Converting sea weed to biogas energy: Utilization of synergism during co-digestion with maize silage

Abstract

Circular economy is a system solution framework replacing the traditional linear approach and aims at creating value from waste. Bladderwrack, a brown sea weed is often cast away in huge volumes on the North Sea coast and is perceived as a waste product. Removal of this algae incurs heavy costs for the municipal authorities since deposits of this sea wrack weakens and poses threat to the flood protective dikes and also to the tourism industry due to its unpleasant sight and smell. This study investigated the biogas potential of the nutrient-rich bladderwrack, Fucus vesiculosus, and co-digestion experiments were performed with maize silage. Mathematical simulations were performed with the Anaerobic Digestion Model No. 1 (ADM1) in order to assess optimal operational conditions and understand the reaction kinetics. While bladderwrack and maize silage on an average yielded 178 ml/g FM together during mono-fermentation, the co-digestion experiment provided 236 ml/g FM, clearly demonstrating the synergistic effect with nearly 33% more biogas. This means reduced dependence on a forage crop like maize by substituting it with a waste product like the brown sea weed along with attaining enhanced biogas production. This positive effect is reasoned to be due to the balanced C/N ratio in the digester during co-digestion. Furthermore, bladderwrack supplements trace metals and vitamins to the nutrient deficient maize silage. The ADM1 model indicated active microbial growth and activities and proved its competence in predicting the synergistic impacts with high accuracy.