**7. Important and challenges**

**Biomass type EBI dose Glucose yield (%) References**

**Table 4.** Summarization of previous research using EBI pretreatment on various types of biomass and biofiber.

In general, sugar substrates from tropical biomass and biofiber are potential sources for biofuel production such as ethanol and butanol because they are abundant, cheap, and renewable [85]. Biomass and biofiber utilization will reduce the dependency on fossil fuel and at the same time it could help in reducing toxic gases emission with an abundant feedstock that can support for a very long period of time. This second generation biofuel does not compete with human food resources which are non-edible in nature [86]. In lignocellulosic biomass conversion for biofuels such as ethanol and butanol, pretreatment plays a major role in separating the major components (lignin, cellulose, and hemicellulose) of the biomass. The conventional chemical and enzymatic pretreatment methods have disadvantages such as producing byproducts and low conversion of biomass components [86]. Numerous numbers of publications reported the potential of bioenergy from biomass wastes through irradiation pretreatment [43, 45, 62, 87, 88]. Most of the studies agreed that irradiation pretreatment could assist the reduction of particle size that provide better access for subsequent process. This pretreatment clearly

proved able to enhance enzymatic saccharification and fermentation performance.

Presently, Malaysia is dependent on fossil fuels such as coils, oil, and natural gas as well as renewable energy sources such as hydro, biomass, and solar energy. The demands for energy is increasing by years with some challenges such as the decreasing source of fossil fuels, food versus fuel crisis, and greenhouse gas (GHG) emission that needs to be taken into consideration [11]. In Malaysia, the development of renewable energy is still rather slow. Although, in 10th Malaysia plan, renewable energy usage has to increase >1% in 2009 to 5.5% of total electricity generation in 2010, although several fiscal incentives have been launched by the Malaysian government [89]. On the other hand, Malaysia is geographically located in the tropical and humid climate region which provides easy access to variety of biomass resources. Biomass resources are mainly from palm oil, wood, and agro-industries [90]. Malaysia devotes 11% of

Rice straw (RS) 80 kGy 35 52 [41] Wheat straw 500 kGy 8.60 10.72 [82] Poplar bark 0–1000 kGy 44.2 66.7a [81] Napier Grass 250 kGy 20 79 [77] Rice straw (RS) 80 kGy 37 70.4b [43] OPEFB 100–500 kGy na na [36]

a, pretreatment added with diluted sulfuric acid. b, pretreatment added with water soaking-based EBI.

**6. Biofuel from biomass and biofiber**

na, not available.

346 Radiation Effects in Materials

**Untreated Pretreated**

Pretreatment process is an important process prior to enzymatic saccharification. Applying the most efficient pretreatment process could reduce production cost, hence reduce the final product price. As per date, the irradiation pretreatment process shows a promising approach and has some advantages compared to other pretreatment processes.

Irradiation pretreatment is an environment friendly process due to less chemical used during the pretreatment process. Also, this process requires less time (<10 minutes) compared to other process, especially biological pretreatment, which requires more than 7 days to remove lignin material from the biomass [95].

The most important advantage of the irradiation process is that this process is very selective to the degradation of the biomass component, unlike chemical pretreatment that could degrade some part of cellulose and hemicellulose during the process [45]. On the other hand, this process also produced less inhibitor that could affect enzymatic saccharification and fermen‐ tation process. According to Bak et al. [43], there was no inhibitors produced from the irradiated biomass when the pretreatment was carried out using water as soaking buffer. Hence, could increase the enzymatic saccharification and fermentation process performance for liquid biofuel production.

Even though this irradiation pretreatment procedure is quite simple, it is undeniable that the high-energy consumption associated with it makes the process not preferable for implemen‐ tation on a commercial scale [40, 96]. Besides, this process requires a special reactor that could affect during large-scale process. For the large-scale pretreatment of biomass, a large micro‐ wave irradiator or reactor is required, which is costly, energy consuming, and limits its use in large-scale operations. This drawback hence also could increase the operational cost.
