Give Your Denitrification Bugs a Sugar High

An alternative substrate to methanol was sought for tertiary denitrification. High fructose corn syrup (HFCS) was identified as the most cost effective alternative, which would also be much safer to handle. This should also render HFCS subject to less legislation at all levels of government. A pilot scale test was conducted. The test confirmed that HFCS is a suitable substrate. A dose of 7.4 g HFCS/g nitrate-nitrogen (NO3-N) removed was achieved and effluent NO3-N was reduced from 8.1 to 3.3 mg/L. Excluding a period of upset conditions, the dose was 5.9 g HFCS/g NO3-N, and the reduction was from 8.8 to 2.7 mg/L. This compares to a theoretical dose of 4.2 g HFCS/g NO3-N based on stoichiometry and a typical methanol dose of 3 g/g NO3-N. Factors that may have contributed to the high dose include variability of the feed NO3-N concentration and occasionally insufficient NO3-N for the available substrate. A preliminary cost estimate indicated that the simple payback for a methanol dosing system would be between 5 and 17 years, depending on the actual HFCS dose.

Methanol is commonly used as a substrate in tertiary denitrification systems. The addition of methanol for denitrification is based on its biodegradability and availability, but methanol also has some disadvantages, including its potential for evaporative loss, a resulting danger of spark ignition, and the effect of evaporative losses on the surrounding air quality. These concerns have resulted in increasingly strict legislation in Southern California regarding the storage and use of

Temecula Valley Regional Water Reclamation Facility (TVRWRF) is one of four wastewater treatment plants (WWTP) operated by Eastern Municipal Water District (EMWD). TVRWRF has an existing tertiary denitrification system that consists of methanol storage and dosing facilities as well as six fluidized bed denitrification towers. Methanol has been classified a hazardous air pollutant under Section 101(14) of the Comprehensive Environmental Responses Compensation and Liability Act (CERCLA). This means that existing methanol storage facilities would have had to add a number of safety and leakage prevention features. In December 2002 the methanol storage tank was removed from the site.

EMWD decided to investigate alternatives that might meet most of methanol’s advantages, while avoiding some of the disadvantages. One alternative carbon source that was identified is HFCS, a sweetener used in the food industry.

The results of pilot testing using HFCS and evaluating the cost to retrofit the current denitrification towers to a system capable of using HFCS is the subject of this paper.

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