Comparative study of UV/H₂O₂ and UV/PMS processes for treating pulp and paper wastewater

Pulp and paper wastewater (PPWW) contains numerous refractory and harmful contaminants that require advanced treatment to meet the discharge criteria. This study compared the efficacy of two PPWW treatments: ultraviolet/peroxymonosulfate (UV/PMS) and ultraviolet/H₂O₂ (UV/H₂O₂) working under similar circumstances. The initial pH value, oxidant dosage, UV radiation intensity, and pseudo-first-order constant k_obs were systematically studied in both systems. Optimally, the UV/PMS process produced an effluent of higher quality than the UV/H₂O₂, as measured by the removal efficiencies of chemical oxygen demand (COD) in 60 min, which were 48.2 and 64.3% for the respective UV/H₂O₂ and UV/PMS processes and corresponding k_obs values of 0.0102 and 0.0159 min^-1, respectively. Radical scavenging experiments demonstrated that •OH was the primary reactive oxygen species in UV/H₂O₂ process, and •OH and SO₄^-• in the UV/PMS process. Moreover, ultraviolet-visible spectroscopy and gas chromatography coupled mass spectroscopy analyses showed that deep treatment of petroleum hydrocarbons with carbon chain lengths greater than 18 and macromolecular semi-volatile organic compounds in paper wastewater is difficult, whereas the UV/PMS process can significantly improve the removal of amides, esters, phenols, and other aromatic compounds.