease, it's time to replace the pre-filters.[6][10] If your system has a pump before the RO membrane, it needs to be turned off to appropriately measure the pressure.
Carbon blocks are rated by the volume capacity of water from which chlorine can be removed. This can range from a few hundred gallons up to 20,000 gallons. Keep in mind this refers to the total amount of water passed through the filter, including the concentrate and not just the permeate collected. For best results, the carbon block should be replaced after it has filtered 50% of the stated capacity.[6][10][12] Manufacturers recommend flushing new carbon block cartridges for at least 10 minutes before using the product water . Don’t run flush water through other stages in your system. This is especially important if you are using catalytic granular activated carbon (CGAC) to treat chloramines.[10]
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 meter should be used to compare the permeate TDA to the source water TDS.[12] Allow the system to run for a few minutes before checking. If you have a pressure tank, the TDS of the permeate needs to be measured with the pressure tank valve closed. Membranes commonly produce purified water more slowly as their function declines.[10] Also be aware that the TDS of the permeate tells you nothing about the condition of your pre-filters or when to change them.[8] If the system is well-maintained and the pre-filters are consistently replaced on time, the RO membrane should last at least a year, and possibly up to 5-10 years.[6] See TDS testing. Manufacturers recommend flushing new RO membranes for up to 40 minutes to remove preservatives before using the product water. Don’t run flush water through other stages in your system.
If your system has a DI resin, it usually has a visual color-change indicator to help determine when it needs to be replaced. However, or is still highly recommended to monitor TDS before and after the DI resin, as well as the source water.[10] A poorly functioning RO membrane will quickly expend the DI resin.
In summary, two tools are required for proper filter monitoring:[15]
- A pressure gauge after the pre-filters
- A TDS meter
Usage frequency
RO membrane manufacturers recommend that the system be used at least once a week to avoid biofouling from microbe growth in stagnant dechlorinated water.[15][8]
Cleaning
The carbon block removes the chlorine that protects the water from microbial growth. Therefore the RO membrane, cartridges, and purified water and anything else downstream from (and including) the carbon filter are all susceptible to accumulating microbes. As such, periodic cleaning of the system is recommended, along with regular use to avoid stagnant water. Additionally a final pass through a sterile filter or UV light sterilizer may be used if the water needs to be sterile (which is generally not necessary for brewing).[5][8]
Sanitize the entire system at least once per year, and wash and lubricate the housing o-rings with food-grade silicone grease every filter change.[12]
See also
- https://www.buckeyehydro.com/ro-systems/
- https://www.buckeyehydro.com/faq/
- https://www.buckeyehydro.com/instructions/
- https://www.freshwatersystems.com/blogs/blog/what-is-a-reverse-osmosis-tank-and-how-does-it-work
- adjusting house water pressure
- more house water pressure info
- chlorine test strips
Photos
- https://www.homebrewtalk.com/threads/setting-up-ro-water.667227/
- https://www.homebrewtalk.com/threads/my-ro-system.666033/
References
- ↑ https://www.dupont.com/water/technologies/reverse-osmosis-ro.html
- ↑ https://www.dupont.com/content/dam/dupont/amer/us/en/water-solutions/public/documents/en/45-D01504-en.pdf
- ↑ Kunze W. Hendel O, ed. Technology Brewing & Malting. 6th ed. VBL Berlin; 2019.
- ↑ a b Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. Handbook of Brewing. 3rd ed. CRC Press; 2017.
- ↑ a b c d e Palmer J, Kaminski C. Water: A Comprehensive Guide for Brewers. Brewers Publications; 2013.
- ↑ a b c d e f Reverse osmosis guide. HomeBrewTalk.com. 2012.
- ↑ Eumann M, Schaeberle C. Water. In: Bamforth CW, ed. Brewing Materials and Processes: A Practical Approach to Beer Excellence. Academic Press; 2016.
- ↑ a b c d e f g h i j Guide to reverse osmosis systems for homebrewers. HomeBrewTalk.com forum. 2018–2019.
- ↑ a b c d e f g Pure brewing water using reverse osmosis. The Screwy Brewer. 2014.
- ↑ a b c d e f g h FAQ. Buckeye Hydro. Accessed October 2020.
- ↑ Dow FilmTec home RO membrane elements. Applied Membranes Inc. Accessed September 2020.
- ↑ a b c d e f g h Reverse osmosis filtration system. HomeBrewTalk.com forum. 2019.
- ↑ RO systems cost effective? HomeBrewTalk.com forum. 2019–2020.
- ↑ RO water filter? HomeBrewTalk.com forum. 2018.
- ↑ a b Reverse osmosis equipment advice. HomeBrewTalk.com forum. 2017.