Bioelectricity generation using two chamber microbial fuel cell treating wastewater from food processing

Electricity generation from microbial fuel cells which treat food processing wastewater was investigated in this study. Anaerobic anode and aerobic cathode chambers were separated by a proton exchange membrane in a two-compartment MFC reactor. Buffer solutions and food industry wastewater were used as electrolytes in the anode and cathode chambers, respectively. The produced voltage and current intensity were measured using a digital multimeter. Effluents from the anode compartment were tested for COD, BOD₅, NH₃, P, TSS, VSS, SO₄ and alkalinity. The maximum current density and power production were measured 527 mA/m² and 230 mW/m² in the anode area, respectively, at operation organic loading (OLR) of 0.364 g COD/l.d. At OLR of 0.182 g COD/l.d, maximum voltage and columbic efficiency production were recorded 0.475 V and 21%, respectively. Maximum removal efficiency of COD, BOD₅, NH₃, P, TSS, VSS, SO₄ and alkalinity were 86, 79, 73, 18, 68, 62, 30 and 58%, respectively. The results indicated that catalysts and mediator-less microbial fuel cells (CAML-MFC) can be considered as a better choice for simple and complete energy conversion from the wastewater of such industries and also this could be considered as a new method to offset wastewater treatment plant operating costs.     

Growth of Chlorinated Solvent‐Degrading Consortia in Fed‐Batch Bioreactors and Development of a Double‐Substrate High‐Performing Microbial Inoculum

The long‐term growth process of two microbial consortia effective in the aerobic cometabolic biodegradation of a mixture of 6‐chlorinated aliphatic hydrocarbons (CAHs), the effectiveness of these consortia as inocula for the bio‐augmentation of different types of microcosms and the development of a double‐substrate, high‐performing consortium is presented. The propane‐utilizing consortium generally proved to be the most effective one, being able to biodegrade vinyl chloride, cis‐ and trans‐1,2‐dichloroethylene, trichloroethylene, 1,1,2‐trichloroethane and 1,1,2,2‐tetrachloroethane at all the CAH concentrations tested (0–4 μM). Both consortia maintained unaltered CAH degradation capacities over a 300‐day growth period in the absence of the CAHs and were effective in inducing the rapid onset of CAH depletion upon inoculation in slurry microcosms set up with five types of aquifer materials. A consortium supplied with both methane and propane combined the best degradation capacities of the two single‐substrate consortia, and maintained stable performances for 150 days under slurry conditions. The degree of conversion of the organic Cl to chloride ions was equal to 90 %.     

Optimal parametric sensitivity control for the estimation of kinetic parameters in bioreactors

In this paper the well-known problem of optimal input design is considered. In particular, the focus is on input design for the estimation of kinetic parameters in bioreactors. The problem is formulated as follows: given the model structure (f,g), which is assumed to be affine in the input, and the specific parameter of interest theta;(k) find a feedback law that maximizes the sensitivity of the model output to the parameter under different flow conditions in the bioreactor and, possibly, minimize the input or state costs. Analytical solutions to these problems are presented. As an example a bioreactor with a biomass that grows according to the well-known Monod kinetics is considered.     

Identification of reaction networks for bioprocesses: determination of a partially unknown pseudo-stoichiometric matrix

In this paper we propose a methodology to determine the structure of the pseudo-stoichiometric coefficient matrix K in a mass balance-based model and to identify its coefficients from a set of available data. The first stage consists in estimating the number of reactions that must be taken into account to represent the main mass transfer within the bioreactor. This provides the dimension of K. Then we propose a method to directly determine the structure of the matrix (i.e. mainly its zeros and the signs of its coefficients). These methods are illustrated with simulations of a process of lipase production from olive oil by Candida rugosa.     

An unstructured model for studies on phenanthrene bioconversion by filamentous fungus Cunninghamella elegans

An unstructured model for phenanthrene bioconversion by filamentous fungus Cunnighamella elegans in stirred tank batch bioreactors was proposed. It was observed that the process of phenanthrene bioconversion is strictly associated with exponential growth of biomass. Therefore, a Monod-type, with Contois term, unstructured model could be applied to describe the process mathematically. The inhibition of biomass growth due to high concentrations of phenanthrene present in the medium was taken into account in the form of Yerusalimski's uncompetitive inhibition term.     

Study of the Operability of a Continuous Bioreactor for the Pre‐fermentation of Cheese Culture

The dynamics of a continuous stirred‐tank bioreactor for cheese pre‐fermentation is analyzed using elementary concepts of bifurcation theory and continuation techniques. The bioreactor model, which was previously developed and validated, explicitly incorporates the effect of uncontrolled pH levels. The stability analysis of the model is carried out for two cases: In the first case, the bioreactor is equipped with a seed tank, while the second case involves no additional seed tank. The static analysis allows useful analytical results for the study of steady state multiplicity of the model to be derived. The results of this paper provide practical guidelines on the selection of operating parameters that can eliminate difficult operating regions and that can consequently improve the operability of the bioreactor.     

Perfusion culture of fetal human hepatocytes in microfluidic environments

Various types of bioreactors composed of microstructured PDMS (Polydimethylsiloxane) layers have recently been fabricated for perfusion culture of mammalian cells such as adult rat hepatocytes. As a new feature of those bioreactors, in this study, cultivation of fetal human hepatocytes (FHHs) was attempted, because they have high possibility to mature in vitro with preserving their normality, which is suitable for inplantation of liver tissue equivalents reconstituted in vitro. During the perfusion culture in the PDMS bioreactors for 1 week, cells showed good attachment, spreading and reached their confluence over the channels. In addition, their albumin production was significantly enhanced in the perfusion culture using the PDMS bioreactors up to about four times during the FHH perfusion culture when compared in dish-level static culture. Hep G2 cell cultures were also performed and have also shown under perfusion conditions an enhanced cell activity multiplied by 2 compared to static conditions. Although, the cellular activities of FHH cells are still low even compared to those of the Hep G2 cells, the conclusions of this work is encouraging toward future liver tissue engineering based on in vitro propagation and maturation of hepatocyte progenitors combined with microfabrication technologies.     

Anaerobic Hydrogen Production from Sucrose Using an Acid‐Enriched Sewage Sludge Microflora

A novel and high‐rate anaerobic sequencing bath reactor (ASBR) process was used to evaluate the hydrogen productivity of an acid‐enriched sewage sludge microflora at a temperature of 35 °C. In this ASBR process a 4 h cycle, including feed, reaction, settle, and decant steps, was repeatedly performed in a 5 L reactor. The sucrose substrate concentration was 20 g COD/L; the hydraulic retention time (HRT) was maintained at 12–120 h at the initial period and thereafter at 4–12 h. The reaction/settle period ratio, which is the most important parameter for ASBR operation was 1.7. The experimental results indicated that the hydrogenic activity of the sludge microflora was HRT‐dependent and that proper pH control was necessary for a stable operation of the bioreactor. The peak hydrogenic activity value was attained at an HRT of 8 h and an organic loading rate of 80 kg COD/m³ × day. Each mole of sucrose in the reactor produced 2.8 mol of hydrogen and each gram of biomass produced 39 mmol of hydrogen per day. An overly‐short HRT might deteriorate the hydrogen productivity. The concentration ratios of butyric acid to’acetic acid, as well as volatile fatty acid and soluble microbial products to alkalinity can be used as monitoring indicators for the hydrogenic bioreactor.     

Relation between Citric Acid Production and Respiration Rate of Aspergillus niger in Solid‐State Fermentation

Among the organic acids produced industrially, citric acid is the most important in quantitative terms. Solid‐state fermentation (SSF) has been an alternative method for citric acid production using agro‐industrial residues such as cassava bagasse (CB). The use of CB as a substrate can avoid environmental problems caused by its disposal into the environment. This study was developed to verify the influence of the treated bagasse amount, and consequently, the influence of the gelatinization degree of CB starch on citric acid production by SSF in Erlenmeyer flasks, horizontal drums, and trays. The best results were obtained in a horizontal drum bioreactor using 100 % of treated CB. However, trays showed advantages and good perspectives for large‐scale citric acid production due to economic reasons such as energy costs. A kinetic study was also carried out in order to compare citric acid production in glass columns (laboratory scale) and horizontal drum bioreactors (semi‐pilot scale). This study was accomplished in order to follow the influence of aeration on citric acid accumulation. In addition, the production of CO₂ was evaluated as an indirect method of biomass estimation. Citric acid production was higher in glass columns (309.70 g/kg of dry CB) than in HD bioreactors (268.94 g/kg of dry CB). Finally, it was possible to show that citric acid production was favored by a limited biomass production, which occurred with low aeration rates. Biomass production is related to CO₂ production and as a result, a respirometry analysis could be used for biomass estimation.     

Different bioreactor configurations for the decolourisation of the azo dye reactive black 5 by Geotrichum sp. CCMI 1019

Decolourisation of the azo dye Reactive Black 5 by Geotrichum sp. CCMI 1019 was studied using stirred tank reactors (STR) and two types of bubble columns (porous plate (PP) bubble column and aeration tube (AT) bubble column). For the bubble columns, the k_La increased with the gas fractional hold-up (ε_G) and the aeration rate. A linear relationship between ε_G and superficial gas velocity was obtained for all reactors. At same aeration rates, the PP bubble columns showed higher k_La and hold-up values than the AT bubble column. In the STRs, large and dense aggregates were formed which adhered to surfaces whereas bubble columns gave smaller and less compact pellets.

Manganese peroxidase and laccase were detected in the extracellular media in all reactors. However, laccase was only detected after the onset of decolourisation, suggesting that additional enzymes may be involved. Mn peroxidase activity was detected (about 46 U/ml) in both the STRs and AT bubble columns but higher values (110 U/ml) were obtained with the PP bubble columns.

Out of the three reactor systems studied, the AT bubble columns gave the most favourable results for Reactive Black 5 decolourisation. Rapid and complete colour removal was obtained throughout the visible spectrum. Bubble columns are simple in design as well as operation and may be useful for the bioremediation of textile wastewater.