Algae-induced photodegradation of antibiotics: A review.

Antibiotics are a typical group of pharmaceutical and personal care products (PPCPs) with emerging pollutant effects. The presence of residual antibiotics in the environment is a prominent issue owing to their potential hazards, toxic effects, and persistence. Several treatments have been carried out in aquatic environments in order to eliminate antibiotic residues. Among these, photodegradation is regarded as an environmentally-friendly and efficient option. Indirect photodegradation is the main pathway for the degradation of residual antibiotics in natural water, as opposed to direct photodegradation. Algae, working as photosensitizers, play an important role in the indirect photolysis of residual antibiotics in natural water bodies. They promote this reaction by secreting extracellular organic matters (EOMs) and inducing the generation of active species. In order to provide a thorough understanding of the effects of algae on residual antibiotic degradation in the environment, this paper comprehensively reviews the latest research regarding algae-induced antibiotic photodegradation. The summary of the different pathways and photosensitive mechanisms involved in this process show that EOMs are indispensable to antibiotic photodegradation. The influencing factors of algae-induced photodegradation are also discussed here: these include algae species, antibiotic types, and environmental variables such as light source, ferric ion presence, temperature, and ultrasound treatment. Based on the review of existing literature, this paper also considers several pathways for the future study of algae-induced antibiotic photodegradation.

Quantification of low molecular weight oxidation byproducts produced from real filtered water after catalytic ozonation with different pathways.

Catalytic ozonation was suggested to be effective for micropollutant removal during water treatment. However, research on organic byproduct formation from catalytic ozonation of real filtered water in water treatment plants was lacking. In this work, two synthesized catalysts, α-FeOOH and CeO2, were applied to catalyze ozonation of real filtered water at different ozone dosages, and the byproducts were quantified. Results showed that the α-FeOOH enhanced hydroxyl radical production, while the CeO2 did not. Both catalysts further reduced dissolved organic carbon (DOC) and UV254 of the filtered water during the catalytic oxidation processes. The O3/CeO2 improved the removal of low molecular weight compounds, especially the refractory compounds such as ketoacids and carboxylic acids, compared to ozonation alone. While the O3/α-FeOOH generated higher concentrations of carboxylic acids than that of ozonation. Thus, in light of DOC and low molecular weight compound reductions, CeO2 was the superior catalyst for micropollutant removal in real filtered water.

Photosensitization mechanism of algogenic extracellular organic matters (EOMs) in the photo-transformation of chlortetracycline: Role of chemical constituents and structure.

The ubiquitous algogenic extracellular organic matters (EOMs) could enhance solar photodegradation of antibiotics such as Chlortetracycline (CTC), however, the role of chemical constituents and structure in their photosensitizing process was not clear. In this paper, EOMs were extracted from chlorella vulgaris (CV-EOMs), scenedesmus meyen (SM-EOMs) and microcystis aeruginosa (MA-EOMs) to explore their photosensitive efficiencies and mechanisms. All of the EOMs showed higher photosensitive efficiencies than natural organic matter (NOM). The quenching assays and competitive kinetics experiments confirmed the dominant role of 3EOMs* in accelerating CTC photodegradation. The quantum yield coefficients of 3EOMs* (fTMP) of CV-EOMs, SM-EOMs, MA-EOMs, NOM were 139.89 ±â€¯5.46, 125.35 ±â€¯4.69, 91.76 ±â€¯3.53, and 72.84 ±â€¯4.45 L/(mol-photon), respectively. Specific chemical constituents and structure of EOMs were characterized by nuclear magnetic resonance (NMR), fourier transform ion cyclotron resonance mass spectrometry (FT-CIR-MS) and X-ray photoelectron spectroscopy (XPS). The results showed the positive linear correlation of fTMP with content of carbonyl groups in EOMs. In addition, reduction of carbonyl groups in EOMs by NaBH4 significantly decreased CTC photodegradation rate. Density Functional Theory (DFT) calculation suggested the susceptible excitation of carbonyl groups in EOMs under solar light was ascribed to the lowest required energy of electronic transition from HOMO to LUMO (assigned as n-π* transition). The energy of triplet excited-states benzophenone, p-methoxy acetophenone and acetophenone (the EOMs model compounds) was calculated to be 284.92, 288.85 and 265.50 kJ/mol, which were higher than that of CTC (i.e., 217.46 kJ/mol), indicating the energy transfer from excited triplet state to excited triplet state CTC was possible. This study provided mechanism insights into photosensitization effects of allogenic EOMs on photochemical fate of pollutants in aqueous environment.