Effect of Alfalfa Seed Washing On the Organic Carbon Concentration in Chlorinated and Ozonated Water

Effect of Alfalfa Seed Washing on the Organic Carbon Concentration in Chlorinated and Ozonated Water

Authors Rajkowski, Kathleen; Rice, Eugene – EPA

Submitted to: Journal Of Food Protection
Publication Acceptance Date: November 3, 2003
Publication Date: N/A

Interpretive Summary: Ozone is used as a disinfectant and is added to water so the ozonated water can also act as a disinfectant. When the ozone level was increased and used to wash alfalfa seeds used for sprouting, the bacteria were not killed. Using both chlorinated and ozonated water, alfalfa seeds used for sprouts were washed and the wash water was tested for quality. The bioassys, assimilable organic carbon (AOC) and coliform growth response (CGR), was used. There was a four-fold increase in AOC value and a ten-fold increase in CGR in the chlorinated wash water, and a four-fold increase in both values for the ozonated wash water. There was no ozone left in this water after washing. The increase in nutrients in the water can now support bacterial growth, including those that cause foodborne illness. To assure that the seeds are decontaminated to prevent the bacteria from growing on the sprouts, washing with ozone water should be followed with another treatment.

Technical Abstract: The bioassays, assimilable organic carbon (AOC) and coliform growth response (CGR), are better indexes than biological oxygen demand (BOD) to determine water quality and water’s ability to support the growth of bacteria. The AOC value increased from 1176 to 1758 gC-eg/liter after the reconditioned wastewater was ozonized. When the ozonated wastewater was inoculated with Salmonella serotypes, the cell survived and increased generation times were observed. Ozonated tap water (5 ppm) was used to wash alfalfa seeds for 30 min. After washing the AOC concentration increased four fold while the dissolved ozone decreased to undetectable levels. The AOC levels for the chlorinated water after the washing also increased. These increases are due to chlorine’s and ozone’s strong oxidizing ability to break down refractory, large molecular weight compounds forming smaller ones, which are readily used as nutrient sources for microorganisms. This same phenomenon was observed when using ozone in the treatment of drinking water. The increased nutrients would now become more readily available to any pathogenic microorganisms located on alfalfa seed surface as seen with the increase in inoculated levels of Salmonella in the ozonated wastewater. If the washing process using ozonated water is not followed by the recommended hypochlorite treatment or continually purged with ozone pathogen growth is still possible.