Adsorption-electrocoagulation process for removal reactive black 5 DYE from aqueous solution / Mook Wei Tze

Mook, Wei Tze (2018) Adsorption-electrocoagulation process for removal reactive black 5 DYE from aqueous solution / Mook Wei Tze. PhD thesis, University of Malaya.

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Abstract

In recent years, a significant amount of residual dye can be found in textile industry wastewater produced from the dyeing rinsing process. The excessive amount of reactive dye discharged into receiving bodies is dangerous and it can threaten the aquatic environment and human health. In this work, combined process of adsorption and electrocoagulation was developed to treat Reactive Black 5 dye (RB5) from aqueous solution. The activated carbon derived from biomass waste, namely commercialise palm shell was evaluated as a potential adsorbent for the removal of RB5. The equilibrium isotherms and the kinetics of the adsorption process were investigated. Adsorption tests were conducted to determine the effects of various parameters, such as contact time, RB5 concentration, temperature, initial solution pH, adsorbent dose and the presence of coexisting anion, on the treatment performance. The Langmuir model provided the best fit for the obtained equilibrium isotherm data, while the adsorption kinetics was best represented by the pseudo-first-order model. The adsorption capacity of the adsorbent used in the study was higher in acidic medium. The activation energy of RB5 adsorption was 12.619 kJ/mol. The maximum adsorption capacity of the adsorbent was 25.12 mg/g at pH 2. Commercial palm shell activated carbon is shown to have great potential in the adsorption of RB5 from aqueous solution. In the second part of the study, a novel anode configuration consisting of a double layer iron mesh is proposed for the electrocoagulation treatment of wastewater. At a constant anode surface area and identical process operating parameters, the double layer iron mesh electrode showed better performance compared with the single layer iron mesh in terms of RB5 and COD removal efficiency, the kinetic rate constant, diffusion coefficient and electrical energy consumption. Besides that, the effect of various parameters such as pH of the solution, current density, supporting electrolyte and electrocoagulation time was investigated. A new approach of combined adsorption and electrocoagulation processes (A-EC) in a single setup was introduced. The effects of initial pH, current density, adsorbent dose and initial RB5 concentration in the combined process were investigated. The A-EC showed great potential to treat higher dye concentration as compared with the individual adsorption and electrocoagulation. Response Surface Methodology (RSM) was used as a computing tool for analysing the data and predict the optimum conditions that maximize the RB5 removal. The application of optimum conditions of combined process, i.e. initial pH of 6.17, an adsorbent dose of 15.04 g/L, a current density of 2.03 mA/cm2 and a process time of 57.18 min, resulted in RB5 and COD removal efficiency of 97.2% and 86.8%, respectively. The A-EC gave the best performance in the subject of RB5 and COD removal efficiency, the kinetic rate constant, sludge volume, electrical energy consumption, and operating costs. The GC-MS results show that no aromatic compounds found in the final effluent after A-EC treatment. The RB5 compound was completely decomposed and transformed into a heterocyclic compound with smaller molecular size. Additionally, the XRD patterns indicated that the iron complexes were found in the sludge.

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