Rimeh Daghrir

Photoelectrocatalytic degradation of chlortetracycline using Ti/TiO2 nanostructured electrodes deposited by means of a Pulsed Laser Deposition process

Ti/TiO(2) electrode was prepared by means of the Pulsed Laser Deposition method and used in a photoelectrocatalytic oxidation (PECO) process in order to degrade chlortetracycline (CTC). The deposited TiO(2) coatings were found to be of rutile structure. High treatment efficiency of CTC was achieved by the PECO process compared to the conventional electrochemical oxidation, direct photolysis and photocatalysis processes. Several factors such as current intensity, treatment time, UV lamp position and initial concentration of CTC were investigated. Using a 2(4) factorial matrix, the best performance for CTC degradation (74.3% of removal) was obtained at a current intensity of 0.5A during 120 min of treatment time and when the UV lamp was immersed in the solution in the presence of 25 mg L(-1) of CTC. The current intensity and treatment time were the main parameters influencing the degradation rate of CTC. Subsequently, a central composite design methodology has been investigated to determine the optimal experimental parameters for CTC degradation. The PECO process applied under optimal conditions (at current intensity of 0.39 A during 120 min with internal position of the UV lamp) is able to oxidize around 74.2 ± 0.57%, of CTC.

Di 2-ethylhexylphtalate in the aquatic and terrestrial environment: A critical review

Phthalates are being increasingly used as softeners-plasticizers to improve the plasticity and the flexibility of materials. Amongst the different plasticizers used, more attention is paid to di (2-ethylhexylphtalate) (DEHP), one of the most representative compounds as it exhibits predominant effects on environment and human health. Meanwhile, several questions related to its sources; toxicity, distribution and fate still remain unanswered. Most of the evidence until date suggests that DEHP is an omnipresent compound found in different ecological compartments and its higher hydrophobicity and low volatility have resulted in significant adsorption to solids matrix. In fact, there are important issues to be addressed with regard to the toxicity of this compound in both animals and humans, its behavior in different ecological systems, and the transformation products generated during different biological or advanced chemical treatments. This article presents detailed review of existing treatment schemes, research gaps and future trends related to DEHP.

Surfactants in aquatic and terrestrial environment: occurrence, behavior, and treatment processes

Surfactants belong to a group of chemicals that are well known for their cleaning properties. Their excessive use as ingredients in care products (e.g., shampoos, body wash) and in household cleaning products (e.g., dishwashing detergents, laundry detergents, hard-surface cleaners) has led to the discharge of highly contaminated wastewaters in aquatic and terrestrial environment. Once reached in the different environmental compartments (rivers, lakes, soils, and sediments), surfactants can undergo aerobic or anaerobic degradation. The most studied surfactants so far are linear alkylbenzene sulfonate (LAS), quaternary ammonium compounds (QACs), alkylphenol ethoxylate (APEOs), and alcohol ethoxylate (AEOs). Concentrations of surfactants in wastewaters can range between few micrograms to hundreds of milligrams in some cases, while it reaches several grams in sludge used for soil amendments in agricultural areas. Above the legislation standards, surfactants can be toxic to aquatic and terrestrial organisms which make treatment processes necessary before their discharge into the environment. Given this fact, biological and chemical processes should be considered for better surfactants removal. In this review, we investigate several issues with regard to: (1) the toxicity of surfactants in the environment, (2) their behavior in different ecological systems, (3) and the different treatment processes used in wastewater treatment plants in order to reduce the effects of surfactants on living organisms.

Photosonochemical degradation of butyl-paraben: Optimization, toxicity and kinetic studies

The objective of the present work is to evaluate the potential of a photosonolysis process for the degradation of butyl-paraben (BPB). After 120 min of treatment time, high removal of BPB was achieved by the photosonolysis (US/UV) process (88.0±0.65%) compared to the photochemical (UV) and the conventional ultrasonication (US) processes. Several factors such as calorimetric power, treatment time, pH and initial concentration of BPB were investigated. Using a 2(4) factorial matrix, the treatment time and the calorimetric power are the main parameters influencing the degradation rate of BPB. Subsequently, a central composite design methodology has been investigated to determine the optimal experimental parameters for BPB degradation. The US/UV process applied under optimal operating conditions (at a calorimetric power of 40 W during 120 min and under pH7) is able to oxidize around 99.2±1.4% of BPB and to record 43.3% of mineralization. During the US/UV process, BPB was mainly transformed into 1 hydroxy BPB, dihydroxy BPB, hydroquinone and 4-hydroxybenzoic acid. Microtox biotests (Vibrio fisheri) showed that the treated effluent was not toxic. The pseudo-first order kinetic model (k=0.0367 min(-1)) described very well the oxidation of BPB.

Electrochemical degradation of chlortetracycline using N-doped Ti/TiO2 photoanode under sunlight irradiations

The appearance and the persistence of pharmaceutical products in the aquatic environment urgently call for the development of an innovative and practical water treatment technology. This study deals with the development of nanostructured nitrogen-doped TiO2 photoanodes and their subsequent use for chlortetracycline (CTC) photoelectrocatalytic oxidation under visible light. The N-doped TiO2 photoanodes with different nitrogen contents were prepared by means of a radiofrequency magnetron sputtering (RF-MS) process, with the objective to tune shift their optical absorption from the UV towards the visible. The N-doped TiO2 consist of nanostructured anatase phase with average TiO2 nanocrystallite size of 29 nm. The nitrogen doping is clearly shown to produce the desired red shift of the absorption onset of the TiO2 coatings (from ~380 nm to ~550 nm). Likewise, the N-doped TiO2 are found to be highly photo-electroactive not only under the UV light but most interestingly under the visible light as well. Using the optimal N-doped photoanodes, 99.6% of CTC (100 μg/L) was successfully degraded after 180 min of treatment time with a current intensity of 0.6 A. Under these conditions, a relatively high mineralization of CTC (92.5% ± 0.26% of TOC removal and 90.3% ± 1.1% of TN removal) was achieved.

Removal of microcystin-LR from spiked water using either activated carbon or anthracite as filter material.

The occurrence of cyanobacterial toxins (blue-green algae) in drinking water sources is a big concern for human health. Removal of microcystin-LR (MC-LR) from drinking water was evaluated at the laboratory pilot scale using either granular activated carbon (GAC) or powdered activated carbon (PAC) and compared with the treatment using anthracite as filter material. Virgin GAC was more effective at removing MC-LR (initial concentration ranging from 9 to 47 μ g L −1) to reach the World Health Organization recommended level (1.0 μ g L −1). When the GAC filter was colonized by bacteria, the filter became less effective at removing MC-LR owing to competitive reactions occurring between protein adsorption (released by bacteria) and MC-LR adsorption. Using PAC, the concentration of MC-LR decreased from 22 to 3 μ g L −1 (removal of 86% of MC-LR) by the addition of 100 mg PAC L−1.

Removal of chlortetracycline from spiked municipal wastewater using a photoelectrocatalytic process operated under sunlight irradiations.

The degradation of chlortetracycline in synthetic solution and in municipal effluent was investigated using a photoelectrocatalytic oxidation process under visible irradiation. The N-doped TiO₂ used as photoanode with 3.4 at.% of nitrogen content was prepared by means of a radiofrequency magnetron sputtering (RF-MS) process. Under visible irradiation, higher photoelectrocatalytic removal efficiency of CTC was recorded using N-doped TiO₂ compared to the conventional electrochemical oxidation, direct photolysis and photocatalysis processes. The photoelectrocatalytic process operated at 0.6A of current intensity during 180 min of treatment time promotes the degradation of 99.1 ± 0.1% of CTC. Under these conditions, removal rates of 85.4 ± 3.6%, 87.4 ± 3.1% and 55.7 ± 2.9% of TOC, TN and NH₄(+) have been recorded. During the treatment, CTC was mainly transformed into CO₂ and H₂O. The process was also found to be effective in removing indicator of pathogens such as fecal coliform (log-inactivation was higher than 1.2 units).

Effectiveness of a hybrid process combining electro-coagulation and electro-oxidation for the treatment of domestic wastewaters using response surface methodology

The performance of a two-stage process combining electro-coagulation (EC) and electro-oxidation (EO) was studied for the treatment of domestic wastewater (DWW) loaded with organic matter. The process was firstly evaluated in terms of its capability of simultaneously producing an oxidant and a coagulant agents using aluminum (Al) (or iron (Fe)) as bipolar and sacrificial electrodes, whereas graphite (Gr) electrodes were used as monopolar electrodes. Relatively high concentrations of chlorine (9.6 mg/min A) and Al (20—40 mg Al/L) or Fe (40–60 mg Fe/L) were produced. Subsequently, the factorial and central composite design methodologies were successively employed to define the optimal operating conditions for total chemical oxygen demand (COD) removal from DWW. Current intensity and treatment time were found to be very meaningful for chemical oxygen demand removal. The effect of these two main factors was around 90% on the investigated response, whereas the type of sacrificial electrode and the other interaction effects represent only 10%. The treatment using aluminum electrode and a current intensity imposed of 0.7 A during 39 min was found to be the optimal conditions in terms of cost/effectiveness. Under these conditions, 78% of COD removal can be obtained for a total cost of 0.78 US

Production and characterization of novel hydrocarbon degrading enzymes from Alcanivorax borkumensis

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Bench-scale production of enzymes from the hydrocarbonoclastic bacteria Alcanivorax borkumensis and biodegradation tests

This study investigates the production of alkane hydroxylase, lipase and esterase by the marine hydrocarbon degrading bacteria Alcanivorax borkumensis. The focus of this study is the remediation of petroleum hydrocarbons, hexane, hexadecane and motor oil as model substrates. A. borkumensis showed an incremental growth on these substrates with a high cell count. Growth on motor oil showed highest alkane hydroxylase and lipase production of 2.62 U/ml and 71 U/ml, respectively, while growth on hexadecane showed the highest esterase production of 57.5 U/ml. The percentage of hexane, hexadecane, and motor oil degradation during A. borkumensis growth after 72 h, was around 80%, 81.5% and 75%, respectively. Zymogram showed two different bands with a molecular weight of approx. 52 and 40 kDa, respectively with lipase and esterase activity. Alkane hydroxylase reached optimum activity at pH 8.0 and 70 ± 1 °C for hexane and hexadecane and 75 ± 1 °C for motor oil. Lipase and esterase showed optimum activity at 35 ± 1 °C and 40 ± 1 °C, respectively and pH 7.0. The crude enzymes showed higher stability in a wide range of pH, but they were not thermostable at higher temperatures.