Impact of Scale Formation on Biofilm Growth in Premise Plumbing
Final Report Prepared for the Salt Institute by
Peter Fox, PhD
Morteza Abbaszadegan, PhD
School of Sustainable Engineering and the Built Environment
Arizona State University
Summary: This study evaluated the effect of scaling on biofilm formation on two of the most common pipe materials used for premise plumbing. The two pipe materials used were copper and polyvinyl chloride (PVC). Biofilm formation was studied with clean coupons, coupons with hard scale and coupons with soft scale. Soft scale occurs when deposition of scale particles occurs during the scaling process. Biofilm formation was studied in biofilm growth reactors under controlled conditions, with constant flowrate, one bacterial source and a controlled nutrient source. Therefore, pipe material and scale were the only variables in the study. The effect of different pip materials was studied with clean coupons. Clean PVC coupons supported more biofilm growth than clean copper coupons. Based on surface roughness, one would expect more growth on copper coupons since it is the rougher surface. It is unlikely that PVC can release nutrients to support microbial growth, therefore, the lower biofilm growth on copper is attributed to the antimicrobial properties of copper. The study of scaled couponds revealted that scale increased biofilm growth on both pipe materials. Scale will increase surface roughness and provide shelter for microbial attachment. The increase in biofilm growth on scaled coupons was 600-620% for copper and 85-90% for PVC. The larger increase in biofilm on copper could be from the scale shielding microbes from the antimicrobial properties of copper. The increase in biofilm formation was similar for both soft scale and hard scale so there was no apparent effect from the type of scale. Since copper is the most commonly used premise pipe material in premise plumbing, the impacts of scale formation on premise plumbing could be quite pronounced.
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