Constructed wetlands for industrial wastewater treatment: Alternative media, input biodegradation ratio and unstable loading

This paper reports comparative pollutant removal performances across two parallel hybrid wetland trains, that were dosed with mixed industrial wastewater (with poor biodegradability); each train included two vertical flow (VF) wetlands arranged in series, followed by a surface flow (SF) wetland as the final treatment stage. VF wetlands of system 1 and 2 were packed with biological and construction materials, respectively. Input hydraulic load (HL) was fluctuated between 113.0-226.0 mm/d across first stage wetland units of both systems. Performance analyses indicated higher organics and nitrogen removal percentages in first stage VF wetland of system 1, due to carbon leaching from the employed organic bagasse and biochar media. On the other hand, lack of carbon supply from inorganic construction materials hindered such removals in first stage VF wetland of system 2, which was counter-balanced as the wastewater passed through second stage VF unit. Enhanced P removals were quantified in VF wetlands of system 2, which could be linked to P adsorption properties of the employed construction materials. VF wetlands of both systems were inefficient in terms of color compounds removal. Physico-chemical and microbial pathways enhanced removal in the last stage SF wetlands of both systems and improved overall removal. Organics and nitrogen removal rates (g/m(2) d) in experimental wetlands were high at upper input loadings; however, load based (g/m(2) d) removal percentages were high in first and third stage wetlands (of both systems) during lower loading ranges. Concentration based mean overall NH4-N, TN, P, BOD, COD and color removal percentages across both systems were: >= 90.0, >= 86.0, >= 91.0, >= 92.0, >= 85.0 and >= 87.0%, respectively. Such performances signify potential combination of VF (packed with biological and construction materials) and SF wetlands, for the treatment of hardly degradable industrial wastewater.