Implication of organic solvents in the precipitation of γ-polyglutamic acid for application as a sustainable flocculating agent

Abstract

γ-Polyglutamic (γ-PGA) acid is a homopolyamide composed of D- and l-glutamic acid units. It is an anionic biopolymer that has properties such as water solubility, non-toxicity, and biodegradability. γ-PGA, has many environmental applications, including use as an increment to the flocculation process in water treatment. This study evaluated the extraction and quantification of γ-PGA using different organic solvents, following by application as a sustainable flocculating agent. The results demonstrate that the use of methanol was able to precipitate 6.83 mg γ-PGA g−1 natto, followed by 5.44 and 4.24 mg γ-PGA g−1 natto, respectively for ethanol and acetone. The adoption of refrigeration (12 h) is an advantage to increase the yield of the biopolymer for methanol (46.27%), ethanol (52.25%), and acetone (14.25%) as a precipitating agent. The γ-PGA yield increased in overnight extraction with ethanol, enabling the use of ethanol as an alternative to methanol. Due to steric stabilization, it was observed that increasing the γ-PGA concentration resulted in a reduction in the flocculation rate. The highest flocculation rate (92.9%) was achieved at 10 mg L−1 of γ-PGA extracted with methanol, followed by acetone at 10 mg L−1 of γ-PGA (92.43%) and ethanol at 5 mg L−1 of γ-PGA (92.2%).