Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages

Abstract

With the aim of solving the wastewater treatment problem in small villages, treatment performance of a pilot-scale subsurface-flow constructed wetland (SFW) was evaluated for removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total and faecal coliform and faecal streptococci bacteria from raw municipal wastewater. Studies of the composition and thermal behaviour of the harvested biomass were achieved in order to assess their possible utilisation as a fuel. Two different hydraulic application rates (150, and 75 mm day −1) and two macrophytes, cattail ( Typha sp.) and reed ( Phragmites sp.), were assayed. High levels of BOD, COD and TSS removal for all treatments were obtained. The best removals were obtained in those beds with the lowest hydraulic application rate. With regard to the type of plant, no significant differences were found between cattail and reed performance; however, cattails showed to be by far (almost a factor of 2) the greatest producer of biomass (22 t [d.m.] ha −1). Both cattails and reeds presented high heating values (17–20 MJ kg −1). According to these results, it can be concluded that the wetland system utilised in this research could be a suitable solution for raw wastewater as a stand-alone treatment, although a previous pre-treatment in order to remove grit, heavy solids and floatable materials would be necessary. Besides, the obtained biomass could be utilised as fuel in a small boiler for domestic uses.