Modelling Industrial Wastewater Ozonation In Bubble Contactors. 1. Rate Coefficient Determination

Abstract

A study of the ozonation of distillery and tomato wastewaters was carried out in a small bubble contactor in order to obtain kinetic data for scaling-up. Thus, several parameters, such as chemical oxygen demand (COD), 254 nm absorbance (AJJ,) and organic carbon content (OC), were followed during ozonation at different experimental conditions.For distillery wastewaters all parameters investigated have the highest decreases during the first minutes of ozonation, A^ showing the highest disappearance rates. Thus, during the first Fifteen minutes of ozonation an important decrease of the 254 nm absorbance (~ 75%) was observed. At further reaction times values of all parameters studied decrease slowly, eventually reaching a plateau value. During approximately the first two hours of reaction, dissolved ozone was never found, which suggested that fast or moderate gas-liquid reactions took place in the wastewaters.Regarding tomato wastewaters, COD, OC and A^ reach reductions of up to 70%, 40% and 90%, respectively, in one hour of ozonation. In this case the presence of dissolved ozone suggested that the kinetic regime of ozone absorption corresponded to a slow reaction.Application of an ozone balance in gas and water phases, along with the kinetic equation for ozone absorption with chemical reaction lead to determination of physico-chemical parameters like Henry's law constant and reaction rate coefficient, e 03 . In spite of the limitations concerning actual values of mass transfer coefficient, specific interfacial areas and ozone diffusivity, the rate coefficient obtained was found to be independent of hydrodynamic conditions, although it diminished with reaction time. This, however, was in agreement with the changing nature of the wastewater content. 355

Kinetic study of ozonation of molasses fermentation wastewater

“…Moreover, the initial concentration of melanoidins in the liquid bulk (3.4 × 10 −3 mol L −1 ) was 100 times greater than the ozone equilibrium concentration ((2.5 × 10 −5 -4 × 10 −5 mol O 3 L −1 ), so it can be considered that the reaction does not cause any significant depletion of colorants through the liquid film. This fact allows us to assume the regime to be fast of pseudo-first-order [17,18]. The kinetic regime can be corroborated determining the reaction factor (E).…”

Ozonation of vinasse in acid and alkaline media

“…In an acid medium, the initial assumption that, by virtue of the low concentration of free radicals formed, the principal reaction mechanism must be molecular ozonolysis, allows one to neglect the second term in eqn (3), so k app ≈ k O 3 [O 3 ]. Taking into account the solubility of ozone in vinasse, 44 as well as its concentration in the reactor exit gases, the average concentration of dissolved ozone in the second segment can be estimated to be ca 5 g m −3 . Therefore, the kinetic constant will be k O 3 ≈ 1.…”

Maleic Acid Ozonation: Reactor Modeling and Rate Constants Determination

“…The mass transport is at steady state within this film and, therefore, there is no accumulation of mass. Thus, the mass balances for ozone, compound A, which dissolves and reacts with a solute B (A + ν B → P) within the film are given by equations [1] and [2]. These equations are combined with four boundary conditions given by [3] and [4].…”

“…Hoigné and Bader (1983) have published an extensive compilation of kinetic data obtained from systems where the reaction occurs within the bulk liquid. Beltran et al (1992Beltran et al ( , 1995Beltran et al ( , 1998 have determined the kinetic rate constant of various fast reactions by assuming a pseudo first order irreversible gas liquid reaction that takes place between ozone and the organic compound. In these studies, the reaction is assumed to occur in the liquid film, which simplifies the rate constant calculations.…”