Date of Award

3-1998

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Mostafa M Kamal

Second Advisor

Abdel Mageed Kiwan

Third Advisor

Dr. Naeem Akhar Rabi

Abstract

Wastewater reuse has a positive and negative environmental impacts and possibly it can have an important role to play in water resources management, as a substituent for freshwater in irrigation. However, the presence of the toxic heavy metals in domestic sewage and in industrial effluents discharge to sewers, wastewater can create unacceptable health and environmental risks. Therefore, the present work includes the determination of the toxic heavy metals in some treated wastewater samples collected from Abu-Dhabi area using polarographic and voltammetric techniques. Differential pulse polarography and anodic stripping voltammetry are well established techniques for trace determination of heavy metals content of environmental water samples.

The most important regions of application of polarography and voltammetry in chemical analysis today are the trace determination of metal ions particularly in environment analysis e.g. water analysis. The main rival to voltammetric methods for trace metal determination is atomic spectroscopy. With a limit of detection about 5x10-5 and 1x10-5 mol/L for DC- and sampled DC-polarography, respectively. These two polarographic methods are similar in sensitivity to atomic absorption spectroscopy using flames. Differential and normal pulse polarography (DPP and NPP) have limits of detection in the range of 10-7 - 10-6 mol/L which is similar to the flameless atomic absorption spectroscopic methods such as graphite furnace and graphite rod techniques. Stripping voltammetric methods with limits of detection, which can reach as low as 10-10 mol/L can be more sensitive than atomic spectroscopic method Moreover the most important advantage of the voltammetric techniques over the atomic spectroscopic techniques is the ability of the voltammetric techniques to differentiate between the different oxidation states of the metal, and hence give environmentally more relevant information.

The sensitivity of any analytical technique can be greatly increased 1) introducing a preliminary preconcentration step, e.g. solvent extraction. In stripping voltammetry an electrochemical preconcentration technique is used. The analyte is concentrated, from very dilute solutions, by electrolysis to an insoluble product (metal atoms in case of anodic stripping voltammetry) which collects at the electrode surface and can be subsequently determined with a very great sensitivity (anodic oxidation step).

⇋ (1)

Forward process by Preconcentration.

Reverse process by Anodic Oxidation.

The preconcentration or deposition step consists of the controlled electrodeposition, at a fixed potential of the species of interest onto a stationary electrode. This is followed by the determination step which consists of electrolytically oxidation of the deposited species back into solution (equation 1).

In the present investigation the differential pulse polarographic (DPP) and the differential pulse - anodic stripping voltammetric (DP-ASV) methods were applied for trace determination of heavy metals in the treated wastewater (TWW) samples collected from Zakher plant and EI-Mafraq plant at AI-Ain and Abu-Dhabi cities, respectively.

The preliminary check of the our investigated samples of TWW samples using DPP and DP-ASV indicates that the samples contain Zn(II) at 2-3x10-6 mol/L, Cu(II) 2-3x10-7 mol/L, 1x10-7 mol/L Pb(II) and 1x10-7 mol/L Cd(II). Therefore a synthetic solution mixture contains 2.5x10-6 mol/L Zn(II), 2.5x10-7 mol/L Cu(II) and 1x10-7 mol/L of Pb(II) and Cd(II) was prepared. The mixture was subjected to full analysis using DPP and DP-ASP under the selected optimum conditions of determination. The results of analysis indicate that the DPP technique was suitable for Zn(II) determination only, whereas all of the metal ions are determined with higher degree of recovery using DP-ASV. The degree of recoveries of the four metal ions analyzed by DP-ASV were in range of 97-106%. These values were calculated by application of standard addition method using spiking procedures of the synthetic solution mixture with standard metal ion solutions.

DPP and DP-ASV methods were applied for trace determination of heavy metal ions, e.g. Zn(II), Cu(II), Pb(II) and Cd(II) in some TWW samples collected from AI-Ain and Abu-Dhabi TWW plants. Sample I and sample II are collected at May 1996 and November 1996, respectively. The samples under investigation are filtrated, acidified to about pH 3 and stored in polyethylene bottles.

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