High Hopes Set on Low-Tech Solution to Sewage Problem

Carlos de la Parra Renteria knows a thing or two about the pitfalls of transposing U.S. technology onto Mexican soil. After all, he spent three years trying to coax a sewage treatment system designed in Cleveland into treating sewage in Tecate, Mexico.

When he arrived in Tecate five years after the plant was built, the system’s operating manual had long since vanished. Ordering replacement parts from the United States was difficult or impossible. From time to time, de la Parra would find workers diligently scrubbing off the very bacteria that are key to breaking down organic wastes.

Now de la Parra, an engineer from Tijuana, is part of a group of Mexicans and Americans trying to develop a “low-tech” solution to the problems of Mexican sewage. Their system is everything Tecate’s was not--economical, easy to operate, lacking in breakable parts.

It sounds impossibly simple:

First, run “the product” through a large sieve. Pump it up a tower and dribble it down over corrugated plastic. Let the weighty stuff settle out, send the rest into a man-made marsh. What emerges, if all goes well, should be reusable water.

For six months, that simple system sucked Mexican sewage out of a manhole and processed it amid the bean fields of the Tijuana River Valley. The waste water that emerged, its operators say, came out cleaner than waste water from San Diego’s Point Loma treatment plant.

Now, de la Parra’s group intends to construct a larger pilot plant in residential Tijuana, treating sewage from about 500 homes. Financed so far by state funds from California, they have received help and some encouragement from Mexican officials.

Their system, they say, is well-suited to Mexico: It is relatively inexpensive, energy-efficient and involves few mechanical parts. It is compact and modular and requires no underground concrete tanks, so it could be constructed on Tijuana’s rocky terrain.

Best of all, its designers say, the system could provide treated waste water that they say could be used for irrigating urban greenery. That would cut the expense of importing water, and the waste of dumping millions of gallons of water into the sea.

“This is a piece of solving the problem (of Mexican sewage),” said Craig Barilotti, a San Diego marine biologist who is acting as a consultant to the sewage system group. “It doesn’t solve all the problems. And it requires planning and integration, and it’s new.”

“The whole question of water supply and treatment and recycling of water is an important issue for Third World nations everywhere,” said Dan Luecke of the Environmental Defense Fund, an environmental group sponsoring the project. “I think if this system proves effective on the pilot scale, there may be applications and opportunities in other parts of the world.”

The system is the creation of a diverse collection of Americans and Mexicans--engineers, marine biologists, political and environmental activists. It has been funded by the state of California’s Coastal Conservancy and has received contributions from private businesses.

But the idea has had a tepid reception from officials at the U.S. Environmental Protection Agency and the people who run San Diego’s sewage system. Several said decentralization and water reuse are appealing ideas, but they were skeptical about whether the system could catch on.

“Basically what you’re dealing with . . . is what I refer to as Third World technology,” said Rod Donnelly of the San Diego Water Utilities Department. “In our country, the requirements necessary are very high. We set very high standards here.”

“I don’t know what they’re up to,” said Fitzhugh Green, an associate administrator of the EPA in Washington, who deals with border sewage issues. “The Mexicans have a perfectly good system they’re doing. . . . So anything these people decide to do with the Mexicans, that’s up to them and we’ll be happy if they succeed.”

The problem of millions of gallons of untreated Tijuana sewage flowing into San Diego County is one of a number of border pollution problems troubling U.S.-Mexican relations. For years, the two countries have considered plans for stopping the flood of untreated waste.

So far, they have agreed on “phase one” of a solution--a series of treatment lagoons being built five miles south of the border. The facility is expected to begin operating in January. Its treated waste water will be dumped into the ocean.

Now, U.S. officials have asked the Mexicans to consider additional facilities. De la Parra and his group are optimistic that they might step in and provide a reliable and more economical alternative to conventional sewage treatment.

The idea germinated a half decade ago in the mind of Dr. Mike McCoy, a systems ecologist turned Imperial Beach veterinarian active in border sewage issues. He had been thinking about water diversion and the ecological changes caused by arid areas importing water.

Meanwhile, San Diego was throwing away 120 million gallons of waste water a day into the ocean through the sewage outfall off Point Loma. And “renegade” sewage from Tijuana was spilling into the new Tijuana River Valley Estuarine Sanctuary.

So McCoy and others secured a grant from the California Coastal Conservancy, a state agency, to develop a new kind of sewage treatment system. It would have to treat sewage, reclaim water and sewage sludge, and be modular, capable of expanding at minimal expense.

Hired to head the project was Susan deTreville, a wildlife biologist and former director of the California affiliate of the National Wildlife Federation. DeTreville had analyzed then-current schemes for halting the flow of Tijuana sewage into the United States.

She concluded that the proposals for big U.S.-style treatment plants were prohibitively expensive and ignored the fact that half the homes in Tijuana are unconnected to sewers. As for shipping Mexican sewage to Point Loma, she said, that would overtax the U.S. plant.

DeTreville and de la Parra began working with a North County biologist, William Stewart, who had been developing a new type of treatment system. He proposed using two simple and proven pieces of treatment technology, a so-called Hydrasieve and a biological filter.

Under Stewart’s system, sewage is pumped through the sieve, a fine screen that catches solids and grit while liquid passes through. Then the screened liquid is pumped to the top of an 18-foot tower of plastic filters and allowed to trickle down through the filters.

The filters, in this case, are made of a kind of corrugated plastic providing a large surface area on which bacteria grow. As the waste trickles down in a thin film, the bacteria feed on nutrients, forcing the organic material to biodegrade and the solids to agglomerate.

“Like a big stomach,” is how de la Parra describes it.

Finally, in a fully constructed system, the waste water would go into a settling tank in which any remaining solids would settle out. The water would go from there into a man-made marsh lined with clay and planted with cat-tails and bulrushes.

With sufficient space, the marsh is supposed to “polish” the water: Oxygen drawn naturally to the roots of the plants would stimulate bacteria that in turn would break down organic matter. Such wetlands have been used on a small scale by industries, campgrounds and some developments in the United States.

Stewart and others contend that U.S. cities never developed an entire system such as his because massive federal funding for sewage treatment left no incentive to economize. So municipalities built oversized systems that could handle, or even encourage, future growth.

Those systems work on similar principles, but often use activated sludge instead of the filter to break down organic waste. Using activated sludge is a complex and fragile process that requires training; federal studies have found that malfunctions are common.

Last year, Stewart, deTreville and others put their pilot system together on land in San Ysidro owned by the International Boundary and Water Commission, which handles disputes with Mexico. Manufacturers donated the sieve and filter. There were gifts of fencing, a crane and pumps.

The plant began operating in June, 1985, looking like a Rube Goldberg contraption against the flat landscape at the foot of the sharp hills of Tijuana. The sewage came from Tijuana’s pump station No. 1, flowing through a connection being used then to ship it to Point Loma.

As its operators describe it, the six months of testing went smoothly, apart from the occasional T-shirt or whole chicken that racked up the pumps. The plant processed 75,000 gallons a day, returning the effluent to the sewer because it was only a test.

In the end, the group reported last summer, tests indicated that the system cut the “biological oxygen demand” of the waste water by 75%. Biological oxygen demand, a measure of the organic content in waste, is a way of judging the strength of waste.

It also reduced the amount of solids by 75%, the group reported.

“Our first phase was really proof of concept on a small scale,” Barilotti said. “This had never been done before. Before you blast someone to the moon, you’ve got to see if the rocket works. The rocket works.”

But sewage stopped flowing through the line in March, when Mexican authorities began diverting their waste to the lagoon system they are constructing. The treatment lagoons are to begin operating in January, 1987. In the meantime, the raw sewage goes straight into the surf.

Then last summer, the IBWC declined to renew the experimental plant’s lease, citing its location in the flood plain. The acting IBWC commissioner also complained that the group had begun digging its proposed artificial wetlands without consulting him first.

In the meantime, de la Parra had met three times with Mexican environmental officials in Mexico City and was encouraged by their response to the project. De la Parra works with one of the project’s sponsors, El Colegio de la Frontera Norte, a government-funded think tank in Tijuana that is an official adviser to the Mexican environmental agency.

Now Mexican authorities have offered a site in Tijuana for a new 200,000-gallon-a-day pilot plant near the Otay border crossing. DeTreville described the site as perfect--near a park that could use the recycled water and near a sewer line that chronically breaks down.

DeTreville hopes to get approval this month from the Coastal Conservancy to build the new plant across the border. If the Conservancy approves, she said, she believes they might begin building the second plant early next year.

EPA and San Diego city officials familiar with the process did not fault the engineering of the system, noting that it involves tried and true components. However, several raised reservations about its effectiveness and whether Mexican authorities would try it.

Richard Reavis, a senior engineer with the EPA, noted that the pilot project’s success statistics were based in part on laboratory simulation of the last stage of the process. Because there was no settling tank, or “clarifier,” attached to pilot system, the operators did the final settling in a lab and measured the results.

“Unfortunately, no settling acts like (a lab test),” he said. “They’re getting much better removal or efficiency than they would get in actual practice.”

Reavis also said that in his experience, the Mexican government had seemed to favor centralized sewage treatment. He questioned whether decentralization would really be cheaper, in light of the economies of scale inherent in large facilities.

Other questions raised by U.S. officials included whether the waste water would be treated sufficiently for irrigation, in view of diseases that might be spread via sewage. One official wondered--as did de la Parra--whether there would be demand for the recycled water--in the rainy season, for example.

“It’s very popular and a lot of people like to talk about effluent disposal on land,” said Frank Covington in the EPA regional office in San Francisco. “There are some real positive sides to that. But the real item is where, who needs it and who wants it?”