Complementary Control Actions for Greenhouse Gas Emissions Reduction in Wastewater Treatment Plant Operation

Wastewater treatment plants are necessary to improve the quality of wastewater before it is discharged into the receiving environment, but they have the disadvantage of generating nitrous oxide emissions during the biological treatment, which is a potent Greenhouse Gas (GHG). This is a serious drawback as the reduction of greenhouse gas emissions due to anthropogenic causes is one of the main challenges to face with reference to climate change effects. In this paper we examine one potential way to reduce nitrous oxide emissions by reducing the dissolved oxygen to minimum levels. To achieve this objective, the present work proposes to use the internal recirculation flow rate of the biological treatment. This is a rather forgotten manipulated variable that, as it is intended to show, may have potential side effects to complement already existing control actions. Therefore, this additional regulation is added to a usual control strategy in wastewater treatment plants, which achieves satisfactory results in water quality and in operational costs but with high nitrous oxide emissions. The Benchmark Simulation Model No.2 Gas (BSM2G) is used as working scenario, which includes the two main nitrous oxide emission pathways: heterotrophic denitrification and ammonia oxidizing bacteria denitrification.