Design and Operations Uncertainty Task Group (DOUTGroup)

The Task Group is officially hosted by the IWA Specialist Group on Systems Analysis and Integrated Assessment 

Introduction

Engineers have dealt with uncertainty from the time the first wastewater treatment plant was designed and commissioned. The unpredictability of certain aspects of wastewater treatment such as influent characteristics or the response of the microbial community, has forced designers to implement large safety factors and owners to require highly redundant systems.

There is increasing agreement to state that the use of mechanistic mathematical models for the design, upgrade and optimisation of treatment plants allows engineers to steer away from semi-arbitrary safety factors, which often result in overly conservative solutions. Mechanistic models provide practitioners with a structure which allows the identification and quantification of the sources of uncertainty. Once uncertainty evaluations have been incorporated explicitly into plant design, current safety factors can be replaced with design factors derived from quantifications of the uncertainty during model development and use. For operations, understanding the degree of uncertainty in model predictions will promote a more realistic use of models targeted to specific operational objectives. Furthermore, uncertainty evaluations will provide an objective method for the assessment of equipment failure risk and other areas that incur operational risk.

The goal of the IWA task group is to critically summarise the work that has already been done on the topic of uncertainty evaluation and identify gaps in available methods or knowledge. It will build on the knowledge already acquired by certain key efforts in the wastewater field. In addition, the project intends to incorporate work done in related fields such as water resources management. The study intends to bring together the collective knowledge of engineers, academics and plant owners, from several countries and continents.

The IWA task group will be the first phase of a multi stage project that will culminate in the development of an industry-wide, recognized protocol that incorporates uncertainty evaluations in model-based plant design and optimisation. The protocol will incorporate transparent and objective methods of estimating new design safety factors that can be widely used by the engineering community.

Goals of the Task Group

The goals of the group can be summarised as follows:
1. Propose a common language for communicating on the subject of uncertainty.
2. Propose a comprehensive list of the sources of uncertainty.
3. Document and evaluate existing methods for assessing and evaluating uncertainty (quantitative and qualitative).
4. Incorporate knowledge from other fields (water resources, atmospheric science, nuclear industry, etc.) on applications of uncertainty evaluation methodologies.
5. Identify gaps in current knowledge. Define the developments required to provide adequate tools to implement uncertainty evaluations in projects for design and operation of WWTPs.

Outcomes

The task group report will provide an overview of the topic of uncertainty in the field of wastewater treatment. It will summarize current knowledge on the available methods for assessing and evaluating uncertainty.

The Task Group has full support from the IWA Specialist Group on Systems Analysis and Integrated Assessment, by the Task Group on Good Modelling Practice (GMP) and by the Modeling Expert Group of the Americas (MEGA), a Water Environment Federation (WEF) subcommittee.