Comparison of thermal and biological pretreatment of oil palm empty fruit bunch for lignin degradation

• Main Author: Intan Nazirah Mohammad
• Format: Thesis
• Language: English; English
• Published: 2021
• Subjects: TP315-360 Fuel
• Online Access: https://eprints.ums.edu.my/id/eprint/41521/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/41521/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/41521/

Oil palm empty fruit bunches (EFB) are recoverable lignocellulosic biomass serving as feedstock for biofuel production. The major hurdle in producing biofuel from biomass is the abundance of embedded recalcitrant lignin. Pretreatment is a key step to increase the accessibility of enzymes to fermentable sugars in EFB. In this study, thermal and biological pretreatment methods were studied and compared for the degradation of lignin in EFB structure. The main objectives of this study were to optimize the operating conditions for pretreatment and characterize the effect on lignin degradations on EFB. The thermal treatment was conducted at different temperatures (150 °C to 210 °C), treatment durations (30 min–120 min) and EFB particle sizes (1 mm–10 mm). The physicochemical changes were observed using scanning electron microscope (SEM), energy dispersive X-ray (EDX) and Fourier transform infrared (FTIR) analyses. Meanwhile, the biological treatment was performed by using locally isolated lignin degraders from soils and decaying wood samples. The lignolytic ability of the isolates was screened using remazol brilliant blue anthraquinone R (RBBR) agar media and assessed via qualitative and quantitative enzymatic assays. Subsequently, the lignin degradation performance of both treatment methods was further evaluated using Klason’s lignin analysis. For the thermal treatment, the characterization studies revealed some disruptions occurred on the EFB structure with removal of silica bodies and other impurities. In addition, a remarkable change on the EFB elemental contents and its functional groups was observed. Elemental analysis shows increasing of carbon compound which might indicate the decomposition of compound. Significant reduction in peak of 1225 nm and 1445 nm was observed in EFB samples treated at high temperature and using smaller EFB particles size using FTIR analysis. Smaller EFB particle sizes (1mm) were found exhibited higher lignin degradation probably due to larger surface area for bioreaction. Applying a longer duration of treatment (120 min) and higher temperature (210 °C) was enhanced lignin degradation up to 60.29 %. For the biological treatment, six fungi and eight bacterial strains were successfully isolated and screened. Both qualitative and quantitative enzymatic studies showed all isolates majorly secreted lignin peroxidase as compared to manganese peroxidase and laccase lignolytic enzymes. Apparently, isolates PWM2 (226.40 U/L) and NWM6 (201.07 U/L) show high LiP activity. Fungi isolates demonstrated superior lignolytic ability than bacterial isolates as evident by the significant RBBR color decolorization. Fungal isolates, denoted as PWM2 and PWC3 indicated a 56.28 % and 51.19 % lignin degradation respectively, whereby the highest degradation by bacterial isolate (NWM5) was determined at 52.24 %. The findings of this study show both thermal and biological treatment methods offered comparable lignin degradation ability. While the thermal treatment could be done fast, the process however required an elevated temperature (above 150 o C). On the other hand, despite a longer duration for pretreatment, the biological method could be carried out within 30 – 37 oC. These studies provide insightful findings and guideline in pretreatment of lignocellulosic materials that beneficial for green and sustainable production of biomass-derived biofuel.