Anaerobic digestion of waste sludges from the alginate extraction process

Abstract

Anaerobic digestion of waste sludges produced during the industrial extraction of alginate from the algal species Laminaria hyperborea (Gunn.) Foslie and Ascophyllum nodosum (L.) Le Jol was studied. Experiments were carried out in beach scale (8-litre) intermittently stirred digesters at 35°C. Sieve and flotation sludges were digested in batch (1 month) and semi-continuous cultures. In the semi-continuous trials, retention times of 23 days and 16 days were tested. Methane production varied from 0·10 to 0·15 litre g −1 VS added during batch; and from 0·07 to 0·28 litre g −1 VS added during semi-continuous fermentation. Specific gas production was significantly higher at 23 days than at 16 days retention time. VS reductions were 20–40% (batch) and 40–50% (semi-continuous). A distinct improvement of the settling qualities of digester effluents was obtained during the anaerobic digestion process.