An overview of Effluent Treatment for the Removal of Pollutant Dyes

 

Sarita Yadav¹_, D.K. Tyagi¹ , O.P. Yadav²

¹Department of Chemistry, D.A.V.P.G. College, Dehradun- 248001, Uttrakhand, India

²Chemistry Department, CCS Haryana Agricultural University, Hisar-125001, India.

*Corresponding Author E-mail: saritayadav1978@yahoo.com

ABSTRACT:

Wastewater effluents from textile, paper, tannery and beverage industries are contaminated with variety of pollutants including dyes. Dyes are skin irritant, carcinogenic and can cause allergic dermatitis and mutation. Environmental legislations are now becoming more stringent to control the release of dyes into the environment. Biological treatment of effluent requires a large land area and is constrained by toxicity of some chemicals, and less flexibility in design and operation. Chemical treatments for the removal of dyes from the polluted effluents are not cost effective. Photocatalytic dye degradation techniques suffer from their low efficiency. Adsorption method has been found to be efficient, economical, renewable and eco-friendly solution in treating effluents contaminated with dyes. An overview of the treatments of dye contaminated effluents by biological, chemical and physical methods have been presented.

 

 

 

INTRODUCTION:

Recently, society has become more sensitive towards the protection of the environment and a general awareness has now increased about the possible potential adverse effects of industrial effluents contaminated with various pollutants, including dyes, on the environment. More than 7x10⁵ tonnes per year of a variety of dyes are being produced, annually ^1,2,3(Pearce et al., 2006, Pearce et al., 2003, McMullan et al., 2001). Wastewater effluents from textile, paper / pulp, electroplating and tanning industries contaminated with various dyes is one of the serious cause of pollution in the environment. The colored effluents from the above sources, on mixing with surface and ground water system, also contaminate the drinking water. Water contaminated with dyes is not only unfit for drinking purpose but is also not suitable for agricultural use due to its inhibitory action on photosynthetic process in plants. Dyes are skin irritant, carcinogenic and can cause allergic dermatitis and mutation⁴ (Namasivayam et al 1996).  Industrial effluents contaminated with dyes are very difficult to treat since the dyes are recalcitrant organic molecules, stable to light and resistant to aerobic digestion. Dye contaminated industrial effluents have   high chemical oxygen demand (COD) which adversely affects the marine lives.

 

Also, the effluent treatment for its dye contents involves high cost and disposal problems at large scale particularly in the textile and paper industries⁵(Ghoreishi and Haghighi, 2003).

 

Due to the federal, state and local regulations, industries must limit the discharge of color from their plants. Therefore, serious efforts are being made to develop more efficient, economical, renewable and eco-friendly  methods for  treating effluents contaminated with dyes. Earlier, Robinson et al., (2001)⁶ published a critical review on current treatment technologies for the remediation of dyes in textiles effluents. Mondal (2008)⁷ presented a review paper describing different methods for the treatment of dye- contaminated wastewater. He described the degradation of color by oxidation reaction and the mechanism involved therein. He also gave an account of degradation of color by anaerobic reduction reaction, adsorption of dye by activated carbon, silica, functional polymer granules, and biomaterials. The colour removing technologies can be divided into three categories: biological, chemical and physical methods⁶ (Robinson et al. 2001).

 

Methods for Color removal:

Biological method:

Biological treatment of effluents is  considered as most economical alternative compared to  chemical or physical processes. Biodegradation methods such as microbial degradation, fungal decolorization, adsorption by living or dead microbial biomass and bioremediation systems are sometimes applied for the treatment of industrial effluents.  Several microorganisms such as: bacteria, yeasts, algaes and fungi are able to accumulate and degrade different pollutants^3,8 (McMullan et al., 2001; Fu and Viraraghavan, 2001). Gholami et al (2001) ⁹ investigated the removal of basic, reactive, disperse and acidic dyes from effluents of textile industries through biodegradability method and membrane technology. However, biological treatment requires a large land area and is constrained by toxicity of some chemicals, and less flexibility in design and operation¹⁰ (Bhattacharyya and Sharma 2003). However, using current conventional biodegradation processes, satisfactory color elimination due to azo dyes can not be achieved⁶(Robinson et al., 2001).

 

Generally  used, aerobic or anaerobaic biological treatment for the reduction of biological oxygen demand(BOD) and chemical oxygen demand (COD) of polluted water is also not an effective method for the color removal from effluent water. Rao and Viraraghavan (1985)¹¹ have reported that brown color present in distillery wastewater is further intensified during its anerobic/aerobic   treatment. However, advantages with biological methods for colour removal are that these are environment friendly, economically attractive and have good public acceptance. Unfortunately, biological processes are very slow  because biological agents like bacteria, fungi, yeasts and algae etc require long time to act on pollutants to degrade them, besides, these  require adequate nutrients and also need a narrow operating temperature range.

 

Chemical methods

Chemical treatment of wastewater contaminated with pollutants such as dyes involves some chemical reactions like neutralization, coagulation /precipitation, or flocculation combined with flotation and filtration to improve the water quality. Lime, a base, is sometimes used in the neutralization of acid wastes.   Coagulation involves the use of a suitable chemical/s such as a salt of Polyvalent metal that, through a chemical reaction, forms an insoluble end product that serves to remove substances like dyes from the wastewater. Generally used coagulants/flocculants are ferric chloride, ferric sulfate and aluminum sulfate (alum). These methods have the advantage of being effective for removing all types of dyes but they produce lots of sludge during the process and also are not cost-effective. However, electro-kinetic coagulation can remove small colloidal particles, involves less cost and produces less sludge but this method is not applicable for all types of dyes.

 

Conventional oxidation method involves the use of oxidizing agents such as chlorine or ozone gas. No sludge is produced in this process and also there is no alteration in volume after the treatment. But the disadvantage is the involvement of higher cost while treating a large volume of industrial effluent. In a few instances, the excessive use of chemicals may also lead to the creation of secondary pollution in the environment.

 

 

Al-Kdasi et. al (2004)¹² reviewed different advanced oxidation processes(AOPS), according to their specific features, for the treatment of textile wastewater. Conventional oxidation processes cannot oxidize dyestuffs at low concentration or if they are refractory to the oxidants due to the complex structure of the organic compounds such as dyes. To ease this problem, advanced oxidation processes have been developed which generate highly reactive hydroxyl free radicals by different techniques. AOPS processes involve combination of ozone (O₃), hydrogen peroxide (H₂O₂) and UV irradiation, which have showed greatest promise to treat textile wastewater for effectively decolorizing dyes. However, these treatments could not reduce chemical oxygen demand (COD) completely^13,14,15 (Lidia et al. 2001; Stanislaw et al. 2001; Ahmet et al 2003). Using H₂O₂/UV process, some researchers have reported complete destruction of reactive dyes and azo dye  in 30-90 min ^16,17(Mariana et al.,2002; Tanja et al., 2003).

 

Recently, other emerging techniques, known as advanced oxidation processes, which are based on the generation of very powerful oxidizing agents such as hydroxyl radicals, have been applied with success for the pollutant degradation. Although these methods are efficient for the treatment of waters contaminated with pollutants, they are very costly and commercially unattractive. The high electrical energy demand and the consumption of chemical reagents are common problems.

 

In several cases, conventional ozonation of organic compounds does not completely oxidize organics to CO₂ and H₂O¹⁸(Rein 2001). The  intermediate products  after oxidation may be as toxic as or even more toxic than initial compound. The O₃/UV process is more effective when the compounds of interest can be degraded through the absorption of the UV irradiation as well as through the reaction with hydroxyl radicals^{18, 19} (Metcalf and Eddy, 2003; Rein, 2001). In the  O₃/UV process photons of ultraviolet radiation   activate ozone molecules, facilitating the formation of hydroxyl radicals which subsequently help in decolorizing the dyes²⁰ (Hung-Yee and Ching-Rong 1995).

 

Electrochemical oxidation method:

Electrochemical oxidation technique was developed in the 1990’s. It’s an effective method for colour removal from the wastewater. During electrochemical oxidation of dyes, there is little or no consumption of chemicals and no sludge production. Even degradation of recalcitrant dyes including those based on  polyaromatic organic compounds, like anthraquinone, can be achieved by this technique ^21,22[Panizza et al (2000); Kim  et. al (2002)].

 

In electrochemical treatment several  pollutants including dyes are degraded due to their oxidation or reduction at anode or cathode surface in the electrolytic cell²³(Lin and Peng 1994). The breakdown products of effluents after treatment are non-hazardous. However, the high electrical energy demand for electrochemical oxidation method is a  common problem. Other emerging techniques, known as advanced oxidation processes,  based on the generation of very powerful oxidizing agents such as hydroxyl radicals, have the advantage of producing non-hazardous end products but are  commercially unattractive due to their high cost of operation.

 

Photocatalytic Methods:

Heterogeneous semiconductor photocatalysis can be an alternative to conventional methods for the removal of dye pollutants from effluent wastewater²⁴(Kyung et al., 2005). When a semiconductor is illuminated with an appropriate radiation source, the electron/hole pairs are produced with electrons promoted to the conduction band leaving behind positive holes in the valence band. The generated electron/hole pairs induce a complex series of reactions that might result in the complete degradation of  organic pollutants including dyes adsorbed on the semiconductor surface.

 

Titanium dioxide (TiO₂) and Zinc oxide (ZnO) have exhibited  potential photo-catalytic activity for the degradation of organic pollutants²⁵(Chen et al., 2008). However, due to high band gap energies of  TiO₂ ( 3.20 eV   ) and ZnO (3.37 eV ), these photocatalysts require excitation photons, in the ultra-violet (UV) region of the electromagnetic radiation. As the solar radiation contains UV only to the extent of 3-4%, therefore, the photo-catalytic efficiency of the above photocatalysts under solar light  is  too low ²⁶(Legrini et al 1993). Further, degradation of dyes can be markedly enhanced  in TiO₂ suspensions under visible light in the presence of metal ions like Cr(VI)²⁴ (Kyung et al., 2005). Recently, there have been several attempts to improve the photocatalytic activity of semiconductors for the degradation of organic pollutants, including dyes, in visible light by doping of transition metals^27,28(Ullah and Dutta 2008,  Xu  et al., 2010;)   and /or a  non-metal^25,29,30(Chen et al., 2008; Shifu et al., 2009;  Patil et al., 2010).

 

Physical methods:

Different physical methods are  widely used, such as membrane – filtration processes (nanofiltration, electrodialysis, reverse osmosis) and adsorption techniques.

 

Membrane – filtration

Mondal (2008)⁷ reviewed the treatment of   dye containing wastewater by nano-filtration.  Membrane filtration involves both microfiltration as well as  ultrafiltration processes. These processes are characterized by their ability to remove  colloidal or suspended particles, including dyes via a sieving mechanism based on the size of the membrane pores relative to that of the particulate matter. Whereas microfilteration membranes are considered to have  pore size range:  0.1 – 10 mm., ultrafiltration membrane pore sizes generally range from 0.01 – 0.05 mm. Ultrafine  membranes can retain larger organic macromolecules and these are  characterized by a molecular weight cutoff (MWCO) rather than by a particular pore size.  MWCO,  expressed in Daltons – a unit of mass, is a measure of the removal characteristic of a membrane in terms of atomic  mass rather than size. Therefore,  ultrafine membranes with a specified MWCO are presumed to act as a barrier to compounds or molecules with a molecular weight exceeding the MWCO.  Typical MWCO levels for UF membranes range from 10,000 to 500,000 Daltons, with most membranes used for water treatment at approximately 100,000 MWCO. Gholami et. al (2001)⁹ used  membrane technology for the removal of dyes from effluents of textile industries.

 

Ahmad et. al (2002)³¹ explored the use of microfiltration membrane separation processes to remove dyes  from  wastewater discharged from the painting and coloring  industries. He studied the effect of dye concentration,  pH, and operating pressure on the efficiency of membrane microfiltration.

 

Among the physical methods for dye removal, membrane – filtration processes has proved very effective for removing  of dyes from the effluents. But this process involves high  investment costs and the effluent requires  further treatment  after filtration. Another  disadvantage of it is that  membrane used in the process has a limited lifetime and it requires frequent   replacement.

 

Adsorption :

The adsorption is a process wherein a material is concentrated at a solid surface from its liquid or gaseous surroundings. In principle, adsorption can occur at any solid-fluid interface i.e gas-solid interface or liquid-solid interface. It is an equilibrium separation process and an effective method for water decontamination applications³² (Dabrowski, 2001). Decolourisation of dyes is a result of two mechanisms: adsorption and ion exchange ³³(Slokar and Le Marechal, 1998), and is influenced by many physio-chemical factors, such as, dye/sorbent interaction, sorbent surface area, particle size, temperature, pH, and contact time ³⁴(Kumar et al., 1998).

 

Adsorption method for the removal of dyes from the effluents is eco-friendly and superior to other techniques for water re-use in terms of initial cost, flexibility and simplicity of design, ease of operation and insensitivity to toxic pollutants.  Basically, there are two types of adsorption:  physical adsorption and chemical adsorption. If the attraction between the solid surface and the adsorbed molecules is of physical  nature,  it is called as physical adsorption. In this case the adsorbate  binds to the adsorbent surface by weak van der Waals force, thus physical adsorption is reversible in nature. When the binding of adsorbate with the  adsorbent surface is of chemical  nature then it is called chemisorption. Due to strong chemical bonding, in this case, it is difficult to remove chemisorbed material from the adsorbent, therefore, chemisorption is of irreversible nature. Another sorption process is ion exchange process, where similarly charged ions are reversibly exchanged between solutions and the adsorbent. . This process is widely used for drinking water treatment. Both adsorption and ion exchange involve the transfer and resulting equilibrium distribution of one or more solutes between a fluid phase and solid particles. For designing the adsorption treatment systems, knowledge of kinetic and mass transfer processes is essential. In adsorption process the pollutants such as dyes are effectively removed from one phase (wastewater/effluent) to solid phase without altering the chemical composition of  pollutant. Adsorption method is an efficient, economic and environment friendly technique with considerable potential for the color removal from the contaminated water ³⁵(Gupta et al 2003).

 

A number of researchers have reported the results of the removal of dyes from the wastewater using a variety of adsorbents.  Asfour et al (1985)³⁶ carried out  adsorption equilibrium studies  of basic dyes on wood powder as adsorbent .  Polard et al (1992)³⁷ and Meyer et al (1992)³⁸ used low cost adsorbent for wastewater treatment. Namasivayam and Kanchana (1992)³⁹ used waste banana pith as  adsorbent for the color removal from wastewaters Warhurst et al (1997)⁴⁰ reported Characterisation and applications of low cost activated carbon produced from Moringa oleifera seed husks by single-step steam pyrolysis at  800°C for 30 min, then the resulting carbon were tested to determine their iodine numbers and adsorption isotherms for phenol, 4-nitrophenol and methylene blue dye. The adsorbance characteristics of the as-synthesized  carbon was superior to those produced  by the conventional two-stage carbonisation-activation, and were competitive with commercial carbons. Ho and McKay (1998)⁴¹ established a kinetic model for the sorption of dye from aqueous solution. Kinetic and adsorption equilibrium studies  of Basic dye  on a low cost  jackfruit peal carbonaceous sorbent- were reported by Stephan and  Sulochana (2002)⁴².

 

Tseng et al (2003)⁴³ studied the equilibria and kinetics of adsorption of some dyes using pinewood carbon. They described adsorption isotherms  of dyes  by the Langmuir–Freundlich equation. The effect of microporosity of the carbons on adsorption capacity was explored. Four simplified kinetic models including pseudo-first-order equation, pseudo-second-order equation, intraparticle diffusion model, and the Elovich equation were selected to follow the adsorption processes. The adsorption of dyes could be best described by the Elovich equation. Guo et al (2003)⁴⁴ studied the adsorption of malachite green (MG) from aqueous medium by rice husk-based porous carbons (RHCs). The extent of adsorption was studied as a function of pH, contact time, adsorbate-adsorbent, temperature, adsorbate concentration, ionic strength and adsorbent with different pore structure. The comparison of adsorption of MG on oxidized carbons and their thermally treated derivatives were studied. The adsorption capacity of carbons activated by NaOH-activation was larger than that of carbons activated by KOH-activation, the adsorption of MG on oxidized carbons was decreased and was enhanced after heat-treatment. Adsorption kinetics of methyl violet onto perlite were reported by Dogan and Alkan (2003)⁴⁵.

 

Acemioglu (2004)⁴⁶ reported adsorption of Congo red from aqueous solution onto calcium-rich fly ash.. Adsorption equilibrium and kinetics of dye removal from wastewater using sawdust as adsorbent were reported by Malik (2004)⁴⁷. Rahman et al (2005)⁴⁸ used Phosphoric acid (H₃PO₄) and sodium hydroxide (NaOH) treated rice husks, followed by carbonization in  nitrogen gas flow to study the adsorption of malachite green (MG) in aqueous solution. The effect of adsorption on contact time, concentration of MG and adsorbent dosage of the samples treated or carbonized at different temperatures revealed that the optimum carbonization temperature for the husks treated by H₃PO₄.  is 500 °C in order to obtain adsorption capacity that is comparable to the commercial activated carbon, It is interesting to note that MG adsorbed preferably on carbon-rich than on silica rich-sites. It was found that the behaviour of H₃PO₄ treated absorbent followed both the Langmuir and Freundlich models while NaOH treated best fitted to only the Langmuir model.

 

Vadivelan and Vasanth (2005)⁴⁹ carried out batch experiments for the sorption of methylene blue dye onto rice husk particles. The operating variables studied were:  solution pH, dye initial concentration, adsorbent amount , and contact time. The monolayer sorption capacity of rice husks for methylene blue was  40.58 mg/g at room temperature (32 °C). The sorption process was found to be controlled by both surface and pore diffusion, surface diffusion preceeding the  pore diffusion. Analysis of sorption data using a Boyd plot confirmed that external mass transfer is the rate limiting step in the sorption process

 

Kadirvelu et al (2005)⁵⁰ used activated carbon from industrial solid waste as an adsorbent for the removal of Rhodamine-B dye  from  aqueous solution: Kinetic study of removal of Congo Red from Aqueous Solution using Bagasse Fly Ash and Activated Carbon  was carried out by Mall et. al ( 2005)⁵¹.  The Freundlich isotherm  shows comparable fit for observed adsorption data.. Thermodynamics of adsorption  showed that the adsorption of congo red on bagasse fly ash was most favourable in comparison to activated carbons. Ozacar and Sengil.(2005)⁵² studied the adsorption of metal complex dyes from aqueous solutions by pine sawdust

 

Gupta et al (2006)⁵³ investigated color removal of Safranin-T from wastewater using activated carbon and activated rice husk as adsorbents. Effects of various factors such as adsorbate concentration, adsorbent dose and particle size, temperature, pH  and contact time were investigated. The adsorption of the dye over  the adsorbents was found to follow Langmuir and Freundlich adsorption isotherm models. Based on these models, different  thermodynamic parameters were evaluated. The adsorption of Safranin-T over activated carbon and activated rice husks followed first-order kinetics and the rate constants for the adsorption processes decreased with increase in temperature.

 

Mohanty et al (2006)54 studied the adsorption of  crystal violet, a basic dye, from aqueous solutions over activated carbons, prepared from low-cost rice husk by sulfuric acid and zinc chloride activation. The effects of various experimental parameters on the dye removal were investigated in batch mode. The kinetic data were fitted to the Lagergren, pseudo-second-order, and intra-particle diffusion models. It was found that intra-particle diffusion plays a significant role in the adsorption mechanism. The isothermal data was described by the Langmuir and Freundlich equations. The maximum uptakes of crystal violet dye by sulfuric acid activated rice husk carbon  and zinc chloride activated  rice husk carbon were found to be 65 and 62 mg/g of adsorbent, respectively. Tor and Cengeloglu (2006)55 investigated the removal of congo red dye from aqueous solution by using an inexpensive adsorbent such as acid activated red mud.

 

Purkait et al. (2007)⁵⁶ reported the removal of congo red using activated carbon and its regeneration. Adsorption characteristics of Congo Red onto the chitosan/montmorillonite nanocomposite were investigated by Wang and Wang (2007)⁵⁷. The as-synthesized nanocomposites were characterized by FTIR and XRD. The effects of initial pH value of the dye solution,  molar ratios of CTS and MMT, and temperature on adsorption capacities of samples for Congo Red (CR) dye have been investigated. The  adsorption capacity of CTS/MMT nanocomposite was higher than the mean values of those of CTS and MMT. The sorption processes were better fitted by pseudo-second-order equation and the Langmuir equation. Adsorption of malachite green dye on groundnut shell waste based powdered activated carbon was investigated by Malik et. al (2007)⁵⁸. Onal, et. al. (2007)⁵⁹ investigated kinetics and mechanisms of adsorption of malachite green onto activated carbon. They used Lignite for preparing activated carbon by chemical activation with KOH. Pore properties of the activated carbon such as  surface area, pore volume, pore size distribution, and pore diameter were characterized by t-plot based on N₂ adsorption isotherm. Adsorption capacity of malachite green (MG) onto  activated carbon was investigated in a batch system by considering the effects of various parameters like initial concentration  and temperature. To examine the mechanisms of adsorption and potential rate controlling steps such as external mass transfer and  intraparticle diffusion, simple mass and kinetic models were applied to the experimental data. Pseudo second-order model was used to explain the kinetics of MG adsorption. Both mass transfer and pore diffusion are found to be  important in determining the adsorption rates. Langmiur isotherm showed better fit than Freundlich isotherm in the studied temperature range.

 

Satyawali and Balakrishnan (2007)⁶⁰ examined 19 carbon samples prepared by acid and thermal activation of various agro-residues viz. bagasse, bagasse flyash, wood ash, rice husk ash and sawdust,  for color removal from bio-methanated distillery effluent. Phosphoric acid carbonized bagasse B  showed the highest color removal efficiency . Adsorption isotherms for melanoidins, a primary coloring compound in distillery spentwash, followed the Langmuir isotherm implying monolayer adsorption. Adsorption of acidic dyes from  aqueous solution  onto low cost activated carbon were reported by Arivoli et al (2008)⁶¹. Tan et. al (2008)⁶² reported the  kinetic and thermodynamics of adsorption of basic dye on high-surface-area activated carbon prepared from coconut husk.

 

Lakshmi et al (2009)⁶³ evaluated adsorptive characteristics for Indigo carmine (IC) dye onto rice husk ash (RHA) adsorbent. They explored the adsorptive characteristics of IC from aqueous solution by carrying out batch experiments. The parameters such as: initial pH, adsorbent dose, adsorbate-adsorbent contact time and dye initial concentration  on the removal of IC were determined. The optimum conditions were found to be: pH 5.4, adsorbent dose 10.0 g/l, contact time 8 hrs. Adsorption of IC on RHA was favorably influenced by an increase in the operation temperature. The observed positive  entropy of adsorption (ΔS_ad), endothermic enthalpy of adsorption (ΔH_ad) and  negative  Gibbs free energy of adsorption (ΔG_ad) indicated that the adsorption of IC on to RHA, although, is opposed by endothermic enthalpy change, is feasible and spontaneous   owing to the predominant entropy gain as a driving force. Amin  (2009)⁶⁴ reported adsorption equilibrium and kinetics of  removal of direct blue-106 dye from aqueous solution using activated carbon developed from pomegranate peel.

 

Sharma et al (2010)⁶⁵, performing batch experiments, investigated the  use of pretreated rice husk (RH) and rice husk ash (RHA) for the removal of methylene blue (MB) from wastewater. They studied the influence of different system variables on the adsorption of methylene blue on these adsorbents. Neutral pH was optimum for the removal of MB and the adsorption process  was favorably influenced by an increase in the temperature of the operation. The  adsorbents, RA and RHA showed higher adsorption capacity than  the earlier reported adsorbents obtained from agricultural and industrial waste products, inorganic materials and bioadsorbents.  Ansari and Mosayebzadeh (2010)⁶⁶ investigated the removal of methylene blue dye using wood sawdust chemically coated with polypyrrole.

 

The use of agricultural waste, as adsorbent, for the removal of dyes or other pollutants from the effluents serves two purposes. Firstly, it provides a low cost material as adsorbent for the effective treatment of industrial effluents. Secondly, it provides a way out for the disposal of the agricultural waste material such as rice and coconut husks, banana, jackfruit and pomegranate peels etc. Rice husk,   an agricultural waste that accumulates in and around rice processing industries, is a big problem for its disposal.  It is a highly porous material with a large specific surface area, is an ideal adsorbent for the treatment of effluents  from industries.  Kinetic and adsorption equilibrium studies of  Aniline blue and Rhodamine-B dyes, using rice husk carbon (RHC) as adsorbent, were reported by Yadav et al (2011a)⁶⁷ and  Yadav et al (2011b)⁶⁸, respectively. The effect of parameters such as:  adsorbate-adsorbent contact time, dye initial concentration, temperature, adsorbent’s amount and  particle size on the color removal efficiency of RHC were investigated.

 

Therefore, abundant available literature data reveals that liquid-phase adsorption can be the most popular method for the removal of pollutants from wastewater. A proper design of the adsorption process can produce a high-quality treated effluent. Adsorption process can provide an attractive alternative for the treatment of dye contaminated effluent waters, provided the sorbent is inexpensive and does not require a pre-treatment step before its application.

 

CONCLUSIONS:

Different methods for the treatment of effluents contaminated with dyes and other pollutants have been reviewed. The work reported during the last two decades reveals that for  the removal of organic  pollutants, including dyes, from  effluent wastewater, adsorption technique is the most effective method and involves low cost of operation. In the recent years, to make the adsorption process viable and cost-effective, several attempts have been made  using raw as well carbonaceous agricultural waste products as adsorbent for the removal of dyes from the effluents.

 

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Received on 11.11.2011         Modified on 04.12.2011

Accepted on 15.12.2011         © AJRC All right reserved