Water Treatment

In reality, it’s not very likely. Water, as they say, is the universal solvent. As it travels through the ground and to our taps, it picks up different types of contaminants that can cause a problem. As a result, water quality varies dramatically around the world, and each problem may require its own solution.

Understanding water treatment basics can help you make an informed decision with your water treatment professional.

Simply put adsorption involves the adhesion of contaminants to an adsorbent material. Activated carbon is very often the material used. It is effective against some organic chemicals, hydrogen sulfide which is famous for giving water a “rotten egg” smell, and, of course, residual chlorine. So, one of the most common applications is in pitcher-style kitchen filters. Unfortunately, activated carbon can make a great home for bacteria, so this type of filter should only be used on bacteriologically-safe water.

The goal of disinfection is to destroy or inactivate diseasecausing microbes like E.coli, Cryptosporidium, and Giardia. Disinfection techniques are either physical, like exposure to ultraviolet (UV) light, or chemical, like chlorine, ozone, or hydrogen peroxide.

Distillation is one of oldest and simplest water purification methods. It depends on the principle that water as a liquid carries all sorts of contaminants but water as a gas carries none. So just by applying heat to convert water to steam, the contaminants are left behind. Then the vapors are passed over cooling coils, condensing the water back to a liquid form. The resulting fluid is nearly pure water. Distillation is very effective but very energy inefficient and upfront costs can be prohibitive.  Furthermore, “…distilled water is now causing some controversy as some claim that it leaches minerals from the body and is overly acidic.”  Canadian Living

Filtration is the process of passing water through a porous material to remove suspended particles. The pore size of the filter will determine what gets rejected and what’s allowed to pass through. Very often, a sediment filter will be used as the first stage of water treatment, to remove the larger particles in the water, and may be followed by more refined filters. Pore size is typically measured in microns (µ).

Ion exchange is like the “swap meet” of water treatment. Water is passed over a resin bed that holds certain ions – particles that hold a charge. But that resin would prefer to swap for ions found in water. The classic example is a water softener, which is a cation (positive charge) exchanger. The softener resin bed is saturated with sodium ions but prefers the calcium ions that make water “hard”. So hardness ions are exchanged for sodium ions that stay in solution. Because iron in water is also positively charged, a water softener can be used for iron removal. This usually only applies to low levels of iron contamination. Check the manufacturer’s recommendations. An anion exchanger can likewise be used to remove negatively charged molecules like nitrates and tannins.

Health Canada has established a guideline for THMs of 0.1 milligrams per litre. The cancer risk at this level over a lifetime is considered extremely low. The guidelines for THMs and other chlorination by-products are currently under review by a task group whose work is coordinated by Health Canada.

Oxidation is really about transferring electrons from the unwanted molecule to the oxidizing agent. A common example in water treatment is the oxidation of iron changing ferrous iron (Fe 2+) which is soluble in water to ferric iron (Fe 3+) which is not. The ferric ions can then form compounds that precipitate and can be filtered out. In water treatment common oxidizing agents are chlorine, ozone, hydrogen peroxide, and oxygen itself.

In reverse osmosis, water is forced through a porous membrane (much finer than filtration) which traps larger molecules and dissolved ions. Reverse osmosis can remove dissolved ions, metals like arsenic, lead and nitrates, organic compounds like trihalomethanes (disinfection byproducts), and pesticides. However, the effectiveness of the RO system will depend on the type of membrane and overall operating conditions. Very often, additional stages of filtration are needed for best results. Because RO produces a high proportion of reject water, it is more practical (but still wasteful) for point-of-use applications rather than whole home treatment – RO typically produces 2-4 gallons of reject water for every gallon of treated water.