FeS as excellent co-activator driving nano calcium peroxide oxidation for contaminants degradation: Performance and mechanisms.

In this study, ferrous sulfide (FeS) was introduced to nano calcium peroxide (nCP)/Fe(III) system to facilitate the generation of Fe(II), more than 90% of naphthalene (NAP) could be removed at a wide pH range of 3-9. As a heterogeneous reductant, FeS could mitigate competitive reactions with reactive oxygen species (ROS), which favored the NAP degradation. As evidenced by scavenging experiments, HO• was the major ROS contributing to NAP degradation. The role of sulfur species (S2-, SO32-, and S2O32-) in nCP/Fe(III) system was investigated with S2O32- showing the preferable reactivity in Fe(III) reduction. In addition, the surface-bound HO• and surface Fe(II) were detected and the role of them on NAP degradation was revealed and concluded that both dissolved and surface Fe(II) contributed to NAP degradation, whereas surface-bound HO• was not superior to solution HO• in degrading NAP. Furthermore, nCP/Fe(III)/FeS system showed high feasibility to different solution matrixes and various types of water as well as the broad-spectrum reactivity to other toxic organic pollutants, exhibiting promise for practical application to remediate complex contaminants.

Comparative studies of organic contaminant removal in different calcium sulfite-enhanced oxidant/Fe(II) systems: Kinetics, mechanisms, and differentiated degradation pathways.

The application of S(IV) for the regeneration of Fe(II) has been widely investigated. As the common S(IV) sources, sodium sulfite (Na2SO3) and sodium bisulfite (NaHSO3) are soluble in the solution, resulting in excessive SO32- concentration and redundant radical scavenging problems. In this research, calcium sulfite (CaSO3) was applied as the substitution for the enhancement of different oxidant/Fe(II) systems. The advantages of CaSO3 could be summarized as follows: (1) it could sustainedly supplement SO32- for Fe(II) regeneration, preventing radical scavenging and unnecessary reagent waste; (2) the cost and toxicity of CaSO3 were extremely lower than that of other S(IV) sources; (3) the concentration of reactive species increased in the presence of CaSO3; and (4) after the reaction, SO42- would form CaSO4 precipitate, which would not increase the burden of SO42- in the solution. In the participation of CaSO3, the removal of trichloroethylene (TCE) and other organic contaminants were significantly promoted and different enhanced systems had high tolerance on complex solution conditions. The major reactive species in different systems were determined through qualitative and quantitative analyses. Eventually, the dechlorination and mineralization of TCE were measured and the differentiated degradation pathways in different CaSO3-enhanced oxidants/Fe(II) systems were elucidated.

Degradation of trichloroethylene in aqueous solution by FeS2 catalyst under innovative oxic environments.

Rapid growth and industrialization have become a major threat to water contamination with carcinogenic chlorinated hydrocarbons such as trichloroethylene (TCE). Therefore, this study aims to assess the TCE degradation performance through advanced oxidation process (AOP) using catalyst FeS2 in combination with oxidants persulfate (PS), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2) in PS/FeS2, PMS/FeS2, and H2O2/FeS2 systems, respectively. TCE concentration was analyzed using gas chromatography (GC). The results found the trend for TCE degradation by the systems was PMS/FeS2>PS/FeS2>H2O2/FeS2 (99.84, 99.63, and 98.47%, respectively). Degradation of TCE was analyzed at different pH ranges (3-11) and maximum degradation at a wide pH range was observed for PMS/FeS2. The analysis using electron paramagnetic resonance (EPR) and scavenging tests explored responsible reactive oxygen species (ROS) for TCE degradation and found that HO• and SO4-• played the most effective role. The results of catalyst stability showed PMS/FeS2 system the most promising with the stability of 99, 96 and 50% for the first, second and third runs, respectively. The system was also found efficient in the presence of surfactants (TW-80, TX-100, and Brij-35) in ultra-pure water (89.41, 34.11, 96.61%, respectively), and actual groundwater (94.37, 33.72, and 73.48%, respectively), but at higher reagents dosages (5X for ultra-pure water and 10X actual ground water). Furthermore, it is demonstrated that the oxic systems have degradation capability for other TCE-like pollutants. In conclusion, due to its high stability, reactivity, and cost-effectiveness, PMS/FeS2 system could be a better choice for the treatment of TCE contaminated water and can be beneficial for field application.

Phycoremediation of industrial wastewater using Vaucheria debaryana and Cladophora glomerata.

Rapid urbanization and industrialization are regarded as the leading causes of environmental pollution, mainly aquatic pollution. This study was carried out to investigate the use of algal species Cladophora glomerata (CG) and Vaucheria debaryana (VD) as a cost-effective and environmentally friendly phycoremediators for composite industrial effluent. After the pot experimentation using algal species, a considerable decrease in electrical conductivity (EC: 49.10-81.46%), dissolved oxygen (DO: 3.76-8.60%), biological oxygen demand (BOD: 7.81-39.28%), chemical oxygen demand (COD: 7.81-39.28%), total suspended solids (TSS: 38.09-62.21%), and total dissolved solids (TDS: 38.09-62.21%) was observed. Before and after experimentation, the heavy metals were also quantified using atomic absorption spectrophotometry (AAS), and considerable reduction was observed in Cd (41.02-48.75%) and Pb (48.72-57.03%) concentrations. The Cd concentration determined in CTCG (control treatment for Cladophora glomerata containing tap water), CG (treatment pot for Cladophora glomerata containing industrial effluents), CTVD (control pot for Vaucheria debaryana containing tap water), and VD (treatment pot for Vaucheria debaryana containing industrial effluents) biomass was 0.06, 0.499, 0.035, and 0.476 mg/kg, respectively. The Pb uptake determined in CTCG, CG, CTVD, and VD was 0.32, 1.12, 0.31, and 0.49 mg/kg, respectively, using wet digestion method and ASS. The data revealed that C. glomerata has the highest bioconcentration factor for Cd (98.42%), followed by Pb (92.57%) in treatment pots containing industrial effluents (CG and VD). Furthermore, C. glomerata showed the highest bioconcentration factor for Pb (86.49%) as compared to Cd (75%) in tap water (CTCG and CTVD). The t test analysis revealed that heavy metal concentrations significantly (p ≤ 0.05) reduced through the phycoremediation process. The analysis found that C. glomerata removed 48.75% of Cd and 57.027% of Pb from industrial effluents. Phytotoxicity assay was also performed by cultivating Triticum sp. in order to analyze the toxicity of the untreated (control) and treated water samples. Phytotoxicity result shows that the effluent treated with both Cladophora glomerata and Vaucheria debaryana gives better wheat (Triticum sp.) plant % germination, plant height (cm), and root height (cm). The highest plant % germination was showed by treated CTCG (90%), followed by CTVD (80%) and CG (70%) and VD (70%). The study concluded that phycoremediation using C. glomerata and V. debaryana is one of the environment-friendly approaches. The proposed algal-based strategy is economically viable and environmentally sustainable that can be utilized for the remediation of industrial effluents.