Effect of discharge parameters on the shock wave pretreatment of wood flour for enzymatic saccharification

Woody bioethanol is expected to be a new biomass fuel because it can reduce CO₂ emissions while avoiding conflict with food issues. The woody bioethanol is obtained by saccharifying cellulose and fermenting the produced sugar. However, saccharification efficiency of cellulose is insufficient since the reaction area of the saccharifying enzyme is limited by a large amount of hydrogen bonds between cellulose molecules. In this work, we applied underwater discharge shock waves to wood flour to physically crush the flour and expand the area of enzymatic reaction by breaking hydrogen bonds.

Shock waves were generated in the water with wood flour dispersed by spark discharges produced by applying a pulsed high voltage via spark gap switch to pin-to-pin electrodes. The shock wave pressure was 2 MPa at 17 mm distant from the electrodes, suggesting that the shock wave mechanically destroyed wood flour. Increasing the discharge frequency from 3.3 to 7.3 Hz improved the obtained glucose sugar from 427 to 518 ppm. However, increasing the discharge energy from 0.85 to 1.13 J/pulse at constant discharge frequency of 3 Hz did not strongly affect the saccharification efficiency. These results indicate that the number of shock wave irradiations is important for improving the pretreatment effect.