Systems and methods of treating flue gas and wastewater generated by treating the flue gas are disclosed and include introducing the flue gas, a flue gas treatment fluid that removes sulfur dioxide from the flue gas; and an organic acid conditioning agent into a wet-oxidation scrubber/absorber; introducing FGD scrubber wastewater generated by the wet-oxidation scrubber/absorber into an anoxic biological reactor to substantially denitrify the FGD scrubber wastewater; and introducing resulting substantially denitrified FGD scrubber wastewater into an anaerobic biological reactor to substantially reduce the amount of sulfate and/or selected heavy metals in the FGD scrubber wastewater.