Selective adsorption of phosphate by carboxyl-modified activated carbon electrodes for capacitive deionization

Sustained Phosphorus Removal and Enrichment through Off-Flow Desorption in a Reservoir of Membrane Capacitive Deionization

In this study, we used a membrane capacitive deionization device with a reservoir (R-MCDI) to enrich phosphorus (P) from synthetic wastewater. This R-MCDI had two small-volume electrode chambers, and most of the electrolyte was contained in the reservoir, which was circulated along the electrode chambers. Compared with conventional MCDI, R-MCDI exhibited a phosphate removal rate of 0.052 μmol/(cm2·min), approximately double that of MCDI. This was attributed to R-MCDI's utilization of OH- alternative adsorption to remove phosphate from the influent. Noticing that around 73.9% of the removed phosphate was stored in the electrolyte in R-MCDI, we proposed a novel off-flow desorption operation to enrich the removed phosphate in the reservoir. Exciting results from the multicycle experiment (∼8 h) of R-MCDI showed that the PO43--P concentration in the reservoir increased all the way from the initial 152 mg/L to the final 361 mg/L, with the increase in the P charge efficiency from 5.5 to 22.9% and the decrease in the energy consumption from 28.2 to 6.8 kW h/kg P. The P recovery performance of R-MCDI was evaluated by viewing other similar studies, which revealed that R-MCDI in this study achieved superior P enrichment with low energy consumption and that the off-flow desorption proposed here considerably simplified the operation and enabled continuous P enrichment.

Advanced capacitive deionization for ion selective separation: Insights into mechanism over a functional classification

Due to the diversity and variability of harmful ions in polluted water bodies, the selective removal and separation for specific ions is of great significance in water purification and resource processes. Capacitive deionization (CDI), an emerging desalination technology, shows great potential to selectively remove harmful ionic pollutants and further recover valuable ions because of the simple operation and low energy consumption. Researchers have done a lot of work to investigate ion selectivity utilizing CDI, including both theoretical and experimental studies. Nevertheless, in the investigation of selective mechanisms, phenomena where carbon materials exhibit entirely opposite selectivity require further analysis. Furthermore, there is a need to summarize the specific chemical reaction mechanisms, including the formation of hydrogen bonds, complexation reactions, and ligand exchanges, within selective electrodes, which have not been thoroughly examined in detail previously. In order to fill these gaps, in this review, we summarized the recent progress of CDI technologies for ion selective separation, and explored the selective separation mechanism of CDI from three aspects: selective physical adsorption, specific chemical reaction, and the utilization of selective barriers. Additionally, this review analyzes in detail the formation process of chemical bonds and ion conversion pathways when ions interact with electrode materials. Finally, some significant development prospects and challenges were offered for the future selective CDI systems. We believe the review will provide new insights for researchers in the field of ion selective separation.

Emerging electro-driven technologies for phosphorus enrichment and recovery from wastewater: A review

The recovery of phosphorus from wastewater is a critical step in addressing the scarcity of phosphorus resources. Electro-driven technologies for phosphorus enrichment have gathered significant attention due to their inherent advantages, such as mild operating conditions, absence of secondary pollution, and potential integration with other technologies. This study presents a comprehensive review of recent advancements in the field of phosphorus enrichment, with a specific focus on capacitive deionization and electrodialysis technologies. It highlights the underlying principles and effectiveness of electro-driven techniques for phosphorus enrichment while systematically comparing energy consumption, enrichment rate, and concentration factor among different technologies. Furthermore, the study provides a thorough analysis of the capacity of various technologies to selectively enrich phosphorus and proposes several methods and strategies to enhance selectivity. These insights offer valuable guidance for advancing the future development of electrochemical techniques with enhanced efficiency and effectiveness in phosphorus enrichment from wastewater.

(Electro)catalytic oxidation of sulfide and recovery of elemental sulfur from sulfide-laden streams

MnxOy coated over TiO2 nanotube array substrate was doped with Mo and polyaniline (PANI) and applied for electrochemical desulfurization of concentrated sulfide (HS-) solutions at basic pH, typical of biogas scrubbing solutions and industrial wastewater. Mo and PANI co-dopants significantly enhanced the anode activity towards sulfide oxidation and ensured its complete stability even in highly corrosive sulfide solutions (e.g., 200 mM HS-). This was due to the increased electrochemically active surface area, improved coating conductivity and reduced charge transfer resistance. The (electro)catalytic oxidation of HS- demonstrated robust performance with very limited impact of different operational parameters (e.g., dissolved oxygen, anode potential, HS- concentration). Due to the formation of elemental sulfur (S0) layer at the anode surface at basic pH, longer term anode usage requires its periodic removal. Chemical dissolution of S0 with toluene allows its rapid removal without affecting the anode activity, and easy recrystallization and recovery of pure sulfur.