Xavier Briand

Anaerobic digestion of Ulva sp. 1. Relationship between Ulva composition and methanisation

Ulva often represents the main component of mass algal growths, and its composition and degradability make it a relatively good methanisation substrate. In ‘green tides’ Ulva sp. from Brittany, the low content oflignin-type components (polyphloroglucinols: 1.3% dry weight), and the large hemicellulosic fraction (9% dry weight) favour the substrates accessibility to enzymes. Anaerobic degradation with a batch orcompletely stirred system is technically possible. However, the methane yield reached only 0.20 m3 kg−1 volatile solids and the epuration rate 50% volatile solids in experiments in batch or completely stirred reactors. More generally, methanisation comes up against various practical obstacles: seasonal growth of Ulva, low density of alga in suspension for loading the digester, high S concentration leading to the production of a biogas with a high H2S content, and, finally, the existence of a refractory or slowly degradable part, which requires a compromise between productivity and biological yield.

Ulvan, a Sulfated Polysaccharide from Green Algae, Activates Plant Immunity through the Jasmonic Acid Signaling Pathway

The industrial use of elicitors as alternative tools for disease control needs the identification of abundant sources of them. We report on an elicitor obtained from the green algae Ulva spp. A fraction containing most exclusively the sulfated polysaccharide known as ulvan-induced expression of a GUS gene placed under the control of a lipoxygenase gene promoter. Gene expression profiling was performed upon ulvan treatments on Medicago truncatula and compared to phytohormone effects. Ulvan induced a gene expression signature similar to that observed upon methyl jasmonate treatment (MeJA). Involvement of jasmonic acid (JA) in ulvan response was confirmed by detecting induction of protease inhibitory activity and by hormonal profiling of JA, salicylic acid (SA) and abscisic acid (ABA). Ulvan activity on the hormonal pathway was further consolidated by using Arabidopsis hormonal mutants. Altogether, our results demonstrate that green algae are a potential reservoir of ulvan elicitor which acts through the JA pathway.

Marine bioactive substances (IPA extract) improve foliar ion uptake and water stress tolerance in potted Vitis vinifera plants

The effect of marine bioactive substances (IPA extract) on K + and Ca 2+ fluxes and water stress tole- rance was evaluated on potted Vitis vinifera plantlets. Different foliar treatments were compared during the experiment: a control treatment (distilled water), a pure fertilizer treatment (9-5-4 at 2%), and a marine bioac - tive substances (IPA extract, supplied by BiotechMarine, Roullier Group, Pontrieux, France) treatment added to a fertilizer (0.1% solution of IPA extract with distilled water and 9-5-4 at 2%). Ion fluxes, measured by selec- tive non-invasive microelectrodes, were monitored in leaves. IPA extract significantly enhanced both potassium and calcium fluxes compared to the other treatments. Total dry weight and macro- and micro-nutrient content were subsequently measured: results showed an improved growth in IPA extract plants, together with a better capacity in accumulating macronutrients in plant organs, but not micronutrients, especially in leaves. Marine bioactive substances were finally tested for their effectiveness in promoting water stress tolerance: IP A extract was very effective in inducing waterstress tolerance, maintaining a higherleaf water potential and stomatal con- ductance during the stress period, and inducing a quick recovery in rehydrated plants.

Anaerobic Digestion of Ulva sp. 3. Liquefaction Juices Extraction by Pressing and a Technico-Economic Budget

In many countries, the algae of “green tides” are harvested in the fight against pollution. Ulva often represents the main component of the tide, and intensive research has been conducted on the possibility to use the algae as a methanisation substrate. However, methanisation is hampered by various practical obstacles, which requires a compromise between productivity and biological yield.The process described here calls upon a pre-digestion phase of Ulva which, besides the economy of time and volume of the digestion, makes it possible to obtain a biogas of good quality. The methanisation substrate is the hydrolysis juice collected by draining, followed by pressing. The cake resulting from the pressing process can be used as organic enriching or fertilizing agent in agriculture. Various presses were tested. The screw press was found the most suitable to recover a great quantity of sufficiently loaded pressing juice after only a short hydrolysis time. For a 3 month hydrolysis period, the different fractions amounted to 158 L of hydrolysis juice, 192 L of pressing juice, and 0.075 m3 of cake per m3 of initial algae.The bi-phasic anaerobic digestion with forced recuperation of juices offers interesting pollution abatement perspectives, with total and soluble chemical oxygen demand cleaning rates of respectively 79 and 95% during the methanogenic phase, for a volume productivity of 1.5 m3 CH4 m−3digester day−1. The quality of the Ulva juice also makes it suitable for use as substrate for industrial processes or co-substrate of methanisation in pre-existing reactors, so that subsequent investment could be avoided.