Effect of the aeration system on water quality parameters and productive performance of red tilapia ( Oreochromis sp. ) grown in a biofloc system

The objective of this work was to assess the performance of two aeration types, splash and blower, used on a commercial biofloc technology (BFT) farm of red tilapia, Oreochromis sp., and their effect on growth performance and water quality parameters. For this, red tilapia juveniles were randomly distributed into twelve tanks. Each tank had an independent aeration system, and two experimental groups were characterized: six tanks used splash aerators (SPL group; one per tank, 1 hp), and the remaining tanks used a blower aerator (BLW group) with the same potency (1 hp). Water quality parameters were registered daily, and after 90 days of commercial culture, we obtained final growth parameters for each batch (tank). We observed no statistical differences on growth parameters, while water quality parameters showed that dissolved oxygen and oxygen saturation were significantly higher for the SPL group. Therefore, this field study corroborated indications from prior research at laboratory conditions that, at a commercial scale, splash aerators are more adequate for the production of red tilapia in BFT conditions.(AU)

Lower nappe aeration in smooth channels: experimental data and numerical simulation

Bed aerators designed to increase air void ratio are used to prevent cavitation and related damages in spillways. Air entrained in spillway discharges also increases the dissolved oxygen concentration of the water, which can be important for the downstream fishery. This study considers results from a systematic series of measurements along the jet formed by a bed aerator, involving concentration profiles, pressure profiles, velocity fields and corresponding air discharges. The experimental results are, then, compared, with results of computational fluid dynamics (CFD) simulations with the aim of predicting the air discharge numerically. Comparisons with jet lengths and the air entrainment coefficients from the literature are also made. It is shown that numerical predictive tools furnish air discharges comparable to measured values. However, if more detailed predictions are desired, verification experiments are still necessary.

Aeradores de fundo projetados para aumentar a concentração de ar são utilizados para previnir a cavitação e danos dela derivados em vertedouros. O oxigênio contido na água também é um parâmetro relevante para garantir alta qualidade das águas a jusante do vertedouro, com reflexos na qualidade ambiental. Equações e critérios de projeto existentes ainda são considerados aproximados, mostrando a necessidade de mais estudos para elucidar os mecanismos que governam o carreamento de ar. Este trabalho apresenta resultados de uma série sistemática de medidas de concentração de ar ao longo da superfície inferior do jato de um aerador de fundo, juntamente com medidas pertinentes de descargas de ar e campos de velocidade da água. Foram feitas comparações com resultados da literatura, considerando perfis de concentração ao longo do jato do aerador até a região de jusante. As medições sob condições controladas forneceram informações necessárias para testar resultados numéricos de aeração obtidos em simulações desses escoamentos, utilizando mecânica dos fluidos computacional (CFD). Mostra-se que ferramentas numéricas preditivas fornecem vazões de ar comparáveis aos valores medidos. Também é concluído que, se detalhes são necessários, experimentos são ainda úteis.