Drinking Water Treatment Plant Optimization

Salt Lake City takes steps to protect public health by optimizing water treatment processes.

Linda Moss, Salt Lake City Water Treatment Process Control Analyst

June 11, 2001

Linda Moss

In 1992 the water industry was given a wake-up call when Milwaukee experienced a water borne disease outbreak caused by the organism Cryptosporidium.  The organism infected one hundred thousand people. The water profession immediately reacted to this new public health threat by optimizing the performance of the nation's water treatment plants. Salt Lake City joined in this effort by setting higher performance standards than required by the federal Safe Drinking Water Act. Salt Lake City’s Department of Public Utilities (DPU) operates the water treatment plants.

As a first step the American Water Works Association recommended a 12-point plan to improve the treatment barrier to prevent pathogenic organisms from reaching the consumer’s tap.  Later a program was formally organized in 1995 when over 300 water suppliers across the United States joined the “EPA Partnership for Safe Water.”  The program consists of four phases, which included data collection, self-assessment and corrections and finally third party assessment and correction. At the conclusion of Phase 3, water suppliers are presented a Partnership for Safe Water “Director’s Certificate of Recognition.”  DPU’s three water treatment plants received the certificate in 1997.

For the past ten years, DPU has engaged in an optimization program in the three drinking water treatment plants.  These three plants, Big Cottonwood Treatment Plant, Parleys Treatment Plant and City Creek Treatment Plant treat surface water from snowmelt and reservoir storage along the Wasatch front. To provide some historical perspective, the regulated limit for turbidity in drinking water during the 1990’s was 0.5 NTU. In 2000, that limit was reduced to 0.3 NTU.

In 1993, the DPU set a goal of no more than 0.1 NTU for no longer than four hours. In 1995, DPU joined the EPA Partnership for Safe Water and adopted this organization’s standard of a turbidity < 0.1 NTU 95% of the time. In 1999, DPU went a step further, and set its goal at never exceeding 0.1 NTU in the drinking water produced at these treatment plants.  All of these goals have been achieved.  In 2000, as illustrated in Figure 1, the maximum daily finished water turbidities never exceeded 0.1 NTU at any of the three treatment plants.  This is an exceptional accomplishment on the part of the operators and supervisors of these plants.

Although turbidity is the regulatory standard for measuring drinking water quality, DPU has employed more sensitive technology to achieve these results. Several years ago particle counter technology was incorporated into the optimization program.  The plant operators embraced this new tool and through its use perfected even better treatment optimization.  The industry standard for particle counts in finished water is 50 particles per milliliter.  DPU has set its standard at 10 particles per milliliter, and optimizing on this basis has resulted in the turbidity performance shown in Figure 1.

Figure 1. City Creek Water Treatment Plant water turbidity is consistently below the voluntary standard of 0.1 NTUs.

DPU is dedicated to the concept of excellence in drinking water quality. Protection of public health by optimizing water treatment beyond regulatory requirements is the primary mission of the department.  This goal is enthusiastically shared by the water treatment plant supervisors and operators who rose to the challenge of optimizing treatment processes. Their dedication and tenacity at each plant have lead to consistently outstanding water quality results. It requires constant operator attention and treatment adjustment to achieve these results. Their efforts have raised water treatment plant performance to the next level.