Pierre Bérubé is working to ensure affordable and cleaner drinking water for all - photo by Martin Dee

UBC Reports | Vol. 53 | No. 3 | Mar. 1, 2007

Water Probe Optimizes Treatment Plants

By Brian Lin

Pierre Bérubé doesn’t think twice about drinking water straight from the tap and shuns consumer water filters and bottled water as “gimmicks.”

One of only a handful of Civil Engineering professors specializing in drinking water treatment in Canada, Bérubé has now developed a tiny tool that could see the rest of us as confident of the purity of tap water as he is. He is working with the City of Kamloops to test his idea.

“We’re very lucky here in the Lower Mainland because our water comes from small, well protected watersheds fed by snow-melt and rain,” says Bérubé. “In other municipalities such as Kamloops, it is impossible to completely protect the water since it often comes from rivers that can be hundreds of kilometres long and as a result, there are more opportunities for impurities such as pathogens to be introduced into the water.”

“In those cases, treatment using conventional sand filtration may fall short, with a large amount of impurities quite literally falling through the cracks.”

In the past decade, membrane-based water filtration systems have become the predominant technology to replace sand-based systems. They cost about the same to install and require a lot less space -- a unit capable of treating water for 5,000 residents is about the size of a large closet. They can also be much cheaper to operate over the long run.

The leading technology in membrane-based systems was developed in Canada by a company called Zenon (which has since been acquired by GE). Dubbed the ZeeWeed®, it is capable of filtering out up to 99.999 per cent of impurities, as opposed to 99.9 per cent for sand filtration systems.

Despite these obvious advantages, membrane-based systems remain out of reach, especially for small municipalities that can’t afford a sand-based system in the first place. Now Bérubé and his team of undergrad and graduate students have developed a microprobe that could make membrane systems cheaper to operate, and in turn make it possible for smaller communities to provide more affordable and cleaner drinking water.

The membrane-based systems consist of thousands of polymer-coated fibres -- hollow tubes 2m in length and about the girth of cooked spaghetti -- vertically submerged in large tanks of water and fixed to the bottom. As source water flows through the tank, suction is applied to the top of the fibres, forcing water to enter through tiny pores on the fibres’ surface, leaving impurities behind.

Meanwhile, air is pumped into the bottom of the tank and as the bubbles rise, they cling to the fibres’ surfaces and the shearing force scrapes off the gunk, so to speak.

“Aeration alone is 30-40 per cent of the operating cost and optimizing it could mean hundreds of thousands of dollars in savings for communities such as Kamloops that use membrane treatment,” says Bérubé.

And that’s where the microprobes come in. Made of platinum and embedded in Teflon-coated fibres identical to their polymer counterparts in size, the microprobes serve as stealthy detectives, collecting valuable data to back up current hypotheses on the complex interaction between air bubbles, water flow and even the bumps-and-grinds among the fibres themselves.

“Up to now, optimizing the system involved a lot of expensive trials and errors,” says Bérubé. “Since we could only measure how pure the water was coming out of the other end, we had no idea which part of the process -- the bubble size, flow path or fibre denseness, for example -- was contributing to better filtration.”

In fact, preliminary data suggests the fibres “clean themselves” more effectively simply by bumping into each other. “If this is true, we may be able to replace the aeration system with an inexpensive mechanical device that promotes fibre contact and achieve the same outcome” says Bérubé, who is working with Zenon and the city of Kamloops to use the microprobes to monitor a full-scale system this summer.