**2.5 Pulse electric field (PEF)**

In this method, pores are created in the cell membrane due to which cellulose exposes to such agents that cause its breakdown by entering into the cell. High voltage ranging between 5.0 and 20.0 kV/cm is applied in a sudden burst to biomass for nano- to milliseconds. Sample was placed between two parallel plate electrodes, and the strength of electric field is given as *E = V*/*d*, where *V* and *d* are voltage and distance, respectively, between plate electrodes. Dramatic increase in mass permeability and tissue rapture occurred on the application of electric field. Electric pulses are applied, generally in the form of square waves or exponential decay. Setup of pulse electric field consisted of pulse generator, control system, data acquisition system, and material handling equipment [40, 41]. At ambient temperatures, the treatment can be performed at low energy. Another advantage of this treatment is the simple design of the instrument. Short duration of pulse time saves the effort and energy [42, 43]. Pulse electric field pretreatment was applied to pig manure and waste activated sludge by Author et al. [44]. As compared to untreated

#### **Figure 5.** *Pulse electric field (Intechopen.com).*

manure and sludge, 80% methane from manure and twofold increase in methane production from sludge were recorded in the study. A PEF system was designed and developed by Kumar et al. [45] that consisted of high-voltage power supply, switch circuit, a function generator, and sample holder. Neutral red dye was used to study the changes in the structure of cellulose by PEF pretreatment. Function generator drives the transistor present in the switching circuit; when pulse is applied by function generator to the switching circuit, switching circuit is turned on. Switching circuit is then transferred to the high voltage across the sample holder. So, by using function generator pulses of desired shape, width and high voltage can be applied to the sample. By using this setup, effects were observed on switch grass and wood. Results showed that at ≥8 kV/cm, switch grass showed high neutral red uptake. At low field strength, structural changes are less likely to occur. Electroporation through pulsed electric field is greatly affected by two parameters, pulse duration and electric field strength. Irreversible electroporation at >4 kV/cm with pulse duration in millisecond and ≥ 10 kV/cm with microsecond pulse duration was observed in *Chlorella vulgaris* which showed that pulse duration with a difference in micro- and milliseconds range can effect electroporation. Pulse electric field can increase hydrolysis rate by exposing cellulose to catalytic agents [40, 41, 46] (**Figure 5**).
