Integrated Water Quality Models for Optimal Design and Control of Restoration Strategies

FRITZ, L.; AMIRA SINISCALCHI; FERNANDO D. RAMOS; M. SOLEDAD DIAZ; VANINA ESTRADA

Buenos Aires

Congreso; WCCE11, 11th World Congress of Chemical Engineering; 2023

Asociación Argentina de Ingenieros Químicos

Freshwater bodies are often sinks for pollutants despite the increasing demand for potable water. One of the growing problems (environmental, economic, and social) is anthropogenic eutrophication due to nitrogen (N) and phosphorus (P) discharge. Cyanobacterial blooms are one of the consequences of eutrophication and the new conditions that are predicted by climate change promote their dominance. In this way, it is necessary to act on the causes to preventdeterioration and restore the affected ecosystems. Mechanistic models are powerful tools to describe freshwater ecosystems and to evaluate and plan water quality restoration strategies. In this work, we propose the integration of a mechanistic drink water reservoir model [1] with and Artificial Floating Islands (AFIs) model, and with a Constructed Wetland model (CW) as internal and external restoration strategies, respectively. AFIs are buoyancy floating structures placed in the surface of the reservoir designed to support plant species that act as biological N and P filters. CW are portions of land covered with macrophytes, built next to the banks of the tributaries to avoid nutrient loading by runoff.The models were formulated in gPROMS within a dynamic optimization framework to address the optimal design and control of AFIs and CW. The case study is Paso de las Piedras Reservoir (PPR), Buenos Aires, Argentina (38-39° S, 61-62° W) and was built to supply drinking water to more than 450,000 inhabitants of two cities and for industrial purposes at a petrochemical complex nearby. As objective function, we consider the minimization of the sum of integrals of the square differences between inorganic P and N concentrations in the water column of the reservoir and a desired value below eutrophication. The parameters used for plant growth and harvest in AFIs and CW correspond to the species Senecio bonariensis, a native plant with known remedial potential [2]. The resulting integrated (PPR+AFIs+CW) differential-algebraic system (DAE) has 64 differential equations and more 200 algebraic ones. Numerical results provide optimal areas of AFIs and CW, as well as nutrients, phytoplankton, zooplankton, fish, dissolved oxygen, S. bonariensis biomass profiles along a five-year time horizon. The implementation of AFIs would be an effective green technology to restore contaminated ecosystems by reducing excess nutrients and controlling cyanobacteria growth. Also, AFIs implementation combined with CW substantially reduces the necessary area of the later.