UTILIZATION OF A FRESHWATER WETLAND FOR NUTRIENT REMOVAL FROM SECONDARILY TREATED WASTE-WATER EFFLUENT

In order to test the feasibility of utilizing a fresh-water wetland for tertiary waste water treatment, secondarily treated waste water was applied to a wetland in the northern lower peninsula of Michigan. During the discharge of 38,840 m3 (10,260,000 gal) and 23,520 m3 (6,213,000 gal) of secondarily treated waste water in 1976 and 1977, respectively, surface water quality, plant productivity, and nutrient status of plants and soils were measured. In 1976 the concentration of (nitrate + nitrite)-N averaged 0.36 mg/liter in the effluent and 0.01 mg/liter at stations 25 m from the discharge pipeline. Total dissolved phosphorus (TDP) averaged 0.41 mg/liter in the effluent and 0.11 mg/liter at sampling stations 25 m from the discharge. The efficiency of phosphorus removal from the effluent was greater when surface water depths were 6 cm compared to 30 cm. Ammonium-N concentrations were rarely higher in the effluent compared to background concentrations in the wetland surface waters. In 1977 a point source distribution system was used. The effluent average 1.50 mg/liter nitrate-N and 1.57 mg/liter TDP. Within 30 m, nitrate-N was <0.10 mg/liter in the surface water and within 80 m TDP was 0.07 mg/liter. Biomass of live plants in 1976 was somewhat greater near the pipeline compared to control areas. Leaves of cattail (Typha latifolia) were longer near the pipeline in 1976 compared to control areas. Chemical analysis of sedge (Carex spp.) leaves and roots, standing dead, and litter sampled in 1976 showed no significant differences in N concentrations among sampling locations, but P concentrations were higher in leaves and roots 6 m from the pipeline compared to control areas.; In order to test the feasibility of utilizing a fresh-water wetland for tertiary waste water treatment, secondarily treated waste water was applied to a wetland in the northern lower peninsula of Michigan. During the discharge of 38,840 m**3 and 23,520 m**3 of secondarily treated waste water in 1976 and 1977, respectively, surface water quality, plant productivity, and nutrient status of plants and soils were measured. Results are discussed for concentrations and removal of nitrate and nitrite, total dissolved phosphorous, and biomass of live plants.