Molecular Characteristics and Formation Mechanisms of Unknown Ozonation Byproducts during the Treatment of Flocculated Nanofiltration Leachate Concentrates Using O3 and UV/O3 Processes

Efficient degradation of ciprofloxacin in water using nZVI/g-C3N4 enhanced dielectric barrier discharge plasma process

Residual antibiotics in aquatic environments pose health and ecological risks due to their persistence and resistance to biodegradation. Thus, it is crucial to develop efficient technologies for the degradation of such antibiotics. This study presents a novel approach using a nano zero-valent iron/graphitic carbon nitride (nZVI/g-C3N4)-enhanced dielectric barrier discharge (DBD) plasma process for the degradation of ciprofloxacin (CIP). The combination of nZVI and g-C3N4 with DBD plasma significantly enhances CIP degradation efficiency, achieving an apparent first-order kinetic constant of 0.2849 min⁻1 at an input voltage of 12 kV, which is 5.22 times higher than standalone DBD treatment and 10.59 times higher than the ozonation treatment. The morphology, elemental valence states, and other properties of nZVI/g-C3N4 have been thoroughly characterized and demonstrate good reusability. Reactive species such as ·OH dominates CIP degradation. The Fe atoms in nZVI/g-C3N4 exhibit a strong tendency to donate electrons, generating reactive oxygen through the dissociation of adsorbed water. The cleavage of C-F bonds, hydroxylation and ring-opening oxidation of the piperazine group are the main pathways for CIP degradation, which helps to reduce biotoxicity after treatment. Overall, this study provides insights into the mechanism of reactive species in a DBD-nZVI/g-C3N4 system, a system that has the potential to become an efficient and environmentally friendly solution for the treatment of antibiotic wastewater.

Effect of a high Cl- concentration on the transformation of waste leachate DOM by the UV/PMS system: A mechanistic study using the Suwannee River natural organic matter (SRNOM) as a simulator of waste leachate DOM

The ultraviolet-activated peroxymosnofulate (UV/PMS) system, an effective advanced oxidation process for removing dissolved organic matter (DOM) from wastewater, is limited by high chloride ion (Cl-) concentrations in landfill leachate. This study used Fourier transform ion cyclotron resonance mass spectrometry to explore the transformation of DOM in the UV/PMS system with a high Cl- concentration. The results revealed that elevated Cl- levels generate reactive chlorine species, including chlorine radicals, dichlorine radicals, and hypochlorous acid/hypochlorite, reducing the total organic carbon (TOC) removal efficiency of Suwannee River natural organic matter (SRNOM) from 78.9 % to 39.3 % at 10,000 mg/L Cl-, 0.5 mM PMS, and 60 min. In the absence of Cl-, the UV/PMS system removes almost all molecular species from SRNOM and generates aliphatic substances with low oxygen contents. When high concentrations of Cl- are present, it preferentially removes aromatic and highly unsaturated molecules and produces 408 unknown chlorinated DOMs with highly unsaturated and high-oxygen content features, including CHOCl, CHONCl, and CHOSCl species. We find that in the UV/PMS system without Cl-, DOM is degraded primarily by dealkylation, decarboxylation, hydrogenation, and dearomatization; high concentrations of Cl- impair these reactions, and chlorinated DOM forms via chlorine addition/substitution along with other oxidative reactions.

Destabilization mechanisms of Semi-aerobic aged refuse biofilters under harsh treatment conditions: Evidence from fluorescence and microbial characteristics

Semi-aerobic aged refuse biofilters (SAARB) are commonly-used biotechnologies for treating landfill leachate. In actual operation, SAARB often faces harsh conditions characterized by high concentrations of chemical oxygen demand (COD) and Cl-, as well as a low carbon-to-nitrogen ratio (C/N), which can disrupt the microbial community within SAARB, leading to operational instability. Maintaining the stable operation of SAARB is crucial for the efficient treatment of landfill leachate. However, the destabilization mechanism of SAARB under harsh conditions remains unclear. To address this, the study simulated the operation of SAARB under three harsh conditions, namely, high COD loading (H-COD), high chloride ion (Cl-) concentration environment (H-Cl-), and low C/N ratio environment (L-C/N). The aim is to reveal the destabilization mechanism of SAARB under harsh conditions by analyzing the fluorescence characteristics of effluent DOM and the microbial community in aged refuse. The results indicate that three harsh conditions have different effects on SAARB. H-COD leads to the accumulation of proteins; H-Cl- impedes the reduction of nitrite nitrogen; L-C/N inhibits the degradation of humic substances. These outcomes are attributed to the specific effects of different factors on the microbial communities in different zones of SAARB. H-COD and L-C/N mainly affect the degradation of organic matter in aerobic zone, while H-Cl- primarily impedes the denitrification process in the anaerobic zone. The abnormal enrichment of Corynebacterium, Castellaniella, and Sporosarcina can indicate the instability of SAARB under three harsh conditions, respectively. To maintain the steady operation of SAARB, targeted acclimation of the microbial community in SAARB should be carried out to cope with potentially harsh operating conditions. Besides, timely mitigation of loads should be implemented when instability characteristics emerge, and carbon sources and electron donors should be provided to restore treatment performance effectively.

Degradation of veterinary antibiotics by the ozonation process: Product identification and ecotoxicity assessment

The purpose of the study was to evaluate the effects of using of ozonation to remove antibiotics used, among others, in veterinary medicine, from the aqueous environment. The effect of this process on the degradation, mineralisation and ecotoxicity of aqueous solutions of ampicillin, doxycycline, tylosin, and sulfathiazole was investigated. Microbiological MARA® bioassay and two in silico methods were used for the ecotoxicity assessment. Ozonation was an effective method for the degradation of the antibiotics studied and the reduction in ecotoxicity of the solutions. However, after ozonation, the solutions contained large amounts of organic products, including compounds much less susceptible to ozonation than the initial antibiotics. Structures of 14, 12, 40 and 10 degradation products for ampicillin, doxycycline, tylosin, and sulfathiazole, respectively, were proposed. It was confirmed that ozone plays a greater role than hydroxyl radicals in the degradation of these antibiotics, with the exception of TYL. The use of ozonation to obtain a high degree of mineralisation is unfavourable and it is suggested to combine ozonation with biodegradation. The pre-ozonation will cause decomposition of antibiotic pharmacophores, which significantly reduces the risk of spread of antimicrobial resistance in the active biocenosis of wastewater treatment plants.

Kinetic modelling assisted balancing of organic pollutant removal and bromate formation during peroxone treatment of bromide-containing waters

The peroxone process (O3/H2O2) is reported to be a more effective process than the ozonation process due to an increased rate of generation of hydroxyl radicals (•OH) and inhibition of bromate (BrO3-) formation which is otherwise formed on ozonation of bromide containing waters. However, the trade-off between the H2O2 dosage required for minimization of BrO3- formation and effective pollutant removal has not been clearly delineated. In this study, employing experimental investigations as well as chemical modelling, we show that the concentration of H2O2 required to achieve maximum pollutant removal may not be the same as that required for minimization of BrO3- formation. At the H2O2 dosage required to minimize BrO3- formation (<10 µg/L), only pollutants with high to moderate reactivity towards O3 and •OH are effectively removed. For pollutants with low reactivity towards O3/•OH, high O3 (O3:DOC>>1 g/g) and high H2O2 dosages (O3:H2O2 ∼1 (g/g)) are required for minimizing BrO3- formation along with effective pollutant removal which may result in a very high residual of H2O2 in the effluent, causing secondary pollution. On balance, we conclude that the peroxone process is not effective for the removal of low reactivity micropollutants if minimization of BrO3- formation is also required.

Enhancing phosphorus source apportionment in watersheds through species-specific analysis

Phosphorus (P) is a pivotal element responsible for triggering watershed eutrophication, and accurate source apportionment is a prerequisite for achieving the targeted prevention and control of P pollution. Current research predominantly emphasizes the allocation of total phosphorus (TP) loads from watershed pollution sources, with limited integration of source apportionment considering P species and their specific implications for eutrophication. This article conducts a retrospective analysis of the current state of research on watershed P source apportionment models, providing a comprehensive evaluation of three source apportionment methods, inventory analysis, diffusion models, and receptor models. Furthermore, a quantitative analysis of the impact of P species on watersheds is carried out, followed by the relationship between P species and the P source apportionment being critically clarified within watersheds. The study reveals that the impact of P on watershed eutrophication is highly dependent on P species, rather than absolute concentration of TP. Current research overlooking P species composition of pollution sources may render the acquired results of source apportionment incapable of assessing the impact of P sources on eutrophication accurately. In order to enhance the accuracy of watershed P pollution source apportionment, the following prospectives are recommended: (1) quantifying the P species composition of typical pollution sources; (2) revealing the mechanisms governing the migration and transformation of P species in watersheds; (3) expanding the application of traditional models and introducing novel methods to achieve quantitative source apportionment specifically for P species. Conducting source apportionment of specific species within a watershed contributes to a deeper understanding of P migration and transformation, enhancing the precise of management of P pollution sources and facilitating the targeted recovery of P resources.