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A modelling study on the anaerobic digestion process of a synthetic mediumstrength wastewater containing molasses as a carbon source was carried out at different influent conditions. The digestion was conducted in a laboratory-scale hybrid anaerobic baffled reactor with three compartments and a working volume of 54 L, which operated at mesophilic temperature (35 ºC). Two different kinetic models (one model was based on completely stirred tank reactors (CSTR) in series and the other an axial diffusion or dispersion model typical of deviations of plug-flow reactors), were assessed and 2 compared to simulate the organic matter removal or fractional conversion. The kinetic constant (k) obtained by using the CSTR in series model was 0.60 ± 0.07 h-1 , while the kinetic parameter achieved with the dispersion model was 0.67 ± 0.06 h-1 , the dispersion coefficient (D) being 46. The flow pattern observed in the reactor studied was intermediate between plug-flow and CSTR in series systems, although the plug-flow system was somewhat predominant. The dispersion model allowed for a better fit of the experimental results of fractional conversions with deviations lower than 8% between the experimental and theoretical values. By contrast, the CSTR in series model predicted the behaviour of the reactor somewhat less accurately showing deviations lower than 10% between the experimental and theoretical values of the fractional conversion.

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The 3D simulation of the hydrodynamic behavior of a rotating disc contactor (RDC) by means of computational fluid dynamics (CFD) was investigated for the n-butanol-succinic acid-water (BSW) system. For the two-phase liquid-liquid flow, the velocity distribution of the continuous phase and drop size distributions were determined using the k-x turbulence model in conjunction with the Eulerian-Eulerian approach and MUSIG model. In this system in which the holdup of the dispersed phase is low, the continuous phase velocity was computed by simultaneously solving the Navier-Stokes equations beside the different models of turbulence. The motions of the dispersed phase was calculated while considering buoyancy, drag and inertia forces, and equations related to the continuous and dispersed phases were coupled to each other by considering the momentum transfer on the interface and the effect of drop motions in turbulence. In this simulation, by considering drops' breakage, their path, the velocity profile, and also the velocity contour plot of the dispersed phase were obtained. A comparison of the holdup experimental values with the results predicted by CFD showed that the k-x model is the best descriptive model for the computation of holdup in a RDC. IntroductionLiquid-liquid extraction is an important separation process that is widely used in the chemical, biochemical, petrochemical, pharmaceutical, and food industries [1][2][3][4]. The rotating disc contactor (RDC) is one of the most important extraction columns, which was initially introduced by the Royal Dutch/ Shell Group [5]. RDC columns have extensively been used in the industry, particularly for liquid-liquid systems with low interfacial tension. The low interfacial tension means small drop sizes, thereby causing the efficiency of the RDC extractor to ameliorate.These columns consist of a set of distinct discs with equal horizontal intervals between the stators. The agitation provided by the discs mounted on the rotor shaft improves the performance of the RDC by breaking the dispersed phase droplets, hence increasing the interfacial area for mass transfer [4,6]. Drop sizes are controlled by the ratio of buoyancy to interfacial tension forces under the conditions of no agitation or low levels of turbulence (Re R N R D 2 R m c < 10000) 1) [7].Too high an agitation speed will exacerbate the axial mixing, thereby reducing the column performance. Axial mixing ends in concentration jumps all over the column so that this phenomenon causes operating lines to be closer to each other, the result of which is the decrease of concentration driving force and the need for more discs inside the column [2,8,9].Experimental investigations with agitated columns reveal that the drop size distributions of rising organic phase drops dispersed in a continuous aqueous phase are broad in the first stages, becoming narrower and shifting toward smaller drop sizes in the later stages of the column, until a final, steady-state distribution has been achieved; thus, providing evidence that dro...

A modelling of the anaerobic digestion process of molasses was conducted in a 70-L multistage anaerobic biofilm reactor or hybrid anaerobic baffled reactor with six compartments at an operating temperature of 26 °C. Five hydraulic retention times (6, 16, 24, 72 and 120 h) were studied at a constant influent COD concentration of 10,000 mg/L. Two different kinetic models (one was based on a dispersion model with first-order kinetics for substrate consumption and the other based on a modification of the Young equation) were evaluated and compared to predict the organic matter removal efficiency or fractional conversion. The first-order kinetic constant obtained with the dispersion model was 0.28 h(-1), the Peclet dispersion number being 45, with a mean relative error of 2%. The model based on the Young equation predicted the behaviour of the reactor more accurately showing deviations lower than 10% between the theoretical and experimental values of the fractional conversion, the mean relative error being 0.9% in this case.