Willow, as a non-food crop, is well suited for the conversion of sewage sludge. For example, Nordic Biomass has worked together with Skagen Municipality, in Denmark, to establish energy forests for the conversion of sludge from their wastewater treatment plants. Sludge applicators have been developed that ensure odour-free sludge application. Both Swedish and Danish researchers have developed the process of sludge application in energy forests, but in practice, sludge application in energy forests currently follows the regulations for the application of sludge in conventional agriculture. The forests can still be harvested as woodchips, which can be used in heating plants or in parks and gardens.