Search

Abstract.--Microalgae photobioreactors are among the most effective systems for capturing gaseous C[O.sub.2], the main contributor to global warming. Their capacity to generate massive amounts of biomass has been exploited serendipitously [...]

Biotechnology has emerged as an affordable, effective, and eco-friendly alternative to treat carbon disulfide ([CS.sub.2]) containing waste gases. Carbon disulfide is a chemical of widespread use both in the past and in the present. Its industry demand has dramatically changed over the last two decades and is expected to grow in future in step with those industries involving fibre, mining, rubber products, and the agro-chemical sector. This compound, classified as a hazardous air pollutant about 20 years ago, has been re-appraised, as increasingly restrictive pollution standards are expected to be introduced. An array of physical-chemical technologies for treating [CS.sub.2] containing air are already in use, but they have a series of drawbacks, such as high energy consumption (incineration, thermal oxidation), the immobilization of the contaminant solely from one phase to another (adsorption), and the generation of secondary by-products that require additional treatment (hydrolysis). Thus, technological research on affordable processing alternatives is of considerable interest for related industries using or producing [CS.sub.2]. The biological technologies whose efficiency is based on the activity of microorganisms to biodegrade air pollutants overcome many of the disadvantages of conventional techniques and are especially useful for the removal of relatively low concentrations of pollutants. In this paper, the main properties, sources, and uses of [CS.sub.2] are summarized, and alternative biotreatments for [CS.sub.2] are reviewed. Several applications of the technical and economical feasibility of biofilters and biotrickling filters are shown, although their widespread industrial application still requires further research. Key words: carbon disulfide, bioreactors, air pollution control, biotechnology, industrial emissions. La biotechnologie devient une alternative abordable, efficace et eecologiquement acceptable pour traiter les deechets gazeux contenant du disulfure de carbone ([CS.sub.2]). Le [CS.sub.2] est une substance chimique d'utilisation tresrepandue dans le passe; aussi bien que presentement. Sa demande industrielle a fortement change; au cours des deux dernieeres decades et l'on s'attend a ce qu'elle prenne de l'expansion dans le future, de concert avec l'engagement de ces industries dans les secteurs de la fibre, des mines, des produits du caoutchouc et du secteur agrochimique. Ce compose, classified comme dangereux polluant de l'air il y a environ 20 ans a ete reeevalue, car on s'attend a l'introduction de nouveaux standards de plus en plus restrictifs de pollution. On utilise deja un ensemble de technologies physico-chimiques pour traiter l'air contenant du [CS.sub.2], mais ils preesentent des probleemes comme une forte consommation d'energie (incineration, oxydation thermique) l'immobilisation du contaminant uniquement d'une phase a une autre (adsorption) et la generation de produits secondaires qui neecessitent un traitement additionnel (hydrolyses). Ainsi, la recherche technologique de procedes alternatifs abordables presente un inteeret considerable pour les industries utilisant ou produisant du disulfure de carbone. Les techniques biologiques, dont l'efficacite est basee sur l'activite de microorganismes degradant les polluants de l'air, evitent plusieurs des desavantages des techniques conventionnelles et deviennent particulieerement utiles pour eeliminer les contaminants a faibles concentrations. Les auteurs passent en revue et reesument les principales proprietees ainsi que les sources et les usages du [CS.sub.2], et examinent les traitements biologiques alternatifs. On presente plusieurs applications de la faisabilite technique et economique des biofiltres et des filtres par biotrickling, bien que leurs applications industrielles generaliseees demandent encore des recherches. Mots-cles: disulfide de carbone, bioreeacteurs, controle de la pollution de l'air, biotechnologie, emissions industrielles. [Traduit par la Redaction], 1. Introduction Carbon disulfide ([CS.sub.2], CAS Reg. No. 75-15-0) is also known as carbon bisulphide or dithiocarbonic anhydride (ATSDR 1996). Carbon disulfide is a colourless to faintly yellow liquid. The [...]

Wide range of dyes and dyestuffs used in textile manufacturing are xenobiotic compounds and attract stricter to strict environmental regulations. The ability of microbial consortia to decolorize and metabolize dyes has long been known, and the use of bioremediation based technologies for treating textile wastewater has attracted interest. These dyes are decolorized by microbial consortia but technologies for their complete mineralization are still not developed. The most logical concept for the removal of azo dyes in biological wastewater treatment systems is based on anaerobic treatment, for the reductive decolorization, in combination with aerobic treatment, for the degradation of the by-products (aromatic amines) generated in the anaerobic bioreactor. Several research and review articles were published on anaerobic decolorization; however, research on complete mineralization of dyes through sequential anaerobic-aerobic bioreactors has received greater attention recently. Bioremediation through sequential anaerobic-aerobic bioreactor system has been reviewed in this article with critical appraisal using data generated through our experiments. While reviewing this work, we realized the importance of microbial diversity in a treatment unit to better understand the functional status to enhance the mineralization activity of the bioreactor. Key words: azo dyes, biodiversity, bioremediation, two-stage, sequential bioreactor. Un ensemble de teintures et substances tinctoriales utilisees dans la fabrication des textiles constituent des composesxeenobiotiques et appellent des reglementations environnementales severes a tresseveres. On connait depuis longtemps la capacite; des populations microbiennes a decolorer et meetaboliser les teintures, et l'utilisation de technologies basees sur la bioremediation pour traiter les eaux usees des industries textiles souleve beaucoup d'interet. Les populations microbiennes arrivent a decolorer ces teintures, mais les technologies pour les mineeraliser completement ne sont pas encore developpees. Le concept le plus logique pour debarrasser les colorants de type azo des systemes de traitement des eaux usees implique un traitement anaeirobie, pour assurer la decoloration reductive, en combinaison avec un traitement aerobie pour degrader les sous-produits (amines aromatiques) genres pendant la phase anaeirobie. Il existe plusieurs articles et revues sur la decoloration anaeerobie; cependant, ce n'est que recemment que la recherche sur la mineralisation complete des teintures avec des reacteurs sequentiels anaerobie-aeerobie a recju une attention soutenue. Les auteurs passent ici en revue la bioremediation en systemes de bioreacteurs anaeerobie-aeerobie, avec une evaluation critique des domtoes generees dans ces experiences. Tout en realisant cette revue, les auteurs ont constate l'importance de la biodiversite microbienne dans une unite; de traitement, pour mieux comprendre le statut fonctionnel permettant d'acceileerer l'activite; de mineralisation du bioreeacteur. Mots-cles: teintures de type azo, biodiversite, bioremediation, deux etapes, bioreacteur sequentiel. [Traduit par la Redaction], Introduction Bioremediation is a pollution-control technology that uses natural biological species to catalyze the degradation or transformation of various toxic chemicals to less harmful forms. Xenobiotic compounds are not naturally [...]

A pilot-scale liquid-solid circulating fluidized bed (LSCFB) bioreactor was employed for biological nutrient removal from municipal wastewater at the Adelaide Pollution Control Plant, London, Ontario, Canada. Lava rock particles of 600 [micro]m were used as a biomass carrier media. The system generated effluent characterized by DOI: 10.1061/(ASCE)EE.1943-7870.0000221 CE Database subject headings: Biofilm: Nitrification; Denitrification: Phosphorus; Nutrients; Dynamic loads: Fluidized bed technology: Abatement and removal. Author keywords: Biofilm; Nitrification; Denitrification; Enhanced biological phosphorus removal; UV disinfection: Nutrient balance.

Pollutants removal from swine wastewater by a submerged biofilm sequencing batch reactor (BSBR) with internal circulation of liquor through a sand filter was studied. The variation of nutrient removal efficiencies with changes in volumetric circulation ratios and rates were determined. The reactor was operated under the following conditions: One cycle per day, hydraulic retention time of 15 days, average [NH.sub.4]--N loading rate of 55 g [m.sup.-3] [d.sup.-1], and without supplemental external carbon source. System performance was enhanced by conducting internal circulation of liquor through the sand filter. When compared with the performance of a single BSBR without sand filter, nitrogen and phosphorus removal efficiencies were found to increase by 18% and over 33%, respectively. With a circulation rate of 170 L [h.sup.-1] [m.sup.-3], and duration of 22 h (circulation ratio of 0.9), TOC, [NH.sub.4]--N, and total soluble inorganic nitrogen (as [NH.sub.4]--N plus [NO.sub.x]--N) removal efficiencies of 73, 97.8, and 85.6%, respectively, were achieved. The enhancement of nitrogen removal was attributed to the occurrence of denitrification in the sand filter during circulation of liquor. The denitrification rate was proportional to the volumetric circulation ratio per day, resulting in an average 15% N[O.sub.x]--N removal in the sand filter. Also, it was found that continuous circulation during the entire reaction phases could be one way to achieve better performance. DOI: 10.1061/(ASCE)EE.1943-7870.0000199 CE Database subject headings: Biofilm; Reactors; Sand, filter; Wastewater management; Animals. Author keywords: Biofilm; Sequencing batch reactor (SBR); Sand filter; Swine wastewater.

Artificial groundwater recharge for drinking water production involves infiltration of surface water through sandy soil and its capture into a groundwater aquifer. The transformation of aqueous organic matter is one of the central issues in this process. The purpose of this work was to assess the potential of indigenous microorganisms in the source water to contribute in the aqueous organic matter biodegradation. For this purpose, microorganisms were enriched from the source water in a fluidized-bed reactor (FBR) and used for kinetic studies on biodegradation of organic matter at ambient temperature range. Lake water (total organic carbon 5.8 mg [L.sup.-1]) was continuously fed to the FBR containing porous carrier material to support biomass retention. In the inlet and outlet water there were on average 21 [+ or -] 6 and 13 [+ or -] 5 x [10.sup.5] cells [mL.sup.-1], respectively. Biofilm accumulation (as volatile solids) reached 13.1 mg [g.sup.-1] dw cartier. In the continuous-flow mode and the batch tests, the highest oxygen consumption rate appeared in the summer, followed by the fall, spring, and winter. At low temperatures, the biodegradation of aqueous organic matter was relatively rapid initially for labile fractions followed by a slower phase for refractory fractions. The average temperature coefficient ([Q.sub.10]) in the system was 2.3 illustrating a strong temperature dependency of oxygen consumption. The isotopic analysis of dissolved inorganic carbon [[delta].sup.13][C.sub.DIC] analysis revealed 27 and 69% mineralizations of dissolved organic carbon at 23 and 6[degrees]C over 65 and 630 min, respectively. These results can be used to construct additional input parameters in modeling applications of artificial groundwater recharge process. The biological component especially, i.e., the biodegradation, is difficult to predict for on-site applications without experimental proof and thus the interpretation in this study will help formulate design predictions for the process. DOI: 10.1061/(ASCE)EE.1943-7870.0000197 CE Database subject headings: Organic carbon; Groundwater recharge; Fluidized beds; Biomass; Biodegradation; Aquifers; Bacteria; Lakes. Author keywords: Organic carbon; Groundwater recharge; Fluidized beds; Biomass; Biodegradation; Aquifers.

We present the development of microbioreactors with a sensitive and accurate optical coupling to a confocal Raman microspectrometer. We show that such devices enable in situ and in vitro investigation of cell cultures for tissue engineering by chemically sensitive Raman spectroscopic imaging techniques. The optical resolution of the Raman microspectrometer allows recognition and chemical analysis of subcellular features. Human bone marrow stromal cells (hBMSCs) have been followed after seeding through a phase of early proliferation until typically 21 days later, well 'after the cells have differentiated to osteoblasts. Long-term perfusion of cells in the dynamic culture conditions was shown to be compatible with experimental optical demands and off-line optical analysis. We show that Raman optical analysis of cells and cellular differentiation in microbioreactors is feasible down to the level of subcellular organelles during development. We conclude that microbioreactors combined with Raman microspectroscopy are a valuable tool to study hBMSC proliferation, differentiation, and development into tissues under in situ and in vitro conditions. 10.1021/ac902515c

The presence of toxic hexavalent chromium poses a great challenge in biological wastewater treatment. In this study, the performance of a membrane bioreactor (MBR) for the treatment of synthetic domestic wastewater in the presence of chromium was investigated. The carbonaceous pollutant removal is not affected by Cr(VI) with concentration ranging from 0.4 to 10 mg/L; it becomes slightly lower when the Cr(VI) is 50 mg/L. The nitrification efficiency of above 99% can be achieved when the waste stream is free of the metal or contains 0.4 mg/L chromium. When its concentration is 10 mg/L, nitrification efficiency above 50% is found; however, it becomes deteriorated in the presence of 50 mg/L chromium. The positive biomass growth, though lower than conventional activated sludge process, can be achieved at Cr(VI) concentration less than 10 mg/L; a decline in the cell growth occurs when the metal concentration is increased to 50 mg/L. Significant accumulation for the metal is observed when its concentration is 0.4 mg/L; however, almost no metal removal is observed when the concentration is above 10 mg/L. During eight-month continuous operation, the presence of Cr(VI) has an insignificant effect on the flux. The nitrifiers in the MBR are more sensitive to the presence of Cr(VI) than heterotrophs. DOI: 10.1061/(ASCE)0733-9372(2009)135:9(796) CE Database subject headings: Water treatment; Wastewater management; Chromium; Membranes; Reactors.

Oxygen transfer is one of the key processes in the bioreactor. Herein a computational fluid dynamics model for the oxygen transfer in high-speed surface aeration tank has been developed and validated through a full-scale aeration test. The test results indicate that the oxygen transfer mainly comes from the spray water in air and that the gas entrainment by the plunging of spray water and the surface reaeration in the aeration tank contribute little to the total oxygen transfer in high-speed surface aerator. A simple method was proposed to measure the oxygen transfer rate for high-speed surface aerator. DOI: 10.1061/(ASCE)EE. 1943-7870.0000023 CE Database subject headings: Oxygen transfer; Mass transfer; Aeration; Reactors; Mathematical models; Computational fluid dynamics technique; Wastewater management.

Problem statement: This study discussed the problem of accumulation of Zn and Cu in the topsoil as a result of application of mineral feed additives that possess low bioavailability in animal diet. The review considered the production process of mineral feed additives in which a product supplies microelements in highly bioavailable form. Enrichment of natural biomass of edible microalgae with microelement metal ions, which supply microelements of feeding significance in livestock diet, is considered in term of sustainable production. Approach: Production of microalgae-derived products as mineral feed additives requires elaboration of the processes for cultivation of alga, enrichment process and afterwards recovery of the enriched biomass from the solution to obtain liquid free of cells that could be reused in the next process. In this study membrane bioreactor was considered as a method for separation, both in photobioreactor (growth of microorganism) as well as in the enrichment process. Results: Effort involved in thermal and chemical separation techniques is higher than that in mechanical techniques. Membrane bioreactors which are usually applied to treat wastewater, both industrial and domestic. This study discussed method to separate a valuable biomass of enriched microalgae and reuse the solution with residual metal ions that can be used once again in the subsequent biosorption process. Conclusion/Recommendation: Taking into consideration care about the environment it is better to apply membrane modules in the production process in terms of sustainable production. The proposed solution assumed the application of membrane modules as a separation step after enrichment process and biomass recovery. Key words: Microalgae, mineral feed additives, biosorption, bioaccumulation, microelements, membrane bioreactors, INTRODUCTION Each process in food and agriculture industry has an impact on the environment and there is much concern about environmental pollution (1). The intensification of agricultural production in Poland [...]

Problem Statement: Mixing filamentous fungi entails delicate balance between promoting high volumetric oxygen transfer coefficient ([k.sub.L]a) while keeping low hydrodynamic stresses in the microenvironment of cultures. This study examined the oxygen transfer capability of a prototype low shear helical impeller as a potential replacement for the standard Rushton turbine. Approach: The dependence of [k.sub.L]a upon specific power uptake, superficial gas velocity and apparent viscosity were examined under coalescent, non-coalescent and viscous pseudoplastic fluids scenario using dynamic gassing out technique. Subsequently, collected data were treated under historical data design of response surface methodology. Results: Three empirical power law [k.sub.L]a correlations were developed for each fluid. Correlation comparison with literature models for single turbine agitation suggest higher [k.sub.L]a augmentation within 1.5-3.6 folds for helical impeller in distilled water and as high as 78% improvement in electrolytes fluid. However impeller performance is comparatively 10% lower against theoretical [k.sub.L]a of triple turbines arrangement for power uptake between 0-1600 W [m.sup.-3]. In case of carboxymethylcellulose, better oxygen transfer is expected for design with higher proportionality of impeller-to-tank internal diameter. Conclusions: Helical impeller performance as gas-liquid contactor is comparable to single and triple Rushtons turbines, with superficial gas velocity proved to be more influential than power uptake in non-viscous liquids and vice versa in viscous pseudoplastic fluids. Key words: oxygen transfer, impeller, stirred tank bioreactor, response surface methodology, INTRODUCTION Solubilization of oxygen in liquid medium constitutes one of the decisive factors leading to the success of fermentation processes. More often than not, wholly oxygenation of vessel would be [...]

Recently a cartilage growth finite element model (CGFEM) was developed to solve non-homogeneous and time-dependent growth boundary-value problems (Davol et al., 2008, 'A Nonlinear Finite Element Model of Cartilage Growth,' Biomech. Model. Mechanobiol., 7, pp. 295-307). The CGFEM allows distinct stress constitutive equations and growth laws for the major components of the solid matrix, collagens and proteoglycans. The objective of the current work was to simulate in vitro growth of articular cartilage explants in a steady-state permeation bioreactor in order to obtain results that aid experimental design. The steady-state permeation protocol induces different types of mechanical stimuli. When the specimen is initially homogeneous, it directly induces homogeneous permeation velocities and indirectly induces nonhomogeneous solid matrix shear stresses; consequently, the steady-state permeation protocol is a good candidate for exploring two competing hypotheses for the growth laws. The analysis protocols were implemented through the alternating interaction of the two CGFEM components: poroelastic finite element analysis (FEA) using ABAQUS and a finite element growth routine using MATLAB. The CGFEM simulated 12 days of growth for immature bovine articular cartilage explants subjected to two competing hypotheses for the growth laws: one that is triggered by permeation velocity and the other by maximum shear stress. The results provide predictions for geometric, biomechanical, and biochemical parameters of grown tissue specimens that may be experimentally measured and, consequently, suggest key biomechanical measures to analyze as pilot experiments are performed. The combined approach of CGFEM analysis and pilot experiments may lead to the refinement of actual experimental protocols and a better understanding of in vitro growth of articular cartilage. [DOI: 10.1115/1.3049856] Keywords: growth, cartilage, mixture, permeation, bioreactor, finite element analysis

A pilot-scale experiment was carried out to study the simultaneous removal of nitrogen and phosphorous from municipal wastewater by an innovative continuous-flow integrated biological reactor (CIBR) process. A three-phase separator was used in the CIBR process, which not only saved energy consumption of sludge returning, but also solved the sludge-gas separating problem. The optimal working condition was 2 h aeration, 1 h agitation, and 1 h settling, with an energy consumption of 0.23 kW h/[m.sup.3]. The average removal of chemical oxygen demand (COD), ammonia nitrogen (N[H.sup.+.sub.4]-N), total nitrogen (TN), and total phosphorus (TP) under the optimal conditions were 72.87, 75.23, 61.25, and 68.25%, respectively. The distributing rules of dissolved oxygen, pH, mixed liquid suspended solid, COD, N[H.sup.+.sub.4]-N, N[O.sup.-.sub.3]-N, TN, and TP in each phase of CIBR was studied. It was indicated that the appropriate condition was created for the simultaneous removal of nitrogen and phosphorus in the integrated reactor. The study demonstrated the feasibility of using CIBR process for simultaneous removal of nitrogen and phosphorus at the average temperature 12.2[degrees]C. DOI: 10.1061/(ASCE)0733-9372(2008)134:3(169) CE Database subject headings: Assets; Sustainable development; Wastewater management; Water quality.

Microchannel bioreactors have applications for manipulating and investigating the fluid microenvironment on cell growth and functions in either single culture or co-culture. This study considers two different types of cells distributed randomly as a co-culture at the base of a microchannel bioreactor: absorption cells, which only consume species based on the Michaelis-Menten process, and release cells, which secrete species, assuming zeroth order reaction, to support the absorption cells. The species concentrations at the co-culture cell base are computed from a three-dimensional numerical flow-model incorporating mass transport. Combined dimensionless parameters are proposed for the co-culture system, developed from a simplified analysis under the condition of decreasing axial-concentration. The numerical results of species concentration at the co-culture cell-base are approximately correlated by the combined parameters under the condition of positive flux-parameter. Based on the correlated results, the critical value of the inlet concentration is determined, which depends on the effective microchannel length. For the flow to develop to the critical inlet concentration, an upstream length consisting only of release cells is needed; this upstream length is determined from an analytical solution. The generalized results may find applications in analyzing the mass transport requirements in a co-culture microchannel bioreactor. [DOI: 10.1115/1.2720913] Keywords: microchannel bioreactor, co-culture cell growth, species concentration

Hybrid-hollow-fiber membrane bioreactors were developed for the enhanced cometabolic biotransformation of phenol and 4-chlorophenol (4-cp) by Pseudomonas putida ATCC49451. Bioreactor performance was investigated, compared, and analyzed under batch and continuous operating modes. The spinning solutions contained polysulfone (PS), N-methyl-2-pyrrolidone, and various weight ratios of granular activated carbon (GAC) (GAC: PS of 0, 1:4, and 1:2). The bioreactor fabricated with 1:2 GAC hybrid-hollow-fiber membranes demonstrated the best performance for the removal of phenol and 4-cp, both under batch and continuous operations. Under batch operation, 500 mg [L.sup.-1] phenol and 4-cp were completely removed within 23 h in the bioreactor, compared with 26 and 30 h for the 1:4 GAC and GAC free bioreactors. Sorption, biotransformation, desorption, and bioregeneration were identified as the four steps for substrate removal during batch operation. The 1:2 GAC hollow-fiber membrane bioreactor also manifested superiority over the other two during continuous operation for start up and the transient phase after shock loadings of the feed. 300 mg [L.sup.-1] phenol and 4-cp were completely removed in the 1:2 GAC hybrid-hollow-fiber membrane bioreactor whereas 4-cp was not completely removed in the other two bioreactors at a feed rate of 30 mLh [h.sup.-1]. From the experimental results, it was inferred that at steady state, biotransformation was achieved through the dynamic equilibrium among sorption, desorption, and biotransformation rates established within the bioreactors. DOI: 10.1061/(ASCE)0733-9372(2007)133:4(404) CE Database subject headings: Hybrid method; Reactors; Transformations: Biological treatment; Phenol.

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCR and toxicity removal performance of the system were investigated for sludge ages between 5 and 30 days, while the feed COD (2600 [+ or -] 100 mg [L.sup.-1]), TCP (370 [+ or -] 10 mg [L.sup.-1]), and the hydraulic residence time (25 h) were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above 20 days. Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCE COD, and toxicity removals. More than 95% of COD, TCR and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum (120 mg TCP g[X.sup.-1] [day.sup.1]) at a sludge age of 20 days. TCP inhibition was eliminated by operation of the system at sludge age above 20 days to obtain nearly complete COD, TCE and toxicity removal. DOI: 10.1061/(ASCE)0733-9372(2007)133:3(340) CE Database subject headings: Wastewater management; Water treatment; Biological treatment; Reactors; Biofilm; Toxicity.

This study examined the effect of the addition of activated carbon to three, 3 L submerged anaerobic membrane bioreactors (SAMBRs) in terms of chemical oxygen demand (COD) removal, flux, and transmembrane pressure (TMP). The feed was a synthetic substrate with a COD of 460 mg [L.sup.-1], with one reactor run as a control, one with 1.7 g [L.sup.-1] of powdered activated carbon (PAC), and the third with 1.7 g [L.sup.-1] of granular activated carbon (GAC). While COD removal was high in all reactors (>90%), in comparison to the control (SAMBR1), the average COD removal in SAMBR2 (PAC) increased by 22.4%, while SAMBR3 with GAC was not significantly better. Because PAC has a significantly greater surface area per mass than GAC, it is probable that this difference was primarily due to the greater absorbance of fine colloidal particles and high molecular weight organics onto the carbon surface. These effects manifested themselves by SAMBR2 having lower TMPs and higher fluxes than both SAMBR3 and SAMBR 1. Volatile fatty acids in the effluent from all three SAMBRs were extremely low (< 18 mg [L.sup.-1]), even during step changes in hydraulic retention tune, and most of the soluble COD in the effluent was soluble microbial products. Biochemical methane potential assays showed that biomass in the SAMBRs was less active than the seed sludge, and it appears that the addition of activated carbon to Reactors SAMBR2 and SAMBR3 provided a solid support for growth, and hence reduced floc breakage. DOI: 10.1061/(ASCE)0733-9372(2007)133:1(73) CE Database subject headings: Reactors; Membranes; Activated carbon treatment; Wastewater management; Pressures.

The accumulation of soluble microbial products (SMP) in a membrane bioreactor (MBR) was investigated both experimentally and theoretically. The sieving mechanism of the microfiltration membrane was experimentally demonstrated as inadequate to explain the salient accumulation of SMP in an MBR. The retarded transport of SMP through porous membranes was postulated as a new mechanism for the elevated SMP concentration in the MBR. Owing to the higher affinity of SMP to the membrane matrix, the convection velocity of SMP across the membrane can be much slower than that of water. The ratio of SMP concentration in the effluent to that in the MBR can be determined with a rigorous solution of the convection-dispersion equation developed based on the retarded transport. In addition, a mass balance model considering SMP generation in the MBR and SMP transport through the membrane was developed to describe the SMP concentrations in the MBR and in the effluent. The simulation results were in good agreement with the experimental data, indicating that the accumulation of SMP in the MBR could be attributed to the retarded transport of SMP through the membrane. The proposed model provides a new conceptual framework for evaluating the fate of SMP and the performance of MBR. DOI: 10.1061/(ASCE)0733-9372(2007)133:1(36) CE Database subject headings: Biological treatment; Environmental engineering; Filtration; Membranes; Organic compounds; Wastewater management; Microbes.

A continuous flow flat sheet hybrid membrane aerated biofilm reactor (MABR) was used to treat a synthetic wastewater containing perchloroethylene (PCE); 1.25-2.5 g chemical oxygen demand (COD)/L of glucose was also added to the synthetic wastewater as a source of COD representative of a real wastewater. The reactor was able to biodegrade 70 mg [L.sup.-1] of PCE in 9 h without the accumulation of any intermediate compounds, resulting in a removal rate of 247 mmol of PCE [h.sup-1] [m.sup.-3] in a reactor with a specific membrane area of 4.048 [m.sup.2] [m.sup.-3]. MABRs have never been used before for PCE degradation, and this rate is one of the highest volumetric PCE degradation rates reported in the literature. COD removal was also good and varied from 85 to 92%. Since very few volatile fatty acids accumulated in the system, most of the residual COD was attributed to soluble microbial products as reported by previous researchers. A mass balance on chloride during this study showed that only 72-81% of it could be accounted for. It is probable that some of the chlorinated ethenes were adsorbed onto the biofilm or that aerobic intermediates of low-chlorinated compounds such as trichloroethanol, dichloroacetyl, and chloroacetaldehyde were produced in the system. Nevertheless the chloride mass balance in this work compares well with the literature. Due to their high PCE and COD removal rates, hybrid MABRs have the potential to be used for a number of refractory organics which require combined anaerobic/aerobic biological treatment for degradation. DOI: 10.1061/(ASCE)0733-9372(2007)133:1(20) CE Database subject headings: Biodegradation; Biofilm; Membranes; Reactors; Hybrid methods.

To meet the increasing need for reduction of exhaust emissions from stationary sources, many technologies have been developed to remove S[O.sub.2] from flue gas. In this study the anodic oxidation of sulfur dioxide in aqueous solutions of sulfuric acid with a unique reactor design and electrode configuration has been investigated. An electrochemical absorption column larger than laboratory scale was employed. A titanium rod cathode and platinum expanded mesh anode separated by a cation exchange membrane were used as electrodes in the cylindrical electrochemical reactor. The effects of current densities of 10, 1, and 0.1 [Am.sup.-2], initial S[O.sub.2] concentrations of 500, 2,500, and 5,000 ppm, gas flow rates of 0.75, 1.5, and 5 L [min.sup.-1], sulfuric acid concentrations of 1, 5, and 10% (w), gas composition, and electrolysis time on removal efficiency, current efficiency, energy consumption, and mass transfer coefficient were reported. Removal efficiency of 94% was obtained with a high current efficiency of 94%, energy consumption of 2.22 x [10.sup.-2] kW [hm.sup.-3], and mass transfer coefficient of 5.9 x [10.sup.-5] [ms.sup.-1] without additives or pretreatment. At the current densities of 0.1, 1, and 10 [Am.sup.-2], the removal efficiencies were 10, 94, and 98%, respectively. Removal efficiency was observed to decrease as inlet S[O.sub.2] concentration, gas flow rate, and electrolyte concentration increased. The presence of C[O.sub.2] in the gas mixture led to a decrease in the S[O.sub.2] removal efficiency. During electrochemical absorption of S[O.sub.2] into the [H.sub.2]S[O.sub.4] solution, the concentration of acid is increased from 5 to 10%. At the end of the studies, electrochemical desulfurization succeeded in meeting the regulation requirement, and the absorbing liquid remained in a reusable form. DOI: 10.1061/(ASCE)0733-9372(2007)133:1(13) CE Database subject headings: Absorption; Air pollution; Gas; Reactors.

Ultraviolet (UV) absorbance measurements are subject to significant error using a standard spectrophotometer when particles or aggregates that scatter light are present. True UV absorbance for highly turbid waters should be measured using integrating sphere (IS) spectrophotometry that allows the collection of reflected and transmitted radiation simultaneously. This is especially important when the effects of scattering impact UV disinfection--such as with the presence of aggregates. The impact of light scattering of particle aggregated microbes on UV disinfection was evaluated by comparing standard spectrophotometer and integrating sphere absorbance measurements for UV fluence determination. Spore--clay aggregates in simulated drinking waters and spore aggregates with natural particles from raw waters were induced by flocculation with alum. Coagulated systems significantly decreased the UV inactivation effectiveness compared to the noncoagulated system with the effects more pronounced for raw natural water. Absorbance measurement of suspensions and aggregates using standard spectrophotometry in the calculations of fluence resulted in overdosing whereas the use of IS spectroscopy did not. The results demonstrated that aggregation protected spores from UV disinfection, and that use of proper absorbance measurement techniques, accounting for particle scattering, is essential for correct interpretation of the results. DOI: 10.1061/(ASCE)0733-9372(2006)132:6(607) CE Database subject headings: Reactors; Particles; Ultraviolet radiation; Disinfection; Microbes; Measurement.

Microchannel bioreactors have been used in many studies to manipulate and investigate the fluid microenvironment around cells. In this study, substrate concentrations and shear stresses at the base were computed from a three-dimensional numerical flow-model incorporating mass transport. Combined dimensionless parameters were developed from a simplified analysis. The numerical results of substrate concentration were well correlated by the combined parameters. The generalized results may find applications in design analysis of microchannel bioreactors. The mass transport and shear stress were related in a generalized result. Based on the generalized results and the condition of dynamic similarity, various means to isolate their respective effects on cells were considered. [DOI: 10.1115/1.2170118] Keywords: microchannel bioreactor, cell culture, substrate concentration, shear stress

An immobilized cell hollow fiber membrane bioreactor was operated continuously for the cometabolic transformation of 4-cp in the presence of phenol. In contrast to the batch operation of the bioreactor in which the immobilized cells were exposed to decreasing substrate concentrations, at high substrate concentrations, under continuous operation, dissolved oxygen was found to be a limiting nutrient. It was found that substrate degradation was enhanced by aerating the feed with pure oxygen. It was also found that the optimum number of hollow fibers in the bioreactor was 25, ca. 30% bioreactor volume. This occurred due to a balance of the pore space available for cell immobilization in the fibers against the extracapillary space available for suspension cell growth. During continuous operation, regardless of feed rate (21-60 mL x [h.sup.-1]), the maximum substrate loading was found to be 9 x [h.sup.-1] each of phenol and 4-cp in order that both substrates were completely transformed. In anticipation of reduced provision of phenol as a specific growth substrate for 4-cp cometabolic transformation, it was concluded that complete transformation of 4-cp could be effected through a minimum substrate concentration ratio of phenol:4-cp of 1:1.8. DOI: 10.1061/(ASCE)0733-9372(2006)132:3(309) CE Database subject headings: Biodegradation; Membranes; Biological treatment: Phenol.