Empty bed residence time regulates synergistic effect of algae-bacteria consortia in volatile organic compounds treatment: Performance and mechanism

Abstract

Biological treatment technology utilizing algal-bacteria consortium (ABC) has shown remarkable effectiveness in synergistically reducing emissions of volatile organic compounds (VOCs) and CO₂. However, the impact of empty bed residence time (EBRT) on the performance and underlying synergistic mechanisms of the ABC has remained unclear. In this study, we systematically compared an algal-bacterial airlift photobioreactor (PB) with a conventional bacterial airlift bioreactor (CB) under varying EBRT conditions. At longer EBRTs of 51 and 34 s, both reactors achieved nearly 100 % removal efficiency (RE) for n-butyl acetate. Simultaneously, the activity of the Rubisco enzyme increased substantially, enhancing the CO₂ assimilation efficiency ($R_{{\mathrm{CO}}_2}$) of the microalgae, which peaked at 92.65 ± 0.88 %. At shorter EBRTs of 26 and 20 s, the PB exhibited n-butyl acetate REs approximately 1.11 and 1.46 times higher than the CB, respectively. Notably, shorter EBRT stimulated the ABC to secrete more extracellular polymeric substances (EPS) and promoted the formation of more complex microbial communities, thereby ensuring more stable and efficient pollutant removal. It is demonstrated in this work that synergistic reductions of VOCs and CO₂ across various environmental conditions can be effectively achieved by the ABC, providing valuable theoretical insights for the development of gas bio-purification technologies.