Yard waste is converted to compost of highest quality

A few yards past the entrance into the Monterey County landfill in Marina are mounds of compost that meet all the standards for use in organic crop production set by the Organic Materials Review Institute.

Local growers enthusiastically line up for the high-quality compost, which also meets the Leafy Greens Marketing Agreement food safety standards, that Keith Day Co. of Salinas creates from yard waste delivered to the waste management facility.

"We recycle the material and make the mulch, and then Keith Day turns it into OMRI-acceptable compost," said Jeff Lindenthal, director of communications and sustainability for the Monterey Regional Waste Management District. "We provide a real benefit by sending that OMRI-approved compost back to the valley. It's a wonderful, high-quality compost that he's able to produce."

Lindenthal made his remarks as organic farmers from around the country got a look at the close relationship between waste management and nearby Salinas Valley agriculture during a tour before the 37th Annual Ecological Farming Conference held in Pacific Grove.

The Monterey County Waste Management facility in Marina is located in the middle of Salinas Valley agriculture, with organic strawberry production on the right as one approaches the entrance, and begonias on the left.

"We're very lucky to be so close to the Salinas Valley," said Angela Gobel, Monterey Regional Waste Management District public education specialist. "Keith Day is able to market the composted yard waste easily."

About 100 yards beyond the piles of compost, a dome-shaped anaerobic digester transforms 5,000 tons of food waste a year from Monterey Bay restaurants and food service establishments into additional compost and methane gas that is then burned to produce energy.

"It's like a 'robo-cow' for the food waste," Gobel said. "We opened the second anaerobic digester in the country in 2013, and others have been put in since. San Jose has the largest anaerobic digester in the world."

On the day of the tour, truckloads of food waste from the nearby University of California campus dining halls were trucked down and fed to this robo-cow.

"They bring in food waste from the University of California at Santa Cruz dining halls," Lindenthal said. "They mix 75 percent food scraps to 25 percent mulch. Eventually, the local refuse trucks will be running on fuel made from the waste they are picking up."

Just three weeks after it is put into this digester, the food waste begins to emit methane gas, which is burned to create electricity. When the process is complete, this composted material is used by vineyard and orchard growers.

Gobel said she is enthusiastic about the results of studies showing the potential of compost to activate growth in rangeland grasses, which can capture carbon dioxide and sequester it in the soil.

"University of California researchers found in a study in Marin County that applying just a quarter-inch of compost to rangeland can sink carbon for 100 years," she said. "If we did that to half the rangeland in California, we could offset all the commercial and residential emissions in the state. That's just half; if we did it to all the rangeland, we could turn the state into a carbon sink."

The potentially polluting methane gas created during this digestion process is also captured and put to good use.

"The gas is sent to an engine generator where it creates enough electricity to run this facility, and the extra power is sent over to our neighbor at the Wastewater Treatment Facility," Gobel said.

With various subsidies through state greenhouse gas-reduction laws, this experiment in turning organic waste into clean energy paid for itself very quickly, and could become a model for additional anaerobic digesters statewide.

"It cost $2 million to put this pilot project in place," said Michael Hardy, senior project manager at Zero Waste Energy. "This project is already paid off, when you count the carbon credits. This success allowed us to develop the larger San Jose project."

The distinctively odiferous methane gas coming from the mounds of refuse at the Marina landfill, a potential greenhouse gas, is also carried through pipes to an electricity generator.

"Within the landfill, an anaerobic system is created and methane is emitted," Gobel said. "We capture that gas and use it to generate electricity. Methane emitted from landfills is huge, and we have a system to capture most of it."

The district also mines the sheetrock brought to the dump for gypsum, which Salinas Valley farmers use to provide the soil with micronutrients sulfur and calcium, which help rehabilitate crusted soil by balancing the excessive levels of magnesium.

(Bob Johnson is a reporter in Davis. He may be contacted at bjohn11135@aol.com.)