Biomass based activated carbon electrodes for capacitative deionization in the context of nitrate and phosphate removal

Abstract

Capacitative deionization (CDI) technique is widely pursued for the removal and recovery of ionic contaminants from wastewater, as it does not leave secondary waste and can operate at low voltages < 1.2V vs. reversible hydrogen electrode (RHE) (Suss, 2015; Pastushok, 2019; Ge, 2018). Most studies in literature concentrate on desalination, however the removal of other ionic contaminants like nitrates, phosphates, sulphates, chlorides, and fluoride are also explored (Zhang, 2022; Zhang, 2023; Chen, 2022; Martinez-Vargas, 2022). In a previous work (Krishnamurthy, 2022), carbon-based electrodes were made from pine-based biomass and these electrodes were tested for their electrochemical properties, through a series of complementary experimental methods. The goal of the present work is to perform a techno-economic analysis (TEA) for the removal of ionic nitrate (NO3–) and phosphate (H2PO4–) contaminants from wastewater using the electrochemical properties. The basis for the design was the removal of nitrates and phosphates from a wastewater stream available at a flowrate of 44l/s and an initial nitrate and phosphate concentration of 1 mM. The final concentration was fixed to be 0.1 mM after the removal of the ionic contaminants. The TEA was based on the information obtained from the characterization of the electrodes. The results showed that CDI process was economical for nitrate removal compared to that of the phosphate removal due to the higher capacitance value. Sensitivity analysis was further performed to evaluate the effect of the capacitance, the electrode replacement and the outlet concentration on the capital and the operating expenditure values.