Influence of pH on the release of colloidal and dissolved organic matter from Vertical Flow Constructed Wetland surface sludge deposits

International audienceThe very rapid development of vertical flow constructed wetlands (VFCW) in Europe and throughout the world has induced a growing concern on the conditions of management of their surface sludge deposits (SD). The leaching of organic components from SD was explored in this study with respect to their potential impact on biochemical oxygen demand (BOD) and their role as complexing agents in the release of trace contaminants. The aromaticity and molecular size of leached organic compounds was investigated over a large range of pHs. Experimental results showed that the pH of the leaching aqueous solution influenced the concentration and characteristics of leached OC. Around the natural pH of SD aqueous suspensions (6 to 8), truly dissolved organics (8), large organic colloids (>30 kDa) were found predominant, exhibiting a low aromaticity growing with pH. Under acidic conditions (pH