A study of heavy metal rejection by forward osmosis

Abstract

This dissertation studies the feasibility and efficiency of utilizing forward osmosis membrane technology to treat heavy metal contaminated water. Arsenic is selected to be the target heavy metal. The evaluation of forward osmosis(FO)process efficiency is based on two important membrane parameters, which are water flux and rejection rate. Water flux is the indicator of production rate or treatment efficiency in quantity aspect. Rejection rate represents the product water quality in terms of the percentage of target heavy metal rejected by the membrane. The major objective of this dissertation is to find optimal draw solution and membrane type to achieve maximum arsenic removal efficiency (rejection rate), at the same time, maintain high water flux.

Several sub-projects with individual experiment are derived from the main objective to test out the performance of different membranes and draw solutions. The relationship between draw solution concentration and water flux is analyzed as well. Cellulose triacetate (CTA) membrane and thin film composite (TFC) membrane as two types of commonly available polymer membrane are used for the experiments. In total, four types of inorganic and organic solutes are included in the comparison of draw solution performance. Lab-scale FO system and one unit of membrane module are adopted for conducting the experiments.

The result shows that using sodium chloride as draw solution and TFC membrane yields the largest flux. For the aspect of rejection rate, both CTA membrane and TFC membrane can reach almost 100% treatment efficiency. The rejection rates obtained in this study fall in the range of 96.7% to 99.9%. The results of this study proved that forward osmosis membrane process has the potential of industrial application in treating heavy metal contaminated water such as industrial wastewater and landfill leachate.