Harvesting microalgae from wastewater treatment systems with natural flocculants: Effect on biomass settling and biogas production

Abstract

Research on new sources of bioenergy is nowadays driving attention to microalgae. Cost-effective biomass harvesting and thickening pose a challenge for massive microalgae production for biofuels. In this study, coagulation–flocculation and sedimentation with natural flocculants (Ecotan and Tanfloc) was evaluated on microalgae grown in an experimental high rate algal pond treating urban wastewater. Jar tests showed how flocculant doses of 10 and 50mg/L of Ecotan and Tanfloc enabled over 90% biomass recovery. Furthermore, settling column tests showed that both flocculants increased microalgae settling velocity, performing fast and efficient biomass recovery (>90% recovery in 10–20min). Thus, the use of either flocculant would enhance microalgal biomass reducing the HRT and settler volume. Finally, the potential toxicity of flocculants upon biomass production was assessed in biochemical methane potential tests. Results indicated that doses of 10–50mg/L of Ecotan and Tanfloc did not affect anaerobic digestion, leading to the same methane yield (162–166mL CH4/g VS) with the same methane content (70%) as the control without flocculants. This study demonstrates that Ecotan and Tanfloc flocculants would be appropriate for microalgae biomass harvesting and subsequent biogas generation.