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The anode material and its configuration represent an important parameter in a microbial fuel cell (MFC), as it influences the development of the microbial community involved in the electrochemical bio-reactions. The aim of this work was to evaluate single chamber microbial fuel cells (SCMFCs) with high anode surface area, achieved by using packed beds of irregular graphite granules. The performance of the SCMFC with the packed bed anode configuration was studied using a mixed microorganism culture from real wastewaters in batch and continuous mode operation. The current output was found to increase with the increase in thickness of the anode bed and with the approximate anode area. The best performance was obtained with the 3 cm anode bed depth SCMFC. When the latter was operated in batch mode, Coulombic efficiencies varied from 30% to 74%, depending upon feed COD. In continuous mode operation, the COD removal was 89% and Coulombic efficiency 68% with a feed COD of 50 ppm, and at a flow rate of 0.0028 cm 3 min −1 . Power performance was also reasonable with a volumetric power density of 1.3 W m −3 , with respect to the net anodic volume (12.5 cm 3 ). Comparable performance was achieved with real wastewater. Over the duration of tests current output was stable. The investigation performed in this study represent a step forward for implementing real applications of MFC technology. A model of the current distribution in the packed bed electrode was applied, which correlates the effective utilization of the electrode to its specific area, solution conductivity and slope of the polarization curve. This model could function as a starting point in designing appropriate electrode geometries.

An analysis of the crossflow microfiltration of water in oil emulsions is reported. The emulsion considered was water, containing copper sulphate with kerosene using Span 80 as surfactant. Three membrane materials were studied: PTFE, PVDF and regenerated cellulose. The effects of crossflow velocity, transmembrane pressure, and temperature are analysed using several cake filtration models. Increases in transmembrane pressure, temperature and flow rate of emulsion all result in an increase in membrane flux. Membrane flux declines initially with time under most conditions of operation, except at a temperature of 50 °C, where values of flux are stable. Analysis of the fall in flux with time for the PTFE and PVDF membranes indicates that cake formation gives the best prediction of behaviour. In the case of PVDF the model does not predict the performance over the complete range of filtration times but rather two stages of filtration appear to occur; possibly cake formation initially followed by some intermediate pore blocking. In the case of the regenerated cellulose membrane, two stages of filtration seem to occur: an initial phase of cake formation or some pore blocking followed by intermediate pore blocking.

The performance of silica-supported zinc triflate (Zn(CF 3 SO 3 ) 2 ) catalyst immobilised on the surface of the spinning disc reactor (SDR) has been studied for the isomerisation reaction of α-pinene oxide to campholenic aldehyde. Process selectivity and conversion were assessed to determine the viability of SDR for performing catalytic reactions under a range of SDR operating conditions. Different catalyst loadings and supports were tested in this study: 0.05 mmol/g Zn-triflate/K60 (Catalyst 1), 0.01 mmol/g Zn-triflate/K100 (Catalyst 2) and 0.05 mmol/g Zn-triflate/HMS 24 (Catalyst 3). The latter catalyst was found to give the best performance in the SDR, with observed selectivity of 75% towards campholenic aldehyde and α-pinene oxide conversion of 85% at a disc temperature of 45 °C, disc speed of 1500 rpm and reactant feed flow rate of 6 cm 3 /s. Empirical models relating conversion and selectivity to disc speed and feed flow rate were developed for each catalyst using multiple linear regression analysis of experimental data collected in the study. A comparison with corresponding batch reactions indicates that the high shear rates in the thin SDR film flowing over the immobilised catalyst may give rise to intense mixing characteristics which overcome any mass transfer limitations within the immobilised matrix which would otherwise restrict the reaction rate. The short and controllable disc residence time in the SDR (of the order of seconds) promotes the desired reaction and minimises unwanted side reactions for enhanced process selectivity. These process advantages demonstrate the potential of the SDR to provide a “greener” approach to catalytic reactions.

Simultaneous reduction of nitrates and oxidation of ammonia in aqueous solutions have been carried out in a zero gap solid polymer electrolyte (ZGSPE) reactor, operated galvanostatically in a batch recycle mode. Complete removal of 16.1 mM nitrate and 9.4 mM ammonia was achieved within 45 h with removal rates of 0.057 mol NO 3 − cm −2 h −1 and 0.017 mol NH 3 cm −2 h −1 . Space–time yields of 5.4 kg NO 3 m −3 h −1 and 0.17 kg NH 3 m −3 h −1 , current efficiencies for nitrogen formation of 24.5% in the nitrate reduction and 1.4% in the ammonia oxidation and energy consumptions of 40.1 kWh (kg NO 3 − ) −1 were obtained during nitrate reduction, no nitrite was formed and N 2 was the main product under the best conditions. However, an improvement in the selectivity for the ammonia oxidation towards nitrogen is required. Effects of reactant concentrations, temperature and flow rate have been investigated. Use of the ZGSPE reactor could treat a wide range of wastes containing nitrate and ammonia, including those with very low levels of nitrate ions and ammonia.

A model for a porous or particulate bed electrode reactor is presented. The model consists of nonlinear second-order ordinary differential equations, a one-dimensional Poisson equation, describing the effect of the electric field on this system, and a one-dimensional diffusion-reaction equation describing the concentration variation associated with diffusion. The model accounts for mass transport and heterogeneous electrochemical reaction. The solution of this model is by the approximate Adomian polynomial method and is used to determine lateral distributions of concentration, overpotential and current density, overall cell polarisation and effectiveness factors, and to simulate the effects of important system and operating parameters, i.e. local diffusion rates and mass transport coefficients.

A model is presented to predict the local pressure and chemical composition in the anode and cathode sides of a liquid feed direct methanol fuel cell. The model is based on the homogeneous two-phase flow theory and mass conservation equation, which describes the hydraulic behaviour of an experimental large cell. The model allows an assessment of the effect of the operating parameters: inlet temperature, current density, flow rates and pressure, on the pressure losses, fluid compositions and chemical equilibrium.

A pressure drop model for the direct methanol fuel cell (DFMC), described in Part 1 of this contribution, based on the homogeneous twophase flow theory and mass conservation equation, which describes the hydraulic behaviour of a large (272 cm 2 ) cell, is used in a parametric analysis. The model allows assessment of the effect of operating parameters (temperature gradient, current density, flow bed design, fuel and oxidant flow rates and pressure) on the pressure losses at the anode and cathode side of the cell. The model is applied to an existing flow bed design, based on a plate heat exchanger, used in current fuel cell scale up studies. The role of the flow bed design is examined by presenting the pressure drop contributions for each of the three sections that comprise the flow bed. # 1999 Elsevier Science S.A. All rights reserved.

Research is reported on the development of a process to electrochemically oxidise sulphur dioxide gas, absorbed into sulphuric acid solutions. This process is aimed at the recovery of potentially valuable sulphur species, from waste and effluent gases, as sulphuric acid. A small pilot scale sieve-plate electrochemical reactor (SPER) is used for the oxidation of SO 2 . The SPER is an undivided cell using, in this case, monopolar connected electrodes. The anode material was platinised titanium or lead dioxide and the cathode material was zirconium metal or Ebonex ® , both materials do not form sulphur in the electrolysis of SO 2 in solutions of sulphuric acid. Typical current efficiencies are above 80% at current densities of 10–20 mA cm −2 . Energy consumptions are between 1.8 and 2.4 kWh kg −1 . Production of sulphuric acid at concentrations of 6 mol dm −3 by anodic oxidation of SO 2 is demonstrated. The mass-transfer behaviour of the sieve-plate reactor is particularly good for this reaction involving relatively low concentrations of dissolved SO 2 concentration. The behaviour of the sieve-plate reactor is mathematically modelled.