Power Generation/Industrial Wastewater Treatment

Critical Water Reuse/Improved Equipment Lifecycle

 

Treatment Drivers

  • Wastewater from the wet scrubbing FGD
  • National Pollutant Discharge Elimination System (NPDES)
  • Typical NPDES parameters include BOD, TSS, heavy metals, selenium, arsenic, boron, temperature, pH, and TDS
  • FGD wastewater typically is combined with other water discharges from the power plant (i.e., wet fly ash handling, cooling water, steam condensate, etc.)
  • High concentrations of TDS, TSS, high buffering capacity, supersaturation in sulfates, high temperature, potentially high organic concentration from dibasic acid (DBA) addition, ammonia, NOx, potentially nitrites and nitrates, heavy metals and trace constituents (i.e., arsenic, mercury, selenium, boron, etc.) present that vary by coal type

 Power Plant Treatment

With coal fire power plants, the complexity of the Flue Gas Desulfurization (FGD) wastewater composition can vary from the type of coal to the type of lime.  In addition, coal can contain sulfates, chlorides, fluorides, etc.  Further exacerbating treatment are the associated metals like mercury, selenium, zinc, cadmium, etc.  The lime source used in the FGD process can add some complexity such as aluminum and iron content that is release during the lime processing during the pulverizing stage via a wet ball mill, iron during lime preparation process is introduced (corrosion/erosion).

Since FGD particles (gypsum) can be abrasive, removal of the gypsum particles is necessary before the service water can be re-used for general water needs in the plant.

Example: Lime Softening and Clarification/Service Water Pretreatment

In the first stage of treatment, the raw water is softened to reduce the calcium and magnesium hardness. After re-carbonation, the treated water is collected in the service water storage tank. Some of the softened water is diverted to the cooling tower and some of the service water is sent to the demineralizer system. The softening system includes a sludge dewatering step (pressure or belt press filtration). The thickener overflow is sent to the clarifier and/or filter.