Study of the Removal Efficiency of Chromium Ions Using a Membrane by Electro-Kinetic Technique from Sludge

Recently, electro-kinetic (EK) remediation has become more popular as a novel method for removing chromium contamination from soil. This approach, however, is ineffective since it uses both cationic and anionic forms of chromium. In this study, a membrane-based technique was employed to increase the efficiency of the electro-kinetic removal of chromium. Chromium removal from polluted sludge was studied using four bench-scale experiments. Two of these experiments employed distilled water (EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>1 and EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>2 and membrane), whereas the other used acetic acid as the catholyte (EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>3 and EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>4 and membrane). The pH, total chromium, and fractionation of chromium in the sludge were measured after remediation. In the EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>1, EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>2 and membrane, and EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>3 and EK<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo></mrow></semantics></math></inline-formula>4 and membrane trials, the average removal efficiencies of total chromium were 47.6%, 58.6%, and 74.4%, 79.6%, respectively. In contrast to the electro-kinetic remediation strategy, which left approximately 80% of the sludge neutral or alkaline after treatment, the membrane created acidic soil conditions throughout the sludge. For example, the high field intensity used in the membrane tests may have helped to facilitate chromium desorption, dissolution, and separation from the sludge and enhanced chromium mobility. The findings show that the membrane can improve the effectiveness of chromium removal from sludge when utilized in the EK remediation process.