Comparative study of UV/H 2 O 2 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/H ₂ O ₂ (UV/H ₂ O ₂ ) 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/H ₂ O ₂ , 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/H ₂ O ₂ 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/H ₂ O ₂ process, and •OH and SO ₄ ^- • 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.