• Energy Research

Abstract The dates production is usually accompanied by considerable loss of fruit byproducts. The chemical analysis showed that ‘Deglet Nour’ discarded flesh is rich in soluble sugars (79.8% ± 0.8%) and fibers (12.3% ± 0.4%). A processing approach was implemented to permit the production of biohydrogen from the flesh and biogas from the crude fiber fraction after soluble sugars extraction. This approach showed interesting results since the obtained biochemical hydrogen potential and the maximum methane yield were 292 mL H2/gVS initial and 235 mL CH4/gVS fibers respectively. Parallelly, the “hot water” soluble sugar fraction (date syrup) was of interest for agro-alimentary applications and showed a high sucrose, glucose and fructose content of 33.5%, 11.8% and 13.17% respectively. This study presents a proof of concept allowing an efficient sustainable energetic conversion of the date by-products biomass to biohydrogen via dark fermentation or to soluble sugars fraction and biogas via a biorefinery approach.

The green macroalgal biomass corresponds to an emerging and promising biofuel feedstock. Their biological pretreatment and energetic conversion to biomethane were investigated and the enhancement of biogas production using the solid-state fermentation (SSF) as an eco-friendly innovative pretreatment of Ulva sp. was precisely assessed. Compared to conventional acid and alkali pretreatments, the highest methane potential of 153±3mLCH4g−1VS with an anaerobic biodegradability of 57% was obtained using SSF pretreatment with a locally isolated Aspergillus fumigatus SL1 strain. It was 132±2mLCH4g−1VS for raw Ulva sp. with biodegradability of 49%. Acid pretreatment with 4% HCl at 150°C had a negative effect on Ulva sp.'s methane potential while alkali pretreatment with 4% NaOH at 20°C showed a significant effect. The proposed SSF-based pretreatment enhanced therefore biogas production of 21% and permitted an eco-friendly valorization of large amounts of abundant macroalgae.

This work aimed to characterize two native microalgal strains newly isolated from South Mediterranean areas and identified as Chlorella sorokiniana ES3 and Neochloris sp. AM2. The growth properties and biochemical composition of these microalgae were evaluated in different culture media (Algal, BG-11, f/2, and Conway). Among the tested media, nitrate- and phosphate-rich Algal medium provided the maximum biomass productivities (85.5 and 111.5 mg l(-1) day(-1) for C. sorokiniana and Neochloris sp., respectively), while the nitrate- and phosphate-deficient f/2 medium resulted in the highest lipid productivities (24.1 and 35.8 mg l(-1) day(-1) for C. sorokiniana and Neochloris sp., respectively). The physiological state of both microalgae was investigated under different light and temperature levels using the pulse amplitude-modulated fluorometry. The better photosynthetic efficiency of C. sorokiniana was obtained at 23 °C with a light saturation of 156 μE m(-2) s(-1), while that of Neochloris sp. was achieved at 15 °C with a light saturation of 151 μE m(-2) s(-1). The analysis of fatty acid profile and biodiesel parameters revealed that C. sorokiniana, cultivated in Algal and f/2 media, can be considered as a suitable candidate for high-quality biodiesel production.

Abstract Microalgae, which are promising candidates for biodiesel production, possess a robust cell wall which prevents the release of intracellular lipids in the medium. The breaking of the algal cell wall for lipid releasing can be energy-intensive. The direct or in situ supercritical transesterification method is considered to have the potential to disrupt the rigid algal cell wall and convert the extracted lipids into biodiesel in only one step, thus reducing significantly the process energy consumption. In this work, wet (∼80 wt.% moisture) and dry unwashed marine microalgae Nannochloropsis gaditana were used directly to synthesize biodiesel in a single-step process by direct transesterification with no added catalysts using supercritical methanol. The effect of main process parameters (methanol to dry algae ratio, reaction time and temperature) was studied. Initially, the methanol to dry algae ratio (6:1–12:1 vol./wt.) was investigated and then the synergic effect between reaction time (10–50 min) and temperature (245–290 °C) was studied using a factorial experimental design. In addition, the effect of the supercritical process on the structure of the algal cell walls was studied by scanning electron microscopy observations. Maximum biodiesel yields of ∼0.46 and ∼0.48 g/g of lipids were reached from wet and dry unwashed algal biomass, respectively, at 255–265 °C, 50 min reaction time, and using a methanol to dry algae ratio of 10:1 (vol./wt.). The highest biodiesel yields obtained from dry microalgae were only between 2% and 9% higher than those reached from wet microalgae, indicating that a high content of water in the unwashed algal biomass did not significantly affect the supercritical process.

Green macroalgae are an abundant and undervalued biomass with a specific cell wall structure. In this context, different pretreatments, namely ethanol organosolv (Org), alkaline, liquid hot water (LHW), and ionic liquid (IL) pretreatments, were applied to the green macroalgae Ulva lactuca biomass and then evaluated. Their effects on chemical composition, biomass crystallinity, enzymatic digestibility, and theoretical ethanol potential were studied. The chemical composition analysis showed that the Org and LHW pretreatments allowed the highest glucan recovery (80.8 ± 3.6 and 62.9 ± 4.4 g/100 g DM, respectively) with ulvan (80.0 and 99.1%) and hemicellulose (55.0 and 42.3%) removal. These findings were in agreement with both thermogravimetric analysis and scanning electron microscopy results that confirm significant structural changes of the pretreated biomasses. It was found that the employed pretreatments did not significantly affect the cellulose crystallinity; however, they both increased the whole crystallinity and the enzymatic digestibility. This later reached 97.5% in the case of LHW pretreatment. Our results showed high efficiency saccharification of Ulva lactuca biomass that will constitute the key step of the implementation of a biorefinery process.

Stranded green macroalgae represents an important and renewable biomass that remains under valorized despite the numerous environmental problems generated by their accumulation in coastal regions. This work describes the isolation of a filamentous thermophile fungus identified as Aspergillus terreus JL1 that produces an efficient cellulolytic activity for green macroalgae saccharification. The characterization of the endoglucanase activity obtained after submerged fermentation showed a differential induction depending on the carbon source used with a unique isoform released when Ulva lactuca was used as inducer. The crude extract obtained hydrolyzed efficiently the untreated algal biomass (70.5%) compared to other cellulolytic extracts. The unique endoglucanase released was then purified to homogeneity (Yield: 49.6%; Specific activity: 30.1 U/mg; Purification fold: 4.36) and characterized biochemically. Its peptidic sequence was then determined and showed its belonging to the GH12. The described enzyme represents a promising biotechnological tool for algal biomass conversion.

Abstract An innovative integrated biorefinery approach using the green macroalgae Chaetomorpha linum was investigated in the present study for the co-production of bioethanol and biogas. Among three pretreatments of C. linum biomass, consisting of acidic, neutral and alkali ones, 3% NaOH pretreatment gave the best result in terms of thallus disintegration, biomass recovery and enzymatic digestibility as demonstrated by scanning electron microscopy and saccharification tests. The hydrolysis of C. linum feedstock with a crude specific enzyme preparation, locally produced from fermentation of Aspergillus awamori, at 45 °C, pH 5 for 30 h gave the maximum yield of fermentable sugar of 0.22 ± 0.02 g/g dry substrate. An ethanol yield of 0.41 g/g reducing sugar corresponding to about 0.093 g/g pretreated algae was obtained after alcoholic fermentation by Saccharomyces cerevisiae. In the integrated proposed process, mycelium issued from the fungal fermentation, liquid issued from alkali pretreatment, residual from the non-hydrolysable biomass and all effluents and co-products represent a heterogeneous substrate that feed an anaerobic digester for biogas production. GC-analysis of this later showed that the biomethane yield reached 0.26 ± 0.045 L/gVS. This study presents therefore an eco-friendly biorefining process, which efficiently coproduce bioethanol and biomethane and generate only a single waste (0.3 ± 0.01 g/g) allowing an almost complete conversion of the algal biomass.