Is Pasteurization The Key To Water Reuse?

In the summer of 1864, French chemist Louis Pasteur was vacationing in the small eastern town of Arbois where he found the local wines too acidic for his palette. Ever the man of science, Pasteur experimented with the wine and found that moderately heating it killed microbes and prohibited souring. The process became known as pasteurization in his honor and is still widely used in the dairy and food industries to reduce pathogens and prevent spoilage.

Though the low-tech method has been around for over 150 years, a novel application may be on the horizon for the water industry. Andrew Salveson, PE and water reuse chief technologist at Carollo Engineers, explored pasteurization as a treatment method for recycling water in his WEFTEC presentation of “Getting Hot — The Expansion Of Pasteurization For Potable And Non-Potable Reuse.”

Salveson’s presentation, based on a project he’s conducting along with 15 other researchers, built on a growing industry reputation he has as an authority on reuse. Indeed, this project comes hot on the heels of another one he’s conducting for the Water Research Foundation on the blending requirements for direct potable reuse (DPR) water, known somewhat cryptically as project 4536.

Regarding this latest project, Salveson pointed out that the researchers are not utilizing your great-great-grandpa’s pasteurization process. He said that he was approached in 2005 by the inventor of a new process that uses waste heat for disinfection.

“Heating water is costly, stopping progress of this concept in many areas,” said Salveson, as an explanation for why pasteurization hasn’t already taken hold in water treatment. “This new work uses heat exchangers to essentially keep the heat in the loop within the reactor, with cold water in and cold water out, and heat in the middle. This makes pasteurization 95 percent more cost and energy efficient.”

“Getting Hot” summarizes tests of this method at four locations since 2006, the ultimate goal being approval under Title 22 of the California Department of Public Health’s “Regulations Related to Recycled Water.”

The first pasteurization tests were done in Santa Rosa, CA in 2006 and 2007. The work resulted in regulatory approval for pasteurization at a target temperature of 176.4°F for 7.7 seconds.

A full-scale (500,000 GPD) test was performed between 2012 and 2014 in Ventura, CA. Per a report on the project, that work demonstrated “robust performance” of the pasteurization system which led to Title 22 clearance for pasteurization at 162°F.

Towards the end of the Ventura testing in 2014, a full-scale pasteurization system came online in Graton, CA and its disinfection results were roughly the same as its predecessor. Regulatory permission of 162° at a contact time of 10 seconds was achieved.

Finally, in 2014 and 2015, the most complete analysis of pasteurization was begun in Melbourne, Australia as demonstration-scale testing. It has confirmed “robust disinfection of a range of bacteria, virus, and protozoa at different temperatures and contact times.” Using the same unit employed in Ventura, researchers successfully treated unfiltered secondary effluent for the first time. They are hopeful that the results will allow pasteurization to replace several combined disinfection methods in Melbourne’s state of Victoria. 

When asked to highlight the most significant successes demonstrated by this research, Salveson notes three: the fact that pasteurization has resulted in the most robust treatment of pathogens for any disinfectant, that there has been long-term effective heat transfer to save energy and costs, and that there has been minimal biological and mineral fouling.

With 18 months of research left, Salveson declined to speculate on the future popularity of pasteurization for water reuse, but there is reason for optimism based on project 4536.

“4536 is looking at how pasteurization can be used as pretreatment ahead of membranes, possibly reducing biofouling in the subsequent membrane processes,” Salveson said. “4563 is also looking at overall water quality, and adding the robust disinfection of pathogens by pasteurization gives greater confidence in water quality and public health protection.”

Long since that fateful summer, Pasteur’s legacy seems to be offering us a toast from the countryside and, maybe soon, the chance to drink up.