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

Abstract

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.