Modelling of particulate adsorption efficacy of bioflocculants

Abstract

Microbial exopolymers are in widespread use as flocculants in several industries as they are potential alternatives to synthetic flocculants due to their biodegradable, non-toxic and eco- friendly nature. In most cases, flocculant adsorption is an essential prerequisite for flocculation process and also to understand the kinetic aspects. In the present study, out of total eighteen bioflocculants, three bioflocculants L2, X4 and W2B showed highest flocculating activity and turbidity removal efficiency against surrogates of two prevalent water borne pathogens, Salmonella typhimurium ATCC 23564 and Shigella flexneri Type 2a cells. Biochemical characterization revealed the polysaccharide nature of all the three bioflocculants and the porous structure of the bioflocculants was reflected in the scanning electron micrographs. Further, the presence of hydroxyl, amino, carbonyl and carboxyl functional groups were indicated by FTIR analysis of the bioflocculants. GPC analysis revealed the high molecular weight of the bioflocculants. The particle sizes of the L2, W2B and X4, were found as 528.2, 527.2 and 419 nm, respectively. Viscosity measurement studies in order to assess the effect of 0.1 mg/mL of bioflocculants on the viscosity of dispersed cells as a function of time, resulted in gradual increase of viscosity during 30 to 60 min of time. The effective orthokinetic and perikinetic flocculation models were developed which demonstrated the significant effect of particle size of the bioflocculants and number of dispersed particles on the adsorption mechanism. The order of bioflocculants leading to maximum adsorption rate against the dispersed particles was found as L2>W2B>X4. The study proves bioflocculants as effective adsorbents over synthetic flocculants with marketing advantages due to the public perception of the relative safety of natural compounds.