Role of extracellular polymeric substance in flocculation of Chlorococcum sphacosum cultivated with different initial inoculum concentrations in municipal wastewater

Abstract

Initial inoculum concentration of microalgae has been proposed to affect wastewater treatment performance. However, it is unclear whether the initial inoculum concentration affects the flocculation efficiency of microalgae. Efficient flocculation of microalgae, after all, was critical to cost-effective large-scale wastewater treatment. Here, it was found that the flocculation efficiency of Chlorococcum sphacosum significantly decreased from 59.46 % to 23.73 % following the increase of microalgal initial inoculum concentration from 50 mg/L to 800 mg/L. Extracellular polymeric substance (EPS) concentration also reduced significantly. Moreover, the proportion of some surface groups, such as hydrophobic amino acid tryptophan, α-helix, and C(C/H), in EPS of the microalga also reduced simultaneously. The correlation analysis and variance partitioning analysis (VPA) indicated that both EPS concentration and composition characteristics had outstanding contributions to microalgal flocculation. It was speculated that the change of EPS concentration and hydrophobic component ratio derived from the variation in microalgal inoculum concentrations was one of the main driving factors for variations in flocculation efficiency. This investigation was valuable for understanding the flocculation mechanism of microalgae.