Biodegradation of tannery dye effluent using Fenton's reagent and bacterial consortium: A biocalorimetric investigation.

The impact caused by dye effluent discharge on the environment is well known. The study explores a hybrid method of combining Fenton oxidation with biological treatment by a defined bacterial consortium for the biodegradation of an effluent containing toxic azo dye (acid blue 113). In actual treatment process, the fluctuation in toxic load and presence of other dyeing chemical inhibits the activity of the bacterial consortium. An effective pre-treatment of effluent would ensure the optimal degradation irrespective of its initial load. The pre-treatment of dye effluent with Fenton (H2O2 & Fe2+), considerably reduced the dye concentration by 40% and a maximum dye degradation of 85% (i.e., 45% by biodegradation) was achieved in shake flask. The biodegradation process was investigated in a bioreaction calorimeter (BioRc1e), the heat profile, bioenergetics data along with CER (Carbon dioxide emission rate) and OUR (Oxygen uptake rate) provided vital information for the effective commercial scale up. Enhanced degradation of up to 97% was achieved in BioRc1, the CER and OUR profile follows the power-time profile alluding that the heat generated is the resultant effect of bacterial metabolic activity. In real dye bath effluent the Fenton pre-oxidized biodegradation reaction showed a degradation efficacy of 89.5% and considerable COD reduction of 93.7%. Fluorescence-activated cell sorting (FACS) analysis revealed a better bacterial cell proliferation in pre-treated experiment and gas chromatography and mass spectrum analysis were used for prediction of metabolites. The unique combination of Fenton and the microbial consortia is a competitive technology for industrial effluent treatment processes.

Effect of aeration and agitation on yeast inulinase production: a biocalorimetric investigation.

Air flow rate and agitation speed for inulinase production by Kluyveromyces marxianus were optimized based on metabolic heat release profiles. Shear stress and oxygen transfer (kLa) values were compared to assess the effects of aeration and agitation. At agitation rates of ≤ 100 rpm, the oxygen mass transfer rates were small and eventually led to less inulinase production, but at agitation rates > 150 rpm, loss of biomass resulted in less inulinase activity. Bio-reaction calorimeter (BioRc1e) experiment with aeration rates ≤ 0.5 lpm showed low kLa while at 1.5 lpm frothing of reactor contents caused loss of biomass and inulinase activity. The optimum conditions for aeration and agitation rate for K. marxianus in BioRc1e were 1 lpm and 150 rpm. Heat yield values obtained for the substrate, product and biomass reinstated the ongoing metabolic process. The heat release pattern could be a promising tool for optimization of bioprocess and in situ monitoring, with a possibility of interventions during the biotransformation process. At optimized aeration and agitation conditions, a two-fold increase in inulinase activity could be noticed.

Metabolic pathway and role of individual species in the bacterial consortium for biodegradation of azo dye: A biocalorimetric investigation.

In this study, an attempt was made to investigate the functional role and metabolic behaviour of the monoculture (Staphylococcus lentus (SL), Bacillus flexus (BF) and Pseudomonas aeruginosa (PA)) in the bacterial biocenosis for biotransformation of an azo dye. The power-time profile obtained from consortia depicted three distinct peaks, which correlated well with the individual bacterial growth (PA > SL > BF), indicating the synergistic relation and division of labour in the biocenosis. The heat release pattern was used to identify the sequential behaviour of microbial consortia in real time. Yield calculation based on total heat liberated to the complete substrate utilization Y (Q/S) for PA, SL, and BF were 15.99, 16.68, 7.32 kJ/L respectively. Similarly, the oxy calorific values Y (Q/O) for the above species are respectively 386, 375, 440 kJ/mol and indicates the aerobic nature of microorganism employed. Further, the metabolome produced during the biotransformation were identified using Gas Chromatography-Mass Spectrometry (GC-MS), based on which a plausible pathway was predicted. The abundant metabolites were palmitic acid (m/z = 256) and diethyl phthalate (m/z = 222.2). The abundance of diethyl phthalate was much lesser in the consortia compared to the monoculture. Thus, the biocalorimetric heat yield calculation along with the stoichiometry and plausible pathway based biochemical elucidation provides a mechanistic basis for understanding the azo-dye biotransformation by the monocultures in consortia.

Modeling of exo-inulinase biosynthesis by Kluyveromyces marxianus in fed-batch mode: correlating production kinetics and metabolic heat fluxes.

A metabolic heat-based model was used for estimating the growth of Kluyveromyces marxianus, and the modified Luedeking-Piret kinetic model was used for describing the inulinase production kinetics. For the first time, a relationship was developed to relate inulinase production kinetics directly to metabolic heat generated, which corroborated well with the experimental data (with R 2 values of above 0.9). It also demonstrated the predominantly growth-associated nature of the inulinase production with Luedeking-Piret parameters α and ß, having values of 0.75 and 0.033, respectively, in the exponential feeding experiment. MATLAB was used for simulating the inulinase production kinetics which demonstrated the model's utility in performing real-time prediction of inulinase concentration with metabolic heat data as input. To validate the model predictions, a biocalorimetric (Bio RC1e) experiment for inulinase production by K. marxianus was performed. The inulinase concentration (IU/mL) values acquired from the model in were validated with the experimental values and the metabolic heat data. This modeling approach enabled the optimization, monitoring, and control of inulinase production process using the real-time biocalorimetric (Bio RC1e) data. Gas chromatography and mass spectrometry analysis were carried out to study the overflow metabolism taking place in K. marxianus inulinase production.