Indicator parameters of biofilm quantity in full-scale drinking water distribution system samplers identified by multivariable statistical methods.

This study aims to identify indicator parameters for biofilms in drinking water distribution systems (DWDS). Biofilms grown on coupons of three pipe materials (cast iron, cement, and polyvinyl chloride) in two sampler types (pipe loops and annular reactors) installed at full scale DWDS were quantified by three analytical methods: heterotrophic plate count (HPC), total cell count by flow cytometry (FC), and in situ by confocal laser scanning microscopy (CLSM). Quantification by both biofilm HPC and CLSM biomass is recommended to avoid under-reporting of viable but non-culturable microbial populations. Multiple multivariable statistical methods were used to explore complex full-scale data sets. Principal component analysis (PCA) showed similar variability of select water parameters and biofilm quantity regardless of sampler type. Indicators of biofilm quantity were identified by taking the preponderance of results of correlation analysis, PCA, and multiple step linear regression. Indicators of biofilm quantity found here include total calcium (average range 55-108 ppm CaCO3), total alkalinity (49-173 ppm CaCO3), and pH (7.3-8.7). Total chlorine decay and HPC of planktonic cells were indicators of biofilms both within a single DWDS and in the aggregated data of all seven utilities sampled. Assimilable organic carbon and phosphorus appear to have secondary impacts on biofilm quantity. Oxygen reduction potential (439-644 mV measured at two utilities) may also be useful as a biofilm indicator worth further investigation.