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.

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