Reverse osmosis (RO) is a water treatment process that removes contaminants from unfiltered water, or treated filtered water containing undesirable constituents or contaminants such as sediment, chlorine taste and odor, heavy metals, lead, etc. when pressure forces it through a semipermeable membrane. Water flows from the high concentration side (more contaminants) of the RO membrane to the low concentration side (fewer contaminants) to provide clean drinking water. The fresh water produced is called the permeate. The concentrated water left over is called the waste or brine. A semipermeable membrane has small pores that block contaminants but allows water molecules to flow through. Figure 1 demonstrates the working principle of reverse osmosis systems.
Figure 1 – Principle of Reverse Osmosis Systems (Source: ESP WATER PRODUCTS)
A RO system has a filter with a pore size of approximately 0.0001 micro which can remove contaminants as small as a molecule. It is considered an optimum treatment for removal of a wide range of common chemical contaminants in drinking water such as sodium, chloride, chromium, arsenic, copper, lead, fluoride, radium, radon, uranium, calcium, magnesium, potassium, nitrate, and phosphorus Reverse Osmosis Systems have a very high effectiveness in removing protozoa (for example, Cryptosporidium, Giardia), bacteria (for example, Campylobacter, Salmonella, Shigella, E. coli), and viruses (for example, Enteric, Hepatitis A, Norovirus, Rotavirus). RO systems are commonly used for reduction of total dissolved solids and suspended particles in drinking water. RO systems can vary depending upon the volume of water to be treated, contaminants to be removed, etc. However, most RO systems have a few common components as listed below:
- Prefilter – Typically a particle filter to remove particles, rust, and other debris.
- Possibly a water softener is the total hardness is elevated and a smaller diameter particle filter.
- RO treatment unit with treated water storage tank and a flush to waste line.
- Most treatments activated carbon filters.
- Post-treatment submicron filter.
MAINTENANCE AND REPLACEMENT OF RO MEMBRANES
A well-maintained RO system can last up to 10 to 15 years depending upon usage and type of contaminants treated. Some of the basic maintenance guidelines include:
- Regular Filter Changes
Pay attention to the filter change schedule in the RO system’s owner’s manual. The RO system may have three, four or five stages, so know exactly what filters are in each stage of the system (per the owner’s manual) and pay careful attention to when each filter is due for replacement.
- Sediment Filter: – sediment filter should be changed out every 12 months. This pre-filter stage is designed to strain out sediment, silt and dirt and is especially important as the sediment filter protects dirt from getting to the delicate RO membranes. If this filter is not changed on schedule, dirt and silt can reach the RO membranes which can then easily become clogged and foul.
- Carbon Filter: – the carbon filter is designed to remove chlorine and other contaminants that affect the performance and life of the RO membrane as well as the taste and odor of the water. This filter should generally be replaced every 12 months.
- Reverse Osmosis Membrane: the semi-permeable RO membrane in the RO system is designed to allow water through but filter out almost all additional contaminants. If care is taken to replace the previous sediment and carbon filters on schedule, the RO membrane should only need to be replaced every two to three years. The schedule will vary based on the quality of your water and household water usage.
- Polishing Filter: in a four-stage RO System, a final post filter will “polish” off the water to remove any remaining taste and odor in the water. This final filter ensures outstanding drinking water quality.
Failure to change out filters per their replacement schedule can not only cause damage to the system but will also cause a decrease in water production. Thus, if there is a noticeable decrease in water flow from the RO faucet, that may be an indication that the filters have reached the end of their life span.
Additionally, the following are the three main guidelines for replacing RO membranes
- time, often after 3 years (the membrane manufacturer’s warranty period)
- an increase in the RO permeate conductivity, as related to their water quality requirement
- a designated reduction in the permeate/product flow rate as related to water demand
SUMMARY
Reverse osmosis filtration system is one of the most extensive methods of filtration. It removes a broad range of contaminants such as total dissolved solids (TDS), chlorine taste and odor, organic compounds, sediment, and cysts, and a broad spectrum of drinking water contaminants. Sani Water is one of the exclusive consultants and experts on providing installation and maintenance services for whole house reverse osmosis systems.
REFERENCES
- Zheng, M., He, C., & He, Q. (2015). Fate of free chlorine in drinking water during distribution in premise plumbing. Ecotoxicology, 24(10), 2151-2155.
- Warsinger, D. M., Tow, E. W., Nayar, K. G., & Maswadeh, L. A. (2016). Energy efficiency of batch and semi-batch (CCRO) reverse osmosis desalination. Water research, 106, 272-282.
- https://www.freshwatersystems.com/blogs/blog/what-is-reverse-osmosis
- https://www.cdc.gov/healthywater/drinking/home-water-treatment/household_water_treatment.html#:~:text=Reverse%20Osmosis%20Systems%20will%20remove,potassium%2C%20nitrate%2C%20and%20phosphorous.
- https://water-research.net/index.php/water-testing/private-well-testing/reverse-osmosis
- https://www.espwaterproducts.com/understanding-ro/
- https://www.espwaterproducts.com/blog/how-to-maintain-your-ro-system-for-best-performance/
- https://www.wateronline.com/doc/when-to-replace-your-ro-membrane-0001
