CHAPTER 1 THE PROBLEM
1.1.
INTRODUCTION
Heavy metals such as lead, zinc, copper, can often be found in industrial wastewater and their discharge to the environment poses a serious threat due to their acute toxicity to aquatic and terrestrial life which includes humans. As a result of increasing industrialization more heavy metals are continually released to the environment and this has prompted environmental engineers and scientists to think of better methods by which heavy metalbearing
wastewaters can be treated effectively and economically. The most used way of
removing heavy metals in wastewater is through the use of activated carbon which is used as an adsorbent. This is due to the adsorptive properties of activated carbon(Cecen & Aktas, 2011).
Agricultural by-products represent a considerable quantity of harvested commodity crops. The use of by-products as precursors for the production of widely used adsorbents, such as activated carbons, may impart a value-added component of the overall biomass harvested. In most developing countries, the activated carbon is imported at high cost, limiting the quantities of safe drinking water available to the people (Gray, 2010, p.72).
In recent years, there has been research focusing on the use of appropriate, low cost technology for the treatment of drinking water in the developing world. Research has also been focused on the indigenous production of water treatment chemicals using locally available raw materials. Generally, the raw materials for the production of Activated Carbon are those with high carbon but low inorganic contents such as wood, lignite, peat and coal.
Activated carbons form a large and important class of porous solids, which have found a wide range of technological applications. The characteristics of activated carbon depend on the physical and chemical properties of the precursor as well as on the activation method. In addition to the starting material and the oxidizing agent, activation time and temperature affect the structural properties of the resulting activated carbon (Hassler, 2009).
A wide range of carbonaceous materials can be used as the carbon precursors such as coal, peat, wood and various agricultural by-products. Recently, agricultural by-products have received an increasing attention for the production of activated carbon due to their lowcost, renewability and wide prevalence (March & Reinoso, 2006). The production of valueadded products such as activated carbon will enlarge its application, reduce waste materials and generate income to rural communities in Valenzuela.
Heavy metal contamination exists in aqueous waste streams of many industries such as metal plating facilities, mining operations and tanners. Activated carbons were used as adsorbent materials because of their extended surface area, microporous structure, high adsorption capacity and high degree of surface reactivity. Furthermore, the presence of different surface functional groups on activated carbon, especially oxygen groups, leads to the adsorption of ions of heavy metals (Ilango, 2012, p. 22).
One of the fastest growing research areas is the environmental applications of activated carbon, such as wastewater treatment. In the treatment of wastewater, it is used for purification, decolorization and the removal of toxic organics and heavy metal ions. year Chernicharo and Sperling (2005) stated that the demand of activated carbon increased over the years and the market growth was estimated at 4.6 % per. This demand can be satisfied considering the large number of raw material available for the production of activated carbon (Bansal, & Goyal, 2005). The aim of the study was to produce activated carbon from local agroforestry wastes and assess the efficiency of the produced carbons in removing dyes and metal ions from wastewater.
The researchers decided to use corncobs as the source of activated carbon to be used in the adsorption of heavy metals present in the waters of Manila Bay, this is because corncobs are widely available and inexpensive macromolecular waste in the agriculture in the Philippines. Bandosz (2006) studied the thermochemical reaction between corncob and CA and obtained a modified corncob, which had a large cation exchange capacity than natural corncob.
Chemical analysis of the corncobs showed that it mostly consisted of 38.4%, cellulose; 40.7%, hemicelluloses; and 9.1%, lignin. Modified ground corncobs using either 0.6 M CA or phosphoric acid have improved natural adsorption capacity.
Physical and chemical agents generated by human activities may often have various adverse effects on both aquatic and terrestrial Iife. Lead is an ubiquitous material in the environment and its presence in varying concentrations can be found in diverse locations. The Water Environment Federation (2010) reported that human exposure to lead has harmful effects on kidney, central nervous and reproductive systems.
Air, food and water generally do not usually contain large amounts of lead, however excessive contamination of these natural sources by industrial activities can result in continuous toxic levels of exposure and consequently clinical poisoning (Ilango, 2012). In order to develop poisoning from organic lead, one has to be continuously exposed to concentrations higher than those in the general environment for some week or months. Lead exposure has both acute and chronic effects (Hassler, 2009).
Another pertinent health problem of lead is bioaccumulation or magnification, which may elevate its concentration to toxic levels (Ilango, 2012). National Research Council Canada reported that fish could absorb lead through their body surface and the food they consume. As a case study the liver of sea bass caught near California Coast at Los Angeles was found to contain about 22 ppm Pb which is considerably higher than the permitted level of 10 ppm for human consumption and twice as high as the concentration in fishes found 300 km away; the major* of the lead was attributed to automotive aerosol (Bandosz 2006).
