Removal of methylene blue from waste water using micellar enhanced ultrafiltration

Ultrafiltration of micellar solutions containing sodium dodecylsulfate (SDS) and oxyethylated coconut fatty acid methyl esters (OMC-10) and their binary mixtures were studied and used to recover methylene blue. This was achieved through solubilization in mixed negatively charged micelles. Under the experimental conditions used, no significant fouling of the membrane comprising of cellulose, polyethersulfone and polyvinylidene fluoride was observed, with no retardation of ultrafiltration. The introduction of a nonionic surfactant to SDS reduced the critical micelle concentration of mixed micelles and then the concentration of surfactants in the permeate, i.e., from 8.3 x 10(-3)M for SDS to 2.0 x 10(-3) M for the mixture of SDS:OMC-10 = 4:1. Such a tailored surfactant mixture enabled the authors to achieve 93-94% retention of methylene blue using a hydrophilic membrane made of cellulose. Ultrafiltration of micellar solutions could also be considered a research method, helpful in determining important parameters such as micelle loading and the micelle binding constant used to characterize micellar solutions. Additionally the distribution coefficient employed in extraction studies can be resolved.     

Arsenic removal from an aqueous solution by a modified fungal biomass

Non-viable fungal biomass of Aspergillus niger, coated with iron oxide was investigated for its potential to remove arsenic from an aqueous solution. A. niger biomass coated with iron oxide showed maximum removal (approximately 95% of As(V) and 75% of As(III)) at a pH of 6. No strong relationship was observed between the surface charge of the biomass and arsenic removal.     

Effect of OH and silanol groups in the removal of dyes from aqueous solution using diatomite

The removal of methylene blue, reactive black (C-NN), and reactive yellow (MI-2RN) from aqueous solution by calcined and raw diatomite at 980 degrees C was studied. These studies demonstrated the importance of the various functional groups on the mechanism of adsorption. The role of pore size distribution in the dye adsorption studies was also investigated. The adsorption isotherms were pH dependent. Henry and Freundlich adsorption isotherms were used to model the adsorption behavior and experimental results for all dyes used exhibited heterogeneous surface binding. The removal of the ionisable functional groups increased the pH(ZPC) value from 5.4 to 7.7, while FTIR, SEM and XRD analysis showed a remarkable decrease of the characteristic Si-OH peaks after calcinations at 980 degrees C. The removal of hydroxyl groups from the surface of diatomite lead to a decrease in the adsorption. It was evident from pH and infrared spectra results that mechanisms of methylene blue and reactive yellow adsorption differed from that of reactive black. Accordingly, adsorption on the external surface by n-pi interaction between the pi system of the RB and the electron lone pairs of the oxygen atoms of siloxane group and columbic attraction between the dye and the surface of calcined diatomite was proposed as a possible adsorption mechanism.     

Photoassisted reduction of metal ions and organic dye by titanium dioxide nanoparticles in aqueous solution under anoxic conditions

The photoassisted reduction of metal ions and organic dye by metal-deposited Degussa P25 TiO₂ nanoparticles was investigated. Copper and silver ions were selected as the target metal ions to modify the surface properties of TiO₂ and to enhance the photocatalytic activity of TiO₂ towards methylene blue (MB) degradation. X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used to characterize the crystallinity, chemical species and morphology of metal-deposited TiO₂, respectively. Results showed that the particle size of metal-deposited TiO₂ was larger than that of Degussa P25 TiO₂. Based on XRPD patterns and XPS spectra, it was observed that the addition of formate promoted the photoreduction of metal ion by lowering its oxidation number, and subsequently enhancing the photodegradation efficiency and rate of MB. The pseudo-first-order rate constant (k_obs) for MB photodegradation by Degussa P25 TiO₂ was 3.94 × 10^− 2 min^− 1 and increased by 1.4-1.7 times in k_obs with metal-deposited TiO₂ for MB photodegradation compared to simple Degussa P25 TiO₂. The increase in mass loading of metal ions significantly enhanced the photodegradation efficiency of MB; the k_obs for MB degradation increased from 3.94 × 10^− 2 min^− 1 in the absence of metal ion to 4.64-7.28 × 10^− 2 min^− 1 for Ag/TiO₂ and to 5.14-7.61 × 10^− 2 min^− 1 for Cu/TiO₂. In addition, the electrons generated from TiO₂ can effectively reduce metal ions and MB simultaneously under anoxic conditions. However, metal ions and organic dye would compete for electrons from the illuminated TiO₂.     

Effect of dissolved oxygen on the photodecomposition of monochloramine and dichloramine in aqueous solution by UV irradiation at 253.7 nm

The effect of dissolved oxygen on the photodecomposition of monochloramine (7.5 < pH < 10) and dichloramine (pH = 3.7 ± 0.2) at 253.7 nm has been investigated. The kinetic study shows that the rate of photodecomposition of monochloramine is about two times faster in the absence of oxygen than in the presence of oxygen, is not significantly affected by pH and by the presence of hydroxyl radical scavengers (hydrogenocarbonate ion and tert-butanol). The apparent quantum yields of photodecomposition of monochloramine at 253.7 nm ([NH₂Cl]₀ ≈ 1.5-2 mM, ?_{253.7 nm} = 371 M⁻¹ cm⁻¹) were equal to 0.28 ± 0.03 and 0.54 ± 0.03 mol E⁻¹ in oxygenated-saturated and in oxygen-free solutions, respectively. The photodecomposition rates or the apparent quantum yields of photodecomposition of dichloramine ([NHCl₂]₀ ≈ 1.5-2 mM, pH = 3.7 ± 0.2) in oxygen-free and in oxygen-saturated solutions were quite identical (Φ = 0.82 ± 0.08 mol E⁻¹; ?_{253.7 nm} = 126 M⁻¹ cm⁻¹). Under O₂ saturation, UV irradiation of NH₂Cl leads to the formation of nitrite (≈0.37 mol/mol of NH₂Cl decomposed), nitrate (≈0.073 mol/mol) and does not form ammonia (<0.01 mol/mol). In oxygen-free solutions, monochloramine decomposes to form ammonia (≈0.37 mol/mol). Photodecomposition of dichloramine did not lead to significant amounts of nitrite and nitrate in the presence and in the absence of oxygen. The nitrogen mass balances also indicate the formation of other nitrogen species (probably N₂ and/or N₂O) during the photodecomposition of monochloramine and dichloramine by UV irradiation at 253.7 nm.     

Effect of humic acids on heavy metal removal by zero-valent iron in batch and continuous flow column systems

The effects of Aldrich humic acids (HA) on the removal of Zero-valent iron (ZVI) was investigated in laboratory systems. In batch, the removal rate of Zn and Ni (5 mg l(-1)) was, respectively, 2.8 and 2.4 times lower in the presence of HA (20 mg l(-1)) than in the absence of HA, presumably due to the formation of HA-heavy metal complexes which prevented the removal reactions at the ZVI surface. Chromate removal was not affected. In a column test, two parallel systems were supplemented with a continuous input of simulated groundwater containing a mixture of the heavy metals Zn, Ni and Cr(VI) (5 mg l(-1) each), with or without HA (at 20 mg l(-1)). Initially, the two column systems efficiently (>90%) removed the heavy metals from the simulated groundwater. When the input heavy metal concentration was increased to 8-10 mg l(-1), a significant breakthrough of Ni and Zn, up to 80%, occurred in the column system fed with HA. Chromate and HA did not significantly break through. After 60 weeks, the effect of HA on leaching of the accumulated metals (approx. 2 mg g(-1)) was investigated. No significant leaching was observed. The results of this study suggest that the impact of dissolved organic matter on the efficiency and lifetime of a ZVI barrier for in situ removal of heavy metals should be considered in the design of the barrier.     

Fe(III) homogeneous photocatalysis for the removal of 1,2-dichlorobenzene in aqueous solution by means UV lamp and solar light

Chlorinated hydrocarbons are widely used in chemical industries as solvents and intermediates for pesticides and dyes manufacture. Their presence was documented in rivers, groundwaters and seawaters.

In this work, the oxidation of 1,2-dichlorobenzene in aqueous solutions by means of Fe(III) homogeneous photocatalysis under UV lamp and sunlight irradiations is studied. The results show that the best working conditions are found for pH=3.0 and initial [Fe(III)] concentration equal to 1.0×10⁻⁴ mol L⁻¹ although the investigated system can be utilized even at pH close to 4.0 but with slower abatement kinetics.

Some dicholoroderivatives, such as 2,3-dichlorophenol, 3,4-dichlorophenol and 2-chlorophenol, are identified as oxidation intermediates. The values of the kinetic constant for the photochemical reoxidation of Fe(II) to Fe(III) are evaluated by a mathematical model in the range 1.58–3.78 L mol⁻¹ s⁻¹ and 0.69–0.78 L mol⁻¹ s⁻¹ for the systems irradiated by UV lamp and sunlight, respectively.     

Some geological and geotechnical factors affecting the performance of a roadheader in an inclined tunnel

The factors affecting the performance of 90 kW-shielded roadheader is investigated in detail in a tunnel excavated for Nuh Cement Factory. The first part of the tunnel is horizontal and the second part is inclined with 9° and excavated uphill. Tunnel passes through a formation of the Upper Cretaceous age with nodular marl, carbonated claystone, thin and thick laminated limestone. Water ingress changes from 0 to 11 l/min. In six different zones it is found that the rock compressive strength changed from 20 to 45 MPa, tensile strength from 1 to 4 MPa, specific energy from 11 to 16 MJ/m³, plastic limit from 15% to 29%, liquid limit from 27% to 43% and water absorption from 4% to 18% in volume.

Detailed in situ observations show that in dry zones for the same rock strength the inclination of the tunnel and the strata help to increase the instantaneous cutting rate from 10 to 25 solid bank m³/cutting hour. The effect of water on cutting rate is dramatic. In the zones where the plastic limit and the amount of Al₂O₃ is low, instantaneous cutting rate increases from 34 to 50 solid bank m³/cutting hour with increasing water content from 3.5 to 11 l/min. However, in the strata having high water absorption characteristic and high amount of Al₂O₃, cutting rate decreases considerably due to the sticky mud, causing problem to the cutterhead. Excavation, muck loading and support works are performed separately due to safety concerns in the wet and inclined sections which reduced the machine utilization time from 38% to 8%. The information gathered is believed to form a sound basis in contributing the performance prediction of roadheaders in difficult ground conditions.     

Effects of water chemistry and flow rate on arsenate removal by adsorption to an iron oxide-based sorbent

Arsenate removal from water using an iron oxide-based sorbent was investigated to determine the optimal operating conditions and the influence of water composition on treatment efficiency. The novel sorbent with a high surface area was studied in flow-through column experiments conducted at different flow rates to quantify the effect of empty bed contact time (EBCT) on treatment performance. Arsenic removal efficiency declined with decreasing EBCT. Arsenic breakthrough curves at different EBCT values were successfully simulated with a pore and surface diffusion model (PSDM). Surface diffusion was the dominant intraparticle mass transfer process. The effect of water composition on arsenic removal efficiency was evaluated by conducting experiments with ultrapure water, ultrapure water with either phosphate or silica, and a synthetic groundwater that contained both phosphate and silica. Silica was more inhibitory than phosphate, and the silica in synthetic groundwater controlled the arsenic removal efficiency.     

Homogeneous iron-catalyzed photochemical degradation of muconic acid in water

Iron photochemical oxidation has been used to remove muconic acid from water. Two different light systems were used: black lamps and solar irradiation. The effect of iron concentration, intensity of incident radiation, pH and presence of oxalic acid was investigated. The first two variables yield positive effects on the removal rate of muconic acid while higher efficiency was achieved at pH 3. Oxalic acid enhances the oxidation rate because of the formation of photoactive ferrioxalate ion. Stoichiometric results indicated formation of two hydroxyl radicals to degrade 1 mol of muconic acid. At similar experimental conditions, initial oxidation rates of muconic acid were higher when solar light was used to irradiate the aqueous solutions, although in this case, the oxidation process is stopped because of the consumption of photoactive species.     

Photocatalysis of p-chlorobenzoic acid in aqueous solution under irradiation of 254 nm and 185 nm UV light

The photolytic and photocatalytic degradation of p-chlorobenzoic acid (p-CBA) in aqueous solution were investigated using two kinds of low-pressure mercury lamps: one emitted at 254 nm and the other emitted at 254 nm and 185 nm. Both the photolytic and photocatalytic degradations of p-CBA followed pseudo first-order reaction rate form. The rate constants decreased with increase of initial concentration in VUV and TiO2/VUV. The TiO2/VUV was the most efficient process, in which rate constants was 3.0-6.5 times as that in TiO2/UV depending on the initial concentration. The gas bubbling efficiently improved the mass transfer and the kind of bubbling gas had evident influence on the reaction rate except in UV photolysis. TOC reduction rate was greatly reduced in VUV and TiO2/VUV processes when bubbled with nitrogen gas, it was no more than one third of that when bubbled with oxygen, however, the degradation rate of p-CBA was not affected by bubbled nitrogen so greatly.     

Removal of benzoic acid in aqueous solution by Fe(III) homogeneous photocatalysis

The behaviour of the system Fe(III)/Air/UV-benzoic acid is investigated in the pH range 2.0-5.5 and Fe(III) concentration up to 60 microM. The oxidation process develops through the establishment of an iron cycle in which HO radicals are produced by Fe(OH)2+ photolysis and the resulting Fe(II) photo-oxidized to Fe(III) by dissolved oxygen. A kinetic model is developed and used to simulate the behaviour of the system.     

Solar photo-Fenton degradation of nalidixic acid in waters and wastewaters of different composition. Analytical assessment by LC-TOF-MS

This work assessed the solar photo-Fenton degradation of nalidixic acid (NXA), a quinolone antibacterial agent, in several different aqueous solutions. It has been proven that the composition of the water clearly affects the efficiency of the photo-Fenton process. The presence of chlorine ions induces the concurrence of different mechanisms involving Cl and Cl₂⁻ radicals, which slow down the process. Up to 35 transformation products (TPs) were identified and their structures characterized by accurate LC-TOF-MS mass measurements during treatment of the different model waters. Photocatalytic degradation was thus observed to proceed mainly through the attack of the hydroxyl radicals on the double bond C₍₂₎C₍₃₎ which induce further ring opening. All the TPs identified persisted after total degradation of NXA. NXA in real pharmaceutical effluent was treated by photo-Fenton as a first stage before biological treatment. As NXA has been demonstrated to be recalcitrant to biological treatment, photo-Fenton treatment of the effluent was continued until its total degradation. Although NXA was efficiently degraded, LC-MS analyses demonstrated that some of the TPs identified after the photo-Fenton treatment were also recalcitrant to biological treatment, persisting after the combined treatment. These results show that analytical assessment of photocatalytic water treatments is essential to assure they are functioning as intended.     

Hydrological and chemical factors controlling the concentrations of Fe, Cu, Zn and As in a river system contaminated by acid mine drainage

The seasonal variations in the trace element concentrations and flow rates in the Carnon River system, south west England have been investigated on a monthly basis for a period of 1 yr. Approximately 85% of Fe, Zn and As, and 45% of Cu originate from mine waters. A strong seasonal dependence of the flux of trace elements in the natural and mine waters is observed. There appears to be a direct correlation between trace element concentrations and the proportion of infiltrated surface drainage in mine waters. Rises in these concentrations in the Carnon River due to increased fluxes from mine waters in winter months are offset by higher flow rates in surface discharge.Iron is transported predominantly in the particulate phase in Carnon River waters and virtually all dissolved Fe (< 0.45 μm) precipitates in estuarine waters. Dissolved concentrations of Cu, Zn and As appear to be regulated by sorptive processes particularly with Fe oxyhydroxides in both fresh and saline waters.     

Iron type catalysts for the ozonation of oxalic acid in water

Two iron catalysts (Fe(III) and Fe2O3/Al2O3) have been used in the ozonation of oxalic acid in water at pH 2.5. Percentage removals of oxalic acid were 1.8%, 7% and 30% corresponding to the non-catalytic, homogeneous (Fe(III)) and heterogeneous (Fe2O3/Al2O3) catalytic ozonations, respectively. Catalytic oxalic acid ozonation leads in all cases to total mineralization. The mechanism of ozonation likely develops through formation of iron-oxalate complexes that further react with ozone without the participation of hydroxyl radicals. Because of the stringent acidic conditions, some metal leaching has been observed and quantified in the heterogeneous process. In the homogeneous catalysis, the kinetics was found to be first order with respect to ozone and oxalic acid while for the heterogeneous catalysis, the kinetic order depends on the concentration of ozone in the gas fed. Thus, at ozone concentrations lower than 30 mg L(-1), the heterogeneous ozonation is between first and zero order with respect to both ozone and oxalic acid while at higher ozone gas concentrations, the kinetics was found to be first and zero order with respect to oxalic acid and ozone, respectively. This kinetics is supported through an Eley-Rideal mechanism that involves a surface reaction between non-adsorbed ozone and adsorbed oxalic acid. Apparent activation energies of the homogeneous and heterogeneous catalytic ozonations were found to be 18.2 and 13.6 kcal mol(-1), respectively.     

Enhanced recovery of arsenite sorbed onto synthetic oxides by L-ascorbic acid addition to phosphate solution: calibrating a sequential leaching method for the speciation analysis of arsenic in natural samples

Stripping voltammetry capable of detecting 0.3microg/L arsenate and arsenite was applied for speciation analysis of arsenic sorbed onto synthetic ferrihydrite, goethite at As/Fe ratio of approximately 1.5mg/g with or without birnessite after sequential extraction using 1M phosphate (24 and 16 h) and 1.2M HCl (1h). Precautions to avoid oxygen were undertaken by extracting under anaerobic conditions and by adding 0.1M l-ascorbic acid to 1M NaH(2)PO(4) (pH 5). Addition of l-ascorbic acid did not reduce As(V) to As(III). The recovery rate for As(III) using l-ascorbic acid for extraction (pH 5) but not for adsorption was 81% and 74% of total sorbed As, and was 99% and 97% of extracted As for ferrihydrite and goethite, respectively. Birnessite oxidized most As(III) during the adsorption procedure. l-ascorbic acid used both in adsorption and extraction procedures improved the recovery of As(III) to 79-94% for ferrihydrite-birnessite and 57-94% for goethite-birnessite systems with Fe/Mn ratios of 7, 70, 140 and 280g/g.