|Heri Hermansyah||Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Dwini Normayulisa Putri||Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Andiko Prasetyanto||Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Zhofran Bintang Chairuddin|
|Meka Saima Perdani|
|Masafumi Yohda||Department of Biotechnology and Life Sciences, Faculty of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan|
Lignocellulosic biomass has great potential as a low-cost source of fermentable sugar for the production of biofuels and high value organic acids. One potential biomass is oil palm empty fruit bunch, since it has high cellulose and hemicellulose content. However, its lignin content can hinder the access of cellulose and hemicellulose during the hydrolysis process. Therefore, an effective pretreatment for the delignification of lignocellulose biomass should be considered to reduce the lignin content. In this study, delignification of oil palm empty fruit bunch using peracetic acid and alkaline peroxide solution combined with the ultrasound method is investigated as a novel combination method of biomass pretreatment. The effect of pretreatment time was observed by using a peracetic acid solution for 1, 3, 5, 7 and 9 hours, followed by an alkaline peroxide solution for 4, 6, 8 and 10 hours. Based on the results, the best delignification was achieved by pretreatment using peracetic acid pretreatment for 3 hours, followed by alkaline peroxide pretreatment for 10 hours. Both pretreatments were assisted by the ultrasound method. The results show hemicellulose, cellulose and lignin content of 14.13%, 77.27% and 8.6% respectively. The lignin content was reduced by 68.73% and the cellulose content increased by 121.85%, relative to the untreated EFB. This result was considered as the best pretreatment, since the pretreatment time was shorter and high cellulose content together with low lignin content was achieved, which will improve the hydrolysis process.
Delignification; Pretreatment; Oil palm empty fruit bunch; Ultrasound
Lignocellulosic biomass has great potential as a low price raw material for the production of biofuels and high value products, such as bioethanol, enzyme and organic acid (Hermansyah et al., 2015; Hermansyah et al., 2018). One potential lignocellulose biomass is oil palm empty fruit bunch (EFB), since annually it is widely generated worldwide, especially in Indonesia, but unfortunately it has limited uses, only as an organic fertilizer or boiler fuel to generate electricity (Palamae et al., 2014).
Typically, EFB is composed of 24-65% cellulose, 21-34% hemicellulose, and 14-31% lignin (Chang, 2014). Based on its composition, EFB can potentially be used as a raw material for biofuels and organic acid production by utilizing the cellulose and hemicellulose content.
Hemicellulose and cellulose can be hydrolyzed into simple sugars for fermentation into biofuels and other products via microbial processes (Pattanamanee et al., 2012; Kim & Kim, 2013; Sklavounos et al., 2013).
Fortunately, EFB is a great source of cellulose and hemicellulose, since the lignin content can be removed, while the loss of hemicellulose and cellulose is kept to a minimum. Therefore, effective pretreatment for the delignification of EFB should be considered in order to improve the removal of lignin content.
In recent years, there have been many studies on the pretreatment of lignocellulosic biomass for the delignification process, either chemically or physically. Chemical pretreatment has been widely reported as a potential method for delignification, including acid and alkaline pretreatments (Mosier et al., 2005). In acid treatment, the bonds between cellulose, hemicellulose and lignin are broken down by H+ ions. The main objective of acid treatment is to solubilize the hemicellulose fraction of the biomass (Alvira et al., 2010) and change the structure of the lignin (Mosier et al., 2005) by solubilizing the acid soluble lignin. Otherwise, the main objective of alkali treatments is to remove nearly all the lignin and some of the hemicellulose. This treatment will have a great affect on the enzymatic hydrolysis of cellulose to sugars (Taherzadeh & Karimi, 2008). Furthermore, in some chemical treatments, the agents mentioned above are combined with oxidizing agents such as hydrogen peroxide and sodium hypochlorite water (Nazir et al., 2013) to assist the delignification and depolymerization processes.
Several researchers have succeeded in achieving the delignification of EFB by using chemical treatment. It has been delignified simultaneously and consecutively by using NaOH and H2O2, with lignin removal of 72% and 99% (Misson et al., 2009). Another chemical treatment has been attempted using peracetic acid solution. In this approach, approximately 53% of the lignin was removed, but nearly all the hemicellulose was retained (Palamae et al., 2014). On the other hand, a recent study has employed a sequential treatment using peracetic acid (PA) solution and alkaline peroxide (AP) solution, with around 92% of the lignin content from the EFB fiber removed (Palamae et al., 2017).
Besides using chemical treatment, physical treatment has also been studied to improve the results of lignocellulose biomass pretreatment. Previously, EFB has been successfully pretreated by using a sequential dilute acid and microwave alkali pretreatment, resulting in high delignification and a large amount of cellulose (Akhtar & Idris, 2017). In addition, ultrasound-assisted dilute aqueous ammonia pretreatment has also been investigated for the intensification of enzyme hydrolysis for corn cob, corn stover and sorghum stalk. It has been found that a combination of ultrasonic pretreatment can increase the accessibility of cellulose in the biomass and increase the enzymatic hydrolysis sugar yield (Xu et al., 2017). However, the combination of ultrasound and chemical pretreatment for EFB is still limited. Therefore, this study will modify the pretreatment method conducted by previous researcher which only using PA and AP solutions (Palamae et al., 2017). The aim of this study is to observe the performance of the delignification of EFB by employing a combination of chemical and physical treatments using PA and AP solutions and assisted by the ultrasound method. The study will focus on the time arrangement of the pretreatment in order to obtain the best delignification process.
Delignification of EFB has been successfully achieved in this study. The best delignification was obtained by pretreatment using PA for 3 hours, followed by AP pretreatment for 10 hours and assisted by ultrasound. Hemicellulose, cellulose and lignin content of 14.13%, 77.27% and 8.6%, respectively was achieved. After pretreatment, lignin content was reduced by 68.37%, while that of cellulose increased by 121.82%, relative to the composition of untreated EFB. Besides, the overall pretreatment time was also reduced if compared to the previous study by Palamae et al. (2017).
The authors are grateful for the research support provided by Universitas Indonesia and the Ministry of Research, Technology and Higher Education Republic of Indonesia through International Research Collaboration Grant with Grant Number NKB-1778/UN2.R3.1/HKP.05.00/2019.
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