VOCs in Water: Complex Matters Explained Simply

volatile organic compounds
Most of VOCs are man-made. Source: Tecam Group

Source: Calgon Carbon Corporation

They can be found in any water source. By volatile organic compounds (VOC) water treatment specialists mean a large group of compounds that dissolve in water and may pose a threat to the quality of water for the final consumer. In this article we give a simple explanation to what VOCs are, what kinds of them exist, and how to detect and remove them.

What are VOCs?

As the name implies, there are two traits to define volatile organic compounds. Firstly, they are volatile, which means they easily change state from liquid to gas with a relatively small amount of energy. Secondly, the chemicals are organic, meaning the molecules are composed primarily of carbon atoms.

Most of these compounds are man-made products. However, certain VOCs like acetone can occur in nature as well. As a result of human activity, the chemicals end up in water supply systems as production waste, chemical spills, and others. This is how VOCs appear in water reservoirs. Acetone, formalin, styrol, toluene — these and dozens of other chemicals are toxic to living beings, and, unless extracted during water treatment, are detrimental to human health and lives.

What are they like?

There are many VOC classifications based on certain criteria. Depending on the type of the chemical, the best extraction method is chosen during water treatment.

Based on their boiling points, VOCs can be divided into volatile and semi-volatile compounds. With boiling points of below 0 to 50-100°C, many volatile compounds exist solely in gaseous state, e.g. butane and propane. Semi-volatile compounds boil at 50-100°C to 380-400°C, e.g. acetone, ethanol, phthalates, and many pesticides. The latter are washed off to water supply from fields, and it is barely possible to control the contamination rate.

Another classification is by their solubility in water. Hydrophobic VOCs, such as benzene, are typically lighter than water, so they accumulate on top of the water body as a file or another layer. Hydrophilic compounds’ molecular masses are close to that of water, which allows them to dissolve in water easily. These compounds present a difficulty when it comes to water treatment.

How to detect VOCs?

Every country in the world has imposed standards for water quality. This is why all water undergoes thorough purification before reaching the final consumer. Gas chromato-mass spectrometry is the most widely used method to detect the presence of VOCs in water. The complex process allows to measure the composition of water and to detect toxic contaminants, including VOCs.

water treatment facility
Today’s water treatment facilities are equipped with all the necessary tools to ensure complete water analysis and purification. Source: School of Chemical Technology of BSTU

To remove volatile organic compounds from water, air or activated carbon are used. The air stripping method implies forcing air through water and forcing unwanted compounds out of it. This works well on VOCs with lower boiling points, as well as on hydrophobic compounds. Another removal method is based on the use of granular activated carbon filters. The activated carbon can adsorb most VOCs, including those that are more difficult to remove via air stripping.

Today’s water treatment facilities are equipped with all the necessary tools to ensure complete water analysis and purification. With due quality control applied, water lines bear pure and safe water, posing no threat to the consumers’ health.

Water composition is hard to analyze, but it is predictable. Based on the peculiarities of the region, one can say which contaminants to look for during water treatment. For example, if there are farms or fields near a water supply, the water is likely to be abundant in pesticides. Or one can expect increased rates of fuel and other VOCs spills in settlements with developed river navigation. Further research and study of the environment, as well as of efficient water treatment tools, shall help ensure the safety and purity of water we consume.