Performance of cocultivation of Chlorella vulgaris and four different fungi in biogas slurry purification and biogas upgrading by induction of strigolactone (GR24) and endophytic bacteria.

This study aimed to determine the best fungi to form the algal-bacterial-fungal symbionts and identify the optimal conditions for the synchronous processing of biogas slurry and biogas. Chlorella vulgaris (C. vulgaris) and endophytic bacteria (S395-2) isolated from it, and four different fungi (Ganoderma lucidum, Pleurotus ostreatus, Pleurotus geesteranus, and Pleurotus corucopiae) were used to form different symbiotic systems. Four different concentrations of GR24 were added to systems to examine the growth characteristics, the content of chlorophyll a (CHL-a), the activity of carbonic anhydrase (CA), the photosynthetic performance, the removal of nutrients, and the biogas purification performance. The results suggested that the growth rate, CA, CHL-a content, and photosynthetic performance of the C. vulgaris-endophytic bacteria-Ganoderma lucidum symbionts were higher than the other three symbiotic systems when 10-9  M GR24 was added. The highest nutrients/CO2 removal efficiency 78.36 ± 6.98% for chemical oxygen demand (COD), 81.63 ± 7.35% for total nitrogen (TN), 84.05 ± 7.16% for total phosphorus (TP), and 65.18 ± 6.12% for CO2 was obtained under the above optimal conditions. This approach will provide a theoretical basis for the selection and optimization of the algal-bacterial-fungal symbionts for biogas slurry and biogas purification. PRACTITIONER POINTS: Algae-bacteria/fungal symbiont presents superior nutrients and CO2 removal capacities. The maximum CO2 removal efficiency was 65.18 ± 6.12%. The removal performance was affected by fungi type.