NOVELTY - The method for treating flue gas and wastewater generated by treating the flue gas comprises introducing the flue gas and an organic acid conditioning agent into a wet-oxidation scrubber/absorber, introducing flue gas desulfurization (FGD) scrubber wastewater generated by the wet-oxidation scrubber/absorber into an anoxic biological reactor to denitrify and/or reduce selected heavy metals in the FGD scrubber wastewater, and introducing resulting denitrified FGD scrubber wastewater into an anaerobic biological reactor to reduce sulfate and/or selected heavy metals in the scrubber wastewater.    USE - The method is useful for treating flue gas and wastewater generated by treating the flue gas (claimed).    ADVANTAGE - The method economically optimizes downstream removal of total nitrogen and heavy metals from flue gas desulfurization wastewater while maintaining sulfur dioxide removal efficiency at the absorber stage.    DETAILED DESCRIPTION - The method for treating flue gas and wastewater generated by treating the flue gas comprises introducing the flue gas and an organic acid conditioning agent into a wet-oxidation scrubber/absorber, introducing flue gas desulfurization (FGD) scrubber wastewater generated by the wet-oxidation scrubber/absorber into an anoxic biological reactor to denitrify and/or reduce selected heavy metals in the FGD scrubber wastewater, and introducing resulting denitrified FGD scrubber wastewater into an anaerobic biological reactor to reduce sulfate and/or selected heavy metals in the scrubber wastewater. The anaerobic reactor contains selected heavy metal reducing organisms to reduce oxidized species of corresponding heavy metals contained in the FGD scrubber wastewater into insoluble form. The anaerobic reactor contains sulfate reducing organisms to reduce sulfate contained in the FGD scrubber wastewater. Introducing the FGD scrubber wastewater into an anaerobic biological reactor to reduce CBOD and/or ammonia contained in the wastewater, maintaining the anoxic biological reactor in -50 to -300 mV or -200 to -500 mV. The method produces less than 200 mu g/L soluble selenium concentration in the treated FGD scrubber wastewater. Introducing a supplemental carbon source and/or other nutrients into the anaerobic biological reactor, introducing FGD scrubber wastewater from the anaerobic biological reactor into an intermediate clarifier and/or media filter, and a final clarifier and/or media filter, recycling a portion of FGD scrubber wastewater from the final clarifier into the anaerobic biological reactor, introducing a sugar into the FGD scrubber wastewater upstream of the anaerobic biological reactor, and introducing an adsorbent to the FGD scrubber wastewater to adsorb organo-heavy metal complexes. A portion of the flue gas treatment fluid is a lime/limestone water slurry. INDEPENDENT CLAIMS are included for:    (1) a system for treating flue gas and wastewater generated by treating the flue gas;    (2) a method of treating FGD scrubber wastewater; and    (3) a system for treating FGD scrubber wastewater.    DESCRIPTION OF DRAWING(S) - The drawing shows a process flow for a wet-oxidation scrubber/absorber system and associated conventional flue gas desulfurization wastewater treatment system.    Absorber (14)    Particle scrubber (16)    Recirculation tank (18)    Supply line (20)    Reheater. (26)