Strategy for the formation of microalgae-bacteria aggregates in high-rate algal ponds

ABSTRACT

This work studied the formation of aggregates used for wastewater treatment in high-rate algal ponds (HRAP). For this, the establishment of microalgae-bacteria aggregates in these systems was evaluated, considering strategies for the inoculation and start-up. Two HRAP were operated in parallel, at first in batch mode and then in continuous flow. The wastewater treatment was efficient, with removal rates around 80% for COD and N-ammoniacal. Volatile suspended solids and chlorophyll for the culture grew continuously reached a concentration of 548 ± 11 mg L⁻¹ and 7.8 mg L⁻¹, respectively. Larger photogranules were observed when the system was placed in a continuous regime. The protein fraction of extracellular polymeric substances was identified as a determinant in photogranules formation. During the continuous regime, more than 50% of the biomass was higher than 0.2 mm, flocculation efficiency of 78 ± 6%, and the volumetric sludge index of 32 ± 5 mL g⁻¹. The genetic sequencing showed the growth of cyanobacteria in the aggregate and the presence of microalgae from the chlorophytes and diatoms groups in the final biomass.

GRAPHICAL ABSTRACT

KEYWORDS:

• Microalgae-bacteria aggregates
• bioflocculation
• high-rate algal ponds
• photogranules

Acknowledgments

This study was financed by CONACYT- ECOS Nord through project 296514, FACEPE (Science and Technology Foundation of the State of Pernambuco, Brazil – process umber – IBPG-0654-3.07/18), and the support of DAAD to the EXCEED SWINDON project. We thank the support of the Pernambuco Sanitation Company, Brazil (COMPESA) and the company BRK Ambiental. Gloria Moreno, Jaime Pérez and Ángel A. Hernández are acknowledged by their technical assistance.

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.

Disclosure statement

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

Additional information

Funding

This work was supported by Consejo Nacional de Ciencia y Tecnología: [Grant Number CONACYT [Mexico]- ECOS Nord through project 296514]; Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco : [Grant Number IBPG-0654-3.07/18]; German Academic Exchange Service: [Grant Number EXCEED SWINDON project].