Ahmed Bedoui

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.

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.

Enhancing the performance of electro-peroxone by incorporation of UV irradiation and BDD anodes

ABSTRACT In this work, the treatment of 4-nitrophenol (NP) in water by ozonation, electrolysis, electro-peroxone (EP), and photo-electro-peroxone (PEP) processes was investigated. PEP process is based on the combination of ozonation, UV irradiation, and electrolysis using a carbon felt cathode and a boron-doped diamond (BDD) anode. In this process, H2O2 is electrochemically generated from reduction of O2 in the ozone generator effluent at a carbon felt cathode. The in situ generated H2O2 is simultaneously decomposed by UV-photolysis and by reaction with O3 to form HO• radicals that can rapidly and non-selectively oxidize organic pollutants. The results showed that PEP is the most efficient process for a rapid NP degradation in water than the other individual and combined methods. In addition, PEP process was able to completely remove total organic carbon (TOC) from NP solution after consumption of 4.1 kWh/kg TOC removed. Hydroquinone, 1,2,4-trihydroxybenzene, oxalic and maleic acids were identified as the main intermediates of NP degradation. The addition of iron to NP solution did not significantly affect the efficiency of PEP process. The results demonstrated that the incorporation of BDD anodes and UV light in PEP process can significantly enhance the kinetics and minimize energy requirements.

Intensification of the Solvent Extraction of Rhus tripartitum Bioactive Molecules Using Instant Controlled Pressure Drop (DIC)

This article discusses the use of Instant Controlled Pressure Drop (DIC) as a pre treatment stage to intensify thesolvent extraction of total phenols and more especially tanninsfrom the bark ofAfrican sumac(TunisianRhus tripartitum).Totalphenol land