Arsenic - Water Treatment

Are you worried about arsenic in your drinking water? Arsenic is a naturally occurring element that can be found in many types of rock and soil. Groundwater flowing through these materials dissolves the arsenic creating health risks for people who drink it. In the U.S., more than 3 million homes have high levels of arsenic in their water. Arsenic can take on various forms when it dissolves in water. Each of these different types of arsenic require different treatment methods. This article explains what the differences are between them and how to select an appropriate treatment method to remove each type of arsenic. We review all of the arsenic removal methods, explain how they work, present their pros and cons, and let you know which type of arsenic they are effective against. We include helpful tips and facts so you can make an informed decision about what method will work best for you and your family. If you want to learn more about removing arsenic from your drinking water, then read on! Arsenic in Drinking Water Arsenic is an abundant mineral that is found in soil, water and air. It has been detected in groundwater throughout the United States as the map below indicates. How does arsenic get into our water Arsenic is present throughout the environment. It is found in soils and rocks throughout the entire US. It can be released into the environment through weathering processes or human activities. The primary pathway for arsenic to get into our water supply is through groundwater flowing through these sediments. Arsenic can also enter surface water through runoff from these same sources. As the water remains in contact with arsenic-containing rocks, soils, and sediments, it dissolves this element. Over time, the arsenic levels can become very high. Eventually, the concentrations can reach the maximum levels possible, known as the solubility limit. Much of the drinking water in the United States comes from wells. These wells are drilled into aquifers, which are underground layers of water-bearing permeable rock. As water flows through the aquifer, it picks up naturally occurring minerals and contaminants, including arsenic. The amount of arsenic in the water can vary depending on the type of rock that the aquifer is made of and how long the water has been in contact with the rock. Public drinking water wells are regulated by the EPA. Private wells, however, are not regulated. It is up to the homeowner to have their water tested and to take steps to remove any contaminants. Different types of arsenic Elemental arsenic is insoluble - meaning it doesn't readily dissolve in water. There are two types of arsenic that can be found in water: Arsenite: Arsenic (III) or As (III) Arsenate: Arsenic (III) or As (V) These two types of arsenic are the same chemical compound - arsenic, but they behave differently in water. They have different solubilities (because of their oxidation state) and respond differently to the arsenic treatment methods. For this reason, it is important to know which type of arsenic is in your water. I'll explain this in more detail below when I review the arsenic treatment technologies. Concerns over arsenic Arsenic is a known human carcinogen. It is also associated with many other health problems. Long-term exposure to arsenic in drinking water is known to cause cancer heart disease high blood pressure skin lesions blood vessel damage nerve damage leading to numbness and pain interference with cell functions The US Environmental Protection Agency (EPA) established the maximum contaminant level (MCL) for arsenic at 10 micrograms per liter (μg/L), or 10 parts per billion (ppb). The MCL is the national drinking water standard, and it represents the highest concentration of arsenic that you can safely drink. How to Remove Arsenic from Drinking Water Arsenic in drinking water is a global problem. Fortunately, there are several methods for removing it. In the following section, we review seven of the effective arsenic removal technologies. We cover how they work, their pros and cons, and other important facts. Arsenic (V) can be filtered out of water much easier than arsenic (III). The methods listed below all work well for arsenic (V), but ion exchange and reverse osmosis are only partially effective for arsenic (III). 1 - Activated alumina Activated alumina is a type of adsorbent media that is made from aluminum oxide. It has a high surface area to weight ratio, which allows it to adsorb (or attach) arsenic molecules from water. It comes in pellets about the size of a pea that are placed in a vessel or housing. I It is also very stable, meaning it can be used over a long period of time without needing to be replaced. As water flows through the media, the arsenic is adsorbed to the pores in the activated alumina. Activated alumina is effective at removing both As (III) and As (V) from drinking water. This filter media also removes other contaminants such as fluoride and lead. 2 - Distillation Distillation is a water treatment technology that involves boiling water and then condensing the steam back into water. This process removes impurities, including arsenic, from drinking water. Distillation removes both As (III) and As (V) from drinking water. As water is heated to its boiling point, contaminants like arsenic are left behind. The steam that is produced is free of these contaminants and can be condensed back into clean drinking water. 3 - Iron oxide adsorption Iron oxide adsorption is a technology that uses granular iron oxide to remove arsenic from water. This media is usually formed into pellets. The pellets are placed in filter vessels or housings and contaminated water is directed over the media. Iron oxide is effective at removing both As(III) and As(V) from drinking water. It also removes other contaminants such as lead, mercury, and chromium. This filter media is relatively inexpensive and can be used for a long period of time without needing to be replaced. However, it does require regular Water flows through the media and the arsenic is adsorbed to the surface 4 - Reverse osmosis Reverse osmosis is a water treatment technology that uses pressure to force water through a semipermeable membrane. This process removes impurities, including arsenic, from drinking water. Reverse osmosis is effective at removing As (V) but it can only remove some of the As (III) from drinking water. A typical RO filter can remove about 40 - 75% of the Arsenic (III) from your water. If you have AS(III) in your water, you'll need to oxidize the arsenic to change it to AS(V) so your RO filter can remove it. Chlorine, ozone, or potassium permanganate can all be used to achieve this. Reverse osmosis is a popular technology because it is effective at removing a wide variety of contaminants from water. However, it does have some drawbacks. It wastes a fair amount of water because the concentrated brine is discharged down the drain. 5 - Ion exchange Ion exchange is a water treatment technology that uses resin beads to remove arsenic from drinking water. The resin beads are charged with positive ions (cations). When the beads come in contact with arsenic, the arsenic molecules attach themselves to the negative ions on the bead. Ion exchange is effective at removing As (III) but it is ineffective at treating As (V) from drinking water. A typical ion exchange filter can remove about 95% of the arsenic (V) from your water. Ion exchange is a popular technology because it is effective at removing a wide variety of contaminants from water. However, it does have some drawbacks. It requires periodic regeneration with salt, and it also wastes a fair amount of water. 6 - Coagulation with filtration Coagulation with filtration is a water treatment technology that uses coagulants (usually iron oxide) to clump arsenic particles together. The clumps become heavy and either settle out or are filtered out of the water. Coagulation with filtration is effective at removing both As (III) and As (V) from drinking water. This method is typically not used for residential treatment because it requires frequent adjustments to optimize the process and remove all of the arsenic. 7 - Oxidation with filtration Oxidation with filtration is a water treatment technology that uses chlorine, ozone, or potassium permanganate to oxidize arsenic (III) to arsenic (V). These chemicals are able to oxidize arsenic very quickly, even in a small reaction tank. Typically, filtering is done with either sand or a mix of sand and coal anthracite. Another filter media that works well is manganese greensand. These filters require backwashing to remove the accumulated solids. Oxidation with filtration is effective at removing both As (III) and As (V) from drinking water. This method is typically not used for residential treatment because it requires frequent adjustments and optimization to work well. Treatment Methods That Do Not Remove Arsenic from Drinking Water 1 - Activated carbon Activated carbon adsorption is a water treatment technology that uses charcoal to remove contaminants from water. While activated carbon is effective at removing many contaminants, it is not effective at removing arsenic from drinking water. This is because arsenic has a very low affinity for carbon's pores. 2 - Pitcher filters Most pitcher water filters do not remove arsenic from water. Several studies have been conducted, and they all conclude that pitcher filters that use activated carbon are ineffective at removing arsenic. PUR filters are not effective at removing arsenic from water. Similarly, Brita filters are not effective at r educing arsenic in water. Some pitcher filters, however, use activated alumina and they are very effective at removing arsenic from drinking water. The ZeroWater filter is able to remove as much as 90% of arsenic (V) and 85% of arsenic (III) from water. 3 - Water softeners Water softeners are ineffective at removing arsenic from drinking water. This is because they are designed to remove hardness minerals, not contaminants. While water softeners will not remove arsenic from your water, they can reduce hardness (calcium and magnesium) from your water. As a pre-treatment method, a water softener can enhance the performance of an arsenic filter and prevent fouling. Testing Your Water for Arsenic The only way to know for sure if your water contains arsenic is to have it tested. Arsenic testing is not typically included in routine water quality tests. You can, however, purchase an arsenic test kit or send a sample of your water to a laboratory for testing. Make certain the test measures both arsenic (III) and arsenic (V) because you'll need to be certain your treatment system can remove this contaminant. If you are on a private well, the Environmental Protection Agency recommends that you test your water for arsenic at least once a year. Check out My Tap Score for more information about testing your water for arsenic. Factors to Consider with Arsenic Treatment When selecting a treatment method for arsenic, there are several factors you need to consider. We present them in the following sections along with a detailed discussion. The quality of your water The treatment method you select should be able to meet the needs of your specific situation. For example, a small household with low levels of arsenic in their water would not need an expensive whole-house system. They could instead use a less expensive point-of-use (POU) treatment method like a reverse osmosis system or an arsenic removal filter. POU treatment methods are installed at the point where water is used. This could be under the sink, at the kitchen faucet, or even at your refrigerator's water dispenser. Whole-house (WH) treatment systems are installed on the main water line coming into your house. This means all of the water that enters your home will be treated for arsenic. Installation Costs The cost of installing a treatment system for arsenic can vary significantly depending on the type of system you select and the size of your household. Point-of-use (POU) systems are typically less expensive to install than whole-house (WH) systems. This is because they are smaller and require less plumbing. POU systems can cost anywhere from $200 to $600 to install, whereas a whole-house system can cost upwards of $2000 or more. Maintenance requirements All water treatment systems require some level of maintenance. This can include regularly changing filters or cartridges, as well as periodically flushing the system. Systems that use filter media (activated alumina or iron oxide) also require that you regularly replace the spent sorbent. Reverse osmosis filters require replacement of t he pre-filters and osmosis membrane. The frequency of maintenance required will depend on the type of system you have and the quality of your water. Flow rate The flow rate is the amount of water that a treatment system can process in a given period of time. For arsenic treatment, you'll want to select a system with a flow rate that meets or exceeds your household's daily water needs. For example, if your household uses 400 gallons of water per day, you'll want to select a treatment system with a flow rate of at least 10 gallons per minute. FAQs Do Brita filters remove arsenic? Britia filters do not remove arsenic. They use activated carbon to purify your water and this media does not work well with arsenic. Do PUR Water filters remove arsenic? PUR Water filters do not work well at removing arsenic. This is because they use a carbon filter, which is not effective at removing this contaminant. Does boiling water remove arsenic? Boiling water does not remove arsenic from drinking water. Arsenic is an element and is not destroyed by the heat of boiling. It is not volatile, so it doesn't evaporate as the water is boiled. Final Take on Arsenic Treatment Arsenic is a dangerous element that can be found in drinking water. If you are worried about the levels of arsenic in your water, don't worry! We have seven methods to help remove the arsenic from your water. Each method has its own benefits and drawbacks, so it is important to consider all of them before making a decision. No matter which method you choose, always test your water for arsenic levels before and after treatment to ensure that the arsenic has been removed. We hope this article has been helpful and provided you with some information about how to treat arsenic contamination in your drinking water.