Treatment of settled piggery waste by a down‐flow anaerobic fixed bed reactor

A study of the effect of organic volumetric loading rate (B_V) on the performance of a down‐flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm^?3 d^?1. The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B_V, process failure was not observed. A logarithmic relationship was found to describe the influence of B_V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO₂/CH₄ ratio in the biogas. The effect of the hydraulic volumetric loading rate (H_V) on the flow pattern of the reactor was evaluated. Dispersion number (D_n) was in the range of 0.17–0.37 for the maximum and minimum values of H_V studied, respectively. The ratio between the real and theoretical HRT increased as the H_V decreased. These results demonstrate that axial dispersion increased as the H_V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K), specific organic loading rate constant (K_L), microbial decay coefficient (K_d), microbial yield coefficient (Y), maximum microbial growth rate (U_M) and saturation constant (K_S) were found to be: 3.1 (g COD g VSS^?1 d^?1), 3.0 (g COD g VSS^?1 d^?1), 0.062 (d^?1), 0.15 (g VSS g COD removed^?1), 0.39 (d^?1) and 2.6 (g SCOD dm^?3), respectively. Copyright © 2004 Society of Chemical Industry     

INTERACTION OF THERMAL RADIATION IN THE LAMINAR PIPE FLOW OF OPTICALLY THIN GASES

The influence of thermal radiation on laminar forced convection of a gray gas in a pipe flow is studied semi-analytically. The gas is considered as an absorbing-emitting medium and the thin gas model approximation is used to describe the radiative heat flux in the energy equation. Invoking the method of lines (MOL), the nonlinear boundary value problem is reduced to an initial value problem which is eventually solved by a standard Runge-Kutta integration scheme. Numerical results are presented graphically for a selected group of thermal parameters encompassing the thin gas behavior. Additionally, it is found that limiting cases namely: laminar plug flow and laminar parabolic flow, both in the absence of radiation define an envelope for the curves of bulk temperature and total Nusselt number describing the combined thermal process for a thin gas in laminar motion. In general, the comparisons reveal that these asymptotic solutions are valid when the entrance-to-wall temperature ratio is less than 2.     

New redox deposition-precipitation method for preparation of supported manganese oxide catalysts

A new preparation method has been developed to produce homogeneous coatings of manganese compounds on alumina-coated monoliths by redox deposition-precipitation using acetone as solvent. The deposition is produced by reduction of manganese permanganate with ethanol. The Lewis acid sites on the alumina catalyze this reaction. Thus, the precipitation is produced preferentially on the surface of the monolith and not in the bulk of the solution. Monoliths prepared by this method are very active for the complete oxidation of oxygenated volatile organic compounds (VOCs). These monoliths consist of a mixture of complex phases including aluminum, sulfated alumina, potassium sulfate and manganese oxide.     

Remarkable improvement of the Lévêque solution for isoflux heating with a combination of the transversal method of lines (TMOL) and a computer-extended Fröbenius power series

This paper addresses the second Lévêque problem with uniform wall heat flux adhering to the original two-dimensional energy conservation equation with variable coefficients in cylindrical coordinates. The semi-analytic procedure to be proposed combines the transversal method of lines (TMOL) with the Fröbenius version of the power series method. The hybrid solution that emerges from this combination holds unique features that distinguish it from the traditional solution methods. In principle, due to the presence of a two-point backward formulation, the approximate analytic solution is considered first-order accurate. However, using as guidance the computed local convection coefficient at various transversal lines, it is demonstrated that the approximate analytic TMOL/Fröbenius solution is better than first-order accurate.     

Depressive symptoms in early marriage: Predictions from relationship confidence and negative marital interaction.

The authors proposed a model of depressive symptoms in early marriage in which relationship confidence, defined as perceived couple-level efficacy to manage conflicts and maintain a healthy relationship, mediates the effect of negative marital interactions on depressive symptoms. The model was tested in a sample of 139 couples assessed prior to marriage and 1 year later. As predicted, relationship confidence demonstrated simple negative associations with negative marital interaction and depressive symptoms for all participants. Longitudinal path analyses supported the mediational model for women only. In women but not men, negative marital interaction indirectly had an impact on depressive symptoms through the mediator of relationship confidence. Findings suggest that relationship confidence may be important to understanding links between marital distress and depressive symptoms, especially in women. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recovering lower bounds of the error by postprocessing implicit residual a posteriori error estimates

Classical residual type error estimators approximate the error flux around the elements and yield upper bounds of the exact (or reference) error. Lower bounds of the error are also needed in goal oriented adaptivity and for bounds on functional outputs. This work introduces a simple and cheap strategy to recover a lower bound estimate from standard upper bound estimates. This lower bound may also be used to assess the effectivity of the former estimate and to improve it. Copyright © 2003 John Wiley & Sons, Ltd.