Desalination (v.270, #1-3)
A review of desalting process techniques and economic analysis of the recovery of salts from retentates
by Dae Hyun Kim (pp. 1-8).
Disposal of saline effluent from desalination plants, agricultural drainage water, and other industries is an increasing problem worldwide. Saline effluent has long been considered waste brine and traditional approaches to its disposal have included evaporation ponds, deep wells, and coastal discharge. However, such effluent is now being considered as a saline resource; therefore, alternative approaches have been developed to extract available salts and to recover purified water. In this study, techniques to dispose of rejected brine were investigated and alternative salt recovery methods that have been developed and widely employed were reviewed. Evaporation and cooling to extract salts from retentate has been widely used worldwide, but use of the membrane separation technique has been increasing rapidly owing to the development of cheaper and higher performance membranes. Electrodialysis, ion-exchange, eutectic freezing, and chemical processing can also be used to recover salts from retentate. Currently, hybrid systems that combine two or more techniques, such as the nanofiltration (pretreatment)–reverse osmosis (concentration)–thermal processes (crystallization), are being developed and used actively to increase the amount of extracted salt and reduce the final volume of rejected brine. Economic analysis of concentrate utilization in comparison with disposal was performed in this study. Based on the cost of producing salts, the multi-stage flash (MSF) distillation and electrodialysis and Dow chemical process were relatively expensive when compared to nanofiltration and membrane crystallization, evaporation, and ion-exchange techniques. However, technical developments for increasing the performance efficiency must be further investigated to reduce the cost of desalting processes.► Desalting process techniques and economic analysis of salt recovery were reviewed. ► Economic analysis of disposal cost of saline feed to processes was performed. ► Disposal costs of the suggested techniques are relatively high. ► The alternative saline effluent treatments are viable by commercializing salts.
Keywords: Abbreviations; ADW; agricultural drainage water; BWRO; brackish water reverse osmosis; ED; electrodialysis; EDR; electrodialysis reversal; EFC; eutectic freezing crystallization; IX; ion-exchange; MCr; membrane crystallizer; MEE; multiple-effect evaporation; MSF; multi-stage flash; NF; nanofiltration; RO; reverse osmosis; UF; ultrafiltration; VC; vapor compressionDesalination; Salt recovery techniques; Retentate; Effluent
On the dependence of chlorine by-products generated species formation of the electrode material and applied charge during electrochemical water treatment
by Djamel Ghernaout; Mohamed Wahib Naceur; Ali Aouabed (pp. 9-22).
Chemical water treatment problems such as disinfection by-products formation have urged on the search of better water treatment technologies such as electrochemical water technologies which have been applied successfully in different water/wastewater pollutant removal. However, their wide extension is hindered by some technical problems such as chlorine by-products (CBPs) generated species. Indeed, during electrochemical process, these carcinogenic substances may be formed depending on the electrode material and applied voltage. This review concerns the dependence of CBPs generated species formation of the electrode material and applied charge during electrochemical water treatment. It is concluded that the use of electrodes producing highly reactive species must be more carefully controlled in hygienically and environmentally oriented applications. From this point of view, Pt and boron-doped diamond (BDD) anodes are proved more convenient than other electrodes. Indeed, the great capability of a BDD anode to produce reactive oxygen species and other oxidising species during the electrolysis allows establishing a chlorine-free disinfection process.► At [Cl−] < 100 mg L–1, free Cl2(g) can be produced with the risk of DBPs formation. ► Electric field conditions must be optimised to avoid DBPs formation. ► The DBPs formed can be removed by passing through activated carbon.
Keywords: Water treatment; Chlorine by-products; Electrodisinfection; Electrooxidation (EO); Electrocoagulation (EC); Electrode
Evaluation of groundwater quantity and quality in the Kashan Basin, Central Iran
by Z. Jamshidzadeh; S.A. Mirbagheri (pp. 23-30).
This paper investigates groundwater changes in the Kashan Basin quantitatively and qualitatively. According to the data obtained from 53 observation wells, it is found that the mean water table is decreased about 7.93m between 1990 and 2006, indicating a mean water table decline of 0.496m/year. To study groundwater quality, 21 samples are analyzed for their physicochemical characteristics such as pH, hardness, chloride (Cl), electrical conductivity (EC) and total dissolved solid (TDS) values. Comparing the results with drinking water quality standards issued by World Health Organization (WHO), it is found that most of the water samples are not potable. Hydrochemical facies using Piper diagram indicate that in most part of this basin, the chemical character of water is dominated by NaCl. However, Na% values indicate that just 53% of samples are permissible for irrigation. The chloride–bicarbonate ratios reveal that salt lake intrusion to this basin is the main source of salinity. It is also found that functional relationships between EC and Cl are logarithmic.► Because of uncontrolled discharge in the Kashan Basin, the mean water table has decreased about 7.93m between1990 and 2006, indicating an average water table decline of 0.496m/year. ► The quality of groundwater in this basin is affected by the Salt Lake intrusion to this basin. According to the ratio of Cl/HCO3, a total of 80% of samples are contaminated by saltwater intrusion. ► The piper diagram shows the dominant cations are in order of Na>Ca>Mg>K and the dominant anions are in order of Cl>SO4>HCO3. So, the hydrochemical facies of water in the Kashan Basin is dominated by Na Cl. ► Functional relationships show a logarithmic relation between EC and Cl in this basin.
Keywords: Groundwater quality; Groundwater quantity; Piper diagram; Salinity; Water table; Kashan Basin
Influence of various aromatic derivatives on the advanced photo Fenton degradation of Amaranth dye
by L. Gomathi Devi; K. Eraiah Rajashekhar; K.S. Anantha Raju; S. Girish Kumar (pp. 31-39).
The photo degradation of Amaranth (AR) dye by advanced photo Fenton process in the presence of symmetrical peroxides like hydrogen peroxide (H2O2) and ammonium persulfate (APS) are investigated. The influence of various reaction parameters like the effect of iron dosage, concentration of H2O2/APS, initial dye concentration, effect of pH and the influence of various aromatic derivatives were studied and optimum conditions are reported. The efficiency of the oxidant was strongly influenced by the nature of aromatic photoproducts formed during the course of the degradation reaction. To study their effect on the rate of degradation these aromatic derivatives were added in known concentration (10ppm). The influence of various aromatic derivatives on the degradation kinetics shows the following order: hydroquinones>chlorophenol>dichlorobenzene>aromatic carboxylic acids>anilidine>nitrophenol. The addition of these derivatives did not influence the degradation pathway although it altered the reaction rate. The percentage COD and TOC removal were determined in presence of aromatic derivatives to evaluate the complete removal of the pollutant. Based on the intermediates obtained in the UV–vis and GC-MS spectroscopic techniques probable degradation mechanism has been proposed.► H2O2 is a well known oxidant in Photo- Fenton process but least approach is made towards the application of ammonium persulfate. ► The problem of precipitation of iron ions in advanced photo Fenton process is overcome by the use of ammonium persulfate as an oxidant. ► The intension of the work is to study the effect of aromatic derivatives (additives) on the degradation rate, since many of these organic derivative molecules are formed as intermediates during the process of photo degradation.
Keywords: Zero-valent metallic iron; Photo Fenton process; Aromatic derivatives; Ammonium persulfate; Kinetic studies
Biosorption characteristics of ammonium from aqueous solutions onto Posidonia oceanica (L.) fibers
by Salah Jellali; Mohammed Ali Wahab; Makram Anane; Khalifa Riahi; Naceur Jedidi (pp. 40-49).
The present paper aims to study the effectiveness of an abundant marine waste named Posidonia oceanica ( P. oceanica) on ammonium removal from aqueous solutions under different experimental conditions. The results of this study have shown that ammonium biosorption onto P. oceanica fibers increases with initial ammonium concentrations and pH increase. Biosorption isothermal data were well fitted by Langmuir model suggesting a monolayer and uniform adsorption process. The kinetic modeling of the experimental data indicated that they were well described by a pseudo-second-order model predicting a chemisorption process. The scanning electron microscopy (SEM), the energy dispersive spectroscopy (EDS) and the Fourier transform Infra-red spectroscopy (FTIR) analysis before and after biosorption of ammonium onto P. oceanica revealed that the main involved mechanisms are both surface ion exchange with magnesium and calcium cations and surface or intraparticle sharing between ammonium and functional groups, such as O–H, N–H, C =O and C–H stretching, and N–H bending.► P. oceanica have high ammonium adsorption capacity. ► P. oceanica can be considered as a promising material for nitrogen adsorption. ► Ammonium adsorption by P. oceanica is essentially chemical. ► Ammonium adsorption by P. oceanica is done by ion exchange and complexation.
Keywords: Ammonium; Biosorption; P. oceanica; fibers; Batch; Kinetic; Mechanism
Formation and performance of Kaolin/MnO2 bi-layer composite dynamic membrane for oily wastewater treatment: Effect of solution conditions
by Tao Yang; Zheng-Fei Ma; Qi-Yong Yang (pp. 50-56).
To develop an efficient dynamic membrane for application in oily wastewater treatment, there is a need to explore an appropriate coating technique and to advance its separation performance. The formation and separation performance of the dynamic membrane from Kaolin and MnO2 were investigated with particular objectives on the choice of an appropriate membrane-coating technique and the discussion of the effect of solution conditions. The microstructures of the dynamic membrane were examined using the scanning electron microscope. The results showed that the deposition of MnO2 particles onto the surface of Kaolin dynamic layer forming a Kaolin/MnO2 bi-layer composite dynamic membrane is an effective coating technique. The optimum concentrations of the Kaolin solution and KMnO4 solution should be 0.4gL−1 and 0.1gL−1 respectively. With the rise of oil concentration, the steady permeate flux decreased and oil retention ratio increased. In the low oil concentration range from 0.1gL−1 to 1.0gL−1, the variation characteristics were more obvious. In neutral or alkaline environments, the dynamic membrane was stable with high permeate flux and oil retention ratio of over 99%. As the temperature rose from 283K to 313K, the steady retention ratio decreased from 99.9% to 98.2% and the steady permeate fluxes increased from 120.1Lm−2h−1 to 153.2Lm−2h−1.► We develope a Kaolin/MnO2 composite dynamic membrane for oily wastewater treatment. ► Concentrations of coating solutions affect its formation and separation performance. ► Conditions of the oily wastewater greatly affect its separation performance. ► Performance of composite dynamic membrane is better than monolayer dynamic membranes.
Keywords: Dynamic membrane; Composite; Oily wastewater; Kaolin; MnO; 2
Arsenate retention from aqueous solution by hydrophilic polymers through ultrafiltration membranes
by Sanchez Julio Sánchez; Bernabé L. Rivas (pp. 57-63).
Combining the liquid-phase polymer-based retention, LPR technique with an ultrafiltration membrane facilitates the separation of arsenic ionic species that are retained by the functional groups of hydrophilic polyelectrolytes.Arsenate retention by P(ClAETA) at a high arsenate concentration (47.6mgL−1) was 58% and this removal capacity increases gradually, reaching 100% retention when the arsenate concentration in the cell was at minimum (5.5mgL−1) using molar ratio (20:1) polymer:As(V).Arsenic removal was also determined at low concentrations (in μgL−1). The results show that P(ClAETA) removes 65% of arsenate at lower concentration and that the arsenate concentration in each 20mL of filtrate above Z=3 is below the maximum permissible level of the World Health Organization (WHO).The charge–discharge process shows that the discharge process of the arsenate ions from polymers can be performed when the polymer–arsenate was in contact with the acid solution from the reservoir.Removal of arsenic from the Camarones River water was also performed by using P(ClAETA). The water-soluble polymer showed a high performance (100%) for the first Z values and then decreased up to 16% for Z=10.Display Omitted►Arsenate can be removed from water by liquid-phase polymer-based retention technique. ►The decrease in the retention ability is due to an increase in the ionic strength. ►The charge–discharge process of the arsenate ions from polymers can be performed. ►Removal of arsenic from Camarones River water shows a high performance until Z=3.
Keywords: Liquid-phase polymer-based retention; Water-soluble polyelectrolyte; Arsenic removal
Oxygen permeation of Ba xSr1− xCo0.8Fe0.2O3− δ perovskite-type membrane: Experimental and modeling
by Ali Ghadimi; Mohammad Ali Alaee; Amir Behrouzifar; Amir Atabak Asadi; Toraj Mohammadi (pp. 64-75).
Ba xSr1− xCo0 .8Fe0 .2O0.3− δ ( x=0.2, 0.5, 0.8) dense membranes were prepared by a combined EDTA and citrate complexing method. In our previous works, effects of sintering temperature, sintering dwell time and pressing pressure on microstructure and theoretical densities of the membranes were examined and finally the best corresponding values were reported as 1100°C, 8–9h and 200–250MPa, respectively. In the present work, effects of temperature (650–950°C), feed flow rate (100–200cm³/min), sweep gas flow rate (40–80cm³/min) and membrane thickness (4–5mm) on oxygen permeation behavior of the Ba xSr1− xCo0 .8Fe0 .2O0.3− δ membranes were investigated. Also, a mathematical model based on Nernst–Planck equation was developed to predict oxygen permeation through the perovskite-type membranes. Both bulk diffusion and surface reactions were incorporated into the model. It was observed that surface reactions are not elementary and a correction term should be introduced into the model to compensate this effect. Also, using a dimensionless Reynolds number, effect of feed flow rate on oxygen flux was taken into account. With aids of these modifications, it was realized that, there is a reasonable agreement between predicted results and experimental data with correlation coefficient (R) of higher than 0.960 and mean squared relative error (MSRE) of lower than 0.022 for all the membranes. Oxygen vacancy bulk diffusion coefficient (Dv), surface exchange rate constants (kf and kr), contribution of each resistance to oxygen permeation and characteristic thickness (Lc) of the BSCF membranes were also estimated.► Oxygen permeation flux in the domain of operating parameters was predicted. ► Oxygen vacancy diffusion coefficient and reaction rate constants were estimated. ► Effect of feed flow rate variations on oxygen permeation was taken into account. ► The developed model is explicit functions of operating conditions.
Keywords: Dense ceramic membrane; Perovskite; Mixed-conducting membrane; Mathematical modeling; Air separation
Effect of surface charge on hydrophilically modified poly(vinylidene fluoride) membrane for microfiltration
by Man Jae Han; Barona Garry Nathaniel B. Baroña; Bumsuk Jung (pp. 76-83).
Charged poly(vinylidene fluoride) microfiltration membranes were prepared using stepwise chemical modification of defluorination and sulfonation. Different degrees of sulfonation with respect to degree of defluorination were controlled by varying the alcoholic potassium hydroxide concentration, reaction temperature and time. The effects of surface modification on the morphology, zeta potential, ion-exchange capacity (IEC), hydrophilicity, pure water flux, fouling, and rejection were investigated. As the degree of surface charge density increased, the IEC and hydrophilicity increased without any deformation on the morphology and pores as observed through scanning electron microscopy (SEM). The surface composition of sulfonic acid groups on the modified membrane was determined by X-ray photoelectron spectroscopy (XPS). As the concentration of sulfonic acid groups increased with the degree of surface charge density, the zeta potentials of membrane surface increased. It was also observed that the pure water flux was enhanced as the intrinsic resistance decreased with different degrees of surface charge density. Fouling of charged polystyrene latex suspension on the modified membrane decreased while rejection value increased as the degree of surface charge density was increased due to enhanced electrostatic repulsion.► Defluorination and sulfonation of PVDF MF membranes are performed and controlled. ► IEC and water uptake increase as degree of substitution by sulfonation increases. ► Increase in surface charge density is due to the increase in sulfonic acid groups. ► Water flux enhances while fouling decreases due to decrease in Rm, Rc and Ra.
Keywords: Poly(vinylidene fluoride); Surface charge density; Hydrophilic; Electrokinetic repulsion; Zeta potential
Evaluating removal of metribuzin pesticide from contaminated groundwater using an electrochemical reactor combined with ultraviolet oxidation
by O. Yahiaoui; L. Aizel; H. Lounici; N. Drouiche; M.F.A. Goosen; A. Pauss; N. Mameri (pp. 84-89).
The main purpose of this study was to evaluate the removal of the pesticide metribuzin from contaminated groundwater by means of an electrochemical reactor equipped with iron cylindrical concentric bipolar electrodes. The optimization of the experimental parameters such as current density, pH, initial concentration of metribuzin and salt concentration, for pesticide removal was first assessed. The elimination of the pollutant was found to be up to 89%. When this electrochemical process was combined with an ultraviolet oxidation process, the contaminant removal rate reached 95%. However, the results also suggested that the addition of hydrogen peroxide may reduce the process performance possibly due to increased turbidity.► Evaluating removal of pesticide from contaminated groundwater using an electrocoagulation combined with ultraviolet oxidation was achieved. ► Investigation on the efficiency of the combination of electrocoagulation with ultraviolet oxidation to remove metribuzin from contaminated groundwater has been done. ► As results pollutant removal from wastewater by means of electrocoagulation was satisfactory. ► The proposed combination of the use of bipolar electrocoagulation combined with UV based advanced oxidation processes was very satisfactory too. ► The proposed process can be used as a pretreatment for reverse osmosis, nanofiltration or biological treatment.
Keywords: Electro coagulation; Ultraviolet oxidation; Optimization; Bipolar electrodes; Metribuzin
Phenolic wastewaters depuration and biodegradability enhancement by ozone over active catalysts
by Rui C. Martins; Rosa M. Quinta-Ferreira (pp. 90-97).
Catalytic and non-catalytic ozonations were investigated in the depuration of simulated phenolic wastewaters. Commercial (N-150: Fe–Mn–O) and laboratory-made (Mn–Ce–O 70/30) catalysts have been used to improve the effluent biodegradability. The N-150 catalytic system followed a free radical pathway detected by means of the application of radical scavengers. After 120min of reaction, the recovered N-150 catalyst showed low carbon adsorption and negligible leaching behaviour. Moreover, the catalyst remained active after various feed-batch trials. Mn–Ce–O 70/30 led to higher mineralization levels and stronger biodegradable characteristics of the final solution measured by respirometry. Nevertheless, a lower BOD5/COD ratio of the treated effluent as well as a higher ecological impact measured by bio-luminescence techniques was detected. Further application of the N-150 catalyst seems to be preferable to enhance ozone action although its activity can be limited by the presence of radical scavengers in real effluents.►N-150 (Fe2O3–MnOx) shows to be an active and stable catalyst for catalytic ozonation. ►Toxicity removal and biodegradability enhancement attained after ozonation over N-150. ►Feasible technology as pre-treatment before a biological depuration. ►N-150 activity can be compromised in the presence of radical scavengers.
Keywords: Biodegradability; Heterogeneous catalysis; Ozonation; Phenolic wastewaters; Toxicity
Influence of glycol additives on the structure and performance of cellulose acetate/zinc oxide blend membranes
by Muddassir Ali; Muhammad Zafar; Tahir Jamil; Muhammad Taqi Zahid Butt (pp. 98-104).
The effects of different types and concentration of glycol additives in the membrane blend formulations for pervaporation studies were investigated. The glycol additives used were polyethylene glycol 600 (PEG 600), propylene glycol (PG) and ethylene glycol (EG). Glycol additive filled cellulose acetate (CA)/zinc oxide (ZnO) blend membranes were prepared for pervaporation separation of isopropanol (IPA)/water mixtures. The structural morphology and thermal stability of the blended membranes were characterized by SEM, FTIR, DSC, and TGA. The mechanical properties were determined by using UTM. It was found that the presence of PEG 600 in the blend membrane enhanced the membrane pervaporation performance. The effect of the PEG 600 content in the blended membranes on the pervaporation was studied and discussed in terms of permeation flux and separation factor. The separation factor and permeation flux were increased by the addition of the PEG 600 content in the range of 7.5–10wt.%. Among all the fabricated blended membranes, the membrane containing 10wt.% PEG 600 showed the highest separation factor of 1448.03 and a permeation flux of 558.63g/m2h for a feed composed of 71wt.% IPA in the aqueous solution at 40°C.► The separation factor decreased with the increase in the additive content. ► The permeation flux increased with the increase in the additive content. ► The PEG/CA blend membrane showed high stability up to 305 °C. ► The addition of glycols additives in CA lowered the Tg of CA blend membranes. ► The additives improved the mechanical properties of membranes.
Keywords: Glycol additives; Pervaporation; Cellulose acetate (CA); Blend membranes; Isopropanol (IPA)
Reductive removal of Cr(VI) by starch-stabilized Fe0 nanoparticles in aqueous solution
by L. Alidokht; A.R. Khataee; A. Reyhanitabar; S. Oustan (pp. 105-110).
A comparative study of hexavalent chromium (Cr(VI)) removal from aqueous solution using Fe0 and Fe3O4 particles in nano and micro-scale was performed. Our results indicated that the Cr(VI) removal efficiency using starch-stabilized Fe0 nanoparticles, nonstabilized Fe0 nanoparticles, Fe3O4 nanoparticles, Fe0 and Fe3O4 microparticles was 99.25%, 60.4%, 9.13%, 6.92% and 6.17%, respectively. Results revealed that the Cr(VI) removal efficiency using Fe3O4 particles was highly dependent on pH with maximum removal efficiency at pH 3. The stabilized Fe0 nanoparticles efficiently remove Cr(VI) from aqueous solution in a wide pH range. In the present of Fe0 nanoparticles, increasing the initial Cr(VI) concentration from 10 to 50mg/L decreased removal efficiency and observed pseudo-first order rate constant ( kobs) from 100% to 56.4%, and 0.101 to 0.015min−1, respectively. Increasing Fe0 nanoparticles dosage from 0.1 to 2g/L increased kobs value from 0.028 to 0.110min−1 and led to a 60% increase in the removal efficiency. The reaction rate constant decreased from 0.075 to 0.043min−1 with increasing pH from 3 to 9, respectively. Our results suggest that stabilized Fe0 nanoparticles may serve as an effective agent for reductive removal of Cr(VI) from contaminated waters.►Preparation of starch-stabled Fe0 nanoparticles by sulfate method. ►Comparative Cr(VI) removal by Fe0 and Fe3O4 nano and microparticles. ►Effect of operational parameters on Cr (VI) removal by stabled Fe0 nanoparticles.
Keywords: Zerovalent iron; Fe; 3; O; 4; nanoparticles; Chromium removal; Wastewater treatment; Chemical reduction
Characterization and anaerobic biodegradability of grey water
by Hernandez Leal L. Hernández Leal; H. Temmink; G. Zeeman; C.J.N. Buisman (pp. 111-115).
Grey water consists of the discharges from kitchen sinks, showers, baths, washing machines and hand basins. Thorough characterization of 192 time proportional samples of grey water from 32 houses was conducted over a period of 14months. COD concentrations were 724±150mgL−1, of which 34% was present as suspended COD, 25% as colloidal COD and 38% as soluble COD. The maximum anaerobic biodegradability of grey water of 70±5% indicates the possibility of recovering the COD as methane. However, the low hydrolysis constant makes the application of anaerobic treatment unsuitable. Surfactants accounted for 15% of the total COD. The concentrations of anionic, cationic and noninonic surfactants were 41.1±12.1mgL−1, 1.7±0.8mgL−1 and 11.3±3.9mgL−1, respectively. Of the trace elements which were measured were present below limits suggested for irrigation. Only boron (0.53±0.19mgL−1) in a few measurements exceeded the 0.75mgL−1 limit established for long term irrigation.►Grey water contains 724mgL−1 of total COD of which 34% was suspended, 25% colloidal and 38% soluble. ►The anaerobic degradability was 70±5% with a hydrolysis rate constant of 0.02±0.01d−1. ►Grey water contained 41±12mgL−1of anionic surfactants, about 15% of the total COD. ►Concentrations of metals in grey water were below limits suggested for irrigation.
Keywords: Characterization; Grey water; Anaerobic biodegradability; Separation at source; Surfactants
Thermally responsive membrane-based microbiological sensing component for early detection of membrane biofouling
by Guang Cai; Colleen Gorey; Amr Zaky; Isabel Escobar; Cyndee Gruden (pp. 116-123).
Early detection of bacteria in water treatment is desired to mitigate system biofouling and potential human health impacts. This research involved the development of an antibody-based sensor, which was attached to a hydroxypropyl cellulose (HPC) modified cellulose acetate ultrafiltration membrane surface, to target bacteria. HPC was chosen because it collapses above and expands below a lower critical solution temperature (43°C), thus allowing temperature modulation. The membrane had a high target recovery efficiency (10–18%) in both single bacterium and complex samples (simulated by adding organics and competitive organisms). Sensor recovery was decreased (to 5–7%) following temperature activation (above 50°C) due to adverse impacts of temperature on the antibody. The membrane was able to be regenerated (with 0.1M NaOH) and reused three consecutive times. The thermally responsive sensing membrane developed from this work was specifically developed to detect biofoulants in membrane-based water treatment processes. However, it could be adapted to address a range of environmental detection concerns, such as pathogen detection.► The membrane-based microbiological sensor provided rapid results (20min) and demonstrated a recovery efficiency (up to 20%) of targeted bacteria, which is comparable to similar findings. ► The membrane was thermally responsive, demonstrating surface roughness changes above and below the activation temperature, and could still detect targeted bacteria. However, target detection was significantly reduced at temperatures above the polymer film LCST (43°C). ► In order to determine if temperature activation results in increased sensor recovery in complex samples, future studies must include either alternative bio-recognition molecules (aptamers) that are unaffected by thermal changes above 43°C or polymer films that have lower LCSTs, preferably below 40°C, to preserve antibody function. ► The membrane-based sensor was able to be regenerated by using the elution reagent 0.1M NaOH up to 3 times, which can greatly reduce the cost of the sensor.
Keywords: Antibody; Detection; Sensor; Membrane
Photo-Fenton mineralization of synthetic municipal wastewater effluent containing acetaminophen in a pilot plant
by Duran A. Durán; J.M. Monteagudo; A. Carnicer; M. Ruiz-Murillo (pp. 124-129).
The aim of this work was to study the mineralization of acetaminophen (ACTP) present in synthetic municipal wastewater effluent (S.E.) in a UV-A/C pilot plant using a homogeneous photo-Fenton oxidation process with continuous addition of H2O2 to the system.The mineralization process was found to follow pseudo-first-order kinetics. Experimental kinetic constants were fitted using neural networks (NNs). The mathematical model reproduced the experimental data to within a 90% confidence level. At the optimum conditions (H2O2 flow rate=50mL/h, [Fe(II)]=2ppm, pH=2.5 and temperature=40°C), 71.5%, 82.1% and 94% of COT, COD and BDO-5 were removed in 120min respectively.Determination of the hydrogen peroxide consumed and remaining in the water revealed that 5.8mol of H2O2 were consumed per each mol of total organic carbon removed from solution. It was also confirmed that an excess of dissolved H2O2 is needed to achieve high mineralization rates, so continuous addition of peroxide is recommended for industrial application of this process.Comparison experiments of scavenger-loaded conditions proved that the reaction takes place mainly through a radical and single oxygen mechanism (96.7%).The molecular pathway (0.7%) and direct photolysis (2.6%) are secondary.►Photo-Fenton process is an alternative for the mineralization of S.E. with ACTP. ►Under optimum conditions, 83% of COD and 71% of TOC are removed in 120min. ►5.8mol of H2O2 were consumed per mol of TOC removed. ►The reaction takes place mainly through a radical mechanism.
Keywords: Hydrogen peroxide; Paracetamol; TOC; UV radiation
Coprecipitation of palladium(II) with 1,5-diphenylcarbazite–copper(II) and determination by flame atomic absorption spectrometry
by Nurcan Ozturk; Volkan Numan Bulut; Celal Duran; Mustafa Soylak (pp. 130-134).
In this study, Cu2+/1,5-diphenylcarbazite precipitate was used for coprecipitation of palladium(II) prior to its flame atomic absorption spectrometric (FAAS) determination. The recovery values of analyte ion were higher than 95%. The parameters including pH, sample volume, centrifuge time, amounts of copper(II) and 1,5-diphenylcarbazite were optimized for the quantitative recoveries of the analyte. The relative standard deviation of Pd(II) was found to be 6.3%. The limit of detection was calculated as 0.40μgL−1. The validation of the procedure was checked by the analysis of CRM-SA-C (standard material). The presented coprecipitation procedure was successfully applied to anodic slime and gold ore samples for determination of analyte ion.Display Omitted► Cu2+/1,5-diphenylcarbazite precipitate as coprecipitant for palladium(II). ► Flame atomic absorption spectrometric determination. ► The recovery values of Pd higher than 95% in this system. ► Application to anodic slime and gold ore samples for Pd determination.
Keywords: Flame atomic absorption spectrometry; Preconcentration; Coprecipitation; 1,5-Diphenylcarbazite
Mechanism of paracetamol removal by vegetable wastes: The contribution of π–π interactions, hydrogen bonding and hydrophobic effect
by Isabel Villaescusa; Núria Fiol; Jordi Poch; Antonio Bianchi; Carla Bazzicalupi (pp. 135-142).
The aim of the present work is to investigate the potential use of some vegetable wastes (grape stalk, yohimbe bark and cork bark) for the removal of paracetamol (acetoaminophen) from water. The factors influencing adsorption like contact time, initial pH, sorbent concentration and temperature were evaluated. The most effective biosorbent resulted to be grape stalk waste. Sorption kinetic and equilibrium data of paracetamol sorption onto grape stalks were submitted to kinetics and equilibrium models in order to get the adsorption constant rate and the maximum capacity of the sorbent. According to modeling calculations, π-stacking interactions between aromatic moieties from lignin of grape stalks and paracetamol and hydrogen bonding should make the major contribution to the sorption process. Further favorable contribution is expected to come from the hydrophobic effect accompanying the association of this species in water.Display Omitted► Grape stalk resulted to be the most efficient for paracetamol removal. ► No effect of pH and slight effect of temperature on sorption. ► Kinetics and equilibrium are described by pseudo-first and Langmuir models. ► Sorption was explained by π–π interactions and hydrogen bonds. ► GS is a significant sorbent for PC in areas producing this waste in large amounts.
Keywords: Acetoaminophen; Vegetable wastes; π–π interactions; Biosorption; Sorption mechanism
Modified cellulose microfibrils as benzene adsorbent
by L. Serrano; I. Urruzola; D. Nemeth; K. Belafi-Bako; J. Labidi (pp. 143-150).
Jute fibres have been used as raw material for cellulose microfibril isolation using two chemical treatments: acid delignification and acetylation to purify the obtained cellulose. Combined with these methods fibres were mechanically treated in order to fibrillate the fibres and microfibrils obtained after each chemical treatment. The isolated microfibrils were treated with palmitic acid in order to obtain a long hydrocarbon chain able to retain organic molecules in water. In this way, palmitic anhydride was firstly obtained from the reaction of palmitic acid and acetic anhydride and used in a second step to esterify cellulose microfibrils promoting the reaction between the carbonyl groups of the obtained anhydride and the hydroxyl groups of cellulosic chains by the addition of 4-(Dimethylamino)pyridine (DMAP) as catalyst.Treated fibres were characterised by Fourier transformed infrared spectroscopy and contact angle measurements. Retention of organic molecules was determined by using ultraviolet spectroscopy.►Isolation of cellulose microfibrils using two chemical treatments. ►Use of mechanical treatment to increase the surface area of microfibrils. ►Enhancement of adsorption capacity of microfibrils by chemical modification. ►Mechanical treatment increases significantly microfibrils adsorption capacity.
Keywords: Jute fibre; Microfibril; Cellulose; Benzene; Adsorption
Photooxidative decolorization of two organic dyes with different chemical structures by UV/H2O2 process: Experimental design
by M.B. Kasiri; A.R. Khataee (pp. 151-159).
The present work deals with the application of Response Surface Methodology (RSM) to study the effects of operational parameters on the photooxidative decolorization of two dyes (C.I. Basic Blue 3 (BB3) and C.I. Acid Green 25 (AG25)) with different molecular structure under UV light illumination (30W) in the presence of hydrogen peroxide (H2O2). The variables investigated were the reaction time, dye and H2O2 initial concentrations and distance of UV lamp from the solution. Central Composite Design (CCD) was used for the optimization of photooxidative decolorization process. Predicted values were found to be in good agreement with experimental values (R2=98.43 and 95.06 and Adj–R2=97.05 and 90.74 for BB3 and AG25, respectively), which indicated suitability of the model and the success of CCD in optimization of UV/H2O2 process. Graphical response surface and contour plots were used to locate the optimum points. The photooxidative removal of the dyes in the optimal conditions was compared and a structure-degradability relationship was established. Moreover, the figure-of-merit electrical energy per order (EEO) was employed to estimate the electrical energy consumption.► Optimization of photooxidative decolorization process by central composite design. ► Effect of operational parameters study by graphical surface and contour plots. ► Establishment of structure-degradability relationship. ► Estimating of the electricity consumption by EEO.
Keywords: Experimental design; Response surface methodology; Decolorization; Textile dye; Chemical structure
Fe3O4 magnetic nanoparticles modified with sodium dodecyl sulfate for removal of safranin O dye from aqueous solutions
by Shahab Shariati; Mohammad Faraji; Yadollah Yamini; Ali Asghar Rajabi (pp. 160-165).
The object of this study was to evaluate the efficiency of safranin O dye removal with application of magnetite nanoparticles (Fe3O4 NPs) as adsorbent. For this propose, NPs of Fe3O4 were synthesized via a chemical precipitation method with addition of sodium hydroxide to solutions of Fe2+ and Fe3+. The prepared NPs were characterized by XRD and TEM and the applicability of the synthesized NPs for removing of safranin O as a cationic dye from aqueous solutions was investigated. The surface of Fe3O4 NPs was modified with addition of sodium dodecyl sulfate as an anionic surfactant. The effects of various parameters on the removal efficiency of safranin O such as the type and amount of surfactant, pH of solution, salt effect and contact time were studied and optimized. The studies of sorption kinetics of the dye showed a rapid sorption dynamics by a second-order kinetic model, suggesting chemisorption mechanism. Dye adsorption equilibrium data were fitted well to the Langmuir isotherm and the maximum monolayer capacity qmax was calculated from the Langmuir as 769.23mg g−1.The obtained results indicate that sodium dodecyl sulfate modified Fe3O4 NPs can be used as an efficient adsorbent material for adsorption of cationic dyes from aqueous solutions.►In this study magnetic nanoparticles of Fe3O4 were synthesized via a chemical method. ►The structural characterizations of prepared magnetic NPs were studied. ►The surface of synthesized NPs was modified by SDS to prepare a negative surface. ►The synthesized NPs were investigated for removal of safranin O from aqueous solutions. ►High adsorption capacity was achieved using the SDS-coated Fe3O4 NPs in short times.
Keywords: Magnetite nanoparticles; Safranin O; Sodium dodecyl Sulfate
Coupling adsorption with photocatalysis process for the Cr(VI) removal
by M. Kebir; M. Chabani; N. Nasrallah; A. Bensmaili; M. Trari (pp. 166-173).
The adsorption of Cr(VI) onto red peanut skin and its photoelectrochemical reduction into Cr3+ were investigated. The material has been characterized by infrared spectroscopy and scanning electron microscopy. It was successfully applied to the removal of chromium in aqueous air equilibrated powder suspension. The influence of the contact time, initial concentration, pH and temperature has been studied. The best performance occurred at 50°C in the acidic solution (200mgL−1, pH 2) with an uptake removal of 85% in less than 30min and the adsorption follows a pseudo second order kinetic. The experiments have been carried out in a batch reactor; the data were evaluated using the linear isotherms of Langmuir and Freundlich models. The maximal adsorption capacity (44.05mgg−1) has been determined from the Langmuir model. The thermal variation obeys to the Arrhenius type law from which the thermodynamic parameters ΔH°, ΔS° and ΔG° have been deduced. The chromate adsorption is spontaneous and endothermic in nature. Red Peanut Skin is used as a post treatment technique and the adsorption is coupled to light driven catalysis over the hetero-system CuAl2O4/TiO2. A reduction of more than 58% of HCrO4− after ~2h is achieved under optimal conditions.► The red peanut skin has been successfully tested for the chromium removal. ► The Langmuir isotherms fitted the adsorption best. ► Maximum adsorption capacity of chromium was achieved at pH~1. ► The coupled process lowers the concentration below that required by the world health organization.
Keywords: Adsorption; Cr(VI); Kinetic; Isotherm; Photoreduction
Visible light photocatalytic activities of plasmonic Ag/AgBr particles synthesized by a double jet method
by Desong Wang; Yandong Duan; Qingzhi Luo; Xueyan Li; Leilei Bao (pp. 174-180).
Ag/AgBr catalyst, synthesized by the simple double jet method, was found to be a novel visible light driven photocatalyst for the degradation of methyl orange. The photocatalytic reaction follows first-order kinetics and the rate constant ( k) for the degradation of methyl orange photocatalyzed by Ag/AgBr is 102 and 16 times of that by commercial TiO2 (Degussa P-25) and mesoporous N-doping TiO2, respectively. The recycling runs experiment shows that the photocatalytic stability of Ag/AgBr photocatalyst is excellent. Total organic carbon experiment indicates that Ag/AgBr photocatalyst can easily mineralize methyl orange. The effects of initial concentration of methyl orange, catalyst dosage, pH of methyl orange solution and scavenger of electrons or holes on methyl orange photodegradation were investigated. The formation of H2O2 was observed in the aqueous Ag/AgBr suspension under visible light irradiation. The photocatalytic mechanism of Ag/AgBr was also discussed.► The Ag/AgBr particles exhibit strong absorption in visible light region. ► Ag/AgBr paticles possess excellent photocatalytic activity and stability. ► MO concentration, pH of solution and Ag/AgBr dosage affect MO photodegradation.
Keywords: Heterogeneous catalysis; Visible light photocatalyst; Silver bromide; Photodegradation; Methyl orange
Sludge characteristics and performances of the sequencing batch reactor at different influent phenol concentrations
by M.L. Leong; K.M. Lee; S.O. Lai; B.S. Ooi (pp. 181-187).
This study presents the sludge characteristics and the treatment performances of the SBR in the removal of varying influent phenol concentrations. The SBR was operated by treating synthetic wastewater containing no phenol and with phenol concentrations ranged from 100 to 400mg/L. Operational mode of the SBR included Fill, React, Settle, Draw and Idle periods in the ratio of 2:8:1:0.5:0.5 for a cycle time of 12h. The sludge characteristics were evaluated through the morphological observation and the sludge settleability while the treatment performance of the SBR was assessed through the phenol removal efficiency. The sludge morphology shifted from predominantly normal floc for SBR treating synthetic wastewater without phenol to predominantly Zoogloeal floc when phenol was introduced to SBR and was increased to 300mg/L. Zoogloeal floc enhanced the sludge settleability, producing clear effluent. As influent phenol concentration increased to 400mg/L, microfloc was prevailed resulting in poor sludge settleability and deteriorated the quality of effluent with discharged suspended solids. However, the change of sludge morphology did not affect the phenol removal efficiency in the SBR with increase phenol loading. Almost complete phenol removal can be achieved with sufficiently long React mode.► Sludge morphology changed from predominantly normal floc to Zoogloeal floc when the activated sludge was exposed to the synthetic wastewater without phenol and then with increasing phenol from 100 to 300mg/L. ► Zoogloeal floc had enhanced the sludge settleability and producing clear effluent. ► At relatively high 400mg/L phenol concentration, microfloc prevailed due to the disintegration of the floc and resulting in poor sludge settleability. ► The change of sludge morphology influenced the sludge settleability and the clarity of the effluent but did not affect the phenol removal efficiency in the SBR with increase phenol loading. ► Almost complete phenol removal can be achieved with sufficiently long React mode in the operation of SBR.
Keywords: Sludge characteristics; Sequencing batch reactor; Phenol; Settleability
The performance of electropositive nanofibrous filter media
by Chunsong Ye; Hong Yang; Jiuyang Lin; Huiming Zeng; Lihui Tong; Fei Yu; Fang Zhang (pp. 188-192).
Four types of nanofibrous filters, EPN-1, EPNPAC-2, EPN-3, and EPNPAC-4, were investigated in this trial, respectively. The microstructures of nanofibrous filters were analyzed through a scanning electron microscope (SEM), while their elements were determined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The Zeta potential, specific surface area, porosity and permeation flux of nanofibrous filters were measured in this study. The isoelectric point and pure water permeability coefficient were also calculated. The result shows that the nanofibers are less than 5μm and are made up of γ-Al2O3, silicate and polyester. The electropositive filter is that the nanofiber contains γ-Al2O3. The nanofibers have different positive and negative charge at different pH. The specific surface areas of nanofibers are 625.58, 509.13, 850.27 and 780.23(m2/g), respectively. The porosity of nanofibrous filters are less than 70%. Pure water permeability coefficients of filters are 80.84, 64.03, 119.17 and 100.26(L·m−2·s−1·MPa−1), respectively. The performances of nanofibers without nano powdered activated carbon (PAC) are better than those with nano PAC.► Four types of electropositive nanofibrous filter with and without nano powdered activated carbon were investigated, named EPN-1, EPNPAC-2, EPN-3, EPNPAC-4. ► The Zeta potential, specific surface area, porosity and permeation flux of nanofibrous filter was measured. The isoelectric point and pure water permeability coefficient were also calculated. ► The microstructures and surface characteristics of nanofibrous were supported in the paper. The foundation of nanofilter was based on the results of this experiment.
Keywords: Nanofibrous; Electropositive; Filter media
Cathodic protection system of copper–zinc–saline water in presence of bacteria
by Aprael S. Yaro; Haidar Al-Jendeel; Anees A. Khadom (pp. 193-198).
Rate of zinc consumption during the cathodic protection of copper pipeline which carries saline water was measured by weight loss technique in the absence and presence of bacteria. Variables studied were solution flow rate, temperature, time and NaCl concentration. It was found that within the present range of variables; the rate of zinc consumption increases with the increase of all operating conditions. The presence of bacteria increases the zinc consumption. Fourth order multi-term model and one-term model were suggested to represent the consumption data. Nonlinear regression analysis was used to estimate the coefficients of these models, while statistical analysis was used to determine the effect of each coefficient. Both models were representing the data successfully.►Work is an attempt to test zinc consumption in presence of bacteria. ►Four variables' effects were studied for zinc–copper–saline water system. ►Statistical analysis was used to determine the effect of each variable.
Keywords: Copper; Zinc; Weight loss; Cathodic protection; Microbiological corrosion
Biosorption of a model basic dye onto Pinus brutia Ten.: Evaluating of equilibrium, kinetic and thermodynamic data
by Fatih Deniz; Sengul Karaman; Saadet D. Saygideger (pp. 199-205).
The potential of pine cones as a natural biosorbent was investigated for adsorptive removal of Basic Red 46 (BR 46) from aqueous solutions. Various physico-chemical parameters were studied such as solution pH, biosorbent dosage, biosorbent size, dye concentration, temperature, contact time and ionic strength. The equilibrium data fitted well with the Langmuir isotherm. The monolayer sorption capacity was found as 73.53mgg−1. Kinetic data were best described by the pseudo-second order model. The thermodynamic studies indicated that the biosorption reactions were spontaneous and endothermic. Activation energy was calculated as 32.33kJmol−1. The BR 46 was desorbed from the pine cones with 0.1M HCl solution. The recovery for the dye was found to be higher than 90%. Thus, this study demonstrated that the pine cones could be used as a low-cost biosorbent for the treatment of the wastewater streams bearing dye.►The monolayer sorption capacity was found as 73.53mgg−1. ►Kinetic data were best described by the pseudo-second order model. ►The biosorption reactions were spontaneous and endothermic. ►The pine cones as a natural biosorbent may be an alternative to more costly materials.
Keywords: Biosorption; Basic Red 46; Pinus brutia; Pine cones
Comparative study on the effectiveness of hydrophobically modified cationic polyacrylamide groups in the flocculation of kaolin
by Khai Ern Lee; Norhashimah Morad; Beng Teik Poh; Tjoon Tow Teng (pp. 206-213).
A series of hydrophobic cationic monomers were introduced into acrylamide chain to form hydrophobically modified cationic polyacrylamide. The hydrophobic cationic monomer used in this study was 3-acrylamido-2-hydroxypropyltrialkylammonium chloride (AHPTAAC) in which the alkyl groups were hexyl, octyl and dodecyl groups. The characteristics of the copolymers were tuned by varying the mole ratios of the hydrophobic cationic monomers (1–6mol %) to obtain copolymers of different molecular weights and charge densities. The effects of hydrophobically modified cationic polyacrylamides, with different hydrophobic cationic groups, molecular weights and charge densities, on flocculation of kaolin suspension, were investigated. A significant inverse correlation was found between molecular weight and charge density. The effects of different hydrophobic groups and monomer substitution ratios on the kaolin turbidity removal were compared. Hexyl group copolymer, which had the highest molecular weight of 2.13×106g/mol, was able to reduce 99% of kaolin suspension turbidity through flocculation. 1mol % of hydrophobic group associated copolymers was found to be the best system in flocculating kaolin suspension, and bridging was the dominant mechanism in flocculating kaolin suspension. Copolymer with the dodecyl group had the least water retention in the flocculated sludge.►Polyacrylamide has been modified with cationic hydrophobic groups: AHPTHAC, AHPTOAC and AHPTDAC. ►Charge densities and molecular weights varied with the addition of different concentration of the hydrophobic group. ►Molecular weight and change density have an inverse relationship. ►The bridging mechanism was the dominant mechanism in flocculating kaolin suspension.
Keywords: Hydrophobically modified; Cationic polyacrylamide; Flocculation; Kaolin
Effect of oxidation and geometrical dimensions of carbon nanotubes on Hg(II) sorption and preconcentration from real waters
by Amjad H. El-Sheikh; Yahya S. Al-Degs; Randa M. Al-As'ad; Jamal A. Sweileh (pp. 214-220).
This study reports for the first time the use of oxidized and non-oxidized multi-walled carbon nanotubes (MWCNTs) of different geometrical dimensions for Hg(II) adsorption and preconcentration in water samples. The shapes of the Hg isotherms varied from L2, C1 and H2 according to the dimensions and oxidation conditions of the MWCNTs. Analysis of adsorption data by Langmuir, Freundlich and Dubinin–Radushkevich isotherms revealed that Hg(II) removal by L-MWCNT-4060-NA (nitric acid-oxidized MWCNT of external diameter 40–60nm and length 5–15μm) has the lowest sorption energy, which reflects the favorable uptake of Hg(II) by this adsorbent. Sorbents showed variable sorption capacities for mercury (0.70–3.83mgg−1). However, in the preconcentration experiments, L-MWCNT-4060-NA exhibited the highest enrichment efficiency for a preconcentration of 100μgL−1 Hg(II) at pH 7. The limit of quantifications of Hg(II) was 0.0123μgL−1 in water. Analysis of Hg(II) in tap and reservoir waters gave high spike recovery (88–95%, RSD<3%). Mineral water was used to check interference from foreign ions. The method was validated by determination of mercury in digested phosphate rock samples and certified reference Polish tobacco leaves, in which the method was highly accurate and precise.► Oxidation and dimensions of MWCNT affect Hg sorption. ► Various sorption models are applied. ► Solid phase extraction procedure of Hg(II) is optimized. ► The method is precise and accurate. ► Hg was determined in real waters, tobacco and phosphate rock.
Keywords: Multi-walled carbon nanotubes; Adsorption; Solid-phase extraction; Mercury(II); Water samples
Effects of UV/H2O2 on NOM fractionation and corresponding DBPs formation
by Hui-Chuan Lin; Gen-Shuh Wang (pp. 221-226).
In this study, UV/H2O2 treatment was used to evaluate its efficacy for control of natural organic matter (NOM) in different water sources in Taiwan and the results were compared with the conventional water treatment process. The NOM fractions analysis showed that compositions of NOM could be very different between the various water sources, and the raw water quality in Kin-Men (an off shore island of Taiwan) was characteristic when compared to other water sources. Raw water taken from Kin-Men generally had high dissolved organic carbon (DOC) concentrations and ~50% of the NOM in the raw water was hydrophilic. After UV/H2O2 treatment, a portion of the hydrophobic fractions of NOM in raw waters were transformed into hydrophilic ones. In conventional water treatment process, coagulation and slow filtration treatments have better efficiency to reduce the NOM in water especially for the hydrophobic portion. However, the pre-chlorination treatment for raw water increased the DOC concentration due to the lysis of algae cells. This study concluded that hydrophobic acids portion is the most sensitive portion of NOM to UV/H2O2 and conventional treatment processes. Trihalomethanes formation potential (THMFP) tests showed that hydrophobic acids portion is also the main contributor to THMs formation after chlorination process.► UV/H2O2 treatment efficiency for NOM from different water sources was assessed. ► The very hydrophobic acid (VHoA) fraction of NOM is sensitive to the UV/H2O2 process. ► The VHoA fraction was the main contributor to THM formation in chlorination process. ► Part of the hydrophobic NOM is transformed into hydrophilic ones after UV photolysis. ► The THMFP decreases with increase of UV photolysis time after UV/H2O2 treatment.
Keywords: Natural organic matters; Disinfection by-product; UV/H; 2; O; 2; process; Conventional treatment; NOM fractionation
Influence of anoxic and anaerobic hydraulic retention time on biological nitrogen and phosphorus removal in a membrane bioreactor
by Patrick Brown; Say Kee Ong; Yong-Woo Lee (pp. 227-232).
Influence of anaerobic and anoxic hydraulic retention time (HRT), a commonly used parameter by treatment plant design engineers and operators, on nitrogen and phosphorus removal was studied in an anaerobic/anoxic/oxic membrane bioreactor with fixed recycle rates. Anaerobic HRTs were varied between 0.5 and 3h, anoxic HRTs were varied between 1 and 5h while the aerobic HRT was fixed at 8h. Total nitrogen removals ranged from 76% to 89% and were found to increase with increasing anoxic HRTs but were minimally impacted by increasing anaerobic HRTs except when the anoxic HRT was at 5h. Phosphorus removals ranged from 40% to 82% and were found to increase with increasing anaerobic HRTs from 0.5 to 2h but decreased for an anaerobic HRT of 3h and with an increase in anoxic HRTs. The study shows that optimal removals for both nitrogen and phosphorus require balancing the conflicting needs of a longer anoxic HRT for increased nitrogen removal but decreased phosphorus removal and an optimal anaerobic HRT for phosphorus removal without impacting the nitrogen removal. The most favorable HRTs for combined optimal nitrogen and phosphorus removal were found to be 2-h anaerobic and 4-h anoxic.► BNR MBR removed 76–89% total nitrogen and 40–82% total phosphorus. ► Favorable hydraulic retention times (HRTs) for anaerobic and anoxic reactors for optimal BNR were 2 and 4h, respectively. ► Total phosphorus removal decreased for an anaerobic HRT of 3h or larger.
Keywords: Hydraulic retention time; Membrane bioreactor; Phosphorus; Nitrogen; BNR; Anoxic; Anaerobic
Wastewater treatment by high-growth bioreactor integrated with settling-cum-membrane separation
by Subrata Hait; Vinod Tare (pp. 233-240).
A different approach of wastewater treatment has been investigated in this study by operating bioreactor at low mixed liquor suspended solids (MLSS) concentrations, thereby maintaining high F/ M ratio to target higher nutrient removal through higher biomass yield. A 10-L capacity laboratory-scale bioreactor followed by settling-cum-membrane separation employing hollow fiber membrane module (pore size: 0.1μm) was set up and operated under batch mode at a hydraulic retention time (HRT) of 24h using simulated domestic wastewater as feed. Average removal efficiencies of bioreactor were approximately 84% soluble chemical oxygen demand (SCOD), 95.5% total COD (TCOD), 90% NH4+–N, and 87% total Kjeldahl nitrogen (TKN). True yield coefficient ( Y T) and decay coefficient ( K d) for bioreactor were estimated at 0.397kg VSS/kg SCOD and 0.0549day−1, respectively. Significant proliferation of non-flocculating microorganisms was observed in the system with decreasing solids retention time (SRT) and thereby deteriorating biomass settling property indicated by enhanced sludge volume index (SVI). Significant proliferation of non-flocculating microorganisms with better ability to access substrate from bulk solution through smaller mass transfer resistance most probably contributed to better organics removal. The modified approach of wastewater treatment can be a good basis to develop high-growth membrane bioreactor (MBR) as opposed to conventional MBR operation.► Reactor at high F/ M ratio with membrane separation for better wastewater treatment. ► Higher true yield coefficient ( Y T) at high F/ M ratio ensured high-growth condition. ► High-growth reactor system showed 84% SCOD, 95.5% TCOD, 90% NH4+–N, 87% TKN removal. ► Excellent organics removal due to significant proliferation of dispersed biomass. ► Modified approach of wastewater treatment is a good basis to develop high-growth MBR.
Keywords: Conventional activated sludge; Membrane separation; High-growth; Non-flocculating microorganisms; Wastewater treatment
Photocatalytic reduction of Hg(II) on TiO2 and Ag/TiO2 prepared by the sol–gel and impregnation methods
by G.G. Lenzi; Favero C.V.B. Fávero; L.M.S. Colpini; H. Bernabe; M.L. Baesso; S. Specchia; O.A.A. Santos (pp. 241-247).
Heterogeneous photocatalysis is a convenient tool for mercury(II) reduction, because it uses inexpensive chemicals and near-UV light. However, structural features of titania (band gap at 3.2eV) make extending its optical absorption in the visible region difficult. This key factor results in low photocatalytic efficiency, as about only 5% of the solar spectrum is used. This study focuses on the characterization and evaluation of the photocatalytic activity of TiO2. The titania preparation method (commercial and sol–gel), the presence of metal on the surface of the oxide (2% wt. Ag), and the calcination temperature (350 and 500°C) were evaluated. The characterization techniques used were: temperature-programmed reduction (TPR), determination of specific surface area (BET method), X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoacoustic spectroscopy. The photocatalytic reduction of Hg2+ to Hg0 was performed by aqueous solution containing formic acid. The results showed that the presence of Ag on the surface of TiO2 (commercial and sol–gel) decreased the band gap energy and increased the photoactivity efficiency, i.e., all the Hg2+ in the solution was reduced to Hg0.► Heterogeneous photocatalysis for mercury(II) reduction. ► Photocatalyst prepared by sol–gel and impregnation method. ► Photocatalytic activity influenced by photocatalyst synthesis method. ► Sol–gel method was photocatalytically more active.
Keywords: Photocatalytic reduction; Mercury; Sol–gel catalyst
Thin-film composite polyamide reverse osmosis membranes with improved acid stability and chlorine resistance by coating N-isopropylacrylamide-co-acrylamide copolymers
by Meihong Liu; Zhiwen Chen; Sanchuan Yu; Dihua Wu; Congjie Gao (pp. 248-257).
This study focus on the surface modification and the improved acid stability and chlorine resistance of the commercial thin-film composite polyamide reverse osmosis membranes coated with hydrophilic copolymers poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)) surface layer. The virgin flat-sheet polyamide membranes were modified in situ with dilute P(NIPAM-co-Am) aqueous solution, and the modified membranes were then tested for their acid stability and chlorine resistance through long-term cross-flow permeation tests with aqueous solution containing 0.5mol/l HCl and 2000ppm NaCl and chlorine exposure experiments with hypochlorite aqueous solutions of different concentrations, respectively. The membrane properties were characterized in terms of reverse osmosis performance and surface chemical structure. The membrane modification was found to improve the chlorine tolerance and acid stability significantly. The P(NIPAM-co-Am) surface coating layer would impede the hydrolysis and the replacement of hydrogen with chlorine on the amide groups of the aromatic polyamide thin-film through enhancing intermolecular hydrogen bonding, and prevent the attack of acid and chlorine on the underlying polyamide film as a protective and sacrificial layer. The P(NIPAM-co-Am)-coated membrane would offer a potential use as a new type of thin-film composite polyamide membrane with improved acid stability and chlorine resistance.► P(NIPAM-co-Am) surface coating layer improves membrane acid stability. ► P(NIPAM-co-Am) surface coating layer enhances membrane chlorine resistance. ► P(NIPAM-co-Am) coating layer increases membrane surface hydrophilicity. ►Membrane modification can be done in situ with dilute polymer solution.
Keywords: Polyamide reverse osmosis membrane; Surface modification; Acid stability; Chlorine resistance; Poly(N-isopropylacrylamide-co-acrylamide)
Selective reinforced competitive biosorption of Ag (I) and Cu (II) on Magnetospirillum gryphiswaldense
by Yanhong Wang; Hong Gao; Jinsheng Sun; Jing Li; Yanxia Su; Yulan Ji; Chunmei Gong (pp. 258-263).
Probing competitive biosorption of Ag (I) and Cu (II), the main concern of this paper, was started with observing individual ion biosorptions on Magnetospirillum gryphiswaldense (MSR-1), for reference to the succeeding selective reinforced processes in binary ion systems. In the control test of unitary ion systems, unsettled cells were substantiated to have better biosorption capacity than pretreated ones and optimum biosorptive conditions screened and defined experimentally. In addition, saturated extents of adsorption were obtained under the optimum conditions. The biosorptive data hereinabove were perfectly described by Langmuir isotherm and pseudo-second-order kinetic model. In binary ion biosorption, Cu (II) was observed to promote the adsorption of Ag (I) compared with that in the above control tests, with that of Cu (II) itself reduced or inhibited correspondingly. This phenomenon indicates that MSR-1 becomes a stronger biosorbent for Ag (I) in aqueous solution under the “catalysis” of Cu (II). A new Cu (II) biosorption isotherm model was worked out, which was more suitable for the inhibited Cu (II) adsorption behavior in this case than the frequently used Langmuir or Freundlich models, which is still valid for Ag (I) in the binary case.►Probing competitive biosorption of Ag (I) and Cu (II) was started with observing individual ion biosorptions on Magnetospirillum gryphiswaldense (MSR-1). ►Cu (II) in the binary solution, something like catalysts to reactants, could promote the adsorption of Ag (I) by MSR-1. ►Langmuir and Freundlich models could not describe the Cu (II) biosorption well. ►A new Cu (II) sigmoidal biosorption isotherm model was figured out in this unusual case.
Keywords: Biosorption; Magnetospirillum gryphiswaldense; Competitive biosorption; Sigmoidal isotherm
Coupling of biological methods with membrane filtration using ozone as pre-treatment for water reuse
by Luqing Qi; Xiaojun Wang; Qikun Xu (pp. 264-268).
This work focused on the advanced treatment of the biologically treated wastewater of a textile plant. Nowadays, treatment methods for water reuse are mainly membrane technologies. According to the difficulty of concentrate stream treatment and fouling problem in membrane process, a combination pre-treatment process including ozonation, biological aerated filter (BAF) and reverse osmosis was developed for textile wastewater treatment. Comparing different ozone dosing methods, the ozone–BAF integrated device allowed a higher COD (chemical oxygen demand) and color reduction. The optimal ozone dosage in the integrated device was 20–30mg/L. After the two-stage BAF treatment, an effluent was obtained with an average COD of 27.4mg/L, a turbidity of 4.2NTU, a SS (suspended solid) of 3.0mg/L, an ammonia nitrogen of 0.7mg/L and a color of 2 degree.After being steadily treated by the reverse osmosis (RO) unit preceded by ultrafiltration, the pH value of permeate water was 7.4–7.9, conductivity was 50–200μs/cm, total hardness was 2–10mg/L, and total alkalinity was 25–60mg/L. The results showed that the membrane permeates could be reused as dyeing process water. Moreover, the pH value of concentrated stream was in the range of 7.3–8.3, a color of 32 degree, and a COD of 45.7–97.9mg/L. The concentrate water could be discharged directly without additional treatment since it had already met the discharge standard.► Membrane filter with pre-treatment including ozone and biological aerated filter was chosen as the treatment technology for textile wastewater reuse. ► Comparing the ways of adding ozone into the water, the integrated device, allowed higher COD and color reduction. ► The concentrated stream could be discharged directly without additional treatment since it had already met the discharge standard.
Keywords: Ozone; Biological aerated filter; Reverse osmosis; Reuse; Concentrate stream
Competitive adsorption of Hg2+, Pb2+ and Co2+ ions on polyacrylamide/attapulgite
by Shouyong Zhou; Ailian Xue; Yijiang Zhao; Qiwei Wang; Yan Chen; Meisheng Li; Weihong Xing (pp. 269-274).
In the present study, the competitive adsorption characteristics of binary and ternary heavy metal ions Hg2+, Pb2+ and Co2+ on polyacrylamide/attapulgite (PAM/ATP) were investigated in batch systems. PAM/ATP was prepared by the solution polymerization of acrylamide (AM) onto γ-methacryloxypropyl trimethoxy silane (KH-570) modified attapulgite (ATP) and characterized by the technique of X-ray photoelectron spectroscopy (XPS). Equilibrium and kinetic adsorption data showed that PAM/ATP displays a high selectivity towards one metal in a two-component or a three-component system with an affinity order of Hg2+ > Pb2+ > Co2+. The equilibrium behaviors of heavy metal species with stronger affinity toward PAM/ATP can be described by the Langmuir equation while the adsorption kinetics of the metals can be well fitted to a pseudo-second-order kinetic model. Desorption was performed using hot acetic acid, and the regenerated adsorbents could be reused with little loss of adsorption capacity.► PAM/ATP displays an affinity order of Hg2+>Pb2+>Co2+ in binary and ternary system. ► The equilibrium behaviors can be described by the Langmuir equation. ► The adsorption kinetics fits pseudo-second-order kinetic model. ► The regenerated adsorbents could be reused with little loss of adsorption capacity.
Keywords: Attapulgite; Polyacrylamide; Heavy metal ions; Competitive adsorption; Selectivity
Optimization of Cr(VI) reduction by zero-valent bimetallic nanoparticles using the response surface modeling approach
by Kunwar P. Singh; Arun K. Singh; Shikha Gupta; Sarita Sinha (pp. 275-284).
Bimetallic iron–silver zero-valent nanoparticles were synthesized, characterised and studied for reduction of Cr(VI) in water solution. A four-factor, central composite design (CCD) combined with response surface modeling (RSM) and optimization was employed for maximizing the Cr(VI) reduction by the bimetallic system. Four independent variables, viz., temperature (10–50°C), pH of solution (2–8), Cr(VI) concentration (30–70mg/l), and particles dose (0.4–1.6g/l) were transformed to coded values and a quadratic model was built to predict the responses. The significance of the independent variables and their interactions were tested by the analysis of variance (ANOVA) and t-test statistics. Adequacy of the model was tested by the correlation between experimental and predicted values of the response and enumeration of prediction errors. Model validation was performed using a second set of data. Optimization of the variables for maximum Cr-reduction by bimetallic nanoparticles was performed using the quadratic model. The model predicted maximum reduction capacity (55.96mg/g) under the optimum conditions of Cr(VI) concentration 65.7mg/l; temperature 43°C; pH 2; and dose 0.4g/l, which was very close to the experimental value (55.18mg/g) determined in batch experiment and about 32% higher than the experimentally determined un-optimized reduction capacity (42.39mg/g).► We synthesize and characterise zero-valent Fe/Ag nanoparticles for Cr(VI) reduction. ► Optimized pH, temperature, particles dose, Cr(VI) concentration for maximum reduction. ► Optimization performed by central composite design and response surface modeling. ► Optimization rendered 32% higher reduction than the experimentally determined value. ► pH of solution produced the largest effect on Cr(VI) reduction process.
Keywords: Bimetallic zero-valent nanoparticles; Hexavalent chromium; Central composite design; Optimization; Response surface modeling
Preparation and electrosorption desalination performance of activated carbon electrode with titania
by Li Min Chang; Xiao Yue Duan; Wei Liu (pp. 285-290).
The activated carbon (AC) electrode was prepared and carbonized at 850°C for electrosorption desalination. As a result, the electrical double-layer capacitance of AC electrode was improved by 2.16 times by carbonization. In order to improve the desalination performance of AC electrode, it was modified by loading titania with sol-gel method. The electrodes were analyzed using scanning electron microscope (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD) and electrochemical workstation. The results revealed that there was a certain amount of titania on the surface of modified AC electrode, which was accumulated on the surface of electrode forming some flocculent substance and its crystalline phase was rutile. After modification, the forming rate of electrical double-layer and electrosorption capacity of AC electrode were obviously improved and its desalination ratio was increased by 62.7%, whereas physical adsorption was decreased. In addition, compared with AC electrode, activated carbon fiber (ACF) electrode, and carbon nanotube (CNT) electrode, the AC loaded titania (AC-TiO2) electrode exhibited relatively higher desalination and desorption ratios as well as a reasonable cost. Therefore, the AC-TiO2 electrode would be suitable for the application of electrosorption desalination in the practical industry.► Activated carbon loaded with titania (AC-TiO2) electrode was prepared. ► Electrosorption desalination of AC electrode was obviously improved by loading tatania. ► AC-TiO2 electrode exhibited relatively higher desalination and desorption ratios as well as a reasonable cost. ► AC-TiO2 electrode would be suitable for the application in the practical industry.
Keywords: AC; Electrosorption; Desalination; Carbonization; Titania