Submitted to: Water Environment Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/11/2011
Publication Date: 6/1/2012
Citation: Zhang, L., Seagren, E., Davis, A., Karns, J.S. 2012. Effects of temperature on bacterial transport and destruction in bioretention media: Field and laboratory evaluations. Water Environment Research. 84:485-496. Interpretive Summary: Water that runs off of urban surfaces such as parking lots, park lands, etc after major rainfall events can contain large amounts of bacteria that originated from human or animal activity on that land. If the runoff water is allowed to flow directly into rivers or streams it can degrade the quality of the water due to elevated bacterial counts. A biorentention cell is a pit filled with sand and compost (bioretention medium) that supports plant growth and is designed to capture and slow runoff water and allow natural processes to reduce the levels of chemicals, bacteria, and other pollutants before the water flows into surface streams. This report describes experiments using several functioning bioretention cells and laboratory studies to describe the effect of temperature on the ability of such structures to reduce the amount of E. coli in runoff water. The results show that the effectiveness of bioretention medium in reducing the number of bacteria in runoff water increases as the temperature of the medium increases and suggest that consumption of bacteria by protozoan predators played a large role in reducing the levels of bacteria in water passing through a bioretention cell. Knowledge of the factors that influence the effectiveness of low-input constructed water treatment systems such as bioretention cells or constructed wetlands will lead to improvements in these low-cost methods to limit the impact of runoff from urban or agricultural lands on surface water quality.
Technical Abstract: Microbial activities (such as metabolism, predation, and proliferation) are significantly influenced by temperature. This study investigated the effects of temperature on the capture and destruction of bacteria from urban stormwater runoff in bioretention media using 2-yr field evaluations coupled with controlled laboratory column studies. Field data from two bioretention cells indicated that the bioretention systems reduced the concentration of indicator bacteria (fecal coliform and Escherichia coli) during most storm events and increased the probability of meeting specific water quality criteria in the discharge. Column tests, however, indicate that the bacterial decay coefficients in conventional bioretention media (CBM) increase exponentially with elevated temperature. Increases in the levels of protozoa and heterotrophic bacteria associated with increasing temperature appear to contribute to faster die-off of trapped E. coli in CBM via predation and competition.