Can the Carbon Metabolism Activity of Biofilm Be Regulated by the Hydrodynamic Conditions in Urban Rivers?

Abstract

Hydrodynamic regulation is widely used to improve the water quality of urban rivers. However, it is yet explore substantially whether hydrodynamics could regulate the metabolic activity of biofilm in such aquatic systems. Herein, the pilot experiment of hydrodynamics in the rotation reactor was designed, including two experiment stages, namely constant flow and fluctuate flow for 21 days and 14 days, respectively. In constant flow stage, biofilms grew in five shear stress gradients (R1~R5, 0.0044~0.12 Pa). The carbon metabolic rate (k) of mature biofilms evaluated by BIOLOG ECO microplates rose and then declined with increasing shear stress, with R3 (0.049 Pa) the highest, while R5 (0.12 Pa) the lowest. To verify whether the metabolic activity of biofilm cultured at constant flow stage can be regulated by shear stress, we initiated the fluctuate flow experiment and shear stress in reactors was reset uniformly at 0.049 Pa (with the highest k). Results showed the carbon metabolism activity of biofilm in reactor R4 and R5 increased rapidly by day 3, and there was no significant difference between the carbon metabolic rates among the five groups by day 14. Meanwhile, the utilization levels of polymers and carbohydrates by biofilms were significantly different among the five groups after hydrodynamic regulations. These results suggested that the total carbon metabolism activity of biofilm can be regulated by hydrodynamics, while the divergent changes of the specific carbon source category might affect the biofilm-mediated carbon biogeochemical processes, which should be considered for the application of hydrodynamic regulation in river ecological restoration projects.

Keywords: Hydrodynamic regulation, Biofilm, Constant flow, Fluctuate flow, Carbon metabolism activity