Simultaneous purification of anaerobic digestion slurry and enhancement in produced biogas using different microalgae-based technologies under a variety of mixed light wavelengths and photoperiods

Microalgae-based technology has attracted increasing attention due to its high efficiency for simultaneous pu-rification of anaerobic digestion slurry and the enhanced purity of biogas. For realizing high nutrients/CO2 removal efficiencies, a Chlorella vulgaris-Ganoderma lucidum-endophytic bacteria symbiont was constructed in the current work. The symbiotic system displayed complementary effects and co-metabolism of Chlorella vulgaris and Ganoderma lucidum/endophytic bacteria, in which Ganoderma lucidum/endophytic bacteria could stimulate the growth of symbiont. Moreover, the compounds produced from the photosynthesis of microalgae were beneficial to the growth of Ganoderma lucidum and endophytic bacteria. The results suggested that the con-structed Chlorella vulgaris-Ganoderma lucidum-endophytic bacteria symbiont displayed the best photosynthetic performance with the addition of 10-9 M GR24 under a mixed wavelength ratio (red:blue) of 5:5 and a light/dark cycle of 14-h:10-h. Meanwhile, the highest nutrients/CO2 removal efficiencies were obtained under the above -mentioned optimal conditions, and had values of 84.09 +/- 8.12%, 83.57 +/- 8.12%, 85.19 +/- 7.97% and 69.34 +/- 6.62% for chemical oxygen demand, total nitrogen, total phosphorus and CO2, respectively. The work provides a theoretical foundation for future scale-up of wastewater treatment and enhancement of biogas upgrading, especially in terms of co-culture of microalgae with bacteria/fungi and light control strategies.