Assessment of the oxygen dynamics in microalgae–bacteria systems through respirometry

BACKGROUND

A microalgae–bacteria consortium applied to the treatment of domestic wastewater can be an alternative to reduce the energy consumption of aerobic systems if the algal biomass produces enough oxygen for bacterial consumption. This study proposed to evaluate the microalgal production of photosynthetic O₂ and consumption by heterotrophic organic matter-removing and autotrophic nitrifying bacteria through respirometric tests.

RESULTS

Aggregates composed of predominantly spherical green microalgae and bacteria were formed in a photosequencing batch reactor, with 6 h cycles, and fed with synthetic domestic wastewater. Biomass reached 800 mgVSS L⁻¹ and chlorophyll-a content of 4 mg gVSS⁻¹. Photosynthetic oxygen production reached 33.4 mgO₂ gSS⁻¹ h⁻¹. Through respirometric tests and oxygen mass balance, oxygen consumption rates by ordinary heterotrophic bacteria (5.9 mgO₂ gSS⁻¹ h⁻¹), ammonia-oxidizing bacteria (8.67 mgO₂ gSS⁻¹ h⁻¹) and nitrite-oxidizing bacteria (0.78 mgO₂ gSS⁻¹ h⁻¹) were obtained.

CONCLUSION

Photosynthetic oxygen production was 28% higher than the total O₂ required by bacteria. Under the conditions studied, an artificial oxygen supply would not be necessary since the algal biomass can supply the bacterial O₂ demand. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).