2,4,6-Trichlorophenol-promoted Catalytic Wet Oxidation Of Humic Substances And Stabilized Landfill Leachate

Humic substances, including humic acid (HA) and fulvic acid (FA), are the majorcomponents of the refractory organics existing in the stabilized landfll leachate. Thestabilized landfill leachate without treatment emissions will cause seriousenvironmental problems, such as pollutiing underground, surface water and soil Inthis study, the NaNO2-catalyzed wet co-oxidation (CWCO) of FA and2,4,6-trichlorophenol (TCP) using TCP as the promoter was investigated. Comparedwith the NaNO2-catalyzed wet air oxidation (CWAO) of FA under the sameconditions, the presence of TCP in the reaction system efficiently promoted thedegradation of FA. For example, when the CWCO of FA and TCP was carried out at150°C and0.5MPa for4h, the color completely turned from yellow-brown tocolorless and61.8%of chemical oxygen demand (COD) was removed, while the colorof FA without addition of TCP remained yellow-brown and19.3%of COD wasremoved after the CWAO process. Thus the optimal operating conditions for CWCOof FA and TCP were systematically investigated with respect to reaction temperature,TCP concentration, NaNO2concentration, oxygen pressure and initial pH by theabsorbance and TOC removal. Under the optimal operating conditions, thebiodegradability (BOD5/COD ratio) was significantly improved from0.10to0.39.Meanwhile we further studied the reaction kinetics of CWCO under differenttemperature and fitted Arrhenius equation with reaction rate of the mixed solution of(FA+TCP), then the activation energy (Ea) worked out as40.3kJ/mol (R2=0.95).Moreover, the possible degradation mechanism of the CWCO of (FA+TCP) waspresented, and the radical scavengers (tert-butyl alcohol and sodium bromide) wereused to study the radical mechanism and the results showed that hydroxyl radicalswere primarily responsible for the destruction of FA and TCP. Furthermore, thisco-oxidation system was also effective for degrading the mixture of (HA+TCP) aswell as the mixture of (landfll leachate+TCP), and the COD removal reached56.5%and56.5%, respectively, and the biodegradability index reached0.50and0.34respectively.