How is turbidity measured?
Turbidity is measured using an instrument called a turbidimeter. There are three common types or classifications of turbidimeters: benchtop (or laboratory) instruments; portable (handheld or field) instruments; and process (or online) instruments. Benchtop or portable instruments are used to analyze grab samples, while process instruments are plumbed and wired into a system to provide a continuous reading from a sampling point.
Depending on the industry, or application, a facility may use only one type of turbidimeter or all three types to control their process. For example, in drinking water plants, it is common to have a benchtop turbidimeter in the on-site laboratory; a portable instrument for taking measurements within the plant along the treatment process or outside of the plant along the distribution network; And a process instrument installed at various points along the treatment process – but especially at the combined filter effluent where a reportable result must be taken at least every 15 minutes.
In addition, a portable or benchtop instrument is often used as part of the routine verification requirement of process instrument readings. This means that a sample is collected from the same point being analyzed by the process turbidimeter and analyzed using the portable (or benchtop) instrument. The results from the process and portable instrument are then compared and are expected to be within a certain tolerance.
Process instruments are typically much more complex than benchtop or portable instruments as they are expected to have water constantly flowing through them and provide constant feedback to the control room about the current turbidity levels.
In all cases, to ensure the best results, users are advised to strictly follow the manufacturer's recommendations regarding installation and sampling protocols associated with the instrument model in use.
The Importance of the Process Turbidimeter
While all three types of turbidity instruments ultimately deliver a turbidity result, it is important understand the ways in which these types of readings tell you and how they can be used.
Think of the measurements taken with different types of turbidimeters this way:
- Benchtop or Portable Turbidimeter: A photograph – it captures a moment in time, but is limited in context.
- Process Turbidimeter: A movie – it provides the whole story of events that contribute to the ending.
When a sample is analyzed using a portable or benchtop model, it tells the user what the turbidity value for that sample at the moment in time the sample was collected. It can not be used as an indicator of what the turbidity was 30 minutes prior – nor can it be used to predict what the turbidity value will be 30 minutes in the future.
A process instrument provides the user with continual feedback about the turbidity levels at the sampling point. Over time, these results come together to form a trend. Operators can see if turbidity levels are rising, stable, or decreasing over a given period of time, and take action if needed. A rising turbidity level could indicate that a filter needs to be backwashed or that that there is some other issue in the treatment process.
Lovibond® Process Turbidimeters
The performance of process turbidimeters is a critical part of ensuring safe drinking water. The PTV Series of Process Turbidimeters from Lovibond® are designed to overcome the issues that customers struggle with when using their existing turbidity systems, while providing a reliable and accurate readings.
Developed in collaboration between globally recognized turbidity experts, Lovibond’s PTV1000, PTV2000 and PTV6000 process turbidimeters are optimized for drinking water applications. They feature a long-lasting LED or Laser light sources and proprietary bubble-exclusion system to deliver accurate and ultra-stable measurements, while a heated optical assembly eliminates condensation and fogging. These features enable Lovibond process turbidimeters to provide unparalleled accuracy below 1 NTU.
PTV process turbidimeters can be completely controlled via a single mobile device app, removing the need for dedicated controllers for each instrument and giving our customers flexibility as their needs and regulatory requirements change over time. Alongside the app, the device features an integrated touchscreen display where basic testing parameters can be controlled.
Thanks to quick-connect fixtures, the unit can be easily drained for cleaning and calibration, and “grab samples” can be easily collected without the need to disconnect any tubing. A low-volume flow body (70% lower than competitive units) not only ensures that a Lovibond® process turbidimeter responds incredibly quickly to turbidity spikes, but also that it uses far less water. With an optimal flow rate of 30 – 150 ml per minute, this translates to over 1 million gallons of water saved over the device’s lifetime compared to competitive units.
PTV series process turbidimeters can be easily configured with additional features, including integrated flow indication, digital communication protocols, and Bluetooth® connectivity.
PTV series process turbidimeters provide flexibility, accuracy, and ease of use at every stage from installation to data collection and management. To find out more about the capabilities of Lovibond® process turbidimeters, get in touch with a member of our team here.
References and Further Reading
1. Turbidity and Water | U.S. Geological Survey. https://www.usgs.gov/special-topics/water-science-school/science/turbidity-and-water.
2. Mann, A. G., Tam, C. C., Higgins, C. D. & Rodrigues, L. C. The association between drinking water turbidity and gastrointestinal illness: a systematic review. BMC Public Health 7, 256 (2007).
3. EPA | Turbidity Guidance Manual. https://www.epa.gov/sites/default/files/2020-06/documents/swtr_turbidity_gm_final_508.pdf.
4. DIRECTIVE (EU) 2020/2184 | On the quality of water intended for human consumption. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32020L2184&from=ES.