Energy efficient pretreatment for enhanced conversion of macroalgal biomass to bioenergy: Detailed energy and cost assessment

Macroalgal biomass disintegration through bacterial pretreatment is considered a time consuming, slower and mild energy consuming process. The resistant and less permeable cell wall of macroalgal biomass makes the bacterial pretreatment less energy efficient. The macroalgal biomass, Ulva sps. comprises a double layered cell wall. A novel attempt has been made in the present study to weaken the cell wall of macroalgae through a nonionic surfactant, Triton X 100 with subsequent pretreatment by cellulase secreting bacteria. An effective cell wall weakening of macroalgae without biomass disintegration (cell lysis) was achieved at an optimal surfactant dose of 0.005 g/g TS and 25 min treatment time. The cell wall weakened, macroalgal biomass (CWW + CE) was subjected to cellulase secreting bacterial pretreatment. The weakening of the cell wall increases the surface area for the enzyme secreting bacteria and makes the overall process energy efficient with greater methane production. The results of bacterial pretreatment showed that CWW + CE exhibited a higher organic release of 1400 mg/L and liquefaction of 25 %, when compared to cellulase secreting bacterially pretreated (CE) sample. The CE showed an organic release of 845 mg/L and liquefaction of 15.1 %, respectively. The results of biomethane production imply that CWW + CE revealed a greater biomethane yield of 0.222 L/g COD in comparison with CE (0.114 L/g COD). The CWW + CE was superior to CE, with a net energy production of 219.785 kWh/Ton.