A Review on the Valorization of Macroalgal Wastes for Biomethane Production

Abstract

The increased use of terrestrial crops for biofuel production and the associated environmental, social and ethical issues have led to a search for alternative biomass materials. Terrestrial crops offer excellent biogas recovery, but compete directly with food production, requiring farmland, fresh water and fertilizers. Using marine macroalgae for the production of biogas circumvents these problems. Their potential lies in their chemical composition, their global abundance and knowledge of their growth requirements and occurrence patterns. Such a biomass industry should focus on the use of residual and waste biomass to avoid competition with the biomass requirements of the seaweed food industry, which has occurred in the case of terrestrial biomass. Overabundant seaweeds represent unutilized biomass in shallow water, beach and coastal areas. These eutrophication processes damage marine ecosystems and impair local tourism; this biomass could serve as biogas feedstock material. Residues from biomass processing in the seaweed industry are also of interest. This is a rapidly growing industry with algae now used in the comestible, pharmaceutical and cosmetic sectors. The simultaneous production of combustible biomethane and disposal of undesirable biomass in a synergistic waste management system is a concept with environmental and resource-conserving advantages.

A Brief Review of Anaerobic Digestion of Algae for Bioenergy

“…The biogas produced from the AD of seaweed typically contains methane 50-70%, carbon dioxide 30-45%, hydrogen < 2% and hydrogen sulphide < 3.5% [23][24][25]. AD is largely the method of choice for biomass with high water content, such as seaweed; it readily tolerates biomass with high moisture content without the energy drawbacks from dewatering and drying [26,27]. It is a relatively simple procedure from an infrastructure/engineering perspective.…”

Experimental processing of seaweeds for biofuels

“…For biogas production Tedesco and Stokes () exploited biomass residues of Fucus serratus , F. vesiculosus , Ascophyllum nodosum , Laminaria digitata , L. hyperborean , Ulva rigida after extracting valuable compounds such as alginic acid, fucoidan, fucoxanthin, laminarin, mannitol, and proteins. Other examples of macroalgal waste products that are available for AD are presented by Barbot et al (). They include: “macroalgae meal” ( Gelidium sesquipedale ), a residue from agar–agar extraction; Gracilaria gracilis residues from phycobiliprotein extraction; Laminaria japonica residues from industrial biomass processing; fermentation and saccharification residues from bioethanol production from Gelidium amani ; alginate extraction residues from Ascophyllum spp.…”

Processed seaweed and winemaking waste co-fermentation for biogas extraction: pilot study

“…is expected to reflect in growing macroalgae cultivation (in this perspective even sea eutrophication could be interpreted as a benefit!) and in subsequent availability of biowaste for energy purposes [1].…”

“…Set of interplaying factors (e.g., temperature, pH, humidity, substrat particle size, algae species-specific physiology, microbial communities' interactions, etc.) is influencing both macroalgae resources development and the waste substrate biodegradation process and, accordingly, affects the yield of biogas [1]; moreover, the biogas output could depend more on the background conditions than the material chosen (example see [11]). …”

“…Rapid growth of energy consumption escalates global community's dependence on nonrenewable fossil fuel (which supplies about 80 % of the world's energy needs [1]) making it more and more urgent to search for alternative, more secure energy sources.…”