Abstract
•TCP could promote the degradation of FA with NaNO2 as catalyst.•The mechanisms of the CWCO of FA and TCP were proposed.•The CWCO was effective for degrading humic substances and landfill leachate.•FA, HA and landfill leachate could be further removed by biological treatment.
Humic substances, including humic acid (HA) and fulvic acid (FA), are the major components of the refractory organics existing in the stabilized landfill leachate. In this study, the NaNO2-catalyzed wet co-oxidation (CWCO) of FA and 2,4,6-trichlorophenol (TCP) using TCP as the promoter was investigated. Compared with the NaNO2-catalyzed wet air oxidation (CWAO) of FA under the same conditions, the presence of TCP in the reaction system efficiently promoted the degradation of FA. For example, when the CWCO of FA and TCP was carried out at 150°C and 0.5MPa for 4h, the color completely turned to colorless and 61.8% of chemical oxygen demand (COD) was removed, while the color of FA without addition of TCP remained yellow–brown and 19.3% of COD was removed after the CWAO process. The biodegradability (BOD5/COD ratio) was significantly improved from 0.10 to 0.39. Moreover, the radical scavengers (tert-butyl alcohol and sodium bromide) were used to study the radical mechanism and the results showed that hydroxyl radicals were primarily responsible for the destruction of FA and TCP. Furthermore, this co-oxidation system was also effective for degrading the mixture of HA and TCP as well as the mixture of landfill leachate and TCP.