Oil palm biomass pretreatment and hydrolysis: a recent biotechnological venture towards bio-based lactic acid production

The effective utilisation of lignocellulosic biomass as fossil-based counterparts in the development of bio-based chemicals manufacturing is progressively relevant. Hence, many works are underway to shift from petrochemical industries to a sustainable lignocellulosic biomass biorefinery in lactic acid production. Malaysia is the leading country as a palm oil producer, with an enormous supply of inexpensive, renewable and non-food, yet untapped oil palm biomass resources. In this regard, oil palm fronds (OPF) rich in glucan content account for 60% of total agricultural biomass in Malaysia, which can accommodate 2 million metric tons per annum of fermentable sugar. The richness of carbohydrates in OPF serves as the key to unlocking bio-based lactic acid commercialization for future sustainable breakthroughs. This paper aims to provide insights into the exploitation of OPF as the novel feedstocks in bio-refinery processes. Special emphasis in this review is put on the technology, global demand, commercial status and future prospects of the production of second-generation lactic acid, as this process has received most research and development efforts so far. It reviews the current research attributed to the compositional analysis of OPF by primarily focusing on the National Renewable Energy Laboratories (NREL) protocol. It then focuses on the recent technological advancements of different pretreatment methods and hydrolysis for carbohydrate recovery in lactic acid production. Given with the tremendous potential, OPF can be exploited as an excellent sugar platform for the production of higher value products such as advanced biofuels, fine-platform chemicals and bioenergy

Biohydrogen production in semicontinuous system using immobilized cell membrane

Hydrogen is considered to be the fuel of the future because of its high energy content (122 kJ/g), and water is the only byproduct of its use. Moreover, the production of hydrogen via fermentation of organic wastes is carbon neutral. This study was conducted to evaluate the performance of immobilized cells on PVDF membrane for biohydrogen production using a sequencing batch reactor by varying the hydraulic retention times (HRT) of the system and to compare the efficiency between suspended and attached systems on the production of biohydrogen. It was found that the biohydrogen fermentation performance was improved in a semi-continuous system, especially with immobilized cells. The optimum HRT that supports the highest biohydrogen yield was for an HRT of 12 hours, where the performance of hydrogen production was improved and in which the maximum hydrogen yield was achieved at 2.43 mol H2/mol and maximum hydrogen production rate (HPR) of 2.46 L H2/L.d as compared to other HRT for both systems. Therefore, the result of this study can be applied as the benchmark for scaling up the process

Strategi pengoptimuman lanjutan untuk meningkatkan penghasilan biohidrogen foto-fermentasi oleh bakteria ungu bukan sulfur

Proses foto-fermentasi ialah suatu laluan penghasilan hidrogen yang menarik. Walau bagaimanapun, didapati bahawa kecekapan penukaran cahaya dan penghasilan biohidrogen foto-fermentasi oleh bakteria ungu bukan sulfur (PNSB) adalah sangat rendah. Maka, pelbagai pendekatan pengoptimuman telah dikaji bagi meningkatkan penghasilan fotohidrogen dan prestasi keseluruhannya. Ulasan ini membincangkan strategi pengoptimuman lanjutan untuk meningkatkan penghasilan biohidrogen foto-fermentasi secara menyeluruh. Antara strategi yang dibincangkan merangkumi pengoptimuman makronutrien dalam media penghasilan biohidrogen, faktor abiotik dan rejim pencahayaan semasa proses foto-fermentasi berlaku. Pendekatan ini menunjukkan keputusan positif dalam meningkatkan penghasilan foto-hidrogen oleh PNSB. Pendekatan gabungan yang mengintegrasikan strategi pengoptimuman individu yang berbeza dipercayai mungkin dapat mendatangkan peningkatan yang sinergistik terhadap produktiviti dan hasil biohidrogen foto-fermentasi oleh PNSB

Isolation and characterization of biohydrogen-producing bacteria for biohydrogen fermentation using oil palm biomass-based carbon source

The effectiveness of biohydrogen conversion from biomass sources is governed by the selection of ideal biohydrogen-producing bacteria to achieve high and consistent production performance. The aim of this research was to isolate and identify a biohydrogen producer in local soil samples, as well as to evaluate its fermentability in biohydrogen production from oil palm empty fruit bunches (OPEFB). To this end, preliminary identification was performed using morphological, phenotype, biological, and 16s rRNA analyses. The fermentability of the isolate was further evaluated in a serum bottle and then in a 1.5 L anaerobic column bioreactor (ACBR) to investigate the potential for biohydrogen production using two OPEFB-based carbon sources: hydrolysate of ammonia fiber expansion (AFEX)-pretreated OPEFB and molasses from dilute acetic acid (DAA)-pretreated OPEFB. The isolated strain, Enterobacter sp. KBH 6958, was found to be capable of producing biohydrogen from various carbon sources via the pyruvate:ferredoxin oxidoreductase (PFOR) pathway. The cumulative conversion of AFEX OPEFB hydrolysate was 45% higher than that observed in DAA OPEFB molasses fermentation in the production of biohydrogen. The biohydrogen yield after fermenting AFEX OPEFB hydrolysate with Enterobacter sp. KBH 6958 was 1.55 mol H2/mol sugar, with a maximum productivity of 98.1 mL H2/h (4.01 mmol H2/L/h), whereas butyrate (10.6 mM), acetate (11.8 mM), and ethanol (4.56 mM) were found to be the major soluble metabolites. This study successfully demonstrated the biotechnological conversion of OPEFB into biohydrogen using a locally isolated strain, which not only solves environmental issues associated with the industry but may also offer a solution to the world’s energy insecurity

Towards Sustainable Production of Bio-based Lactic Acid via a Bio-based Technical Route: Recent Developments and the Use of Palm Kernel Cakes in the Bioconversion

The continued reliance on non-renewable fossil resources has led to serious environmental issues. In light of these concerns, the transition from non-renewable sources to more sustainable ones have been explored, as exemplified by the production of bio-based lactic acid via lignocellulosic biomass bio-refinery process. Malaysia, the second-largest producer of palm oil in the world, generates abundant, cheap, and underutilized oil palm biomass in the form of palm kernel cakes. Comprised of 50% fermentable hexose sugars, palm kernel cakes have emerged as an interesting feedstock substitute in the production of bio-based fine chemicals, e.g., lactic acid. This paper focuses on current work based on selected literature published in the 21st century on the exploitation of palm kernel cakes as a novel feedstock in bio-refinery processes after addressing the current global demand and potential commodity applications of bio-based lactic acid. It then discusses current research on potential lactic acid-producing microorganisms, with particular attention to bacteria, and different pretreatment methods for carbohydrate recovery from palm kernel cakes. It also highlights the potential of oil palm biomass, especially palm kernel cakes, as a promising commodity that contributes to sugar platforms in value-added products, e.g., biofuel, bioenergy, ethanol, acids, and fine chemicals

Kinetic study and model of fermentation parameters affected growth and xylitol production in bioreactor by Kluyveromyces marxianus ATCC 36,907

Optimum conditions for xylitol production from xylose based on the reliable kinetic models of the fermentative performance are important to design lignocellulosic xylitol production. The model was validated by comparing the simulation results with experimental data in batch culture of Kluyveromyces marxianus ATCC 36,907 under various concentrations of initial substrate (36 to 122 g/L) and agitation speed of the impeller (200 to 500 rpm) in a 3.6-L bioreactor. The model suggested that the kinetics of K. marxianus ATCC 36,907 using a modified Monod equation was regulated by the effects of xylose concentrations and oxygen levels during the fermentation. Xylitol production appeared favorable with maximum yield of 0.43 g/g corresponded to kLa value of 29.9 h−1 with low microbial growth. Sensitivity analysis on the obtained model parameters showed that the maximum specific growth rates (µmax) and substrate consumption constant (KS) are the most influential model parameters for xylitol production

An overview on the factors affecting enzymatic saccharification of lignocellulosic biomass into fermentable sugars

Lignocellulosic biomass (LCB) is a widely available and sustainable energy resource that can be directly or indirectly converted to biofuels and value-added bioproducts. In such LCB conversion, enzymatic saccharification is commonly regarded as a green alternative to chemical hydrolysis due to less energy-intensive, less toxic, and more environment-benign for efficient fermentable sugar recovery. However, enzymatic saccharification faces substantial challenges, since the complex polymeric matrices of LCB necessitates a variety of enzymes for complete and adequate saccharification. Empirical evidence on enzymatic saccharification has paved the way for optimizing the processes and design for enhancing the performance in LCB. This review examines the enzymatic saccharification of LCB, focusing on the important parameters affecting the process, such as pH, temperature, agitation, enzyme/substrate loading, residence time, and the enzymes required to degrade various LCB components. Various strategies have been reported to improve the performance in saccharification and to address the non-productive adsorption of enzymes. A preliminary economic competency valuation of enzymederived fermentable sugars is proposed. Wheat straw, sugarcane bagasse and corn stalk appear, in this case, to be the most economic competent LCBs for commercial enzyme-derived fermentable sugar production. Lastly, practical challenges and future research directions on the enzymatic saccharification of LCB are discussed

Unraveling the effect of redox potential on dark fermentative hydrogen production

Biological hydrogen production by dark fermentation is an environmentally benign alternative to the conventional fossil-based hydrogen production process. However, low biological hydrogen yields remain a major constraint to commercial production. Unraveling the metabolic pathway for hydrogen production will unlock the potential to enhance biohydrogen yield. In this regard, the key fundamentals of various important dark fermentative hydrogen-producing metabolic pathways are scrutinized in this review, including those in strict and facultative anaerobic bacteria such as Clostridia, Enterobacter, Thermotoga, and Thermoanaerobacterium. Since the hydrogen metabolic pathway is governed by a series of redox reactions during fermentation, manipulation of the redox potential not only indicates the extent of an anaerobic condition, but also affects the growth of anaerobic bacteria. This article reviews the types of hydrogen-producing bacteria and their fundamental metabolic pathways, the effect of redox potential on metabolic fluxes towards growth and hydrogen production and discusses various important redox potential control strategies. In pure culture, strict anaerobes are more suitable to grow in a more reducing environment (lower redox potential), while facultative anaerobes thrive in the presence of oxygen where the redox potential is relatively higher. Redox potential control could minimize the carbon flow towards the propionate-producing pathway by avoiding the redox potential value of around ˆ’ 280 mV. Avoiding the propionate- and lactate-producing pathways results in a higher chance of producing hydrogen via the pyruvate decarboxylation process. Overall, the review provides an all-rounded investigation on the manipulation and impact of redox potential to achieve better hydrogen production for sustainable energy resources