Factors affect the oxygen production of Chlorella pyrenoidosa in a bacterial-algal symbiotic system: Light intensity, temperature, pH and static magnetic field

Abstract

In the municipal wastewater bacteria-algae symbiotic system (BASS) (bacteria-Chlorella pyrenoidosa), aerobic bacteria use the oxygen released by microalgae during photosynthesis, and carbon dioxide and carbonate produced by the breakdown of organic matter and nutrients like nitrogen and phosphorus from the wastewater help the growth of the microalgae. As a result, the effectiveness of oxygen delivery becomes critical for the whole system. The result was found that the maximum rate of oxygen production by C. pyrenoidosa was up to 136.39 μmolO2·mg-1Chla·h-1 at 500 μmol·m-2·s-1, 35 °C, pH = 10. In addition, a 1000 GS magnetic field was applied to the C. pyrenoidosa for 1 h during logarithmic phase. After cultivation for 6 days, the chlorophyll-a and dissolved oxygen (DO) concentrations increased by 22.14% and 16.89%, respectively. Light intensity, temperature, pH and static magnetic field indirectly affected the DO by influencing the growth of C. pyrenoidosa in system, while the study also focused on the oxygen transfer between the system and nature, thus providing insights into the application of the bacteria-C. pyrenoidosa in practice. The results show increases in stirring intensity and temperature accelerate the escape of saturated DO, and conversely, increases in water depth and chemical oxygen demand (COD) concentration mitigate the supersaturated DO escape.