Biodegradation of Methyl Orange by alginate-immobilized Aeromonas sp. in a packed bed reactor: external mass transfer modeling.

Azo dyes are recalcitrant and xenobiotic nature makes these compounds a challenging task for continuous biodegradation up to satisfactorily levels in large-scale. In the present report, the biodegradation efficiency of alginate immobilized indigenous Aeromonas sp. MNK1 on Methyl Orange (MO) in a packed bed reactor was explored. The experimental results were used to determine the external mass transfer model. Complete MO degradation and COD removal were observed at 0.20 cm bead size and 120 ml/h flow rate at 300 mg/l of initial dye concentration. The degradation of MO decreased with increasing bead sizes and flow rates, which may be attributed to the decrease in surface of the beads and higher flux of MO, respectively. The experimental rate constants (k ps) for various beads sizes and flow rates were calculated and compared with theoretically obtained rate constants using external film diffusion models. From the experimental data, the external mass transfer effect was correlated with a model J D = K Re (-(1 - n)). The model was tested with K value (5.7) and the Colburn factor correlation model for 0.20, 0.40 and 0.60 bead sizes were J D = 5.7 Re (-0.15), J D = 5.7 Re (-0.36) and J D = 5.7 Re (-0.48), respectively. Based on the results, the Colburn factor correlation models were found to predict the experimental data accurately. The proposed model was constructive to design and direct industrial applications in packed bed reactors within acceptable limits.

Comparison of biomass production and total lipid content of freshwater green microalgae cultivated under various culture conditions.

The growth and total lipid content of four green microalgae (Chlorella sp., Chlorella vulgaris CCAP211/11B, Botryococcus braunii FC124 and Scenedesmus obliquus R8) were investigated under different culture conditions. Among the various carbon sources tested, glucose produced the largest biomass or microalgae grown heterotrophically. It was found that 1% (w/v) glucose was actively utilized by Chlorella sp., C. vulgaris CCAP211/11B and B. braunii FC124, whereas S. obliquus R8 preferred 2% (w/v) glucose. No significant difference in biomass production was noted between heterotrophic and mixotrophic (heterotrophic with light illumination/exposure) growth conditions, however, less production was observed for autotrophic cultivation. Total lipid content in cells increased by approximately two-fold under mixotrophic cultivation with respect to heterotrophic and autotrophic cultivation. In addition, light intensity had an impact on microalgal growth and total lipid content. The highest total lipid content was observed at 100 µmol m(-2)s(-1) for Chlorella sp. (22.5%) and S. obliquus R8 (23.7%) and 80 µmol m(-2)s(-1) for C. vulgaris CCAP211/11B (20.1%) and B. braunii FC124 (34.9%).

Biodegradation of Endosulfan-a Chlorinated Cyclodiene Pesticide by Indigenous Pseudomonas sp. MSCAS BT01.

Endosulfan remains as a lipophilic insecticide that causes serious medical problems because of biological stability and toxicity also found in air, water, soil sediments, and foodstuffs. Henceforward, the present study reveals a novel bacterial species isolated from pesticide-contaminated soil for enhanced endosulfan degradation. Next, isolated bacterial species was characterized with biochemical assays and 16S rRNA sequencing technique. Subsequently, the optimal conditions for endosulfan biodegradation such as pH, concentration of endosulfan, and bacterial growth were estimated with non-sulfur medium (NSM). Sequentially, the amount of endosulfan and compound degradation were analyzed through thin-layer chromatography and gas chromatography/mass spectrometry. Overall, the obtained results revealed the endosulfan acting as primary carbon source for bacterial growth. From the GC-MS analysis, the metabolic products released during endosulfan degradation by Pseudomonas sp. MSCAS BT01 were compared with standard GC-MS spectra. The highest (98%) endosulfan degradation was obtained at pH 7.0. The complete endosulfan degradation was achieved at 14th day of incubation and the less toxic endosulfan diol produced was observed via GC-MS. To conclude, the pesticide-contaminated isolate Pseudomonas sp. MSCAS BT01 emerged as a promising bioremediation tool and effectively employed to degrade endosulfan from contaminated soils, sediments, and wastewaters in the days yet to come.

Ultrasound mediated reduction of Cr(VI) using sludge obtained during electrocoagulation.

This study presents the ultrasound mediated reduction of toxic hexavalent chromium (Cr(VI)) into non-toxic trivalent chromium (Cr(III)) using sludge obtained during the electrocoagulation of pharmaceutical wastewater (EC sludge). Experiments were carried out with and without ultrasound to explore its influence. The effect of initial concentration of Cr(VI) (100-200 mg/l), pH (6-8) and EC sludge dosage (5-10 g/l) on Cr(VI) reduction was studied. The morphological and functional group changes of EC sludge due to Cr(VI) reduction were analysed with scanning electron microscopy and Fourier transform infrared, respectively. The reduction rates observed in the presence of ultrasound were found to be higher than the rates observed for without ultrasound. The results concluded that the EC sludge can be successfully used for reduction of Cr(VI) at lower cost.

Enhanced method for microbial community DNA extraction and purification from agricultural yellow loess soil.

In this study, novel DNA extraction and purification methods were developed to obtain high-quantity and reliable quality DNA from the microbial community of agricultural yellow loess soil samples. The efficiencies of five different soil DNAextraction protocols were evaluated on the basis of DNA yield, quality and DNA shearing. Our suggested extraction method, which used CTAB, EDTA and cell membrane lytic enzymes in the extraction followed by DNA precipitation using isopropanol, yielded a maximum DNA content of 42.28 ± 5.59 µg/g soil. In addition, among the five different purification protocols, the acid-treated polyvinyl polypyrrolidone (PVPP) spin column purification method yielded high-quality DNA and recovered 91% of DNA from the crude DNA. Spectrophotometry revealed that the ultraviolet A 260/A 230 and A 260/A 280 absorbance ratios of the purified DNA were 1.82 ± 0.03 and 1.94 ± 0.05, respectively. PCR-based 16S rRNA amplification showed clear bands at ~1.5 kb with acid-treated PVPP-purified DNA templates. In conclusion, our suggested extraction and purification protocols can be used to recover high concentration, high purity, and high-molecular-weight DNA from clay and silica-rich agricultural soil samples.

Degradation of Tectilon Yellow 2G by hybrid technique: combination of sonolysis and biodegradation using mutant Pseudomonas putida.

Degradation of Tectilon Yellow 2G (TY2G), an azo dye has been studied by hybrid technique involving pretreatment by sonochemical method and further biological treatment by Pseudomonas putida mutant. Pretreatment experiments were carried out by sonolysis of the dye solution at different concentrations (100-1000 mg/L). Wild type Gram-negative P. putida species isolated from the textile effluent contaminated soil, which was found to be effective towards dye degradation, has been acclimatized so as to consume TY2G as the sole source of nutrition. Mutant strain was obtained from the acclimatized species by random mutagenesis using the chemical mutagen ethidium bromide for various time intervals (6-30 min). The optimum mutagenesis exposure time for obtaining the most efficient species for dye degradation was found to be 18 min. An efficient mutant strain P. putida ACT 1 has been isolated and was used for growth experiments. The mutant strain showed a better growth compared to the wild strain. The substrate utilization kinetics has been modeled using Monod and Haldane model equations of which the Haldane model provided a better fit. The enzyme kinetics of the mutant and wild species was obtained using Michaelis-Menten equation. The mutated species showed better enzyme kinetics towards the degradation of TY2G.

Mass transfer studies on the reduction of Cr(VI) using calcium alginate immobilized Bacillus sp. in packed bed reactor.

This study presents the external mass transfer effects on the reduction of hexavalent chromium (Cr(VI)) using calcium alginate immobilized Bacillus sp. in a re-circulated packed bed batch reactor (RPBR). The effect of flow rate on the reduction Cr(VI) was studied. Theoretically calculated rate constants for various flow rates were analyzed using external film diffusion models and compared with experimental values. The external mass transfer coefficients for the bioconversion of Cr(VI) were also investigated. The external mass transfer effect was correlated with a model of the type J(D)=K Re(-(1-n). The model was tested with various K values and the mass transfer correlation J(D)=5.7 Re(-0.70) was found to predict the experimental data accurately. The proposed model would be useful for the design of industrial reactor and scale up.

Sonoassisted microbial reduction of chromium.

This study presents sonoassisted microbial reduction of hexavalent chromium (Cr(VI)) using Bacillus sp. isolated from tannery effluent contaminated site. The experiments were carried out with free cells in the presence and absence of ultrasound. The optimum pH and temperature for the reduction of Cr(VI) by Bacillus sp. were found to be 7.0 and 37 degrees C, respectively. The Cr(VI) reduction was significantly influenced by the electron donors and among the various electron donors studied, glucose offered maximum reduction. The ultrasound-irradiated reduction of Cr(VI) with Bacillus sp. showed efficient Cr(VI) reduction. The percent reduction was found to increase with an increase in biomass concentration and decrease with an increase in initial concentration. The changes in the functional groups of Bacillus sp., before and after chromium reduction were observed with FTIR spectra. Microbial growth was described with Monod and Andrews model and best fit was observed with Andrews model.