A modeling of the carbon-nitrogen cycle transport at Igap\'o I Lake - Londrina, Paran\'a, Brazil

TL;DR

This study models the transport and reactions of pollutants, focusing on the carbon-nitrogen cycle, in Igapó I Lake to understand the impact of domestic sewage discharges using advanced numerical methods.

Contribution

It introduces a combined hydrodynamic and reactive transport model using finite differences and finite elements methods for Igapó I Lake, incorporating the carbon-nitrogen cycle.

Findings

Insights into nitrification and oxygen dynamics in the lake

Effect of diffusion coefficient on pollutant transport

Understanding of biochemical oxygen demand processes

Abstract

This work is a contribution to better understand the effect that domestic sewage discharges may cause in a water body, specifically Igap\'o I Lake, in Londrina, Paran\'a, Brazil. The simulation of the dynamics of pollutant concentrations all over the water body is conducted by means of structured discretization of the geometry of Igap\'o I Lake, together with the finite differences and the finite elements methods. Firstly, the hydrodynamic flow (without the pollutants), modeled by Navier-Stokes and pressure equations, is numerically resolved by the finite differences method, and associated with the fourth order Runge-Kutta procedure. After that, by using the hydrodynamic field velocity, the flow of the reactive species (pollutants) is described through a transport model, which considers advective and diffusive processes, as well as through a reactions model, restricted to the carbon-nitrogen cycle. The transport and reactions model is numerically resolved by the stabilized finite elements method, by means of a semidiscrete formulation. A qualitative analysis of the numerical simulations conducted in function of the diffusion coefficient provided better understanding of the dynamics of the processes involved in the flow of the reactive species, such as the dynamics of the nitrification process, of the biochemical requirement of oxygen and of the level of oxygen dissolved in the water body at Igap\'o I Lake.