Floating treatment wetlands as a suitable option for large-scale wastewater treatment

In many developing countries, there are limited or insufficient wastewater treatment infrastructures. Floating treatment wetlands (FTWs) can be a cost-effective phytoremediation approach to treat various types of wastewater. The buoyancy of the FTWs is due to air-filled rhizomes and entrapment of gas bubbles by the interwoven roots, which can be supported further by rafts. The performance of full-scale systems for treating genuine wastewater is largely unknown because studies so far have been experimental. Here, we installed full-scale FTWs in stabilization ponds receiving sewage (60%) and industrial (40%) wastewater from Faisalabad, Pakistan, and evaluated their treatment performance over a period of three years. The FTWs promoted a substantial improvement of all recorded water quality indicators and a reduction of heavy metal concentrations in the effluent compared to the influent. The maximum removal capacities of the system were 79% of chemical oxygen demand (COD), 88% of biochemical oxygen demand (BOD) and 65% of total dissolved solids (TDS). The performance was optimal in the second and third years of operation during which about 60 million m3 per year of wastewater was treated at a cost of US$0.00026 per m3. This study demonstrates that FTWs are an appropriate ecotechnology for the large-scale cleanup of sewage and industrial wastewater.