Reduced depth stacked constructed wetlands for enhanced urban wastewater treatment

This work presents a new configuration for constructed wetlands (CW) for treating urban and domestic wastewater with enhanced chemical oxygen demand (COD) and nitrogen removal efficiencies. In the new configuration three stacked stages of shallow depth, operated under partial saturation replace a traditional single stage vertical down flow CW. A single pulse of wastewater produces sequential aeration steps on each stage, improving convective oxygen transfer and therefore boosting the aerobic degradation of COD and nitrogen removal via nitrification denitrification reactions. When a conductive filling was used in the systems, the treatment performance was further improved due to direct interspecies electron transfer (DIET) among bacteria in the bed. As a result, systems operated under a high organic load rate (75 g m(-2) d(-1)), removed 92% of the COD, 80% of the ammonia nitrogen (NH4-N) and 55% of the total nitrogen (TN). Besides, under a higher loading rate of 126 g m(-2) d(-1), COD degradation reached 85%. Traditional single-stage conductive units showed a poorer performance, indicating that high oxygen input may be a requirement for achieving high nitrogen and COD degradation efficiencies in treatment wetlands filled with conductive materials.