MenuISSN (0970-2083)
ISSN (0970-2083)
Meena Solanki * and A.K. Dwivedi
Department of Chemical Engineering, UEC, Ujjain, M.P., India
Received date: 10 July 2011; Accepted date: 24 August 2011
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In the fiber manufacturing industry the effluent waste water consider the parameter BOD, COD, TDS and pH. The high values of BOD, the untreated textile waste water can cause rapid depletion of dissolved oxygen if it is directly discharged into the surface water sources. The effluents with high levels of COD are toxic to biological life. The high alkalinity and traces of chromium (employed in dyes) adversely affect the aquatic life and also interfere with the biological treatment process. Dissolved solids in effluent may also be harmful to vegetation and restrict its use for agricultural purpose. In this research paper the value of BOD, COD, TDS and adjusted values of pH using the poly aluminum chloride chemical coagulation are presented. The key advantage of PAC using the chemical coagulation is the cost effectiveness and produces larger and more readily settleable flocs than alum. The sludge volume generated by PAC is less than that generated by alum. Results evaluated that the percentage removal of BOD 83.34%, percentage removal of COD 64.04%, percentage removal of TDS 62.97% and values of pH adjusted 6.2 to 6.9.
BOD, COD, pH, Polyaluminum chloride (PAC), Total dissolved solid.
Wastewater reuse in the textile industry is necessary due to the high water consumption required for its processes. This has to be considered, especially in areas that suffer from water scarcity such as Iran. Although several studies have been conducted, in the developed countries, in to the treatment of water and wastewater through Granular Activated Carbons (Bansode et al., 2004; Ahmedna et al., 2000), adsorbent (Pala and Tokat, 2000; Guohua, 2004), Fenton’s reagent (Martinez et al., 2003), wet oxidation (Hung et al., 2003), coagulation - electro - oxidation (Xiong et al., 2000), and advanced oxidation with biological oxidation (Gogate and Pandit, 2004), developing countries still lack basic technology of water and wastewater treatment. In typical dyeing processes, 50-95% of the dye is fixed on to the fiber and unfixed dyes from subsequent washing operations are discharged in the spent dye-bath or in the wastewaters (Jiraratananon et al., 2000). How ever application of textile treatment methods in an industrial plant becomes difficult due to operational problems and costs. Biological treatment by activated sludge offers high efficiencies in COD removal, but does not completely eliminate the color of the wastewater and frequently operational problems such as bulking appear. Chemical oxidation by ozone, or a combination of UV-radiation and ozone and H2O2, has great interest, but the costs are still very high due to the high doses required. Among the above mentioned methods, adsorption is considered to be relatively superior to other techniques because of low cost, simplicity of design, availability and ability to treat dyes in more concentrated form (Meshko et al., 2001); (Kannan and Sundaram, 2001).
Coagulation - flocculation is also an essential process in water and in industrial wastewater treatment (Ismail, 1978; Abdel-Shafy et al., 1987). Several studies have been reported on the performance and optimization of coagulants, determination of pH and investigation of flocculants addition (Tatsi et al., 2003; Abdel- Shafy et al., 1991). Coagulation – flocculation process has been found to be cost effective, easy to operate and energy saving treatment alternatives (Bromley et al., 2002) Coagulant dosages varies in a wide range aiming at maximum removal efficiency of pollutants using minimum doses at optimum pH (Watanabe et al., 1993; Szpak et al., 1996). Coagulation can be interpreted as the conversion of colloidal and dispersal particles in to small visible floc upon addition of a simple electrolyte. Increasing the concentration of the electrolyte results in a compression of the electrical double layer surrounding each suspended particle, a decrease in the magnitude of the repulsive interactions between particles and destabilization of the particles.
The most common coagulant used in wastewater treatment is alum Al2 (SO4)3.4H2O and PAC (Poly Aluminum Chloride). Flocculation is used to describe the process whereby the size of particles increases as a result of particle collisions. The purpose of flocculation is to produce particles, by means of aggregation, that can be removed by inexpensive particle - separation procedures such as gravity sedimentation and filtration (Metcalf and Eddy, 2003). Meric et al., (2004) studied the effectiveness of fenton’s oxidation (FO) process and ozone (O3) oxidation compared with coagulation - flocculation (CF) process to remove effluent toxicity as well as color and COD from textile industry wastewater. The FO process removed COD at a higher rate (59%) than O3 (33%) while color removal was similar (89% and 91%, respectively). The CF process removed both COD and color at rates similar to the FO process (Meric et al., 2004). Sources of pollution in textile manufacturing industry as shown in Figure 1.
Figure 1: Sources of pollution in textile manufacturing (Source: NIIR Board, 2003b)
Reagents used for the BOD (Biological oxygen demand) test
BOD is determined by the dilution method. Distilled water, MgSO4, CaCl2, Phosphate buffer, FeCl3, KI, H2SO4, 0.025N Sodium thio -sulphate solution, starch solution.
Reagents used for the COD (Chemical oxygen demand) test
0.25N potassium dichromate, silver sulphate sulphuric acid solution, std. ferrous ammonium sulphate 0.1N, ferroin indicator, potassium acid phthalate for standards.
Coagulant
A commercial grade Poly Aluminum Chloride (AlCl3.6H2O) is used as coagulant with varying doses of 10 mg/L to 45 mg/L.
Experimental Set up
BOD incubator, COD digestion apparatus Model 2015. TDS meter, pH meter.
Experimental method
Coagulation studies were conducted in duplicate using Jar-test Apparatus with five beakers of one liter capacity. The samples were stirred for one minute at 500 rpm followed by 10 minutes slow mixing of 25 to 30 rpm. The contents are then settled for two hours. At the end of two hours, the supernatant is withdrawn, filtered and was used for COD analysis and BOD analysis (APHA, 1995). All the experiments were conducted at room temperature of 27 ± 3oC.
In experiments obtained the Initial COD = 712 mg/L Initial BOD = 215 mg/L,
Initial pH = 6.2 Initial TDS (Total dissolved solid) = 5875 mg/L
The results are shown clearly in Table 1 & Figures 2, 3, 4 & 5.
Table 1: Percentage removal of BOD, COD, TDS and pH
Figure 2: % Removal of COD V/S PAC dose mg/L
Figure 3: Effect of PAC dose (mg/L) on percentage removal of BOD
Figure 4: Effect of PAC dose (mg/L) on pH of treated water
Figure 5: Effect of PAC dose (mg/L) on percentage removal of TDS
Figure 2 shows the effect of PAC (poly aluminum chloride) dose on percentage removal of COD. The initial COD of fiber waste water was 712 mg/L. The value of COD is higher than the permissible limits. In experiments we reduced the value of COD using the poly aluminum chloride coagulation. We have added the different doses of polyaluminum chloride in the fiber waste water from 10 mg/l to 45 mg/L and the value of COD reduced from 712 mg/L to 256 mg/L. Percent removal of COD was found to be 64.04%.
The result show that the most effective and economic dose is 45 mg/L. The figure indicates that percentage removal of COD is incrementaly increased with increase in PAC dose.This trend is due to the decrease in concentration of organic material present in the water sample measured by the COD test.
It is clear from Fig. 3 that maximum removal of BOD at PAC dose 45 mg/L. Figures reveal that incremental PAC dose increases the percentage removal of BOD. The initial BOD of fiber waste water was 215 mg/L. We found percent removal of BOD to be 83.34%.
The result show that the most effective and economic dose is 45 mg/L, which shows that graph reaches almost constant. In this graph the amount of food (or organic carbon) that bacteria can oxidize measured by the BOD test were reduced when added the poly aluminum chloride (PAC) dose.
Figure 4 shows the effect of PAC dose on pH values of the treated water. The initial value of the waste water pH is 6.2. We have added the poly aluminum chloride dose in the waste water to adjust the value of pH. Because the value of pH is low (acidic). Added the poly aluminum chloride dose in the waste water from 10 mg/L to 45 mg/L. Poly aluminum chloride is cost effective and it is a very good coagulant to increase the value of pH .
Figure 5 shows the graph between the percentage removal of TDS (Total dissolved solid) and PAC (poly aluminum chloride). The initial TDS of fiber waste water was 5875 mg/L. Dissolved solids contained in the industrial effluents are also a critical parameter. Use of common salt and glauber salt etc. in processes directly increases total dissolved solids (TDS) level in the effluent. TDS are difficult to be treated with conventional treatment systems. Disposal of high TDS bearing effluents can lead to increase in TDS of ground water and surface water. Dissolved solids in effluent may also be harmful to vegetation and restrict its use for agricultural purpose.
In experiments we reduced the value of TDS using the poly aluminum chloride coagulation. Added the different doses of polyaluminum chloride in the fiber waste water from 10 mg/L to 45 mg/L. The value of TDS reduced from 5875 mg/L to 2175 mg/L and % removal of TDS was 62.97%.
The waste water from the textile industry is characterized by high values of Biochemical oxygen demand (BOD), Chemical oxygen demand (COD), color and pH.
In experimentation we used the treatment of wastewater by PAC (Poly Aluminum Chloride), due to its effectiveness in treating a wide range of wastewater type and relatively low cost. The use of performed polymerized forms of Al has become more common as alternative coagulants, such as poly aluminum chloride and poly aluminum sulphate. The higher charge density of poly aluminum chloride species often results in a decrease in the coagulant dose and the associated solids production.
The most common coagulant used in wastewater treatment is alum Al2(SO4)3.4H2O and PAC (Poly Aluminum Chloride), due to its effectiveness in treating a wide range of wastewater type and relatively low cost. The use of performed polymerized forms of Al has become more common as alternative coagulants, such as poly aluminum chloride and poly aluminum sulphate. The higher charge density of poly aluminum chloride species often results in a decrease in the coagulant dose and the associated solids production. These coagulants have the advantage of being more effective at lower temperatures and a boarder pH range than alum.
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