Constructed Wetlands Using Treated Membrane Concentrate for Coastal Wetland Restoration and the Renewal of Multiple Ecosystem Services

Abstract

The management of reverse osmosis concentrate (ROC) poses a challenge to utilities as it requires expensive disposal methods and advanced treatment in order to comply with regulations. This paper presents studies of natural treatment approaches, such as constructed wetlands (CWs), that have been tailored to treat ROC. Conceptually, with testing and planning, these wetlands could meet regulatory criteria before discharging to the surface water and achieving multiple benefits. Lessons learned from pilot studies of wetland treatment of ROC point to the potential benefits of designing full-scale wetlands for concentrate management. Studies have illustrated the ability of CWs to reduce the concentrations of metals and simultaneously remove nutrients to meet state standards for aquatic and wildlife designated uses. Nutrient removal processes include denitrification for nitrogen removal (possibly supplemented with Annamox reduction of NO3-N), labile carbon assimilation supporting oxidized nitrogen reduction, and phosphate-P uptake and precipitation. Because of the evaporative water loss, mass removal efficiencies were greater than concentration reductions. Studies illustrate how engineered wetlands help with the management of ROC produced from reclaimed water through reductions in concentration and volume for disposal through evapotranspiration. The associated creation of wildlife habitats and coastal wetland restoration could result in the renewal of multiple ecosystem services.