WEF/WERF Cooperative Study of BNR Plants Approaching the Limit of Technology: II. Statistical Evaluation of Process Reliability
The Water Environment Federation (WEF) and the Water Environment Research Foundation (WERF) cooperated in a comprehensive study of nutrient removal plants designed and operated to meet the “Limit of Technology” (LOT) for nutrient removal. LOT is loosely defined as plants meeting either 3 mg/L TN and 0.1 mg/L TP. This effort was focused on maximizing what can be learned from existing full scale plants. In the first year of the project, eleven exemplary plants were studied. The objective of this paper was to describe the common statistical methods employed to analyze final effluent data from each treatment plant and to describe alternative methods for assessing process reliability and the relationship between reliability and permit limits. The degree to which nutrient removal efficiency is related to effluent quality variability was also considered. It is clear from this work that calculating the probability or reliability of achieving a given permit limit is useful. If the data reasonably follow a log-normal distribution, these calculations are relatively straightforward and can be accomplished in a standard spreadsheet package. If not, it is a relatively trivial matter to calculate probabilities (percentiles from the data) and to develop log-transformed probability plots from which the reliability of complying with a given treatment objective can be determined. Equally useful is evaluating process performance under an appropriate set of averaging conditions (e.g. daily data, 30-day moving average, annual moving average) at a selection of probability values that have important meaning with respect to permit compliance (e.g. 50, 91.8, 95%). This concept immediately lends itself to employing a statistical basis for permitting as well as defining the Limit of Technology or Technology Achievable Limits (although this terminology may need further refinement). Although water quality protection must be the focus of point source nutrient permitting efforts, nearly all discharge permits applied to treatment plants in the United States require near-100% reliability; the consequence of not achieving this level of reliability is a permit violation. Based on this limited study of 11 plants approaching the LOT, deterministic permit limits may not be appropriate for plants achieving very low nutrient limits, particularly when the limit is technology- rather than water quality-based.
No Reference information available - sign in for access.
No Citation information available - sign in for access.
No Supplementary Data.
No Article Media
Document Type: Research Article
Publication date: 2009-01-01
More about this publication?
- Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed. A subscription to the Proceedings of the Water Environment Federation includes access to most papers presented at the annual WEF Technical Exhibition and Conference (WEFTEC) and other conferences held since 2000. Subscription access begins 12 months after the event and is valid for 12 months from month of purchase. A subscription to the Proceedings of the Water Environment Federation is included in Water Environment Federation (WEF) membership.
WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access. Access begins 12 months after the conference or event
- Subscribe to this Title
- Membership Information
- About WEF Proceedings
- WEFTEC Conference Information
- Learn about the many other WEF member benefits and join today
- Ingenta Connect is not responsible for the content or availability of external websites