Removal of nitrates requires a carbon source for heterotrophic, denitrifying bacteria to consume. Ethanol and methanol are common dosing agents used to provide such a source. Micro-C 2000 is a commercially produced, concentrated, glycerin-based carbon source for biological processes. Suitable for denitrification, Micro-C 2000 is a safer alternative for small facility denitrification. Since it is nonflammable, it avoids stringent storage requirements. The objective of this study was to examine the effectiveness of Micro-C 2000 supporting denitrification in a floating bead format.
A series of studies were conducted to determine warm water denitrification rates sustainable by Micro-C 2000 fed into a bed of enhanced nitrification media. Nitrate enriched, aerobic freshwater from a 1200-gallon reservoir was injected with Micro-C 2000 into a 3 ft3 (85 L) Bubble Bead® filter and discharged. Hydraulic residence time (20-60 minutes) in the unit was manipulated by variations in flow rate to achieve desired redox ranges (-100 to -500 mV). Impact of nitrate concentration, Micro-C 2000 feed rate, retention time, and redox potential on conversion rates were examined. Discharge concentrations of nitrate and nitrite were also examined.
Denitrification rates ranged from 0.5 to 2.5 kg-N/m3-day across several conditions of operation. Best performance occurred when redox was less than -250 with excess Micro-C 2000. Flow rates ranged from 900 to 1800 mL/min and excess Micro-C 2000 feed rates ranged from 15 to 60 mL/min. Nitrate and nitrite values of less than 2 mg/L were obtainable with the high conversion rates. A denitrification sizing of 1 kg-N/m3-day (SF=1.5) appears appropriate for this type of application.