Table 3 Advantages and disadvantages of macroalgae as a feedstock for anaerobic digestion (modified from [4, 19])
From: A review of the current potential of European brown seaweed for the production of biofuels
Advantages | Disadvantages |
|---|---|
• Anaerobic digestion can be performed on wet algal biomass negating the need for energy using dry methods [155]. Drying of seaweed is not required for anaerobic digestion • High polysaccharide content in seaweeds is favourable for anaerobic digestion [96] • Low or negligible amounts of recalcitrant lignin, low cellulose content and easily biodegradable sugars making algal biomass to methane by anaerobic digestion easier than lignocellulosic substrate [92, 101] • No competing with agricultural crops for land or freshwater [11] • Space efficient in terms of energy yield per unit area • Wastewater, brackish water and even seawater can be used for algal cultivation; therefore, water quality is less critical • Carbon dioxide sequestration as seaweeds convert carbon dioxide into biomass and exports significant quantities of detritus • Socio-economic benefits particularly in rural and coastal areas • Integration with other technologies. The anaerobic digestion process can be used as a co-technology for algal residues utilisation after biodiesel [4] | • In general, seaweeds contain significantly higher levels of ash, mainly chlorine and sulphur salts, than terrestrial biomass [82] • Methane production can be inhibited by high content of alkali earth metals, sodium concentrations above 10 g Na+/L can strongly inhibit methanogenesis [125] • The combination of high sulphur along with nitrogen content, particularly in green seaweeds, can be problematic in biogas production due to NH3 toxicity [92, 127, 156] • During anaerobic digestion seaweeds can produce high levels of hydrogen sulphide (H2S), up to 3.5% making it unsuitable for energy recovery without specific treatment [140] • High fibre content can lower methane production as insoluble fibres can be difficult to degrade [96] • Polyphenols and tannins present in seaweed are potential inhibitors in anaerobic digestion [96, 127] • Lack of knowledge of the characterisation and biomethane potential, particularly seasonal variation, of selected seaweeds [4] |