Dodecylpyridinium chloride removal by persulfate activation using UVA radiation or temperature: experimental design and kinetic modeling

The degradation of dodecylpyridinium chloride (DPC) by SO₄•⁻ and HO• radicals, generated by UVA and thermal-activated persulfate (PS) was investigated. Temperatures of 30–50°C were used for the heat activation of PS. In the case of UVA/PS, the effects of [PS]₀ and specific photon emission rate (EP,₀) were studied through a Doehlert design coupled with statistical analysis and response surface methodology. The results showed high DPC removal (99.8%) and pseudo-first-order degradation rate (kₒbₛ = 0.0971 min⁻¹) for [DPC]₀ = 4.60 ± 0.11 mg L⁻¹, [PS]₀ = 7.75 mmol L⁻¹, and EP,₀ = 0.437 μmol photons L⁻¹ s⁻¹, with a major role of SO₄•⁻ radicals in comparison with HO•. The specific DPC degradation rate found under these conditions was higher than that observed for thermal activation at 50°C and [PS]₀ = 5.5 mmol L⁻¹ (kₒbₛ = 0.0712 min⁻¹) over the same time, although complete DPC removal was also achieved in the latter. The positive effect of EP,₀ on DPC degradation by the UVA/PS process depends on PS concentrations, with kₒbₛ values increasing linearly with [PS]₀ in the range 7.75–10 mmol L⁻¹, whereas lower EP,₀ values can be compensated by increasing [PS]₀ up to about 10 mmol L⁻¹, without significant scavenging. The second-order rate constants of DPC with HO• and SO₄•⁻, estimated by comprehensive kinetic modeling, were 8.26 × 10⁹ and 4.44 × 10⁹ L mol⁻¹ s⁻¹, respectively. Furthermore, higher [DPC]₀ would negatively affect the DPC degradation rate by the UVA/PS process, while 62% DPC removal was obtained in WWTP water, which can be considered good given the complexity of the real matrix. Finally, our results shed light on the possibility of using available UVA radiation (4.5%) in solar irradiance on the Earth’s surface, making this treatment process more sustainable and cost-effective.