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What is the Limit of Technology (LOT)? A Rational and Quantitative Approach
Author: J.B. Neethling, David Stensel, Denny Parker, Charles Bott, Sudhir Murthy, Amit Pramanik and Dave Clark
Date: 5/209
Nutrient Removal 2009 Conference Preprint

What is the Limit of Technology (LOT)? This question has been raised and answered by regulators, designers, operators, researchers and others. However, in each case, the answer was typically generated without a detailed quantitative analysis and represents the perspective of the investigator, his/her objective, goals, and overt or covert agenda. The term “Limit of Technology” is typically used to convey the lowest possible concentration to which a compound of interest can be reduced using a particular technique. In its broadest sense, the term is applied to convey the lowest achievable concentration using any technology. The deficiency with this approach is that the definition is not robust and is subject to the interpretation of the analyst. This paper presents a simple statistical method to provide a rational and repeatable method to determine the performance of a technology. The term “Limit of Technology” or “LOT” is expanded by introducing a new term: “Technology Achievable Limit” (TAL). Three TAL levels are evaluated to represents the lowest, median, and reliably achievable performance. The best performance is determined from the best 14-day (14d) performance achievable in a year – the TAL-14d representing the 3.84th percentile of the performance data. The reliable performance is determined by the treatment objectives and reliability. The reliable TAL could be represented by the TAL-90%, TAL-95%, TAL-99%, or even some other value, depending on the permit requirements (annual, monthly, or daily) and the reliability required by the owner/operator. Designers can use TAL values to assess the ability to meet certain permit requirements. Operating data shows that the TAL-14d is between 50 to 60 percent and 40 to 50 percent of the median for total nitrogen and total phosphorus removal plants, respectively. The TAL-95% values range from 180 to 250 percent of the median for nitrogen, and 200 to 300 percent for phosphorus, respectively.