Biohydrogen production using native carbon monoxide converting anaerobic microbial consortium predominantly Petrobacter sp.

In this study, anaerobic mixed microbial consortium isolated from a local sewage treatment plant in Guwahati, India, was used to convert carbon monoxide (CO) to hydrogen. The consortium was initially grown in acetate containing medium and later acclimatized to utilize CO as the sole carbon source for hydrogen production. By 16S rDNA analysis, the consortium was identified to be predominantly Petrobacter sp. Statistically designed experiments were then applied to optimize the CO conversion and hydrogen production by the anaerobic mixed consortium. To evaluate the significant factors that influenced the biohydrogen production, Plackett–Burman screening design of experiments was applied, which revealed that temperature and Fe²⁺ influenced the most on hydrogen production with P values less than 0.05 each. The effect due to pH and Ni²⁺ was less with P values 0.120 and 0.132, respectively. Concentration of Fe²⁺ and Ni²⁺ in the medium was then subsequently optimized by using Central Composite Design (CCD) of experiments followed by response surface methodology (RSM) which yielded the optimum value of 213 mg/L for Fe²⁺ and 2.2 mg/L for Ni²⁺. At these optimum conditions, 60.8 mol hydrogen production was achieved which was 8% higher than that observed from the screening experiment.     

An Immobilized Cell System for Biodegradation of Pyrene by Mycobacterium Frederiksbergense

Abstract

Pyrene biodegradation by immobilized cells of Mycobacterium frederiksbergense was investigated in the present study. For immobilizing the cells, ion tropic gelation method using sodium alginate and CaCl₂ as the immobilizing materials was applied. Concentration of sodium alginate was optimized based on immobilized cell growth and mechanical stability of the resulting beads. Based on the results obtained beads prepared using 5% sodium alginate and 3.5% CaCl₂ was chosen for pyrene biodegradation by M. frederiksbergense in which encapsulated silicone oil containing pyrene was used for delivery of pyrene. For a very high pyrene concentration of 2000 mg/l in the oil phase, nearly 90% degradation of pyrene could be achieved by the immobilized cell system without any significant lag phase in degradation. Further, the study indicated the possibility of using non-biocompatible and bio-available non aqueous phase liquid (NAPL) in two phase partitioning bioreactor system for pyrene biodegradation by the immobilized microorganism present in the aqueous phase.     

Sophorolipids production by <Emphasis Type="Italic">Candida bombicola</Emphasis> using dairy industry wastewater

Wastewater obtained from a local dairy industry was simultaneously utilized and treated for the production of sophorolipids (SLs), a glycolipids type of biosurfactant, by the yeast Candida bombicola. The dairy wastewater, after initial characterization, was utilized as media with or without adding extra carbon and nitrogen source in the study. A maximum yield of 62 g/l of SLs was found when the yeast was grown on the dairy wastewater supplemented with glucose (10% w/v), yeast extract (0.2% w/v), and soybean oil (10% v/v) in batch shake flasks. Chemical oxygen demand (COD) analysis of the wastewater during the yeast fermentation revealed more than 80% COD removal efficiency in all the experiments. High yield of SLs together with high COD removal efficiency of the yeast in the present study revealed good potential of the system in pretreating such wastewaters and for the production of valuable bioproducts. In addition, the critical micelle concentration and minimum surface tension against water using the produced SLs were found to be 30 mg/l and 33.6 mN/m, respectively. Further, its stability over a wide range of pH (2–10), temperature (up to 120 min of boiling) and salt concentrations (20% NaCl) confirmed the potential of the produced SLs in environmental applications.     

Methane free biohydrogen production from carbon monoxide using a continuously operated moving bed biofilm reactor

Biological water-gas shift (WGS) reaction is a green and sustainable alternative to thermochemical-catalytic WGS process for hydrogen production from carbon monoxide (CO). However, CO tolerant carboxydotrophic microbes for hydrogen production and scaling up the technology using a bioreactor system present challenges in successful application of this technology. This study demonstrated the capability of anaerobic microbial consortium for biohydrogen production from CO using a moving bed biofilm reactor (MBBR). The CO conversion pathway followed by the anaerobic biomass was first elucidated by inhibiting the methanogens present using 2-bromoethanesulfonate (BES) at an optimum concentration of 10 mmol/L. An increase in inlet CO concentration to the MBBR enhanced the H₂ production, but the CO conversion efficiency was low. More than 80% CO conversion efficiency was obtained only for a low inlet CO concentration. A maximum H₂ concentration of 19.5 mmol/L along with 2 mmol/L of acetate were obtained for 36 mmol/L of inlet CO concentration in the bioreactor. The carbon flux analysis showed that the CO was mainly utilized for methane free H₂ production, and only <10% of carbon flux was diverted towards acetate formation. Overall, this study demonstrated that MBBR system can be used for steady state biohydrogen production over a prolonged operation period.     

Kinetics of growth on dual substrates,production of novel glutaminase-free L-asparaginase and substrates utilization by <Emphasis Type="Italic">Pectobacterium carotovorum</Emphasis> MTCC 1428 in a batch bioreactor

Bacterial L-asparaginase has been widely used as a potential therapeutic agent in the treatment of various lymphoblastic leukemia diseases. We studied product and dual substrates utilization kinetics by P. carotovorum MTCC 1428 in batch bioreactor. The kinetic study revealed that the maximum growth of P. carotovorum MTCC 1428 was achieved at 2 g l ^?1 and 5 g l ^?1 of glucose and L-asparagine, respectively. Different substrate inhibition models were fitted to the growth kinetic data and the additive form of double Luong model was found to best explain the growth kinetics of P. carotovorum MTCC 1428. The kinetic parameters of growth studies showed that the predicted maximum inhibition concentration of glucose (S _mg ) and L-asparagine (S _ma ) was close to the experimentally observed value 15.0 and 10 g l ^?1, respectively. Modified form of the Luedeking-Piret model was used to describe the kinetics of L-asparaginase production, and the system seems to be mixed growth associated. Kinetic models of dual substrate growth, L-asparaginase production and substrate(s) utilization by P. carotovorum MTCC 1428 well fitted with experimental data with regression coefficients (R²) value of 0.97, 0.96 and 0.93, respectively.     

Feasibility of <Emphasis Type="Italic">m</Emphasis>-cresol degradation using an indigenous mixed microbial culture with glucose as co-substrate

An indigenous mixed culture of microorganisms, isolated from the soil of a gasoline filling station, was used in degrading m-cresol in presence of glucose as an alternative carbon source. Initial glucose concentration was kept at either 250 or 500 mg l⁻¹, to initiate and support necessary culture growth, and that of m-cresol was varied between 50 and 400 mg l⁻¹. A maximum total biomass yield value of 0.925 g g⁻¹ was obtained at 100 mg l⁻¹ m-cresol and 500 mg l⁻¹ glucose initial concentrations in the media. Variation in the experimentally observed specific growth rate revealed that m-cresol initial concentrations, above 100 mg l⁻¹, inhibited the culture growth irrespective of the glucose concentrations used in the study. Complete degradation of m-cresol was observed within a time period of 18–26 h depending upon the initial concentrations of m-cresol and glucose in the media; on the other hand, glucose utilization was quick and preceded m-cresol degradation. A sum kinetics model was used to describe the variation in the culture specific growth rate, which gave a high coefficient of determination (R ²) value >0.98. From the interaction parameter values obtained by solving this model, the inhibitory effect of glucose on m-cresol degradation by the culture was found to be more pronounced compared to the effect of m-cresol on glucose utilization. This study showed good potential of the indigenous mixed culture in degrading m-cresol when it is provided with a simple alternative carbon source, such as glucose, for supporting its growth.     

Removal of Cu(II) by biosorption onto coconut shell in fixed-bed column systems

Biosorption of Cu(II) onto coconut shell, an agricultural biomaterial, was studied in a fixed-bed column. The Cu(II) biosorption column had the best performance at 10 mg L^?1 inlet Cu(II) concentration, 10 mL min^?1 flow rate and 20 cm bed depth. The equilibrium uptake of Cu(II) amounted to 7.25 mg g^?1. The simulation of the breakthrough curve was successful with the BDST and Yoon–Nelson models, but the entire breakthrough curve was best predicted by the Clark model. The design of a fixed bed column for Cu(II) removal from wastewater by biosorption onto coconut shell can be done based on these models.     

Batch biodegradation of PAHs in mixture by Mycobacterium frederiksbergense: analysis of main and interaction effects

Biodegradation is an effective technique to remediate soil and water contaminated with polycyclic aromatic hydrocarbons (PAHs). In the present experimental study, Mycobacterium frederiksbergense, a fast growing mycobacterium, was used to degrade anthracene, naphthalene and pyrene in mixture each at initial concentrations varying between 1 and 50 mg l⁻¹. Experiments were conducted according to the 2³ factorial design at the low (1 mg l⁻¹) and high (50 mg l⁻¹) levels of the PAHs in combination, to identify the main and interaction effects of the compounds on their biodegradation. The results showed that the PAH removals varied 54–81% when each PAHs were at low concentrations in the mixture and 67–89% at their higher concentration combinations. Statistical analysis of the results in the form of ANOVA and Student t test indicated significant role played by the main effects of pyrene on its degradation. Similarly on anthracene degradation, interaction effect with pyrene was found to be highly significant with P value less than 0.1.     

Screening and optimization of media constituents for decolourization of Mordant Blue-9 dye by Phanerochaete chrysosporium

Decolourization of Mordant Blue-9 (MB-9) by the white-rot fungi Phanerochaete chrysosporium MTCC 787 was investigated by screening and optimization of the media constituents used for growing the fungus. Both % decolourization and specific removal of MB-9 by the fungus were taken as the responses to screen and optimize the media constituents using statistically valid Plackett–Burman and response surface methodology (RSM) design of experiments, respectively. Amongst the media constituents screened, glucose, veratryl alcohol, KH₂PO₄ and CaCl₂ were selected as the most important (P value < 0.05) media constituents for MB-9 dye decolourization; the other media constituents, viz. MgSO₄, tween 20, NH₄Cl₂ and inoculum size were, however, found to be insignificant in the study. Central composite design followed by RSM used in optimizing the important media constituents for enhancing the decolourization of MB-9 dye revealed optimum combinations of glucose, 13.46 g l⁻¹; veratryl alcohol, 9.30 mM; KH₂PO₄, 24.52 g l⁻¹; CaCl₂, 2.18 g l⁻¹; MgSO₄, 9.89 g l⁻¹; NH₄Cl₂, 4.68 g l⁻¹; tween 20, 0.050% and inoculum size, 0.8 OD₆₅₀, which gave a maximum % dye decolourization of 100% and specific dye removal of 0.1571 mg U⁻¹.     

Degradation of phenol by TiO2-based heterogeneousphotocatalysts in presence of sunlight

This paper reports the results of a study on the titanium dioxide Anjatox^®, which shows very interesting photocatalytic activity. Produced for commercial purposes as a white pigment, its features make it very interesting in the field of heterogeneous photocatalysis. The results obtained with this photocatalyst are compared with the behavior of the well-studied and widely used TiO₂ Degussa P-25^® under identical conditions. The degradation experiments showed that the photocatalytic efficiency of Anjatox^® is comparatively close to that of Degussa P-25^®. Both Anjatox^® and Degussa P-25^® show optimum degradation efficiency at a certain loading rate. The particle crystallite size and the BET surface area of the Anjatox^® TiO₂ are also compared with Degussa P-25^®. Moreover the XRD study showed that TiO₂ Anjatox^® was more crystalline than the TiO₂ Degussa P-25. The particle size histogram of TiO₂ Anjatox^® was found to be comparatively uniform like TiO₂ Degussa P-25^®. The use of TiO₂ Anjatox^® in heterogeneous photocatalysis is more desirable when high photocatalyst loading is required because of its low cost. The cost of Anjatox TiO₂ was INR.110.00/Kg and the cost of Degussa P-25 was INR 1000/Kg (Jan 2006).