Nasr Bensalah

Treatment of aqueous wastes contaminated with Congo Red dye by electrochemical oxidation and ozonation processes.

Synthetic aqueous wastes polluted with Congo Red (CR) have been treated by two advanced oxidation processes: electrochemical oxidation on boron doped diamond anodes (BDD-EO) and ozonation under alkaline conditions. For same concentrations, galvanostatic electrolyses have led to total COD and TOC removals but ozonation process can reach only 85% and 81% of COD and TOC removals, respectively. UV-vis qualitative analyses have shown different behaviors of CR molecules towards ozonation and electrochemical oxidation. Rapid discoloration has been observed during ozonation, whereas color persistence till the end of galvanostatic electrolyses has been seen during BDD-EO process. It seems that the oxidation mechanisms involved in the two processes are different: simultaneous destruction of azoic groups is suggested during ozonation process but consecutive destruction of these groups is proposed during BDD-EO. However, energetic study has evidenced that BDD-EO appears more efficient and more economic than ozonation in terms of TOC removals. These results have been explained by the fact that during BDD-EO, other strong oxidants electrogenerated from the electrolyte oxidation such as persulfates and direct-oxidation of CR and its byproducts on BDD anodes complement the hydroxyl radicals mediated oxidation to accomplish the total mineralization of organics.

Kinetic and mechanistic investigations of mesotrione degradation in aqueous medium by Fenton process

In this work, chemical oxidation of mesotrione herbicide by Fenton process in acidic medium (pH 3.5) was investigated. Total disappearance of mesotrione and up to 95% removal of total organic carbon (TOC) were achieved by Fentons reagent under optimized initial concentrations of hydrogen peroxide (H(2)O(2)) and ferrous iron (Fe(2+)) at pH 3.5. The time-dependent degradation profiles of mesotrione were satisfactorily fitted by first-order kinetics. Competition kinetic model was used to evaluate a rate constant of 8.8(± 0.2) × 10(9)M(-1) s(-1) for the reaction of mesotrione with hydroxyl radicals. Aromatic and aliphatic intermediates of mesotrione oxidation were identified and quantified by high performance liquid chromatography (HPLC). It seems that the degradation of mesotrione by Fenton process begins with the rupture of mesotrione molecule into two moieties: cyclohexane-1,3-dione derivative and 2-nitro-4-methylsulfonylbenzoic acid. Hydroxylation and release of sulfonyl and/or nitro groups from 2-nitro-4-methylsulfonylbenzoic acid lead to the formation of polyhydroxylated benzoic acid derivatives which undergo an oxidative opening of benzene ring into carboxylic acids that end to be transformed into carbon dioxide.

Electrochemical oxidation of succinic acid in aqueous solutions using boron doped diamond anodes

In this work, the electrochemical oxidation of succinic acid on boron-doped diamond (BDD) anodes was investigated. Voltammetric study had shown that no peaks appeared in the region of electrolyte stability which indicates that succinic acid oxidation can take place at a potential close to the potential region of electrolyte oxidation. Galvanostatic electrolyses achieved total chemical oxygen demand (COD) removals and high mineralization yields under different operating conditions (initial COD, current density and nature of supporting electrolyte). Oxalic, glycolic and formic acids were the main intermediates detected during anodic oxidation of succinic acid on BDD electrode and carbon dioxide as the final product. The mean oxidation state of carbon reached the value of 4 at the end of electrolysis which is indicative of mineralization of almost all organics present in aqueous solution. The exponential profile of COD versus specific electrical charge has shown that mass transfer is the limiting factor for the kinetics of electrochemical process. A simple mechanism was proposed for the mineralization of succinic acid. First, hydroxyl radicals attack of succinic acid leading to formation of glycolic, glyoxylic, fumaric and maleic acids. Then, theses acids undergo rapid and non-selective oxidation by hydroxyl radicals to be transformed into oxalic and formic acids which leads to further oxidation steps to mineralize these acids into carbon dioxide and water.

Bromate reduction by ultraviolet light irradiation using medium pressure lamp

Bromate reduction in water by ultraviolet irradiation using medium-pressure lamps (UV-M) emitting light in the range of 200–600 nm has been investigated. Effects of certain experimental parameters including the initial bromate concentration, UV light intensity, initial pH, and presence of dissolved organic and inorganic carbon and nitrate on the kinetics and efficiency of UV irradiation for bromate reduction were evaluated. Experimental results showed that UV-M irradiation achieved complete destruction of bromate and almost total conversion of bromate into bromide for the initial bromate concentrations ranging from 10 to 1000 μg/L under different pH conditions. A simple kinetic model for bromate destruction was developed. Bromate decay with time during UV-M irradiation follows pseudo-first-order kinetics. The observed rate constant (kobs) decreased with increasing bromate concentrations upto 100 μg/L and then it becomes constant at 0.058 min−1 for higher bromate concentrations. Increasing the UV light intensity resulted in the increase of the rate of bromate destruction. The kobs increased linearly with increasing light intensity. A UV dose of 1000 mJ/cm2 was sufficient to reduce the bromate concentration to less than 10 μg/L within 10 min. The presence of dissolved organic carbon or carbonate/bicarbonate slowed the bromate reduction rate due to absorption of non-negligible fraction of UV light by these compounds. Presence of nitrate affects both the kinetics and efficiency of bromate reduction.

Inland Desalination: Potentials and Challenges

Groundwater is the main source of drinking water in many countries all over the world. In absence of surface water supply, the use of groundwater as the main water source for drinking, industrial, and agricultural use becomes essential especially in the case of rural communities. Underground reservoirs constitute a major source of fresh water, in terms of storage capacity; underground aquifers worldwide contain over 95% of the total fresh water available for human use. Typical groundwater supplies have low coliform counts and total bacterial counts, low turbidity, clear color, pleasant taste, and low odor. Accordingly, groundwater has higher quality than surface water, and the quality is quite uniform throughout the year that makes it easy to treat. A disadvantage of groundwater supplies is that many groundwater aquifers have moderate to high dissolved solids such as calcium, magnesium, iron, sulfate, sodium, chloride, and silica. The high concentration of dissolved solids particularly, sodium chloride, makes the water brackish and thus requires to be desalinated before its use for a certain purpose.

Removal of fluoride from aluminum fluoride manufacturing wastewater by precipitation and adsorption processes

In this study, the treatment of aluminum fluoride manufacturing Wastewaters (AFMW) by precipitation‐neutralization using calcium hydroxide (lime) or calcium carbonate (limestone) and adsorption using activated clay has been investigated. Effects of experimental conditions such as lime or limestone dose, clay mass, initial fluoride concentration and initial pH on the fluoride removal efficiency and the final pH have been evaluated. Results of this study indicated that precipitation‐neutralization processes can be successfully used to remove more than 90% of fluoride from AFMW. The treatment of AFMW containing different fluoride concentrations ranging from 167 to 5295 mg/L by precipitation with lime using [Ca 2+ ]/[F − ] molar ratio of 0.8 led to fluoride removal higher than 95% with a final pH within the range 6.5 ± 0.1 to 8.5 ± 0.1. Precipitation with CaCO3 needed higher [Ca 2+ ]/[F ‐ ] molar ratio of 2 to reach 90% of fluoride removal and obtain a final pH in the range from 6.5 ± 0.1 to 8.5 ± 0.1. The results of the treatment of AFMW by adsorption on activated bentonite clay indicated that using [clay]/[F ‐ ] mass ratio of 60 under different pH varying from pH 2 ± 0.1 to pH 12 ± 0.1 can lead to 80% fluoride removal. Synthetic calcium fluoride (SCFL) generated by precipitation‐neutralization with lime SCFL contains 77.9% of CaF2; however, only 48.3% of CaF2 are contained in solids generated from precipitation‐neutralization with limestone SCFLS.

Treatment of Pharmaceutical-manufacturing Wastewaters by UV Irradiation/Hydrogen Peroxide Process

Abstract In this study, the treatment of pharmaceutical-manufacturing wastewaters (PMWW) by advanced chemical oxidation using UV irradiation/hydrogen peroxide (H2O2) process has been investigated. Effects of experimental conditions such as H2O2 dose, initial organic matter concentration, temperature and initial pH value on the removal efficiency and kinetics of organic matter were investigated. Results of this study indicated that UV/H2O2 process can be successfully used to completely destroy aromatic compounds, and to remove chemical oxygen demand (COD) and total organic carbon (TOC) with removal efficiencies more than 95% and 90%, respectively. Kinetic experiments have demonstrated that TOC removal rate followed pseudo-second order kinetics. Rate constants of 1.12×10-3 A-1 min-1 and 2×10-5 L mg-1 min-1 were calculated for UV absorbance at 277 nm and TOC decay, respectively. These results indicate that the mechanism of pharmaceuticals degradation involves two main steps: (i) Rapid degradation of aromatic compounds by hydroxylation followed by oxidative opening of benzene rings to form aliphatic derivatives and (ii) subsequent slow fragmentation of aliphatic derivatives into small carboxylic acids which are mineralized into CO2, H2O and other inorganic ions during the final steps of degradation.

Electrochemical Inactivation of P. Aeruginosa, A. hydrophila, L. pneumophila using Boron Doped Diamond Anodes

Abstract Pseudomonas Aeruginosa, Aeromonas hydrophila, Legionella pneumophila bacteria are waterborne pathogens commonly found in water and linked to infectious diseases. Especially, they can survive and colonize water systems, particularly in worm water system. On-site supplemental disinfection of water systems might be one of the approaches to prevent water born diseases. In this work, the inactivation of these waterborne pathogens using a single compartment electrochemical flow cell equipped with Boron Doped Diamond (BDD) anode and Titanium cathode was investigated. The bactericidal activity of galvanostatic electrolysis using BDD anode was evaluated on synthetic contaminated waters containing P. Aeruginosa, A. hydrophila, L. pneumophila. BDDanodic oxidation at current density of 50 mA cm-2 achieved total death of waterborne bacteria in treated water samples for bacterial cell density in the range 107 - 108 CFU mL-1. The effects of certain experimental parameters (current density, NaCl concentration, cell density, and flow rate) on kinetics and efficiency of BDD-anodic oxidation during electrochemical disinfection of bacteria suspensions were also examined. The results have indicated that the bactericidal activity of BDD anodes increases with increasing current density and NaCl concentration. This can be explained by the contribution of mediated oxidation with electrogenerated oxidants including hydroxyl radicals, hydrogen peroxide, ozone and free chlorine in the inactivation mechanism of waterborne bacteria at high current densities. This research work has shown that BDD anode is promising tool for inactivation of waterborne pathogens in water and wastewater disinfection.

The contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using diamond anodes.

In this work, the contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using boron-doped diamond (BDD) anodes was investigated in different electrolytes. A complete mineralization of cyanuric acid was obtained in NaCl; however lower degrees of mineralization of 70% and 40% were obtained in Na2SO4 and NaClO4, respectively. This can be explained by the nature of the oxidants electrogenerated in each electrolyte. It is clear that the contribution of active chlorine (Cl2, HClO, ClO(-)) electrogenerated from oxidation of chlorides on BDD is much more important in the electrolytic degradation of cyanuric acid than the persulfate and hydroxyl radicals produced by electro-oxidation of sulfate and water on BDD anodes. This could be explained by the high affinity of active chlorine towards nitrogen compounds. No organic intermediates were detected during the electrolytic degradation of cyanuric acid in any the electrolytes, which can be explained by their immediate depletion by hydroxyl radicals produced on the BDD surface. Nitrates and ammonium were the final products of electrolytic degradation of cyanuric acid on BDD anodes in all electrolytes. In addition, small amounts of chloramines were formed in the chloride medium. Low current density (≤10mA/cm(2)) and neutral medium (pH in the range 6-9) should be used for high efficiency electrolytic degradation and negligible formation of hazardous chlorate and perchlorate.

Mechanism and kinetics of electrochemical degradation of uric acid using conductive-diamond anodes

ABSTRACT Uric acid (UA) is one of the principal effluents of urine wastewaters, widely used in agriculture as fertilizer, which is potentially dangerous and biorefractory. Hence, the degradation of UA (2,6,8-trihydroxy purine) in aqueous solution of pH 3.0 has been studied by conductive-diamond electrochemical oxidation. Hydroxyl radicals formed from water oxidation at the surface of boron-doped diamond anodes were the main oxidizing agents. Effects of current density and supporting electrolyte on the degradation rate and process efficiency are assessed. Results show that the increase of current density from 20 to 60 mA cm–2 leads to a decrease in the efficiency of the electrochemical process. In addition, the best degradation occurred in the presence of NaCl as conductive electrolyte. Interestingly, an almost total mineralization of 50 ppm UA was obtained when anodic oxidation was performed at low current densities (20 mA cm–2) and in the presence of NaCl. This result confirmed that the electrolysis using diamond anodes is a very interesting technology for the treatment of UA. The identification of UA transformation products was performed by high-performance liquid chromatography (HPLC). HPLC analysis of treated solutions revealed that oxalic acid and urea were the two intermediates found. Oxalic acid was the most persistent product. Based on detected intermediates and bibliographic research, a mechanism of UA mineralization by anodic oxidation has been proposed. Ionic chromatography analysis confirmed the release of and ions during UA mineralization.