Hydrothermal carbonization of snow crab processing by-product: Hydrochar characterization

Abstract

Fishery processing (crab) is an important industry in Atlantic Canada. However, up to half of the landed product ends as processing by-product with over 70 wt% water content. Often regarded as a “waste” this by-product has applications in soils, wastewater treatment, and other industries, an area of research largely unexplored. Hydrothermal carbonization (HTC) converts biomass into a more stable and useable material (hydrochar) and uses water as a medium. This valorization not only creates a profit stream but also reduces the environmental impacts of the crab by-product treatment and disposal. In this work, HTC hydrochar from snow crab (Chionoecetes opilio) processing by-product/feedstock is characterized with respect to key properties in an effort to delineate potential end use applications and the impact of process parameters (temperature, residence time, and water to biomass ratio) on these properties. The temperature range was 180–260 ℃, residence time of 0.5–3 h, and water to biomass ratio of 2–4 (wt:wt). The solids yield decreased as water ratio and temperature increased (time did not impact yield to the same extent). The hydrochar ash content increased from 33 to 45 wt% as water ratio and temperature increased to the maximums studied in this work. XRD analysis showed that the hydrochar retained chitin and CaCO₃. Trace analysis showed calcium was the most abundant mineral in the feedstock and hydrochar, consistent with the XRD CaCO₃ peak. Compared to the feedstock (11 m²/g), the hydrochar BET surface area increased with temperature and water ratio, reaching a maximum of 26 m²/g at 260 °C, water ratio 3 and 30 min. However, increasing the time to 3 h reduced the surface area to 13.47 m²/g. Hydrochar carbon content is similar or slightly higher than the feedstock due to competing polymerization reaction and CaCO₃ dissolution. Nitrogen decreased as temperature increased possibly due to protein degradation. Hydrochar and feedstock showed similar functional groups. The functional groups in the hydrochar have potential to facilitate chemosorption as a bioadsorbent.