His research interest comprises the development of cost-effective technologies for (waste)water treatment, recovering resources such as water, nutrients, biogas, elements from waste streams. Research projects are focused on closing water cycles in industries and sewage water recovery for irrigated agriculture. He promoted 17 and co-promoted 5 PhD students and is supervising 18 PhD students at this moment. Jules van Lier chaired the IWA Anaerobic Digestion Specialist group between 2001 and 2009. In 2011 he became nominated member of the IWA Fellow program. He is associated editor of the scientific journals Water Science Technology.