Combined system for wastewater treatment: ozonization and coagulation via tannin-based agent for harvesting microalgae by dissolved air flotation

ABSTRACT

This study evaluated the performance of urban wastewater treatment in pilot-plant by an integrated system consisting of anaerobic reactor, microalgae cultivation, Venturi tube ozone recirculation, coagulation/flocculation with tannin-based agent natural coagulant, and dissolved air flotation (DAF). Ozone concentrations (without ozone, 0.13 and 0.25 mg O₃/mg of biomass) and tannin dosages (65, 85 and 105 mg/L) were evaluated regarding microalgae separation and their influences on wastewater treatment performance. During the experiments, it was verified that the treatment efficiency increased when ozone was applied and with higher tannin dosages. The best results were found with 0.13 mg O₃/mg of biomass and 105 mg/L of tannin, obtaining excellent removal of turbidity removal (99.4%), apparent colour at 420 nm (94.5%), TN (83.2%), N-NH₃ (100%), TOC (86.8%), BOD₅ (86.5%) and COD (100%), 47.6% reduction in electric conductivity, 46.1% in TDS, 66.4% TP removal for the integrated system and 84% microalgae biomass recovery were obtained. Our results showed that the system proved to be a viable alternative for the treatment of urban wastewater and the recovery of microalgae through the insertion of ozone via Venturi tube combined with tannin-based agent.

GRAPHICAL ABSTRACT

KEYWORDS:

• Microalgae harvesting
• eutrophication
• Venturi tube
• tannin-based coagulant
• wastewater treatment
• integrated system

Acknowledgements

Gislayne Alves Oliveria thanks the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES) for the post-doctoral fellowship that generated this work. To TANAC S.A. for donating the tannin-based coagulant for this research. To the Master Elizandro Silveira for his willingness to cultivate microalgae and to Master Fagner Pereira for his assistance in assembling the ozone system.

Disclosure statement

No potential conflict of interest was reported by the author(s).