Something in the Air: Sewage Plant Assailed

Here’s a real stinker of a story.

In south Carlsbad, long known for the acres of fragrant flower fields that straddle Interstate 5, a rather offensive odor has been wafting across the freeway of late.

The culprit is the Encina sewage plant, a sprawling, ultramodern facility that normally has a solid record of odor control.

Method Changed

In late October, however, its operators raised treatment standards for the millions of gallons of effluent pumped into the Pacific more than a mile offshore from the plant, which stretches along Interstate 5 south of Palomar Airport Road.

Unfortunately, a cleaner ocean has meant a stinkier Carlsbad.

In the days after the switch, nearby residents began to get a snout-full of the stench. Complaints to the plant skyrocketed. Motorists along Interstate 5, meanwhile, debated whether to roll their windows up or roll them down.

Plant operators rushed to respond. On Wednesday, a technical advisory committee recommended the installation of an odor-control system featuring plastic or fiberglass covers over the sewage basins causing the putrid problem.

But that solution, which is to go before the full Encina board later this month, will not come cheap, nor will it come soon.

Rick Graff, general manager of the plant, said the price tag for the odor-control upgrading is pegged at $4.3 million. The system, which includes a complex network of scrubbers and filters to cleanse the troublesome smell, would probably not be in place until 1991 at the earliest, when a $49-million plant expansion is scheduled for completion, he said.

Bacteria Blamed

Graff said the malodorous mess is caused by the biological reaction used during the secondary-treatment phase of sewage processing.

As the sewage flows through long basins, known as secondary-aeration tanks, air is

pumped through the foul broth to encourage the growth of bacteria that consume waste products suspended in the effluent. The process also releases odors, most notably the ammonia-like one that has hovered over the plant in recent weeks.

Before the switch to upgraded treatment in late October, only half the sewage at Encina was run through the aeration tanks. Now, however, every single gallon of effluent flows through the secondary-treatment basins.

“Basically, we doubled the possible source of odor,” Graff said. “It got to a point where it was not only noticeable but quite frequently objectionable to some people.”

Indeed, in the estimation of residents, twice as much sewage in the aeration tanks has meant twice as bad an odor problem. The plant, which got 10 odor complaints in 1987, registered 24 in the last two months of 1988.

Although noting the irony of the situation, Graff has tried to remain philosophical.

“You don’t get something for nothing in any business, especially this one,” he said Wednesday. “To solve one problem, you sometimes compound another. You pay a price.”