Untitled Document

Abstract

With the large amount of saline wastewater being discharged, efficient, economical and resource-recycling saline wastewater treatment methods need to be researched urgently. Microalgae are widely used in wastewater treatment since they can deal with nitrogen and phosphorus pollutions as well as reduce CO2 emissions and recycle resources, but they are hard to be collected due to their tiny cell sizes. Microalgae flocculated by fungi to form the algal-mycelial pellets (AMPs) is one of the efficient collecting methods. However, whether this method can work in high salinity environment has not been reported. This paper studies the effects and mechanisms of flocculation of AMPs in wastewater with different salinities. Results show that the flocculating efficiency and the flocculating algal biomass were decreased with the increasing salinity. According to morphological observations, fungi pellets increased in volume and mass at high salinity, resulting in a more compact mycelium structure with less space for microalgae to attach, which was not conducive to flocculation. Furthermore, contents of proteins (PN) and polysaccharides (PS) in the tightly bound EPS (TB-EPS) of AMPs at 4% salinity decreased by 44%±8% and 33%±4% respectively compared to those at 0% salinity. The decreasing content of PN and PS in the TB-EPS at high salinity resulted in weaker hydrophobicity, greater electrostatic repulsion and a higher energy barrier of AMPs, all of which consequently inhibited the flocculation. This study will provide theoretical bases for the recovery of microalgae in wastewater and culture solution especially those at high salinities.