Date of Award
Master of Science (MS)
Biofilms occur when planktonic bacteria attach to a surface, forming a sticky, extracellular matrix that makes them difficult to remove. Biofilms are especially troublesome in water filtration membrane systems due to their strong adhesive properties. Once attached, biofilms cause a decrease in water production (biofouling) and an increase in membrane degradation. Traditional cleaning methods use harsh chemicals and require modules being taken offline, which reduces water production rates. Moreover, despite current cleaning efforts, irreversible biofouling inevitably leads to membrane module replacement. The implementation of low-intensity UV irradiation for biofilm prevention could decrease waste and increase production. However, while much is known about the effects of high-intensity UV on planktonic bacteria death, we know little about the impact of low-intensity UV on biofilm formation.
This study evaluated the effects of low-intensity UV on biofilm formation. To accomplish this task, this thesis also evaluated the effect of low-intensity UV irradiation on planktonic bacteria under stagnant growth conditions, identified a relevant disinfection kinetics model, and determined the effect of UV on bacterial motility.
This study investigated the model bacterium E. coli in three media: a newly designed medium referred to as HT medium (publishing pending by Clemson University), tryptic soy broth (TSB), and M9 minimal medium. Both M9 medium and TSB medium are commonly utilized in bacterial cultivation. HT medium is specially formulated to augment biofilm growth while minimizing UV absorbance encountered with TSB medium.
Overall, no statistically significant decrease in biofilm formation was observed under sub-lethal irradiation with UVC in the three media tested. For E. coli in HT medium, biofilm growth was only reduced at the highest, lethal applied dose (p = 0.001). At all intensities studied (12.96 to 240.5 mJcm-2), biofilm growth in TSB (p ≥ 0.989) and M9 (p ≥ 0.366) was not significantly reduced.
It was observed, however, that low-intensity UVC irradiation may reduce bacterial motility. Swimming motility of E. coli was significantly reduced (p ≤ 0.003) at all intensities studied. Similarly, swarming motility was significantly reduced (p ≤ 0.046) at all intensities above 53.64 mJcm-2. Therefore, while sub-lethal irradiation by UVC may significantly reduce swimming and swarming motility in E. coli, there was no evidence that biofilm formation is significantly affected.
Conrad, Stephanie, "EVALUATION OF CONTINUOUS, LOW-INTENSITY ULTRAVIOLET IRRADIATION FOR BIOFILM PREVENTION" (2018). Graduate Theses & Non-Theses. 194.