M. Noel

Degradation of pentachlorophenol by hydroxyl radicals and sulfate radicals using electrochemical activation of peroxomonosulfate, peroxodisulfate and hydrogen peroxide.

The present study is to investigate the reactivity of free radicals (SO4(-) and HO) generated from common oxidants (peroxomonosulfate (PMS), peroxodisulfate (PDS) and hydrogen peroxide (HP)) activated by electrochemically generated Fe(2+)/Fe(3+) ions which furthermore are evaluated to destroy pentachlorophenol (PCP) in aqueous solution. The effect of solution pH and amount of oxidants (PMS, PDS and HP) in electrocoagulation (EC) on PCP degradation is analyzed in detail. The experimental results reveal that, optimum initial solution pH is 4.5 and PMS is more efficient oxidant addition in EC. 75% PCP degradation is achieved at 60min electrolysis time from PMS assisted EC. According to the first order rate constant, faster PCP degradation rate is obtained by PMS assisted EC. The PCP degradation rate by oxidant assisted EC is observed in the following order: EC/PMS>EC/PDS>EC/HP>EC. Further to identify the influences of experimental factors involved in PCP degradation by oxidant assisted EC, an experimental design based on an orthogonal array (OA) L9 (3(3)) is proposed using Taguchi method. The factors that most significantly affect the process robustness are identified as A (oxidant) and B (pH) which together account for nearly 86% of the variance.

Membrane Processes for Dye Wastewater Treatment: Recent Progress in Fouling Control

The textile industry generates large volumes of effluents on a daily basis, which contains substantial loads of organic compounds, inorganic salts, and suspended impurities. Membrane filtration has become an essential part of advanced treatment plants for dye wastewater treatment. Prevention of membrane fouling is one of the critical objectives for making the overall treatment process commercially viable. Development in this area during the past decade is critically evaluated in this review. Recent developments in the primary, secondary, and tertiary treatment steps in textile wastewater treatment are outlined. The methods employed for measuring, modeling, and understanding membrane fouling processes are discussed. Specific efforts toward fouling control by (a) pretreatment stages of textile wastewater and (b) modifying and optimizing the membrane separation process parameters such as feed composition, hydrodynamic conditions, and membrane properties are then assessed. Fouling related investigations for microfiltration/ultrafiltration membranes, membrane bioreactors, reverse osmosis, and nanofiltration membranes with special focus on textile wastewater treatment are discussed. Recent efforts toward developing new membranes and cleaning processes for fouled membrane activation are also discussed. Pilot plant studies involving membrane separation in combination with other treatment processes are also summarized. Strategies evolved and experiences gained from the industrial scale textile wastewater treatment plants in India are discussed. The authors also summarize the opportunities and the challenges remaining at different stages of industrial textile wastewater treatment units.

Analysis and understanding of amido black 10B dye degradation in aqueous solution by electrocoagulation with the conventional oxidants peroxomonosulfate, peroxodisulfate and hydrogen peroxide

We investigated the degradation of amido black 10B dye by electrocoagulation (EC) processes assisted by the conventional oxidants peroxomonosulfate (PMS), peroxodisulfate (PDS) and hydrogen peroxide (HP). These EC processes were based on the formation of hydroxyl (HO˙) and sulfate (SO4˙−) radicals through electrochemically generated Fe2+/Fe3+-mediated activation of PMS, HP and PDS. Special attention was given to understanding the influence of the applied current, the initial solution pH and the concentration of the different oxidants on the degradation of the amido black 10B dye. The optimum operating conditions for each of these parameters was verified experimentally using Fe electrodes. Our results suggested that a low applied current and an acidic environment (pH 5) were favorable and very effective conditions for oxidant-assisted EC processes. The experimental results also showed that the oxidant-assisted EC processes produced exceptional degradation (99%) of amido black 10B dye with low energy consumption under the optimum conditions of CAB = 0.16 mM, CNaCl = 17 mM, CPMS = CPDS = 0. 16 mM, CHP = 0.13 mM and pH 5. The efficiency of degradation of amido black 10B dye by oxidant-assisted EC was in the order PMS > PDS > HP. The UV–visible spectral changes clearly showed that the azo linkage (–NN–) was degraded more easily by oxidant-assisted EC processes than the aromatic rings of the amido black 10B dye molecule. The maximum mineralization efficiencies attained for EC and EC assisted by PMS, PDS and HP were 34, 66, 57 and 46%, respectively.