Fractionation, Biodegradability and Particle-Size Distribution of Organic Matter in Horizontal Subsurface-Flow Constructed Wetlands

In order to analyse the fate of organic matter and particles along the length of horizontal subsurface-flow constructed wetlands, two pilot wetlands were monitored in terms of BOD 5 , COD and their fractions, TOC and particle counts in various sampling campaigns. Anaerobic biodegradability properties of the effluent organic matter were also measured by means of a methane-production test. The most abundant particles in the influent, at intermediate points along the length of the wetlands, and in the effluent were those comprised in the range of 0.7 to 2 μm. Most of the particles (close to 80%) were removed within the first quarter of the wetland length. Most organic matter was also removed within the first quarter (50% and 80% in terms of TOC and COD, respectively). Further organic matter removal along the rest of the length of the wetland only accounted for a 0–10% of the total removal. The organic matter of the effluents is difficult to biodegrade under anaerobic conditions, but it is readily biodegradable under aerobic conditions.