Flue Gas Desulfurization (FGD)


FGD Overview 

The flue gas desulfurization (FGD) process is designed to remove sulfur dioxide from fossil-fuel power plant exhaust. Flue gas desulphurization wastewater (FGDW) is a byproduct of FGD process. This wastewater must be treated to meet selenium (Se), Arsenic (As), Mercury (Hg) and nitrate/nitrite (NOx) limits prior to discharge. With over 600 coal burning power plants in the United State alone, FGD wastewater is becoming of greater and greater concern. As regulations tighten on contaminant discharge concentrations, the treatment of FGD wastewater is becoming a must. 


EPA recommended physical-chemical treatment followed by biological treatment as a BAT (Best Available Technology Economically Achievable) for existing sources of FGD wastewater. Depending on the site-specific conditions, biological treatment may not be suitable for selenium and nitrate removal. High TDS (Total Dissolved Solids) levels impedes the microorganisms ability to grow at an appropriate rate. For this reason, not all FGD wastewater streams may be suitable for biological processes and may need to be treated using evaporators or RO.

Chemical precipitation + biological treatment
Daily Max 30 Day Avg
As 11 μg/L 8 μg/L
Hg 788 ng/L 356 ng/L
Se 23 μg/L 12 μg/L
NO3/NO2 as N 17.0 mg/L 4.4 mg/L

Daily Max 30 Day Avg
As 4 μg/L - -
Hg 39 ng/L 24 ng/L
Se 5 μg/L - -
TDS 50 mg/L 24 mg/L

Evaporator can be a solution, technologically, but its CAPEX and OPEX is extremely costly. Reverse Osmosis (RO) can be financially and technologically feasible,but there are some limitations on fouling and rejection rate. RO's functionality is limited by hardness which causes frequent scaling and high TDS (>25000 ppm) which causes low rejection rate.


fMX Standard Solution for FGD

FMX is a system that can enable the use of RO by preventing scaling and lowering the TDS. RO's functionality will be greatly enhanced by FMX pretreated FGD wastewater.
• FMX-NF can reject over 90% of scalant contents in FGD wastewater
• FMX-NF can reject 30-50% of TDS level, so that RO can do the rest of the job more easily
• FMX-NF also reject target contaminants to a certain degree
• Overall, FMX-NF can reduce significant amount of CAPEX & OPEX for RO and/or for Evaporator

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As seen below, FMX also simplifies the FGD treatment process train. 

Simplified FGD Process.png

additional solution: fMX as a kidney function

Alternatively, FMX can play the kidney function in closed recycling FGD wastewater treatment process. FMX- NF can reject significant amounts of target contaminants from the loop, making the closed loop more sustainable and more economical. 

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Click to Learn More

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EUEC Presentation Abstract 

Flue gas desulphurization wastewater (FGDW) is a byproduct of pollution control processes at coal-fired power plants. This wastewater must be treated to meet selenium (Se), Arsenic (As), Mercury (Hg) and nitrate/nitrite (NOx) limits prior to discharge. In 2017, BKT piloted a new anti-fouling membrane treatment technology for FGDW at a 2,240 MW power plant. Trade-named FMX, the system uses rotating blades to create hydraulic vortices at the membrane surface, preventing the fouling and scaling experienced by conventional membranes. The pilot treated 5,000 gal/d using a membrane surface area of 54.5ft2 to compare FMX removal performance to an existing membrane bioreactor (MBR). Over 3 months of treatment, Se influent concentrations ranged from 71-697ug/l (mean 200ug/l). FMX achieved 61% average Se removal with min 47% and max 85% removal. Average removal for other target pollutants were 74%, 94%, and 35% for As, Hg, and NOx, respectively. Influent concentrations were 10mg/L for As, 51ng/L for Hg, and 24mg/L for NOx. FMX achieved an average flux of 61 gal/(ft2∙day) with negligible scaling/fouling observed. FMX effluent was able to meet the US EPA’s BAT and BADCT treatment standards for FGD discharge (2015 rule 40 CFR Part 423) but was not able to guarantee adherence to Se and NOx limits without downstream membrane processes. BKT is now testing a smaller pore membrane with a MWCO of 200Da intended to guarantee single-stage adherence to revised EPA standards.


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