Text and photos by Stephanie Johnston

It's been almost four years since the water and sanitation districts of Orange County, Calif., began operating the world's largest system to turn wastewater into potable water via the same three-step treatment process that purifies baby food and medicines: microfiltration, reverse osmosis, and ultraviolet light with hydrogen peroxide disinfection.

That effort piggybacked on an earlier partnership: the agencies' 1970s-era effort to keep the Pacific Ocean from entering the aquifer that supplies 65% of the drinking water for 2.4 million people. That's when the Orange Conty Sanitation District began supplying secondary treated wastewater at no charge to the Orange County Water District, which purified the effluent via reverse osmosis before injecting up to 22.6 mgd into wells to recharge the aquifer

By the 1990s, population growth and seawater intrusion prompted the agencies' next partnership via the Groundwater Replenishment System. Instead of increasing its existing plant's capacity to 35 mgd, the water district's $481 million, 70-mgd advanced water treatment facility processes 96 mgd of secondary treated wastewater. By 2020, water managers expect the system to supply 43% of the region's water.

I jumped at the chance to see the world-renowned facility when Siemens Water Technologies, which provided the facility's Memcor CS microfiltration system, invited me on a tour after the recent WEFTEC water/wastewater trade show in Los Angeles.

The hour-long presentation was led by Mehul Patel, PE, who has worked for the Orange County Water District since interning there in 1996. He loves what he does and has mastered the art of boiling down complex engineering concepts into layman's terms. If you ever get a chance to pick his brain, do it.