Behavior of organic carbon during subsurface wetland treatment in the Sonoran Desert.

We examined the fate of organics during wetland treatment of secondary effluent and groundwater (control) flows in parallel, research-scale, subsurface-flow (SSF) wetland raceways at the Constructed Ecosystem Research Facility (CERF) located in Tucson, Arizona. The CERF facility enabled us to distinguish experimentally among effects on effluent quality due to season-dependent processes of evapotranspiration (ET) and wetlands-derived production of organics. Organics of wastewater and wetlands origin were compared in terms of their contributions to dissolved organic carbon (DOC) in wetland effluent. Elevated temperatures and associated biochemical activities increased DOC levels in wetland effluents during summer. In other words, DOC removal efficiency was negatively correlated to temperature. The contributions of ET and wetland-derived organics to elevation of DOC in wetland effluents during summer were roughly comparable. The elevation of organic carbon concentration during wetland polishing of wastewater effluent will lead to higher levels of disinfection by-products when treated waters are chlorinated prior to reuse. Results of this work are relevant to water managers in arid regions, which may incorporate wetlands into sequential wastewater treatments leading to potable reuse of reclaimed water.