Reactive Cibacron Blue Dye Wastewater Treatment Using Combined Technology Of Thermolysis And Inorganic-Organic Hybrid Polymer Coagulation-Flocculation
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Date
2016-03
Authors
Su, Claire Xin-Hui
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Publisher
Universiti Sains Malaysia
Abstract
A reactive dye, cibacron blue F3GA (RCB), was subjected to a combined and hybrid technology of thermolysis and coagulation-flocculation using the magnesium chloride-polyethylene oxide (MgCl2-PEO) hybrid polymer. When the synthetic dye wastewater was subjected to catalytic thermolysis alone, maximum colour removal and COD reduction achieved were 63.78% and 56.33%, respectively. The catalyst used was copper sulphate (CuSO4). Maximum efficiency of thermolysis was found to be at pH 2, catalyst mass loading of 5000 mg/L, heating temperature of 95°C and heating time 120 minutes. The MgCl2-PEO hybrid polymer was prepared and characterised. It was then applied in the coagulation-flocculation of RCB. Various ratios of MgCl2 to PEO were prepared through physical blending. The viscosities of the hybrid polymer showed a descending trend as the composition of MgCl2 increased. However, the conductivities of the hybrid polymer aqueous solutions showed an ascending trend. For the application in RCB dye wastewater treatment, 90% MgCl2:10% PEO ratio showed the best performance, recording 98.58% colour removal and 91.09% COD reduction at pH 11 and coagulant dosage of 1500 mg/L. The comparison between the efficiency of MgCl2 coagulant and MgCl2-PEO hybrid polymer showed that the hybrid polymer was more efficient. It required a lower coagulant dosage, which was 1500 mg/L, compared to 2000 mg/L MgCl2, while producing greater colour removal efficiency. The zeta potential measurements obtained ranged from -25.78 mV to 24.97 mV, which showed that charge neutralisation was the dominant mechanism for the flocculation of RCB dyes using MgCl2-PEO hybrid polymer. To further enhance the percentage of colour removal and COD reduction, thermolysis and coagulation-flocculation were combined. For the combined process, the wastewater was subjected to thermolysis and the wastewater allowed to cool to room temperature, then treated with coagulation-flocculation. For the hybrid process, the RCB dye wastewater was treated with thermolysis and coagulant was added to the wastewater while at 95°C. In the combined process, only 1250 mg/L of MgCl2 and 1000 mg/L of MgCl2-PEO hybrid polymer were necessary to achieve maximum efficiency, compared to when coagulation-flocculation was carried out on its own. The optimum pH for both coagulants were pH 6. Under these conditions, 98.43% colour removal and 85.93% COD reduction were achieved when MgCl2 was used, while 99.13% colour removal and 91.85% COD reduction were achieved when MgCl2-PEO hybrid polymer was used. When RCB synthetic dye wastewater was subjected to the hybrid process, the maximum colour removal and COD reduction for MgCl2 were 99.21% colour removal and 91.11% COD reduction, while for MgCl2-PEO hybrid polymer, the 99.69% colour removal and 93.33% COD reduction were achieved. In the hybrid process, the required coagulant dosages were further reduced, where only 750 mg/L of both coagulants were required to achieve maximum efficiency. In terms of sludge production, the use of the hybrid polymer in the hybrid process produced the lowest volume of sludge. The efficiency of the hybrid process using the hybrid polymer for the treatment of industrial textile wastewater was also evaluated. By using 750 mg/L of hybrid polymer at pH 6, 99.01% colour removal and 90.86% COD reduction was achieved.
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Keywords
Hybrid technology