Case Study

Prototype Sensor under Development to Automatically Detect Chlorine Levels in Poultry Chiller Water

Published: November 3, 2007

Each year the U.S. poultry industry processes 20 billion pounds of chicken. In one of the closing steps in first-processing, eviscerated and defeathered carcasses are dropped into an immersion chiller, which rapidly chills the carcasses to 40°F or below. To further ensure microbiological safety, processors also add chlorine to sanitize and disinfect the chiller water. Because varying levels of chlorine can affect product quality and taste as well as disinfection efficiency, the chiller water must be constantly monitored.

Free chlorine levels are typically measured by colorimetric analysis. The most commonly used method is based on a chemical reagent known as DPD (N, N-diethyl-p-phenylenediamine). However, the current DPD-based method has a narrow working range and suffers from interferences by organic material present in the chiller water and chloramine formation.

In response, researchers with Georgia Tech’s Food Processing Technology Division are developing an electronic sensor that they believe will more accurately track chlorine compounds, including free chlorine, and their concentrations.

“Our research is focused on developing an accurate, cost-effective, and field-deployable approach capable of replacing or complementing the current DPD method for the measurement of free chlorine concentration in process waters, particularly red-water chillers,” says Jie Xu, research scientist and project director.

“Colorimetric analysis such as the DPD-based method can suffer from interferences caused by turbidity and natural organic coloring constituents like chicken blood,” explains Xu. In addition, she notes, several significant problems are associated with the DPD-based method: (1) the DPD reagent is not very stable; (2) the oxidized colored products show fading within a few minutes; (3) the color developed with DPD is reported to be temperature sensitive; (4) there is interference from combined chlorine, and (5) it is typically a manual, off-line method. As a result, says Xu, the concentration of free chlorine measured by the DPD method can be inaccurate resulting either in a marginal disinfection process or wasted money associated with adding unnecessary chlorine.

The sensor under development by Xu and her team uses an interferometric measurement principle previously developed by Georgia Tech researchers. The technique can be used to detect both chemical and biological species, and is fast, has high sensitivity, and provides a direct measurement with no additional steps or consumable reagents. The sensor platform is designed for mobile, on-site field analysis with real-time results. For the current project, researchers have incorporated a novel reactive sensing film into the sensor to create an assay for rapid, on-line quantification of free chlorine (hypochlorous acid). According to Xu, preliminary data suggest it will be possible to detect levels below one part-per-million of chlorine within a matter of minutes, independent of sample matrix or interfering substances.

In addition, researchers are exploring sensing chemistry development for monochloramine (which measures combined chlorine). “Monochloramine has become a disinfectant with widespread acceptance due to its biocidal capability, persistence in water, and lower formation of disinfection byproduct trihalomethanes,” explains Xu. Several sensing chemistries have already been investigated based on the specific reactivities of monochloramine, and initial results indicate a sensitive, reversible measurement for monochloramine.

The team has also designed and fabricated a waveguide chip with eight interferometers. With this new design, simultaneous multiple detection becomes achievable. In addition, researchers plan to integrate sensing chemistries for free chlorine, combined chlorine, and pH on a single-chip to provide real-time measurement for free chlorine, combined chlorine, and pH.

“A well-managed chiller will provide an important step in helping control bacterial counts and prevalence. This sensor, which provides near real-time information on chiller killing power, should be able to more dynamically track and hence control chiller management,” says Xu.

Funding for the project is being provided by Georgia’s Traditional Industries Program for Food Processing with additional support from Georgia Tech’s Agricultural Technology Research Program (ATRP).