<![CDATA[Fish waste is organic biomass that may cause environmental pollution; however, its nitrogen and phosphorus contents can serve as nutrient sources for struvite synthesis. This study aimed to synthesize and characterize struvite derived from fermented fish waste and coated with chitosan for use as a slow-release fertilizer. Fish waste was anaerobically fermented using EM4 and molasses. The resulting filtrate was reacted with Mg²⁺:NH₄⁺:PO₄³⁻ molar ratios of 1:1:1, 1:1:2, and 1.2:1:1 under pH conditions ranging from 8 to 10. The resulting struvite was coated with chitosan extracted from shrimp-shell waste and characterized using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Fertilizer effectiveness was evaluated on pak choi plants based on plant height, leaf number, and leaf width. The optimum condition was achieved at pH 9 and a molar ratio of 1.2:1:1, yielding 83.03% phosphate-removal efficiency and 2.40 g of product. FTIR spectra confirmed the presence of P–O and Mg–O bonds and interactions between chitosan functional groups and struvite. SEM revealed orthorhombic prismatic struvite crystals with an amorphous coating. Plant tests indicated that chitosan-coated struvite gradually released nutrients and supported stable pak choi growth. These findings demonstrate its potential as an environmentally sustainable slow-release fertilizer.]]>
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