Abstract
Bioburden data of municipal water, generated continuously with on on-line water burden analyzer every two seconds, were subjected to a statistical analysis for the purpose of charting, evaluating the monitoring process behavior and understanding when to take action and maintain the process under a state of control. The bio counts were recorded by a commercial analyzer that employs intrinsic fluorescence of microorganisms due to LASER excitation in order to generate a light-induced fluorescence (LIF) signal. The real-time and continuous counting of optical signals leads to a stream of positively autocorrelated data. This high-frequency data, when plotted on Shewhart control charts, are difficult to interpret and exhibit a high rate of false alarm signals due to the autocorrelation. This paper analyses an example set of the data of water biocounts of one single day with the purpose of removing or minimizing the autocorrelation using model-based and model-free methods. This analysis can be applied equally to environmental monitoring of inert particles and microbes in air in controlled rooms. The methods of skip sampling and of time series model were shown to remove the autocorrelation. The author favors the model-free method of ″batch means control charts″ whereby a ″batch″ or a number successive data points is averaged and plotted on standard a Shewhart chart. The magnitude of this number depends on the knowledge of the given process and the purpose of the process control chart. Subsequently, the ″batch means control charts″ were further made meaningful and practical control charts by setting limits that are determined under relaxed constraints. The ultimate outcome is converting high-frequency data to low-frequency data plotted onto standard control charts with practical limits and much less false alarms, charts that reveal more clearly the underlying behavior and trends of the monitoring process.
- ARIMA model
- Batch means control charts
- Laser-induced fluorescence
- Rapid microbiological method
- Real-time continuous monitoring
- Water bioburden
- Received December 31, 2018.
- Accepted May 15, 2019.
- Copyright © 2019, Parenteral Drug Association
PDA members receive access to all articles published in the current year and previous volume year. Institutional subscribers received access to all content. Log in below to receive access to this article if you are either of these.
If you are neither or you are a PDA member trying to access an article outside of your membership license, then you must purchase access to this article (below). If you do not have a username or password for JPST, you will be required to create an account prior to purchasing.
Full issue PDFs are for PDA members only.
Note to pda.org users
The PDA and PDA bookstore websites (www.pda.org and www.pda.org/bookstore) are separate websites from the PDA JPST website. When you first join PDA, your initial UserID and Password are sent to HighWirePress to create your PDA JPST account. Subsequent UserrID and Password changes required at the PDA websites will not pass on to PDA JPST and vice versa. If you forget your PDA JPST UserID and/or Password, you can request help to retrieve UserID and reset Password below.