FGD WASTEWATER TREATMENT

Flue gas desulfurization (FGD) wastewater contains high total suspended solids of 250-20,000 mg/L and total dissolved solids of 15,000-35,000 mg/L.  Among the FGD wastewater constituents are chlorides, boron, arsenic, calcium, mercury, magnesium, selenium and also aluminum, nitrates and ammonia.  Wastewater flow rates can range from 100 to 1000 gpm with the average flow rate of 450 GPM.

Historical FGD wastewater regulations have focused on COD, TSS and TDS and FGD wastewater treatment has focused on removing these solids.  Recent regulatory interest on FGD wastewater treatment is looking to reducing metals, ammonia and selenium loading in streams, rivers and estuaries.


Traditional FGD Wastewater Treatment

Traditional FGD wastewater treatment for COD, TDS and TSS consists of a number of process steps including:

• Flow equalization
• Primary clarification of suspended solids
• pH elevation and CaSO4 desaturation
• Sludge recirculation to enhance desaturation
• Heavy metal precipitation with organo-sulfide chemical addition
• Coagulation with ferric-chloride addition
• Polymer addition to enhance flocculation of solids
• Solids separation and thickening
• Final clarification
• Solids dewatering

For ammonia and selenium removal additional biological treatment after the solids dewatering  would be needed to remove these contaminates. 

The drawbacks of these traditional FGD wastewater treatment systems are:

• Multiple process steps involving chemical, physical, and biological processes
• Large land requirements for the wastewater treatments
• Large tankage and pumping requirements particularly for biological processes
• High energy costs
• High capital costs
• Advanced FGD Wastewater Treatment

CASTion offers an advanced FGD wastewater treatment that can remove both the suspended and dissolved solids as well as the ammonia and selenium present in FGD wastewater treatment.  Coupled with reverse osmosis and other off the shelf  filtration components, CASTion’s advanced FGD wastewater Treatment systems are a two stage CAST/RCAST units with a pH adjustment.  The reject water from the reverse osmosis unit is dewatered in the CAST units to remove the selenium and 80% of the ammonia is removed by using CASTion’s RCAST with the wastewater recycled back into the power plant.  CASTion’s RCAST can also be retrofitted to an existing FGD wastewater treatment system to remove only the ammonia. 

The advantages of CASTion’s FGD wastewater treatment system are:

• Small footprint
• Simple Chemical/physical  operations
• Lower energy and operating costs
• Lower capital costs