Effects of exogenous GR24 on biogas upgrading and nutrient removal by co-culturing microalgae with fungi under mixed LED light wavelengths

To realize the synchronous purification of raw biogas and biogas slurry, the algal-fungal symbiont pellets were cultivated by supplementing strigolactone (GR24) under different mixed LED light wavelengths. The optimal light intensity was proved to be red and blue in the ratio of 5:5. The symbionts treated with 10^-9 M GR24 had the highest growth rate and mean daily productivity. The extracellular carbonic anhydrase activity and the content of chlorophyll were also affected by GR24 concentrations and mixed light wavelengths. With the induction of 10^-9 M GR24, the maximum removal efficiency of chemical oxygen demand, total nitrogen, and total phosphorus reached 76.35 ± 6.87%, 78.77 ± 7.13% and 79.49 ± 7.43%, respectively. Besides, the CO₂ removal efficiency reached 59.32 ± 5.19% when the concentration of GR24 was 10^-7 M. This work will be beneficial for large-scale biogas slurry purification and biogas upgrading using co-cultivation of microalgae and fungi.