Dec 16, 2008

Enhancing Water Quality and Reliability

Racine, Wis., Water Utility's (RWU) of commitment to safe, high-quality drinking water for its rapidly growing system of 200,000 customers was galvanized after a Cryptosporidium outbreak crippled a neighboring community. To proactively protect its customers, RWU commissioned a new 50-million-gal-per-day (mgd) submerged ultrafiltration membrane facility—Wisconsin's first and the nation's largest at that time—that would set the industry standard for membrane projects.

An aerial view of RWU’s advanced disinfection system along the lakefront of Racine, Wis.

The system was developed on the site of an old factory complex, contributing to the beautification and revitalization of Racine’s Lake Michigan lakefront. Careful construction planning for the facility minimized impact to the operation of the existing facilities to ensure water quality reliability.

Designed by CDM, this $20 million advanced disinfection system represents a technological leap and will provide critical, multi-barrier protection from protozoan and bacteriological contaminants. The value-added facility maximizes savings, enhances system performance and delivers exceptional quality at an unprecedented total project cost of $0.40 per gal of capacity—far below the industry average.

Unique site constraints necessitated innovative engineering solutions, including connecting new 72-in. piping within an existing 1920s-era concrete water storage reservoir.

Site limitations required creative engineering solutions

The membranes, configured in a hollow-fiber shape, form an absolute physical barrier to waterborne pathogens, such as Giardia and Cryptosporidium, providing significant protection of the public water system and surpassing all water quality requirements. Clean water passes through the membrane surface, while microorganisms and solids are rejected.

The Racine membrane system contains more than 109 million individual membrane fibers to treat the drinking water. The membrane fibers are housed within modules that form the building blocks of the membrane system.

Multiple cassettes contained within a membrane tank form a process train. The Racine system has seven process trains that treat a total of 50 mgd. The project’s novel procurement process for the membrane equipment evaluated both economic and non-economic factors, allowing RWU to consider important system aspects—service support, vendor experience and membrane characteristics—that are sometimes difficult to quantify.

While installation of the membranes post-sedimentation would have allowed the existing filter basins to be converted into submerged membrane tanks, a life-cycle cost analysis confirmed that better performance, greater system reliability and redundancy, and longer membrane life could be achieved by placing the membranes after the existing dual-media gravity filters.

Membranes were installed after the existing dual-media gravity filters.

A custom-designed pumping system arrangement utilizes vertical pumps, rather than standard horizontal pumps, to reduce building space requirements, improve hydraulic conditions, increase reliability through motor flood protection and reduce piping costs.

Project highlights and benefits include:

  • A novel equipment procurement process identified a cost-effective solution.
  • Unique post-filtration installation reduces capital cost and energy and chemical usage, and maximizes membrane life.
  • An integrated technical review committee collaborated to address numerous technical and regulatory challenges.
  • An innovative air gap design prevents contamination and optimizes the site's hydraulic profile.
  • A temperature-based capacity rating assures the ability to treat an extreme range of water temperatures and demands.
  • The membrane facility provides an absolute physical barrier to water-borne pathogens, such as Giardia and Cryptosporidium.

Michael Kosterman, water plant superintendent, has been operating the Racine membrane treatment facility successfully for more than three years, providing high-quality drinking water to Racine residents and their wholesale customers.

About the author

Leonard Rago, P.E., BCEE, is vice president of CDM. Rago can be reached at 312.346.5000.