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

BACKGROUNDA 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.RESULTSAggregates 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.CONCLUSIONPhotosynthetic 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. (c) 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).