Home\Educate\Water Reuse 101\Research Projects\Year\2009\Collecting, Exploring and Interpreting Microbiological Data Associated with Reclaimed Water Systems

Collecting, Exploring and Interpreting Microbiological Data Associated with Reclaimed Water Systems

Project: 04-12
Type: Decision Making Tool
Year Released: 2009

Program: Principal
Funding Partners: Bureau of Reclamation, California State Water Resources Control Board
Total Investment: $89,402 (Cash)

Principal Investigators: Audrey D. Levine, U.S. Environmental Protection Agency, Valerie J. Harwood, University of South Florida, and Gordon A. Fox, University of South Florida

Background

Reclaimed water systems have evolved to fill an important role in water resources management by providing an alternative water source for a wide range of applications. The importance of assurance of microbiological water quality becomes more important as the use of reclaimed water grows. Approaches used to characterize microbiological water quality including routine monitoring of process parameters and water quality surrogates such as turbidity, periodic monitoring of indicator bacteria, and intermittent monitoring of pathogens. Microbiological monitoring is conducted to satisfy regulatory requirements and/or to provide inputs for process control. The sampling context, i.e. sampling frequency, methods used, detection limits, and the measurement end-point(s) (presence/absence, concentration, viability, etc.) can complicate statistical analysis and cloud interpretation of microbiological data.

Goals and Objectives

The project developed a guidance manual to provide users with a context for collecting, exploring, and interpreting microbiological data associated with reclaimed water. Basic concepts are presented to facilitate collection of meaningful information with an emphasis on design of sampling programs, data interpretation, and statistical analysis. The information provided here can help with routine monitoring programs and design of studies for detailed microbiological investigations. The examples and illustrations provided in this document are intended to help the reader tackle a range of microbial investigations associated with reclaimed water facilities.

Research Approach

The manual is not a textbook, but is an effort to demystify some of the challenges of statistically based analyses. We hope that this manual provides the basis for exploring statistical considerations for the average user, who may have previously shied away from a subject that can be intimidating. The main “take-home” messages are:

  • Frame your questions carefully, with consideration of available supporting data and resources.
  • Plan your experimental design with system characteristics and specific goals in mind; e.g. are analyses to be paired or unpaired; can many samples be analyzed or are there cost considerations that will necessitate compromises?
  • Obtain preliminary data; carry out descriptive statistical analysis and make graphs to gain an understanding of the variability and other characteristics of the data.
  • Determine the expected necessary sample size given the variability and the magnitude of the difference you wish to detect.
  • Have fun with statistical calculations and interpretation of results! Don’t be afraid to try using different statistical approaches. Once you start exploring data and seeing relationships within and among data sets, it can become an absorbing and very helpful part of your skill set.

Findings and Conclusions

This guidance manual was developed to provide users with a context for collecting, exploring, and interpreting microbiological data associated with reclaimed water. Basic concepts are presented to facilitate collection of meaningful information with an emphasis on design of sampling programs, data interpretation, and statistical analysis. The information provided here can help with routine monitoring programs and design of studies for detailed microbiological investigations. The examples and illustrations provided in this document are intended to help the reader tackle a range of microbial investigations associated with reclaimed water facilities. The tools provided herein will facilitate comparison within and among reclaimed water facilities, allow a better understanding of microbial water quality, and ultimately facilitate risk assessment efforts and the safeguarding of public health.

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