Removal of Dyes from Wastewater Using Flyash, a Low-Cost Adsorbent†

Modified Cenospheres as an Adsorbent for the Removal of Disperse Dyes

The main objective of this investigation was to use modified cenospheres for the removal of disperse blue 79:1 (DB) and disperse orange 25 (DO) dyes from aqueous solution by batch adsorption process under different conditions (pH, adsorbent dose, adsorbate concentration, agitation speed, contact time, and temperature). Modified cenosphere was capable of removing up to 78% of DB and 81% of DO dyes from aqueous solutions of 40 mg/L dyes concentration. The investigated data was explained by the Langmuir isotherm. The experimental data were found to follow the pseudo-second-order kinetic model. The results of this study suggested that modified cenospheres could be used as a low-cost alternative to expensive adsorbents like activated carbon in wastewater treatment for the removal of disperse dyes.

Removal of Direct Red 23 from aqueous solution using corn stalks: isotherms, kinetics and thermodynamic studies

The objective of this study was to assess the suitability and efficiency of corn stalk (CS) for the removal of diazo dye Direct Red 23 (DR23) from aqueous solutions. The effect of different variables in the batch method as a function of solution pH, contact time, initial dye concentration, CS amount, temperature, and so forth by the optimization method has been investigated. The color reduction was monitored by spectrophotometry at 503 nm before and after DR23 adsorption on the CS, and the removal percentage was calculated using the difference in absorbance. The sorption processes followed the pseudo second order in addition to intraparticle diffusion kinetics models with a good correlation coefficient with the overall entire adsorption of DR23 on adsorbent. The experimental equilibrium data were tested by four widely used isotherm models namely, Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich (D-R). It was found that adsorption of DR23 on CS well with the Freindlich isotherm model, implying monolayer coverage of dye molecules onto the surface of the adsorbent. More than 99% removal efficiency was obtained within 10 min at adsorbent dose of 0.2 g for initial dye concentration of 10-90 mg L(-1) at pH 3. Various thermodynamic parameters, such as Gibbs free energy, entropy, and enthalpy, of the ongoing adsorption process have been calculated. Judgment based on the obtained results of thermodynamic values shows the spontaneous and endothermic nature adsorption processes on adsorbent.

Decolorization of Reactive Black 39 and Acid Red 360 by Pseudomonas aeruginosa

The aim of this work is to evaluate decolorization of Reactive Black 39 (RB39) and Acid Red 360 (AR360) by Pseudomonas aeruginosa, which was isolated from a non-dye-contaminated activated sludge biomass. In the present study, the effect of various physicochemical parameters, initial dye concentration, temperature, pH, inoculum size and yeast extract concentration as an organic source on decolorization were investigated. P. aeruginosa was able to decolorize 20 mg/L RB39 completely within 144 hours in the presence of 0.5 g/L yeast extract at 25°C. Decolorization efficiencies for AR360 were found to be higher than RB39 under the same conditions. Optimal temperature to decolorize RB39 and AR360 was found to be 30 and 25°C, respectively. The activation energy (Ea) values for decolorization of RB39 and AR360 were found to be 61.89 kJ/mol and 81.18 kJ/mol, respectively. Experience showed that the pH and inoculum size had a considerable effect on decolorization of RB39 and AR360 by P. aeruginosa.

Preliminary study on removing Cs⁺/Sr²⁺ by activated porous calcium silicate-A by-product from high-alumina fly ash recycling industry

¹³⁷Cs⁺/⁹⁰Sr²⁺-containing radioactive wastewater is one of the most important problems that the world has been facing with. A by-product, activated porous calcium silicate, is generated at high levels by the pre-desiliconizing and soda-lime-sintering processes for producing Al₂O₃from high-alumina fly ash. In order to examine if this by-product could be used as an absorbent for removal of ¹³⁷Cs⁺/⁹⁰Sr²⁺ from radioactive wastewater, various parameters, such as pH, adsorbent dose, contact time, and initial concentration, were discussed. Results indicated that the equilibrium reached in about 2 hr. Activated porous calcium silicate was highly pH sensitive and able to remove Cs(+)/Sr²⁺ in a near-neutral environment. The adsorption equilibrium was best described by Freundlich isotherm equations, and the adsorption of Cs⁺/Sr²⁺ was a physical process. The adsorption kinetic data could be better fitted by the pseudo-second-order model, and the adsorption was controlled by multidiffusion. Current study showed that activated porous calcium silicate has a good adsorption of Cs⁺/Sr²⁺ for their removal. However, other characteristics, such as selectivity because of coexisting cations, elution and regeneration, thermal stability, and acid resistance, should be discussed carefully before using it in an actual field.

Surface-functionalized silica gel adsorbents for efficient remediation of cationic dyes

The toxic and non-biodegradable nature of organic dyes necessitates the design and synthesis of novel adsorbents for their effective removal from the environment. This study reports an effective remediation behavior of surface-functionalized silica gel against water-soluble cationic dyes (up to 98 % removal). Thiol groups were functionalized at the surface of silica gel (SiO2–SH). The surface-tethered –SH groups were further oxidized to sulfonic acid groups to generate the negatively charged moieties at the surface of silica gel (SiO2–SO3 H). The morphology of the developed adsorbents and the surface modifications were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Uptake study of three cationic dyes, namely, rhodamine B (Rh B), rhodamine 6G (Rh 6G), and crystal violet (CV) with SiO2–SH and SiO2–SO3 H adsorbents was performed by varying the adsorbent amount, contact time, pH of solution, and temperature. The presence of negatively charged species at the surface of SiO2–SO3 H results in an increased electrostatic interaction with the cationic dyes, which leads to better remediation characteristics for SiO2–SO3 H as compared to SiO2–SH. The reusability of the developed adsorbents was also assessed by investigating adsorption/desorption of dyes. The simple fabrication process provides a facile avenue to the adsorbents with efficient remediation towards cationic dyes.

Biological neutralization and biosorption of dyes of alkaline textile industry wastewater

The present work was aimed to secure biological neutralization and biosorption of dyes of an alkaline textile industrial effluent (ATIE) using an alkaliphilic bacterium, Enterococcus faecalis strain R-16 isolated from Gujarat coast. The isolate was capable and competent to bring down the pH of ATIE from 12.1 to 7.0 within 2 h in the presence of carbon and nitrogen sources. Carboxylic group concentration (CGC), NMR and FT-IR analysis revealed production of carboxylic acid as a result of neutralization. The unconventional carbon and nitrogen sources like Madhuca indica flowers or sugar cane bagasse supported the growth of bacterium with effective neutralization and biosorption of dyes from ATIE. The process proved to be efficient, inexpensive and eco-friendly as compared to conventional chemical neutralization process.

Dye and its removal from aqueous solution by adsorption: a review

In this review article the authors presented up to-date development on the application of adsorption in the removal of dyes from aqueous solution. This review article provides extensive literature information about dyes, its classification and toxicity, various treatment methods, and dye adsorption characteristics by various adsorbents. One of the objectives of this review article is to organise the scattered available information on various aspects on a wide range of potentially effective adsorbents in the removal of dyes. Therefore, an extensive list of various adsorbents such as natural materials, waste materials from industry, agricultural by-products, and biomass based activated carbon in the removal of various dyes has been compiled here. Dye bearing waste treatment by adsorption using low cost alternative adsorbent is a demanding area as it has double benefits i.e. water treatment and waste management. Further, activated carbon from biomass has the advantage of offering an effected low cost replacement for non-renewable coal based granular activated carbon provided that they have similar or better adsorption on efficiency. The effectiveness of various adsorbents under different physico-chemical process parameters and their comparative adsorption capacity towards dye adsorption has also been presented. This review paper also includes the affective adsorption factors of dye such as solution pH, initial dye concentration, adsorbent dosage, and temperature. The applicability of various adsorption kinetic models and isotherm models for dye removal by wide range of adsorbents is also reported here. Conclusions have been drawn from the literature reviewed and few suggestions for future research are proposed.

Artificial neural network-genetic algorithm based optimization for the adsorption of methylene blue and brilliant green from aqueous solution by graphite oxide nanoparticle

In this study, graphite oxide (GO) nano according to Hummers method was synthesized and subsequently was used for the removal of methylene blue (MB) and brilliant green (BG). The detail information about the structure and physicochemical properties of GO are investigated by different techniques such as XRD and FTIR analysis. The influence of solution pH, initial dye concentration, contact time and adsorbent dosage was examined in batch mode and optimum conditions was set as pH=7.0, 2 mg of GO and 10 min contact time. Employment of equilibrium isotherm models for description of adsorption capacities of GO explore the good efficiency of Langmuir model for the best presentation of experimental data with maximum adsorption capacity of 476.19 and 416.67 for MB and BG dyes in single solution. The analysis of adsorption rate at various stirring times shows that both dyes adsorption followed a pseudo second-order kinetic model with cooperation with interparticle diffusion model. Subsequently, the adsorption data as new combination of artificial neural network was modeled to evaluate and obtain the real conditions for fast and efficient removal of dyes. A three-layer artificial neural network (ANN) model is applicable for accurate prediction of dyes removal percentage from aqueous solution by GO following conduction of 336 experimental data. The network was trained using the obtained experimental data at optimum pH with different GO amount (0.002-0.008 g) and 5-40 mg/L of both dyes over contact time of 0.5-30 min. The ANN model was able to predict the removal efficiency with Levenberg-Marquardt algorithm (LMA), a linear transfer function (purelin) at output layer and a tangent sigmoid transfer function (tansig) at hidden layer with 10 and 11 neurons for MB and BG dyes, respectively. The minimum mean squared error (MSE) of 0.0012 and coefficient of determination (R(2)) of 0.982 were found for prediction and modeling of MB removal, while the respective value for BG was the MSE and R(2) of 0.001 and 0.981, respectively. The ANN model results show good agreement with experimental data.

Novel SiO2@MgxSiyOz composite with high-efficiency adsorption of Rhodamine B in water

A novel core–shell SiO₂@Mg_xSi_yO_z composite was synthesized, which can be repeatedly used as an efficient adsorbent for the removal of RhB.

An investigation into the effect of porosities on the adsorption of rhodamine B using titania-silica mixed oxide xerogels

Aperiodic mesoporous titania-silica (TiO2·SiO2) xerogels with varying silica contents were synthesized under ambient conditions. The physico-chemical properties of the xerogels were examined by a variety of techniques that include powder X-Ray Diffraction (XRD), nitrogen adsorption, Fourier Transform-Infra-Red spectroscopy (FT-IR), Scanning and Transmission Electron Microscopies (SEM and TEM), Thermo Gravimetric Analysis (TGA), zeta potential, and Diffuse Reflectance Spectroscopic (DRS) studies. The adsorption of a model dye molecule, rhodamine B (RhB) was studied over the titania-silica xerogels and compared with titania and silica. It was determined that the pore volume of the xerogels mainly influences the adsorption of RhB. The xerogels exhibited good adsorption capacity with more than 90% dye removal at low dye concentrations. Our results suggest that low cost approaches to the synthesis of xerogels with tailored properties such as large pore volume could provide cost-effective solutions to mitigate environmental problems related to removal of water based toxic pollutants such as dyes by simple adsorption processes.

Organic xenobiotics removal in constructed wetlands, with emphasis on the importance of the support matrix

Constructed wetlands (CWs) are increasingly popular as an efficient and economical alternative to conventional wastewater treatment processes for removal, among other pollutants, of organic xenobiotics. In CWs, pollutants are removed through the concerted action of their components, whose contribution can be maximized by careful selection of those components. Specifically for non-biodegradable organic pollutants, the materials used as support matrix of CWs can play a major role through sorption phenomena. In this review the role played by such materials in CWs is examined with special focus on the amount of research that has been conducted to date on their sorption properties relatively to organic compounds. Where available, the reports on the utilization of some of those materials on pilot or full-scale CWs are also recognized. Greatest interest has been directed to cheaper and widely available materials. Among these, clays are generally regarded as efficient sorbents, but materials originated from agricultural wastes have also gained recent popularity. Most available studies are lab-scale batch sorption experiments, whereas assays performed in full-scale CWs are still scarce. However, the available lab-scale data points to an interesting potential of many of these materials for experimentation as support matrix of CWs targeted for organic xenobiotics removal.

Effectiveness of Alkali-Acid Treatment in Enhancement the Adsorption Capacity for Rice Straw: The Removal of Methylene Blue Dye

The effectiveness of alkali-acid modification in enhancement the adsorption capacity of rice straw (RS) for removing a basic dye was studied. The obtained adsorbents were characterized by slurry pH, pHPZC, iodine number, methylene blue number, FTIR, and SEM analyses. Adsorption of methylene blue (MB) was described by the Langmuir, Freundlich, Tempkin, and Redlich-Peterson isotherm models. Effects of contact time, initial concentration of MB dye, pH of solution, adsorbent dose, salt concentration of NaCl, and desorbing agents on the removal of MB were reported. Kinetic studies were analyzed using the pseudo-first-order, pseudo-second-order, and the intraparticle diffusion models and were found to follow closely the pseudo-second-order model. Equilibrium data were best represented by the Langmuir and Redlich-Peterson isotherms. The adsorption capacities were varied between 32.6 and 131.5 mg/g for untreated and treated RS samples with NaOH-1M citric acid (ARS-1C), respectively. Adsorption behavior of the ARS-1C sample was experimented in a binary mixture containing methylene blue (basic) and reactive blue 19 (acidic) dyes which showed its ability to remove MB higher than RB19. Overall, the results indicate that the alkali-acid treatment proved to be potential modification for producing effective low-cost adsorbents for the removal of the basic dyes from wastewater.

A review on applicability of naturally available adsorbents for the removal of hazardous dyes from aqueous waste

The effluent water of many industries, such as textiles, leather, paper, printing, cosmetics, etc., contains large amount of hazardous dyes. There is huge number of treatment processes as well as adsorbent which are available for the processing of this effluent water-containing dye content. The applicability of naturally available low cast and eco-friendly adsorbents, for the removal of hazardous dyes from aqueous waste by adsorption treatment, has been reviewed. In this review paper, we have provided a compiled list of low-cost, easily available, safe to handle, and easy-to-dispose-off adsorbents. These adsorbents have been classified into five different categories on the basis of their state of availability: (1) waste materials from agriculture and industry, (2) fruit waste, (3) plant waste, (4) natural inorganic materials, and (5) bioadsorbents. Some of the treated adsorbents have shown good adsorption capacities for methylene blue, congo red, crystal violet, rhodamine B, basic red, etc., but this adsorption process is highly pH dependent, and the pH of the medium plays an important role in the treatment process. Thus, in this review paper, we have made some efforts to discuss the role of pH in the treatment of wastewater.

Valorization of solid waste in sugar factories with possible applications in India : a review

Sugar production is a major agro-based industry in India that generates various solid wastes viz. sugarcane trash, bagasse, press mud and bagasse fly ash. This work examines the state-of-the-art in innovative value added products that can be obtained from the transformation of these wastes. Challenges in implementing these waste valorization solutions are also highlighted. It is observed that the extent of research and adoption of these solutions vary considerably. Both industry involvement as well as government encouragement is required in translating the research findings into commercial products.

Continuous water treatment by adsorption and electrochemical regeneration

This study describes a process for water treatment by continuous adsorption and electrochemical regeneration using an air-lift reactor. The process is based on the adsorption of dissolved organic pollutants onto an adsorbent material (a graphite intercalation compound, Nyex(®)1000) and subsequent electrochemical regeneration of the adsorbent leading to oxidation of the adsorbed pollutant. Batch experiments were carried out to determine the adsorption kinetics and equilibrium isotherm for adsorption of a sample contaminant, the organic dye Acid Violet 17. The adsorbent circulation rate, the residence time distribution (RTD) of the reactor, and treatment by continuous adsorption and electrochemical regeneration were studied to investigate the process performance. The RTD behaviour could be approximated as a continuously stirred tank. It was found that greater than 98% removal could be achieved for continuous treatment by adsorption and electrochemical regeneration for feed concentrations of up to 300 mg L(-1). A steady state model has been developed for the process performance, assuming full regeneration of the adsorbent in the electrochemical cell. Experimental data and modelled predictions (using parameters for the adsorbent circulation rate, adsorption kinetics and isotherm obtained experimentally) of the dye removal achieved were found to be in good agreement.

Adsorption of anionic dyes from aqueous solution on fly ash

The adsorption behavior of two reactive dyes (Reactive Red 23 and Reactive Blue 171) and two acid dyes (Acid Black 1 and Acid Blue193) from aqueous solution on fly ash was investigated in order to identify the ability of this waste-material to remove colored textile dyes from wastewater. For this purpose a series of batch tests were carried out as a function of solution pH value, contact time, dye concentration and adsorption temperature. The experimental findings showed that the removal of four dyes on fly ash was a pH-dependent process with the maximum adsorption capacity at the initial solution pH of 7.5-8.5 for reactive dyes and 5-6 for acid dyes. Adsorption equilibriums of each anionic dye on fly ash could be reached within 60 min at respective optimum pH at 293 K. An increase in the initial dye concentration enhanced the adsorption capacity, but failed to increase the dye removal efficiency. The adsorption capacity for Reactive Red 23, Reactive Blue 171, Acid Blue193 and Acid Black 1 was found to be 2.102, 1.860, 10.937 and 10.331 mg g(-1), respectively. Kinetic studies of four dyes followed the pseudo-second-order modal. Freundlich isotherm described the equilibrium data of acid dyes on fly ash better than Langmuir isotherm, but Langmuir isotherm showed better fit to the equilibrium data of reactive dyes. Different thermodynamic parameters such as the free energy, enthalpy and entropy of adsorption of the dye-fly ash systems were evaluated and it was found that the reaction was spontaneous and endothermic in nature.

Removal of Brilliant Green from Aqueous Solution Using Diatomite-Attapulgite Composite Nano-Size Adsorbent

Diatomite-attapulgite composite nano-size adsorbent was prepared using natural diatomite and attapulgite through compounding, granulation, calcination and activation. After elementary characterization of this adsorbent by mercury porosimeter, batch tests were carried out to examine its removal mechanism of brilliant green. The influence of adsorbent concentration, contact time, pH, temperature and initial brilliant green concentration on the dye removal were investigated. Increase in adsorbent dosage led to increase in brilliant green adsorption due to increased number of adsorption sites. Maximum adsorption of brilliant green was found at adsorbent dosage of 100 g/L. Adsorption equilibrium attained within 2 h time. The pH variation studies showed that the adsorption process was highly pH dependent. The optimum pH for adsorption of brilliant green was found to be >7. The sorption of brilliant green decreased with the rise of temperature because adsorption process was exothermic. Adsorption isotherm studies showed that Langmuir model fitted the experimental data better than Freundlich model.

Application of low-cost adsorbents for dye removal--a review

Dyes are an important class of pollutants, and can even be identified by the human eye. Disposal of dyes in precious water resources must be avoided, however, and for that various treatment technologies are in use. Among various methods adsorption occupies a prominent place in dye removal. The growing demand for efficient and low-cost treatment methods and the importance of adsorption has given rise to low-cost alternative adsorbents (LCAs). This review highlights and provides an overview of these LCAs comprising natural, industrial as well as synthetic materials/wastes and their application for dyes removal. In addition, various other methods used for dye removal from water and wastewater are also complied in brief. From a comprehensive literature review, it was found that some LCAs, in addition to having wide availability, have fast kinetics and appreciable adsorption capacities too. Advantages and disadvantages of adsorbents, favourable conditions for particular adsorbate-adsorbent systems, and adsorption capacities of various low-cost adsorbents and commercial activated carbons as available in the literature are presented. Conclusions have been drawn from the literature reviewed, and suggestions for future research are proposed.

Fenton degradation of 4,6-dinitro-o-cresol with Fe(2+)-substituted ion-exchange resin

The Fenton degradation of 4,6-dinitro-o-cresol (DNOC) was studied under different experimental conditions using Amberlyst 15 ion-exchange resin containing ferrous ion. DNOC was found to be effectively degraded under most conditions, and it was observed that, with the addition of HCl, the desorption of ferrous ion from the resin into the solution played a major role in this degradation. The total iron concentration in the reaction solution was found to increase with the addition of HCl, and a pseudo-first-order kinetic model was applied to the desorption of ferrous ion from the resin on the basis of the assumption of a first-order ion-exchange process. The degradation rate of DNOC also increased as a function of HCl. A kinetic model was developed to simulate the degradation of DNOC under different operating conditions, assuming the first-order desorption of ferrous ion. Different cations were compared with H(+), and H(+) was found to be the most efficient at facilitating the degradation reaction at low concentrations, whereas Ca(2+) was found to be most efficient at high concentrations. pH was measured during the reaction, and its effect on degradation was explored. It was found that a lower pH could lead to faster degradation of the target compound. Degradation of DNOC under different delivery rates of H(2)O(2) was studied, and optimal conditions were determined. The results also showed that the delivery rate of H(2)O(2) did not affect the ion-exchange process of the resin.

Production of a new wastewater treatment coagulant from fly ash with concomitant flue gas scrubbing

The research focused on the production of a complex wastewater coagulant containing polymeric sulfates of aluminum and iron from fly ash. At the same time, SO(2) in the simulated flu gas was removed by absorption in a fly ash slurry and oxidized with sodium chlorate. Extraction efficiency of iron and aluminum oxides from fly ash was affected greatly by reaction temperature and time. The extraction efficiency increases as temperature increases. Removal efficiency of SO(2) was influenced by temperature, SO(2) feed concentration and feed gas dispersing method. The produced complex coagulant containing both polymeric ferric sulfate (PFS) and polymeric aluminum sulfate (PAS) was proven to be effective in removing total suspended solids (TSS) and turbidity in wastewater. The complex coagulant is more effective than conventional iron and aluminum sulfates in turbidity removal.

Adsorption characteristics of Orange II and Chrysophenine on sludge adsorbent and activated carbon fibers

Sludge adsorbent (SA) and commercial activated carbon fibers (ACFC and ACFT) were applied to Orange II and Chrysophenine (CH) adsorption (BET surface area: ACFC>ACFT>SA). ACFT was primarily in the micropore range, while SA was approximately 500 A (macropore) and 80 A (mesopore). The ACFC pore volume was high in both the mesopore and micropore regions. Measurement of the oxygen surface functional groups of the adsorbents using Boehm's titration method showed a similar distribution on the carbon fibers (mainly in the carbonyl group), while SA was mainly in the carboxyl, lactone and phenolic groups. The SA, ACFC and ACFT adsorption capacities of Orange II (30-80 mg/l) ranged from 83 to 270, 209-438, and 25-185 mg/g at temperatures ranging from 10 to 60 degrees C, respectively. CH concentration ranged from 30 to 80 mg/l, corresponding to SA and ACFC adsorption capacities of 39-191 and 48-374 mg/g over the defined temperature range, from 10 to 60 degrees C. CH adsorption on ACFT was low. The adsorption capacity of Orange II on ACFT was lower than on SA at 10 degrees C, but at higher temperatures the Orange II molecules were transported into the ACFT, producing an adsorption capacity similar to that of SA. Mass transfer increased with temperature, overcoming the adsorption energy barrier. Overall, SA and ACFC were more effective than ACFT.

Evaluation of zeolites synthesized from fly ash as potential adsorbents for wastewater containing heavy metals

The pure-form zeolites (A and X) were synthesized by applying a two-stage method during hydrothermal treatment of fly ash prepared initial Cu and Zn gel. The difference of adsorption capacity of both synthesized zeolites was assessed using Cu and Zn as target heavy metal ions. It was found that adsorption capacity of zeolite A showed much higher value than that of zeolite X. Thus, attention was focused on investigating the removal performance of heavy metal ions in aqueous solution on zeolite A, comparing with zeolite HS (hydroxyl-solidate) prepared from the residual fly ash (after synthesis of pure-form zeolite A from fly ash) and a commercial grade zeolite A. Batch method was used to study the influential parameters of the adsorption process. The equilibrium data were well fitted by the Langmuir model. The removal mechanism of metal ions followed adsorption and ion exchange processes. Attempts were also made to recover heavy metal ions and regenerate adsorbents.