The impact of particulate and soluble organic matter on physicochemical properties of extracellular polymeric substances in a microalga Neocystis mucosa SX

Abstract

Microalgal harvesting is an important link for the integration microalgae-based wastewater treatment with biodiesel production. Extracellular polymAAeric substances (EPS) are considered to be an important factor affecting the flocculation of microalgae. Because the remarkable amount of particulate organic matter exists in real wastewater and is thought to be not readily biodegradable, the effect of particulate organic matter on EPS properties cannot be ignored. Nevertheless, the response of EPS in microalgae to particulate organic matter has still remained unclear. In the study, starch, glucose and sucrose were used to simulate particulate and soluble organic matter to investigate the effect of particulate and soluble organic matter on physicochemical properties of EPS in a microalga Neocystis mucosa SX. The results clearly showed that particulate organic matter significantly promoted the production of EPS, especially extracellular polysaccharides, in the microalga via the cell lysis and the stress induced by available carbon starvation. Compared to notable change on EPS content, the chemical structure and the monomer composition of extracellular polysaccharides did not significantly respond to particulate and soluble organic matter. However, the proportion of functional groups and monomers had a notable response. EPS in the microalga cultivated with particulate organic matter had a lower proportion of some hydrophilic groups C-OH and CO, compared to the microalga cultivated with soluble organic matter. The high content of extracellular polysaccharides and the low proportion of hydrophilic components in EPS as binding sites for the flocculation significantly reduced the flocculation efficiency of the microalga. The results were conducive to reveal the potential mechanism on the response of physicochemical properties of EPS to particulate and soluble organic matter in the process of microalgae-based wastewater treatment, which was essential for microalgal harvesting.