Biogas production from macroalgae wastes

Problem statement

Laminaria japonica is a marine macroalgae that is widely cultivated for biofuel production, pharmaceuticals and the food industry. Even so, waste is generated from these algae, which can still be used to produce biomethane.

Executive summary

The digestion of Laminaria japonica in batch and continuous bioreactors produced acceptable biomethane production rates at laboratory and pilot plant scale. On the other hand, against all odds, a pre-treatment of the algae does not increase biomethane production, recommending fermenting them in their "native"" state.

Technology description

Macroalgae production is increasing considerably every year worldwide. Most of this production is destined for food, but other industries also use macroalgae as biomass (pharmaceuticals, paper, textiles, etc.). Between harvesting and further processing of Laminaria in industries, between 10% and 30% of residual biomass is generated, which ends up being discharged into the sea or treated as low impact waste. Macroalgae are a type of biomass with potential for biomethane production. Its fractionated carbohydrate structure (soluble and easily hydrolysable sugars) makes it suitable for anaerobic digestion. In short, the absence of large amounts of lignin and cellulose makes them suitable for digestion by microorganisms. The study was carried out on Laminaria waste, at laboratory scale and at pilot plant scale. In both cases, pretreatment of the biomass was not positive for fermentation, contrary to the recommendation in the literature. On the other hand, when these algal wastes were fermented without any pretreatment or mixing with other substances, acceptable amounts of biomethane were produced, despite being waste biomass and thus possessing less fermentable compounds than if a whole plant was fermented.

Market deployment considerations

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Environmental considerations

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