Optimization of cultural factors of newly isolated microalga Spirulina subsalsa and its co-digestion with paddy straw for enhanced biogas production

Spirulina subsalsa (MF191711) isolated from the waterlogged area of Punjab, India, was identified by 16S rRNA sequence analysis. The Placket- Burman design and central composite design (CCD) were used to screen and optimize the significant cultural factors. The most desirable results correspond to the optimal conditions: 11.5 pH, 20 °C temperature, 81 μmolm−2 s−1 light intensity, 25 days growth period, 15 mM CaCl2, NaNO3 5 mM and 2 mM K2HPO4, which were very proximate to the CCD predicted optimal values. These optimal conditions resulted in 1.60-fold higher biomass compared to basal conditions (0.987gL−1). Further, co-digestion of 70% paddy straw with 30% microalgal biomass resulted in the highest ultimate biogas yield (P:260.03 mLg−1VS) with reduced lag phase (λ:3.84 d) and increased rate of biogas production (Rm:8.16 mLg−1d −1), compared to paddy straw and microalgal biomass individually. Thus, it can be concluded that co-digestion of Spirulina subsalsa with paddy straw results in enhanced biogas production.