La production de nitrites lors de la d\'enitrification des eaux us\'ees par biofiltration - Strat\'egie de contr\^ole et de r\'eduction des concentrations r\'esiduelles

摘要

The recent popularity of post-denitrification processes in the greater Parisarea wastewater treatment plants has caused a resurgence of the presence ofnitrite in the Seine river. Controlling the production of nitrite during thepost-denitrification has thus become a major technical issue. Research studieshave been led in the MOCOPEE program (www.mocopee.com) to better understand theunderlying mechanisms behind the production of nitrite during wastewaterdenitrification and to develop technical tools (measurement and controlsolutions) to assist on-site reductions of nitrite productions. Prior studieshave shown that typical methanol dosage strategies produce a varyingcarbon-to-nitrogen ratio in the reactor, which in turn leads to unstablenitrite concentrations in the effluent. The possibility of adding a model-freecontrol to the actual classical dosage strategy has thus been tested on theSimBio model, which simulates the behavior of wastewater biofilters. Thecorresponding "intelligent" feedback loop, which is using effluent nitriteconcentrations, compensates the classical strategy only when needed. Simulationresults show a clear improvement in average nitrite concentration level andlevel stability in the effluent, without a notable overcost in methanol.