Per Halkjær Nielsen is heading the multidisciplinary Center for Microbial Communities at Aalborg University, DK. He has been active in environmental biotechnology for over 30 years, focusing on the microbial ecology of biological wastewater treatment, bioenergy production and recovery of nutrients. He has been among the pioneers in the development and implementation of the new DNA sequencing technologies in the water engineering field, has studied in great detail community composition and ecophysiology of process-critical members. He has established the MiDAS platform encompassing online tools and field guide for microbes in wastewater treatment systems.