Environmental Engineering and Management Journal September/October 2009, Vol. 8, No.5, 1097-1102 http://omicron.ch.tuiasi.ro/EEMJ/

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USING OF INDUSTRIAL WASTE MATERIALS FOR TEXTILE

WASTEWATER TREATMENT

Daniela Suteu1∗, Carmen Zaharia1, Augustin Muresan2, Rodica Muresan2, Alina Popescu3

1”Gheorghe Asachi” Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, 71A D. Mangeron Blvd, 700050 Iasi, Romania

2”Gheorghe Asachi” Technical University of Iasi, Faculty of Textiles, Leather and Industrial Management and Environmental Protection, Department of Chemical Textile Finishing, 53-55 D. Mangeron Blvd, 700050 Iasi, Romania

3National Institute of Research – Development for Textiles and Leather, 16 Lucretiu Patrascanu Str., 030508 Bucureşti, Romania

Abstract Sorption is one of the several methods that have been successfully utilized for dyes removal. A large number of materials have been used as suitable sorbents for decolourization of industrial effluents: activated carbon (the most common but expensive adsorbent), polymeric resins, various low-cost adsorbents (agricultural and industrial by-products, peat, chitin, silica, bentonite, other clays, fly ash). Our paper is a review about our researches regarding different types of industrial and agricultural waste materials with sorptive properties (ashes, textile fibres, sawdust, lignin, sun flower shells, corn cob, etc.) that were utilized into textile wastewater treatment. Batch sorption experiments were carried out in order to establish the favourable conditions to uptake of dyes. The studied operating variables were: pH, sorbent dose, dyes concentration, temperature and sorption time. The sorption systems were described using Freundlich, Langmuir and Dubinin-Radushkevich isotherm models. Key words: dyes, industrial and agricultural wastes, sorption, textile wastewaters

∗ Author to whom all correspondence should be addressed: e-mail: danasuteu67@yahoo.com; Phone: +40-726-280598

1. Introduction

The textile effluents resulted in tinctorial processes contain many types of dangerous chemical compounds that influence the quality of wastewaters and need to be treated before their disposal in municipal pipe network or other receiving basins. One type of those dangerous compounds are represented by the textile dyes, synthetic compounds with aromatic molecular structures, resistant to light, heat and oxidizing agents and other non-biodegradable materials. It has been suggested that the presence of coloured compounds in aqueous environments can reduce light penetration, thus affecting the photosynthetic process of aquatic plants. In addition to their visual effect (aesthetic impact on receiving waters), many synthetic dyes are toxic, mutagenic and carcinogenic.

In this context, severe physical and chemical processes are required in order to treat and reuse the textile effluents as micro filtration, ultra filtration,

nano-filtration, UV/ozone treatment, photocatalitic oxidation, other advanced oxidations, coagulation - flocculation, electro-coagulation, chemical reduction, adsorption (Suteu et al., 2009).

One of the most important group of dyes are represented by the reactive dyes as industrial compounds for dying the celluloses fibres, and can be characterized by low absorbability on a wide range of adsorbent, and limited biodegradability in an aerobic environment (Senthilkumaar et al., 2006). However, many reactive dyes contain in their molecules some azo compounds that transform these dyes into important organic pollutants for aquatic ecosystems because of their potential to form dangerous aromatic amines, other cancerigenic and mutagenic compounds.

There are a large number of procedures for dyes removal, such as oxidative destruction via UV/ozone treatment, photo catalytic oxidation which have certain efficiency but their initial and operational costs are too high (Anjaneyulu et al., 2005; Babu et

“Gheorghe Asachi” Technical University of Iasi, Romania

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al., 2007; Forgacs et al., 2004; Suteu et al., 2009). Sorption is one of the several procedures that have been successfully utilized for dyes removal. A large number of materials have been used as suitable sorbents for decolourization of industrial effluents such as activated carbon (the most common but expensive adsorbent), polymeric resins, various low-cost adsorbents (agricultural products, peat, chitin, silica, bentonite, other clays, fly ash) (Crini, 2006; Grupta et al., 2009; Suteu et al., 2006; Suteu et al., 2007a; Suteu and Zaharia, 2008a;).

This work systematizes our research studies about the use of some industrial and agricultural waste materials (sawdust, ash, sun flower seed shells, corncob, lignin, and seashell) in removal of anionic and cationic dyes from textile wastewaters.

2. Experimental 2.1. Materials

The selected textile dyes used as commercial salts are characterized in Table 1.

The selected solid sorbents, represented by some agricultural or industrial wastes, are described in Table 2.

These materials are characterized by: low cost and accessibility, high inner and outer surface, macro and micro-porous structure, hydrophilic character which determines a rapid kinetics of the sorption process, presence of varied functional groups as sorption sites, the possibility to utilize some materials in different shapes (particles of different dimensions, fibres, filters, textures) and non-pollutant character.

Table 1. The main characteristics of the studied textile dyes

Name/ Abbreviation C.I. Type of dye MW, g/mol

λmax, nm

Concentration of the stock dye solution, mg/L

Brilliant Red HE-3B / BRed 25810 anionic reactive

1463

530 500

Reactive Orange 16 / RO 17757 anionic reactive 617.54 495 617.5 Reactive Violet 5 / RV 18097 anionic reactive 735.6 560 735.6

Methylene Blue (Basic Blue 9) / MB

52015 cationic phenothiazine

319.85 660 320

Crystal Violet (Basic Violet 3) / CV

42555 cationic triphenylmethane

407.99

590 408

Rhodamine B (Basic Violet 10) / RB

45170 cationic xanthenic 479.2 550 479

Table 2. The mail characteristics of the studied sorbents

Fibrous sorbent Characteristics

Ash (Harja et al., 2007)

The chemical characterization of coal ash from CET IASI- Romania Company has been done on the SR EN standard - 450-1:2006 and the specific surface has been determined with the Blaine permeabilimeter. The composition is (%): 51.83 SiO2; 22.62 Al2O3; 3.44 Fe2O3; 7.52 CaO; 1.075 MgO; 2.312 SO3. Other characteristics are: 7.483% ignition loss at 700°C; 12.580% ignition loss at 1200°C - total loss; 0.883% humidity at 105°C; 2155 density (kg/m3); 0.75- oversize 0.04 (mass fraction); 3298 specific surface Blaine (cm2/g).

Physically modified ash (Suteu et al., 2008a)

Samples of 5 g fly ash and 10 g NaOH, namely 14-1 h and 16 – 2 h were treated at 873 K into an electric furnace by mixing the fly ash with solid NaOH in platinum ball, cooled during 11 hours, diluted with 150 cm3 distillated water and boiled for crystallization 3 hours at T = 373 K.

Sawdust (Suteu et al., 2008b)

Romanian sawdust obtained as waste material from the conifer wood processing. The sawdust was dried in air, sieved and two fractions were collected: sawdust 1 (particle size 1-2 mm, designed SD-1) and sawdust 2 (powdered, < 0.1 mm, SD-2). The major constituents of sawdust are cellulose, hemicelluloses and lignin; the humidity was of 4%.

Sun flower seed shells (this paper)

These materials were obtained from local oil industry and used after air drying at room temperature for two days. The seed shells were grounded and sieved to obtain a particle size range of 0.8 mm and stored in plastic bottle for further use. No other chemical or physical treatments were performed. The major constituents of sunflower seed shells are cellulose, lignin and pentose.

Corn cob (Suteu and Zaharia, 2009)

The material represents an important by-product from local agro-industrial activities and can be included in the lignocellulosic groups of the sorptive materials. The crude material was dried at room temperature, granulated and sieved to obtain different fractions. We used the fractions with size < 800 �m.

Lignin: can be the main by-product of the pulp industry and also can represent a product obtained from renewable resources (Suteu et al., 2008c)

The characteristics has been: acid insoluble lignin, 90%; acid soluble lignin, 1 %; COOH, 3.8 mmol/g; aromatic OH, 1.7-1.8 mmol/g; OH/C9 groups chemical method = 1.02; Ash, 2.5 %; pH (10% dispersion) = 2.7; Mw = 3510; T softening, 170 0C; Solubility in furfural alcohol, 88.5 %; Solubility in aqueous alkali, pH 12, 98.5%

Seashell: wastes of the Rapana Venosa Gastropod species from Romanian Black Sea coast (Suteu et al., 2010a)

The main characteristics are: inorganic compounds as two crystallized forms of CaCO3 - aragonites (59%) and calcites (21.7%), together with magnesium carbonate (1.6%), quartz (1%) and a protein structure – conchinoline, a mixture of some amino acids having fibrous structure. The crystalline structure is the result of an alternative deposition of laminar layers of calcium carbonate and conchinoline. Ash = 54.93-57.72%.

Using of industrial waste materials for textile wastewater treatment

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Fig. 1. The influence of some operational parameters of the dye sorption onto different waste materials at room temperature: a) influence of solution pH on the dye sorption on sawdust; b) influence of initial RO dye concentration on sorption onto

sunflower shells and corncob; c) influence of seashell dose on sorption the BRed dye; d) influence of temperature on the BRed dye sorption on lignin; e) influence of contact time on the BRed dye sorption on seashell; f) influence of sawdust particles size on

sorption of dyes (SD-1 - particle size 1-2 mm, SD-2 –powdered with particle size < 0.1 mm) 2.2. Equilibrium studies

Sorption experiments were performed in batch

conditions, by suspending weighted samples of sorbent in 25 mL volume of aqueous dyes solutions of known initial concentration, in flasks placed in a thermostated bath at desired temperature.

The initial solution pH was adjusted by adding dilute HCl solutions and directly measured with a Radelkis OP-271 pH-Ion analyzer. After an adequate time (usually 24 hours) the phases were separated and the amount of dyes in supernatant was measured by spectrophotometric method at specific wavelength, using an UV-VIS Digital Spectrophotometer, model S104D /WPA or Jasco V-550.

The sorption capacity of the sorbents was evaluated by amount of sorbed dyes:

G/10V)CC(q 30

−⋅⋅−= , (mg of dye/g sorbent), and by percent of dye removal: ( )0 0R% C C 100/C= − ⋅ , where: C0 and C are the initial and the equilibrium concentration of dye in aqueous solution (mg/L), G is amount of sorbent (g), and V is volume of solution (mL).

3. Results and discussion Our previous experimental studies released

that the main factors influencing the sorption equilibrium can be classified in two groups: 1- process variables such as pH, temperature, sorbent dose, initial dye concentration, sorption time and 2- variables depending on sorbent and sorbet such as structure of dyes and sorbent, and the particle size of sorbent (Suteu et al., 2007a; Suteu et al., 2007b; Suteu et al., 2008a; Suteu et al., 2008b; Suteu et al., 2008c; Suteu et al., 2008d; Suteu and Zaharia, 2008a; Suteu and Zaharia, 2008b).

The sorption of different dyes on the selected materials is strongly dependent on the solution pH. These sorbents are characterized by the pH of zero charge (pHpzc), as neutral pH beyond which the material surface is either positively or negatively charged (Suteu et al., 2008d). At pH lower that pHpzc the sorbent has affinity for anionic dyes, but at pH higher than pHpzc the sorbent is available to interaction with cationic dyes (Fig. 1a).

The capacity of sorbents to remove anionic and cationic dyes at the favourable pH was determined into different dye solutions of various initial concentrations. The results show that the

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amount of dyes retained increases with increases in initial dye concentration (Fig. 1b) (Suteu and Zaharia, 2009).

The studies about the importance of sorbent dose (Fig. 1c) showed that the removal percentage of dye increased with the increase of sorbent dose (Suteu et al., 2010a). This fact can be attributed to increase of sorbent surface area availability for more sorption sites that resulting from an increase of sorbent amount. In the same time, the amount of sorbed dye

per unit mass of seashell decreased with the increase of sorbent dose.

The obtained results also show that the amount of sorbed dyes onto the studied waste materials increase with an increase in temperature suggesting an endothermic process and, also, the fact that the high temperatures favour the dye molecule diffusion in the internal porous structure of sorbent (Fig. 1d) (Suteu et al., 2008c). This effect is important at high concentrations.

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Fig. 2. The sorption isotherms of the studied dyes onto: a) sawdust; b) modified ash; c) sunflower seed shell, corncob, lignin and seashell at room temperature

Table 3. The isotherm constants for the sorption of the studied textile dyes onto fibrous materials

Sorbent Experimental conditions and sorption constants

(KL - Langmuir constant; q0 - the maximum value of sorption capacity; KF and n – Freundlich constants; C0 – concentration of dye working solution;

E (kJ⁄ mol) - mean energy of sorption)

References

RB: (pH = 1; sorbent dose – 12 g/L; C0= (9.6- 153.3) mg/L) q0= 3.4 mg/g; KL= 0.735 L/mg; KF = 1.228; n = 3.338;

Suteu et al., 2007a, Suteu et al., 2008a

BRed: (pH = 4; sorbent dose = 8 g/L; C0= (20- 150) mg/L) q0= 4.541 mg/g; KL= 0.2572 L/mg; KF= 1.831; n = 4.982;

Suteu et al., 2007b, Suteu et al., 2008a

RO: (pH = 1; sorbent dose = 6g/L; C0=(24.7-159.25) mg/L) q0= 4.242 mg/g; KL= 0.0585 L/mg; KF= 0.713; n = 2.754;

Suteu et al., 2008a

Ash

MB: (sorbent dose – 8 g/L; C0= (19- 134) mg/L) q0= 5.89 mg/g; KL= 0.5286 L/mg; KF= 2.685; n = 4.585; E = 17.678 kJ⁄ mol

Suteu and Zaharia, 2008a Suteu et al., 2008a

RO: (pH = 1; sorbent dose= 6 g/L; C0= (24.7- 159.25) mg/L) q0= 7.524 mg/g; KL= 0.01398 L/mg; KF= 0.265; n = 1.633;

Suteu et al., 2008a Z-14

BRed: (pH=1.5; sorbent dose = 6g/L; C0= (20-150 mg/L) q0= 10.235 mg/g; KL= 0.0196 L/mg; KF= 0.595; n = 1.908

this paper

Z-16 RO: (pH =1; sorbent dose = 6g/L; C0= (24.7-159.25) mg/L) q0= 6.305 mg/g; KL= 0.0115 L/mg; KF= 0.155; n = 1.48

Suteu et al., 2008a

BRed: (pH = 2; sorbent dose –20g/L; C0= (20-150) mg/L) q0= 11.61 mg/g; KL= 0.0146 L/mg; KF= 0.293; n = 1.36; MB:(pH = 5.7; sorbent dose – 4g/L; C0= (6.4-38.4) mg/L) q0= 7.215 mg/g; KL= 0.479 L/mg; KF= 2.236; n = 1.99 CV: (pH= 5.7; sorbent dose– 4g/L; C0= (8.16-48.96) mg/L) q0= 12.594 mg/g; KL= 0.0899 L/mg; KF= 1.151; n = 1.391 RB: (pH = 5.7; sorbent dose – 4g/L; C0= (9.58-57.5) mg/L) q0= 7.309 mg/g; KL= 0.056 L/mg; KF= 1.95; n = 1.482

Suteu et al., 2008b

Sawdust

RO: (pH= 1;sorbent dose – 8g/L; C0= (24.7- 159.25) mg/L) q0= 8.554 mg/g; KL= 0.0175 L/mg; KF= 0.307; n = 1.562

this paper

Lignine BRed: (pH = 1.5; sorbent dose –14g/L; C0= (20-300) mg/L) q0= 10.173mg/g; KL= 10.19 L/mg; KF= 1.9602; n = 2.621; E = 13.13 kj/mol

Suteu et al., 2008c Suteu et al., 2010b

Sunflower seed shell

RO: (pH= 1; sorbent dose – 8g/L; C0= (24.7- 159.25) mg/L) q0= 8.554 mg/g;KL= 0.0175 L/mg; KF= 0.307; n = 1.562; E = 8.276 kj/mol

this paper

Corncob RO: (pH= 1; sorbent dose – 8g/L; C0= (24.7-159.25) mg/L) q0= 8.554 mg/g; KL= 0.0175 L/mg; KF= 0.307; n= 1.562; E = 8.28 kj/mol

Suteu and Zaharia, 2009

Seashell BRed: (pH = 1.5; sorbent dose –14 g/L;C0= (20-300) mg/L) q0= 10.173mg/g; KL= 10.19 L/g; KF= 1.9602; n= 2.621; E = 8.98 kj/mol

this paper

Using of industrial waste materials for textile wastewater treatment

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The influence of sorption time on the

decolourization of aqueous solutions containing different textile dyes is different, depending on the sorbent structure (Figs. 1e, 1f) (Suteu et al., 2010a; Suteu et al., 2008b). For example, in the case of seashell (Fig. 1e) the experimental data showed that the removal of dye is faster into initial stages of contact period and then, the amounts of sorbed dye slowly increases near the equilibrium (more rapid in dye solution with high concentration): after 5 hours were removed 90 % from the total amount of BRed dye corresponding to the dye amount removed after 24 h (Suteu et al., 2010a).

Fig. 2 presents the sorption isotherms for some dye removal onto different studied waste materials. The equilibrium sorption data were adequately analyzed by the Freundlich, Langmuir and Dubinin-Radushkevich sorption isotherm models, in order to calculate the values of sorption constants. The best fit equilibrium model was established based on the linear regression correlation coefficients (Suteu et al., 2008a; Suteu et al., 2008b; Suteu and Zaharia, 2009; Suteu et al., 2010b). Some of the most important parameters of sorption processes were presented in Table 3, together with the main experimental conditions.

The analysis of Fig. 2 and Table 3 permits to mention the following observations:

- the sorption data can be adequately modelled by the Langmuir, Freundlich and/or Dubinin-Radushkevich sorption isotherms;

- generally, the sorption of dyes follows the Langmuir isotherm, indicating the formation of monolayer coverage of dye molecules at the external surface of the sorbent;

- the data concerning the sorption of cationic dyes - MB, CV and RB onto sawdust are better represented by the Freundlich model, indicating a heterogeneous adsorption surface, with sorption sites of different energies and availability;

- the high values of Langmuir constant (KL), values of Freundlich constant n higher than one, the energy of sorption (E) higher than 8 kJ/mol, and, also, the increasing of sorption constants with temperature increase confirm the chemical nature of the dye sorption onto the studied fibrous materials. 4. Conclusions • For the dye sorption from textile effluents can be

used a large variety of solid materials but their choice is based on dye nature/structure and treated wastewater required quality (e.g., imposed treatment degrees or removal degrees for textile dye contents or colour). • The tested fibrous materials correspond to the

actual tendency of using the non-conventional solid materials, natural or synthetic ones, agricultural wastes or secondary products from different industries, to reduce the overall cost of sorbent

preparation and of treatment process, and no generate of supplementary dangerous products. • The experimental results obtained in our research

studies indicate that the sorption capacity of some agricultural and industrial wastes is dependent on the sorbent and dye structure, the operational parameters (pH of textile dye solutions, sorbent dose, initial dye concentration, temperature, sorption time). • Comparing the maximum sorption capacity value

for dye removal of the studied waste materials with those reported in literature we can say that the sorbents with a macro-porous structure (lignocellulosic materials) have a satisfactory capacity towards the dyes that have no high molecular weight (such as MB, RB, CV) and a moderate sorption capacity for the other dyes. In these conditions, the sorption onto cheaper waste materials can be considered a feasible step for textile wastewater treatment. • To increase the treatment efficiency when is used

a sorption process, a great interest will have the use of combined treatment steps with conventional and unconventional sorbents and also to combine this treatment with other biological, physical and chemical steps. One of the main criteria of textile effluent treatment that must be followed is the operating cost.

References Anjaneyulu Y., Sreedhara Chary N., Samuel Suman Raj D.,

(2005), Decolourization of industrial effluents – available methods and emerging technologies – a review, Reviews in Environmental Science and Bio/Technology, 4, 245-273.

Babu R., Parande B., Prem A.K., Kumar T., (2007), Textile Technology: Cotton Textile Processing: Waste Generation and Effluent Treatment, The Journal of Cotton Science, 11, 141-153.

Crini G., (2006), Non-conventional low-cost adsorbents for dyes removal: A review, Bioresource Technology, 97, 1061-1085.

Gupta V.K., Suhas S., (2009), Application of low cost adsorbent for dye removal – A review, Journal of Environmental Management, 90, 2313-2342.

Harja M., Suteu D., Ciobanu G., Rusu L., (2007), Materials based on ash for environmental protection. I. Obtaining and characterization, Scientific Papers of USAMV Iasi, Series Agronomy, 50, 17-22.

Forgacs E., Cserhati T., Oros G., (2004), Removal of synthetic dyes from wastewaters: a review, Environ. Int., 30, 953-971.

Senthilkumaar S., Kalaamani P., Porkodi K., Varadarajan P.R., Subburaam C.V., (2006), Adsorption of dissolved reactive red dye from aqueous phase onto activated carbon prepared from agricultural waste, Bioresource Technology, 97, 1618-1625.

Suteu D., Volf I., Macoveanu M., (2006), Ligno-cellulosic materials for wastewater treatment, Journal of Environmental Engineering and Management, 5, 119 -134.

Suteu D., Zaharia C., Bilba D., Surpateanu M., (2007a), Conventional and unconventional materials for wastewater treatment, Bulletin of the Transilvania University of Brasov (Romania), IV, 692 –696.

Suteu et al./Environmental Engineering and Management Journal 8 (2009), 5, 1097-1102

1102

Suteu D., Harja M., Rusu L., (2007b), Sorption of dyes from aqueous solution onto lime-coal ash sorbent, Proceeding of International Scientific Conference, 23-24 November 2007, Gabrovo, Bulgaria, 2, 317–321.

Suteu D., Harja M., Rusu G., (2007c), Materials based on ash for environmental protection. II. Preliminary studies about dye sorption onto materials based on ash, Lucrari Stiintifice USAMV IASI, Series Agronomy, 9, 90-95.

Suteu D., Zaharia C., (2008a), Studies about sorption equilibrium of Methylene Blue dye onto solid materials based on coal ashes, Bull.Inst.Polytech.Iasi, Tome LIV (LVIII), 3, 81-90.

Suteu D., Zaharia C., Harja M., (2008a), Residual ash for textile wastewater treatment, Proceeding of International Scientific Conference, 23 – 24 November 2008, Gabrovo, Bulgaria, 3, 475–480.

Suteu D., Bilba D., Zaharia C., Popescu A., (2008b), Removal of dyes from textile wastewater by sorption onto ligno-cellulosic materials, Scientific Study & Research, IX, 293-302.

Suteu D., Malutan T., Rusu G., (2008c), Use of Industrial Lignin for dye removal from aqueous solution by sorption, Lucrari Stiintifice USAMV IASI, Series Agronomy, 51, 71-78.

Suteu D., Bilba D., Muresan R., Muresan M., (2008d), Using fibrous materials for textile wastewaters treatment, Proceeding of 4th International Textile,

Clothing & Design Conference – Magic World of Textiles, October 5th - 8th 2008, Dubrovnik, Croatia, 1112-1117.

Suteu D., Zaharia C., (2008b), Removal of textile reactive dye Brilliant Red HE-3B onto materials based on lime and coal ash, Proceeding of 4th International Textile, Clothing & Design Conference – Magic World of Textiles, October 5th - 8th 2008, Dubrovnik, Croatia, 1118-1123.

Suteu D., Zaharia C., Bilba D., Muresan R., Popescu R., (2009), Decolourization of textile wastewaters – Chemical and Physical methods, Textile Industry (in press).

Suteu D., Zaharia C., (2009), Orange 16 reactive dye removal from aqueous system using corn cob waste, Proceeding of the International Scientific Conference – UNITECH’09, November 23th – 24th 2009, Gabrovo, Bulgaria (in press).

Suteu D., Bilba D., Aflori M., Doroftei F., Lisa G., Badeanu M., Malutan T., (2010a), Seashells as a new biosorbent for dye removal from aqueous solutions, Acta Chem.Slov. (in press).

Suteu D., Malutan T., Bilba D., (2010b), Removal of Reactive Dye Brilliant Red HE-3B from aqueous solutions by industrial lignin: Equilibrium and Kinetics Modeling, Dessalination (in press).