Crayfish Waste-shells Integrated Valorization for Added Value Materials Production: Calcium Hydroxide, Calcium Carbonate, Chitin, Chitosan, and N-S co-doped Carbon Quantum Dots

Crayfish treatment leads to the production of waste and byproducts up to 80% of the total initial seafood amount. The current common method to handle such waste is the landfilling practice which produces remarkable amounts of hazardous gasses and substances due to the anaerobic decomposition process. In this study, an integrated procedure is proposed for the valorization of wastes produced by a fish and crustaceous enterprise.

According to the circular economy and environmentally friendly practices spirit, integrated vertical production and waste valorization methods are adopted globally to reduce food waste. In this study, a process consisting of four sequential steps was proposed to valorize crayfish-treatment waste. Four final added-value materials were produced during this study. The first was chitosan which was identified via the NMR technique exhibiting 91% deacetylation degree. The other two were calcium hydroxide particles of size 6.32 μm and calcium carbonate particles of size 16.9 μm exhibiting meso-macro-pore structure with S_g = 46m²/g and S_g = 20m²/g respectively. Pore specific surface area values of these two products are similar to values reported in the literature for applications such as drug carriers etc. The last product was nitrogen/sulfur-doped carbon quantum dots which exhibited an identified via AFM technique mean size of 5.01 nm. This material was successfully tested for its advanced antioxidant capabilities via the DPPH assay and for its antimicrobial properties via MIC routine measurements with E. coli and L. monocytogenes.

Experimental data indicated that the valorization process proposed in this study could lead to a yield of 10% w/w for chitosan after three stages treatment, to a yield of 35% w/w for Ca(OH)₂ or CaCO₃ after 1 stage treatment, and to a yield of 5% w/w N-S co-dopped Carbon QDs.

The globally big amount of waste-shells from Crayfish and other crustaceous could be integratedly exploited for added-value materials production yielding economic and environmental benefits.