Removal and recovery of copper(II) ions from industrial wastewater by bacteria isolated from activated sludge

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Removal and recovery of copper(II) ions from industrial wastewater by bacteria isolated from activated sludge

 

Author: Wong, Mui-fong
Title: Removal and recovery of copper(II) ions from industrial wastewater by bacteria isolated from activated sludge
Degree: M.Phil.
Year: 2001
Subject: Sewage -- Purification -- Activated sludge process
Factory and trade waste
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Structural Engineering
Pages: xv, 140 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1578431
URI: http://theses.lib.polyu.edu.hk/handle/200/5311
Abstract: Studies were conducted to investigate the removal and recovery of copper (II) ions from aqueous solutions by Micrococcus sp., which was isolated from a local activated sludge process. The kinetics of biosorptive removal of copper by the cells was relatively fast with 75% of the final value attained within the first 3 minutes of contact. The equilibrium of copper biosorption followed the Langmuir isotherm model very well with maximum biosorption capacity (qmax) reaching 36.5 mg Cu2+ / g dry cell at pH 5 and 52.1 mg Cu2+/ g dry cell at pH 6. Cells harvested at exponential growth phase and stationary phase showed similar biosorption characteristics for copper. Biomass prewashed with sulphuric acid (0.05 M) and sodium sulphate (1 M) solutions were shown to increase the copper removal capabilities up to 27% and 16%, respectively. Copper uptake by cells was negligible at pH 2 and then increased rapidly with increasing pH until pH 6.In multimetal systems, Micrococcus sp. exhibited preferential biosorption order: Cu2+~ Pb2+> Ni2+~ Zn2+. The presence of Cl-, SO4 2- and NO3- anions (0~500 mg/L) did not interfere with copper uptake by Micrococcus sp. Sulphuric acid (0.05 M) was the most efficient desorption medium recovering 99% of the initial copper sorbed, while the DDI water control demonstrated no copper desorption. When the volume ratio of the sulphuric acid (0.05 M) in desorption to that of copper solution (50 mg Cu2+/ L) in biosorption was 10 / 50, the recovery percentage was found to reach more than 90%. The kinetics of copper desorption from the loaded biomass by the acid was very rapid, with more than 90% of copper desorbed within the first 2 minutes of contact. Desorption equilibrium was attained at about 45 minutes. The copper capacity of Micrococcus sp. remained unchanged after five successive biosorption and desorprion cycles. Immobilization of Micrococcus sp. in 2% calcium alginate and 10% polyacrylamide gel beads exhibited higher maximum removal capacity (qmax) when compared with freely suspended cells. When the immobilized Micrococcus sp. was employed to remove copper (II) ions from industrial wastewater, no significant difference could be observed between the performance for treating real industrial wastewater and that for treating pure copper solution. Also, the final effluent of each cycle could be maintained at a low level of copper concentration with only a minimum amount of desorbing agent used. The immobilized cell system is a promising technology to remove and recover copper from metal-bearing industrial wastewater. A preliminary study on the copper sequestering mechanisms by Micrococcus sp. was carried out using instrumental techniques such as infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray energy dispersion analysis (EDAX). The infrared spectra of the biornass confirmed the presence of carboxyl or thiocarbonyl, phosphate, amine and amide groups on the biomass surface. Carboxyl group (C=O) was believed to be involved in the copper biosorption. The results of EDAX revealed that sodium and potassium ions were more abundant than magnesium and calcium ions on the cell surface of Mierococcus sp. In the experiment of the release of light ions, the presence of copper ions in biomass suspension increased the extraction of light ions from the biomass. This result was also confirmed by the EDAX spectra, which displayed the increase in the amount of copper with the decrease of the amount of potassium and sodium on the biomass surface after exposure to copper solution. The facts obtained revealed ion exchange may be associated with copper biosorption. With the ratio of the amount of copper bound to the total amount of light ions released higher than unity, ion exchange mechanism was believed not to be the only mechanism responsible for copper binding. Other copper uptake mechanisms, such as complexation, coordination, chelation, physical adsorption, inorganic microprecipitation and/or mineral nucleation might be involved in the metal removal processes.

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