Keywords: arsenic, water treatment

Description: Arsenic contaminating groundwater aquifers is public health concern for virtually every region of the continent. Sometimes it can be caused by human activity and sometimes it can occur naturally. There are a variety of different methods that can be used to remove the arsenic and make the water safe for human consumption. Each method has its own set of optimal conditions and will produce different forms of waste.

Whether you are a farmer that is looking to keep a localized water table free of toxins, or a small municipality that is in need of greater reservoirs, having access to the right filtration technology can make or break any water planning enterprise. Sadly, arsenic often appears in unsafe quantities in aquifers where the surrounding soil became contaminated with arsenic from pesticides. If arsenic containing pesticides were used consistently in each growing season over a period of many years, the arsenic becomes deposited into the soil and is then leeched into the groundwater. If the concentration of it exceeds 10 ppb, consuming the water can cause skin legions, problems with the circulatory system and even cancer. Because of the salience of these harmful effects, there is increasing demand for cost effective technologies to remove it from aquifers.

The technologies

Most of the arsenic removal methods available today involve pushing the water through a resin that alters the physical or chemical composition of the arsenic. When such a change occurs, the particles that result become easy to filter away, hence removing the arsenic from the water. One issue is that all of the particles that are filtered away must be safely disposed of. If there is one technique that works particularly well at catching the arsenic, but produces waste that is too difficult to dispose of, then it cannot be used.

One of the simplest methods to remove arsenic is to pass the untreated water through an adsorptive granular media that is contained in a pressure vessel. As the water travels through it, the negatively charged arsenic ions become absorbed into the outer layer of the positively charged media. The media are often metallic, usually consisting of iron or aluminum, because they are easily disposed of after they have bonded with arsenic. The downside is that they become less effective when the water has high phosphate or silica content.

Another method is called ion exchange. Ion exchange is more sophisticated than adsorptive media because it involves a sequence of chemical reactions, where chlorine is introduced to the arsenic and then salt is added at a later phase. The net result is that much of the arsenic is discharged in the form of sulfates and nitrates. The main drawback for this method is that it only works against the oxidized arsenic V variety. This is because the chlorine atoms bind with the arsenic more readily when they are of the oxidized form. Because of this, many arsenic removal systems will use the ion exchange method after oxidizing the arsenic in the water.

Make a plan

Before deciding on which treatment method may be best, it is important to have the water tested. It is important to know whether you are dealing with oxidized or unoxidized arsenic, whether there is a high concentration of phosphates or silica and what the pH of the water reads. Having all of this information will be the first step in forming your arsenic water removal plan.

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