In my opinion, the answer is generally no. Reverse osmosis, commonly referred to simply as RO, is not the right tool for most First Nations Water Treatment plants. While reverse osmosis is a very powerful technology, it is best suited to address the 2 issues for which it was originally designed:

  1. Desalinating brackish or sea water sources and
  2. Reducing specific chemical solutes such as Benzene, Magnesium Sulphate and other solute compounds.

The Reputation of RO

Reverse osmosis has a reputation as being the ultimate in water purification technology. This often stems from its use in military theatre. Military users may be deployed anywhere in the world and often need to be prepared to desalinate brackish or sea water sources. Reverse Osmosis Water Purification Units (ROWPU) are also designed to remove some pretty nasty chemical, biological, radiological, and nuclear contaminants (referred to as CBRN) but many of these contaminants are addressed within the ROWPU with specialized media and/or carbon based technologies, not the core reverse osmosis technology. Specialized media, granular activated carbon and even ultraviolet light disinfection are used to fill in the gaps that RO itself does not address. For instance, reverse osmosis may not sufficiently remove or reduce volatile chemicals such as MTBE, heavy metals like mercury, hydrocarbons such as benzene and toulene, chemicals pesticides and gasses such as radon. The following websites and articles are great references if you are looking for more information about what reverse osmosis can or cannot remove or a rate of rejection for a specific contaminant.

RO and Microbiological Contaminants

While reverse osmosis technically provides a mechanical barrier that is more than suitable for the reduction of biological contaminants such as protozoan cysts, bacteria and viruses, it is important to realize that most reverse osmosis membrane manufacturers have not performed testing and/or received certification for these contaminants and generally issue statements such as the following:

Notice: The use of this product in and of itself does not necessarily guarantee the removal of cysts and pathogens from water. Effective cyst and pathogen reduction is dependent on the complete system design and on the operation and maintenance of the system.

http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0660/0901b8038066098e.pdf?filepath=liquidseps/pdfs/noreg/609-00240.pdf&fromPage=GetDoc

Because RO membranes are subject to degradation and/or deterioration by sediment, chlorine and even bacteriological growth (we all know what happens to an old kitchen sponge), most manufacturers cannot provide a means of notifying end users should the membranes be compromised. For most drinking water applications, generally accepted practice is to provide an additional barrier for microbiological contaminants such as that provided by ultraviolet light and/or chlorination. Both of these technologies provide a means of testing and documentation to ensure that pathogens such as bacteria and viruses are no longer present.

Is low TDS water produced by reverse osmosis or desalination healthy?

Desalination and reverse osmosis water treatment systems produce water with such low levels of total dissolved solids (TDS) that it may adversely affect human health. The World Health Organization produced a report in 2004 titled “Health risks from drinking demineralised water which states the following:

  • It has been adequately demonstrated that consuming water of low mineral content has a negative effect on homeostasis mechanisms, compromising the mineral and water metabolism in the body.
  • Results of experiments in human volunteers evaluated by researchers for the WHO report (1980) are in agreement with those reported in animal experiments. Low-mineral water markedly: 1) increased diuresis (almost by 20%, on average), body water volume, and serum sodium concentrations, 2) decreased serum potassium concentration, and 3) increased the elimination of sodium, potassium, chloride, calcium and magnesium ions from the body.
  • When used for cooking, soft water was found to cause substantial losses of all essential elements from food (vegetables, meat, cereals). Since most nutrients are ingested with food, the use of low-mineral water for cooking and processing food may cause a marked deficiency in total intake of some essential elements that was much higher than expected with the use of such water for drinking only. The current diet of many persons usually does not provide all necessary elements in sufficient quantities, and therefore, any factor that results in the loss of essential elements and nutrients during the processing and preparation of food could be detrimental for them.
  • The corrosive nature of demineralised water and potential health risks related to the distribution and consumption of low TDS water has led to recommendations of the minimum and optimum mineral content in drinking water.
  • Demineralised water is highly aggressive and if untreated, its distribution through pipes and storage tanks would not be possible. The aggressive water attacks the water distribution piping and leaches metals and other materials from the pipes and associated plumbing materials.
  • Low-mineralized water is unstable and therefore, highly aggressive to materials with which it comes into contact. Such water more readily absorbs metals and some organic substances from pipes, coatings, storage tanks and containers, hose lines and fittings.
  • Demineralised water that has not been remineralized , or low-mineral content water in the light of the absence or substantial lack of essential minerals in it is not considered ideal drinking water, and therefore, its regular consumption may not be providing adequate levels of some beneficial nutrients.

http://www.who.int/water_sanitation_health/dwq/nutdemineralized.pdf

The High Financial and Operating Cost of Reverse Osmosis Water Treatment Plants

When used properly, there is no denying that reverse osmosis is a powerful water treatment technology. And while best suited to specific contaminants such as sodium and a selection of chemicals and heavy metals, it can be combined with microbiological disinfection to create a very advanced water treatment plant. However, most RO water treatment plants come with a high price tag, both financially and operationally as follows:

  • Higher capital and maintenance costs. I would suggest that a good rule of thumb would be 3x more expensive. This also holds true for capital costs as well as ongoing maintenance and repair costs including the advanced pre-filtration that RO requires.
  • Increased power consumption. Reverse osmosis systems use substantially more electricity than alternative solutions such as ultrafiltration (UF) and may also require significant upgrades to electrical panels, etc.
  • Increased cost associated with remineralization equipment. For long term use within water treatment plants, water produced by reverse osmosis should be re-mineralized as per the World Health Organization as discussed above. This can significantly complicate and increase overall capital and operating costs.
  • Most reverse osmosis systems are substantially larger and heavier than alternative solutions such as ultrafiltration (UF). Larger systems of course can increase secondary operating costs related to building design, electricity needs, HVAC, etc. while also requiring higher logistics and freight costs for delivery and commissioning.
  • Additional costs for microbiological disinfection. Most reverse osmosis systems will require secondary disinfection via UV light to meet potable water drinking standards.
  • Additional costs to accommodate high volumes of waste water. Most reverse osmosis systems have a recovery rate of 15-50% which means that for every 100 L of water going into the system, 50-85 L go down the drain as waste water or concentrate and only 15-50 L is kept as permeate or drinking water. If your water source is limited in quantity, RO may not be the best tool for you. Furthermore, if operating in a cold weather environment or an ecologically sensitive environment, the high output of concentrated waste water may be difficult to accommodate.
  • Additional costs required to heat raw water or purchase additional modules when faced with cold water sources. Most reverse osmosis systems have their output based on a feed water temperature of 25° C (77° F), a temperature rarely seen in First Nations lakes, rivers and wells. The rated output can drop by as much as 50% or more when faced with water sources close to freezing.
  • Increased health and safety costs and/or risk. Some reverse osmosis systems can have very high operating pressures, ranging from 200 , 800 psi. This can create potentially dangerous operating conditions in the event of a leak.

Summary

In my opinion, reverse osmosis is simply not the correct tool for the job when it comes to designing water treatment plants for most First Nations communities.

  1. Reverse osmosis was originally invented as a means of desalinating brackish or seawater sources and should be used as the tool for which it was intended.
  2. Contrary to its reputation, reverse osmosis does not remove 100% of all contaminants. Reduction rates vary widely depending on the contaminant in question with some such as Benzene, Cyanide, hydrocarbons, Mercury and pesticides not being removed at all. In fact, RO membranes can be damaged, destroyed or fouled by contaminants such as chlorine, iron and calcium, even sand.
  3. Again, contrary to its reputation, RO is not recommended as the only barrier against microbiological contaminants such as bacteria, protozoan cysts and viruses.
  4. According to the World Health Organization, low TDS water produced by reverse osmosis or distillation is not suitable for long term human consumption and in fact, can create negative health affects to those consuming it.
  5. Reverse osmosis water treatment plants can be expensive projects. From the initial purchase to operations, maintenance and even logistics, reverse osmosis systems and plants have substantially higher operating costs than alternative solutions such as ultrafiltration (UF).

What then is the correct tool for the job when designing or commissioning water treatment plants for First Nations communities?

In my experience, the ideal treatment chain for most First Nations water treatment plants is microfiltration (MF) based pre-filtration, inside-out (IO) ultrafiltration (UF), ultraviolet light (UV) disinfection (NSF 55, Class A) followed by granular activated carbon (GAC) and residual chlorination. In some instances we would also recommend an organic colour removal system for the reduction of specific organics such as naturally occurring tannins.

Global Hydration offers turn-key, skid mounted systems based on this treatment chain which can produce up to 70,000 L per day per module. What makes them unique is that they use zero disposable paper pre-filters, generally only require a Level 1 operator ticket, reduce turbidity to less than 0.1 NTU in most situations and operate with a maximum consumed power draw of only 2.5 kw. If your First Nations water treatment plant is reaching end of life or you are designing a new plant, please give Global Hydration a call or email to see if we can help. First Nations Water Treatment Plant.

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