Pre-treatment of zostera marina and ulva armoricana for production of bioethanol and biogas

The seaweed Zostera marina and the alga Ulva armoricana have been investigated to test the effect of the steam explosion treatment on their conversion in biofuels, namely ethanol and methane. Zostera has been collected on the beach of Arcachon while Ulva in Britanny (both places in France). Several analytical methods have been tested and compared to analyse the raw materials and the derivate products. The composition has been determined in terms of carbohydrates (rhamnose, glucose, xylose, arabinose, mannose, galactose, galacturonic acid, glucuronic acid, fucose) sand and other impurities, ash, extractives (chlorophills) zosterine. Both Zostera and Ulva have been treated by steam esplosion and the best conditions were assessed to improve sugar extractability and cellulose hydrolysis by enzymes. An experimental design was set up and the relationships were obtained to for sugar recovery and glucose production as function of the SE severity in the range 160-180°C, 60-300 s. Zostera marina was investigated for the bioethanol production. This biomass contains over 30% of cellulose. The effect of the impregnation with oxalic acid on the quality of the produced substrate was evaluated. Tests of SHF (Separate Hydrolysis and Fermentation) and SSF (Simultaneous Saccharification and Fermentation) were carried out at bench scale and the yield of ethanol production was optimized by varying the enzyme load, the amount of yeast and the solid to liquid ratio. Ethanol can be produced with yields over 90% by SHF with 6% of enzyme and 3 g/l of yeast. The best steam explosion treatment resulted that at 180°C, 300 s, with the addition of 20 g of oxalic acid per kg of raw Zostera. Ulva armoricana and Zostera marina were investigated for the methane production by means of anaerobic digestion. It was tested the effect of the steam explosion on the yield and the kinetics of biogas production. The overall biogas production of steam exploded Ulva and Zostera was higher than raw material. The steam explosion treatment positively affected the kinetics of the process. Biogas yields resulted different between Ulva and Zostera: 0.22 m3/kg versus 0.11 m3/kg; differences in the biogas composition were also detected. Cost analysis was carried out on the SE process applied on the Zostera and Ulva. It is based on data collected from batch (0.5kg/cycle) and continuous plant (350 kg/h, included of the fractionation section). The treatment cost has been evaluated as a function of the plant scale. Variable and fixed cost breakdown has been detailed in the case of a 1,000 and 10,000 t/y plant. Steam explosion process costs range between 0.25 and 0.27 €/kgDM in the case of a 10,000 t/y size plant.