Reactive dyes are the principal dyes used in the cotton industry which makes up 50% of the world's fiber consumption (1). They are commonly used in the textile industry because of their bright colours, excellent colourfastness and ease of application (2,3). A large number of reactive dyes are azo compounds that are linked by an azo group (4). Many reactive dyes are toxic to some organisms and may cause direct destruction of aquatic life due to the presence of aromatic and metal chlorides (5). It has been reported that some azo dyes are able to produce carcinogenic aromatic amines in the process of reductive degradation (6,7). Their high solubility, synthetic origin and complex aromatic molecular structure make their removal a very difficult task (8,9).
Methods for treating textile dye wastewaters consist of various chemical, physical and biological processes. These include: adsorption (10), nanofiltration (11,12), colloidal gas aphrons (13), ultrasonic decomposition (14), electro coagulation (15), coagulation and precipitation (16), advanced chemical oxidation (17), electrochemical oxidation (18-19), photooxidation (18), predispersed solvent extraction (20), ozonation (21-24), supported liquid membrane (2, 25, 26), liquidliquid extraction (25,27) and aerobic and anaerobic biological processes (28,29). The advantages and disadvantages of some methods of dye removal from wastewater are given in Table 1.
The liquid membrane technique known as ''Supported Liquid Membrane'' (SLM) has the advantage of achieving selective removal and concentration in single stage, thus having great potential for reducing cost significantly (2). SLM system has several advantages including: (a) low capital investment and operating cost, (b) low energy consumption, (c) minimal loss of extractant, (d) low liquid membrane requirement and thus less amount of expensive extractants which offer good selectivity and (e) simple to operate and easy to scale up. There have been a number of studies dealing with organic compound transport through SLM in synthetic solutions (27). However, no work has been carried out on the use of liquid membrane technology to recover textile dyes.
Table 1: The advantages and disadvantages of some methods of dye removal from wastewater (10, 15-18, 25-31) Method Advantages Disadvantages Adsorption low cost some adsorbents have low surface area no regencration possible side reactions loss of needed adsorbents dye-adsorbed performance dependents on wastewater materials can be characteristics used as substrates in solid state fermentation Nanofiltration removes all dye high investment costs membrane types fouling effluent must be high effluent treated quality easy to scale-up Electro removes small no effective for all dyes coagulation colloidal articles no use of coagulants low sludge production low cost Coagulation and effective for high cost perception all dyes high sludge production Advanced non-hazer douse high cost chemical end products oxidation Electro no sludge high cost oxidation production breakdown compounds are non-harzardous no chemical used Photo no sludge releases aromatic amines oxidation production Ozonation no sludge high cost production no alteration of short half life volume Supported minimal loss of emulsification may occurs liquid extractants membrane simple to operate low energy consumption easy to scale up low cost Liquid-liqued low cost emulsification may occur extraction low energy effluent must be treated consumption variety of solvents available easy to scale-up Biological environmentally slow process processes friendly public needs adequate nutrients acceptance economically norrow operating temperature range attractive Table 2: Some properties of the oils used (33-35) Properties Cottonseed Olive Canola Sunflower Used oil oil oil oil oil Volatile 1000 1000 1000 1000 999.45 solids (mg/g) Ash (mg/g) 0.00 0.00 0.50 0.00 0.55 Density (p/g 0.917 0.912 0.915 0.920 0.930 [cm.sup.-3] Viscosity 33.5 41.0 31.0 30.3 46.1 (mPas)at 38 [degrees]C Fatty acids (%) Unsaturated 17.6 71.3 66.0 23.0 - Polysaturated 56.0 12.7 29.0 65.0 - Saturated 26.4 16.0 5.0 12.0 - The aim of this study was to investigate the potential of using renewal, non-toxic, natural plant oils as a liquid membrane for the removal of the dye remazal brilliant blue from the textile wastewater. The specific objectives were: (a) to evaluate the effectiveness of five oils (cottonseed oil, olive oil, canola oil, sunflower oil and used cooking oil) for removal of the textile dye remazol brilliant blue and (b) to investigate the effects of pH and temperature on the dye removal efficiency.
MATERIALS AND METHODS
Oils: Four types of commercially available plant oils (cottonseed oil, olive oil, canola oil and sunflower oil) were purchased from a local supermarket in Halifax. Used cooking oil was obtained from a local restaurant in Halifax. Some properties of these oils are shown in Table 2. The viscosity of the fresh oil was given by the manufactories, while the viscosity of cooked oil was measured using Bohlin VOR Rheometer (Bohlin Instroments, Cranbooy N.J., USA).
Reagents: The chemicals used in this study included sodium hydroxide (NaOH), sulphuric acid ([H.sub.2]S[O.sub.4]) and remazol Brilliant blue dye (1-amino-4-[4-(1-sulfonylethyl2-sulfoxy)]-2-(9, 10-anthraquinone)-sulfonic acid; disodium salt,). The 98.6% NaOH and 98% [H.sub.2]S[O.sub.4] were obtained from Fisher Scientific (Ca # S 318-3 and Ca #A 300 212, Fisher Scientific, Montreal, Quebec, Canada). The remazol brilliant blue,dye content ~ 50% was obtained from Sigma (R8001, Ca # 22-324-7, Sigma, Oakville, Ontario, Canada).
Standard curve: To determine the concentration of the remazol brilliant blue dye using colorimetric techniques, a standard curve was developed from the standard solution of remazol brilliant blue dye according to the procedure described by Mahmoud et al. (36). The standard solution was prepared by dissolving 0.1 g of the dye in 1000 mL of distilled deionized water at ambient conditions (pH of 7 and a temperature of 25[degrees]C). Then, a set of 9 solutions with remazol blue dye concentrations of 10, 20, 30, 40, 50, 60, 70, 80 and 100 mg/L was prepared. Finally, the absorbance of the prepared solutions was measured (in triplicate) using a spectrophotometer (Spectronic 601, Fisher scientific, Montreal, Quebec, Canada). The absorbance was then plotted against the known remazol blue dye concentrations (mg/L) as shown in Fig. 1. A blank sample was used to zero the spectrophotometer.
[FIGURE 1 OMITTED]
Experimental design: The effects of oil type, pH and temperature on the removal of remazol brilliant blue from textile wastewater were investigated. Five types of plant oil (cottonseed oil, olive oil, canola oil, sunflower oil and used cooking oil), five levels of pH (1, 4,7,10 and 13) and five temperatures (15, 25, 35, 45 and 55[degrees]C) were investigated. The experiments were designed as [5.sup.3] factorials with 3 replicates. This resulted in 375 treatments.
Experimental procedure: A volume of 500 mL of each of the five solutions (pH = 1,4,7,10 or 13) was prepared according to the procedure described by...