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Aqueous two phase systems for the recovery of biomolecules from tannery wastewater

Raja, Selvaraj (2014) Aqueous two phase systems for the recovery of biomolecules from tannery wastewater. Phd. Thesis thesis, Manipal Institute of Technology, Manipal.

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Abstract

The thesis deals with the development and evaluation of eco-friendly aqueous two phase systems composed of poly-ethylene-glycol (PEG) + sodium citrate (SC) + water to recover soluble proteins from a model tannery wastewater. Liquid- liquid equilibrium data of aqueous two-phase systems (ATPS) formed by sodium citrate (SC) and poly-ethylene-glycol (PEG) of different molecular weights (600, 1000, 2000, 4000, and 6000) with water were developed at different pH (6, 7, and 8) and constant temperature 25°C. Binodal data was described using a third order polynomial equation. An increase in molecular weight of PEG shifted the binodal curve to lower PEG and salt concentrations. An increase in pH showed similar shape and tend to merge at high concentration of PEG and salt. Tie-Line Length (TLL) and the slope of the tie-line (STL) were related to the equilibrium phase composition. The tie-lines were correlated using the Othmer-Tobias and Bancroft equations and the coefficient values were calculated. ATPS made up of PEG 2000, 4000 and 6000 + SC was used to recover the valuable biomolecules from a model tannery wastewater system. The effect of various protein partitioning parameters like PEG molecular weight (MW), concentration of phase forming components, system pH, temperature and concentration of sodium chloride were studied. In all the systems, the crude proteins preferentially partitioned towards the salt rich bottom phase. Furthermore, the thermodynamic parameters as a function of temperature were calculated for the PEG 6000/ SC system by using Van’t Hoff relationship. It was possible to recover 83.47 % in the bottom phase by employing an ATPS consisted of PEG MW 6000 20% (w/w) / SC 15% (w/w) / 0.3M NaCl at a temperature of 30°C and pH 8. iii ATPSs containing high molecular weight poly-ethylene glycol, PEG (10000) and biodegradable citrate salts (sodium citrate, potassium citrate and ammonium citrate) with water were developed to recover the wastewater proteins from a model tannery wastewater system. The variations in the phase diagram were explained on the basis of ionic radius of cations, Gibbs free energy of hydration (ΔGhydation) of cations and effective excluded volume (EEV) of salts. The salting out capability of the cations followed the sequence: Sodium citrate > Potassium citrate > Ammonium citrate. Setschenow type equations were used to correlate tie-line compositions. During partitioning studies, recovery of tannery wastewater proteins in PEG 10000 + Sodium citrate ATPS was found superior to other systems. It was possible to recover 95.86% of proteins from tannery wastewater in the bottom phase with PEG 10000 30% (w/w) + Sodium citrate 13% (w/w) at 30ºC. The partition coefficients were correlated with the salt compositions by a quadratic equation and the coefficients were calculated. Enhanced recovery of proteins was attempted with PEG 6000 +SC +Water system using response surface methodology (RSM). In this method, a sequential optimization strategy (MINITAB – 15.0) which included fractional factorial design (fFD) and central composite design (CCD) were used. Five factors namely, concentration of PEG 6000, concentration of SC, pH of the system, concentration of NaCl and temperature were chosen as the factors that affect the protein partitioning. The fFD revealed that only pH, concentration of NaCl and temperature were the significant factors. These factors were further optimized by using CCD experiments. From this strategy, a second order polynomial model was obtained for the protein recovery and it was validated. The optimum recovery was found as 93.46% when pH, NaCl concentration and temperature were kept at 7.5, 0.1 M and 33ºC iv respectively, for a phase system composed of 20% (w/w) PEG 6000 + 15% (w/w) SC. Thus the proposed ATPS can serve as an alternative to the conventional precipitation method to recover the soluble proteins from tannery wastewater.

Item Type: Thesis (Phd. Thesis)
Uncontrolled Keywords: Leather Industry, Tannery Wastewater, Protein Recovery, Aqueous Two Phase System,Tie-Line Length, Partition Coefficient, Batch Extraction, fractional Factorial Design, Central Composite Design, Response Surface Methodology
Subjects: Engineering > MIT Manipal > Biotechnology
Depositing User: MIT Library
Date Deposited: 21 May 2014 09:12
Last Modified: 23 Sep 2015 15:13
URI: http://eprints.manipal.edu/id/eprint/139555

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