The urban wastewater treatment plants (WWTP) play a key role in the treatment of urban waste water and sludge. The improvement of energy efficiency and reduction of the environmental impact of their sludge is necessary. Energy consumption accounts for 30% of the total operation costs of a WWTP, and more than 50% of those came from sludge management. The challenge is to achieve an energy self-sufficiency.
Sludge energy potential could cover more than 50% of WWTP’ s energy needs. The integration of anaerobic digesters in waste water treatment plants results in the generation of biogas to be used in the WWTP itself and biofertilizers for agriculture. What reduces therefore the sludge generation.
Pre-treating sludge can recover more energy during anaerobic digestion and also reduces the volume of sludge to manage. Oxidative, ultrasonic cavitation or hydrodynamic techniques can be used to try to disrupt cell membranes. New techniques are aimed at improving the hygienic characteristics of sludge; therefore, improving its agronomic valorization
The implementation of oxidation systems with supercritical water allows the complete oxidation of any organic compound or simple molecule. Through this technology, organic contaminants do not require subsequent treatments from inertization [hygienic cleaning], facilitating the eventual disposal of only a small fraction. Moreover, the process may show a positive energy balance because it is possible to use the heat produced by exothermic reactions and the expansion of water after the supercritical process.