Effect of GR24 concentrations on biogas upgrade and nutrient removal by microalgae-based technology

Freshwater microalgae Chlorella vulgaris was cultured and induced with strigolactone (GR24) to simultaneously eliminate nutrients in biogas slurry and purify biogas. Treatment with 10^-7 M GR24 yielded maximum growth rate and mean daily productivity for algae at 0.187 ± 0.06 d^-1 and 0.097 ± 0.008 g L^-1 d^-1, respectively. Results from chlorophyll fluorescence transients method demonstrated that moderate concentration of GR24 could enhance the photosynthetic performance of microalgae. In addition, GR24 affected intracellular carbonic anhydrase activity and chlorophyll-a content. Maximum chemical oxygen demand, total nitrogen, and CO₂ removal efficiencies were 78.62 ± 2.36%, 76.47 ± 1.53% and 64.05 ± 1.15% with 10^-7 M GR24 induction, respectively. Further, highest total phosphorus removal efficiency (80.27 ± 1.93%) was observed at 10^-9 M. The optimal GR24 concentration range was determined to be between 10^-9 and 10^-7 M in consideration with nutrient and CO₂ removal efficiencies.