Power Generation

EOSi can help coal-fired power plants develop compliance strategies for pending nitrate, and selenium limits in wastewater from flue gas desulfurization (FGD) processes. MicroC® supplemental carbon sources support the healthy biomass needed for efficient and cost-effective treatment of these contaminants.


On September 30th, 2015, US Environmental Protection Agency (EPA) finalized the rule revising the Effluent Limitations Guidelines (ELGs) for the Steam Electric Power Generating Point Source Category. The rule sets federal limits on the levels of toxic contaminants in wastewater that can be discharged from steam power plants. The rule requires specific treatment of wastewater discharged from wet scrubber systems, such as FGD units at coal-fired power plants. For FGD wastewater, the final rule contains limits for nitrate/nitrite, selenium, mercury, and arsenic.

The diverse chemistry of these contaminants as well as the very low numeric effluent limitations present a challenge to coal-fired power plants. To meet the ELGs effluent limits for nitrate, nitrite and selenium, FGD wastewater treatment plants will likely have to add a new treatment process to supplement existing solids and metals removal processes.

Biological treatment is a cost-effective and established technology for removing nitrate, nitrite and selenium from FGD wastewater. Under anoxic conditions, microbes will first convert nitrate and nitrite to harmless nitrogen gas, carbon dioxide gas, and water. When the nitrate is depleted, the microbes will begin using less preferred electron acceptors such as selenate and selenite, the most common forms of selenium found in water. The microbes reduce selenate and selenite to elemental selenium, which either precipitates or is trapped in the biomass. These biological treatment systems require a high quality supplemental carbon source with superior kinetics that serves as an electron donor for these microbiological processes.

How EOSi can help

MicroC® supplemental carbon sources provide a consistent, readily-available source of food and energy to support the microbial populations needed for biological treatment of nitrate, nitrite and selenium in FGD wastewater. MicroC® is also used for BOD augmentation to sustain the biomass during periods of low flows or loadings due to seasonal variations or maintenance shut-downs, and for establishing an acclimated biomass during startup of new or upgraded biological treatment systems. EOSi can conduct nutrient deficiency analyses and, if necessary, design a custom MicroC® blend that includes essential microbial nutrients not present in the FGD wastewater.

For power plants installing new or upgraded biological treatment systems, EOSi provides related services such as bench-scale treatability studies, modeling and simulations, and equipment selection and procurement. EOSi also delivers solutions through our Objective Based Programs such as ongoing technical and application support, remote process monitoring, troubleshooting and optimization programs to our MicroC® customers.