ABSTRACT
Abstract .......................................................................................................................................... 128 5.1 Heavy Metals ........................................................................................................................ 128
5.1.1 Chromium ................................................................................................................. 128 5.1.2 Copper....................................................................................................................... 130 5.1.3 Cadmium .................................................................................................................. 130
5.2 Treatment of Heavy Metals .................................................................................................. 131 5.2.1 Chemical Precipitation ............................................................................................. 131 5.2.2 Ion Exchange ............................................................................................................ 133 5.2.3 Membrane System .................................................................................................... 135 5.2.4 Adsorption ................................................................................................................ 136 5.2.5 Biosorption ................................................................................................................ 137
5.3 Application of Low-Cost Adsorbents for Heavy Metals Removal ....................................... 141 5.3.1 Fly Ash ...................................................................................................................... 141 5.3.2 Rice Husk .................................................................................................................. 146 5.3.3 Wheat Straw and Wheat Bran .................................................................................. 154 5.3.4 Chitin, Chitosan, and Chitosan Composites ............................................................. 154 5.3.5 Algae ......................................................................................................................... 155 5.3.6 Bacteria ..................................................................................................................... 157
5.4 Chemical Properties and Characterization Studies .............................................................. 157 5.5 Inuence of Operational Parameters .................................................................................... 158
5.5.1 Effect of pH .............................................................................................................. 158 5.5.2 Effect of Initial Concentration of Heavy Metals and Contact Time ........................ 158 5.5.3 Effect of the Chelator ................................................................................................ 159
5.6Experimental Methods and Modeling of Heavy Metals Adsorption ................................... 159 5.6.1 Batch Adsorption Experiments ................................................................................. 159 5.6.2 Equilibrium Modeling of Biosorption in a Batch System ........................................ 159
5.6.2.1 Two-Parameter Isotherms .......................................................................... 160 5.6.2.2 Three-Parameter Isotherms ....................................................................... 165
5.6.3 Kinetic Modeling of Biosorption in a Batch System ................................................ 167 5.6.3.1 Intraparticle Diffussion Model .................................................................. 168 5.6.3.2 Pseudo-First-Order Kinetic Model ............................................................ 168 5.6.3.3 Pseudo-Second-Order Kinetic Model ........................................................ 169
5.6.4 Continuous Packed-Bed System in the Biosorption of Heavy Metals ..................... 170 5.6.4.1 Adams-Bohart Model................................................................................ 171 5.6.4.2 Bed Depth-Service Time Model ............................................................... 171
Owing to the environmental impact as well as the growing awareness among the public, it is imperative to remove or reduce the concentration of heavy metals to environmentally acceptable levels before being discharged to open stream. The conventional methods for removing heavy metals suffer from many drawbacks such as high cost, sludge disposal problem, complex technology, and limited applicability. Therefore, intensive research has been carried out using low-cost materials to remove these heavy metals at an affordable cost. This chapter examines (i) some commonly found heavy metals in wastewater, (ii) main treatment technologies and their limitations, (iii) various studies using waste materials from agriculture and industry or naturally occurring biosorbents, (iv) chemical properties and characterization studies on the low-cost adsorbents, (v) inuential parameters in affecting the removal efciency, and (vi) equilibrium, kinetic models, and process design used in the adsorption process.
