Critical parametric influence on microalgae cultivation towards maximizing biomass growth with simultaneous lipid productivity

• Mixotrophic cultivation of microalgae showed high biomass and lipid productivity along with reducing sugars synthesis.
• Carbon concentration individually showed significant influence.
• Presence of macronutrients (Nitrates) and micronutrients (Magnesium) showed greater influence.
• Light and temperature has significant influence on mixotrophic nutrition.

Enhancing microalgae biomass productivity through different abiotic and environmental factors optimization is crucial. Design of experimental (DOE) methodology using Taguchi orthogonal array (OA) was studied to evaluate the specific influence of eight important factors (light, pH, temperature, carbon concentration, nitrates, phosphates, magnesium ion concentration and carbon source) on the biomass production using three levels of factor (21 × 37) variation with experimental matrix [L18-18 experimental trails]. All the factors were assigned with three levels except light illumination (21). Substantial influence on biomass productivity is observed with carbon concentration contributing 16.8%, followed by nitrates 12.8% and light 9.3%. Experimental setup eight (Light, pH-8.5, Temperature 25°C, Carbon concentration 10 g/l, nitrates 1.5 g/l, phosphates 0 g/l, magnesium 150 mg/l, Carbon source (glucose)) showed maximum biomass growth (5.26 g/l) and good substrate degradation (63%, COD removal efficiency) contributing to carbohydrate production (257 mg/g biomass) which is further converted to lipids (20% Total lipid and 10% Neutral lipids). Chlorophyll (a, b), carbohydrates composition, FAME analysis for lipid percentage were monitored during process operation. Elemental analysis reveals that the carbon to hydrogen and oxygen ratio present in dried algal biomass can be hydrothermally liquefied (HTL) to produce biocrude.