Ozone counters Cryptosporidium in Milwaukee

The US city of Milwaukee has used ozonation to tackle a serious Crypto problem and ended up with safe, economical drinking water for its citizens. Robert Hulsey, process engineer, Black & Veatch, Dan McCarthy, senior vice president and project manager, Black & Veatch, and Carrie Lewis, superintendent, Milwaukee Water Works, report.

In 1993, an outbreak of cryptosporidiosis highlighted the need for rapid action to protect Milwaukee’s 800,000 residents from possible future occurrences. In the summer of 1998, ozonation facilities installed at the

city’s 275MGD (12,000l/sec) Linnwood and 105MGD (4600l/sec) Howard Avenue WTWs became the first in the US specifically designed to inactivate Cryptosporidium. As an added benefit, the new facilities have also effectively eliminated seasonal taste and odour problems sometimes associated with the use of water from Lake Michigan.

Project success

Along with the addition of ozonation, modifications were also made to improve performance at both plants under separate contract. These improvements included relocation of the intake pipe to deeper water to avoid water quality impacts from surface water run-off; rehabilitation of filters; and modifications to two reservoirs, a chemical feed system, yard piping, raw water pumping, two clearwells, and flocculation basins.

Prior to ozonation, Milwaukee had used free chlorine from the plant inlet through filtration with conversion to chloramines at the inlet to the clearwell. With ozonation, the two facilities will be converted to biological filtration. Modifications to the clearwells allowed for chlorine to be added immediately after biological filtration to reduce heterotrophic plate counts followed by ammonia addition to convert to chloramines for the distribution system.

To get the ozonation project on line as quickly as possible, Milwaukee took a chance on a project approach not previously used for municipal WTWs in the state of Wisconsin – design-build.

The jv team of Black & Veatch and Alberici Construction was not only up against the clock, but also had to make sure that both plants remained operational during installation of the new facilities. Retrofitting ozone facilities into existing treatment processes at both plants required careful engineering design of large diameter piping modifications and connections to existing structures in a way that avoided outages.

A phased construction approach was combined with temporary operational modifications to keep the Linnwood plant on-line while major clearwell, reservoir, piping, and chemical feed modifications were made. Milwaukee’s

decision and the team’s technology-led design-build expertise resulted in a successful outcome. The project was operational in 17 months and came in $11M under budget.


Action inspires action. Stay ahead of the curve with sustainability and energy newsletters from edie