Biodiesel-derived crude glycerol bioconversion to animal feed: a sustainable option for a biodiesel refinery

This study examined the potential of producing an edible fungus, Rhizopus microsporus var. oligosporus, on biodiesel-derived crude glycerol. Prolific fungal growth was observed with a fungal biomass yield of 0.83 ± 0.02 (g biomass increase/g initial biomass) under optimal cultivation conditions (e.g. nonsterile crude glycerol at a concentration of 75% (w/v) with nutrient supplementation and without pH control). The potential of utilizing front-end processed banagrass (Pennisetum purpureum) juice as a source of nutrients for crude glycerol fermentation was evaluated with a 2.3-fold improvement in the fungal biomass yield. The glycerol-derived fungal biomass showed high amounts of threonine, one of the main limiting amino acids in non-ruminant feeds. An inexpensive fungal protein has the potential to reduce meat product prices by lowering the production costs of animal feeds. The application of fungal technology thus provides a unique sustainable option for biodiesel refineries by providing an additional source of revenue from fungal products.     

Preliminary investigation on the production of fuels and bio-char from Chlamydomonas reinhardtii biomass residue after bio-hydrogen production

The aim of this work was to investigate the potential conversion of Chlamydomonas reinhardtii biomass harvested after hydrogen production. The spent algal biomass was converted into nitrogen-rich bio-char, biodiesel and pyrolysis oil (bio-oil). The yield of lipids (algal oil), obtained by solvent extraction, was 15 ± 2% w/w_dry-biomass. This oil was converted into biodiesel with a 8.7 ± 1% w/w_dry-biomass yield. The extraction residue was pyrolysed in a fixed bed reactor at 350 °C obtaining bio-char as the principal fraction (44 ± 1% w/w_dry-biomass) and 28 ± 2% w/w_dry-biomass of bio-oil. Pyrolysis fractions were characterized by elemental analysis, while the chemical composition of bio-oil was fully characterized by GC-MS, using various derivatization techniques. Energy outputs resulting from this approach were distributed in hydrogen (40%), biodiesel (12%) and pyrolysis fractions (48%), whereas bio-char was the largest fraction in terms of mass.     

Lipid production from Yarrowia lipolytica Po1g grown in sugarcane bagasse hydrolysate

This study investigated the possibility of utilizing detoxified sugarcane bagasse hydrolysate (DSCBH) as an alternative carbon source to culture Yarrowia lipolytica Po1g for microbial oil and biodiesel production. Sugarcane bagasse hydrolysis with 2.5% HCl resulted in maximum total sugar concentration (21.38 g/L) in which 13.59 g/L is xylose, 3.98 g/L is glucose, and 2.78 g/L is arabinose. Detoxification of SCBH by Ca(OH)₂ neutralization reduced the concentration of 5-hydroxymethylfurfural and furfural by 21.31% and 24.84%, respectively. Growth of Y. lipolytica Po1g in DSCBH with peptone as the nitrogen source gave maximum biomass concentration (11.42 g/L) compared to NH₄NO₃ (6.49 g/L). With peptone as the nitrogen source, DSCBH resulted in better biomass concentration than d-glucose (10.19 g/L), d-xylose (9.89 g/L) and NDSCBH (5.88 g/L). The maximum lipid content, lipid yield and lipid productivity of Y. lipolytica Po1g grown in DSCBH and peptone was 58.5%, 6.68 g/L and 1.76 g/L-day, respectively.     

Microbial oil production from rice straw hydrolysate by Trichosporon fermentans

Microbial oil production from sulphuric acid treated rice straw hydrolysate (SARSH) by Trichosporon fermentans was performed for the first time. Fermentation of SARSH without detoxification gave a poor lipid yield of 1.7 g/l, which was much lower than the result with glucose or xylose as the single carbon source (13.6 g/l or 9.9 g/l). The detoxification pretreatment, including overliming, concentration, and adsorption by Amberlite XAD-4 improved the fermentability of SARSH significantly by removing the inhibitors in SARSH. A total biomass of 28.6 g/l with a lipid content of 40.1% (corresponding to a lipid yield of 11.5 g/l) could be achieved after cultivation of T. fermentans on the detoxified SARSH for 8 days. Moreover, besides SARSH, T. fermentans could also utilize mannose, galactose, or cellobiose, in hydrolysates of other natural lignocellulosic materials as the single carbon source to grow and accumulate lipid with a high yield (at least 10.4 g/l). Hence, it is a promising strain for microbial oil production and thus biodiesel preparation from agro-industrial residues, especially lignocellulosic materials.     

Continuous culture of the microalgae Schizochytrium limacinum on biodiesel-derived crude glycerol for producing docosahexaenoic acid

Crude glycerol is a major byproduct of the biodiesel industry; previous research has proved the feasibility of producing docosahexaenoic acid (DHA, 22:6 n − 3) through fermentation of the algae Schizochytrium limacinum on crude glycerol. The objective of this work is to investigate the cell growth kinetics, substrate utilization efficiency, and DHA production of the algae through a continuous culture. Steady-state biomass yield, biomass productivity, growth yield on glycerol, specific glycerol consumption rate, and fatty acid composition were investigated within the range of dilution rate (D) from 0.2 to 0.6 day⁻¹, and the range of feed crude glycerol concentration (S₀) from 15 to 120 g/L. The maximum specific growth rate was determined as 0.692 day⁻¹. The cells had a true growth yield of 0.283 g/g but with a relatively high maintenance coefficient (0.2216 day⁻¹). The highest biomass productivity of 3.88 g/L-day was obtained at D = 0.3 day⁻¹ and S₀ = 60 g/L, while the highest DHA productivity (0.52 g/L-day) was obtained at D = 0.3 day⁻¹ and S₀ = 90 g/L due to the higher DHA content at S₀ = 90 g/L. The biomass and DHA productivity of the continuous culture was comparable to those of batch culture, while lower than the fed-batch culture, mainly because of the lower DHA content obtained by the continuous culture. Overall, the results show that continuous culture is a powerful tool to investigate the cell growth kinetics and physiological behaviors of the algae growing on biodiesel-derived crude glycerol.     

Integration of algae cultivation as biodiesel production feedstock with municipal wastewater treatment: strains screening and significance evaluation of environmental factors

The objectives of this study are to find the robust strains for the centrate cultivation system and to evaluate the effect of environmental factors including light intensity, light–dark cycle, and exogenous CO₂ concentration on biomass accumulation, wastewater nutrient removal and biodiesel production. The results showed that all 14 algae strains from the genus of Chlorella, Haematococcus, Scenedesmus, Chlamydomonas, and Chloroccum were able to grow on centrate. The highest net biomass accumulation (2.01 g/L) was observed with Chlorella kessleri followed by Chlorella protothecoides (1.31 g/L), and both of them were proved to be capable of mixotrophic growth when cultivated on centrate. Environmental factors had significant effect on algal biomass accumulation, wastewater nutrients removal and biodiesel production. Higher light intensity and exogenous CO₂ concentration with longer lighting period promote biomass accumulation, biodiesel production, as well as the removal of chemical oxygen demand and nitrogen, while, lower exogenous CO₂ concentration promotes phosphorus removal.     

Growth characteristics of Botryococcus braunii 765 under high CO2 concentration in photobioreactor

To understand the potential of cultivating Botryococcus braunii with flue gas (normally containing high CO₂) for biofuel production, growth characteristics of B. braunii 765 with 2-20% CO₂ aeration were investigated. The results showed that the strain could grow well without any obvious inhibition under all tested CO₂ concentrations with an aeration rate of 0.2 vvm, even without any culture pH adjustment (ranged from 6.0 to 8.0). The maximum biomass among all conditions was 2.31 g L⁻¹ on 25th day at 20% CO₂. Hydrocarbon content and algal colony size increased with the increase of CO₂ concentration. A negative correlation between algal biomass and culture total phosphorus was observed (from −0.828 to −0.911, P < 0.01). Additionally, 2% sodium hypochlorite solution was used for photobioreactor sterilization to cultivate B. braunii.     

Fed-batch fermentation of Tuber melanosporum for the hyperproduction of mycelia and bioactive Tuber polysaccharides

For the first time, a fed-batch fermentation process of Tuber melanosporum was developed for the efficient production of bioactive mycelia and Tuber polysaccharides. Each 1.67 g/L of peptone and 8.33 g/L of yeast extract were added on day 3, 6, and 9, respectively, and sucrose was fed to maintain its concentration around 35–5 g/L when its residual level decreased to 10–5 g/L. Then, the maximal biomass, the production of extracellular polysaccharides (EPS) and intracellular polysaccharides (IPS) reached 53.72 ± 2.57 g DW/L, 7.09 ± 0.62 and 4.43 ± 0.21 g/L, respectively. Compared with the batch culture conducted in the enriched medium, the biomass, the production of EPS and IPS were enhanced by 55.8%, 222.3% and 103.2%, respectively. Not only the cell density but also the production of EPS and IPS were the highest ever reported in truffle fermentation, and the biomass was also the highest as ever reported in mushroom fermentation.     

Isomerization and biodegradation of beta-cypermethrin by Pseudomonas aeruginosa CH7 with biosurfactant production

Pseudomonas aeruginosa CH7, isolated from activated sludge, was able not only to isomerize and degrade beta-cypermethrin but also to utilize it as the sole source of carbon and energy for growth and produce biosurfactant. The strain effectively degraded beta-cypermethrin with inocula biomass of 0.1-0.2 g L⁻¹ at 25-35 °C, pH 6-9, and a final concentration of beta-cypermethrin 25-900 mg L⁻¹. Via response surface methodology analysis, we found the optimal condition was 29.4 °C, pH 7.0, and inocula biomass of 0.15 g L⁻¹; under these conditions, about 90% of the beta-cypermethrin could be degraded within 12 days. Noticeably, biosurfactant was detected in the MSM culture of strain CH7, suggesting that the biosurfactant (rhamnolipid) could potentially enhance the degradation of beta-cypermethrin by promoting the dissolution, adsorption, and absorption of the hydrophobic compounds. Therefore, CH7 may serve as a promising strain in the bioremediation of wastewater and soil polluted by beta-cypermethrin.     

Preparation of cross-linked lipase-coated micro-crystals for biodiesel production from waste cooking oil

A dual modification procedure composed of cross-linking and protein coating with K₂SO₄ was employed to modify Geotrichum sp. lipase for catalyzing biodiesel production from waste cooking oil. Compared to single modification of protein coating with K₂SO₄, the dual modification of cross-linking and lipase coating improved catalytic properties in terms of thermostable stability, organic solvent tolerance, pH stability and operational stability in biodiesel production process, although biodiesel yield and initial reaction rate for CLPCMCs were not improved. After five successive batch reactions, CLPCMCs could still maintain 80% of relative biodiesel yield. CLPCMCs retained 64% of relative biodiesel yield after incubation in a pH range of 4-6 for 4 h, and 85% of relative biodiesel yield after incubation in a range of 45-50 °C for 4 h. CLPCMCs still maintained 83% of relative biodiesel yield after both treated in polar organic solvent and non-polar organic solvent for 4 h.     

Comparative lipid profiling of two endophytic fungal isolates--Colletotrichum sp. and Alternaria sp. having potential utilities as biodiesel feedstock

Lipid accumulation abilities of two endophytic fungal isolates - Colletotrichum sp. and Alternaria sp. grown under optimum and nutrient-stress conditions were investigated and compared. Significant variations in lipid contents, ranging from 30% to 58% of their dry biomass were found in liquid culture using various carbon sources. Since, >50% of the total lipid was estimated to be neutral lipid for both the fungal species, predicted biodiesel properties were theoretically calculated based upon the determined fatty acid profiles; and the values were found to be comparable to those of commonly used plant oils for biodiesel production. The two endophytes grew successfully on the combined rice straw and wheat bran as substrate that was degraded by their secretory enzymes including cellulase [1.21-2.51 FPU/g dry substrate (gds)] in solid state fermentation and produced substantial amount of lipid (60.32-84.30 mg/gds). Our study highlights the potential utilities of these two novel endophytic fungi as biodiesel feedstock.     

On the nitrogen and phosphorus removal in algal photobioreactors

This study shows results of nitrogen and phosphorus removal by microalgae (tertiary treatment) in a prototype of tubular photobioreactor tested under controlled and uncontrolled conditions. The wastewater was the supernatant coming from a secondary settler of a municipal wastewater activated sludge treatment plant without nitrification and denitrification units. The algal biomass was directly selected from the supernatant and it was principally composed of genus Scenedesmus (autochthonous algae). All the experiments evaluated both nitrogen and phosphorus removal and biomass and lipid production. A satisfactory nutrients removal - about 99.9% for the nitrogen and phosphorus - and a specific biomass productivity of 0.25 g/l d have been obtained in the indoor photobioreactor; less satisfactory results have been reached in the outdoor photobioreactor because of ambient condition instability and limiting nutrients concentration.     

Increased lipid production of the marine oleaginous microalgae Isochrysis zhangjiangensis (Chrysophyta) by nitrogen supplement

Effects of nitrate feeding on the cell growth and lipid accumulation of marine microalgae Isochrysis zhangjiangensis were investigated. When nitrate was supplied at interval of 24 h, instead of 72 h, a high lipid content of 40.9% and a biomass density of 3.1 g L⁻¹ were obtained. To confirm whether I. zhangjiangensis accumulates lipid during nitrogen-repletion, a two-stage cultivation method was applied. This algal strain had a high lipid content during sustained nitrate addition and showed a high carbohydrate content under nitrate-depletion conditions. These results revealed that this algal strain can accumulate lipids under nitrogen-repletion conditions and accumulate carbohydrate under nitrogen-depletion conditions. When cultured in an extremely high nitrate concentration, 9 g L⁻¹ at 24 h intervals, the growth of algal cells was suppressed, but the highest lipid content of 53% was attained. This special characteristic of lipid accumulation makes I. zhangjiangensis an ideal candidate for producing biodiesel using N-rich wastewater.     

Assessment of carotenoid production by Dunaliella salina in different culture systems and operation regimes

The effect of operation regime and culture system on carotenoid productivity by the halotolerant alga Dunaliella salina has been analyzed. Operation strategies tested included batch and semi continuous regime, as well as a two-stage approach run simultaneously in both, open tanks and closed reactor. The best results were obtained with the closed tubular photobioreactor. The highest carotenoid production (328.8 mg carotenoid l⁻¹ culture per month) was achieved with this culture system operated following the two-stage strategy. Also, closed tubular photobioreactor provided the highest carotenoid contents (10% of dry weight) in Dunaliella biomass and β-carotene abundance (90% of total carotenoids) as well as the highest 9-cis to all-trans β-carotene isomer ratio (1.5 at sunrise).     

Influence of inoculum density and aeration volume on biomass and bioactive compound production in bulb-type bubble bioreactor cultures of Eleutherococcus koreanum Nakai

This study deals with the effects of initial inoculum density and aeration volume on biomass and bioactive compound production in adventitious roots of Eleutherococcus koreanum Nakai in bulb-type bubble bioreactors (3-L capacity). While the fresh and dry weights of the roots increased with increasing inoculum density, the highest percentage dry weight and accumulation of total target compounds (eleutheroside B and E, chlorogenic acid, total phenolics, and flavonoids) were noted at an inoculum density of 5.0 g L⁻¹. Poor aeration volume (0.05 vvm) stunted root growth, and high aeration volume (0.4 vvm) caused physiological disorders. Moreover, an inoculum density of 5.0 g L⁻¹ and an aeration volume of 0.1 vvm resulted in the highest concentration of total target compounds and least root death. Such optimization of culture conditions will be beneficial for the large-scale production of E. koreanum biomass and bioactive compounds.     

Optimization of culture conditions for production of yeast biomass using bamboo wastewater by response surface methodology

Response surface methodology (RSM) was applied to optimize culture conditions for the growth of Candida utilis with bamboo wastewater. A significant influence of initial pH, fermentation time and yeast extract on biomass of C. utilis was evaluated by Plackett–Burman design (PBD). These factors were further optimized using a central composite design (CCD) and RSM. A combination of initial pH 6.1, fermentation time 69 h and yeast extract 1.17 g/L was optimum for maximum biomass of C. utilis. A 1.7-fold enhancement of biomass of C. utilis was gained after optimization in shake-flask cultivation. The biomass of C. utilis reached 19.17 g/L in 3 L fermentor.     

Performance of a submerged membrane bioreactor for the aerobic treatment of abattoir wastewater

The performance of a submerged membrane bioreactor (SMBR) has been investigated for abattoir wastewater (AW) treatment. The chemical oxygen demand (COD) of permeate has not exceeded 25 mg L⁻¹ providing an average COD removal of 98%. Microbiological analysis showed that the SMBR has allowed a complete removal of fecal coliforms, Listeria and Salmonella. A significant reduction in the excess biomass production was also observed. In fact, the yield of biomass production (Yobs) ranged between 0 and 0.106 g suspended solids/g COD removed.The study of the dynamic of bacterial communities using the single strand conformation polymorphism (SSCP) method showed a significant change in the population structure and revealed a correlation between the sludge production yield and the bacterial communities.     

Enhancement of cell growth rate by light irradiation in the cultivation of Rhodotorula glutinis

A yeast, Rhodotorula glutinis, is regarded as a potential microbial oil producer, due to its high lipid content. The flask results of this study indicated that irradiation could increase the growth of R. glutinis compared to that of a batch without irradiation. Further 5-l fermenter results confirmed that irradiation could greatly enhance the cells’ growth rate and total lipid productivity. The maximum lipid productivity obtained in the fed-batch operation with 3 LED (light emitting diode) lamps was 0.39 g/l h as compared to 0.34 g/l h in the batch with 3 LED lamps and 0.19 g/l h in the batch without irradiation. Conclusively, the irradiation could significantly increase the cells’ growth rate, which, in turn, could be applied to the commercialized production of biodiesel from single cell oils.     

Differential lipid and fatty acid profiles of photoautotrophic and heterotrophic Chlorella zofingiensis: Assessment of algal oils for biodiesel production

The objective of this study was to document and compare the lipid class and fatty acid composition of the green microalga Chlorella zofingiensis cultivated under photoautotrophic and heterotrophic conditions. Compared with photoautotrophic cells, a 900% increase in lipid yield was achieved in heterotrophic cells fed with 30 g L⁻¹ of glucose. Furthermore heterotrophic cells accumulated predominantly neutral lipids (NL) that accounted for 79.5% of total lipids with 88.7% being triacylglycerol (TAG); whereas photoautotrophic cells contained mainly the membrane lipids glycolipids (GL) and phospholipids (PL). Together with the much higher content of oleic acid (C18:1) (35.2% of total fatty acids), oils from heterotrophic C. zofingiensis appear to be more feasible for biodiesel production. Our study highlights the possibility of using heterotrophic algae for producing high quality biodiesel.