IntroductionThe design and performance of anaerobic digesters is commonly based on volatile solids analyses. For example, expressing digester load as mass of volatile solids (VS) per digester volume per day (i.e., lbs VS ft -3 day -1 ), measuring stabilization performance in terms of VS reduction (VSR), and evaluating/estimating gas production in terms of specific gas production (gas volume produced per mass of VS removed). This approach is frequently used due to regulatory requirements for vector attraction reduction and the relative simplicity associated with TS/VS laboratory analyses. While monitoring VS in anaerobic digestion systems provides valuable information regarding degradability and solids destruction, the use of VS data to evaluate/estimate gas production has serious limitations due to a wide variability in specific gas production between different anaerobic digestion facilities. Chemical Oxygen Demand (COD)-based process models have come to dominate the wastewater field, in part because COD is conserved throughout the treatment systems (Barker & Dold, 1995). The addition of COD to routine digester monitoring programs can provide valuable information for the accurate estimation of gas production performance.
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 (NO 3 -N) removed was achieved and effluent NO 3 -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 NO 3 -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 NO 3 -N based on stoichiometry and a typical methanol dose of 3 g/g NO 3 -N. Factors that may have contributed to the high dose include variability of the feed NO 3 -N concentration and occasionally insufficient NO 3 -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.
KEYWORDSTertiary denitrification, methanol, high fructose corn syrup, fluidized bed denitrification towers.
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