Importance of calibration for mathematical modeling of self-purification of lotic environments

• Published in: Acta limnológica brasiliensia 2016, Vol.28
• Main Authors: Salla, Marcio Ricardo, Fernandes, Lucianno Eduardo, Pereira, Carlos Eugênio, Silva Jhunior, Hélio Correia da, Lima, Guilherme de
• Format: Article
• Language: English
• Subjects: Brasil; comparação de modelos; LIMNOLOGY; monitoramento; qualidade da água; Rio
• ISSN: 0102-6712; 2179-975X; 2179-975X
• DOI: 10.1590/s2179-975x5016

Aim To demonstrate the importance of calibration in mathematical modeling of self-purification in lotic environments, this study simulated the behavior of various parameters in a river with average annual flows between 4.0 and 32.0 m3.s-1, in a segment downstream from the entry of treated wastewater from a sewage treatment station (average monthly flow of 2.1 m3.s-1). Methods Numerical solution by finite difference of the advection-diffusion equation was used to study the dispersion and to quantify and monitor the evolution over time of the parameters DO, BOD5, Ptotal, NH3, NO3- and the levels of the heavy metals cadmium, chromium, copper, lead and zinc. The longitudinal behavior of the water quality parameters simulated by calibrating the state variables was compared with the behavior of the same parameters simulated via state variables available in the literature. The sensitivity of the state variables was also analyzed. Results The calibration process led to good fits between the simulated and actual data for all the parameters analyzed. On the other hand, the comparison of the water quality model using calibrated state variables with the model based on state variables obtained in the literature revealed inconsistencies regarding the parameters DO, Ptotal, ammonia, nitrate and all the heavy metals. Conclusions Considering the wide threshold ranges of the state variables in the literature and the dearth of studies on calibrating the coefficient of decay and quantifying the release of heavy metals by bottom sediment, this study can serve as a base for future investigations in lotic environments with similar hydraulic and water quality characteristics. Resumo: Objetivo A fim de demonstrar a importância da calibração na modelagem matemática de autodepuração em ambiente lótico, este estudo simulou o comportamento de diversos parâmetros em um rio com vazões médias anuais entre 4,0 a 32,0 m3.s-1, em um trecho a jusante do lançamento de efluente tratado por Estação de Tratamento de Esgoto (vazão média mensal de 2,1 m3.s-1). Métodos a partir de solução numérica por diferença finita, foi utilizada a equação de difusão-advecção para estudar a dispersão, quantificação e acompanhamento da evolução ao longo do tempo dos parâmetros OD, DBO5, Ptotal, NH3, NO3- e dos metais pesados cádmio, cromo, cobre, chumbo e zinco. O comportamento longitudinal dos parâmetros de qualidade da água simulados via calibração de variáveis de estado foi comparado com o comportamento dos me