132 research outputs found

    Kinetic and degradation efficiency of trichloroethylene (TCE) via photochemical process from contaminated water

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    Trichloroethylene (TCE) is a common pollutant in groundwater and one of the priority pollutants listed by the U.S. EPA. With regard to concentration ranges in previous studies exceeding environmental levels by far with millimolar concentrations of TCE, this study deals with the degradation of TCE at micromolar concentrations by UV/H2O2. The degradation rate of TCE at different dilute solution levels, 30, 300 and 3000 g L-1 (0.22, 2.28 and 22.83 micromolar) at different initial pHs was examined. In addition, samples were taken from four contaminated wells to measure the degradation rate of TCE. It was shown that thedegradation rate of TCE increased due to the reduction of initial concentration in both aqueous solution and groundwater samples. The TCE degradation constants in groundwater samples increased by a factor of 2.05, while the initial concentration reduced from 1345.7 to 97.7 μg1 L-1. By increasing the molar ratios of H2O2 to TCE from 13 to 129, caused the degradation rates to increase in aqueous solutions. No harmful byproducts such as aloacetic acids (HAAs) were detected at these low levels of initial concentration of TCE during process. This study confirmed that application of UV/H2O2 process could be an effective method in treating contaminated groundwater by TCE at low concentrations

    Efficiency of advanced oxidation and hydroxyl technology in methyl terciary – butyl ether (MTBE)

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    زمینه و هدف: فرآیندهای اکسیداسیون پیشرفته بعنوان روش های سریع و موثر برای تصفیه دامنه وسیعی از آلایندهای آلی مقاوم به اثبات رسیده است. هدف از این تحقیق آزمایش استفاده از O3 در ترکیب با یونهای هیدروکسیل (pH بالا) بعنوان تسریع کننده واکنش ها برای تجزیه MTBE در فاضلاب های صنعتی و آبهای آلوده به آن بود. روش مطالعه: در این مطالعه که از نوع نیمه تجربی می باشد: اثر O3 در ترکیب با یونهای هیدروکسیل (pH بالا) بعنوان تسریع کننده واکنش هایی که منجر به تولید رادیکال های هیدروکسیل می شوند برای تجزیه متیل ـ ترشیاری ـ بوتیل اتر ( MTBE) در فاز مائی مورد آزمایش قرار گرفت. تمامی واکنش ها در داخل یک راکتور ستونی حبابی نیمه پیوسته نسبت به جریان ازن و پیوسته نسبت به MTBE رخ داد. در این تحقیق اثر pH و زمان واکنش و میزان ازن مورد نیاز برای رسیدن به تجزیه کامل MTBE در غلظت ثابتی از ازن و در پنج pH مختلف (10،5/10،11،5/11 و 12) به مدت 100 دقیقه برای هر pH مورد آزمایش قرار گرفت. نتایج: آزمایش نشان داد که 5/11=pH، نسبت Intermediates / MTBE º=0.60 v/mM بود که در مقایسه با نزدیکترین نسبت بعد از آن ( مربوط به 11pH=) به میزان20% بیشتر است.کمترین زمان و ازن مورد نیاز برای تجزیه 90% هر مول از MTBE که به ترتیب معادل 70دقیقه و 3/5 مول بود در 5/11pH= رخ داد. آزمایشات انجام شده برای تعیین میزان MTBE حذف شده به سبب فراریت به هوا نشان داد که این میزان در مدت 100 دقیقه در pH های مختلف 5/19-11% بود. آزمایشات نشان داد که در سطح خطای 5% هیچگونه رابطه معنی داری بین میزان MTBE حذف شده از محیط بدلیل فراریت به هوا و pH محیط در محدوده pH های 12-10 وجود ندارد. نتیجه گیری: MTBE یک ترکیب سنتزی است که حتی در فرآیندهای اکسیداسیون پیشرفته نسبتا در مقابل تجزیه از خود مقاومت نشان می دهد ولی با ادامه اکسیداسیون به طور کامل قابل تجزیه است. بهترین pH برای تجزیه MTBE به وسیله واکنش های رادیکال 5/11 است

    Modes of Transmission of Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) and Factors Influencing on the Airborne Transmission: A Review

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    The multiple modes of SARS-CoV-2 transmission including airborne, droplet, contact, and fecal–oral transmissions that cause coronavirus disease 2019 (COVID-19) contribute to a public threat to the lives of people worldwide. Herein, different databases are reviewed to evaluate modes of transmission of SARS-CoV-2 and study the effects of negative pressure ventilation, air conditioning system, and related protection approaches of this virus. Droplet transmission was commonly reported to occur in particles with diameter \u3e5 µm that can quickly settle gravitationally on surfaces (1–2 m). Instead, fine and ultrafine particles (airborne transmission) can stay suspended for an extended period of time (≥2 h) and be transported further, e.g., up to 8 m through simple diffusion and convection mechanisms. Droplet and airborne transmission of SARS-CoV-2 can be limited indoors with adequate ventilation of rooms, by routine disinfection of toilets, using negative pressure rooms, using face masks, and maintaining social distancing. Other preventive measures recommended include increasing the number of screening tests of suspected carriers of SARS-CoV-2, reducing the number of persons in a room to minimize sharing indoor air, and monitoring people’s temperature before accessing a building. The work reviews a body of literature supporting the transmission of SARS-CoV-2 through air, causing COVID-19 disease, which requires coordinated worldwide strategies

    Evaluation of Diethyl phthalate and Diallyl phthalate biodegradation mechanisms in the treatment of synthetic wastewater

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    Background and Aims: Over the last few years, Phethalic Acid Esters (PAEs) have attracted a widespread attention due to their widespread production and use. These compounds are not only linked to endocrine disruption and cancer but also considered as emerging and hazardous pollutants. Large amounts of PAEs have been detected in industrial wastewaters. Given the widespread use of biological processes in industrialwastewater treatment, this study aimed to identify biodegradation pathways of PAEs and their potential metabolites.Materials and Methods: Two short-chain esters from phthalic acid esters including diethyl phthalate (DEP) and diallyl phthalate (DAP) were selected in the present study. We used the survey of metabolites in a moving bed biofilm reactor effluent to determine biodegradation pathways of designated esters at hydraulic retention times of 1 to 12 hours. Influent concentration of 100 mg/l was also considered throughout the study.Results: Phthalic acid, mono-methyl phthalate, dimethyl phthalate and catechol were identified as the most noteworthy metabolites in biodegradation of both esters. The degradation pathway of both studied compounds was similar and involves either detachment of ester-chain or removal of methyl group, followed by few decomposition steps resulting in the production of benzene ring. The degradation can proceed further with ring cleavage and it ends with 2-hydroxy muconic semi-aldehyde.Conclusion: The main route for removal of studied compounds was de-esterification followed by demethylation. According to identifies degradation pathways and metabolites produced, biodegradation can be considered as a reliable treatment process for industrial wastewaters containing PAEs.Key words: Biodegradation, Phthalic Acid Esters, Synthetic wastewater

    Continuous adsorption of natural organic matters in a column packed with carbon nanotubes

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    In the present study, continuous adsorption experiments were carried out in an adsorption column to survey the efficiency of the carbon nanotubes (CNTs) for removal of natural organic matters (NOMs) from aqueous solution. Parameters such as mass of CNTs, initial NOMs concentration were evaluated and also the breakthrough curves were obtained. Experiments performed with various initial NOMs concentration and various CNTs masses. The breakthrough period was longer at lower initial NOMs concentration. Increase of the initial NOMs concentration, expectedly, resulted in the faster saturation of the CNTs bed. The adsorption capacities for multi wall carbon nanotubes (MWCNT) and single wall carbon nanotubes (SWCNT) in highest initial NOMs concentration were 53.46 and 66.24 mg/g, respectively. The effect of amount of CNTs on breakthrough time and volume of treated water was investigated and resulted that with an increase in the mass of CNTs, breakthrough time occurs very late and the volume of treated water increased. These findings suggested that CNTs present a great potential in removal of NOMs from aqueous solutions

    Determination of Heavy Metals through Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) in Iranian Cheese and Their Potential Health Risks to the Adult Consumers

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    In Iran, cheese is one of the dairy products that widely consumed as a main diet for breakfast. Moreover, trace metals in dairy products have recently gained considerable attention. Iranian cheese samples were collected from Tehran, Iran (February to May 2013). Trace metals including Pb, Cd, Ni, Fe, Sn, Zn, Cr, and Cu were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) after dry ashing. All the tested metals were detected in the cheese samples. The mean concentration of metals in cheese showed the following decreasing order Zn > Fe > Cu > Ni > Sn > Cr > Pb > Cd, with values of 12.98, 7.95, 1.96, 0.83, 0.46, 0.37, 0.34, and 0.01 mg/kg, respectively. There were no significant differences between types of cheese samples in terms of content of trace metals (p>0.05). All the samples had Pb contents of greater than Codex limit (0.02 mg/kg). According to the measured values of the metals in this study, the intake of all the studied elements through the common consumption of cheese in Iran was below the dangerous level according to permissible intake value for each metal. Also, levels of correlations between the element pairs were analyzed

    Health impact assessment of air pollution in Shiraz, Iran : a two-part study

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    We aimed to assess health-impacts of short-term exposure to the air pollutants including PM10, SO2, and NO2 in Shiraz, Iran in a two-part study from 2008 to 2010. In part I, local relative risks (RRs) and baseline incidences (BIs) were calculate using generalized additive models. In part II, we estimated the number of excess hospitalizations (NEHs) due to cardiovascular diseases (CDs), respiratory diseases (RDs), respiratory diseases in elderly group (RDsE-people older than 65 years old), and chronic obstructive pulmonary diseases (COPDs) as a result of exposure to air pollutants using AirQ model, which is proposed approach for air pollution health impact assessment by World Health Organization. In part I, exposure to increase in daily mean concentration of PM10 was associated with hospitalizations due to RDs with a RR of 1.0049 [95% confidence interval (CI), 1.0004 to 1.0110]. In addition, exposure to increase in daily mean concentration of SO2 and NO2 were associated with hospitalizations due to RDsE and COPDs with RRs of 1.0540 [95% CI, 1.0050 to 1.1200], 1.0950 [95% CI, 1.0700 to 1.1100], 1.0280 [95% CI, 1.0110 to 1.0450] and 1.0360 [95% CI, 1.0210 to 1.0510] per 10 μg/m3 rise of these pollutants, respectively. In part II, the maximum NEHs due to CDs because of exposure to PM10 were in 2009-1489 excess cases (ECs). The maximum NEHs due to RDs because of exposure to PM10 were in 2009-1163 ECs. Meanwhile, the maximum NEHs due to RDsE and COPDs because of exposure to SO2 were in 2008, which are 520 and 900 ECs, respectively. In conclusion, elevated morbidity risks were found from acute exposure to air pollutants
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