The Feasibility of Energy Extraction from Acidic Wastewater by Capacitive Mixing with a Molecular-Sieving Carbon Electrode.

Capacitive mixing is a newly emerging technique for the production of renewable energy from differences in salinity, usually of wastewater streams. The method is based on the controlled mixing of two streams with different salt concentrations, which are alternatingly brought into contact with precharged porous electrodes, thus taking advantage of the fact that modification of the electrical double layer of the electrodes results in changes in the solution salinity. Usually, the renewable energy resources are seawater and river water streams. Here, we demonstrated that electrical energy can be extracted by capacitive mixing of acidic wastewater and seawater. This concept is proven by the use of proton-selective carbon as the cation-capturing electrode, fabricated by carbonization of cellulose filter paper followed by mild activation in concentrated nitric acid. Considerable energy extraction was demonstrated even if the concentration of the NaCl solution was tenfold higher than that of the acidic solution.