Alginate degradation during anaerobic digestion of Laminaria hyperborea stipes

Polyphenols and divalent metal ions present in the tissue may seriously affect the degradation of alginate during anaerobic digestion of brown seaweeds. Laminaria hyperborea stipes, harvested at 59 °N off the Norwegian coast in the autumn, were degraded at different concentrations of polyphenols in anaerobic batch reactors at 35 °C and pH 7. This was done by removing or adding the mechanically peeled outer phenolic layer of the algae, and using methanogenic and alginate degrading inocula already adapted to L. hyperborea degradation. Initial alginate released from the algal particles was affected by NaOH titrations because the Ca/Na-ratio was reduced. After a rapid consumption of the mannitol, alginate lyases were induced, and guluronate lyases showed the highest extracellular activity. Then the microbes digested 0.12–0.23 g Na-alginate L⁻¹ h⁻¹. Later the degradation rate of alginates declined almost to zero, and 13–50% of the alginate remained insoluble. The total solubilisation of alginates was apparently limited by both Ca-crosslinked guluronate residues and complexation with compounds such as polyphenols. The methane production had a lag phase that increased at higher amounts of soluble polyphenols, and the total fermentation probably also became product inhibited if soluble compounds such as acetate, ethanol and butyrate were accumulated. This revised version was published online in September 2006 with corrections to the Cover Date.