The aim of the current study is to compare the chemical oxygen demand (COD) removal efficiency of a Venturi device to that of an orifice plate. The inlet pressure in the devices was optimized and the degradation kinetics was analyzed. In addition, the synergistic effect resulting from the combination between cavitation and H2O2 was investigated. An experimental apparatus was built to achieve these goals. A sucrose solution and an effluent from a sucrose-based soft drink industry were treated. Results showed that the Venturi device recorded 90% COD removal efficiency after three treatment minutes. On the other hand, the orifice plate recorded 90% COD removal efficiency after 9 min. The degradation kinetics-reaction order was 3.5, except for the highest Venturi inlet pressure (7.3 bar), which led to coalescence of cavities and to reduced degradation rate. The synergistic coefficient (Sc) was 185.20 and showed that the hybrid process (HC + H2O2) was much more efficient than the cavitation process applied alone. The high COD concentration in the effluent generated by the soft drink industry (2,512.8 mg L-1) was significantly decreased by 72%. The combined use of cavitation and Venturi has significant potential to remove high organic matter concentrations in short treatment periods.
The aim of this study was to investigate the influence of humic substances (HS) on volumetric oxygen-transfer coefficient (K L a) under different turbulence intensities at the air-water interface. The experiments were carried out in an oscillating grid tank which provided three levels of turbulence intensities (Reynolds numbers of 5,116, 10,316, and 15,433). For each turbulence level, 15 different HS concentrations were tested and the K L a was estimated. The results showed that, regardless of the turbulence level in the tank, HS reduces K L a. The maximum reduction was 17%. The barrier effect, produced by the occupation of HS molecules at the interface, was the main phenomenon responsible for the reduction in the oxygen transfer. A relationship between the oxygen transfer velocity and turbulent kinetic energy showed that in the presence of HS, the air-water interface behaves like an immobile surface, reducing the oxygen diffusion and surface renewal.gas-water interface, grid-stirred tank, humic substances, oxygen mass transfer, reaeration
Os modelos matemáticos têm considerável aplicabilidade na esfera ambiental e, dentre os usos possíveis, pode-se destacar a aferição de parâmetros de qualidade da água com a simulação de diversos cenários, o que os tornam uma importante ferramenta para a gestão dos recursos hídricos. O objetivo do presente estudo foi avaliar a qualidade da água do Córrego Lanoso, no município de Uberaba (MG), bem como inferir a carga máxima de efluente admissível no córrego por meio do modelo QUAL2K. As coletas foram realizadas em quatro pontos de amostragem ao longo do córrego Lanoso. Foram analisados os seguintes parâmetros: vazão, turbidez, pH, condutividade, oxigênio dissolvido, DBO5, DQO,alcalinidade, cloreto, fósforo total, nitrato, sólidos totais e em suspensão. A modelagem do processo de autodepuração foi realizada com o uso do modelo QUAL2K. Mediante aos resultados das análises de vazão e dos parâmetros físico-químicos de qualidade da água, o modelo QUAL2K simulou diversos tipos de cenários do córrego Lanoso, sendo possível estimar a capacidade máxima de suporte do curso d’água, bem como os possíveis impactos da implantação de diversas atividades agropecuárias ao longo do seu leito, sem alterar as suas características atuais. A carga máxima admissível pelo córrego Lanoso foi de 288 g.s-1. Os pontos a jusante da bacia apresentaram maior capacidade para depuração da carga poluidora.
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