Wastewater from a coal mining and processing operation is treated through a set of subsurface flow constructed wetlands. The gravel in the root zone is adequately aerated with O2 concentration values about 4.5 mg/L. COD is provided by blending the influent with municipal wastewater at 3:1 ratio, with municipal wastewater = 1. Using half reactions provided in Appendix 6, provide the balanced reaction for the three competing electron donors, Fe2+, S2-, and COD reported as Acetate and report net energy yield (fe) for the reaction