Performance comparison of plant root biofilm, gravel attached biofilm and planktonic microbial populations, in phenol removal within a constructed wetland wastewater treatment system

Abstract

This study was performed in order to understand the relative contribution of a constructed wetland (CW) system's various components to phenol degradation (100 mg•L -1 ) under controlled plant biomass/gravel/ water experimental ratios. This was done by division of a pilot-scale CW system into its components, with or without their associated bacteria: (i) gravel, plant and water; (ii) gravel and water; (iii) water; (iv) gravel; (v) plant; (vi) control (sterile water). The highest phenol biodegradation rate occurred for the gravel-attached biofilm followed by root-attached biofilm and planktonic population, which recorded a similar rate to each other and a much lower rate than the gravel-attached biofilm. A control containing CW planktonic inactivated bacteria (autoclaved water) did not impact phenol removal, revealing that microbial populations are the major factor in phenol removal. The differences in the phenol removal achieved could be attributed to higher numbers of specific phenol degraders on the gravel surface, compared to lower numbers of root-attached and planktonic bacterial fractions, as isolated using phenol-agar plates which contained phenol as the sole carbon source. The main contributor to our findings appears to be the larger surface area provided by the gravel bed compared to plant roots.

The Partial Contribution of Constructed Wetland Components (Roots, Gravel, Microorganisms) in the Removal of Phenols: A Mini Review

“…Higher total numbers of bacteria on the gravel surface compared to the root surface were attributed to the high surface area of the gravel, although a comparison of the actual surface area of these two components was difficult to perform. The stark differences between the findings of this study and those of Kurzbaum et al [23] are due to the more concentrated effluent (435 mg/L COD) used by Kurzbaum et al [47].…”

“…When the effluent has a high concentration of organic matter, CW treatment may facilitate biofilm development on any surface, thus the contributions of the plant roots and the gravel bed may be equivalent. After separating CW components among tanks and monitoring phenol degradation, Kurzbaum et al [47] were able to attribute the highest contribution to phenol degradation to the gravel-attached biofilm, while the contributions and rates of phenol degradation of the root-attached biofilm and planktonic bacteria were negligible (see graphical abstract for a schematic illustration of the experimental system). In this case, the numbers of specialized phenol degraders were much higher on the gravel surface.…”

New insights into the effects of support matrix on the removal of organic micro-pollutants and the microbial community in constructed wetlands

“…Kurzbaum et al [71] also found that higher total cultivable bacteria and specific phenol-degrading bacteria in gravel attached biofilm than in free water when studying the different CW components to understand the relative contribution for phenol biodegradation. In addition, we also observed that pH and DO were the main variables connecting with biofilm communities (Table S6).…”