Résumé
Intensive biological processes are increasingly used in wastewater field due to their principlesto operate on a reduced surface and produce good quality waters. However, studies show thatintensification and high energy consumption go hand in hand, pointing out the value of energybenchmarking. In this work, two intensive systems have been studied: a membrane bioreactor,MBR, (64000 p.e.) and a conventional active sludge, CAS, (24000 p.e.).Our objectives wereto know where and why this energy is consumed, what factors influence these consumptions,and to give tools to optimize the energy efficiency. A three years energy audit was done forboth stations confirming that aeration is the major energy expense (more than 44% of the totalplant consumption:0.82kWh/m3). Several factors influence this energy were identified: hydrauliccapacity, temperature and sludge age... High energy consumption has been noted incase of low hydraulic loading underlining the seasonal consumption. Moreover, the impact ofSuspended Solid (SS) concentration on the energy consumption and on the overall treatmentcost was determined at different SS concentration (ranged from 1 to 8 gSS/L) by softwaresimulation (GPS-X) and data analysis. Simulation results showed that an increase of SS leadsto an increase in oxygen demand (increased energy cost) but leads also to a decrease of sludgeproduction (reduction of sludge disposal cost).In a full scale plant based on CAS process, theSS concentration must be carefully chosen in order to find the best compromise between thelevels of treatment required, the energy demand to ensure biological activity and the sludgedisposal cost while minimizing overall costs.