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Comparing Nitrate Removal Efficiency Between Gravel and PVC Biocarriers
Citation:
Woodruff, P., A. Keithley, D. Williams, N. Dugan, AND D. Lytle. Comparing Nitrate Removal Efficiency Between Gravel and PVC Biocarriers. EPA Drinking Water Workshop, Covington, KY, August 29 - September 01, 2022.
Impact/Purpose:
Nitrate has an EPA mandated maximum contaminant level (MCL) of 10 mg N/L. Ground waters with high nitrate are predominantly in small and intermediate sized systems that service 500-100,000 people. Consumption of water with high nitrate levels can cause methemoglobinemia or blue baby syndrome, may cause colorectal cancers, thyroid disease, and birth defects. Biological treatment converts nitrate to nitrogen gas through denitrification via anaerobic respiration. A pilot system was developed consisting of contactors with material inside, called biocarriers, to promote microbial growth. Nitrogen gas was sparged into the contactor to remove oxygen and promote the consumption of nitrate. Gravel and PVC were used as biocariers to compare nitrate removal efficiency in the contactors. Once acclimated, gravel and PVC biocarriers removed nitrate completely but gravel had a higher rate of removal. Comparatively lower cell activity was observed in the PVC contactor signifying lower biomass. PVC, as a biocarrier, may not be as conducive to microbe growth due to shape and surface charge of the material; higher and diversified biomass is imperative for denitrification.
Description:
Consumption of water with high nitrate levels can cause methemoglobinemia or blue baby syndrome, and may cause colorectal cancers, thyroid disease, and birth defects. Biological treatment is used a remediation tool to convert nitrate to nitrogen gas through denitrification via anaerobic respiration within a column structure known as a contactor. Nitrogen gas sparging was used to create an anoxic environment, promoting anaerobic respiration from bacteria in the contactor. Biocarriers are a medium used to anchor microbes and promote growth within the column. The two biocarriers used in this project were gravel, which is a cheaper material, and PVC, a comparatively more expensive material but has a higher surface area. The objective of this project was to compare nitrate removal of biological contactors with two different biocarriers. Gravel and PVC removed nitrate completely but gravel had a higher rate of removal. Comparatively lower cell activity was observed in the PVC contactor signifying lower biomass; higher and diversified biomass is imperative for efficient contaminant removal.