Thesis Abstract

Thesis Overview

<p> </p><p>1.0 Introduction<br>1.1 Background of the Study<br>The presence of trace heavy metals in natural water has aroused the interest of many Nigerian<br>scientists as a result of their environmental effects on the health of both plants and animals. More<br>so, concerns about environmental protection has increased due to the technology1 development<br>which keeps on changing, producing industrial product, as well as waste. Manufacturing<br>industries have played an important role for economic growth in major countries. This sector<br>provides services and product for better way and quality of life. However, rapid change in<br>industrialization produces vast amount of waste and will cause harm and deterioration of the<br>environment and ecosystem if improperly managed. Pollutants from textiles industry was<br>declared as one of the major sources of wastewater in Asian country1 as it is considered as<br>possible carcinogenic or mutagen. Apart from that, heavy metals such as cadmium, chromium,<br>lead, copper, manganese, zinc as well as mercury and nickel are widely discharged in the<br>wastewater from industries and are very toxic and harmful to living organisms by lowering the<br>reproductive success, preventing proper growth and even causing death2. Some of the heavy<br>metals are important for our body requirement; however exceeding the tolerance limit may create<br>harm to body functions.<br>The most toxic heavy metals are Cd, Pb and Hg ions due to their high attraction for sulphur<br>which will disturb enzyme function by forming bon d with sulphur. The ions will hinder the<br>transport process through the cell wall, thereby disturbing the cell function. Other pollutants<br>from the industries are phenol; from refineries, petrochemical wastewater, pulp mills and coal<br>mines. Presence of phenols in water bodies caused carbolic odor to receiving water bodies, thus<br>causing toxic effects on aquatic flora and fauna3. Apart from that it is also toxic to humans and<br>affects several biochemical functions4.<br>Unlike organic pollutants, heavy metals do not biodegrade and thus, pose a different kind of<br>challenge for remediation. To alleviate the problem of water pollution by heavy metals, various<br>2<br>methods have been used to remove them from waste water such as chemical precipitation,<br>coagulation, floatation, adsorption, ion exchange, reverse osmosis and electrodialysis5-7. The<br>production of the sludge in the precipitation methods poses challenges in handling treatment and<br>hand filling of the solid sludge. Ion exchange usually requires a high – capital investment for the<br>equipment as well as high operational cost. Electrolysis allows the removal of metal ions with<br>the advantage that there is no need for additional chemicals and also there is no sludge<br>generation. However, it is inefficient at a low metal concentration. Membrane processes such as<br>reverse osmosis and electrodialysis tend to suffer from the in-stability of the membranes in salty<br>or acidic conditions and fouling by inorganic and organic substances present in waste water8.<br>Most of these techniques have some pretreatments and additional treatments. In addition, some<br>of them are less effective and require high cost9.<br>It was only in the 1990s that a new scientific area, biosorption was developed that could help in<br>the recovery of heavy metals. The first reports described how abundant biological materials<br>could be used to remove, at very low cost, even small amounts of toxic heavy metals from<br>industrial effluents9-11. Metal-sequestering properties of non-viable microbial biomass provide a<br>basis for the removal of heavy metals when they occur at low concentrations9. Therefore, many<br>researchers have applied regenerated wastes to treat heavy metals from aqueous solutions.<br>The main objective of the method is to treat the wastewater before discharging to water source,<br>thus decreasing the threat and deterioration to the environment and promising better<br>sustainability of the environment. There are many technologies that have been developed for<br>purification and treatment of waste water including chemical precipitation, solvent extraction,<br>oxidation, reduction, dialysis/electro dialysis, electrolytic extraction, reverse osmosis, ionexchange,<br>evaporation, cementation, dilution, adsorption, filtration, floatation, air stripping,<br>steam stripping, flocculation, sedimentation and soil flushing/washing chelation12. The selection<br>technologies must be analyzed accordingly based on several factors such as available space for<br>construction of treatment facilities, ability of process equipment, limitation of waste disposal,<br>desired final water quality and cost of operation. Mostly, all the technologies listed above are<br>less likely to be selected because they required large financial input and their applications are<br>limited due to the associated cost factors. Adsorption process is found to be the most suitable<br>3<br>technique to remove pollutants from wastewater. It is mostly preferred due to its convenience,<br>ease of operation and simplicity of design. Apart from removing many types of pollutants, it also<br>has wide application in water pollution control. Activated carbon (AC) is widely used as<br>absorbent due to its high surface area and pore volume as well as inert properties. However,<br>conventional AC is expensive due to the depletion of coal-based source and especially for<br>producing high quality AC13.<br>To counter the high cost of AC, low cost precursors have been of high interest for researchers to<br>replace the conventional AC. The factors affecting substitution of raw material are high carbon<br>content, low inorganic content, high density and sufficient volatile content, stability of supply in<br>the countries, potential extent of activation and inexpensive material6. The AC is mainly<br>comprised of carbon with large surface area, large pore volume and porosity where the<br>adsorptions take place.<br>There are some reviews reporting the use of coconut and palm shell for the production of AC14;<br>however such studies are restricted to either type of wastes, preparation procedures, or specific<br>aqueous-phase applications. But, due to the abundant source of precursors, with high volatile,<br>carbon contents, and hardness; coconut shells are an excellent raw material source to produce<br>activated carbon suitable to replace conventional AC14. Moreover, this can be said to be,<br>“substitution of waste to wealth”. The adsorption capacity of the adsorbent could be improved by<br>its modification. This is because; the functional groups on the surface of the AC could be<br>improved by modification with a ligand that has electron donating groups like hydroxyl group,<br>amide group, etc.<br>It is the aim of the research to adsorb Pd2+, Cd2+ and Ni2+ from waste water sample on locally<br>prepared activated charcoal from coconut shell modified with an azo ligand; 1,2 –dihydro -1,5-<br>dimethyl-2-phenyl-4-(E)- (2,3,4-trihydrophenyl)-3H-pyrazol-3-one (DDPTP).<br>4<br>1.2. Statement of the Problem<br>i. In a developing country, the technology development keeps on changing, producing<br>industrial product, as well as waste. Also, rapid growth in industry produces vast amount<br>of waste and causes harm and deterioration of the environment and ecosystem.<br>ii. These wastes enter the water body to cause water pollution and therefore must be treated<br>before it is used domestically or otherwise.<br>iii. Many techniques have been employed for this treatment but they are less likely to be<br>selected because they required large financial input and their applications are limited due<br>to the associated cost factors.<br>iv. Adsorption process is found to be the most suitable technique to remove pollutants from<br>wastewater due to its convenience, ease of operation and simplicity of design.<br>Conventional AC could not see to that because it is expensive due to the depletion of<br>coal-based source and especially for producing high quality AC13.<br>v. Many industries and individuals discard coconut shell as wastes and this local agricultural<br>waste could cause environmental nuisance.<br>vi. Coconut shell has been used for the production activated carbon but the modification of<br>this adsorbent made from coconut shell with a ligand has not been executed.<br>1.3. The Justification of the Research<br>The world production of AC in 1990 was estimated to be 375,000 ton, excluding what was then<br>Eastern Europe and also China. In 2002, the demand for activated carbon reached 200,000 ton<br>per year in United States. The demands for AC were increased over the years from 2003 and<br>market growth was estimated at 4.6 % per year. The strong market position held by AC relates to<br>their unique properties and low cost compared with that of possible competitive inorganic<br>adsorbents like zeolites6. AC is used primarily as an adsorbent to remove organic compounds<br>and pollutant from liquid and gas streams. The market has been increasing constantly as a<br>consequence of environmental issues, especially water and air purification. Furthermore, as more<br>and more countries are becoming industrialized, the need for activated carbon to comply with<br>environmental regulation will grow at faster rate. Liquid phase applications represent the largest<br>5<br>outlet for AC. In these applications, AC is used in the purification of a variety of liquid streams,<br>such as those used in water and the processing of food, beverages and pharmaceuticals. The<br>growth of the activated carbon market in the last two decades in the most industrialized region<br>will very probably continue in the near future as more developing areas of the world will realized<br>the importance of controlling water and air pollution. This demand can be satisfied considering<br>the large number of raw material available for the production of AC, the variety of activation<br>processes described, and the available forms of AC6. This is why we ventured into the<br>modification of coconut shell activated carbon to study its potential in controlling water<br>treatment.<br>1.4. Aims and Objectives of the Research<br>The aim of this research is to investigate the sorption capacity of modified coconut shell<br>activated carbon (MCSAC) for the removal of Pb2+, Cd2+ and Ni2+ from polluted water. The<br>charcoal was activated with an activating agent (CaCO3) and modified with an azo ligand; 1,2<br>dihydro-1,5-dimethy1-2phenyl-4-(E)–(2,3,4-trihydroxyphenyl)–3H-pyrazol-3-one (DDPTP) in<br>order to improve its adsorption capacity and used to adsorb trace heavy metals; Cd2+, Pb2+, and<br>Ni2+ from synthetic water sample. To achieve these, studies were carried out with the following<br>objectives:<br>I. Production of activation carbon from coconut shell using calcium carbonate as the<br>activating agent.<br>II. Modification of the coconut shell activated carbon with an azo ligand: 1,2-dihydro-<br>1,5-dimethyl-2-phenyl-4-(E)-(2,3,4-trihydroxylphenyl)-3H-pyrazol-3-one (DDPTP).<br>III. Evaluation of the adsorption potentials of the adsorbent with respect to Pb2+, Cd2+ and<br>Ni2+.<br>IV. Evaluation of the influences of the analytical parameters like pH, temperature of<br>carbonization, equilibration time(contact time), initial concentration of the metal ions,<br>ligand amount, particle sizes, degree of treatment of adsorbent.<br>V. To study the adsorption isotherms and adsorption kinetics of the adsorption process.</p><p>&nbsp;</p> <br><p></p>