Enhanced biovalorization of palm biomass wastes as biodiesel feedstocks through integrated solid-state and submerged fermentations by fungal co-cultures.

Palm empty fruit bunches (EFB) were valorized into fungal lipids by oleaginous fungus Aspergillus tubingensis TSIP9 under solid-state fermentation (SSF) and submerged fermentation (SmF). An integrated SSF-SmF process increased lipid production from 116.2 ± 0.1 mg/g-EFB under SSF and 60.1 ± 0.2 under SmF up to 124.9 ± 0.5 mg/g-EFB, possibly due to the combined benefits of dispersed mycelia forming during SSF and better mass transfer during SmF. As A. tubingensis lacks sufficient ß-glucosidase, it was co-cultured with high ß-glucosidase-producing Trichoderma reesei QM 9414. The co-cultures improved overall lipid yields likely due to synergistic interaction of the two fungi. After inoculum size was optimized and the co-cultures were performed in bioreactors, the lipid yield was increased up to 205.1 ± 1.1 mg/g-EFB. The fatty acid composition of fungal lipids indicated their potential use as biodiesel feedstocks. The fungal fermentation of EFB also provided cellulose pulp residues. These strategies could be practical options for low-cost biovalorization of biomass wastes.

Solid-state fermentation of Saba banana peel for pigment production by Monascus purpureus.

Eco-friendly natural pigment demand has ever-increasing popularity due to health and environmental concerns. In this context, the aim of this study was to evaluate the feasibility use of Saba banana peel as low-cost fermentable substrate for the production of pigments, xylanase and cellulase enzymes by Monascus purpureus. Among the strains tested, M. purpureus TISTR 3385 produced pigments better and had higher enzyme activities. Under the optimal pigment-producing conditions at the initial moisture content of 40% and initial pH of 6.0, the pigments comprising yellow, orange, and red produced by the fungi were achieved in the range of 0.40-0.93 UA/g/day. The maximum xylanase and cellulase activities of 8.92 ± 0.46 U/g and 4.72 ± 0.04 U/g were also obtained, respectively. More importantly, solid-state fermentation of non-sterile peel could be achieved without sacrificing the production of the pigments and both enzymes. These indicated the potential use of the peel as fermentable feedstock for pigment production by the fungi and an environmental-friendly approach for sustainable waste management and industrial pigment and enzyme application.

Potential use of industrial by-products as promising feedstock for microbial lipid and lipase production and direct transesterification of wet yeast into biodiesel by lipase and acid catalysts.

This work attempted the conversion of crude glycerol to lipid and lipase by Yarrowia lipolytica and the direct transesterification of wet yeast by its lipase into biodiesel via response surface methodology to enhance the cost-effectiveness of biodiesel production from the lipids. The yeast grew better and accumulated a high amount of lipids on the waste combined with fish waste hydrolysate, but only exhibited high lipase activity on the waste supplemented with surfactants (i.e., gum Arabic, Tween 20, Tween 80). However, the combination of both wastes and Tween 80 further improved growth, lipid productivity, and lipase activity. More importantly, lipase-direct transesterification under optimal conditions (wet cell concentration of 17.97 mg-DCW, methanol loading of 8.21 µL, and hexane loading of 10.26 µL) followed by acid-catalyst transesterification (0.4 M H2SO4), offered high FAME yields (>90%), showing the efficiency of the process when applied for the industrialization of biodiesel production from microbial lipids.

Consolidated bioprocesses for efficient bioconversion of palm biomass wastes into biodiesel feedstocks by oleaginous fungi and yeasts.

Consolidated bioprocesses for bioconversion of lignocellulosic biomass into biodiesel feedstocks were developed. Palm empty fruit bunch (EFB) was biologically pretreated coupling with fungal lipid production (121.4 ± 2.7 mg/g-EFB) by lignocellulolytic oleaginous fungi prior to lipid production by oleaginous yeasts. In subsequent separate hydrolysis and fermentation (SHF) of fungal pretreated EFB (FPEFB), the oleaginous yeast with the maximum lipid yield of 37.0 ± 0.1 mg/g-FPEFB was screened. While a higher lipid yield of 47.9 ± 1.5 mg/g-FPEFB was achieved in simultaneous saccharification and fermentation (SSF) with less enzyme requirement. Fed-batch SSF of non-sterile FPEFB was proven as a practical and efficient strategy to increase lipid yield up to 53.4 ± 0.5 mg/g-FPEFB. Total lipid yield by both fungi and yeast was 165.0 ± 4.4 mg/g-EFB. Interestingly, the consolidated bioprocesses of enzyme and lipid production also achieved comparable total lipid yield of 149.3 ± 6.6 mg/g-EFB. These strategies may contribute greatly to cost-effective and sustainable bioconversion of lignocellulosic biomass into biodiesel feedstocks.

Metagenomic insights into bioaugmentation and biovalorization of oily industrial wastes by lipolytic oleaginous yeast Yarrowia lipolytica during successive batch fermentation.

The lipolytic oleaginous yeast Yarrowia lipolytica was used in the bioaugmentation and biovalorization of oily industrial wastes during successive-batch fermentation. Five cycles of nonsterile successive batch fermentation with 70% medium replacement achieved the highest oil removal of 68.1 ± 5.60% and produced biomass and lipid yields of 0.213 ± 0.07 g/g-COD and 146.2 ± 46.5 mg/g-COD, respectively. The cell-bound lipase activity observed in the system was 170.74 ± 32 U/L. The auto-flocculation efficiency of the biomass was >90% within 60 Min. The microbial community changes between Y. lipolytica and indigenous microorganisms were monitored by metagenomic next-generation sequencing of internal transcribed spacer rDNA regions for yeasts and 16S rRNA gene for bacteria. Ylipolytica lipolytica was retained in the consortium together with other indigenous strains until the fifth cycle. Other minor oleaginous yeasts such as Kodamaea ohmeri and Candida tropicalis as well as polyhydroxyalkanoate-accumulating bacteria were found and are likely to have participated in lipid production. This study has shown the robustness of Y. lipolytica in nonsterile successive batch fermentation and its use could contribute greatly to the practical valorization of industrial wastes for lipids and lipases.

Valorization of palm biomass wastes for biodiesel feedstock and clean solid biofuel through non-sterile repeated solid-state fermentation.

Palm biomass wastes are currently considered as promising solid biofuels. However, their high potassium content leads to formation of slag in combustion chambers and causes frequent power-plant shutdowns for maintenance. Therefore, this study aimed to develop a low-cost practical biological pretreatment for these wastes. Oleaginous fungi Aspergillus tubingensis TSIP9, which originates from palm wastes, was used to pretreat biomass wastes and simultaneously produce oils through non-sterile solid state fermentation (SoSF). The operating conditions were optimized through response surface methodology. The fungi could grow and produce oils with good biodiesel fuel properties. After SoSF, potassium content in biomass wastes was reduced by 90% and cellulose content increased to >57%, making it suitable as clean solid biofuel. Repeated-SoSF with 90% substrate replacement was highly effective in continuously pretreating biomass wastes and producing fungal oils. This study demonstrates the cost-effective and environmentally friendly process for production of clean renewable energy through zero-waste strategy.

Mitigation of carbon dioxide by oleaginous microalgae for lipids and pigments production: Effect of light illumination and carbon dioxide feeding strategies.

Oleaginous microalgae Nannochloropsis sp. was selected as potential strain for CO2 mitigation into lipids and pigments. The synergistic effects of light intensity and photoperiod were evaluated to provide the adequate light energy for this strain. The saturation light intensity was 60µmol·photon·m(-2)s(-1). With full illumination, the biomass obtained was 0.850±0.16g·L(-1) with a lipid content of 44.7±1.2%. The pigments content increased with increasing light energy supply. Three main operating factors including initial cell concentration, CO2 content and gas flow rate were optimized through Response Surface Methodology. The feedings with low CO2 content at high gas flow rate gave the maximum biomass but with low lipid content. After optimization, the biomass and lipid production were increased up to 1.30±0.103g·L(-1) and 0.515±0.010g·L(-1), respectively. The CO2 fixation rate was as high as 0.729±0.04g·L(-1)d(-1). The fatty acids of Nannochloropsis sp. lipids were mainly C16-C18 indicating its potential use as biodiesel feedstocks.

Lipid Production from Hemicellulose and Holocellulose Hydrolysate of Palm Empty Fruit Bunches by Newly Isolated Oleaginous Yeasts.

Palm empty fruit bunches (EFBs) are abundant lignocellulosic wastes from palm oil mills. They are potential sources of sugars which can be converted to microbial lipids by oleaginous yeasts. To produce sugars from EFB, two-step and one-step hydrolysis reactions were performed. In the first step, the use of diluted sulfuric acid (0.5 % w/v) hydrolyzed hemicelluloses and released mainly pentoses, and in the second step of hydrolysis of residual pulp using 2.5 % (w/v), sulfuric acid released more hexoses. The use of 2.5 % (w/v) sulfuric acid in one-step hydrolysis of holocelluloses released the highest amount of sugars (38.3 g/L), but it also produced high concentration of potential inhibitors (>1 g/L). Three oleaginous yeasts, Rhodotorula mucilaginosa, Kluyveromyces marxianus, and Candida tropicalis, were isolated and screened for their ability to convert EFB hydrolysates into lipids. These yeasts grew well and produced lipids from EFB hemicellulose and holocellulose hydrolysate after potential inhibitors were removed. This study shows that EFB can be used for lipid production.

Industrial wastes as a promising renewable source for production of microbial lipid and direct transesterification of the lipid into biodiesel.

Two strategies of converting industrial wastes to microbial lipid and direct transesterification of obtained lipid into biodiesel were attempted. Several oleaginous yeasts were cultivated on industrial wastes. The yeasts grew well on the wastes with low C/N ratio (i.e. serum latex) but accumulated high lipid content only when the wastes had a high C/N ratio (i.e. palm oil mill effluent and crude glycerol). The yeast lipids have similar fatty acid composition to that of plant oil indicating their potential use as biodiesel feedstocks. The combination of these wastes and two-phase cultivation for cell growth and lipid accumulation improved lipid productivity of the selected yeast. The direct transesterification process that eliminates cell drying and lipid extraction steps, gave comparable yield of biodiesel (fatty acid methyl ester >70% within 1h) to that of conventional method. These two successful strategies may contribute greatly to industrializing oil production from microbes and industrial wastes.

Industrial waste utilization for low-cost production of raw material oil through microbial fermentation.

In view of ever-growing demand of biodiesel, there is an urgent need to look for inexpensive and promising renewable raw material oils for its production. In this context, the aim of this study was to evaluate the potential use of industrial wastes for low-cost production of oils through microbial fermentation. Among the strains tested, Yarrowia lipolytica grew best and produced highest lipid when grown on decanter effluent from palm oil mill. When crude glycerol by-product from a biodiesel plant was added into the effluent as a co-substrate, Y. lipolytica produced a higher biomass of 3.21 g/L and a higher amount of lipid of 2.21 g/L which was 68 % of the dry weight. The scale up and process improvement in a 5-L bioreactor increased the biomass and lipid up to 5.53 and 2.81 g/L, respectively. A semi-continuous mode of operation was an effective mode for biomass enhancement while a fed-batch mode was effective for lipid enhancement. These yeast lipids have potential to be used as biodiesel feedstocks because of their similar fatty acid composition to that of plant oil.