Formation Of Oxidation By-products Research Articles

Decomposition pathways and reaction intermediate formation of the purified, hydrolyzed azo reactive dye C.I. Reactive Red 120 during ozonation

In this study, an aqueous solution of purified, hydrolyzed C.I. Reactive Red 120 (RR 120, Color Index), was selected as a model to investigate the degradation pathways and to obtain additional information on the reaction intermediate formation. The dye was purified to avoid the influence of the impurities on the ozonation process and on the formation of oxidation by-products. To simulate the dye-bath effluents from dyeing processes with azo reactive dyes, a hydrolyzed form of the dye was chosen as a representative compound. High performance liquid chromatography/mass spectrometry and its tandem mass spectrometry was chosen to identify the decomposition pathways and reaction intermediate formation during the ozonation process. In addition total organic carbon and high performance ion chromatography analysis were employed to obtain further information on the reaction processes during ozonation. Purified, hydrolyzed RR 120 was decomposed under the direct nucleophilic attack by ozone resulting in oxidation and cleavage of azo group and aromatic ring, while the triazine group still remained in the solution even after prolonged oxidation time (120 min) due to its high resistance to ozonation. Phenol, 1,2-dihydroxysulfobezene, 1-hydroxysulfonbezene were detected as the degradation intermediates, which were further oxidized by O(3) and *OH to other open-ring products and then eventually led to simple oxalic and formic acid identified by HPIC.

Ozonation of haloacetic acid precursor using phenol as a model compound: effect of ozonation by-products

The formation pattern of haloacetic acids (HAAs) was investigated using phenol as a model precursor of HAAs, and the oxidation by-products formed from phenol ozonation, such as hydroquinone, catechol, glyoxal, glyoxylic acid and oxalic acid, were also chlorinated to measure the HAAs formation potential (HAAFP). Of these, phenol showed the highest reactivity with chlorine, yielding the most HAAFP. Even though HAAFP of the tested by-products was lower than that of phenol, it was confirmed that all by-products can act as the precursor of HAAs. Regarding the ozonation of phenol-containing water, the efficiency of ozone in controlling HAAs can be reduced by the formation of oxidation by-products. When comparing conditions for pH 7 and 3, the ozonation for pH 7 was more effective in removing the overall HAA precursors than the ozonation for pH 3. This result was attributed to complete oxidation by the production of the secondary oxidant, such as the OH radical (OH·) from ozone decay, and ionization of phenol.

Effects of dye additives on the ozonation process and oxidation by-products: a comparative study using hydrolyzed C.I. Reactive Red 120

Decolorization of azo reactive dyes by ozone has been described by several authors. However, the efficiency of ozonation and the by-products produced by dye additives/impurities such as synthetic precursors, by-products, salts and dispersing agents in commercial azo dyes during the oxidative treatment have not been reported. To investigate the effects of such impurities on the ozonation process and on the formation of oxidation by-products, a commercially available azo reactive dye C.I. Reactive Red 120 was chosen as a model compound. Experiments were conducted in aqueous solutions of hydrolyzed C.I. Reactive Red 120 (200 mg/l) either with or without purification. Treatment efficiencies of purified and unpurified dye were evaluated in terms of COD, BOD 28, absorbance and initial decolorization rates. Additionally, organic and inorganic anions were analyzed by HPIC. After 28 days of incubation the BOD 28/COD ratio increased from 0.22 to 0.48 and from 0.05 to 0.26 for purified and unpurified C.I. Reactive Red 120, respectively, indicating an enhancement of biodegradable compounds in the ozonated solutions. The results also illustrate that the dye additives/impurities in commercial dyes affect the microbial activity as well as the biodegradability. It is therefore recommended that dyes should be purified before ozonation, if detailed information on the degradation processes and the resulting oxidation by-products are required.

Oxidation of Herbicides in Groundwater by the Fenton Process: A Realistic Alternative for O3/H2O2 Treatment?

Oxidation with O3/H2O2 and Fe2+/H2O2 are optional for the degradation of herbicides and pesticides in water. The choice of which process will be applied depends upon the degree of degradation of organic micropollutants and the process conditions related to the formation of oxidation by-products, and also on the total costs and the safety and reliability of the process. Under real conditions, atrazine and some phenylureaherbicides were oxidized with O3/H2O2. Comparable experiments under conditions of different pH, iron and DOC content were performed with Fe2+/H2O2, in order to gain information on the influence of these parameters. The oxidation results of both processes as well as the formation of bromate as one of the oxidation by-products are described. It was found that 80% of atrazine and >99% of some phenylureaherbicides could be degraded with O3/H2O2 at pH 7.8 (H2O2/O3 ratio 3.7 g/g). Under these conditions, bromate was formed up to 5 μg/1. Comparable results were obtained with Fe2+/H2O2 at a pH value of 5.5, whereas the formation of bromate was kept below 0.2 μg/L.