October 20, 2015 - The October 2015 issue of Industrial WaterWorld featured the article “Zero Liquid Discharge Strategies for Compliance with Proposed Effluent Guidelines for FGD Wastewater.” Read the article online.
Additional details from the case study are available in the full paper that can be downloaded.
The U.S. Environmental Protection Agency’s (EPA) proposed Effluent Guidelines for the Steam Electric Power Generating Category was published in June 2013. The proposed guidelines provide new discharge limitations on various metal species in certain waste streams (i.e., mercury, arsenic, selenium) and nitrates/nitrites. The most significant impact of the proposed changes will be to coal-fired power plants that discharge flue gas desulfurization (FGD) wastewater and fly ash or bottom ash transportation water. Once the rule is finalized, the new limits will be incorporated into National Pollutant Discharge Elimination System (NPDES) permits as the permits enter renewal cycles.
Coal-fired power plants with newer wet FGD applications more commonly include physical/ chemical wastewater treatment facilities, which remove mercury and arsenic through precipitation and filtration. In order to be in compliance with the proposed guidelines, these stations will likely require further treatment to remove remaining nitrates/nitrites and selenium via biological treatment or eliminate the waste stream altogether (zero liquid discharge or ZLD).
Using a case study, this paper evaluated different combinations of ZLD approaches, such as a brine crystallizer/evaporator, a wastewater spray dryer, and fixation/stabilization, to achieve compliance for coal-fired power plants with existing physical/chemical wastewater treatment facilities on their wet FGDs. In order to reduce the cost of ZLD approaches, variation of plant operation with changes in FGD absorber material of construction and the variations in capital and operating costs impacts are presented as part of this evaluation.