Gas Sensing in the Purification Process of Drinking Water

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Image Credit: People Image Studio/Shutterstock.com

The processing of clean and safe drinking water is an issue that affects people around the world. Estimates suggest that, if no steps are taken to further improve the availability of safe water sources, over 135 million people will die from potentially preventable diseases by 2020.1

In the UK alone, investments in water purification and treatment amounted to £2.1 billion in England and Wales between 2013 and 2014.2 The purification process involves removing undesirable chemicals, bacteria, solids and gases from water, to ensure that it is safe to drink and use. There is not just one standard of purified water, as this can vary depending on what the water will be used for. Water used for fine chemical synthesis, for example, may need to be ‘cleaner’ i.e. have fewer chemicals present, than is tolerable for drinking water, the most common use of purified water.

Purification Process

To get water to a baseline purity, there are several steps involved. The first is to filter the water to remove any large debris and solids once the water has been piped to the purification plant. At this point, there needs to be an assessment of how dirty the water is to design the purification strategy. A degree of pretreatment may occur here by using carbon dioxide to rebalance pH levels and clean up the wastewater to some extent. Gas monitors are a necessary tool here to ensure the correct amounts of gas are being added to the water and that there is no build-up of unsafe levels of the gas.

The following steps include chemical treatment and filtration to remove dissolved ionic compounds.3 The water is also disinfected to destroy any remaining bacteria or viruses, and additional chemicals are added to provide sustained protection.4 At every point of this process, water quality must be constantly monitored. This is so that any remaining pollutants are identified and targeted for removal to ensure the water is safe for its intended purpose.

In-line gas monitors are a common tool in the water treatment process as a means of monitoring total organic carbon (TOC) content. Carbon may be present in the water due to a variety of sources, including bacteria, plastics or sediments that have not been successfully removed by the filtration process.5 TOC is a useful measure of water cleanliness as it covers contamination from a variety of different sources.

There are a few extra chemical reactions and vaporization that must be performed that cause the release of COgas to properly use non-dispersive infrared (NDIR) gas monitors to analyze the TOC content of water. With the gas released from these reactions, the resulting concentrations can then be used as a proxy of TOC levels.6 This provides a metric that can be analyzed to see if additional purification is required or to check the water is safe for use.

Need for Gas Monitors

NDIR gas sensors can be used as a safety device in the water purification process as they monitor carbon dioxide, methane, and carbon monoxide; some of the key gases produced during the treatment process.5 The sensors may also be used for analysis of TOC content for confirming water purity.7

NDIR sensors are particularly well-suited for this as carbon dioxide is a strong absorber of infrared light. This makes it easy to detect even very low carbon dioxide concentrations, making it a highly sensitive measurement approach.6 NDIR can also easily detect other hydrocarbon gases, making NDIR sensors a highly flexible, adaptable approach to monitoring TOC and dissolved gas levels in water.

Sensor Solutions

Constant gas monitoring is a necessary part of the purification process as it provides information that guides the wastewater treatment. This means that water purification plants need permanent, easy-to-install sensors to perform continual online monitoring. One particularly effective way of doing this is to have OEM sensors that can be connected into existing water testing equipment to provide additional information on water purity.

The above reasons are why Edinburgh Sensors range of nondispersive infrared (NDIR) gas sensors are the ideal solution for water purification plants. NDIR sensors are highly robust with superior sensitivity and accuracy over a wide range of gas concentrations. Their two flagship sensors, the Gascard NG8 and the Guardian NG9 ­­­­can detect carbon monoxide, carbon dioxide or other hydrocarbon gases even at low concentrations. If it is only carbon dioxide that is being monitored, then Edinburgh Sensors offers a more extensive range of monitors, including the Gascheck10 and the IRgaskiT.11

The advantage of NDIR detection for these gases is, in the case of the Guardian NG, the devices initial warm-up times, which are less than one minute. It is also capable of 0 – 100 % measurements of these gases with a response time of fewer than 30 seconds from the sample inlet. The accuracy of the readout is ± 2 %, and all of the mentioned sensors maintain this accuracy during challenging environmental conditions of 0 – 95 % humidity, with a self-compensating readout.

Guardian NG

Guardian NG

The Guardian NG has a dedicated readout and menu display for the rapid gathering of information and requires only a reference gas and power supply to get running. The Gascard is particularly popular for water purification purposes, as the card-based device is easy to integrate into existing water testing equipment, allowing gas testing to occur while checking purity.

On top of this, Edinburgh Sensors also offers custom gas sensing solutions and its full technical support throughout the sales, installation and maintenance process.

References and Further Reading

  1. Gleick, P. H. (2002). Dirty Water: Estimated Deaths from Water-Related Diseases 2000-2020 Pacific. Pacific Institute Researc Report, 1–12.
  2. Water and Treated Water (2019), https://www.gov.uk/government/publications/water-and-treated-water/water-and-treated-water
  3. Pangarkar, B. L., Deshmukh, S. K., Sapkal, V. S., & Sapkal, R. S. (2016). Review of membrane distillation process for water purification. Desalination and Water Treatment, 57(7), 2959–2981. https://doi.org/10.1080/19443994.2014.985728
  4. Hijnen, W. A. M., Beerendonk, E. F., & Medema, G. J. (2006). Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cysts in water: A review. Water Research, 40(1), 3–22. https://doi.org/10.1016/j.watres.2005.10.030
  5. McCarty, P. L., & Smith, D. P. (1986). Anaerobic wastewater treatment. Environmental Science and Technology, 20(12), 1200–1206. https://doi.org/10.1021/es00154a002
  6. Scott, J. P., & Ollis, D. F. (1995). Integration of chemical and biological oxidation processes for water treatment: Review and recommendations. Environmental Progress, 14(2), 88–103. https://doi.org/10.1002/ep.670140212
  7. Florescu, D., Iordache, A. M., Costinel, D., Horj, E., Ionete, R. E., & Culea, M. (2013). Validation procedure for assessing the total organic carbon in water samples. Romanian Reports of Physics, 58(1–2), 211–219.
  8. Gascard NG, (2019), https://edinburghsensors.com/products/oem/gascard-ng/
  9. Guardian NG (2019) https://edinburghsensors.com/products/gas-monitors/guardian-ng/
  10. Gascheck (2019), https://edinburghsensors.com/products/oem/gascheck/
  11. IRgaskiT (2019), https://edinburghsensors.com/products/oem-co2-sensor/irgaskit/
  12. Boxed GasCard (2019) https://edinburghsensors.com/products/oem/boxed-gascard/

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.

For more information on this source, please visit Edinburgh Sensors.

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