Influence of structural and thermal characteristics of chitosan on the recovery of protein-rich biomass from shrimp processing wash water under various operating conditions

Shrimp processing plants produce wastewater with a high organic load that requires treatment before discharge. This study investigated the recovery of protein-rich biomass from shrimp processing wash water (SPW) using chitosan with different properties to understand its role under different operating conditions. Chitosan samples with varying degrees of deacetylation (DD), molecular weights (Mw) and thermal properties were prepared, designated as CS76H (76.14 ± 0.80 % DD and a high-Mw of 226.79 ± 0.90 kDa), CS85M (85.72 ± 1.63 % DD and a medium-Mw of 38.05 ± 0.33 kDa), and CS88L (88.90 ± 0.57 % DD and a low-Mw of 2.84 ± 0.21 kDa). Optimal conditions for protein recovery were pH 5.5, chitosan concentration of 200 mg/L, temperature of 80 °C and a settling time of 60 min. Under these conditions, CS85M achieved the highest turbidity removal efficiency (99.62 ± 0.20 %), outperforming CS76H (92.19 ± 0.40 %) and CS88L (98.51 ± 0.29 %). This superior performance is attributed to its moderate-Mw and high DD, which promote particle bridging, electrostatic attraction and protein aggregation. The resulting supernatant had optical clarity comparable to clear water, indicating effective removal of soluble proteins. The Differential scanning calorimetry (DSC) analysis showed that CS85M exhibited the highest peak temperature (T_p = 314.60 °C), indicating superior thermal stability, which correlates with its enhanced performance in flocculation due to better structural integrity and functional group availability. These results demonstrate the potential of chitosan with optimized structural and thermal properties for efficient SPW treatment, offering a promising approach to sustainable wastewater management in the seafood processing sector.