Abstract
Eutrophication is a phenomenon which can rapidly generate masses of marine macroalgae, particularly in areas with high nutrient pollution. Washed ashore, this biomass impairs coastal tourism and negatively affects the coastal ecosystem. The present study evaluates the biochemical methane potential (BMP) of a macroalgae mix (Rügen-Mix, RM (RM = Rügen-Mix)) originating from Rügen, Germany. To improve biomethane recovery, thermo-acidic pretreatment was applied to the biomass prior to biomethanation to disintegrate the biomass macrostructure. Acid hydrolysis was successfully triggered with 0.2 M industry-grade HCl at 80 °C for a 2 h period, increasing biomethane recovery by +39%, with a maximum BMP of 121 mL·g−1 volatile solids (VS). To reduce the necessity for input material, HCl was replaced by the acidic waste product flue gas condensate (FGC). Improved performance was achieved by showing an increase in biomethane recovery of +24% and a maximum BMP of 108 mL·g−1 VS. Continuous anaerobic digestion trials of RM were conducted for three hydraulic retention times, showing the feasibility of monodigestion. The biomethane recovery was 60 mL and 65 mL·g−1 VS·d−1 for thermophilic and mesophilic operation, respectively. The quality of biomethanation performance aligned to the composition of the source material which exhibited a low carbon/nitrogen ratio and an increased concentration of sulfur compounds.
Highlights
An elementary analysis of Rügen-Mix to determine the concentration of macro- and micronutrients, as well as the quantity of heavy metals, was performed and values were matched with the limiting concentrations according to the German Biowaste Act Bioabfallverordnung (BioAbfV) (Table 1)
The biomethane recovery rate was shown to be considerably inferior when compared to popular feedstock substrates, such as maize silage or cattle manure
RM can be subject to acid hydrolysis pretreatment which successfully increased the methane conversion efficiency and the methane formation rate
Summary
Biomass-based, gaseous energy carrier, similar to natural gas, and in the last decades, it has enjoyed intensive government promotion and private sector investments [4,5]. Intensified energy crop agriculture, necessary to serve the market demand, has led to a variety of environmental problems and social conflicts. These include the food-fuel debate [7], the excessive use of fertilizers and fresh water [8], soil leaching and soil erosion [9], threats to biodiversity sources [3,10,11] and conservation [9], additional greenhouse gas emissions [12], and the danger of monocultures [8]. Using marine or aqueous biomass, such as macroalgae, for biogas and biofuel production would circumvent many of these problems and allow a substantial detachment of food and biofuel production with regard to the raw biomaterial
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