Landfill leachate has been reported to contain high concentration of 1,4-dioxane, which is hardly biodegradable and classified as a possible human carcinogen. Although advanced oxidation processes have been widely used for 1,4-dioxane removal in pure water (PW), high concentrations of coexistent substances in landfill leachate strongly inhibit the reactions, and ozone-electrolysis was the only process that can be applied for landfill leachate after pre-treatment of reverse osmosis. Development of more energy saving and lower cost technology is urgently required. This study aims to develop a rotating advanced oxidation contactor (RAOC) equipped with activated carbon (AC) / titanium dioxide (TiO2) composite sheets, and to apply it for 1,4-dioxane removal from biologically treated landfill leachate (BTLL). The composite sheets containing AC and TiO2 were prepared by a papermaking technique and fixed on both sides of a disk. The disk was mounted on a lab-scale reactor and rotated at 10 rpm. Bottom half of the disk (45% of the disk area) was submerged in water for adsorption, while top half of the disk was illuminated with ultraviolet lamps (UVA) for photocatalysis. The 1,4-dioxane solution (1 mg/L, 2 L) was prepared using PW and BTLL, and was poured into the reactor for batch treatment. The 1,4-dioxane amounts both in water and in the composite sheet were determined to evaluate adsorption and photocatalysis separately. The RAOC successfully removed 89% of 1,4-dioxane (1.78 mg) from BTLL through adsorption and 81% of the adsorbed 1,4-dioxane (1.62 mg) was decomposed through photocatalysis during 66 h treatment despite the presence of coexistent substances at high concentration. The ratio of photocatalytic decomposition rate constants kd of 1,4-dioxane in BTLL and PW (kd,BTLL/kd,PW) by RAOC was higher than that by TiO2 powder, and this result indicates that RAOC could mitigate the inhibition by coexistent substances in BTLL to photocatalytic decomposition. The inhibition was mitigated possibly by the increase of UVA photon flux at the surface of TiO2 in the composite sheet, because water film formed on the top half of the disk was extremely thin and UVA-absorbing substances in BTLL was captured by AC in the composite sheet. The RAOC equipped with the AC/TiO2 composite sheets might have a potential for sustainable removal of 1,4-dioxane from BTLL judging from regeneration of adsorption sites occupied by 1,4-dioxane.

Removal of 1,4-dioxane from landfill leachate by a rotating advanced oxidation contactor equipped with activated carbon/TiO2 composite sheets

256th National Meeting (2018)

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