Aram Boghosian for The Boston Globe

Boston spends about $5 million a year on recycling, but its recycling rate still lags behind those of comparable American cities.

Aram Boghosian for The Boston Globe

Three years ago, Boston introduced single-stream recycling, which is sorted later at sites like Casella Waste System’s Zero-Sort recycling center.

Aram Boghosian for The Boston Globe

The city’s residential recycling rate hit 19 percent last year. Seattle and San Jose, Calif., by comparison, reported rates of around 60 percent.

Aram Boghosian for The Boston Globe

Casella's Charlestown plant processes about 60 percent of Boston’s 200,000 tons of residential waste.

Aram Boghosian for The Boston Globe

In Charlestown, workers helped machines sort through plastic bottles as they move along conveyor belts.

Aram Boghosian for The Boston Globe

The city is attempting to expand access to recycling, especially in public spaces, schools, and large businesses.