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The proper way to treat Arsenic in Drinking Water

The proper Way to remove Arsenic from Drinking Water

In one of our prior newsletters we have provided information on Arsenic (see article published on our web page) in general.

Since we feel there are still some misconceptions about the proper treatment of arsenic, we would like to take this space to explain some crucial considerations.

The first thing to notice is there are 2 types of arsenic, called Arsenic III (type 3 or arsenite) and Arsenic V (type 5 or arsenate). Arsenic V is basically oxidized Arsenic III and it is important to remember this for later! As well, when it comes to arsenic, on-site testing can provide some indication but in terms of a clear result, we would always recommend involving a lab for testing purposes.

Generally speaking, numerous ways of treating Arsenic can be taken into account. There are methods of adsorption, ion exchange, distillation and reverse osmosis.

Distillation is in most cases beyond most people’s budget and whereas an RO system does a good job, it usually comes down – again a price-related matter – to a so called under-the-sink application, which is not necessarily geared towards taking out large amounts of Arsenic contamination over an extended period (unless you are prepared to change membranes very frequently) and the small RO constitutes a so called point-of-use (usually one designated faucet) rather than a point-of-entry (whole home) solution.

On the other hand, Arsenic – as long as the levels aren’t really high or someone has sensitive skin – usually can only do harm through ingestion and cannot be absorbed through the skin.

When it comes to treatment solutions, please allow us to spread a few words of caution with respect to the ion exchange method. A so called anion resin – recharged with Chloride, the second main component of salt (or with potassium chloride, another salt type with significantly less sodium content) – can treat Arsenic; but with limitations! By the way: If you buy a house and see a salt bin as part of a treatment system, do not just assume it is a softener, it could be a anion system.

An anion resin only takes out Arsenic V in the first place and since there is absolutely no ratio or formula that could be applied to find out the allocation of As III versus As V, this method is usable with slightly elevated levels of Arsenic in the water but still with the risk of leaving Arsenic III untreated in our most precious liquid.

At this point the logical question must arise, if it is not be possible to just oxidize Arsenic III and convert it into Arsenic V, thus having a chance to use anion resin as the usually less expensive option for treatment purposes.

Well, yes, it can be done but requires a strong oxidizer, such as chlorine, permanganate, ozone, chlorine dioxide, monochloramine, ultraviolet (UV) irradiation or Filox and potentially introduces substances to your water, which you would not like to see in there (e.g. potassium permanganate) or substances, which need to be removed afterwards again (chlorine) to provide good water quality and avoiding compromising possible other applications.

In other words: converting Arsenic regularly requires at least one more step in the equation. This adds expenses and all of a sudden, the next consideration – treating Arsenic through the use of an Arsenic specific adsorption medium – is not the most expensive solution any longer.

On top, there is something called the table of affinity, when using anion resins. This chart provides information as to what impurities in the water are attracted in which order by a specific resin under which circumstances. A regular anion resin attacks Uranium, Sulphates, Nitrates and Nitrites first, before it gets to the Arsenic (and then later to Fluorides and Carbonates). As such it is necessary to find out the concentration of other contaminants and water conditions (such as pH and alkalinity for example), before weighing your treatment options properly.

Adsorption media are more expensive than Anion resins. But – if it is the correct medium – a good adsorption medium removes type 5 and most of type III Arsenic, while at the same type converting more from Arsenic III into As V. On top they are regularly just backwashed with water and do not need salt as aregenerant. And yet, the beads (the small parts of resin medium inside a tank), still require some charging or coating in order to work properly.

On the other hand, when putting in a filtration system with an Arsenic-specific medium, knowing the other parameters in your water is crucial. Sulphates, silica, phosphates and fluorides for example all can have a negative impact on the efficiency and life expectancy of an adsorption-type medium.

But as long as the even more expensive solutions of distillation or whole-home RO are not an option, specific adsorption resin to attack both types of Arsenic right at source, is the proper way to go, when it comes to whole home applications.

One final word of caution with respect to boiling alerts: In certain areas in our province, there might be seasonal boiling alerts. Be aware that since Arsenic III is considered “metallic Arsenic” (rather than elemental Arsenic) boiling the water will increase the relative level of Arsenic.

So if you know, there is Arsenic in your water supply – even if a boiling alert is open (which usually is meant to deal with bacteria in the water) – please refrain from boiling your water in hopes to remove any Arsenic.

Thank you for your interest. For any further questions, please contact our office.

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