But it's a pioneering program that promises enough cost savings and environmental accolades that Cassidy, the prisons' green-programs coordinator, is expanding it even as its funding runs out.
"We're diverting about 600 pounds [of food waste] a day from the women's facility [Riverside]. That's 600 pounds not going down the drain or into a landfill," she said.
"It is a great cost savings, and it's going really well," Riverside deputy warden Marcella Moore said.
Cassidy got the prisons recycling plastics and other materials about five years ago. That effort was so successful, the city's six prisons now recycle about 310 tons of nonfood waste a year, she said.
"Then the lightbulb dawned - what else could we recycle?" Cassidy said, adding that cutting food waste from all city prisons could slash the system's $250,000 annual disposal costs by up to 70 percent.
She chose Riverside, which houses about 800 inmates, to pilot the program "because women are the best recyclers."
Workers haul Riverside's food waste to a field beside the old Holmesburg Prison, where it cooks into a black mulch in four compost bays. Once there's enough to distribute, it's free to employees and community gardens.
A $15,000 grant from the U.S. Environmental Protection Agency funded the pilot. The money's gone, but Cassidy has applied for a $60,000 grant from the city Office of Sustainability to expand the program to all city prisons and buy heavy equipment.
She also aims to create a green-jobs certificate program, in which inmates who learn composting skills at Holmesburg can earn credentials to land work once they're freed.
On Twitter: @DanaDiFilippo