Foreword

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This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 3, Risk and performance evaluation of water reuse systems.

A list of all parts in the ISO 20468 series can be found on the ISO website.

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Introduction

The purpose of this document is to define a methodology to evaluate the dependability of treatment systems, which is listed as one of “treatment technology non-functional requirements” in ISO 20468-1 . Although the targeted performance requirement can be selected depending on the purpose, functional requirements related to water quality should be targeted with high priority in conventional water reuse projects.

As a consequence, the dependability of a treatment system can be represented and evaluated by availability as the ability to perform long-term operation without a failure and the fulfilment of functional requirements related to the water quality target to be conformed with. As well, dependability as a “non-functional requirement” can be evaluated by benchmarking for making comparisons or improving treatment system performance.

Performance indicators other than dependability for the non-functional requirements of treatment systems have already been specified in ISO 20468-2 for environmental performance based on greenhouse gas (GHG) emissions and in ISO 20468-8 for economic evaluations based on life cycle cost (LCC). If functional requirements related to water quality performance are satisfied, dependability can provide appropriate information on operation and maintenance used for calculating GHG emissions and LCC.

A comprehensive evaluation of dependability, environmental, and economic performance can be used to select an appropriate and cost-effective treatment system in the planning phase and to identify improvement for operations and optimization opportunities on a life cycle basis. A variety of stakeholders, including managers of water reuse projects and owners of water infrastructure and facilities can find beneficial opportunities and options through a comprehensive performance evaluation using the guidelines in the ISO 20468 series .

1 Scope

This document provides guidelines for evaluating the dependability represented by the availability of treatment systems for water reuse.

The document specifies methodologies for both qualitative and quantitative assessments of availability on a life cycle basis.

2 Normative references

3 Terms, definitions, and list of abbreviated terms

3.1 Terms and definitions

3.2 Abbreviated terms

4 Concept of dependability evaluation of treatment systems

4.1 Dependability evaluation by availability

4.2 Treatment system and critical unit processes as performance control points (PCPs)

5 Evaluation procedure for dependability of treatment systems

5.1 General

5.2 Setting PCPs, confirming requirements and defining failure state

5.3 Qualitative assessment of availability

5.4 Quantitative assessment of availability

Bibliography