Inorganic Anions Mediated Persulfate Activation For Degradation Of Typical Organic Pollutants In Wastewater

With the rapid development of industry, water pollution is becoming serious. The treatment of refractory organic wastewater is the difficult point for water pollution control. Advanced oxidation processes(AOPs) have attracted increasing attention, due to their high efficiency, mild reaction conditions, and wide application. In recent years, sulfate radicals(SO4·-) based persulfate activation technology is one of the emerging AOPs.The development of new persulfate activation method is one of the research focuses in persulfate AOPs research. The traditional persulfate activation method is radiation excitation(light, heat, and ultrasound), transition metals activation, and base activation. However, all these methods have limitations. High energy input is required in radiation activation. Metal toxicity and risks of the secondary pollution constrain the further industrial application of transition metals activation. Base activation has high requirement on the equipment of the alkaline resistance. In this paper, several kinds of novel green persulfate activation methods were put forward. Inorganic anions, including phosphate ions, polyphosphate ions and chloride ions(Cl-), could be the efficient activators for persulfate. Common dyes and assistants, Acid orange(AO7), Rhodamine B(Rh B), 2,4,6-trichlorophenol(2,4,6-TCP), were selected as the model pollutants to examine the activation efficiency of the persulfate activation processes. The kinetics of the degradation of these pollutants, influence factors and preliminary reaction mechanism were also investigated. Besides, the effect of halide ions(Cl- and Br-) on typical persulfate activation method(UV/persulfate system) was studied. And the possible toxic organic byproducts were detected. The specific researches are as follows:(1) Phosphate buffer solution(PBS) was used to offer phosphate ions. The degradation efficiency of AO7 in PBS/peroxymonosulfate(PMS) system was investigated. The results showed that, the degradation of AO7 in PBS/PMS system was fitted for the pseudo-first-order kinetic model. Increasing p H and concentrations of PMS and PBS significantly accelerated the degradation of AO7. The UV-Vis scan, gas chromatograph-mass spectrometer(GC-MS), and total organic carbon(TOC) analysis showed that AO7 was not only bleached but also mineralized by the destroying of function groups in ultraviolet and visible ranges. The radical quenching experiments demonstrated that both ·OH and SO4·- would coexist at neutral p H, which might be responsible for AO7 degradation in PBS/PMS system.(2) Polyphosphate, such as pyrophosphate(PA) and tripolyphosphate(PB), is one of the causes of eutrophication in water. This study found that polyphosphate could enhance the activation performance of base/PMS system. It was shown that AO7 and 2,4,6-TCP could be degradation in PA/base/PMS and PB/base/PMS systems in weak alkaline condition. GC-MS analysis displayed that some intermediates of small molecule weights were generated, which implied that organic compounds were indeed decomposed in this polyphosphate/base/PMS system, rather than a simple chromophore destruction occuring. The kinetic study indicated that the degradation efficiency was significantly enhanced with the increasing PMS concentration, polyphosphate dosage. And high p H would be favorable for the polyphosphate/base/PMS system. The radical quenching experiments indicated PA/base/PMS and PB/base/PMS processes were simple chemical reactions not reliant on radical species. This work provides a novel way to activate PMS for contaminant removal using industrial polyphosphate wastewaters.(3) Cl- is common anions in natural water and wastewater. Here we report reactions between PMS and chloride, without a need of transition metals, also can be used to degrade organic dye pollutant(Rh B). Some important operating parameters, such as dosages of PMS and Cl-, p H of solution, temperature, ionic strength, and several common cations, were systematically investigated. It was found that Rh B bleaching rate increased with the increased dosages of both PMS and chloride ion, following the pseudo-first-order kinetic model. The lower p H had a positive effect on the decoloration of dye in acid condition. Rh B decoloration could be significantly accelerated due to the high ionic strength and increasing temperature. Bleaching rate of Rh B with the examined cations increased with the order of NH4+ < Na+ < K+ < Al3+ < Ca2+ < Mg2+. Some major degradation products of Rh B, such as aromatic compounds with different substituent groups and the resultants with relatively lower molecular weights, were identified by GC-MS.(4) The existence of halide ions(Cl- and Br-) might have significant effect on contaminants degradation in the AOPs. The effect of halide ions on humic acid(HA) degradation by typical persulfate-based AOPs(UV/peroxydisulfate(PDS)) and traditional AOPs(UV/hydrogen peroxide(H2O2)) was investigated in this study. High dosage of peroxides(0~7.5 m M) would lead to an increase in HA removal while excess dosage(> 10 m M) would slightly inhibit the efficiency. Both Cl- and Br- would have depressing impact on the two AOPs, but the inhibiting effect of Br- was more obvious than that of Cl-, even the concentration of Cl- was far above that of Br-. The increasing p H would have an adverse effect on HA decomposition in UV/H2O2 system, whereas there was no significant impact of p H in UV/PDS process. Furthermore, infrared spectrometer was used to provide the information of degraded HA in the processes, and halogenated byproducts were identified using GC-MS analysis in the two processes.