Characterization of Amphora sp., a newly isolated diatom wild strain, potentially usable for biodiesel production.

Microalgae as feedstock for biofuel production have attracted serious consideration as an important sustainable source of energy. For biodiesel production with microalgae, a series of consecutive processes should be performed as selection of adequate microalgal strains, mass culture, cell harvesting, oil extraction and transesterification. The aim of this study was to investigate the growth and lipid accumulation of a new isolated marine microalgal strain by optimizing culture medium composition and applying different stressful culture conditions. Microalga CTM 20023 was isolated from the evaporating salt-ponds at Sfax, Tunisia, using serial-dilution technique from enriched cultures. Phylogenetic analysis based on SSU rDNA and rbcL-3P sequences attributed this isolate to a new species of the Amphora genus. This wild strain possesses rapid gravity sedimentation of 2.91 m h(-1), suitable for an easy and low-cost biomass harvest. The optimization of the composition of the culture medium through statistical experimental designs improved the specific growth rate of Amphora sp. from 0.149 to 0.262 day(-1) and increased its 15-day culture biomass production from 465 to 2200 mg L(-1) (dw) and its lipid content from 140 to 370 mg g(-1) (dw). Highest biomass productivity of 178 mg L(-1) day(-1) was achieved at the 10th day of culture. Highest lipid content of 530 mg g(-1) (dw) was obtained under phosphorus starvation and 64.34% of these lipids were saturated fatty acids. A first growth stage, in optimized condition, would thus offer the maximum productivity for an algal biomass feed stream, followed by second stressful stage for lipid accumulation, thus suitable for biodiesel production.

Optimisation of the critical medium components for better growth of Picochlorum sp. and the role of stressful environments for higher lipid production.

BACKGROUND: Coastal countries that suffer from a scarcity of water, such as Tunisia, have to cultivate marine microalgae on non-arable land in order to produce feedstock and overcome their demands of nutrition and energy. In this framework, a green microalga, CTM 20019, was isolated, identified as Picochlorum sp. and tested for its lipid production. RESULTS: The dry weight of Picochlorum sp. is composed of 163 g kg(-1) lipids, 225 g kg(-1) total sugars, 440 g kg(-1) proteins and 112 g kg(-1) ash rich in potassium, calcium, iron, magnesium and zinc. Gas chromatography-mass spectrometry analysis showed that the main fatty acids were palmitic acid (29%), linolenic acid (26.5%), linoleic acid (23.5%), hexadecatrienoic acid (11%) and hexadecadienoic acid (8.5%). As it is known that culture conditions greatly influence the composition of microalgae, the experiments were designed to optimise the composition of the medium in order to increase Picochlorum sp. growth from OD680nm = 0.53 to OD680nm = 2.2 and lipid accumulation from 163 g kg(-1) to 190 g kg(-1) . The highest lipid contents of 570 and 585 g kg(-1) were achieved under phosphate starvation and sodium carbonate supplementation, respectively. Under these conditions, the fatty acid profile is dominated by mono-unsaturated and polyunsaturated acids, and is therefore suitable for aqua-culture feeding. However, under high salinity, growth and lipid synthesis are inhibited, and the fatty acids are saturate, and the product is therefore suitable for biodiesel. CONCLUSION: This high lipid content rich in essential fatty acids, omega-6 and omega-3, endorses this wild strain of Picochlorum sp. as a promising feedstock for aqua-culture and human nutrition or for the production of biodiesel. © 2013 Society of Chemical Industry.

The saltern-derived Paludifilum halophilum DSM 102817T is a new high-yield ectoines producer in minimal medium and under salt stress conditions.

In the present study, the growth conditions and accumulation of ectoines (ectoine and hydroxyectoine) by Paludifilum halophilum DSM 102817T under salt stress conditions have been investigated. The productivity assay of this strain for ectoines revealed that the highest cellular content was reached in the minimal glucose sea water medium (SW-15) within 15% salinity. The addition of 0.1% (w/v) aspartic acid to the medium allowed an average of four times higher biomass production, and a dry mycelial biomass of 1.76 g L-1 was obtained after 6 days of growth in shake flasks at 40 °C and 200 rpm. Among the inorganic cations supplemented to the glucose SW-15 medium, the addition of 1 mM Fe2+ yielded the highest amount of mycelial biomass (3.45 g L-1) and total ectoines content (119 mg g-1), resulting in about 410 mg L-1 of products at the end of exponential growth phase. After 1 h of incubation in an osmotic downshock solution containing 2% NaCl, 70% of this content was released by the mycelium, and recovering cells maintained a high survival, with a maximal growth rate (µ max) of about 93% of the control population exposed to 15% NaCl. During growth at optimal salinity and temperature (15% NaCl and 40 °C), P. halophilum developed a compact and circular pellets that were easy to separate by simple decantation from both fermentation media and after hypoosmotic shock. Overall, the ectoines excreting P. halophilum could be a promising resource for ectoines production in a commercially valuable culture medium and at a large-scale fermentation process.

Anaerobic membrane reactor with phase separation for the treatment of cheese whey.

Two-phase anaerobic digestion of cheese whey was investigated in a system consisting of a stirred acidogenic reactor followed by a stirred methanogenic reactor, the latter being coupled to a membrane filtration system to enable removal of soluble effluent whilst retaining solids. The acidogenic reactor was operated at a hydraulic retention time (HRT) of one day, giving maximum acidification of 52.25% with up to 5 g/l volatile fatty acids, of which 63.7% was acetic acid and 24.7% was propionic acid. The methanogenic reactor received an organic load up to 19.78 g COD/ld, corresponding to a HRT of 4 days, at which 79% CODs and 83% BOD(5) removal efficiencies were obtained. Average removals of COD, BOD(5) and TSS in the two-phase anaerobic digestion process were 98.5%, 99% and 100%, respectively. The daily biogas production exceeded 10 times reactor volume and biogas methane content was greater than 70%.