Effect of Freshwater Washing Pretreatment on Sargassum muticum as a Feedstock for Biogas Production

John Milledge,Birthe Nielsen,Patricia Harvey,Manar Sadek

doi:10.3390/en11071771

John Milledge, Birthe Nielsen + Show 2 more

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https://doi.org/10.3390/en11071771

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Abstract

The pretreatment of seaweed by washing in freshwater is often used in seaweed biofuel research studies. However, the effect of washing seaweed prior to anaerobic digestion (AD) does not appear to have been greatly studied. This study examines washing Sargassum muticum with freshwater and its effect on ultimate and proximate analyses, salt content, methane production from anaerobic digestion, and leachate loss from ensiling. Washing with freshwater significantly (p < 0.01) increased moisture content (unwashed 85.6%, washed 89.1%) but significantly (p < 0.05) reduced ash (unwashed 32.7% dry weight dw, washed 30.6% dw) and salt content (unwashed ash containing 51.5%, washed 42.5%). The dry biomass higher heating value was significantly (p < 0.05) increased by washing due to the lower ash content (11.5 to 12.6 kJ g−1 dw). There was no significant change in the protein or lipid content, although washing increased the nitrogen content (3.85–4.77% dw). Washing significantly (p < 0.05) increased leachate losses during ensiling, with total leachate losses increasing after washing (12.7–25.2%). The methane yield from anaerobic digestion (28 days) was not statistically significantly different (p > 0.05) between unwashed (0.225 L CH4 g−1 VS) and washed samples (0.177 L CH4 g−1 VS). However, washing delayed biomethane production.

Highlights

Seaweeds grow in brackish or salt water and, unlike terrestrial crops, do not require agricultural land for cultivation, avoiding competition for freshwater and land needed for food production [1].The potential biomass yield can be higher for seaweed than for terrestrial plants per unit area.Brown seaweeds which are grown “under cultured conditions” can have yields of ~13.1 kg dry weight m−2 year−1 compared to the yield from sugarcane of only ~10 kg dw m−2 year−1 [2].Growth systems that do not compete for land or freshwater, which are needed for crops, and high potential biomass yields have led to considerable research interest in the use of both micro- and macroalgae as sources of biofuel
Washing in freshwater seems to have an effect on the composition of seaweed and must be taken into account when comparing research studies
Washing seaweeds in freshwater prior to anaerobic digestion can reduce salt, an inhibitor of Anaerobic digestion (AD), it will add to the overall processing costs

Summary

Introduction

Seaweeds grow in brackish or salt water and, unlike terrestrial crops, do not require agricultural land for cultivation, avoiding competition for freshwater and land needed for food production [1].The potential biomass yield can be higher for seaweed than for terrestrial plants per unit area.Brown seaweeds which are grown “under cultured conditions” can have yields of ~13.1 kg dry weight (dw) m−2 year−1 compared to the yield from sugarcane of only ~10 kg dw m−2 year−1 [2].Growth systems that do not compete for land or freshwater, which are needed for crops, and high potential biomass yields have led to considerable research interest in the use of both micro- and macroalgae as sources of biofuel. Seaweeds grow in brackish or salt water and, unlike terrestrial crops, do not require agricultural land for cultivation, avoiding competition for freshwater and land needed for food production [1]. The potential biomass yield can be higher for seaweed than for terrestrial plants per unit area. Growth systems that do not compete for land or freshwater, which are needed for crops, and high potential biomass yields have led to considerable research interest in the use of both micro- and macroalgae as sources of biofuel. A brown seaweed which is an invasive species to Europe, is attracting research interest as a potential feedstock for biofuels and biorefineries [3,4,5,6]. Practical yields of biogas from the AD of seaweed are considerably below the theoretical maximum, and increasing CH4 yield is, the most critical factor in improving

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