Design of household level arsenic treatment system in Cambodia : evaluation of adsorbents in batch adsorption study

• Main Author: Loh, Chun Heng.
• Other Authors: Lim Teik Thye
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/15917
• Institution: Nanyang Technological University

Arsenic (As) has been found to contaminate groundwater in many countries and cause serious health problem around the world, including Cambodia. Hence, there is a need to develop simple, affordable and sustainable techniques in Cambodia for lowering As concentrations in drinking water. In this project, various studies on As removal by adsorbents, especially laterites, were carried out in batch adsorption system. The adsorption of As on different materials from Cambodia is investigated. The results showed high As removal efficiencies by laterites from different locations in Cambodia while As(III) adsorption on the laterites was lower than As(V). Kinetic study demonstrated rapid initial As(V) adsorption followed by slow reaction and it could be best describe with pseudo-second order kinetic model. With adsorbent dose of 5 g/L, the adsorption equilibrium data was well fitted (R2 > 0.9) to both Langmuir and Freundlich isotherms, and the data fitting to Freundlich isotherm was relatively better with R2 of 0.976 and 0.986 for PP Laterite B and AD Laterite, respectively. This confirms the heterogeneous properties of the laterite surface. Maximum As(V) adsorption capacity of both laterites based on Langmuir isotherms was found to be 0.144 mg/g. Experiments were carried out to investigate the effects of potential competitive anions on As(V) adsorption on the laterites. At 0.5 mg/L of As(V), SO42- and Cl-, showed no significant effects on As(V) removal at concentrations of anions as high as 250 mg/L. On the other hand, SiO32-, HCO3 , and humic acid demonstrated significant competitive effects on As(V) removal by the laterites, with decreasing sequence for the strength of competition. The adsorption of these anions, as well as As, may be based on ligand exchange reactions. It was concluded that pretreatment is required to minimize the presence of the competitive anions before the adsorbents are applied in the actual As treatment system.