2007_6_Nr6_EEMJ

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Surpateanu et al. /Environmental Engineering and Management Journal 6 (<strong>2007</strong>), 6, 521-527 air dried to constant mass at room temperature and sieved (size 2 mm) were subjected to microwave heating with 8 ml of ultrapure water at 600 W. After that the extract containing POPs was transferred to a 10 ml volumetric flask. Sediments were further rinsed with 2 ml ultrapure water and the rinsate was transferred to the same 10 ml volumetric flask. For the enrichment and extraction procedure a particular syringe with a cone-tipped needle was used and toluene was selected as solvent. Toluene (5 µl) was drawn into the syringe and the needle was tightly fitted to a 1.3-cm length of HFM that was previously heat-sealed at the other end. The HFM was impregnated with toluene for 10 s to dilate the membrane pores then the syringe needle-HFM was immersed 5 mm below the surface of the sample solution under agitation on the magnetic stirrer. Extraction between the toluene within the HFM and the sample solution was allowed to proceed, allowing the analytes to diffuse though porous membrane and dissolve into the toluene. After the mass transfer of analytes from the aqueous sample solution to organic phase the toluene in the HFM was withdrawn into the syringe, which was then removed from sample solution. The extracted compounds (organochlorine pesticides such as Lindane, Heptachlor, Aldrin, Dieldrin etc. and polychlorinated biphenyls such as 2- dichlorobiphenyl, 2,3-dichlorobiphenyl, 2,4,5- trichlorobiphenyl etc.) were analysed by GC-MS. The proposed method for quantifying POPs exhibits some advantages compared to SE or conventional heating because is relatively simple, requires a low volume of solvent and eliminates carry-over effects through the use of disposable HFM. Other categories of compounds analysed by intermediate of MWAE include nonylphenol ethoxylates (NPEO) and nonylphenol (NP), the first representing a significant fraction of non-ionic surfactant market. NPEO and their metabolites exhibit toxic effects on the aquatic organisms due to their ability to mimic natural hormones (estrogens) inducing endocrine disruption. Those compounds are discharged to the environment through the wastewater treatment plant effluents and they have been detected both in soils and aquatic organisms (Johnes and Heathwaite, 1992). MWAE was used for the determination of NPEO and NO in sewage sludge and method efficiency was evaluated as to linearity, repeatability, accuracy, and sensitivity (Fountoulakis et al., 2005). Thus, it was pursue to develop and optimise MWAE for the specifically extraction of the two compounds followed by their determination using HPL coupled with fluorescence detector. Environmental samples were collected from the sewage treatment plants in Greece, conserved by immediate addition of 1% formaldehyde and, when not immediately analysed, were stored in the dark at 4°C. Prior to the analysis of NP and NPEO, the samples were filtered and dried in the oven at 35°C, and the resulting solids were grinded. MWAE procedure was performed on the dried samples (0.03-0.3 g) in perfluoroalcoxy (PFA) copolymer resin Teflon-lined extraction vessel after the addition of 20 ml solvent, namely hexane/acetone: 1/1 (v/v) or dichloromethan/methanol: 3/7 (v/v). The extractions were performed at various conditions of temperature (100 and 120°C) and power (600 and 1200 W). The extraction time was 17 min. After cooling, the extracts were concentrated to an approximate volume of 1 ml using a rotary vacuum evaporator; the resulted concentrate was redisolved in 10 ml acetonitrile and the organic phase was analysed by HPLC-FD after filtration. It was observed higher extraction recoveries (61.4% for NPEO and 91.4% for NP) when 1 ml water was added to dry sample prior to extraction. MWAE technique was successful aplicated for the determination of some quinolone antibacterial agents (flumequine and oxolinic acid) from sediments and soils (Prat et al., 2006). Such as many antibacterial agents, oxolinic acid (OXO) and flumequine (FLU) exhibit great chemical stability and high sorption coefficients and these characteristics contribute to their accumulation in sediments and soils. Half-lives of these compounds are appreciated at 150 days (Johnes et al., 2002). The extraction of the analytes was performed by liquid-liquid partition between a sample homogenate in an aqueous buffer solution and a non-miscible organic solvent and MWAE was used to improve the speed and efficiency of the extraction process. The environmental samples (marine sediments and soils) were oven-dried (110°C), sieved (90 µm) and stored in the dark at – 20°C. Before the analysis the samples were thawed and, for recoveries studies, were spiked by adding 0.5 ml of an aqueous standard solution containing OXO and FLU to 0.5 g dray sediment or soil sample. The mixture was equilibrated by shaking for 15 min and then left standing overnight at room temperature in the dark. Microwave-assisted extraction was performed in a PFTE vessel before the addition of 10 ml of 1 M phosphoric acid buffer at pH 2 to samples prepared as above mentioned with 10 ml dichloromethane. After microwave irradiation (22 min, 90°C) the vessel was air-cooled to below 40°C then the content was transferred in a 30-ml glass tube and centrifuge (5 min, 4000 rpm). A clean-up step to remove some of coextracted compounds was introduced consisting in back-extraction in 1 M sodium hydroxide. The determination was carried out by reversed phase liquid chromatography on an octyl silica-based column and fluorimetric detection. Resulted solution was filtered by a 0.45 µm nylon membrane and injects into chromatograph. The absolute recoveries rates were determined from spiked samples by comparing peak areas of calibration standard solutions. The values range from 79% to 94% for the whole process. In the same manner, microwave assisted extraction was used to determine methylmercury from polluted sediments in comparison with manual and supercritical fluid extraction techniques (Lorenzo et al., 1999). The experiments were carried out on freeze dried sediment samples sieved to a particle size below 524
Microwave assisted chemistry-a review of environmental application 300 µm. Spiked samples were prepared with methanol containing known concentration of methylmercury to appreciate the extent of recoveries. The determination is based on the separation by gas chromatography followed by electron capture detection. It was showed that manual (conventional) and microwave-assisted extraction produce almost identical extract. Nevertheless, the conventional extraction procedure is time- and labour-intensive (2- 3 hours) and requires the uses of relatively large amounts of toxic organic solvents. Supercritical fluid extraction in most cases produces similar recoveries with manual extraction and has the advantage that is relatively fast (50 min) but matrix effects may be important. MWAE provide a reliable and advantageous extraction procedure because requires smaller volumes of organic solvents than the manual technique, and total sample-processing time is reduced by the shorter extraction time (usually no more than 10 min) and simultaneous extraction of several samples. Moreover, the microwave-assisted extraction appears to be much less dependent on the sediment matrix. A novel application of microwave heating effect in environmental protection regards the treatment and disposal of healthcare wastes (Diaz et al., 2005). Wastes produced in healthcare facilities in developing countries have raised serious concerns because of the inappropriate treatment and final disposal practices accorded to them. Inappropriate treatment and final disposal of wastes can result in negative impacts to public health and to environment. Some of the more common treatment and disposal methods used in the management of infectious healthcare wastes in developing countries are: autoclaves and retorts; microwave disinfection systems; chemical disinfections; combustion and disposal on land (dump site, controlled landfill, pits, and sanitary landfill). Microwave systems in the healthcare waste sector commonly require the addition of water. Microwave disinfection systems typically consist of three major types of equipment: (1) material handling equipment, (2) the disinfection equipment itself, and (3) environmental control equipment. The disinfection area or enclosure includes a hermetically enclosed chamber, where the materials to be treated are placed and into which the microwaves are focused. Microwave systems are designed and built in a variety of sizes, ranging from a few kg per hour to more than 400 kg per hour. The units can be operated as a batch process or in a semi-continous mode. Large-scale systems can have from 1 to 6 microwave generators and, generally, each generator has a power output on the order of 1.2 kW. For microwave disinfection process the waste to be treated is placed in carts and transported to the treatment facility (e.g. a mobile microwave unit). The carts are lifted by a hydraulic mechanism and the waste is discharged into a hopper after the gate is opened. As the waste is introduced into the hopper, steam is injected there and the air is extracted from the unit. All extracted air is passed through a high efficiency particulate air filter. The waste in hopper is forced into a shredder. The shredded waste is transported via a rotating screw, exposed to steam, and then heated between 95-100 °C by means of microwaves. The treated waste may be passed through a secondary shredder to achieve a higher degree of particle size reduction than with only one shredder. The disinfection in microwave units is not a result of material exposure to the microwaves. The steam produced from the moisture in the waste by the microwave energy brings about the destruction of the pathogenic organisms in the waste. Other papers indicate that microwaves proved effective in destruction of pathogens in sewage sludge (Hong et al., 2004). Thus, the mechanisms and roles of microwaves on fecal coliform destruction were investigated by different methods like as bacterial viability tests, electron transport system and β- galactosidase activity assay, gel electrophoresis etc. Live/dead cell bacterial viability kits were used to investigate the cell wall damage of fecal coliforms caused by microwaves compared with that by external heating. Sludge samples from wastewater treatment plant were irradiated in a 200 ml beaker in a microwave oven, which operate at a frequency of 2450 MHz. In general, microwave irradiation for 60 s led to almost complete destruction of coliforms while external heating needed 100°C. This indicates that microwave technology is superior to external heating in terms of pathogen destruction, methane generation and energy requirement. So, the microwave irradiation of sludge appears to be a viable and economical method of destructing pathogens and generating environmentally safe sludge. By means of microwave technology it is possible the processing of industrial of hazardous industrial waste. Such wastes are currently disposed on landfill sites and this practice is concerned in groundwater’s pollution as result of some toxic compounds leaching. Differing from conventional treatments microwave irradiation may catalyse chemical reactions by a selective heating explained by a special dipolar oscillating and dielectric losses effect. Thus, reversed temperature gradients can be generated in a microwave field and the activation energy in sterilisation, sintering and chemical reactions can be reduced. The microwave irradiation was also used to denature the β-glucosidase fraction associated with viable microorganisms from soils as an estimate of extracelular (abiontic) activity (Knight and Dick, 2004). This is because the β-glucosidase activity can detect soil management effects and has potential as a soil quality indicator that could be used in conjunction with other soil analyses for several reasons. First, it catalyzes the final step in the biodegradation of cellulose compounds and the subsequent release of glucose to microorganisms. 525
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Editor-in-Chief: Prof. Matei Macove
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