Optimizing biocoagulant aid from shrimp shells (Litopenaeus vannamei) for enhancing microplastics removal from aqueous solutions

The escalating concern over microplastic pollution in surface water has led to the exploration of effective removal methods, including coagulation and flocculation (CF). This study investigates the potential of chitosan, derived from shrimp shell waste (Litopenaeus vannamei), as a promising biocoagulant aid for pollutant and microplastic removal. The characteristics of chitosan were analyzed for moisture, ashes, protein content, the degree of deacetylation (DD), solubility, pH, viscosity, and Fourier Transform Infrared (FTIR). Systematic examinations of coagulant, biocoagulant aid dosages and pH levels were conducted to optimize the removal efficiency for various pollutants. Subsequently, Low Density Polyethylene (LDPE) microplastics with particle sizes of 1.00, 0.30, and 0.090 mm were employed to assess the efficacy of CF for microplastic removal. The results demonstrated that the optimal dosages of 20 mg/L of alum, 1 mg/L of chitosan, and pH 5, exhibited the highest efficiency for pollutant removal, encompassing turbidity, total suspended solids (TSS), and chemical oxygen demand (COD). Furthermore, the size of LDPE microplastics significantly influenced their removal efficiency, with smaller microplastics (0.090 mm) exhibiting higher removal rates compared to larger ones (0.30 mm and 1.00 mm). The maximum removal efficiencies for LDPE microplastics were 92.13 ± 1.41% for sizes of 0.090 mm. The removal mechanisms for LDPE microplastics involved charge neutralization, inter-particle bridging, and hydrophobic flocculation between LDPE and the coagulant/biocoagulant aid. This study highlights the potential of chitosan from shrimp shell waste as a sustainable and efficient biocoagulant aid for pollutants and microplastic removal in aqueous solutions.