Optimization strategies of alkaline thermo-chemical pretreatment for the enhancement of biogas production from de-oiled algae

Abstract This research work aims to evaluate the lipid extraction from algae and biogas production using thermo-chemical pretreatment of extracted (de-oiled) algae in co-digestion with corn husk. The hexane is found as a suitable solvent for the lipid extraction with the maximum yield of 1.8%, which is higher than the other solvent such as di-ethyl ether (1.2%), iso-propanol (0.8%), ethanol (0.2%) and methanol (0.5%). The FTIR characterization results confirms the presence of alkyl esters at 1724 cm−1 and methyl esters at 3000–2853 cm−1. The optimum biogas yield was determined using the Box-Behnken design of experiments. The pretreatment parameters such as temperature, heating time and sodium hydroxide concentration in three levels were investigated. After pretreatment, 17 experimental trails were carried at the thermophilic condition in batch mode. From the experimental investigations, sodium hydroxide showed the most influential in biogas yield. Response surface methodology predicted the maximum yield of 740 ml/gVS under the optimum reaction conditions such as 6% sodium hydroxide concentration at 70 °C in 3 h reaction time. Pretreated algae and corn husk produced 60% higher biogas yield than the untreated algae. The high value of regression R2 0.98 showed the predicted model can be effectively applied for the mass application from de-oiled algae with the co-digestion of corn husk.