Simultaneous modeling of competitive adsorption and dual substrate biodegradation in completely mixed GAC reactors

The fluidized-bed anaerobic GAC reactor, operating with GAC replacement, has been demonstrated to promote effective treatment of high strength industrial wastewaters which contain refractory and toxic chemicals that resist biodegradation and inhibit the fermentation of the biodegradable constituents of a wastewater.The objective of this study was, to develop a mathematical model, capable of predicting the steady-state and transient performance of three fluidized-bed anaerobic GAC reactors treating synthetic wastewaters consisting of the readily biodegradable acetate, the biodegradable, adsorbable, but self-inhibitory phenol, and the non-biodegradable, inhibitory but adsorbable o-cresol. These reactors were operated with different GAC mean solids residence times, varying from 8 days to 60 days.Special features of the activated carbon mixed-culture biofilm model include: diffusional mass transport across a concentration boundary layer and within the biofilm, and the distinction between two microbial species, namely the phenol and the acetate utilizing microorganisms, which compete for attachment surface and spatial occupation within the limited space of the biofilm. Transport of phenol and o-cresol within the GAC particle was modeled using competitive adsorption and the homogeneous surface diffusion model. The model furthermore incorporated the effects of inhibition of phenol degradation by o-cresol, and biomass loss by shearing.Equilibrium and kinetic parameters in this model were obtained from independent isotherm and closed batch adsorption experiments. Biokinetic constants were determined from closed batch experiments using fermenter effluent as a source for microorganisms.The model predictions were in good agreement with the experimental data for the full range of operational conditions of the anaerobic reactors. In this study it was found that the overall first-order shear loss coefficient can not be assumed constant, but varies with the degree of biomass coverage of the carbon particles. This finding was supported by experimental results of biological activity measurements on the active biomass. Since no a priori distribution was assigned for the two microbial species present in the biofilm, the composition within the biofilm changed for each steady-state of operation. The non-uniform species distribution of the microorganisms resulted in preferential shearing of one microbial group over another. This differential shear was verified experimentally.U of I OnlyETDs are only available to UIUC Users without author permissio

Steady State Performance of Activated Carbon Contactors

A mathematical model for the steady state adsorption of pollutants from completely mixed activated carbon contactors is derived in this paper. In order to accurately describe these processes, a sludge age distribution is incorporated for the adsorbent. The resulting mathematical model is solvable analytically using the homogeneous surface diffusion model (HSDM) as a descriptor of intraparticle mass transfer resistance. Various examples are included in this paper to illustrate the use of this new derivation. Effects of particle size, particle size distribution of commercial carbon, surface diffusion coefficients, and solids mass flow rate, on the performance of the completely mixed adsorption system are studied in detail. Examples of multicomponent, competitive adsorption as well as an equivalent single component representation of a target component are discussed.</jats:p

Prediction of Incompressible Flow in Labyrinth Seals

A new approach was developed and tested for alleviating the substantial convergence difficulty which results from implementation of the QUICK differencing scheme into a TEACH-type computer code. It is relatively simple, and the resulting CPU time and number of numerical iterations required to obtain a solution compare favorably with a previously recommended method. This approach has been employed in developing a computer code for calculating the pressure drop for a specified incompressible flow leakage rate in a labyrinth seal. The numerical model is widely applicable and does not require an estimate of the kinetic energy carry-over coefficient for example, whose value is often uncertain. Good agreement with measurements is demonstrated for both straight-through and stepped labyrinths. These new detailed results are examined, and several suggestions are offered for the advancement of simple analytical leakage as well as rotordynamic stability models.</jats:p