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 kobs 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 kobs 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.

Role of a "surface wettability switch" in inter-fiber bonding properties.

The fiber surface wettability is one of the most important lignocellulosic fiber characteristics affecting the inter-fiber bonding properties of final bio-products. In this study, the surface wettability (evaluated by the surface free energy, surface lignin and surface charge) of mechanically refined fibers and the bonding properties of the fiber matrix (handsheets) were measured and correlated to each other. The results showed that the fiber surface charge increased from 48.38 mmol kg-1 to 60.38 mmol kg-1 and the surface lignin decreased from 87.1% to 77.5% during the fiber mechanical treatment, leading to the improvement of the fiber surface free energy from 46.63 mJ m-2 to 54.45 mJ m-2. As a result, the bonding strength index increased from 2.60 N m g-1 to 9.73 N m g-1 without significant loss of bulk properties. In a word, the fiber surface wettability could be adjusted to facilitate the inter-fiber bonding properties of the paper or paperboard products using lignin-rich fibers as raw materials.