Base Activation Of Permonosulfate And Its Application In Dye Wastewater Treatment

Dyes wastewaters which characterized by high colority, high pH and highconcentration have been received much more attention. It is one group of organicwastewaters which are difficult to treat. Persulfate is a new oxidant that has beenused for advanced oxidation technologies （AOTs） in the dye wastewater treatment.AOTs based on sulfate radicals （SO₄·^-） have the potential to treat all types oforganic and inorganic contaminants and thus gain great development. Generally,SO₄·^-was generated through a combination of oxidation agent persulfate （S2O82-）or permonosulfate （HSO5-）, irradiation （ultraviolet, heat, microwave） and catalysts（transition metal ions）. Base is the commonly used activator of persulfate for thetreatment of contaminated groundwater by in situ chemical oxidation （ISCO）.Considering the persulfate and permonosulfate（PMS） are similar in structure ofhaving O-O bond, we anticipate that base is a good candidate for activation ofpermonosulfate.The present work focused on the ability of base to enhance thedecomposition of PMS for degrading dyes. Not only an efficient oxidation processwas developed to degrade dyes, but also the activation mechanism was discussed.The main results included three aspects as follows.（1） The activation of PMS by NaOH was studied for the degradation of methylblue （MB）. It was found that MB could be degradated rapidly and effectively.Under the conditions of25oC,2.0mM NaOH,0.5mM PMS, the removal of MB （c0=10μM） was observed to be high decolorized as98%within40min. The effects oftypical inorganic anions (Cl^-、CO₃^2-、NO₃^-、HPO₄^2-、SO₄^2-) were examined in batchexperiments. It was speculated that existence of these inorganic anions did not affectthe degradation of MB much, because the degradation removal of MB in the presenceof these anions could still reach to90%within40min.（2）This work discussed the mechanism of MB degradation by NaOH/PMS.MeOH, TBA and p-quinone were used as free radical quenchers to verify majorradicals in the system. It speculated that unlike the usual AOTs systems which were reported, the active species in NaOH/PMS system was neither OH nor SO₄·^-, butO₂·^-/HO₂·.（3） In addition, NaOH/PMS system, Fe²⁺/PMS system and Fe²⁺/H₂O₂systemwere used as the typical systems with the main active species respectively as O₂·^-,SO₄·^-and OH. Eight dyes such as MB, rhodamine B （RhB）, methyl orange （MO）,methyl violet （MV）, orange Ⅱ, orange G （OG）, naphthol green B （NGB）, Congo red（CR） were selected and degraded in the mentioned systems in order to study theeffects of different dye structures on the degradation. It was found that the Fe²⁺/H₂O₂system could reach82%to100%decolorization ratio within5min for all the dyesexcept for CR. The Fe²⁺/PMS system was effective for the decolorization of the testedeight dyes, giving decolorization removals from66%to100%. Unfortunately, thedegradation was generally limited due to the irreversible process of Fe²⁺transformedto Fe³⁺during the experiments. The NaOH/PMS system reached the best degradationstowards MB and MV, which were90%and100%within30min, also, these two dyescould be mineralized during the degradation. Among the azo dyes, such as MO,Orange Ⅱ and OG could be decolorized and the decolorization ratios reached from25%to60%. Meanwhile, Orange Ⅱ and OG had also been mineralized.