Anaerobic digestion of Laminaria spp. and Ascophyllum nodosum and application of end products

Abstract

Microbial digestion was carried out using three species of brown algae, Laminaria hyperborea (Gunn.) Foslie, L. saccharina (L.) Lamour, and Ascophyllum nodosum (L.) Le Jol, harvested from the Norwegian coast. Anaerobic digestion of these algae was investigated in a series of benchscale experiments in batch and semicontinuous cultures. The experiments included investigations on loading rate, retention time, gas yield and corresponding changes in total solids (TS) and volatile solids (VS). The specific gas production from the two Laminaria species was almost double that obtained from A. nodosum. Retention times of 8–16 days gave the highest daily gas production, about 1ß-2 times the reactor volume per day. By controlling the loading rate carefully the digestion process could be run without addition of alkali and still maintain the pH above 7. Retention times of less than 8 days gave a partially digested material with binding properties which was tested as an additive to peat briquettes suitable for seeding and production of plantlets. Retention times of 16–24 days resulted in extensive degradation of organic polymeric material that yielded a water soluble extract after filtration and evaporation. This material was tested as a fertilizer on lettuce, including application as a foliar spray.