Solar-Powered Iron Electrocoagulation for Paracetamol Removal: Optimization, Colloidal Evidence, and Techno-Economic...

The occurrence of paracetamol in water motivates the development of treatment processes that combine contaminant removal with reduced dependence on grid electricity. Iron-electrode electrocoagulation was optimized using a regulated direct-current power supply, a face-centered central composite design, and response surface methodology. The initial paracetamol concentration (0.1-0.3 mg·mL^-1), reaction time (10-30 min), current density (0.95-6.67 A·m^-2), and initial pH (3.0-10.0) were evaluated. The quadratic model was statistically significant (F = 3.072; p = 0.0293; R² = 0.7818; adjusted R² = 0.5273) and revealed significant interactions between current density and pH, concentration and current density, concentration and pH, and reaction time and pH. The highest experimental removal was 90.7%, obtained at 0.2 mg·mL^-1, 30 min, 3.81 A·m^-2, and pH 6.5, with a residual concentration of 18.6 mg·L^-1. Near-zero ζ-potential values and floc growth up to approximately 44 μm were consistent with charge neutralization and sweep coagulation, although they did not establish a unique removal mechanism. The selected condition was subsequently operated using a configuration comprising a photovoltaic module, an MPPT controller, and a battery; photovoltaic supply was not a factor in the experimental design. At the maximum-removal condition, both configurations exhibited the same reactor energy consumption (0.018315 kWh·m^-3) and theoretical iron dissolution (0.001737 kg·m^-3). However, when a marginal purchase price of zero was assigned to photovoltaic electricity, the solar configuration was more cost-efficient than the conventional configuration: the partial variable cost decreased from BRL 0.013482·m^-3to BRL 0.000495·m^-3, corresponding to a 96.33% reduction. This comparison excludes photovoltaic system capital investment, battery replacement, maintenance, sludge management, labor, and life-cycle costs. The results identify a favorable operating region at the batch scale, although the resulting residual concentration does not demonstrate compliance with a discharge criterion.