Antoine Ghauch

Antibiotic removal from water : Elimination of amoxicillin and ampicillin by microscale and nanoscale iron particles

Zerovalent iron powder (ZVI or Fe(0)) and nanoparticulate ZVI (nZVI or nFe(0)) are proposed as cost-effective materials for the removal of aqueous antibiotics. Results showed complete removal of Amoxicillin (AMX) and Ampicillin (AMP) upon contact with Fe(0) and nFe(0). Antibiotics removal was attributed to three different mechanisms: (i) a rapid rupture of the beta-lactam ring (reduction), (ii) an adsorption of AMX and AMP onto iron corrosion products and (iii) sequestration of AMX and AMP in the matrix of precipitating iron hydroxides (co-precipitation with iron corrosion products). Kinetic studies demonstrated that AMP and AMX (20 mg L(-1)) undergo first-order decay with half-lives of about 60.3+/-3.1 and 43.5+/-2.1 min respectively after contact with ZVI under oxic conditions. In contrast, reactions under anoxic conditions demonstrated better degradation with t(1/2) of about 11.5+/-0.6 and 11.2+/-0.6 min for AMP and AMX respectively. NaCl additions accelerated Fe(0) consumption, shortening the service life of Fe(0) treatment systems.

Degradation of benomyl, picloram, and dicamba in a conical apparatus by zero-valent iron powder.

Reduction of some pesticides (benomyl, picloram, and dicamba) was studied in an aerobic batch conical pilot system to investigate the disappearance of these pesticides on contact with iron powder (20 g/l, 325-mesh). Aqueous buffered solutions of the compounds were added to the system followed by zero-valent iron powder (ZVIP), and the decline in the pesticide concentrations was monitored over time. HPLC analyses show a complete disappearance of picloram (1.20 mg/l) after 20 min of reaction. Benomyl (1.00 mg/l) and dicamba (1.25 mg/l) disappear after 25 and 40 min, respectively. The t50 values ranged from 3 to 5.5 min, and were about slightly less than the t1/2 values reported when the log of the relative HPLC peak area was plotted versus time, where the relative peak area was calculated by dividing the measured peak area by the initial peak area. Pathways for the degradation of the studied pesticides by ZVIP are proposed.

Aqueous removal of diclofenac by plated elemental iron: bimetallic systems.

The aqueous removal of diclofenac (DF) by micrometric iron particles (Fe(0)) and amended Fe(0) (Me(0)(Fe(0))) under oxic and anoxic conditions was investigated. Bimetallic systems were obtained by plating the surface of Fe with Co, Cu, Ir, Ni, Pd and Sn. Experimental results confirmed the superiority of (Me(0)(Fe(0))) for DF removal except for IrFe (oxic) and SnFe (anoxic). Under anoxic conditions, Pd was by far the most efficient plating element followed by Ir, Ni, Cu, Co and Sn. However, under oxic conditions, Pd and Cu showed almost the same efficiency in removing DF followed by Ni, Co, Sn and Ir. Oxidative and reductive DF transformation products were identified under oxic and anoxic conditions respectively. In some systems (e.g. CoFe and SnFe oxic/anoxic; PdFe oxic; NiFe anoxic), no transformation products could be detected. This was ascribed to the nature of the plating element and its impact on the process of the formation of metal corrosion products (MCPs). MCPs are known for their high potential to strongly adsorb, bond, sequestrate and enmesh both the original contaminant and its reaction products. Obtained results corroborate the universal validity of the view, that aqueous contaminants are basically removed by adsorption and co-precipitation.

Catalytic degradation of chlorothalonil in water using bimetallic iron-based systems.

Modified zero valent iron (MZVI) was used to study the transformation of a chlorothalonil (CLT) solution and the variation of the observed degradation rate of the reduction reactions. This was carried out when transition metals e.g. Pd, Cu and Co plated on the surface of micrometric iron particles (< 150 microm) were used as reducing catalytic agents for pesticide removal. Reactions were undertaken under both oxic and anoxic conditions in the presence and the absence of a phosphate buffer solution (PBS). Results of batch studies in nitrogen sparged solutions revealed that incomplete slow dechlorination merely occurred with zero valent iron (ZVI), however, complete rapid dechlorination reactions took place with MZVI especially Fe/Pd. Dechlorination was depicted by studying UV absorbance and MS spectra of CLT and all corresponding by-products. Typical blue shifts (deltalambda = 4-6 nm/chlorine atom) were observed at the same time as chlorine cluster isotopes disappeared. After the plating process, metal loading was controlled by analyzing the remaining metal in the solution by atomic absorption spectroscopy. Experiments showed that CLT degradation mechanism is faster in nitrogen sparged solutions in the absence of PBS. Time needed for complete removal of 2.08 +/- 0.19 microM CLT solution was about 2 h when experiments were conducted with ZVI (t1/2 = 15.0 min) and about 10 min when the reaction was carried out under the same conditions with Fe/Pd 1% (t1/2 = 1.0 min). Degradation rates for all bimetallic systems were determined showing that Pd is the more exciting catalytic transition metal followed by Cu and Co. Furthermore, MZVI method showed obvious advantage to traditional CLT treatment methods.

Investigating the mechanism of clofibric acid removal in Fe0/H2O systems.

Since the introduction of iron wall technology, the inherent relationship between contaminant removal and iron corrosion has been mostly attributed to electron transfer from the metal body (direct reduction). This thermodynamically founded premise has failed to explain several experimental facts. Recently, a new concept considering adsorption and co-precipitation as fundamental contaminant removal mechanisms was introduced. This consistent concept has faced very skeptic views and necessarily needs experimental validation. The present work was the first independent attempt to validate the new concept using clofibric acid (CLO) as model compound. For this purpose, a powdered Fe(0) material (Fe(0)) was used in CLO removal experiments under various experimental conditions. Additional experiments were performed with plated Fe(0) (mFe(0): Fe(0)/Pd(0), Fe(0)/Ni(0)) to support the discussion of removal mechanism. Main investigated experimental variables included: abundance of O(2), abundance of iron corrosion products (ICPs) and shaking operations. Results corroborated the concept that quantitative contaminant removal in Fe(0)/H(2)O systems occurs within the oxide-film in the vicinity of Fe(0). Additionally, mixing type and shaking intensity significantly influenced the extent of CLO removal. More importantly, HPLC/MS revealed that the identity of reaction products depends on the extent of iron corrosion or the abundance of ICPs. The investigation of the CLO/Fe(0)/H(2)O system disproved the popular view that direct reduction mediates contaminant removal in the presence of Fe(0).

Remediation of s-triazines contaminated water in a laboratory scale apparatus using zero-valent iron powder

Atrazine, propazine and simazine were tested separately and in mixture by batch procedure in a laboratory-constructed apparatus. 3.75 l of a buffered s-triazines pesticide solution was treated at room temperature by 325-mesh zero-valent iron powder (ZVIP) (20 g/l). High performance liquid chromatography was used to separate by-products and study the decline in the pesticides concentrations. Results obtained show that the order of degradation was simazine, atrazine and then propazine. The half-lives (t1/2) of the s-triazines pesticides are, respectively, 7.4, 9.0 and 10.6 min when they are treated separately, and 9.8, 11.2 and 13.7 min when they are treated together under the same conditions. The final by-product obtained after 50 min of contact of simazine with ZVIP shows a shift to longer wavelength in its UV spectrum. A similar phenomenon is shown for atrazine and propazine. Identical primary by-products are produced and subsequently degraded to 4,6-(diamino)-s-triazine, which seems to be the major by-product of the reductive treatment process. Pathways for the degradation of the studied s-triazines by ZVIP are proposed.

Submicrometric Iron Particles for the Removal of Pharmaceuticals from Water: Application to b-Lactam Antibiotics

Sub-micrometric iron particles (Fe0) and amended Fe0 (Cu0Fe0) were tested for the aqueous removal of b-lactam antibiotics. Comparative batch experiments were performed separately on aqueous solutions of dicloxacillin (DCX), cloxacillin (CLX) and oxacillin (OXA). Three different initial concentrations (1, 5 and 10 mg L-1) and four different iron loads (r = 10, 20, 40 and 53 g L-1) were tested. Furthermore, two different mixing regimes were tested: (i) non-disturbed conditions, and (ii) vortex mixing. This experimental design enabled the confirmation of the crucial role of in-situ formed iron corrosion products (Fe oxides) on the removal process. The dynamic process of Fe oxides formation induces adsorption and enmeshment (sequestration or co-precipitation) of dissolved antibiotics. Results clearly delineated the superiority of Cu0Fe0 bimetallics compared to Fe0. For example, after 4 h of contact with iron particles at r = 40 g L-1, OXA, CLX and DCX (10 mg L-1 each) disappeared to an extent of 31, 46 and 71%. However, quantitative antibiotic removal (~90%) was noticed when Cu0Fe0 bimetallic was used at lesser load (r = 20 g L-1)under vortex mixing. On the other hand, non-disturbed systems showed partial removal (~ 25%) of antibiotics over 7 h of reaction at r = 10 g L-1 (Fe0) while almost complete removals were noticed for the Cu0Fe0 bimetallic system for the same metal load and period e.g. 75, 79 and 86% removal for OXA, CLX and DCX respectively.

Rapid quantification of persulfate in aqueous systems using a modified HPLC unit

Existing analytical techniques used for the quantification of persulfate (PS) in water mostly rely on polarography, reductometry or spectrophotometry. Although acceptable to a certain extent, these methods did not satisfy environmental chemists seeking rapid, reproducible and accurate quantification of PS upon the application of ISCO and AOPs technologies. Accordingly, a novel flow injection/spectroscopy analytical technique is developed via the use of an HPLC coupled to bypass capillary columns and a DAD detector. Special HPLC configuration uses concentrated KI solution as mobile phase to readily reduce PS present in the sample. The reaction takes place inside the capillary columns, under moderate pressure facilitating the production of Iodine suspension (I2), to yield finally the formation of the Triiodide anion (I3-) in the presence of an excess of I-. Triiodide absorbs at 352nm which minimizes interferences from other organic contaminants (OCs). The method was validated by comparison to traditional PS quantification methods and tested on several environmental samples. The new method proved its superiority in terms of time requirement, labor need, material consumption, sample volume and simplicity. It eliminates the inconsistency present in other idiometric methods which is caused by the delay between the PS/I- reaction and I3- measurement. The obtained LDR extends from 0.075 to 300mmolL-1 with a LOD of 6.6 × 10-3mmol L-1 and a LOQ of 2.20 × 10-2mmolL-1. The method is successfully implemented in our laboratory to rapidly and automatically monitor the variation in the concentration of PS used in different projects, which facilitates the rapid determination of the reaction stoichiometric efficiency (RSE) of the oxidation reaction, a key factor toward the optimization of the mineralization process and its sustainability.

The fate of selected pharmaceuticals in solar stills: Transfer, thermal degradation or photolysis?

The increase in demand for, and disposal of, pharmaceuticals, positively correlated with the growing human population, has led to the emergence of contaminants with high environmental and health impacts. Several developing countries that endure problems related to water sufficiency and/or quality resort to the use solar stills as an affordable water treatment method. This research is aimed at investigating the fate of five chemically distinct pharmaceuticals that might pervade solar stills; ibuprofen (IBU), diclofenac (DCF), carbamazepine (CBZ), ampicillin (AMP) and naproxen (NPX). The experiments were conducted under three conditions. The first condition studied the combined effect of temperature and light in simulated field-test-scale solar stills. The effect of temperature as a sole variable was investigated in the second while the third condition studied the effect of light only via concentrated solar power (CSP). Results show that distillates from solar stills did not contain the parent compounds for four out of the five pharmaceuticals. IBU was the only pharmaceutical that showed a transfer via vapor into the distillate with the highest recorded transfer percentage of 2.1% at 50°C when subjected to temperature alone and 0.6% under the combined effect of temperature and light. In the case of NPX and DCF, the parent compounds did not undergo transfer into the distillate phase; however their degradation by-products did. In addition, the results also showed that in the case of NPX, IBU and CBZ both high temperatures and sunlight combined were required to attain noticeable degradation. CSP accelerated the degradation of DCF, NPX and IBU with a three-minutes-degradation percentage of 44%, 13% and 2% respectively.