Here’s a very good video showing cutting edge technologies that make rooftop gardening profitable. At 19:54 they show how they’re making compost from food scraps very quickly in a machine.
“This documentary showcases the people behind the urban farms that have been mushrooming amidst the glass and steel towers of Singapore’s central district. The film follows the trials and tribulations of Comcrop’s Allan Lim and his vertical farming venture, as well as the challenges and triumphs of social entrepreneur Bjorn Low and his bespoke farm-to-table approach. Can cutting-edge agricultural technology and an enduring Singapore spirit of community & collaboration start to influence Singaporeans’ approach to food sustainability? This film captures this changing mindscape.”