Optimization of pulp fibre removal by flotation using colloidal gas aphrons generated from a natural surfactant

Abstract

Colloidal gas aphrons (CGAs) are a system of highly stable micro bubbles in colloidal state. In this study, the CGAs prepared from a natural surfactant saponin, extracted from the fruit pericarp of Sapindus mukorossi or soapnut plant, was utilized for the recovery of pulp fibres from paper machine backwater in a flotation column. The performance of soapnut CGAs was compared with that of CGAs generated from cationic, anionic and non-ionic surfactants. Performance optimization of soapnut CGAs was undertaken using central composite design (CCD). CGAs characterization showed that soapnut surfactant produced the most stable CGAs. Under various CGAs sparging rate, pH and flow rate of wastewater, soapnut CGAs performed best by removing up to 60% total suspended solids (TSS) from paper machine effluent as compared to 50%, 37% and 30% TSS removal by cationic, anionic and non-ionic surfactants respectively. Optimized TSS removal of 76% was attained through CCD at soapnut CGAs sparging rate of 0.013 L/min, wastewater flow rate of 16 L/min and pH of 7.5. Treatment of effluent using natural surfactant CGAs is a cost effective and green process which can be replicated in industries.