Plants Fail to Blossom Into Solution for Sewage

In the high-tech world of sewage treatment, it was an invitingly simple recipe.

Fill a few shallow ponds with raw sewage. Add crayfish and other marine life. Top off with a thatch of water hyacinths. Then, stand back as nature transforms the sewage into clean water. Natural and cheap.

The process is called aquaculture, and for years it has been touted by San Diego officials as the nascent answer to the area’s most important water dilemma: How to keep the cost of treating sewage down while weaning the city from its overwhelming dependence on imported water for irrigation and drinking.

The allure of aquaculture was so strong that the media and sewer experts from around the world came to ogle water department demonstration projects. Aquaculture was considered to be on the forefront of the various natural methods of reclaiming sewage for reuse.

“We’re talking about turning the world upside down, making drinking water out of sewage,” Dick King, retired Water Utilities Department director and chief aquaculture cheerleader, said in a recent interview.

It hasn’t been that easy.

City water officials now say the smelly, mosquito-ridden process will be of little or no use in finding the magic solution to sewage treatment in San Diego.

Treatment Cost Rises

The water hyacinth--star of the aquaculture theory--has failed to live up to its billing, and the city has been forced to add high-tech equipment just to bring sewage treatment at its new Mission Valley demonstration project up to expected levels. The cost of adding the equipment makes aquaculture less economically attractive, officials say.

Meanwhile, calculations show that, even with the additional equipment, aquaculture still takes 5 acres to treat 1 million gallons of sewage. At a daily rate of 180 million gallons going through the Point Loma treatment plant, that would require at least 900 acres--a prohibitively expensive proposition.

“I think it was a little oversold before the results were in,” said Frank Maitski, aquaculture project engineer.

“If you took this and stuck it in the boonies somewhere, it will work,” he said. “In my opinion, I don’t think it’s something to be used on a large scale.”

Yvonne Rehg, the department’s spokeswoman, added: “I think that there are times that individuals, possibly in the news media, have taken an overzealous approach to the program and have tried to sell it to the public as the total solution to San Diego’s sewage treatment problems. This is certainly not true.

“Appealing as it may be, it certainly won’t work.”

The idea of aquaculture came to the forefront during the 1970s, when the city was also seeking an exemption from a federal mandate to build a costly secondary treatment plant. Foremost among its proponents was former director King.

“It was billed as the ultimate solution to San Diego’s sewage problems in the 21st Century,” said Municipal Judge Dick Murphy, who served on the City Council between 1980 and 1985. “The money had to be invested now so we could develop the state of the art.”

“I think there were many of us on the City Council that were skeptical, but we didn’t want to stand in the way of some major technological breakthrough because we didn’t have the ‘vision’ that King had,” said Murphy, a critic of past water department policies.

Eventually, the city in 1981 built a prototype plant next to the parking lot at San Diego Jack Murphy Stadium, and the experiment was successful enough that it built a second, larger plant on a 17-acre plot off Camino del Rio North. The $1.1-million plant opened in 1984.

The city has received $20 million in federal grants to help build the second plant and study the quality of the water produced there. After all the studies, the city will have invested $600,000 of its own money, Maitski said.

High Hopes Continue

With so much interest, high hopes for aquaculture continue. The subject of using hyacinths to reclaim water in San Diego still comes up during City Council discussions and in the media.

For instance, when the City Council voted in February to bite the bullet and build a $1.5-billion secondary sewage treatment plant, a move certain to sharply increase sewer bills, Michael Tuck, the popular Channel 10 television anchorman and commentator, scoffed.

“We already have two water reclamation plants in San Diego,” he said in his on-air commentary. “These are working models. They’re being copied by other countries all over the world, but we just ignore them.”

In theory, aquaculture is a riveting idea. It is supposed to work something like this:

First, sewage is sent through primary treatment using conventional methods to remove 40% to 60% of the suspended solids.

Then, the effluent is piped into shallow ponds filled with hyacinths for secondary treatment, which is supposed to take out as much as 90% of the suspended solids.

The fast-growing plants are supposed to do two things: Add oxygen to the water--an essential step for secondary treatment--and act as a home for microorganisms that feast on the suspended solids still floating in the waste water. Also added to the water are fish that eat the mosquitoes that might breed among the plants.

Traditional Treatment

While traditional secondary treatment yields gooey sludge as a byproduct, aquaculture yields very little sludge. The major waste product is the plants, which proliferate as they feed off the sewage. The plants can be put into a landfill, fed to animals, or added to soil as fertilizer.

The water emerging from the hyacinth ponds could then be chlorinated and used for irrigation. Or it could be put through an expensive reverse-osmosis process and be consumed by people and animals.

But now city officials say the plants sitting atop the six 50,000-gallon ponds in Mission Valley aren’t doing enough--at least not without a stench and the threat of attracting mosquitoes. And officials say that just won’t do, with the ponds in the shadows of high-rise office and bank buildings.

So water administrators were forced to retrofit the ponds with air injectors, virtually the same method that is used in a conventional secondary treatment system.

“To be honest with you, when there is no extra air, we could only get 5,000 gallons through each pond, and they are designed for 50,000 gallons a day,” Maitski said. “When we add the air, then it (rate of sewage treatment) comes up.

“The hope was that the plants would produce enough oxygen and you wouldn’t have to aerate and you would not have odors and mosquitoes. That way, you would save in the operations cost and that would make up for the land value. As it turns out, the plants are not putting in as much oxygen in the water as what was hoped.”

Even after the sewage passes by the plants, it is still not fit for human consumption. It must be put through a high-tech, reverse osmosis process, which purifies the water. Reverse osmosis, which is expensive, is the same kind of treatment that is used for many bottled waters, Maitski said.

Then, and only then, can the aquaculture water be considered for reuse.

Water Lost

But that step has never been taken. Health authorities--leery of disease-causing viruses in the water--have forced the city to simply dump the 300,000 gallons that passes through aquaculture daily back into the sewers, Maitski said.

Health officials also vetoed an idea by the city’s water department to build an aquaculture plant at Balboa Park so that reclaimed water could be used to water the grounds, he said. There was worry about controlling mosquitoes without spraying the water with oil, a method used at Mission Valley.

The city, however, has received permission to sell water to Caltrans. The state agency has agreed to buy 100,000 gallons daily of the reclaimed water to irrigate highway embankments along Interstate 15. Caltrans was supposed to begin using the water last month, but that start date is now on hold because of problems with the pumping system, said Maitski.

Asked if he thought the aquaculture project has been worth the hoopla and effort, Maitski responded, “Yes and no.” He said the money “could have been better spent somewhere else. . . .

“We learned a lot of things. I think we developed a pretty good system, personally. It’s use is pretty limited for San Diego and that’s admitted right up front.”

Other alternative technologies tested in this county and elsewhere have shown some promise but also are limited in their application in San Diego.

Hub of Innovation

Perhaps the hub of innovation on the local front can be found in Santee, at the San Diego Region Water Reclamation Agency. Founded in 1977 through a joint powers agreement, the agency has used local funds and federal grants to pioneer several new methods of treating sewage.

Its first experiment--conducted at a cost of $500,000 and concluded in 1986--used artificial wetlands to produce treated sewage that advocates say is as clean as the effluent leaving a modern, mechanical secondary processing plant.

The system involved running sewage through a long, shallow trench filled with bulrushes and reeds. The plants, which perform the same function as hyacinths in aquaculture, provide a home for bacteria, which consume contaminants in sewage--like nitrates and ammonia--and break down solid material. Tests showed that even disease-causing viruses were removed in the process.

Also, the vegetation draws oxygen into its roots, which helps in the sewage cleansing process. Aerating sewage is a mechanical step done at high energy cost in a typical secondary sewage treatment plant.

“It’s so simple it hurts,” said Burt Elkins, who runs the Santee agency. “It’s low-technology, fairly low in operating costs and very low in energy and maintenance costs.”

There are fewer problems with mosquitoes because the water level can be reduced to control the insects, said Elkins. Plus, he noted, the treatment facility is not a sterile concrete plant but resembles a lagoon that attracts birds. The trouble is, it’s land-intensive: Treating one million gallons of raw sewage would take about 20 acres. The Point Loma plant covers about 20 acres and treats 180 million gallons daily. That ratio would translate to 3,600 acres, even more than the area required by aquaculture.

Another Process

“It could be done here, but it’s ideally made for a small community,” said Elkins, who has published his findings from the wetlands project. “I got a call from the mayor of an Oklahoma town of about 500 people. One acre would take care of all their sewage.”

Another process under development since 1979 and now being tested in Santee produces a sludge that can be converted to a lightweight concrete that can be used for building.

Dubbed the “See-ba” system, it mixes sewage with highly absorptive clay and a few other additives, causing sewage solids to form a “flock” that settles to the bottom of the treatment tank.

The cleaner water--similar in quality to sewage after it is treated at the secondary level--is siphoned off. The clay mixture is then heated in a kiln, from which it emerges as pellets of iron and carbon compounds resembling puffed wheat.

The ceramic-like material, purged of contaminants during heating, can then be used to make a concrete aggregate with a strength Elkins says is suitable for high-rise construction. Sale of the material could make the process all the more cost-effective.

So far, the process has been tested only on small amounts of sewage, from a one-gallon bottle size to the 70-gallon-a-minute plant in operation today. But Elkins is confident that this technology will have payoffs on a larger scale. A federal grant of $2 million already has been awarded for construction of a plant able to treat 1.5 million gallons a day.

“The larger the scale, the more economical it gets,” said Elkins, noting that he has fielded calls about the project from China and other distant corners of the world.

In Tijuana, the Environmental Defense Fund is working with a Mexican group on that city’s stubborn sewage problem. They have devised a low-tech system that they plan to use on a 23-acre site south of the border this year.

Using a $239,000 grant from the state Coastal Conservancy, the group pumps sewage through a sieve that sifts out solids and grit and then trickles it down an 18-foot-high tower strung with filters.

The filters are made of corrugated plastic and provide a home for bacteria, which digest nutrients in the sewage as it dribbles down. The remaining water then goes into a tank for further settling, and finally, on to a man-made bed of cattails and bulrushes. As with the Santee marsh, this one uses bacteria on the plants’ roots to digest waste. The plants also gather oxygen that further stimulates the bacteria.

After a six-month test in 1985, the system’s innovators reported that it removed 75% of suspended solids in sewage and 75% of the so-called biological oxygen demand--a term that refers to the amount of organic matter in waste.

Simple, low-cost and involving few mechanical parts, the system is being billed as one piece of the solution to Tijuana’s sewage problem. Treated wastewater will be used to irrigate a municipal park.