Impact of light spectra on photo-fermentative biohydrogen production by Rhodobacter sphaeroides KKU-PS1.

Purple non-sulphur bacteria can only capture up to 10 % light spectra and only 1-5 % of light is converted efficiently for biohydrogen production. To enhance light capture and conversion efficiencies, it is necessary to understand the impact of various light spectra on light harvesting pigments. During photo-fermentation, Rhodobacter sphaeroides KKU-PS1 cultivated at 30 °C and 150 rpm under different light spectra has been investigated. Results revealed that red light is more beneficial for biomass accumulation, whereas green light showed the greatest impact on photo-fermentative biohydrogen production. Light conversion efficiency by green light is 2-folds of that under control white light, hence photo-hydrogen productivity is ranked as green > red > orange > violet > blue > yellow. These experimental data demonstrated that green and red lights are essential for photo-hydrogen and biomass productions of R. sphaeroides and a clearer understanding that possibly pave the way for further photosynthetic enhancement research.

Enhancing biohydrogen gas production in anaerobic system via comparative chemical pre-treatment on palm oil mill effluent (POME).

Biological hydrogen production using palm oil mill effluent (POME) as a carbon source through dark fermentation process has been suggested to be a promising bioenergy potential and enacts as alternative renewable energy source. Results have indicated that among various 1.5% (w/v) chemical pre-treatments (sodium hydroxide, NaOH; hydrochloric acid, HCl; sulphuric acid, H2SO4; phosphoric acid, H3PO4 and nitric acid, HNO3) on POME, using H3PO4 would generate maximum biohydrogen production of 0.193 mmol/L/h, which corresponded to a yield of 1.51 mol H2/mol TCconsumed with an initial total soluble carbohydrate concentration of 23.52 g/L. Among H3PO4 concentrations (1%-10%), the soluble carbohydrate content and the biohydrogen produced was highest and increased by 1.70-fold and 2.35-fold respectively at 2.5% (w/v), as compared to untreated POME. The batch fermentation maximum hydrogen production rate and yield of 0.208 mmol/L/h and 1.69 mol H2/mol TCconsumed were achieved at optimum pre-treatment conditions of pH 5.5 and thermophilic temperature (60 °C). This study suggests that chemical pre-treatment approaches manage to produce and improve the carbohydrate utilisation process further. Continuous fermentation in CSTR at the optimum conditions produce heightened 1.5-fold biohydrogen yield for 2.5% H3PO4 at 6 h HRT as compared to batch scale. Bacterial community via next-generation sequencing analysis at optimum HRT (6 h) revealed that Thermoanaerobacterium thermosaccharolyticum registered the highest relative frequency of 20.24%. At the class level, Clostridia, Bacilli, Bacteroidia, Thermoanaerobacteria, and Gammaproteobacteria were identified as the biohydrogen-producing bacteria in the continuous system. Insightful findings from this study suggest the substantial practical utility of dilute chemical pre-treatment in improving biohydrogen production.

Investigation into Lewis and Brønsted acid interactions between metal chloride and aqueous choline chloride-oxalic acid for enhanced furfural production from lignocellulosic biomass.

Furfural has been identified as a valuable biobased platform chemical that can be further converted into bioenergy and biochemicals. Furfural is derived from lignocellulosic biomass and can also be regarded as a sustainable alternative to petrochemical products. Herein, the performance of trivalent metal chlorides (FeCl3, AlCl3) and tetravalent metal chlorides (SnCl4, TeCl4) as Lewis acidic cocatalysts was investigated in an aqueous choline chloride-oxalic acid (16.4 wt% H2O) deep eutectic solvent (DES) system for producing furfural from oil palm fronds (OPFs). The metal chlorides with greater electrical field gradients were stronger Lewis acids that enhanced both furfural production and degradation reactions. The main degradation product in this reaction system was humin, and this result was confirmed by FTIR analysis. By subjecting OPFs to an aqueous DES reaction (120 °C, 45 min) with SnCl4 (2.50 wt%), a furfural yield of 59.4% was obtained; without incorporated metal chlorides, the furfural yield was 46.1%. Characterization studies showed synergistic Lewis and Brønsted acid interactions between metal chlorides and DES components. Overall, the residual OPFs showed high glucan content, which led to the production of glucose (71.4%) as a byproduct via enzymatic hydrolysis. Additionally, the aqueous DES system was recycled and reused for several additional runs. The proposed aqueous DES system presents a promising biorefinery approach for the conversion of OPFs to biochemicals.

Low cost nutrient-rich oil palm trunk bagasse hydrolysate for bio-succinic acid production by Actinobacillus succinogenes.

Economical source of succinic acid (SA) is most sought-after as a key platform chemical for a wide range of applications. Low-cost production of bio-succinic acid (bio-SA) from a renewable biomass resource i.e., oil palm trunk (OPT) is reported in this paper. Apart from carbon source, nitrogen source and mineral salts are other important nutrients affecting microbial cell growth and bio-SA biosynthesis by Actinobacillus succinogenes 130Z. In order to access and optimize nutrient requirement of the latter two sources, their effects in terms of types and concentrations were investigated. The findings highlighted the importance of selecting proper nitrogen source in A. succinogenes fermentation. The possibility of producing bio-SA from OPT economically can be achieved through minimal supply of 5 g/L yeast extract compared to that generally supplemented 15 g/L with a similar yield (0.47 g/g). In addition, a higher bio-SA yield (0.49 g/g) was achieved without adding mineral salts, which could further reduce fermentation cost. The use of minimally supplemented hydrolysate resulted in 21.1 g/L of bio-SA with a satisfactory yield (0.58 g/g) in a batch bioreactor system with an estimated 56.4% in cost savings. Conclusively, OPT bagasse hydrolysate is a nutrient-rich feedstock that can be practically utilized for bio-SA production.

Dose-response analysis of toxic effect from palm oil mill effluent (POME) by-products on biohydrogen producing bacteria - A preliminary study on microbial density and determination of EC50.

The stimulant and toxicity effects of reported organic (acetic acid, propionic acid, butyric acid, formic acid, oil & grease) and inorganic (copper) by-products presented in palm oil mill effluent on anaerobic bacterial population were examined in this paper. The toxicity test had shown that acetic, propionic and butyric acids tend to stimulate the bacterial density level (survival rate more than 50%), while formic acid, copper, oil and grease were shown to have suppressed the density level (survival rate less than 50%). The highest biomass recorded was 1.66 mg/L for the concentration of acetic acid at 216 mg/L and lowest biomass concentration, 0.90 mg/L for copper at 1.40 mg/L. Biohydrogen-producing bacteria have a favourable growth rate around pH 5.5. The comparison of half maximal effective concentration (EC50) values between two test duration on the effects of organic and inorganic by-products postulate that bacteria had a higher tolerance towards volatile fatty acids. While acetic, butyric and propionic acids had exhibited higher tolerance EC50 values for bacteria, but the opposite trend was observed for formic acid, copper and oil & grease.

Low-cost novel clay earthenware as separator in microbial electrochemical technology for power output improvement.

A conventional reactor in microbial electrochemical technology (MET) consists of anode and cathode compartments divided by a separator, which is usually a proton exchange membrane (PEM), such as Nafion 117. In this study, a novel porous clay earthenware (NCE) was fabricated as the separator to replace the highly cost PEM. The fabrication of NCEs is with raw clay powder and starch powder that acts as a pore-forming agent at different starch powder contents (10 vol%, 20 vol%, and 30 vol%), ball-milled before hydraulically pressed to form green ceramic pellets and sintered up to 1200 °C. The highest power density of 2250 ± 21 mW/m2 (6.0 A/m2), the internal resistance of 75 ± 24 Ω and coulombic efficiency (CE) of 44 ± 21% were produced for MFC-NCE from 30 vol% starch powder content under batch mode operation. The MFC-PEM combination produced the lowest power density, CE and the highest internal resistance up to 1350 ± 17 mW/m2 (3.0 A/m2), 23 ± 15% and 326 ± 13 Ω, respectively.

Multiple crystallization as a potential strategy for efficient recovery of succinic acid following fermentation with immobilized cells.

This study aimed to enhance the crystallizability of bio-based succinic acid for its efficient recovery while maintaining the end product at the highest purity. Immobilization of Actinobacillus succinogenes was initially evaluated based on three different carriers: volcanic glass, clay pebbles, and silica particles. The adsorption capacity of metabolites with a low concentration (10 g/L) and a high concentration (40 g/L) was investigated. It was demonstrated that clay pebbles adsorbed the least succinic acid (< 11 mg/g clay pebbles). The repeated batch-fermentation trials with immobilized cells highlighted that succinic acid with an average concentration of up to 36.3 g/L with a metabolite-production ratio of 3:1 (succinic acid to by-products) could be attained within 130 h. Subsequently, the purification of succinic acid through crystallization was assessed in terms of pH, temperature, crystallization time, initial succinic acid concentration and multiple recrystallization processes. Increasing the crystallization time from 6 h to 9 h afforded an improvement of 17% in the recovery of succinic acid crystals. Moreover, a fourfold concentration coefficient of the broth yielded the highest purity percentage (99.9%). The crystallization in three consecutive stages at 9 h (with a fourfold concentration coefficient) successfully improved the total recovery percentage of succinic acid from 55.0 to 84.8%.

Compatibility of utilising nitrogen-rich oil palm trunk sap for succinic acid fermentation by Actinobacillus succinogenes 130Z.

In this study, the potential of oil palm trunk (OPT) sap as a sole substrate for succinic acid (SA) production was evaluated using Actinobacillus succinogenes 130Z. After OPT sap was characterised, the effects of adding carbonate, yeast extract (YE) and minerals to this medium were investigated in an attempt to develop a low-cost fermentation medium. The OPT sap alone, gave comparable SA yield and productivity (0.54 g/g and 0.35 g/L/h) to those supplemented with YE (0.50 g/g and 0.36 g/L/h) and minerals (0.55 g/g and 0.40 g/L/h). The findings showed that OPT sap has sufficient amount of nutrients for SA biosynthesis by A. succinogenes 130Z and could potentially reduce cost without requiring expensive nutrients supplementation.

Preparation of kenaf stem hemicellulosic hydrolysate and its fermentability in microbial production of xylitol by Escherichia coli BL21.

Kenaf (Hibiscus cannabinus L.), a potential fibre crop with a desirably high growth rate, could serve as a sustainable feedstock in the production of xylitol. In this work, the extraction of soluble products of kenaf through dilute nitric-acid hydrolysis was elucidated with respect to three parameters, namely temperature, residence time, and acid concentration. The study will assist in evaluating the performance in terms of xylose recovery. The result point out that the maximum xylose yield of 30.7 g per 100 g of dry kenaf was attained from 2% (v/v) HNO3 at 130 °C for 60 min. The detoxified hydrolysate was incorporated as the primary carbon source for subsequent fermentation by recombinant Escherichia coli and the performance of strain on five different semi-synthetic media on xylitol production were evaluated herein. Among these media, batch cultivation in a basal salt medium (BSM) afforded the highest xylitol yield of 0.35 g/g based on xylose consumption, which corresponded to 92.8% substrate utilization after 38 h. Subsequently, fermentation by E. coli in the xylose-based kenaf hydrolysate supplemented with BSM resulting in 6.8 g/L xylitol which corresponding to xylitol yield of 0.38 g/g. These findings suggested that the use of kenaf as the fermentation feedstock could be advantageous for the development of sustainable xylitol production.

Homogeneous solid dispersion (HSD) system for rapid and stable production of succinic acid from lignocellulosic hydrolysate.

Continuous bio-production of succinic acid was reported in homogeneous solid dispersion (HSD) system utilizing porous coconut shell activated carbon (CSAC) as immobilization carrier. The aim of the present work was to implement the HSD system to increase the area of cell immobilization and the rate of succinic-acid production from the lignocellulosic medium. The ratio of the two enzymes (cellulase-to-hemicellulase) was initially optimized to break down the lignocellulose into its free monomers, wherein the best ratio was determined as 4:1. Succinic-acid production was evaluated in the HSD system by varying the substrate loading and dilution rate. The results showed that high productivities of succinic acid were obtained when 60 g/L glucose was fed over a dilution rates ranging from 0.03 to 0.4/h. The titer of succinic acid decreased gradually with higher dilution rate, whereas the residual substrate concentration increased with it. Critical dilution rate was determined to be 0.4/h at which the best productivity of succinic acid of 6.58 g/L h and its yield of 0.66 g/g were achieved using oil palm fronds (OPF) hydrolysate. This work lends evidence to the use of CSAC and lignocellulosic hydrolysate to further exploit the potential economies of scale.

Preeminent productivity of 1,3-propanediol by Clostridium butyricum JKT37 and the role of using calcium carbonate as pH neutraliser in glycerol fermentation.

Calcium carbonate was evaluated as a replacement for the base during the fermentation of glycerol by a highly productive strain of 1,3-propanediol (PDO), viz., Clostridium butyricum JKT37. Due to its high specific growth rate (µmax=0.53h-1), 40g/L of glycerol was completely converted into 19.6g/L of PDO in merely 7h of batch fermentation, leaving only acetate and butyrate as the by-products. The accumulation of these volatile fatty acids was circumvented with the addition of calcium carbonate as the pH neutraliser before the fermentation was inoculated. An optimal amount of 15g/L of calcium carbonate was statistically determined from screening with various glycerol concentrations (20-120g/L). By substituting potassium hydroxide with calcium carbonate as the pH neutraliser for fermentation in a bioreactor, a similar yield (YPDO/glycerol=0.6mol/mol) with a constant pH was achieved at the end of the fermentation.

Biotechnological route for sustainable succinate production utilizing oil palm frond and kenaf as potential carbon sources.

Due to the world's dwindling energy supplies, greater thrust has been placed on the utilization of renewable resources for global succinate production. Exploration of such biotechnological route could be seen as an act of counterbalance to the continued fossil fuel dominance. Malaysia being a tropical country stands out among many other nations for its plenty of resources in the form of lignocellulosic biomass. To date, oil palm frond (OPF) contributes to the largest fraction of agricultural residues in Malaysia, while kenaf, a newly introduced fiber crop with relatively high growth rate, holds great potential for developing sustainable succinate production, apart from OPF. Utilization of non-food, inexhaustible, and low-cost derived biomass in the form of OPF and kenaf for bio-based succinate production remains largely untapped. Owing to the richness of carbohydrates in OPF and kenaf, bio-succinate commercialization using these sources appears as an attractive proposition for future sustainable developments. The aim of this paper was to review some research efforts in developing a biorefinery system based on OPF and kenaf as processing inputs. It presents the importance of the current progress in bio-succinate commercialization, in addition to describing the potential use of different succinate production hosts and various pretreatments-saccharifications under development for OPF and kenaf. Evaluations on the feasibility of OPF and kenaf as fermentation substrates are also discussed.

Effects of changes in chemical and structural characteristic of ammonia fibre expansion (AFEX) pretreated oil palm empty fruit bunch fibre on enzymatic saccharification and fermentability for biohydrogen.

Oil palm empty fruit bunch (OPEFB) fibre is widely available in Southeast Asian countries and found to have 60% (w/w) sugar components. OPEFB was pretreated using the ammonia fibre expansion (AFEX) method and characterised physically by the Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that there were significant structural changes in OPEFB after the pretreatment step, and the sugar yield after enzymatic hydrolysis using a cocktail of Cellic Ctec2® and Cellic Htec2® increased from 0.15gg(-1) of OPEFB in the raw untreated OPEFB sample to 0.53gg(-1) of OPEFB in AFEX-pretreated OPEFB (i.e. almost a fourfold increase in sugar conversion), which enhances the economic value of OPEFB. A biohydrogen fermentability test of this hydrolysate was carried out using a locally isolated bacterium, Enterobacter sp. KBH6958. The biohydrogen yield after 72h of fermentation was 1.68mol H2 per mol sugar. Butyrate, ethanol, and acetate were the major metabolites.

Recent Advances in the Application of Inorganic Salt Pretreatment for Transforming Lignocellulosic Biomass into Reducing Sugars.

Currently, the transformation of lignocellulosic biomass into value-added products such as reducing sugars is garnering attention worldwide. However, efficient hydrolysis is usually hindered by the recalcitrant structure of the biomass. Many pretreatment technologies have been developed to overcome the recalcitrance of lignocellulose such that the components can be reutilized more effectively to enhance sugar recovery. Among all of the utilized pretreatment methods, inorganic salt pretreatment represents a more novel method and offers comparable sugar recovery with the potential for reducing costs. The use of inorganic salt also shows improved performance when it is integrated with other pretreatment technologies. Hence, this paper is aimed to provide a detailed overview of the current situation for lignocellulosic biomass and its physicochemical characteristics. Furthermore, this review discusses some recent studies using inorganic salt for pretreating biomass and the mechanisms involved during the process. Finally, some prospects and challenges using inorganic salt are highlighted.

Simplified feeding strategies for the fed-batch cultivation of Kluyveromyces lactis GG799 for enhanced recombinant xylanase production.

A xylanase gene (xyn2) from Trichoderma reesei ATCC 58350 was previously cloned and expressed in Kluyveromyces lactis GG799. The production of the recombinant xylanase was conducted in a developed medium with an optimised batch and with fed-batches that were processed with glucose. The glucose served as a carbon source for cell growth and as an inducer for xylanase production. In a 1-L batch system, a glucose concentration of 20 g L(-1) and 80 % dissolved oxygen were found to provide the best conditions for the tested ranges. A xylanase activity of 75.53 U mL(-1) was obtained. However, in the batch mode, glucose depletions reduced the synthesis of recombinant xylanase by K. lactis GG799. To maximise the production of xylanase, further optimisation was performed using exponential feeding. We investigated the effects of various nitrogen sources combined with the carbon to nitrogen (C/N) molar ratio on the production of xylanase. Of the various nitrogen sources, yeast extract was found to be the most useful for recombinant xylanase production. The highest xylanase production (110.13 U mL(-1)) was measured at a C/N ratio of 50.08. These conditions led to a 45.8 % increase in xylanase activity compared with the batch cultures. Interestingly, the further addition of 500 g L(-1) glucose led to a 6.2-fold increase (465.07 U mL(-1)) in recombinant xylanase activity. These findings, together with those of the exponential feeding strategy, indicate that the composition of the C/N molar ratio has a substantial impact on recombinant protein production in K. lactis.

Pollution control technologies for the treatment of palm oil mill effluent (POME) through end-of-pipe processes.

Palm oil production is one of the major industries in Malaysia and this country ranks one of the largest productions in the world. In Malaysia, the total production of crude palm oil in 2008 was 17,734,441 tonnes. However, the production of this amount of crude palm oil results in even larger amounts of palm oil mill effluent (POME). In the year 2008 alone, at least 44 million tonnes of POME was generated in Malaysia. Currently, the ponding system is the most common treatment method for POME but other processes such as aerobic and anaerobic digestion, physicochemical treatment and membrane filtration may also provide the palm oil industries with possible insights into the improvement of POME treatment processes. Generally, open ponding offers low capital and operating costs but this conventional method is becoming less attractive because the methane produced is wasted to the atmosphere and the system can not be certified for Carbon Emission Reduction trading. On the other hand, anaerobic digestion of POME provides the fastest payback of investment because the treatment enables biogas recovery for heat generation and treated effluent for land application. Lastly, it is proposed herewith that wastewater management based on the promotion of cleaner production and environmentally sound biotechnologies should be prioritized and included as a part of the POME management in Malaysia for attaining sustainable development. This paper thus discusses and compares state-of-the-art POME treatment methods as well as their individual performances.

A holistic approach to managing palm oil mill effluent (POME): biotechnological advances in the sustainable reuse of POME.

During the last century, a great deal of research and development as well as applications has been devoted to waste. These include waste minimization and treatment, the environmental assessment of waste, minimization of environmental impact, life cycle assessment and others. The major reason for such huge efforts is that waste generation constitutes one of the major environmental problems where production industries are concerned. Until now, an increasing pressure has been put on finding methods of reusing waste, for instance through cleaner production, thus mirroring rapid changes in environmental policies. The palm oil industry is one of the leading industries in Malaysia with a yearly production of more than 13 million tons of crude palm oil and plantations covering 11% of the Malaysian land area. However, the production of such amounts of crude palm oil result in even larger amounts of palm oil mill effluent (POME), estimated at nearly three times the quantity of crude palm oil. Normally, POME is treated using end-of-pipe processes, but it is worth considering the potential value of POME prior to its treatment through introduction of a cleaner production. It is envisaged that POME can be sustainably reused as a fermentation substrate in the production of various metabolites, fertilizers and animal feeds through biotechnological advances. The present paper thus discusses various technically feasible and economically beneficial means of transforming the POME into low or preferably high value added products.