Temesgen Garoma

Removal of sulfadiazine, sulfamethizole, sulfamethoxazole, and sulfathiazole from aqueous solution by ozonation.

The removal of sulfadiazine, sulfamethizole, sulfamethoxazole, and sulfathiazole from aqueous solution by ozonation was studied. The study was conducted experimentally in a semi-batch reactor under different experimental conditions, i.e., varying influent ozone gas concentration, bicarbonate ion concentration, and pH. The results of the study indicated that ozonation could be used to effectively remove the sulfonamides from water. The sulfonamides exhibited moderate reactivity towards aqueous ozone, k(O)(3) >2 x 10(4) M(-1)s(-1) at pH of 2 and 22 degrees C. The mol of ozone absorbed by the solution per mol of sulfonamides removed varied in the range of 5.5-12.0 with lower ranges representing ozone absorption by the solution at the beginning of the ozonation process whereas higher ratios correspond to >99.9% removal of the target sulfonamides. The removal rate of the sulfonamides improved with bicarbonate ion concentration up to 8mM but further increase in bicarbonate ion decreased removal efficiency. It was also observed that increasing the pH from 2.0 to 10.0 resulted in enhanced removal of the sulfonamides.

Ozonation of aqueous solution containing bisphenol A: effect of operational parameters.

The degradation of bisphenol A (BPA) in aqueous solution by ozonation was studied. The study was conducted experimentally in a semi-batch reactor under different operational conditions, i.e., varying influent ozone gas concentration, initial BPA concentration, pH, and bicarbonate ion concentration. The results of the study indicated that ozonation could be used to effectively remove BPA from contaminated water. Keeping other operational parameters constant, the rate of BPA degradation linearly increased with ozone dosage. At pH value of 7.0, the second-order rate constants for the reaction of BPA with aqueous ozone were determined as 1.22 x 10(5), 1.71 x 10(5), and 2.59 x 10(5)M(-1)s(-1) for ozone gas dosages of 1.4, 2.2, and 5.1 mg L(-1), respectively. Bicarbonate ion in the range of 1.0-8.0 mM (61-488 ppm) showed no significant effect on BPA degradation for concentrations of BPA used in the study (23.0-57.0 microM). It was also observed that the rate of BPA degradation increased with pH up to 7.0, resulting in rate constants of 0.48 x 10(5), 0.94 x 10(5), and 1.71 x 10(5)M(-1)s(-1) at pH values of 2.0, 5.0, and 7.0, respectively; and the rate constant decreased to 1.16 x 10(5)M(-1)s(-1) at pH of 10.0.

Treatment of groundwater contaminated with gasoline components by an ozone/UV process

In this paper, the treatment of real groundwater samples contaminated with gasoline components, such as benzene, toluene, ethylbenzene, and xylene (BTEX), methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), and other gasoline constituents in terms of total petroleum hydrocarbons as gasoline (TPHg) by an ozone/UV process was investigated. The treatment was conducted in a semi-batch reactor under different experimental conditions by varying ozone gas dosage and incident UV light intensity. The groundwater samples contained BTEX compounds, MTBE, TBA, and TPHg in the ranges of 5-10000, 3000-5500, 80-1400, and 2400-20000 microgl(-1), respectively. The ozone/UV process was very effective compared to ozonation in the removal of the gasoline components from the groundwater samples. For the various gasoline constituents, more than 99% removal efficiency was achieved for the ozone/UV process and the removal efficiency for ozonation was as low as 27%. The net ozone consumed per mol of organic carbon (from BTEX, MTBE, and TBA) oxidized varied in the range of 5-60 for different types of groundwater samples treated by the ozone/UV process. In ozonation experiments, it was observed that the presence of sufficient amount of iron in groundwater samples improved the removal of BTEX, MTBE, TBA, and TPHg.

SMX degradation by ozonation and UV radiation: A kinetic study

The rate constants of sulfamethoxazole (SMX) degradation by ozonation and UV(254) radiation were investigated under various parameters including influent ozone gas concentration, initial SMX concentration, UV light intensity, ionic strength, water quality in terms of varying anions (bicarbonate, sulfate and nitrate), humic acid (HA) and pH. The results indicated that the removal of SMX by ozonation and UV(254) radiation fitted well to a pseudo first-order kinetic model and the rate constants were in the range of (0.9-9.8)×10(-3) and (1.7-18.9)×10(-3) s(-1), respectively. The second-order rate constants of SMX with ozone (ko(3)), under varying operational parameters, were also determined and varied in the range of (0.60-3.38)±0.13×10(5)M(-1) s(-1). In addition, SMX degradation through UV pretreatment followed by ozonation in the presence of HA was proved to be an effective method which can remove SMX with a low ozone dose. The results suggested that ozonation of SMX was more affected by concentration of influent ozone gas, alkalinity, and HA, while incident UV light intensity, pH, and HA were the dominant factors influencing UV degradation of SMX.

Treatment of persistent organic compounds by integrated advanced oxidation processes and sequential batch reactor

The objective of this study was to evaluate the extent of improvement in the biodegradability of persistent organic compounds by pre-oxidation by using Sequential Batch Reactors (SBRs). Dichlorodiethyl ether (DCDE), a non-biodegradable compound, was used as a test chemical. Ozonation, Fenton reagent and ultra-violet light coupled with hydrogen peroxide (UV/H(2)O(2)) were used for oxidation of DCDE at levels of 50-100%. Pre-oxidized DCDE solutions were then subjected to SBR studies using activated sludge to determine the rate and extent of biodegradation of oxidation by-products. The results indicated that the biodegradability of pre-oxidized DCDE increased drastically, reaching an average of 90% for all three oxidation methods versus zero for non-oxidized DCDE. It was concluded that the results of SBR experiments may be better indicators of biodegradability of chemically-oxidized wastewaters due to significant acclimation of microorganisms in SBRs, which cannot be observed in conventional respirometric laboratory studies.

Removal of Bisphenol A and its Reaction-Intermediates from Aqueous Solution by Ozonation

In this study, the oxidation of Bisphenol A (BPA) and its reaction-intermediates in aqueous solution by ozonation was investigated. The results of the study indicated that ozonation is effective in oxidizing BPA. Catechol, resorcinol, acetone, formaldehyde and organic acids, acetic, formic, maleic, and oxalic acid, are identified as reaction-intermediates. Ozonation of 51 μM (770 μM C) of BPA resulted in peak concentrations of 16.3, 8.7, 6.8, and 2.0 μM C of catechol, resorcinol, acetone, and formaldehyde, respectively. These concentrations correspond to 2.1, 1.1, 0.9, and 0.3% of the initial concentration of BPA in terms of total organic carbon for catechol, resorcinol, acetone, and formaldehyde, respectively. It was observed that BPAs reaction-intermediates were resistant to ozonation compared to the parent compound and complete mineralization of BPA may need extended ozonation.

Modeling the influence of ethanol on the adsorption and desorption of selected BTEX compounds on bentonite and kaolin.

The influence of ethanol on the adsorption capacity and desorption kinetics of benzene and toluene on bentonite and kaolin through modeling and experimental study was investigated. The results showed that the adsorption capacity of both soils for the target compounds decreased as ethanol content increased. As ethanol content increased from 0 to 50%, the adsorption capacity for benzene and toluene on bentonite decreased from 3.6 to 0.54 microg(n+1)/(L(n) x g) (by 85%) and 1.91 to 0.01 microg(n+1)/(L(n) x g) (by 99.5%), respectively. For benzene and toluene adsorption on kaolin, the adsorption capacity decreased by 86.5% (from 0.26 to 0.04 microg(n+1)/(L(n) x g) and 98.2% (from 0.13 to 0.002 microg(n+1)/(L(n) x g)), respectively, as ethanol content increased from 0 to 50%. In addition, the desorption rate of benzene and toluene from bentonite decreased by about one order of magnitude as the ethanol increased from 0 to 25% and 0 to 50%, respectively. It can be inferred that ethanol could affect the effectiveness of natural attenuation processes that rely on adsorption to soils as a containment technique for benzene and toluene by retarding the adsorption to soils and remobilizing compounds that had already been adsorbed to soils.

Degradation of tert-butyl formate and its intermediates by an ozone/UV process

In this paper, the oxidation of tert-butyl formate (TBF) in aqueous solution by an ozone/UV process was described. The oxidation process was investigated experimentally in a semibatch reactor. The results of the study indicated that the ozone/UV process was very effective in oxidizing TBF. tert-Butyl alcohol (TBA), hydroxy-iso-butyraldehyde (HiBA), acetone, formaldehyde, and formic acid were identified as major primary intermediates during the oxidation of TBF. About 90% organic carbon balance was obtained indicating that most reaction intermediates have been identified and quantified. Some of the primary intermediates were also oxidized in the ozone/UV system. Accordingly, HiBA, acetone, formaldehyde, and formic acid were the primary intermediates of TBA oxidation. The oxidation of acetone in the ozone/UV system generated formaldehyde, pyruvaldehyde, acetic acid, formic acid as primary intermediates. It was also observed that the reaction intermediates formed during the oxidation of TBF react well in the ozone/UV system and complete mineralization could be achieved by the process.

Electroporation of Chlorella vulgaris to enhance biomethane production

This research investigated the feasibility of using electroporation (EP) as a pretreatment method for algal biomass used as feedstock for anaerobic digestion. The results showed that pretreating algal biomass with EP significantly improved the soluble COD (SCOD), increasing it to more than 830% at 28 kWh/m(3) treatment intensity (TI). Besides TI, culture conditions also affected the performance of the EP process. On the basis of SCOD, a sample pH of 7.0 and cell concentration of 13.2g/L were found to be optimal for the EP process. Despite a direct relationship between TI and ionic strength (IS), SCOD decreased with increasing IS. At 35 kWh/m(3) TI, bio-CH4 production increased by as high as 110%. It was also observed that lower TI levels resulted in high rates of gain per energy input compared to higher degrees of treatment.

An investigation of ultrasound effect on digestate solubilization and methane yield

In this study, different ultrasound power intensities of 0.05-0.21kW/L (4.13-16.52kWh/kg TS) were applied at a frequency of 20kHz and for durations of 5-20min to digestate obtained from a domestic wastewater treatment plant. The ultrasonic effect on digestate solubilization was revealed by increased levels of soluble Chemical Oxygen Demand (sCOD), soluble Total Organic Carbon (sTOC), and soluble Total Nitrogen (sTN) released into the solution. The highest material release was achieved at an ultrasonic energy intensity of 0.21kWh/L. Furthermore, the ultrasonic effect on CH4 production was studied using the anaerobic digestion process. The application of ultrasound at 0.05-0.21kWh/L provided 1.6-2.3-fold increase in net CH4 production. Analysis of the energetics of the system showed that only about 4 and 11% of the energy input was recovered in terms of additional CH4 production at 0.21 and 0.05kWh/L, respectively. A comprehensive cost-benefit analysis of the system is required for making a conclusion on the feasibility of the system, and such analysis should include environmental, economic, and societal benefits of the system, among others.