Photochemical degradation of typical halogenated herbicide 2,4-D in drinking water with UV/H2O2/micro-aeration

Occurrence of herbicides in the aquatic environment and their removal using advanced oxidation processes: a critical review

Herbicides are chemicals used globally to kill unwanted plants so as to obtain high agricultural yields and good agricultural products. Herbicides are sometimes transported from the farmlands into water bodies mainly through runoffs. These chemicals are recalcitrant, and their accumulation is hazardous to abiotic and biotic components of the ecosystem. At present, the best alternative technology for elimination of herbicides in water is the usage of advanced oxidation processes (AOPs). The AOPs, which are performed homogeneously or heterogeneously, are capable of breaking down complex pollutants in water into carbon dioxide and mineral compounds. In these processes, ^·OH is produced and used for degradation process. It is recommended that the total organic carbon (TOC) produced during degradation reaction be monitored because the ‧OH produced or generated can react to form intermediates before complete mineralisation is achieved. Different kinds of AOPs for degradation of herbicides have their specific advantages as well as limitations. This report shows that AOPs are excellent techniques for degradation of herbicides in aqueous solutions, and the mechanisms showed that herbicides were mineralised. The amount and type of photocatalysts, pH of the medium, surface characteristics of the photocatalysts, doping of the photocatalysts, temperature of the medium, concentration of herbicides, presence of competing ions, intensity and irradiation period, and type of oxidants have great influence on the degradation of herbicides in water. Overall, this report showed that most AOPs could not completely degrade herbicides in water and complete degradation can be achieved by developing novel and robust AOPs that will completely mineralise herbicides in water-this will pave way for water and environmental safety.

Photocatalytic Activity of TiO2 for the Degradation of Anticancer Drugs

To prevent water pollution, photocatalysis is often used to remove small molecules such as drugs by generating reactive species. This study aimed to determine the photocatalytic activity of two anticancer drugs, imatinib and crizotinib, and to investigate various influences that may alter the kinetic degradation rate and ultimately the efficacy of the process. In order to obtain optimal parameters for the removal of drugs with immobilized TiO₂, the mutual influence of the initial concentration of the contaminant at environmentally relevant pH values was investigated using the response surface modeling approach. The faster kinetic rate of photocatalysis was obtained at pH 5 and at the smallest applied concentration of both drugs. The photocatalytic efficiency was mostly decreased by adding various inorganic salts and organic compounds to the drug mixture. Regarding the degradation mechanism of imatinib and crizotinib, hydroxyl radicals and singlet oxygen showed a major role in photochemical reactions. The formation of seven degradation products for imatinib and fifteen for crizotinib during the optimal photocatalytic process was monitored by high-resolution mass spectrometry (HPLC-QqTOF). Since the newly formed products may pose a hazard to the environment, their toxicity was studied using Vibrio fischeri, where the significant luminescence inhibition was assessed for the mixture of crizotinib degradants during the photocatalysis from 90 to 120 min.

Occurrence and transformation of phenoxy acids in aquatic environment and photochemical methods of their removal: a review

The article presents the behavior of phenoxy acids in water, the levels in aquatic ecosystems, and their transformations in the water environment. Phenoxy acids are highly soluble in water and weakly absorbed in soil. These highly mobile compounds are readily transported to surface and groundwater. Monitoring studies conducted in Europe and in other parts of the world indicate that the predominant phenoxy acids in the aquatic environment are mecoprop, 4-chloro-2-methylphenoxyacetic acid (MCPA), dichlorprop, 2,4-dichlorophenoxyacetic acid (2,4-D), and their metabolites which are chlorophenol derivatives. In water, the concentrations of phenoxy acids are effectively lowered by hydrolysis, biodegradation, and photodegradation, and a key role is played by microbial decomposition. This process is determined by the qualitative and quantitative composition of microorganisms, oxygen levels in water, and the properties and concentrations of phenoxy acids. In shallow and highly insolated waters, phenoxy acids can be decomposed mainly by photodegradation whose efficiency is determined by the form of the degraded compound. Numerous studies are underway on the use of advanced oxidation processes (AOPs) to remove phenoxy acids. The efficiency of phenoxy acid degradation using AOPs varies depending on the choice of oxidizing system and the conditions optimizing the oxidation process. Most often, methods combining UV radiation with other reagents are used to oxidize phenoxy acids. It has been found that this solution is more effective compared with the oxidation process carried out using only UV.

Photochemical degradation of ciprofloxacin in UV and UV/H₂O₂ process: kinetics, parameters, and products

Photochemical degradation of fluoroquinolone ciprofloxacin (CIP) in water by UV and UV/H₂O₂ were investigated. The degradation rate of CIP was affected by pH, H₂O₂ dosage, as well as the presence of other inorganic components. The optimized pH value and H₂O₂ concentration were 7.0 and 5 mM. Carbonate and nitrate both impeded CIP degradation. According to liquid chromatography-tandem mass spectrometry analysis, four and 16 products were identified in UV and UV/H₂O₂ system, respectively. Proposed degradation pathways suggest that reactions including the piperazinyl substituent, quinolone moiety, and cyclopropyl group lead to the photochemical degradation of CIP. Toxicity of products assessed by Vibrio qinghaiensis demonstrated that UV/H₂O₂ process was more capable on controlling the toxicity of intermediates in CIP degradation than UV process.