Technical Bulletin No. 0971: Assessment of Test Methods for Enumeration of Escherichia coli (E. coli) and Enterococci in Pulp and Paper Mill Wastewaters

NCASI conducted a study to evaluate the performance of test methods for enumeration of the indicator bacteria Escherichia coli (E. coli) and enterococci in pulp and paper wastewaters. The study evaluated three method types approved by the U.S. Environmental Protection Agency for wastewater monitoring for each target organism: multiple-tube fermentation (MTF); enzyme substrate (ES); and membrane filtration (MF). The results indicate that MTF and EPA Method 1603 MF methods are statistically comparable for measuring E. coli. Enterococci enumerations conducted using MF procedures were highly varied because each of the three laboratories used different types of agar, resulting, essentially, in the use of three different methods. EPA Method 1600 for enumeration of enterococci was high biased compared to all other methods, although it was not possible to determine if the bias was associated with matrix effects, method performance, or laboratory bias. Only one laboratory met the acceptance criteria for the performance evaluation check using all three method types, suggesting that there are problems in properly implementing enterococci test methods among laboratories. Laboratories implemented the ES procedures using multiple-well, multiple-tube, and presence/absence procedures to measure both E. coli and enterococci. Although these procedural variations are acceptable, they may be a contributing factor when assessing variability among laboratories and can confound interpretation of data associated with matrix effects for either bacterial parameter. Further work is needed to validate ES procedures in pulp and paper matrices.