Radiolytic degradation of carbaryl in aqueous solution by gamma-irradiation/H2O2 process.

In this study the synergetic effect of gamma-ray and hydrogen peroxide on the degradation of carbaryl in aqueous solution were investigated. Aqueous solution of carbaryl was exposed to five different irradiation doses in the presence and absence of hydrogen peroxide. The intermediate species and aliphatic acids formed during irradiation were determined by Gas chromatography-Mass spectrometer and Ion Chromatography, respectively. It was found that the gamma-irradiation accelerate the degradation process of carbaryl with and without hydrogen peroxide. The inconstancy in pH, dissolved oxygen and total acidity was evaluated before and after treatment by gamma. It was found that the pH was decline from 6.71 to 5, dissolved oxygen from 2.64 to 0.9 mgL-1 and the total acidity was raised from 0.44 to 0.61 mgL-1. The entirely degradation of Carbaryl takes place at 3.0 kGy and 9.6 mM hydrogen peroxide, H2O2. As a consequence, the possible degradation pathway was suggested.

Degradation of N-Nitrosodiethylamine in aqueous solution by gamma-irradiation.

N-Nitrosodiethylamine (NNDEA) is a toxic compound which is affranchised into the medium mostly via industrial wastewater. For the investigation of degradation mechanism of NNDEA, the aqueous solutions of NNDEA were exposed to Advanced Oxidation processes (AOP's) such as gamma-irradiation, ozonation, UV irradiation and UV/Ozone (ozone effect) and UV/H2O2 (hydrogen peroxide effect). Since the structure of NNDEA is small, it is rapidly degraded in all processes except UV-irradiation process but forming acetic acid and formic acid just was seen in gamma and UV/H2O2processes. In the other processes, NNDEA is transformed directly to nitrite and nitrate which they can form NNDEA again in the medium. The concentration of NNDEA was decreased from 50 to 21 mg L-1 after 2.20 kGy gamma-irradiation. After 2.85 kGy gamma irradiation, NNDEA was completely removed from the medium. The results showed that the concentration of NNDEA decreased with UV-irradiation time, the concentration of 50 mg L-1 NNDEA was 42, 30, 24 and 19 mg L-1 after 10, 20, 40 and 60 min UV-irradiation, respectively. It has been investigated that the UV-irradiation does not have much effect on the degradation of 50 mg L-1 NNDEA solution and requires long-term irradiation. In this study, gamma-irradiation was chosen as the best method because of the complete degradation effect and the prevention of the reformation of the NNDEA.

The effect of ozonation on the degradation of carbaryl in aqueous solution.

The aim of this study is to investigate the synergetic effect of ozonation on ultraviolet irradiation on the degradation of carbaryl (CBL) (1-naphthyl-N-methylcarbamate) in aqueous solutions (40 mg L-1). The degradation of CBL and the intermediates formed during ozonation were determined by gas chromatography-mass spectrometer. The change in formaldehyde, dissolved oxygen, pH, and total acidity were determined as a function of ozonation time. It was found that the dissolved oxygen and total acidity were increased with the increasing ozonation time but the pH was decreased with the increasing ozonation time. The aliphatic acids formed during ozonation were followed by ion chromatography as a function of ozonation time. It was found that the effect of ozonation is highly effective on the degradation of CBL. The complete degradation of CBL has occurred at 75-second ozonation time. As a consequence of the obtained results the possible degradation pathway was proposed. The results confirmed that ozonation is an effective method for the degradation of CBL.

Analytical studies on degradation mechanism of herbicide 4-chlorophenoxyacetic acid in water by gamma/H2O2 and gamma/ozone processes.

Radiolytic degradation of 4-chlorophenoxyacetic acid was followed in the presence of hydrogen peroxide and ozone. The synergic effect of ozone is found to be relatively high since the amounts of detected aromatic intermediates are lower as well as the amounts of small aliphatic acids are higher. Chloride ions are one of the most important mineralization products and splitted with a yield of more than 80%. The amounts of small aliphatic acids formed in the last step before mineralization (oxalic, acetic and formic acid) were followed and their formation from 4-chlorophenoxyacetic acid was confirmed. Dissolved oxygen was consumed to form reactive radicals during irradiation. Product analysis and confirmation are followed by gas chromatography/mass spectrometry and ion chromatography. The degradation path of 4-chlorophenoxyacetic acid was suggested with determined intermediates.

Mineralization of paracetamol in aqueous solution with advanced oxidation processes.

Paracetamol is a common analgesic drug widely used in all regions of the world more than hundred tonnes per year and it poses a great problem for the aquatic environment. Its phenolic intermediates are classified as persistent organic pollutants and toxic for the environment as well as human beings. In the present study, the irradiation of aqueous solutions of paracetamol with 60Co gamma-rays was examined on a laboratory scale and its degradation path was suggested with detected radiolysis products. The synergic effect of ozone on gamma-irradiation was investigated by preliminary ozonation before irradiation which reduced the irradiation dose from 5 to 3 kGy to completely remove paracetamol and its toxic intermediate hydroquinone from 6 to 4 kGy as well as increasing the radiation chemical yield (Gi values 1.36 and 1.66 in the absence and presence of ozone, respectively). The observed amount of formed hydroquinone was also decreased in the presence of ozone. There is a decrease in pH from 6.4 to 5.2 and dissolved oxygen consumed, which is up to 0.8 mg l(-1), to form some peroxyl radicals used for oxidation. Analytical measurements were carried out with gas chromatography/mass spectrometry and ion chromatography (IC) both qualitatively and quantitatively. Amounts of paracetamol and hydroquinone were measured with gas chromatography after trimethylsilane derivatization. Small aliphatic acids, such as acetic acid, formic acid and oxalic acid, were measured quantitatively with IC as well as inorganic ions (nitrite and nitrate) in which their yields increase with irradiation.