Material revalorization of beach wrack comprising seaweed and marine phanerogams: Optimization of hydrothermal treatments

Abstract

Tidal waste causes accumulation of seaweed and marine plants on coasts, resulting in an.eutrophication process and proliferation of insects, nematodes, and bacteria that negatively affect the beach ecosystem and local human economic activities. This work highlights the potential of beach wrack from the Andalusian Mediterranean coastline as cellulosic materials, in the frame of concepts such as waste management, revalorization, and reduction of hazardous chemicals. With this purpose, beach waste was harvested, washed with water, characterized, and subjected to chemical-free hydrothermal treatments. A central composite design was defined in order to relate the hydrothermal treatment conditions to the composition of the liquid and solid fractions. It was concluded that polynomial models encompassing linear, quadratic, and binary effect parameters reproduce the experimental results satisfactorily (e.g., R2 = 0.97–0.98 for saccharides released). As expected, severe conditions resulted in higher removal of hemicellulose, and of small amounts of lignin along with it, but at the expense of the yield. Results allowed us to choose high temperature (150 °C), short time (30 min) and low liquid/solid ratio (8) as a compromise solution, by which the yield and the outlet concentrations of glucose, xylose, and arabinose approached their optimal values. Although longer times grant further removal of non-fibrous materials, this small difference is compensated by energy savings and reduction on water consumption.