Wetlands Assimilation

Breaux Bridge Project

     The Breaux Bridge projects demonstrates that 60 years of discharging treated effluent to a wetland resulted in nutrient assimilation to background concentrations, stimulating wetland productivity, and causing no measureable impacts to the wetland or to the receiving river.

     Secondarily-treated municipal effluent has been discharged into the Cypriere Perdue wetland since the early 1950's. Over the past six decades, the type of treatment has changed. Initially, a trickling filter was used, then the first oxidation pond was constructed in 1970, and the second and third oxidation ponds were put into operation by 1980. The Cypriere Perdue Swamp is a freshwater, forested wetland located in St. Martin Parish, 3.5 km west of Breaux Bridge, Louisiana. This wetland is dominated by water tupelo (Nyssa aquatica), baldcypress (Taxodium distichum), red maple (Acer rubrum), black willow (Salix nigra), and Chinese tallow (Sapium sebiferum).

     In the late 1980's the City of Breux Bridge, population 6,000, was facing stricter discharge limits (10 mg/l BOD5 and 15 mg/l TSS) from its oxidation ponds. These limits normally apply to discharge to water bodies such as streams or lakes. The discharge at Breaux Bridge, however, flows through more than 1400 ha of wetlands before reaching a receiving stream. Because of the lack of ecological impact, the City suggested the possibility of obtaining less stringent effluent discharge limits for water flowing into wetlands prior to release into open waters. Comite Resources, Inc. conducted a one-year baseline study to determine the status of the system before a permit was granted. This study included measurements of vegetation structure and productivity, hydrology, and soil and water chemistry, and monitoring water, soil, and biota for toxins.

     In 1997, the City was issued a discharge permit for its wastewater treatment facility that includes three oxidation ponds and a chlorination/dechlorination system with the capacity to treat a flow of one million gallons per day. Discharge limits were 30 mg/l BOD and 90 mg/l TSS. Permit guidelines require that water quality, primary productivity, and hydrology in the assimilation wetland be monitored and compared to a reference wetland, a nearby and ecologically similar wetland not impacted by the effluent.

     Monitoring has been carried out at the Cypriere Perdue Swamp since the early 1990's. The overall monitoring program was designed to accomplish three objectives: 1) to meet the monitoring requirements of the LPDES permit; 2) to determine the impacts of the discharge on the structure and productivity of the wetland community; and 3) to determine the ability of the wetland system to assimilate nutrients in the treated effluent.

     The results of Comite Resources, Inc., Inc. nutrient analysis show that the Cypriere Perdue assimilation wetland was effectively removing nutrients from treated effluent in the early 1990s and it continues to do so. Today it is a healthy forested wetland with no apparent negative impacts to ecosystem function or water quality after 60 years of receiving treated municipal effluent.

     Go to Education/Peer-Reviewed Publications by Comite Resources, Inc. Staff/Impacts of Secondarily Treated Municipal Effluent on a Freshwater Forested Wetland After 60 Years of Discharge by Hunter, et al 2009 for the full publication.