Wastewater monitoring made easy with real-time liquid concentration measurements

Nearly every industry, from food and beverage production to wood pulp processing, generates wastewater. Controlling contaminants in wastewater is therefore crucial for both regulatory compliance and environmental protection. Quick identification of effluent or side stream concentrations that exceed safety limits can allow operators to make the necessary adjustments in a timely manner to avoid costly fines, surcharges, and potential process shutdowns.

Vaisala Polaris™ Process Refractometers provide real-time, inline measurements of Total Dissolved Solids in wastewater streams, allowing for continuous monitoring and control of effluent quality. By detecting high levels of Total Organic Carbon (TOC), such as alcohols, proteins, and sugars, these sensors help identify potential issues before the wastewater reaches treatment plants.

We got to hear from Michael Kohlmann (Regional Sales Manager and Industry Expert) and Jeremiah Fitzgerald (Application Sales Engineer) from Vaisala regarding the value these solutions bring to industrial manufacturers.

Engineered Sales Co.: Can a refractometer identify what and how much is in the wastewater?

Vaisala: In most process applications, the refractometer uses a refractive index measurement to measure a binary solution, i.e., the concentration of only one chemical in solution. But in an industrial wastewater application, many chemicals could be present in an upset condition, perhaps sugar or a cleaning chemical that accidentally enters the waste stream. Although a refractometer can nearly immediately detect this upset condition, it can’t give you the exact makeup of the waste stream, but rather an aggregate of all the solids in that stream. Operators generally establish a baseline reading over a short period of time, usually a few days, then set a threshold just above that baseline. Any time the reading rises above this empirically derived baseline value, it sets off an alarm to notify operators that something is in the waste stream and further analysis is needed to identify just what is causing the high reading.   

ESC: What is a "refractive index”?

V: As light passes through a liquid medium, the light rays reflect, refract, and slow down.  Refractive index, or nD, is an optical method for determining the amount of dissolved solids in a liquid. It is the ratio of the speed of light in a vacuum to the speed of light through the medium being measured. Our refractometers measure this ratio, and we correlate the nD to a chemical curve to display % concentration of many chemicals (Brix or sugar, acids, caustics, coolants, salts, proteins, etc.) for nearly every industry.  Although Vaisala has hundreds of unique chemical curves, our scientists can create custom curves as well. 

ESC: What is the accuracy of refractive index measurements in the case of scattering medium?

V: In most cases, our refractometer has an accuracy of ±0.00014 nD which correlates to 0.1 °Brix or 0.1% solids (or ±500 mg/l TDS), with no influence from air bubbles or color of the media.  

ESC: Will foam influence the reading?

V: Foam in the process will not typically cause any issues for the refractometer. As long as the refractometers prism is clean and in contact with a constant flow of process fluid, the measurement is not influenced by foam, bubbles, or suspended solids.

ESC: Can this measure at low temperatures and what is the lowest temperature it can measure?

V: The refractometer measuring range is –40 to +150 °C (–40 to +302 °F)

ESC: Regarding the prism wash, when and why would this be needed in an application?

V: It is important to keep the prism clean and free of any coatings. In perhaps 80% of the applications, simply having a velocity of >5 feet per second and installing the sensor in an elbow allows the process to self-clean the prism. In some tough applications, we offer an active prism wash system that directs either hot water or steam across the prism. The frequency and duration is user-adjustable to fit nearly every application.     

ESC: Are there any consumable parts in your refractometer that will need to be exchanged over time?

V: There are no consumables or parts that would typically require replacement.  Although the sensors are extremely robust and many go years without any required maintenance at all, the prisms can get scratched or abraded over time, especially in some slurries.  In these cases, we recommend sending the sensor back to Vaisala for evaluation. In most cases we can repair the sensor for a fraction of the cost of a new sensor.

Let’s talk about your specific wastewater monitoring needs.  

Vaisala Polaris™ Process Refractometers offer significant value to customers by enabling precise, real-time monitoring of wastewater quality, which helps ensure environmental and regulatory compliance. As an authorized distributor, Engineered Sales Co. can pair your application with the right sensor and accessories. Contact us today to schedule a meeting.