Analysis of a low organic load constructed wetland (CW) system was performed in order to understand the relative role of its various components contribution in phenol removal (100 mg/L) under controlled plant biomass/gravel/water experimental ratios (50 g/450 g/100 mL). The results [expressed as phenol50/time (hours) required to remove 50% of the initial phenol concentration] showed that the highest phenol removal occurred by combined biofilms from roots and gravel attached (phenol50=19), followed by gravel biofilm (phenol50=105) and planktonic (suspended in water) bacteria (phenol50=>200). An in depth analysis revealed that plants contribution alone (antibiotics sterilized) was minor (phenol50=>89) while roots supported biofilm resulted in a significant phenol removal (phenol50=15). Therefore in this type of CW, the main phenol removal active fraction could be attributed to plant roots' biofilm bacteria.
Keywords: biofilm, constructed wetland, gravel, microbial activity, phenol, rhizosphere