Elimination of Faecal Indicator Microorganisms From Wastewater by Combining Constructed Wetlands And Heterogeneous Photocatalysis: From Laboratory To Pilot-Scale Implementation

Abstract

[Abstract] A combined system comprising a hybrid anaerobic digester (HD), a vertical subsurface flow constructed wetland (VF), and a heterogeneous photocatalysis unit was evaluated at pilot-scale for the elimination of faecal indicator microorganisms—total coliforms, Escherichia coli and Clostridium perfringens. The VF effluent was subjected to laboratory-scale experiments using different photodegradation post-treatments: UVC photolysis, heterogeneous photocatalysis with ultraviolet light (UVA/TiO2), and sunlight-driven heterogeneous photocatalysis (Sol/TiO2). Subsequently, the Sol/TiO2 system was scaled up and implemented at pilot-scale (p.Sol/TiO2). The total footprint of the combined HD+VF+p.Sol/TiO2 system was 4.4 m2. Under continuous operation, the combined HD+VF system was able to remove approximately 1.0, 1.3 and 1.1 log units for total coliforms, E. coli and C. perfringens, respectively, with the VF unit accounting for more than 80% of the overall elimination during biological treatment. Laboratory-scale experiments showed high removal efficiency, following the order UVC< UVA/TiO2 > Sol/TiO2. In contrast, the p.Sol/TiO2 post-treatment (after 2 h of exposure) achieved lower removals of approximately 0.5, 1.2 and 0.1 log units for total coliforms, E. coli and C. perfringens, respectively. To our knowledge, this is the first study on the combination of VF constructed wetlands and photodegradation processes with the aim of improving the quality of reclaimed water for potential reuse. As a general conclusion, the photocatalysis pond employed in the present study improved the quality of the VF effluent, widening the possibilities for reuse of the reclaimed water.