Improvement in lipids extraction processes for biodiesel production from wet microalgal pellets grown on diammonium phosphate and sodium bicarbonate combinations

•Microalgae grown on Sodium Bicarbonate (NaHCO3) and Diammonium Phosphate (DAP) combination.•Effect of thermolysis and sonolysis was highlighted as effective cell disruption methods.•Biodiesel synthesis was accomplished after lipids extraction from wet microalgae biomass.•Transesterification of extracted lipids with methanol has resulted fatty acid methyl esters (FAMEs). Biomass productivity and growth kinetics for microalgae grown on sodium bicarbonate and diammonium phosphate were investigated. Different carbon and nitrogen ratios have shown different growth rates and biomass productivity and C:N ratio 50:10 as mgL−1 has shown the best production than all. For effective lipids extraction from biomass thermolysis and sonolysis were carried out from wet biomass. Sonolysis at 2.3W intensity for 5min has released 8.58mg at neutral pH. More quantity of lipids was extracted when extraction was made at pH 4 and 10 which resulted 9mg and 9.28mg lipids respectively. Thermal treatment at 100°C for 10min has released 12.82mg lipid at neutral pH. In the same thermolysis at pH 4 and 10 more quantity of lipids was extracted which were 15.16mg and 14.81mg respectively. Finally transesterified lipids were analyzed through GC–MS for FAME composition analysis.