Assimilation wetlands are natural wetlands into which secondarily treated and disinfected effluent from a wastewater treatment plant is discharged to improve water quality and wetland sustainability. Nutrients in the municipal effluent increases wetland plant growth, and organic matter deposition on the wetland surface, which increases elevation and offsets subsidence and produces a positive feedback loop of increased ecosystem vigor and resiliency. Freshwater in the effluent provides a buffer against saltwater intrusion events, especially during drought. Thus, the introduction of treated municipal effluent into disturbed and isolated wetlands is a positive step towards their ecological restoration. This practice also benefits dischargers by reducing capital, operations, and maintenance costs compared to conventional wastewater treatment.
The concept of using municipal effluent for restoration of wetlands in coastal Louisiana originated with Breaux and Day (1994), who proposed that adding nutrient-rich effluent to hydrologically isolated and subsiding wetlands could promote vertical accretion through increased organic matter production and deposition. Their work, and other studies, has shown that treated municipal effluent does stimulate productivity and accretion in wetlands (Hesse et al. 1998; Hunter et al. 2009a; Shaffer et al. 2015; Hunter et al. 2018). In addition, removal of nutrients and sediments from municipal effluent by assimilation wetlands has been well documented at the cities of Amelia (Day et al. 2006), Breaux Bridge (Blahnik & Day 2000; Hunter et al. 2009a,b; Hunter et al. 2018), Broussard (Hunter et al. 2018), Hammond (Shaffer et al. 2015; Hunter et al. 2018), Luling (Hunter et al. 2009b; Hunter et al. 2018), Mandeville (Brantley et al. 2008; Hunter et al. 2018), St. Bernard (Day et al. 1997), and Thibodaux (Zhang et al. 2000; Izdepski et al. 2009).
Design and construction of an assimilation wetland typically requires a Louisiana Department of Natural Resources (LDNR) Coastal Use Permit (CUP), Louisiana Department of Environmental Quality (LDEQ) Louisiana Pollutant Discharge Elimination System (LPDES) permit, and US Army Corps of Engineers (USACE) 404 permit and Water Quality Standards certification, along with potential levee board permits, all of which Comite Resources has obtained for numerous projects.
Comite Resources works with municipalities to assess wastewater treatment needs and to identify potential wetland areas that would benefit from effluent discharge. Comite Resources collaborates with project engineers to design the effluent distribution pipeline and with LDEQ, LDNR, and USACE to secure permits. Comite Resources monitors assimilation wetlands serving the cities of Breaux Bridge, St. Martinville, Luling, Hammond and Mandeville and visits each wetland monthly to collect ecological data.