Food waste processing turns garbage into fertilizer

April 15, 2013

At St. Cloud Hospital in St. Cloud, Minn., the kitchen crew is slow-cooking food waste into something good for the garden.

Since June, food-service workers have diverted cooking scraps and leftovers from patient trays into a three-step reprocessing that creates a dry pulp suitable for use outdoors. Far from creating more work, the largely automatic operation speeds kitchen cleanup and dries the ground-up waste overnight.

The result each morning is a large bucket or two of brown, crumbly substance — known as "soil amendment" — that doesn't foul the hospital's wastewater or add to the trash-hauling bill.

Kathy Frenn, of Morrison Healthcare Food Service, said the system is good for the bottom line and the environment. Morrison handles all food operations for the 489-bed hospital in St. Cloud, northwest of Minneapolis-St. Paul.

"The hospital wants us to be as 'green' as possible, and we were looking for a sustainable way to deal with food waste," said Frenn, director of nutrition services at St. Cloud Hospital. "The resulting product is something we can mix into gardens."

Frenn said it cost $163,000 to buy the equipment and $111,000 to install, the latter cost mainly a function of running pipes through walls and floors. She said the system is projected to save $18,000 annually over 15 years through reduced water consumption, fewer repairs to drains and less time spent by workers gathering and hauling trash.

Dustin Maddy, the hospital's sustainability specialist, said it also solved a problem with wastewater. Before the pulping system was installed, the hospital was exceeding discharge limits for phosphorus. Maddy said production of that polluting by-product has been cut by more than half.

The system is straightforward. In the kitchen, workers push scraps from food preparations and returned patient trays into a trough along their work surfaces. The scraps are flushed into the pulper, a squat, barrel-shaped machine that operates like a garbage disposal and can handle anything from Jello to beef bones.

Instead of flushing the grindings into the drain, the system pipes it along to the next stop — the extractor, a turbine device that spins out most of the water. The extractor then dumps the moist grindings into two dehydrators, which resemble top-loading washing machines. During each cycle, water spun from the extractor is recycled back through the scrap-collecting trough and not drained until the cycle is over. That saves on water, said Frenn.

The dehydrators dry the pulp overnight. In the morning, a worker dumps 5 to 8 gallons of it into a plastic tub for hauling to a storage container outside.

Paul Ruszat, executive chef for Morrison's kitchen at St. Cloud Hospital, said the process requires about one hour of staff time daily and reduces time spent gathering and hauling trash. Ruszat said the efficient removal of cooking scraps also helps to keep the kitchen cleaner.

The reduction in volume of waste is impressive as well. Maddy said seven months of effort have produced about 5 cubic yards of the pulp, not counting what was used for gardening tests last summer. And that is from a hospital kitchen that produces food for a general cafeteria, three coffee bistros and 900 patient meals daily.

Customer leftovers in the cafeteria and bistros, which get thrown into trash cans with other items, are not included in the pulping process.

Maddy said workers haul each morning's final product outside to a closed steel container. A secure lid is important, he said, "because wildlife loves the stuff."

Maintenance workers have been experimenting with the best blends for vegetation, from lawns to flower gardens, even mixing in some sawdust from the carpentry shop. Maddy advised using blends in gardens because the product is too high in nitrogen to be used on plants in pure form.

Maddy said the hospital plans to spread some of it on the lawns after the spring thaw. And a group that runs a community garden nearby is interested in getting some dry pulp.

"It makes a good fertilizer," he said.


Copyright © 2013 by the Catholic Health Association of the United States
For reprint permission, contact Betty Crosby or call (314) 253-3477.

Copyright © 2013 by the Catholic Health Association of the United States

For reprint permission, contact Betty Crosby or call (314) 253-3490.