INTRODUCTION

A reliable public water supply is essential to the health and welfare of the customers served. Reliability provisions in water treatment plant designs can ensure the production of an adequate quantity of high-quality water at all times. The selection of reliability provisions during design is dictated by regulatory requirements and by the consequences of loss of all or part of the plant for a time, or by the consequences of treated water that does not meet drinking water standards (1, 2).

The design of water treatment facilities should be based on the premise that failure of any single plant component must not prevent the plant from operating at the design flow or from meeting drinking water standards. Sufficient operational flexibility should be included in the design to handle a variety of water quality problems where raw water quality is variable. Reserve or redundant capacity should be provided in each unit process, so that process efficiency can be maintained even when a single treatment unit within the unit process must be removed from service altogether.

RELIABILITY AND REDUNDANCY CONCEPTS

Reliability and redundancy, although related to each other in plant design, have different meanings.

• Reliability refers to the inherent dependability of a piece of equipment, a unit process, or the overall treatment process train in achieving the design objective.

• Redundancy refers to the provision of

1. Standby equipment or unit process

2. More than one process in the process...