In Search of Sun: Solar Pretreatment to enhance the Biomethane Potential of Empty Fruit Bunch (EFB) Fibres

Abstract

In the past decades, fossil fuels have become an increasing concern, due them being a non-renewable energy source and due to the environmental concerns related to the production and use of this fuel. This has led to increasingly more research in the value of bio-sourced lignocellulosic biomass such as Empty Fruit Bunch (EFB) fibres from the palm oil industry. EFB fibres are a major by-product of the palm oil industry and globally, over 30 million tons are produced annually. Due to its biomass characteristic, it is a potential source of energy in processes such as anaerobic digestion, however, its complex structure results in poor biological degradation. A pretreatment such as a hydrothermal (HT) pretreatment can be used, to improve the biodegradability, prior to anaerobic digestion; however, this is an energy intensive process and has led to investigating the use of alternative energy sources for the pretreatment such as solar power. The geographical position of Malaysia is beneficial to make use of solar radiation as an alternative energy source. Concentrated Solar Power (CSP) is a technology that is gaining more interest as a way to convert solar radiation into usable energy and in particular the Fresnel lens. This research investigates if a Fresnel lens can be used to improve the biodegradability of the EFB fibres and analysed what effect this pretreatment has on the fibres (in terms of the solar radiation and the duration of exposure). Two conditions are investigated; wet (water and EFB fibre mixture) and dry conditions (dry fibres in an inert environment). These two pretreatments are compared to a conventional HT pretreatment in terms of the biodegradability based on the Biomethane Potential (BMP). From the experimental results, it was found that the Fresnel lens can achieve very high temperatures (>400oC) and possesses fast heating rates resulting in a predominantly photothermal pretreatment. The biodegradability of the EFB fibres (using the Fresnel lens) was significantly improved in comparison to the HT pretreatment under the wet conditions; however, based on the analytical methods used in this research, no conclusive explanation can be given to why the biodegradability increased. Possible explanations are increased available surface area and pore size, which will need to be further researched. The dry condition pretreatment was too inhomogeneous to observe a significant improvement in the biodegradability. However, based on the overall biodegradability and the structural changes observed in the EFB fibres, it is expected that with improved operating conditions that this pretreatment will also improve the biodegradability. Overall, based on this research, the CSP pretreatment has potential to be used as alternative to the conventional HT pretreatment and the surface area for the CSP required by this process is estimated to be 2% of the actual plantation size. Therefore, CSP pretreatment has potential to be feasible in large-scale, however process efficiency needs to be improved due to the low efficiency of the lens and high energy requirements. Secondly, and most importantly, an economic analysis is crucial to validate the economic feasibility of implementing such a pretreatment.