Modélisation du fonctionnement de la station d'épuration de Nîmes et validation de l'algorithme de régulation de l'aération Ammonair pour de faibles consommations énergétiques et émissions de N2O

International audienceIn activated sludge systems, aeration provides the oxygen that is required by the aerobic micro-organisms; ensures mixing and homogenization of the liquor; and facilitates stripping the gaseous by-products of the degradation processes. On the other hand, aeration is generally the single largest contributor to energy consumption in wastewater facilities. With the increasing need for containing operating costs, new aeration control strategies have recently been proposed. Solutions based on the continuous monitoring of nitrogen forms (NH4+, NO3-) for instance ensure a sufficient air supply to treat the nitrogen load while maintaining relatively low dissolved oxygen concentrations in the basin which in turns translates into lower energy consumption. Whether such strategies have an impact on nitrous oxide (N2O) emissions is yet to be ascertained. Nitrous oxide is a key greenhouse gas, about 300 times more effective than carbon dioxide, and a major sink for stratospheric ozone (IPCC, 2007). The wastewater treatment plant of Nîmes (230 000 PE) located in France consists of two parallel activated sludge lines operated with different aeration strategies. Ammonair, an aeration control logic based on ammonia and DO concentration, was implemented to reduce energy consumption of one treatment line. This work combines field measurements and mathematical modelling and is aimed at investigating the impact of the Ammonair control system on nutrient removal and energy consumption. The model developed was also used to assess the potential for GHGs emissions in relation to the specific aeration regime

An integrated modelling framework to assess cascade water reuse in urban areas

Water scarcity is an increasing problem for many countries worldwide, and the need for sustainable management of water resources is an urgent concern to face rising environmental challenges (Fernandes and Cunha Marques, 2023). This has prompted a rethink of water resources management and the reuse of water has gain growing interest. There is currently a strong focus on increasing reclaimed wastewater reuse, especially for agriculture (Delli Compagni et al., 2020). Besides, the ever-increasing costs associated with conventional energy sources have impelled the energy sector to transition towards more distributed and efficient energy production for heating/cooling purposes by exploiting local sources, especially across urban areas (Valancius et al., 2019). Typical applications are heat pumps using local groundwater reservoirs, and subsequently discharging the withdrawn water into the nearby surface water recipients, being natural or artificial water channels. Moreover, to enhance the water quality of these recipients and optimize the capacity of wastewater treatment plants (WWTPs), stormwater can be collected in separated sewers, discharging only the urban runoff to the recipient (Pálfy et al., 2017). In this context of rethinking the water management of urban areas, potential cross-contaminations across different compartments can occur, posing a risk for the environment, especially if water is subjected to multiple (re)uses (e.g. water from the recipient used for crop irrigation). Hence, there is a strong need for tools capable of supporting stakeholders towards a wiser and safer use of water resources, to ensure long-term resilience, stability, sustainability and security of the society with regard to water (re)use.In this work, an integrated model was developed to simulate the fate and associated risk of hazardous contaminants in a cascade water reuse system, located in the city of Milan. The model allows the evaluation of the feasibility of future water management strategies based on the risk assessment