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

TL;DR

This study investigates controlling nitrite production during wastewater post-denitrification using model-free control techniques, improving effluent quality and stability without increasing costs.

Contribution

It introduces a novel model-free control approach integrated with classical dosage strategies to stabilize nitrite levels in biofilter wastewater treatment.

Findings

Model-free control improves nitrite stability in simulations

Effluent nitrite levels are reduced and stabilized

No significant increase in methanol costs observed

Abstract

The recent popularity of post-denitrification processes in the greater Paris area wastewater treatment plants has caused a resurgence of the presence of nitrite in the Seine river. Controlling the production of nitrite during the post-denitrification has thus become a major technical issue. Research studies have been led in the MOCOPEE program (www.mocopee.com) to better understand the underlying mechanisms behind the production of nitrite during wastewater denitrification and to develop technical tools (measurement and control solutions) to assist on-site reductions of nitrite productions. Prior studies have shown that typical methanol dosage strategies produce a varying carbon-to-nitrogen ratio in the reactor, which in turn leads to unstable nitrite concentrations in the effluent. The possibility of adding a model-free control to the actual classical dosage strategy has thus been tested on the SimBio model, which simulates the behavior of wastewater biofilters. The corresponding "intelligent" feedback loop, which is using effluent nitrite concentrations, compensates the classical strategy only when needed. Simulation results show a clear improvement in average nitrite concentration level and level stability in the effluent, without a notable overcost in methanol.