TREATMENT OF TEXTILE WASTEWATER USING BIOLOGICAL ACTIVATED SLUDGE METHOD COMBINED WITH COAGULATION

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1 TREATMENT OF TEXTILE WASTEWATER USING BIOLOGICAL ACTIVATED SLUDGE METHOD COMBINED WITH COAGULATION ABSTRACT The wastewater treatment plant (WWTP) in the pilot scale and the reality (1000 m 3 /day capacity) of Xuan Huong Textile Co. was investigated and built by a combination between the activated sludge treatment and the coagulation-flocculation method. The analyzed wastewater results showed the effective performance in the COD and TSS removal. With 80% removal efficiency for all factors, our chosen technology was proved as a right choice in textile wastewater treatment. The effluent meets Vietnamese standard TCVN 5945:2005, C level. Keywords: Textile wastewater, Aerotank, Coagulation-Flocculation tank 1. INTRODUCTION Textile wastewater is the combination of wastewater from various stages of production: fibers preparation, yarn, thread, webbing, dyeing and finishing. According to experts, a textile factory uses a large amount of water for manufacturing utilization in average, in which dyeing and finishing stages use almost 72.3% [3]. Considering both the volume generated and the effluent composition, the textile industry wastewater is reated as the most polluting among all industrial sectors [5]. Important pollutants in textile effluent are mainly recalcitrant organics, color, toxicants and inhibitory compounds, surfactants, chlorinated compounds (AOX- Adsorbable Organohalogens), salts, high temperature (at least 40 C), and high ph due to the large amount of alkali in wastewater. Dye is the most difficult constituent of the textile wastewater to treat, especially azo dyes-the class of dyes most widely used industrially, having a world market share of 60-70%. However, reactive dyes are easily washed off during the dyeing process, therefore, the residue dye always presents in the dye bath effluent, as much as 50% of the initial dye load [5]. This is the reason why the color and the pollutants concentration in textile wastewater are high. The factors considered to choose the appropriate textile wastewater treatment plant are: treatment efficiency, economic efficiency, characteristics and flowrates of the influent, composition and concentration of the influent, Three methods which are usually used in textile wastewater treatment plant are: physico-chemical methods, advanced oxidation methods, and biological sludge methods. The physico-chemical methods with coagulation-flocculation, flotation and adsorption can treat effectively the color and BOD in the influent. However, the disadvantages of this method are the high chemical cost and the large amount of physic-chemical sludge ( kg TS/ m 3 treated wastewater). With the advanced oxidation methods, the usual oxidants are Chlorine (Cl 2 ), Hydroxy Peroxide (H 2 O 2 ), and Ozone (O 3 ), in which Cl 2 is the most economical oxidant. The disadvantages of the advanced oxidation methods are the high investment and 1

2 operation costs. In addition, aerobic and anaerobic activated sludge processes are also evaluated as high performance treatments; however, the long retention time and low recalcitrant organics removal performance reduce their widely utilization in textile wastewater treatment. In recent years, textile wastewater is usually treated by the combination of activated sludge process and coagulation-flocculation process. The activated sludge process removes all or a part of organic compounds in the development and growing of biological microorganisms, and reduces treatment loading for the next process. The arrangement in which the activated sludge process is in front of the coagulation-flocculation process reduces the chemical cost and sludge treatment cost. This is also our chosen technology in the WWTP of Xuan Huong Textile Co. All investigation and operation steps in Xuan Huong Textile Co. in pilot scale as well as the reality scale will be described and summarized in this paper. 2. MATERIAL AND METHODS 2.1. Material Activated sludge used in textile WWTP was taken from stable aerotanks in other WWTPs which have the similar characteristics. Aluminium sulfate [Al 2 (SO 4 ) 3 ].nh 2 O, PAC-Poly Aluminium Chloride, NaOH baz, H 2 SO 4 acid and Profloc PC 1748 Polymer used in laboratory and in facility were provided by Hoang Giang Ltd., Co. (HCMC, Vietnam). Figure 1: Formula of aluminium sulfate Wastewater described in this paper is textile wastewater from Xuan Huong Textile Co. (Tan Tao Industrial Park, Binh Tan District, HCMC, Vietnam) Methods Textile WWTP in pilot scale We built the pilot scale textile WWTP for investigation the reality WWTP performance. Here is the technology of the pilot scale textile WWTP: Textile wastewater ph Adjustment Activated sludge treatment Physico-chemical treatment Receiving water Figure 2: Textile wastewater treatment pilot Because the ph of the influent changes in a wide range from 9-12, the textile wastewater need to be neutralized to the appropriate value before flowing to biological activated sludge treatment. According to our former studies about textile WWTP technologies, the technology with the 2

3 activated sludge process in front of the physico-chemical process was proved the most efficient technology. The advantages of this arrangement are the reduction of the chemical cost and the sludge treatment cost. Wastewater from Xuan Huong Textile Co. was analyzed ph, COD, BOD, and SS before going to the pilot scale WWTP. Because the high initial temperature of textile wastewater ( 40 C) was not appropriate for the development of biological microorganisms, the influent must be retained to reduce the temperature. Then wastewater was flowed to the pilot aerotank in 8 hours for biological activated sludge treatment. After biological treatment, wastewater was treated by coagulation-flocculation process by PAC and polymer. The influent wastewater, wastewater after biological treatment and the effluent wastewater of the pilot scale WWTP were sampled and analyzed in Environmental Engineering Laboratory Institute of Environment and Resources, Vietnam National University-Ho Chi Minh city. The analyzed results from the pilot scale WWTP is described hereinafter: Table 1: Analyzed sample results from the pilot WWTP Source: Green Tech Co., May 08, 2008 ph COD, BOD 5, Tổng chất rắn hòa tan, Influent Wastewater after biological treatment Wastewater after coagulation-flocculation Standard TCVN 5945:2005, C level According to the results from the pilot scale WWTP, the wastewater effluent always met the standard TCVN 5945:2005. Therefore, the pilot scale WWTP could be applied in the reality Treatment process The wastewater effluent of Xuan Huong Textile Co. was collected in Pump sum, then through Water aeration tower to reduce the wastewater temperature in appropriate range from C before going to Aerotank. Physico-chemical treatment was conducted in Coagulation- Flocculation tank to remove pollutants in the influent. Sludge in coagulation-flocculation tank was splitted by the Dissolved air flotation unit. The effluent meets the Vietnamese standard TCVN 5945:2005 before going to the receiving water. 3

4 Blower Textile wastewater Pump sum Aeration tower Aerotank Pressurized tank Al salt, Polymer, Acid Dissolved Air Flotation Coagulation- Flocculation tank Transfer tank Settling tank Receiving water Sludge drying bed Figure 3: Diagram of the textile WWTP Investigated parameters and sample collection methods To find the treatment performance of each system, these factors were investigated: COD, BOD 5, TSS, and ph. Here is the way to collect samples: 500 ml glass bottles were used to collect effluent sample from each stage of treatment. Duplicate samples were collected and stored in a refrigerator. After collection, all the samples were processed in Environmental Engineering Laboratory Institute of Environment and Resources, Vietnam National University-Ho Chi Minh city. 1. RESULTS AND DISCUSSION The analyzed results of wastewater from the WWTP of Xuan Huong Textile Co. were described in Table 1. Table 1: The characteristics of the influent and the effluent of the WWTP of Xuan Huong Textile Co. Source: Green Tech Co., November 04, 2008 ph COD, BOD 5, Total suspended solids, Inffluent Wastewater after biological treatment Wastewater after coagulationflocculation Standard TCVN 5945:2005, C level

5 1.1. COD removal performance B6-319 Ly Thuong Kiet Street, Ward 15, District 11, HCMC Figure 4 shows the COD removal performance of the pilot scale WWTP and the WWTP in reality. The results express that COD was removed 79% (in the pilot scale) and 83% (in the reality) after the aerotank. COD removal performance results prove that the chosen technology with activated sludge treatment and the coagulation-flocculation treatment is an effectively process. Figure 4: COD removal performance of the WWTP in pilot scale and in the reality % COD treated =(COD inffluent COD effluent )/COD inffluent 1.2. Suspended solids removal performance Figure 5: TSS removal performance in the WWTP in pilot scale and in the reality 5

6 Figure 5 shows the TSS removal performance of the WWTP in the pilot scale and in the reality is very high and meets the effluent standard. In the WWTP, the TSS is removed 98.8% after aeration tank. After physico-chemical treatment, the TSS concentration increases due to the production of sludge in coagulation-flloculation tank; however, this phenomenon doesn t affect the final result of our technology. The effluent still meets the standard TCVN 5945:2005, C level. 2. CONCLUSIONS - The WWTP in pilot scale and in the reality of Xuan Huong Textile Co. with the activated sludge treatment and coagulation-flocculation process show an effective efficiency in textile wastewater treatment. The COD removal performance is over 90%; the TSS removal performance is over 80%. - All factors in the effluent of the WWTP meet the TCVN 5945:2005, C level. REFERENCES [1] Bes-Piá, A. et al. Reuse of wastewater of the textile industry after its treatment with a combination of physic-chemical treatment and membrane technologies. Desalination 149, 2002: [2] Cheng, W.P. et al. A study of coagulation mechanisms of polyferric sulfate reacting with humic acid using a fluorescence-quenching method. Water Research 36, 2002: [3] Rosli. Development of biological treatment system for reduction of COD from textile wastewater. Master Dessertation, University Technology Malaysia, [4] Sarasa, J. et al. Treatment of a wastewater resulting from dyes manufacturing with ozone and chemical coagulation. Water Research 32, 1998: [5] Sen, S. and Demirer, G.N. Anaerobic treatment of real textile wastewater with a fluidized bed reactor. Water Research 37, 2003: [6] Wallace, T.H. Biological treatment of a synthetic dye water and an industrial textile wastewater containing azo dye compounds. Master thesis, Virginia Polytechnic Institute and State University, [7] Yuan, Y. et al. Treatment of wastewater from dye manufacturing industry by coagulation. Journal of Zhejiang University Science A, 2006: