Mechanochemical treatment with CaO-activated PDS of HCB contaminated soils.

Mechanochemical methods with co-milling reagents have been widely used to degrade organic pollutants. In this study, calcium oxide and persulfate were employed as co-milling reagents in a mechanochemical process that showed highly effective degradation of hexachlorobenzene in contaminated soil. The influences of soil particle size and organic matter content were also investigated. The interaction between different factors was analyzed by response surface methodology, and a multi-variate regression equation was obtained relating the soil-to-oxidant mass ratio, rotation speed and organic matter content. The existence of SO4- and OH during the mechanochemical reaction was proved by the indirect detection of benzoquinone and p-hydroxybenzoic acid for the first time, providing a new method for testing free radicals in solid-phase reactions. Finally, a possible activation mechanism and hexachlorobenzene degradation pathway were proposed. This study successfully presents a mild degradation method in the field of hexachlorobenzene contaminated site remediation.

Peroxymonosulfate activation by hydroxylamine-drinking water treatment residuals for the degradation of atrazine.

Drinking water treatment residuals (WTRs) have been applied in organic pollutants degradation in water by generating reactive oxygen species from peroxymonosulfate (PMS), however, the slow transformation of Fe(III) to Fe(II) may limit its widespread application. Hydroxylamine (HA) was introduced into the system to enhance the degradation efficiency of atrazine (ATZ) and several key reaction parameters (HA concentration, PMS concentration, pH and temperature) were concerned to study their influence on ATZ degradation. The results revealed that ATZ degradation efficiency was enhanced in the HA/WTRs/PMS system. Effects of some basic inorganic ions (Cl-, SO42- and NO3-) and natural organic matter on ATZ degradation were investigated and results showed that both have an inhibitory effect on ATZ removal. In addition to the reduction role, HA can also react directly with PMS to produce free radicals that helpful for ATZ degradation. Sulfate radical and hydroxyl radicals were generated and sulfate radical was identified as primary radicals in the HA/WTRs/PMS system by alcohol quenching experiments. Moreover, the HA/WTRs/PMS system also showed good performance for ATZ degradation in authentic water like surface water and groundwater. Introduction of hydroxylamine into the system may promote organic pollutant degradation and use of WTRs as an iron source for PMS activation provides new ideas for sludge treatment.

Activation of peroxydisulfate by nanoscale zero-valent iron for sulfamethoxazole removal in agricultural soil: Effect, mechanism and ecotoxicity.

In this study, peroxydisulfate (PDS) was successfully activated by nanoscale zero-valent iron (nZVI) for the degradation of sulfamethoxazole (SMX, antibiotic frequently detected in the environment) in agricultural soils. The results indicated that the degradation of SMX was affected by the nZVI dose, the ratio of SMX/PDS, the ratio of soil/water and reaction temperature, and in cinnamon soils 87.6% of SMX degradation can be achieved within 4 h at 30 °C when the initial nZVI dose was 0.03 g g-1 soil, the molar ratio of SMX/PDS = 1/75 and the soil/water = 1/1. The results of radical scavenger experiments and electron spin resonance (ESR) tests showed that hydroxyl radical (OH) was the dominant reactive species in this system. The ecotoxicity tests of the soil by germination test, luminescent bacteria experiment and enzyme activity test indicated that the ecotoxicity of soil after treatment was obviously lower than the contaminated soil. In addition, there was almost no effect on plant growth when compared with original soil. Furthermore, this system exhibited a great degradation capacity for SMX in different types of agricultural soils, and the degradation efficiencies of SMX in other four soils were 90.6% (yellow brown earths), 80.8% (brown earths), 86.5% (black soils) and 96.1% (red earths), respectively. This work provides an optional method for agricultural soil pollution control.

Activation of peroxymonosulfate by magnetic catalysts derived from drinking water treatment residuals for the degradation of atrazine.

Magnetic catalysts (MCs) derived from iron-rich drinking water treatment residuals (WTRs) were prepared through pyrolysis treatment and introduced as activators of peroxymonosulfate (PMS) for refractory atrazine (ATZ) degradation. Comprehensive characterization analysis indicated that pyrolytic temperature could manipulate the crystalline structure evolution of the MCs and influence their physicochemical and catalytic properties. The catalytic performances of the as-prepared samples pyrolyzed at 600 °C (MC-600) and 1000 °C (MC-1000) were evaluated, and MC-1000 exhibited far more excellent catalytic reactivity than MC-600 in PMS oxidation system. Such difference was mainly attributed to that Fe3O4 and Fe° are the dominant active ingredients of MC-600 and MC-1000, respectively. The electron spin resonance (ESR) tests and radical quenching experiments revealed that hydroxyl radical (•OH) and sulfate radical (SO4•-) predominated in the MC-600/PMS and MC-1000/PMS systems, respectively. The mechanisms of the MCs-mediated PMS activation process were elucidated, among which the role of iron mineral phase was emphatically explored. Furtherly, possible degradation by-products were identified by LC-MS, and potential degradation pathways were proposed. Ultimately, the effects of pivotal parameters (i.e. MC-1000 dosage, PMS concentration, initial pH, and water matrix species) on ATZ degradation were investigated to assess the applicability of the MC-1000/PMS system.

Activation of peroxymonosulfate using drinking water treatment residuals for the degradation of atrazine.

Drinking water treatment residuals (WTRs) are safe byproducts of water treatment plants containing iron. This work studies the degradation of atrazine (ATZ) by WTR-catalyzed peroxymonosulfate (PMS) in aqueous solutions. Factors that affect the catalytic performance (the PMS concentration, catalyst dose, initial solution pH, reaction temperature and water matrix species) were investigated. The results show that the catalytic degradation efficiency of ATZ increases with the increase in PMS concentration and temperature, whereas a higher content of WTRs results in lower removal efficiency because of the quenching effect and negative effect of high pH. For an initial solution pH of 3 and 5, 94.1% and 87.4% of ATZ degradation can be achieved within 6h, whereas the value is only 26% for pH of 7. The production of sulfate radicals (SO4-) and hydroxyl radicals (OH) was confirmed by classic radical quenching and electron spin resonance (ESR) tests. Based on the GC-MS and LC-MS results, the main degradation pathways of ATZ may contain dealkylation, dechlorination-hydroxylation, and alkyl chain oxidation processes. In addition to the ATZ removal ability, the WTRs/PMS system can simultaneously remove phosphorus. This article provides a new idea for wastewater treatment and usage of WTRs as a resource.