Impacts of Denitrification on Biological Phosphorus Removal Using Several Carbon Source Types

The effects of denitrification on phosphorus release and uptake of EBPR systems have been investigated using acetate, methanol, and MicroC‐G ™ as carbon sources. MicroC‐G ™ is a proprietary chemical marketed as a carbon source for denitrification. Batch experiments were performed using actual wastewater from a wastewater treatment plant that performs EBPR. Nitrate-rich effluent was mixed with influent wastewater to simulate a denitrification system that uses internal mixed-liquor return. The results show that adding acetate to EBPR system promotes complete denitrification, but it delays phosphorus release. When acetate was added above the stoichiometric need, complete denitrification was obtained and more phosphorus was released. However phosphorus uptake, during the anaerobic period, was hindered resulting in high effluent phosphorus concentration. Therefore, it is necessary to balance phosphorus release in the anoxic zone with phosphorus uptake in the aerated zone, when both, denitrification and phosphorus removal are to be attained using acetate. Methanol was able to support denitrification, but the kinetic rates were very slow. While denitrification could be achieved within 40 minutes using acetate, more than 120 minutes were needed when methanol was used. As a consequence phosphorus release only occurred after 120 minutes when all nitrate had been reduced. Methanol use as a carbon source for denitrification, in EBPR systems, would therefore require increased anoxic retention times. MicroC‐G ™ works well to promote denitrification and the kinetics is as fast as that for acetate. However, MicroC‐G ™ does not promote phosphorus release in the anoxic zone. More studies are needed to understand why MicroC‐G ™ does not favor P-release. In summary, EBPR plants considering implementation of denitrification have to carefully consider the carbon source to be used. Acetate works well, but too much acetate will hinder uptake of phosphorus in the aerobic zone. Methanol addition will require greater retention times, depending on the level of denitrification to be achieved.