The effects of co-digestion of separately collected organic fraction of municipal solid waste and mixed sludge in a 95,000 equivalent inhabitants municipal wastewater treatment plant (WWTP) was studied for 18 months. It was observed that the treatment of 10,000 kg per day of organic waste increased the organic loading rate of digesters from 0.73 to 138 kgVS per m(3) per day and allowed for a substantial increase in biogas generation from 1321 to 2723 m(3)/d (average data) determining a clear increase in energy recovery: potential power generation passed from 3900 kWh per day (only sludge treated) to 7800 kWh per day (co-digestion regime) or 85% of the total energy consumption of the wastewater treatment plant. (C) 2017 Elsevier Ltd. All rights reserved.