Long-term wastewater treatment effectiveness of a northern Wisconsin peatland

Secondary effluent from the Drummond, WI wastewater stabilization lagoon sy stem was applied to an acidic, nutrient-poor, 8.3-ha peatland for the purpo se of advanced wastewater treatment. Application occurred from June through October at an average rate of 10 cm yr(-1) from 1979 to 1982, 24 cm yr(-1) from 1983 to 1988, and 40 cm yr(-1) from 1989 to 1996, increasing surface flow from the application area by 47,78, and 154%, respectively. The pH of the peatland outflow increased from 4.2 to 6.7, chloride rose from 1.1 mg L -1 to 80 mg L-1, and total phosphorus increased from 0.05 mg L-1 to 0.6 mg L-1 Because raw sewage input was only one-half of the lagoon system's desig n capacity, the lagoons provided a high degree of sewage treatment, removin g 95% of suspended solids (SS), biochemical oxygen demand (BOD), and nitrog en from the wastewater stream. Phosphorus removal in the lagoons, which was 98% in the first years of operation, declined to 85% by 1995. The peatland contributed little additional treatment, removing only 37% of the nitrogen and 17% of the phosphorus remaining in the lagoon effluent. The peatland's capacity to retain phosphorus was exhausted after a few years of applicati on. Increased pH, nutrient availability, and water levels altered the peatl and vegetation community. The Sphagnum ground cover was reduced or eliminat ed in many places, and dense stands of cattail (Typha sp,) developed in som e areas. Small peatlands such as this one seem poor candidates for use as t ertiary treatment systems.