Optimising the initial mixture as a critical factor is composting sewage plant sludge

Waste sludge obtained in the biological treatment of urban wastewater contains high amounts of organic matter and nutrients that can be recovered through composting. Moisture content, carbon-nitrogen ratio and porosity are key parameters in the composting process of this type of residue. In the present work, experimental design technique is used to determine optimal conditions for sludge composting (raw sludge and anaerobically digested sludge). Such conditions, obtained at the laboratory scale, have been also verified at pilot scale. Thus, the proposed methodology seems to be appropriate to determine the best conditions for the composting process of different types of sludge and organic wastes.