While volunteering for the green teams, as they are called, of these gatherings, Mr. Robertson said, "We came to realize that there was a way to express our zero-waste passions within the event industry.”

They learned their craft at Green Mary, a two-decades-old company dedicated to making events sustainable that was founded by Mary Munat, an environmental activist and former Army reservist.

“They are fast, hard-working, green-hearted people,” she said of the Pirates. “I love their energy and greenness, and I am so glad my age-old eco-passions gave birth to so many little green pirates.”

The Trash Pirates was a nickname they gave each other early on, when festivals were more haphazard, and it stuck. In the beginning, Mr. Robertson, said “It was more seat-of-the-pants. Many of us were living out of our vehicles. That’s the thing: Trash can attract people who don’t feel like they have a place to go, giving people purpose in a space where they had none. Kind of like the Lost Boys. People are interested in the party, but it becomes empty if you don’t have a purpose.”

Next year , they hope to work upward of 30 events. “The work isn’t going to stop, I’m almost scared of it,” Mr. Robertson said, adding that he and many of his colleagues are looking to expand beyond the festivals and tackle community projects in Los Angeles, where he now lives, and beyond.

Mx. Mandel is devoted to filmmaking; Ms. Nielsen to art and activism. “But we are all still united by trash,” Mr. Robertson said. “We recognize that festivals are a stage and a platform to reach people, but we also know that it’s just a Band-Aid and the best thing we can do is to concentrate on government policies and community work.”