Evaluation of in-situ sludge reduction technologies for wastewater treatment plants

Excess sludge treatment and disposal accounts for between 50 and 60% of the operating costs of wastewater treatment plants (WWTPs). Nowadays the main alternative methods for sludge disposal in the EU are land application (agriculture and silviculture) (49%), landfill (40%) and incineration (11%). All these methods represent several disadvantages with regard to economical factors (need for dewatering, transport, or drying) and environmental factors (risk of heavy metal or pathogen discharges). Therefore, an alternative way to solve sludge-associated problems is to reduce sludge production at the WWTP rather than to change post-treatment of all the sludge produced. A state-of-the-art review of in-situ technologies for reducing sludge generated from both primary and biological treatments is provided in this work. The application of disintegration techniques seems to be very interesting due to the high reduction of excess sludge achieved and the possibility of energy recovery as biogas. However full-scale investigations have shown that disintegration technology is only efficient if the total sludge disposal costs are high, the limiting factor being the efficiency of disintegration units. Future research should lead to improved energy recovery by increasing the efficiency of the disintegration units and to recover phosphorus as a usable product.