Photochemical treatment of 2-chlorophenol aqueous solutions using ultraviolet radiation, hydrogen peroxide and photo-Fenton reaction.

In the present work, the photochemical oxidation of 2-chlorophenol aqueous solutions in a batch recycle photochemical reactor using ultraviolet irradiation and hydrogen peroxide was studied. Specifically, the effect of hydrogen peroxide initial concentration (0-10316 mg L(-1)) and 2-chlorophenol initial concentration (150-3000 mg L(-1)) was examined. The process was attended via total organic carbon (TOC), 2-chlorophenol, chloride ion, acetic acid, formic acid and pH measurements. The conversion of 2-chlorophenol observed was always much higher than the corresponding total organic carbon removal, whereas the increase in hydrogen peroxide amount in the solution led to higher values of 2-chlorophenol conversion and total organic carbon removal. Finally, the photo-Fenton reaction was applied to the oxidation of 2-chlorophenol, leading to a higher degree of mineralization of the parent compound.

Treatment of 2-chlorophenol aqueous solutions by wet oxidation.

In the present work, the wet oxidation (WO) of 2-chlorophenol (2-CP) was studied in aqueous solutions, in a high-pressure agitated autoclave reactor. Specifically, the effect of temperature (160-190 degrees C), oxygen partial pressure (5-40 bar) and 2-CP initial concentration (250-1500 mg L(-1)) was examined. The process was attended via total organic carbon (TOC), 2-CP, chloride ion, acetic acid, formic acid and pH measurements. Significant rates of 2-CP disappearance and TOC removal were achieved above 170 degrees C. A decrease in 2-CP initial concentration below 1000 mg L(-1) resulted in a dramatic decrease in the TOC removal achieved, whereas an increase in oxygen partial pressure enhanced greatly the decontamination of the 2-CP aqueous solution, especially from 10 to 20 bar. Much attention was given on the chloride ion removal from the phenolic ring in order to attend the dechlorination of 2-CP during WO. In the WO process, the majority of chloride ions were detached from organic compounds. Finally, a parallel and in series reaction scheme has been proposed for the interpretation of the experimental results.

Photocatalytical degradation of 1,3-dichloro-2-propanol aqueous solutions by using an immobilized TiO2 photoreactor.

The photocatalytic oxidation of 1,3-dichloro-2-propanol (1,3-DCP) was studied by following the target compound degradation, the total organic carbon removal rate and by identifying the oxidation products. The reaction was performed in a batch recycle reactor, at room temperature, using UV radiation, H2O2 as oxidant, and immobilized TiO2 as catalyst. 1,3-Dichloro-2-propanone, chloroacetyl-chloride, chloroacetic acid, formic and acetic acid were detected as reaction intermediates and a possible pathway for the oxidation of 1,3-dichloro-2-propanol is proposed. The effect of the oxidative agent's initial concentration was investigated and it was established that higher concentrations of H2O2 slow down the reaction rate. The investigation of the effect of the 1,3-DCP initial concentration showed no influence on the degradation process. The carbon and chloride ion mass balance calculations confirmed the fact that chlorinated intermediates are formed and that they degrade with a lower rate than 1,3-DCP.

Photochemical treatment of phenol aqueous solutions using ultraviolet radiation and hydrogen peroxide.

The potential of purifying phenol aqueous solutions (0.0006-0.0064 M) using ultraviolet (UV) radiation and hydrogen peroxide (H2O2; 0.005-0.073 M) was investigated. Although the direct photolysis of phenol and its oxidation by hydrogen peroxide (without ultraviolet light) were insignificant, the combination of UV and H2O2 was extremely effective on phenol degradation. However, the chemical oxygen demand was on no occasion entirely eliminated, indicating the resistance of the intermediate products formed to the photo-oxidation. Increasing the initial concentration of phenol had as a result lower phenol conversions achieved, whereas the increase in hydrogen peroxide initial concentration enhanced significantly the degradation of phenol. In contrast, COD removal was less sensitive to these changes.

Stripping as a pretreatment process of industrial oily wastewater.

In the present work, the potential of purifying an oily wastewater from a lubricant production unit, consisting mainly of alcohols, phenols and heavy linear saturated hydrocarbons, using the stripping process was examined. The effect of stripping gas flow (75-300 L(N2) L(WW)(-1) h(-1)) and system temperature (295-355 K) on the chemical oxygen demand (COD) of the effluent was investigated. A decrease in COD content of 25-30% was achieved after 4 h for stripping gas flow rates over 150 L(N2)L(WW)(-1) h(-1), whereas the rate of organic compounds removal was enhanced by increasing temperature up to 333 K. At higher temperatures an effluent condensation was observed. Gas chromatography-mass spectrometry analysis of both liquid and gas phase showed that linear saturated hydrocarbons of high molecular weight were stripped out from the wastewater. The results are in agreement with the equilibrium ratio of these compounds as predicted from by theoretical calculations.

Photo-assisted oxidation of chlorophenols in aqueous solutions using hydrogen peroxide and titanium dioxide.

In the present work, the efficiency of phenol and chlorophenol degradation under irradiation using hydrogen peroxide as oxidant and titanium dioxide powder as photo-catalyst was investigated. In the absence of titanium oxide, increased concentrations of hydrogen peroxide resulted in higher conversions. Generally, phenol was the most readily oxidized compound, whereas in excess of hydrogen peroxide, the more chlorine atoms were present in the ring, the less degradable the chlorophenol was, in terms of initial rate of oxidation. In the case of 4-chlorophenol, the catalytic photo-oxidation efficiency with hydrogen peroxide and titanium oxide was dependent on the catalyst concentration exhibiting a maximum at 0.025-0.05 g L(-1) titanium oxide. The combined use of titanium oxide and hydrogen peroxide resulted in higher degree of oxidation compared to results obtained when using hydrogen peroxide. Finally, the presence of Fe(III) proved to be beneficial for the photo-catalytic oxidation only in the presence of hydrogen peroxide.

Photo-assisted oxidation of an oily wastewater using hydrogen peroxide.

The primary objective was to study the purification of an oily wastewater from a lubricant production unit using ultraviolet irradiation and hydrogen peroxide. The influence of hydrogen peroxide concentration, initial pH of the solution and of the addition of ferric ions on the chemical oxygen demand (COD) was examined. In each case, the concentration of the compounds contained in the oily wastewater was determined. It was shown that a 20-45% COD removal was achieved with 830-1660 mg l(-1) H(2)O(2). Gas chromatography-mass spectrometry analysis showed that the organic compounds of the wastewater decomposed to organic acids that were very resistant to photo-oxidation. Among these compounds, ethylene glycol remained almost unchanged by the attack from hydroxyl radicals. Acidic pH and Fe(III) addition enhanced significantly the photo-oxidation of the wastewater.

Treatment of industrial oily wastewaters by wet oxidation.

In the present work, the homogeneous wet oxidation (WO) of an oily wastewater (COD approximately 11,000 mg l(-1)), composed mainly of alcohols and phenolic compounds, was studied in a high-pressure agitated autoclave reactor in the temperature range of 180-260 degrees C and oxygen pressure 1 MPa. Temperature was found to have a significant impact on the oxidation of the contaminants in the wastewater. Among the compounds contained in the wastewater, ethylene glycol showed great resistance to wet oxidation. Temperatures above 240 degrees C were required for its effective degradation. Organic acids, mainly acetic acid, were the intermediate products of the wet oxidation process and their conversion to carbon dioxide was very slow. A generalised model based on a parallel reaction scheme was used to interpret the experimental data obtained. The activation energies obtained were in the range of 90-130 kJ mol(-1).

Speciated hydrocarbon and carbon monoxide emissions from an internal combustion engine operating on methyl tertiary butyl ether-containing fuels.

In the present work, engine and tailpipe (after a three-way catalytic converter) emissions from an internal combustion engine operating on two oxygenated blend fuels [containing 2 and 11% weight/weight (w/w) methyl tertiary butyl ether (MTBE)] and on a nonoxygenated base fuel were characterized. The engine (OPEL 1.6 L) was operated under various conditions, in the range of 0-20 HP. Total unburned hydrocarbons, carbon monoxide, methane, hexane, ethylene, acetaldehyde, acetone, 2-propanol, benzene, toluene, 1,3-butadiene, acetic acid, and MTBE were measured at each engine operating condition. As concerns the total HC emissions, the use of MTBE was beneficial from 1.90 to 3.81 HP, which were by far the most polluting conditions. Moreover, CO emissions in tailpipe exhaust were decreased in the whole operation range with increasing MTBE in the fuel. The greatest advantage of MTBE addition to gasoline was the decrease in ethylene, acetaldehyde, benzene, toluene, and acetic acid emissions in engine exhaust, especially when MTBE content in the fuel was increased to 11% w/w. In tailpipe exhaust, the catalyst operation diminished the observed differences. Ethylene, methane, and acetaldehyde were the main compounds present in exhaust gases. Ethylene was easily oxidized over the catalyst, while acetaldehyde and methane were quite resistant to oxidation.