Abstract

To explore the interaction between a bioflocculant produced using Bacillus cereus and tannery wastewater, four flocculation mechanisms were studied including chemical interaction, charge neutralisation, adsorption and bridging, and sweep-floc coagulation. First, the interaction of the bioflocculant and tannery wastewater was evaluated using the infrared spectrum. It was found that there was no significant difference of spectrum before and after flocculation, indicating no chemical interaction between the bioflocculant and tannery wastewater. Second, it was found that no electric potential change was detected when comparing the samples before and after the addition of the bioflocculant into the tannery wastewater, indicating no charge neutralization during flocculation. Third, the presence of adsorption and bridging was determined by testing the molecular weight, covalent bonds and particle sizes during flocculation. These factors showed that the adsorption and bridging took place during the flocculation process. Finally, the morphological observation of the flocs exhibited network structures, indicating the existence of sweep-floc coagulation. The results represented that the interaction between the bioflocculant and tannery wastewater mainly involved adsorption and bridging, and sweep-floc coagulation.