Performance of co-culture strategy on nutrient removal and biogas upgrading by strigolactone induction

In this study, we investigated the performance and elucidated the synergistic effects of microalgae-fungi symbionts co-cultured with 10^-7 and 10^-9  mol L^-1 of GR24 and supplemented with endophytic bacteria, multi-walled carbon nanotubes (MWCNTs) or vitamin B12 (VB12), on nutrient removal and biogas upgrading. The results showed that the microalgae-fungi-bacteria symbiotic system co-cultured with 10^-9  mol L^-1 GR24 presented the optimal growth performance of 0.368 ± 0.04 d^-1 , chlorophyll a of 249.36 ± 22.31 μg L^-1 , and extracellular carbonic anhydrase activity of 42.55 ± 3.755 enzyme units. In this co-culture system, the organic matter, nutrients, and CO₂ purification obtained the highest removal efficiency, with 81.35 ± 7.96% for chemical oxygen demand, 83.56 ± 7.91% total nitrogen, 84.17 ± 7.95% total phosphorus, and 63.72 ± 6.06% CO₂ . The symbiont system also greatly increased the methane content in the biogas by 30.67%. The remarkable performance of the microalgae-fungi-bacteria symbiotic system shows its ability to be broadly applied in simultaneous biogas upgrading and wastewater treatment. PRACTITIONER POINTS: The optimal GR24 concentration for microalgae-fungi consortia was 10^-9  M. Endophytic bacteria were superior to MWCNTs and VB12. Fungi-algae-bacteria consortia presented excellent growth and removal performance. Removal efficiencies of COD, TN, and TP were about 81% under optimum treatment.