Kinetic modelling and process optimization of textile effluent treatment with bacterial gamma polyglutamic acid

Abstract

Aim: The present study aims to synthesize gamma poly glutamic acid from the optimized starch-based glutamate-dependent medium for wastewater treatment with kinetic studies for an effective decolorization process. Methodology: Microbial coagulant (γ-PGA) was synthesized from the optimized glutamate-dependent medium with sago as a substrate and Bacillus subtilis as fermenter. Synthesized γ-PGA was harvested by ethanol precipitation and lyophilization method. The presence of γ-PGA was determined by UV-visible spectrum and ninhydrin analysis and its flocculating activity was screened by ninhydrin assay. Harvested γ-PGA was treated with different types of wastewater samples (Textile, tannery, dairy and sewage) in the preliminary screening. Process optimization was performed to screen the maximal decolorization for textile effluent (light and dark color). The physical and chemical characterization of treated wastewater samples with kinetic studies was performed to improve the treatment process. Results: The synthesized γ-PGA weighed as 41.20 g l-1 from the fermented medium and its presence was confirmed by characterization techniques. The flocculating activity of synthesized γ-PGA was 40.56 and 58.78 % against the kaolin suspension. The maximal decolorization percentage was 59.58% for γ- PGA treatment against textile effluent. The significance of optimized parameters such as pH, temperature, rotation speed and contact time were determined in the treatment of textile effluents (light and dark color) with maximal reduction of solids profile COD and BOD concentration. Kinetic studies revealed that the isotherm Langmuir isotherm was fit for the experimental data with R2 as 0.9943, 0.9692 and Pseudo second order fitted with R2 as 0.9871 and 0.9594 respective to light and dark color effluent. Interpretation: This study confirmed the maximal yield of γ-PGA from a sago-based glutamate-dependent medium and revealed its effective flocculating and decolorization activity against textile effluent which suggest them as a better alternative coagulants. Key words: γ- PGA, Bacillus subtilis, Kinetic modelling, Process optimization