M. S. Sheldon

Treatment of paper mill effluent using an anaerobic/aerobic hybrid side-stream membrane bioreactor.

This paper presents the design and operational performance data of an anaerobic/aerobic hybrid side-stream Membrane Bioreactor (MBR) process for treating paper mill effluent operated over a 6 month period. The paper mill effluent stream was characterized by a chemical oxygen demand (COD) range of between 1,600 and 4,400 mg/L and an average BOD of 2,400 mg/L. Despite large fluctuations in COD feed concentration, stable process performance was achieved. The anaerobic Expanded Granular Sludge Bed (EGSB) pre-treatment step effectively lowered the organic loading by 65 to 85%, thus lowering the MBR COD feed concentration to consistently below 750 mg/L. The overall MBR COD removal was consistent at an average of 96%, regardless of the effluent COD or changes in the hydraulic retention time (HRT) and organic loading rate (OLR). Combining a high-rate anaerobic pre-treatment EGSB with a Modified Ludzack-Ettinger (MLE) MBR process configuration produced a high quality permeate. Preliminary NF and RO results indicated an overall COD removal of around 97 and 98%, respectively.

Oxygen mass transfer for an immobilised biofilm of Phanerochaete chrysosporium in a membrane gradostat reactor

Abstract - A novel system, the membrane gradostat reactor (MGR), designed for the continuous production of secondary metabolites, has been shown to have higher production per reactor volume than batch culture systems. The MGR system mimics the natural environment in which wild occurring microorganism biofilms flourish. The biofilms are immobilised on the external surface of an ultrafiltration membrane where substrate distribution gradients are established across the biofilm. The hypothesis that, dissolved oxygen (DO) mass transfer parameters obtained in submerged pellets can be used to describe and model DO mass transfer parameters in the MGR, was refuted. Phanerochaete chrysosporium biofilms, immobilised on ultrafiltration capillary membranes in the MGR systems were used to quantify DO distribution using a Clark-type microsensor. The DO penetration depth decreased with increasing biofilm thickness, which resulted in the formation of anaerobic zones in the biofilms. Oxygen flux values of 0.27 to 0.7 g/(m

A Solution of the Convective-Diffusion Equation for Solute Mass Transfer inside a Capillary Membrane Bioreactor

This paper presents an analytical model of substrate mass transfer through the lumen of a membrane bioreactor. The model is a solution of the convective-diffusion equation in two dimensions using a regular perturbation technique. The analysis accounts for radial-convective flow as well as axial diffusion of the substrate specie. The model is applicable to the different modes of operation of membrane bioreactor (MBR) systems (e.g., dead-end, open-shell, or closed-shell mode), as well as the vertical or horizontal orientation. The first-order limit of the Michaelis-Menten equation for substrate consumption was used to test the developed model against available analytical results. The results obtained from the application of this model, along with a biofilm growth kinetic model, will be useful in the derivation of an efficiency expression for enzyme production in an MBR.

Overview of parameters influencing biomass and bioreactor performance used for extracellular ligninase production from Phanerochaete chrysosporium

The production of extracellular enzymes is gaining momentum as commercial interests seek alternative ways to improve the productivity in the biotechnology and pharmaceutical industries. Early research studies looked at improving batch bioreactor operational challenges; however, the use of continuous cultures was indicated to be favourable. This led to a new approach developed to produce extracellular enzymes continuously using fixed-film bioreactors from biofilms immobilised on polymeric and inorganic membranes. In this review, the performance of P. chrysosporium biomass, evaluated in terms of ligninase production using different bioreactor operation conditions, is highlighted. Furthermore, the limitations related to the implementation of optimised batch culture conditions to continuous fixed-film bioreactors are discussed. DO transportation, trace element toxicity and lipid peroxidation effects on P. chrysosporium biomass in fixed-film bioreactors operated for elongated periods, are also discussed.

Membrane bioreactor application within the treatment of high strength textile effluent

A pilot-scale dual-stage membrane bioreactor (dsMBR) incorporating two ultra-filtration (UF) side-stream membrane modules was designed, constructed, operated and evaluated on-site for treating high-strength textile effluent. The effluent stream was characterised by a COD range of between 45 to 2,820 mg/L and an average BOD of 192.5 mg/L. The dsMBR achieved an average COD reduction of 75% with a maximum of 97% over the 9 month test period. The COD concentration obtained after dsMBR treatment averaged at 190 mg/L, which was well within the discharge standard. The average reduction in turbidity and TSS were 94% and 19.6%, respectively, during the UF-MBR stage of the system. Subsequent treatment of the UF-permeate with nanofiltration (NF) and reverse osmosis (RO) removed both the residual colour and remaining salt. A consistent reduction in the color of the incoming effluent was evident. The ADMI was reduced from an average of 659 to ∼20, a lower ADMI and colour compared to the potable water. An average conductivity rejection of 91% was achieved with conductivity being reduced from an average of 7,700 to 693 μS/cm and the TDS reduced from an average of 5,700 to 473 mg/L, which facilitated an average TDS rejection of 92%.

Treatment of poultry slaughterhouse wastewater using a static granular bed reactor (SGBR) coupled with ultrafiltration (UF) membrane system

The South African poultry industry has grown exponentially in recent years due to an increased demand for their products. As a result, poultry plants consume large volumes of high quality water to ensure that hygienically safe poultry products are produced. Furthermore, poultry industries generate high strength wastewater, which can be treated successfully at low cost using anaerobic digesters. In this study, the performance of a bench-scale mesophilic static granular bed reactor (SGBR) containing fully anaerobic granules coupled with an ultrafiltration (UF) membrane system, as a post-treatment system, was investigated. The poultry slaughterhouse wastewater was characterized by a chemical oxygen demand (COD) range between 1,223 and 9,695mg/L, average biological oxygen demand of 2,375mg/L and average fats, oil and grease (FOG) of 554mg/L. The SGBR anaerobic reactor was operated for 9 weeks at different hydraulic retention times (HRTs), i.e. 55 and 40 h, with an average organic loading rate (OLR) of 1.01 and 3.14g COD/L.day. The SGBR results showed an average COD, total suspended solids (TSS) and FOG removal of 93%, 95% and 90% respectively, for both OLR. The UF post-treatment results showed an average of COD, TSS and FOG removal of 64%, 88% and 48%, respectively. The overall COD, TSS and FOG removal of the system (SGBR and UF membrane) was 98%, 99.8%, and 92.4%, respectively. The results of the combined SGBR reactor coupled with the UF membrane showed a potential to ensure environmentally friendly treatment of poultry slaughterhouse wastewater.

Limitations of a membrane gradostat bioreactor designed for enzyme production from biofilms of Phanerochaete chrysosporium

Growing interest has been shown in the continuous production of high-value products such as extracellular secondary metabolites used in the biotechnology, bioremediation and pharmaceutical industries. These high-value extracellular secondary metabolites are mostly produced in submerged fermentations. However, the use of continuous membrane bioreactors was determined to be highly productive. A novel membrane bioreactor, classified as a membrane gradostat reactor (MGR) was developed to immobilize biofilms to produce extracellular secondary metabolites continuously using an externally unskinned and internally skinned membrane. Anaerobic zones were identified in the MGR system when air was used for aeration. To improve the MGR system, limitations related to the performance of the bioreactor were determined using P. chrysosporium. A DO penetration depth of +/-450 microm was identified after 264 h, with the anaerobic zone thickness reaching approximately 1,943 microm in the immobilised biofilms. The penetration ratio, decreased from 0.42 after 72 h to 0.14 after 264 h. This led to the production of ethanol in the range of 10 to 56 mg/L in the MCMGR and 7 to 54 mg/L in SCMGR systems. This was attributed to an increase in beta-glucan within immobilised biofilms when an oxygen enriched aeration source was used. Increasing lipid peroxidation and trace element accumulation was observed with the use of an oxygen enriched aeration source.

A Finite-Difference Solution of Solute Transport through a Membrane Bioreactor

The current paper presents a theoretical analysis of the transport of solutes through a fixed-film membrane bioreactor (MBR), immobilised with an active biocatalyst. The dimensionless convection-diffusion equation with variable coefficients was solved analytically and numerically for concentration profiles of the solutes through the MBR. The analytical solution makes use of regular perturbation and accounts for radial convective flow as well as axial diffusion of the substrate species. The Michaelis-Menten (or Monod) rate equation was assumed for the sink term, and the perturbation was extended up to second-order. In the analytical solution only the first-order limit of the Michaelis-Menten equation was considered; hence the linearized equation was solved. In the numerical solution, however, this restriction was lifted. The solution of the nonlinear, elliptic, partial differential equation was based on an implicit finite-difference method (FDM). An upwind scheme was employed for numerical stability. The resulting algebraic equations were solved simultaneously using the multivariate Newton-Raphson iteration method. The solution allows for the evaluation of the effect on the concentration profiles of (i) the radial and axial convective velocity, (ii) the convective mass transfer rates, (iii) the reaction rates, (iv) the fraction retentate, and (v) the aspect ratio.

Lithium 7 Isotope (7Li+) Desorption from a Degraded Amberlite IRN 217 Lithiated Mixed-Bed Ion-Exchange Resin

This study investigated the possibility of desorpting the lithium isotope (7Li+) from the cation part of an Amberlite IRN 217 lithiated mixed-bed resin that had been deemed unsuitable for use as a result of anion degradation and the release of organically bound impurities. The desorption of the isotope from the cation part of the mixed-bed resin was studied using dilute hydrochloric (HCl) and sulphuric acid (H2SO4) solutions. The initial experiments were carried out in a batch reactor in order to determine the best eluent acid concentration to be used in a continuous ion-exchange packed-bed column. The favorable eluant concentration was found to be 1 M HCl and 1 M H2SO4, respectively. In the continuous desorption ion-exchange column, a desorption rate >90% was achieved within 18 bed volumes (BV) of HCl and H2SO4 eluants. The concentration of the released anion and cation leachates in the effluent that had been recovered was also determined. The mathematical model developed and the kinetic parameters used in the model represented the desorption kinetics of the 7Li+ isotope from the cation part of the lithiated resin. The correlation coefficient (R2) between the experimental and the simulated data proved to be 0.99 and 0.94 for 1 M HCl and 1 M H2SO4, respectively. This revealed a sufficient correlation for comparison between the experimental and simulated data.

Performance and Kinetic Analysis of a Static Granular Bed Reactor Treating Poultry Slaughterhouse Wastewater

Poultry slaughterhouses consume a substantial quantity of clean water during processing of live birds. Subsequently, high strength poultry slaughterhouse wastewater (PSW) is generated at different stages during poultry product processing. In this study, Static Granular Bed Reactor (SGBR) was used to treat the PSW from a poultry product processing facility in the Western Cape, South Africa. The performance of the SGBR was primarily evaluated for chemical oxygen demand (COD) removal with the kinetics of the treatment process of the PSW being evaluated using the modified Stover-Kincannon and the Grau second order models. Overall, the treatment efficiency averaged >90% when the SGBR were operated at steady state for a 68 days experimental trial. Furthermore, both the Grau second-order and the modified Stover-Kincannon models were used to develop a kinetic model which sufficiently described the COD removal. The Grau second-order model produced a better fit (R2 > 0.99) when compared to the Stover-Kincannon model (R2 > 0.80). The kinetic relationship derived from the lab-scale SGBRs can thus be used to predict the performance of the pilot scale SGBRs treating the PSW under mesophilic conditions.