Every day, with bare hands, Rukmini Baburao Kumbhar, collects around 50kg (eight stone) of fresh cow dung. She is part of a spiritual group that runs a small ashram (a religious retreat) in a village in the north-western Indian state of Maharashtra. Collecting cow dung is not, primarily, an effort to keep the place tidy. Instead, the cow dung is used to make biomethane.