Ron Patalano, director of operations at Roger Williams Park Zoo, has high praise for his staff. After all, it takes a mighty amount of shoveling to fill the two 30-yard Dumpsters of animal excrement that are hauled away weekly as part of the zoo’s recycling program. Added to the grass clippings, vegetable scraps, animal bedding, hay and other natural materials trucked to Earth Care Farm in Charleston for composting, are 624 tons of manure produced annually by the zoo’s 280 inhabitants. Keeping yards and buildings waste free “is not an easy job,” Patalano noted. The zoo’s relationship with Earth Care Farm — Rhode Island’s longtime composting mecca — goes back at least 15 years, according to John Barth, the farm’s manager.