Dewatering treatments to increase dry matter content of the brown seaweed, kelp (Laminaria digitata ((Hudson) JV Lamouroux))

Joe A Gallagher,Lesley B Turner,Jessica M.M Adams,Philip W Dyer,Michael K Theodorou

doi:10.1016/j.biortech.2016.11.091

Abstract

Macroalgal water content is an on-going problem for the use of readily accessible seaweeds in sustainable biorefining, including fuel production. Silage is a reduced-water, compactable, easily stored, transportable material. Ensiling could establish a non-seasonal supply of preserved algal biomass, but requires high initial dry matter content to mitigate environmental pollution risks from effluent. This study investigated potential dewatering methods for kelp harvested throughout the year. Treatments included air-drying, osmotic media and acids. Significant interactions between treatment and harvest-time were observed for traits of interest. Fresh weight loss during treatment was composed of changes in water and dry matter content. Air-drying gave reliable increase in final dry matter content; in summer and autumn 30% dry matter content was reached after 24h. Dilute hydrochloric acid reduced stickiness and rendered material suitable for dewatering by screw-pressing; it may be possible to use the consequent pH reduction to promote efficient preservation.

Highlights

Kelps, seaweeds within the Phaeophyceae, have high photochemical efficiencies and growth rates in temperate coastal regions
Pre-ensiling treatments which significantly increased macroalgal dry matter (DM) content have been identified, it is not known if optimum values for ensiling were reached
Air drying increased % DM with minimal loss of DM and maintenance of maximum energy content, which is beneficial for sustainable fuel production

Summary

Introduction

Seaweeds within the Phaeophyceae, have high photochemical efficiencies and growth rates in temperate coastal regions. These macroalgal species offer the opportunity to produce large quantities of environmentally and socially advantageous ‘green’ biomass for biorenewable applications by avoiding conflict with crop production for the use of agricultural land and fresh water. Dewatering is of particular interest for sustainable fuel applications because wet biomass is subject to rapid deterioration in quality, is heavy to transport, bulky to store and the fossil energy (and economic) costs of traditional drying processes can be high (Milledge et al, 2014; Herrmann et al, 2015; Milledge and Harvey, 2016a; Soomro et al, 2016)

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Conclusion