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."
