Low-Cost Test : Plant Copes With Sewage Near Border

Carlos de la Parra, a Mexican civil engineer who lives at Las Playas de Tijuana, a beach area west of Tijuana, likes to joke about Baja California’s sewage problems.

“For fun in Las Playas we run down to the beach after flushing the toilet to watch the sewage flow into the ocean,” De la Parra said.

The 30-year-old engineer believes he is entitled to joke about Mexico’s sewage woes. Now, as operating manager of an experimental waste water treatment plant in the Tijuana River Valley, De la Parra says there is hope for a change.

That hope is a homemade sewage treatment plant that De la Para and San Diego biologist Bill Stewart have developed. The pair say the plant, which is being run with a $95,000 grant from the state Coastal Conservancy, is an affordable way to deal with the decades-old problem of Mexican sewage washing ashore in such areas as Imperial Beach.

For years, Tijuana’s inadequate waste water system has sent millions of gallons of raw sewage spilling into the ocean and the Tijuana River, only to be carried to South Bay beaches and wetlands. The spills have forced San Diego County health officials to close the beaches for long periods because of persistent health threats.

To solve that environmental problem, the men have erected their experimental sewage plant about two miles north of the border, amid fields of lima beans at the end of Dairy Mart Road.

Since June 6, they have been taking in about 300,000 gallons of Mexican sewage a day to run through the plant’s simple system of grids and filters.

The system, which Stewart designed after six years of research, uses only two pumps, making it energy-efficient and easy to operate.

“It doesn’t take a brain surgeon to run one,” De la Parra said.

The sewage is pumped onto a “static screen,” which separates large, solid particles from the liquid waste. While the solid particles are discarded, the liquid is transported to a holding chamber, where it is forced through hundreds of layers of molded plastic laden with bacteria, which feeds on any sewage left suspended in the water.

When it gets through the cycle, the water is fairly clean, said Stewart. But it is not clean enough to use for even irrigation, and it is emptied into a sewer for more conventional treatment at the City of San Diego’s Point Loma waste water plant.

Stewart said he believed that the water one day could be treated further to meet state and federal water reclamation standards.

Stewart said his prototype could help attain the elusive dream of environmentalists: changing waste water into useable water.

“If we’re going to have environmental protection, which I think everyone wants, and waste water reclamation, which San Diego really needs, then this is the solution,” Stewart said.

Stewart also said his system, when expanded to normal capacity, would yield a plant that costs less than half the price of a conventional treatment facility. The experimental plant cost about $16,000 to build.

At least one politician has lent cautious support to the prototype plant.

“Each technology has its advantages,” said County Supervisor Brian Bilbray, the former mayor of Imperial Beach. “It is a complex, comprehensive problem that demands a combination of technologies.”

But for one environmental group, the experimental plant represents a promise for a clean environment.

“It is a real answer to a bad problem,” said Patty Emond of the Southwest Wetlands Interpretative Assn., a group formed to protect the Imperial Beach wetland sanctuary plagued by constant sewage spills from Tijuana.

The group was instrumental in obtaining the state grant for the project, an infusion of money that is expected to pay for the experimental plant’s operation for at least another six months.