| Enhanced biofilm growth on corrodible materials commonly used in drinking water distribution systems (DWDSs) is well documented and can result in deterioration of water quality. Assimilable organic carbon (AOC) in bulk water is used to assess biofilm growth potential, but only limited research has focused on direct measurements of DWDS biofilms.;Here, I compare three methods for direct measurement of DWDS biofilm growth (biofilm HPC, biofilm biovolume by CLSM and biofilm total cell count by FCM). Biofilm HPC proved to be a simple and robust method for detection of viable microorganisms on all three pipe materials investigated. Biofilm biovolume by CLSM was able to measure intact biofilms, thus avoiding biofilm detachment. FCM results showed lower signal to background ratios for the three materials compared to the other two methods.;I sampled seven DWDSs (27 sample sites) twice for biofilm growth on three coupon materials (cement, cast iron and PVC) installed in two sample types (pipe loops and annular reactors) for 90 days. Analysis of variance and post-hoc analysis indicated significantly higher biofilm HPC and total cell count by FCM on cast iron vs. cement and PVC coupons regardless of sampler type. Planktonic HPC (+), total hardness (+), hydrogen ion (+), pH (-), and nitrate (-) were consistently correlated with biofilm growth measured on three coupon materials by in data collected from five or more utilities. Total chlorine decay (+), planktonic HPC (+), hydrogen ion (+) and pH (-), turbidity (+), temperature (+), alkalinity (+), and AOC (+) showed correlations consistent with aggregate data (i.e., data from all utilities treated together as one data set) and in the majority of utility-specific data for biofilm HPC and biofilm biovolume by CLSM on all three materials. Total chlorine decay was most consistently correlated with 71 percent of utility tests and aggregate data both showing a positive correlation to biofilm growth. Calcium and total hardness (both +) and nitrate (-) also showed consistent correlation in aggregate data but only showed 26 to 42 percent agreement in utility-specific tests. |
