Integration of wastewater treatment and flocculation for harvesting biomass for lipid production by a newly isolated self-flocculating microalga Scenedesmus rubescens SX

Abstract

Abstract A microalga with high self-flocculating efficiency was isolated and identified as Scenedesmus rubescens SX. When S. rubescens SX was cultivated in ammonium-containing wastewater, the pH of wastewater was significantly acidic and inhibited the growth of the microalga. By adjusting the pH of ammonium-containing wastewater, both the growth and nutrients removal were enhanced and superior to those from nitrate-containing wastewater. The flocculation of S. rubescens SX was also affected by nitrogen sources. When S. rubescens SX was cultivated in nitrate-containing wastewater, more extracellular polymeric substances (EPS) with rich hydroxyl and carboxyl groups as binding sites for flocculation were produced. Moreover, positively charged precipitates of magnesium and calcium salts were formed via high pH induction. These precipitates neutralized negative charge groups from EPS, and S. rubescens SX exhibited the highest flocculating efficiency in nitrate-containing wastewater. The flocculation of S. rubescens SX in ammonium-containing wastewater was mainly due to the neutralization between negative charge groups from EPS and protons released by pH reduction. Moreover, the lipid content of the microalga ranged from 22.44% to 25.80%, which typically consisted of linoleic and linolenic acids (48.85%–55.24%) for dietary supplements and aquacultures. In short, it is a very promising avenue for integrating wastewater treatment and flocculation for harvesting biomass for lipid production by a newly isolated self-flocculating microalga S. rubescens SX.