Co-culturing microalgae with endophytic bacteria increases nutrient removal efficiency for biogas purification

Endophytic bacteria were isolated from Chlorella vulgaris and co-cultured with its host microalgae to determine whether this symbiotic system is suitable for purifying biogas and biogas slurry. Results showed that endophytic bacteria S395-1 and S395-2 belonged to different genera. Both strains promoted microalgae growth while improving photosynthetic performance, carbonic anhydrase activity, nutrient removal efficiency, and CO2 fixation. The optimal bacteria (S395-2)-to-microalgae ratio and co-culture duration were 10:1 and 7 days. Under this condition, the growth rate and carbonic anhydrase activity were 0.196 +/- 0.06 d(-1) and 31.24 +/- 0.28 EU/cell, respectively. The symbiotic system had removal efficiencies of 88.29 +/- 5.03%, 88.31 +/- 4.29%, 88.21 +/- 4.51%, and 68.13 +/- 1.69% for chemical oxygen demand, nitrogen, phosphorus, and CO2, respectively. These results will provide a framework for constructing a microalgal-bacterial consortium that can improve wastewater treatment and enhance biogas quality.