Biofilm morphology as related to the porous media clogging

Authors: Kim, Jung Woo; CHOI, HEECHUL - GWANGJU INSTITUTE,KOREA; Pachepsky, Yakov

Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2009
Publication Date: 7/2/2009
Citation: Kim, J., Choi, H., Pachepsky, Y.A. 2009. Biofilm morphology as related to the porous media clogging. Water Research. http://dx.doi.org/10.1016j.watres.2009.05.049.

Interpretive Summary: Releasing wastewater to infiltrate through soil to enhance groundwater recharge is a common practice in agricultural, industrial and urban environments to combat water scarcity. Bacterial biofilms are typically formed in soils receiving wastewater. The role of biofilms in water purification is controversial as they can affect soil permeability and remove nutrients from infiltrating water, but can also serve as reservoirs of bacteria that can be released to groundwater. Relatively little is known about the effect of infiltration rate and nutrient availability on the development and function of biofilms in porous media. The objective of this work was to provide data on biofilm morphology and stability in artificial porous media using confocal laser scanning microscopy and an array of morfometric parameters characterizing various aspects of biofilm structure. It was found that, at a high flow rates ,clogging can be accelerated by entrapped and accumulated biofilms, but that biofilms can be easily sloughed due to high shear force. At low flow rates, clogging can be delayed as biofilms grow on narrow pore necks, but these biofilms appear to be more rigid and resistant to sloughing. High nutrient concentrations stimulate growth of dense biofilms that are stable and cannot be destroyed by shear forces. These findings are important for researchers and practitioners in the field of wastewater purification. They illustrate the necessity of elucidating mechanisms of biofilm development and subsequent porous clogging in developing the theory and technology of wastewater reuse for groundwater recharge.

Technical Abstract: Aquifer recharge for the wastewater reuse has been considered and studied as a promising process to cope with the worldwide water scarcity. Soil clogging by an excessive growth of bacteria is often accompanied with the aquifer recharge. In this study, biofilm morphology and hydraulic conductivity decrease in porous media were concurrently characterized at two flow rates and two levels of nutrient concentrations. The experiments were conducted using a biofilm flow cell that was filled with glass beads. The biofilm images taken by confocal laser scanning microscopy (CLSM) were quantified by textural, areal, and fractal parameters, and hydraulic conductivity was monitored during the experimental runs. The flow velocity influenced the superficial morphology of biofilms and the initial clogging time, while the nutrient concentration affected the biofilm density and the clogging rate. Three different clogging mechanisms were suggested depending on the flow rate and nutrient concentration: (1) clogging at a high flow rate can be not only accelerated by entrapped and accumulated biofilms, but also can be easily eliminated by high shear force, (2) clogging at a low flow rate can be delayed for the time of the biofilm growths on narrow pore necks, but the biofilm appears to be rigid enough to be not sloughed easily, and (3) clogging in a solution with high nutrient concentrations can be hardly eliminated because of the growth of dense biofilms. The depicted biological clogging mechanisms will play a role of supporting concept in the further study about aquifer recharge.