Winter and spring evaluations of a wetland for tertiary wastewater treatment

The Union Electric Callaway Nuclear Power Plant currently uses a wetland that evolved after the retirement of a water treatment lagoon to supplement the existing mechanical wastewater treatment plant. The purpose of this study was to evaluate the wastewater treatment performance of the evolved wetland. Removal of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), ammonium, nitrate, phosphate, and sulfate were monitored during winter 1992 and early spring 1993. Hydraulic and hydrologic assessments were also conducted to determine the effective treatment area and actual detention times. The organic loading during the study was low, resulting in moderate decreases or increases in BOD, COD, TSS, and ammonium. The wetland system provided excellent reduction in phosphate, nitrate, and sulfate. Removal of all constituents was significantly greater during the early spring sampling period than the winter period. Increased performance was probably caused by increased surface water temperature, vegetative uptake, and greater detention times. A large amount of short circuiting was observed within the system, reducing detention time and wastewater treatment performance.