Sustainable Treatment of Fisheries Wastewater Using Azadirachta indica Leaf Biocoagulant: Optimization of Chemical Oxygen Demand and Total Suspended Solid Removal

Fisheries wastewater contains high levels of suspended solids and organic matter, posing significant environmental risks and necessitating effective and sustainable treatment approaches. This study aims to determine the characteristics of the neem (Azadirachta indica) leaf biocoagulant, assess the interactions among research variables, and optimize its use to reduce total suspended solids (TSS) and chemical oxygen demand (COD) levels in fisheries wastewater. The method used is response surface methodology (RSM), specifically the Box–Behnken Design (BBD), which involves three variables (biocoagulant concentration, fast stirring speed, and sedimentation time) and two responses (TSS and COD removal). Characterization results (Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and zeta potential) indicated that the biocoagulant contains functional groups such as hydroxyl, carboxyl, and amine, contributing to coagulation–flocculation through adsorption and polymer bridging mechanisms. Statistical analysis confirmed that the developed quadratic models were significant (p-value < 0.05), with high F-values, non-significant lack of fit, and strong coefficients of determination (R2 = 0.9111 for TSS and 0.9419 for COD), along with low coefficients of variation (CV < 5%), indicating good model reliability. Although the model generally has a significant effect on the response, the fast stirring speed does not, while the other two factors do. The optimal conditions (based on desirability) were determined to be a biocoagulant concentration of 79.8 mg/L, a fast stirring speed of 100 rpm, and a sedimentation time of 27.5 min. Under these conditions, TSS and COD removals of 88.72% and 79.98%, respectively, were achieved. These findings demonstrate the potential of neem leaf biocoagulant as a sustainable, environmentally friendly alternative to conventional chemical coagulation, supporting cleaner production in aquaculture systems.