Marco Antonio Penalva Reali

Characterization of micro-bubble size distribution and flow configuration in DAF contact zone by a non-intrusive image analysis system and tracer tests

This paper aims to investigate the influence of some dissolved air flotation (DAF) process variables (specifically: the hydraulic detention time in the contact zone and the supplied dissolved air concentration) and the pH values, as pretreatment chemical variables, on the micro-bubble size distribution (BSD) in a DAF contact zone. This work was carried out in a pilot plant where bubbles were measured by an appropriate non-intrusive image acquisition system. The results show that the obtained diameter ranges were in agreement with values reported in the literature (10-100 microm), quite independently of the investigated conditions. The linear average diameter varied from 20 to 30 microm, or equivalently, the Sauter (d(3,2)) diameter varied from 40 to 50 microm. In all investigated conditions, D(50) was between 75% and 95%. The BSD might present different profile (with a bimodal curve trend), however, when analyzing the volumetric frequency distribution (in some cases with the appearance of peaks in diameters ranging from 90-100 microm). Regarding volumetric frequency analysis, all the investigated parameters can modify the BSD in DAF contact zone after the release point, thus potentially causing changes in DAF kinetics. This finding prompts further research in order to verify the effect of these BSD changes on solid particle removal efficiency by DAF.

Método para determinação de distribuição de tamanho de microbolhas (DTMB) em sistemas flotação (FAD) para tratamento de águas utilizando a análise de imagem digital

An image analysis method proposed for assessing bubble size distribution applied to dissolved air flotation (DAF) systems for drinking water treatment is presented. Further, a pilot plant investigation is presented. A digital camera together with a group of lens was used. In order to eliminate samples interferences the images were captured in a continuous flow system working in steady state. The freeware ImageTool was applied for treating and obtaining size distribution. Results were presented in good relationship with traditional methods. The role image system showed to be efficient for image capturing and the proposed method may be an useful tool to other researches areas.

Emprego de bomba multifásica como unidade geradora de microbolhas de ar em sistema de flotação aplicado ao pré-tratamento de efluente têxtil

O artigo apresenta os resultados de uma pesquisa desenvolvida com o objetivo de avaliar o desempenho de bomba multifasica (mistura de ar e agua) aplicada em substituicao a câmara de saturacao, em sistema de flotacao localizado em uma industria textil. Na unidade piloto (taxa de aplicacao superficial de clarificacao igual a 128,6 ± 10 m.d-1), foi verificado que os melhores resultados em termos de eficiencia de remocao de turbidez e cor aparente (eficiencia de remocao superior a 95%) foram obtidos nos ensaios realizados com razao de recirculacao em torno de 30% associada a composicao volumetrica de ar de 13%.

The influence of floc size and hydraulic detention time on the performance of a dissolved air flotation (DAF) pilot unit in the light of a mathematical model

The influence of floc size and hydraulic detention time on the performance of a dissolved air flotation (DAF) pilot unit was investigated in the light of a known mathematical model. The following design and operational parameters were considered: the hydraulic detention time (tdcz) and hydraulic loading rate in the contact zone, the down-flow loading rate in the clarification zone, the particle size distribution (dF), and the recirculation rate (p). As a reference for DAF performance analysis, the proposed β.td parameter from the above mentioned mathematical model was employed. The results indicated that tdcz is an important factor in DAF performance and that dF and floc size are also determinants of DAF efficiency. Further, β.td was sensitive to both design and operational parameters, which were varied in the DAF pilot plant. The performance of the DAF unit decreases with increasing β.td values because a higher td (considering a fixed β) or a higher β (e.g., higher hydrophobicity of the flocs for a fixed td) would be necessary in the reaction zone to reach desired flotation efficiency.

Dissolved-air flotation associated with an anaerobic reactor, as applied to sewage treatment

This paper presents the results of a study performed with a pilot sewage treatment plant consisting of an aerobic reactor followed by a flotation unit. To coagulate the anaerobic effluent, different ferric chloride dosages were applied by adopting two approaches: applying constant dosages during the essay and varying the dosages according to the anaerobic effluent turbidity. To obtain more than 95% TSS, 90% COD and 70% phosphorous removals a critical chemical ratio ranging 0.012 - 0.013 (in terms of Fe/Turbidity ratio) was required. When aiming higher phosphorous removal (above 95%) the required Fe/Turbidity ratio range rose to 0.016-0.018.