California Reopens Well by Treating H2S with Catalytic Carbon

Contents
Catalytic Carbon
California's Results
Designing a Catalytic Carbon System
Streamlined Operations
Changeout
Future Plans
Residential Well Owners Benefit

When high levels of H2S are detected at a residential well site, water purveyors often feel they have little alternative but to cap off the well. That was the situation faced by the California Water Service Company in 1993. Unable to cost effectively treat H2S at one of their sites in Bakersfield, CA, they reluctantly shut it down.

"We drilled the well about four years ago and capped it off when we found H2S," recalls Bruce Cabral, water quality manager for the California Water Service Company. "Then we heard about catalytic carbon."

Catalytic Carbon
Catalytic carbon is the result of altering the surface structure of activated carbon. Catalytic carbon is produced through a patented process that modifies the electronic properties of the carbon surface. The result is added catalytic functionality, which is significantly greater than traditional activated carbons.

Activated carbon is typically associated with adsorption‹a physical process where molecules adhere to the internal surface of contaminants. Catalytic carbon retains all the adsorptive characteristics of conventional activated carbons, but combines them with the ability to promote chemical reactions. In addition to concentrating reactants via adsorption, catalytic carbon promotes their chemical conversion.

Centaur HSL catalytic carbon is specially designed by Calgon Carbon Corporation for liquid phase applications. For treatment of hydrogen sulfide in groundwater, H2S is first adsorbed and then oxidized on the surface of the catalytic carbon. The H2S is oxidized to sulfate and other forms, which are not odorous, thus eliminating the offensive nature of the influent H2S.

California's Results
"We felt the data on catalytic carbon was worth a trial," said Cabral. "We re-opened the Bakersfield well, reworked it and installed the catalytic carbon filters. The results were instantaneous."

Before treatment, the Bakersfield water exhibited hydrogen sulfide levels ranging from .01-.2 ppm, with dissolved oxygen levels in the 4-5 ppm range. California Water Service installed Centaur HSL in a two-vessel system in parallel configuration to treat the 750-1000 gpm groundwater stream. After catalytic carbon treatment, H2S levels were zero.

Based on those results—which have continued for over three years—California Water Service has installed catalytic carbon at three more sites in the area.

According to Tim Treloar, assistant district manager for California Water Service Company, catalytic carbon's benefits are well demonstrated in numerous sites in Bakersfield. "We're using it at sites now that have relatively low levels of H2S. One was a new well and the others were existing wells where H2S presented itself over time. Any amount of H2S is objectionable to customers. It could be in the hundredths of a part per million, but it is still detectable." Generally, the California wells have flow rates between 750 to 1000 gpm through two vessels, each of which are loaded with 5,000 to 8,000 pounds of product, depending on the site.

"We're looking at H2S levels anywhere from .01 to .2 ppm at these sites. By using catalytic carbon, we're completely removing any trace of H2S—and with it any customer taste or odor objections."

Designing a Catalytic Carbon System
To treat groundwater streams effectively with catalytic carbon, three factors must be considered:

• H2S influent concentrations;
• dissolved oxygen; and
• desired flow rates.

Catalytic carbon is recommended for groundwater streams where the dissolved H2S level is less than 2 ppm. Since the reaction on the surface of the carbon involves oxidation, a minimum level of dissolved oxygen is required within the influent stream. This is a strict stoichiometric relationship where twice as much oxygen as H2S is required, with a minimum dissolved oxygen level of 3 ppm.

For example, if 1.8 ppm of H2S is present, then 3.6 ppm of dissolved oxygen is required. If sufficient levels of dissolved oxygen are not inherent in the influent, they can be supplemented with direct oxygen injection prior to the carbon bed. To allow for the complete oxidation of H2S, it also is important to maintain a minimum contact time of five minutes. Maintaining this minimum contact time in conjunction with the required flow rate will dictate equipment selection.

As iron often is present in streams contaminated with H2S, it is important to note that catalytic carbon also provides an effective method for iron removal as well. The oxidation reaction that is promoted on the surface of the catalytic carbon precipitates insoluble iron, eliminating the iron fouling problems typical in these applications.

Streamlined Operations
Cabral reports that California Water Service had previous experience with chlorine injection to treat for H2S. "The end result was effective," he admits, "but it was difficult to control. Catalytic carbon is a passive system. You can nearly turn it on and walk away."

Treloar agrees, "Catalytic carbon doesn't require much in terms of maintenance, particularly if you're using an automated backwash system."

Changeout
California Water Service has not yet had to change out the catalytic carbon at any of their sites—even though the original installation has been on-line for over three years.

"Changeout depends on several factors," explains Treloar, "including background organics, solids loading, throughput, influent contaminant levels and how well you backwash. If an ongoing chemical equilibrium can be achieved, it could extend the life of the carbon significantly."

Currently, California Water Service backwashes weekly, discharging the backwash water either to storm drains or sumps. "I'm trying to institute an automatic backwash system right now based on a predetermined run time or differential pressure," says Treloar.

Future Plans
Cabral and Treloar describe catalytic carbon as "a cost effective solution." As a result of their experiences, four more catalytic carbon treatment sites are planned for in the next year.

Residential Well Owners Benefit
Smaller, domestic wells are also taking advantage of the capabilities of catalytic carbon. Mark Kavish, water quality specialist for Eichelbergers, Inc., recommends catalytic carbon to his customers, which range from Fortune 500 commercial and industrial corporations to small, residential installations.

"The less ‘hands-on' our customers have to deal with, the better. The ease of use and performance advantages of a passive, activated carbon system have always been attractive," Kavish claims, "but the longevity of traditional activated carbon for most of our H2S removal applications made it prohibitive."

Not anymore. Eichelbergers uses catalytic carbon in six distinct sites with, according to Kavish, "absolutely no bleed-through problems." They supply Centaur HSL for both manual filter systems and those with automatic backwashing filters.

At one Eichelbergers site, catalytic carbon has been treating a well with 6 ppm of H2S. Based on the customer's personal observations, the product is succeeding in removing 100% of the sulfur odor. Another installation teams up catalytic carbon with chlorination, using the Centaur product as a post filter. Here the customer noticed at one point that the chlorinator wasn't pumping correctly—in fact it had shut down completely. Eichelbergers was pleasantly surprised to discover that the catalytic carbon—on its own—had continued to remove 5-10 ppm of sulfur from the water.

"Our customers who already have water softeners installed are particularly attracted to catalytic carbon," notes Kavish. In those sites, the catalytic carbon system is easily put in place after the softener, where it serves as a polisher of the sulfur odor.

The longevity of catalytic carbon is a big selling point for homeowners attracted by the promise of keeping maintenance to the barest minimum. It also appeals to users anxious to control initial installation costs.

"Catalytic carbon is a straight forward, passive technology. Its capability for automatic backwashing means the system virtually maintains itself. That's a big plus for many of our clients," says Kavish.