The potential of tropical fruit peels as ion exchangers for water hardness removal

Abstract

The presence of high amount of mineral compounds such as calcium (Ca2+) and magnesium (Mg2+) in water attributed to occurrence of water hardness. Hard water causes lime scale in the kettle when boiling, and forms reddish brown stains on the clothes after washing. This study was carried out to investigate peels of durian, jackfruit and passion fruit as a potential cation exchanger for water hardness removal determining by EDTA titration. A synthetic hard water of 714.05 mg CaCO3/L was prepared to evaluate the removal efficiency of cation exchangers prepared from raw and sodium hydroxide-citric acid (NaOH-CA) modified fruit peels for 30 min, 60 min, and 90 min contact times. Results showed that raw peel of durian had the highest (p ≤ 0.05) efficiency (24%) for water hardness removal followed by jackfruit (21.87%) and passion fruit (6.5%). This was because the total cellulose content in durian peel powder and fibre was higher as compared to jackfruit peel and passion fruit peel. Hydroxyl group in the cellulose was the main group responsible in ion exchange with Ca2+ and Mg2+ for water hardness removal. For NaOH-CA modified peels, jackfruit demonstrated the highest (p ≤ 0.05) water hardness removal efficiency (62.05%) as compared to passion fruit (29.63%) and durian (10.42%) for 90 min contact time. This phenomenon can be explained by citric acid anhydride produced from esterification. Citric acid anhydride produced was combined with hydroxyl groups of cellulose and hemicellulose and formed the ester linkage and increased the number of carboxylate groups on the ion exchange surface. Result showed that water retention capacity is directly proportional to water hardness removal efficiency for modified fruit peels (R2 = 0.8181). This evidence that water retention capacity of lignocellulosic material is a good indicator of cross-linking which has a direct effect on ion exchange capability. Both raw durian peel and NaOH-CA modified jackfruit peel showed great ability in water hardness removal, hence the cost of chemicals involved in modification has to be considered for a good recommendation as great potential lignocellulosic material to be used for water hardness removal.