Sugarcane Biowaste-Derived Biochars as Capacitive Deionization Electrodes for Brackish Water Desalination and Water-Softening Applications

Abstract

The sugarcane ethanol industry is currently generating an intensive amount of biowaste while consuming significant water resources. In this work, sugarcane bagasse fly ash (SCBFA), a major biowaste with high amounts of fixed carbon, is employed as a precursor for activated carbon (SCBFA-AC) production. Here, SCBFA-ACs are valorized as the main component of carbon electrodes employed in capacitive deionization (CDI), an emerging desalination technology. In this way, an abundant and low-cost biowaste could be used as a green alternative to treat the water. Different activation methods of SCBFA were explored obtaining SCBFA-AC with a broad spectrum of structural and chemical properties. The electrochemical characterization of SCBFA-AC showed the positive impact of large surface areas, good combination of micro- and mesopores, and the presence of surface functional groups on specific capacitances (117 F g–1). Subsequently, CDI and membrane CDI experiments showed the importance of ion-exchange membranes on improving charge efficiency values (from 5–30 to 80–95%) and consequently, salt adsorption capacity, SAC, from ≈5 to 22 mg g–1. This SAC value, one of the highest ever obtained with biowaste electrodes, only suffered a slight reduction (19 mg g–1) after 70 CDI cycles. Finally, SCBFA electrodes were successfully tested for water-softening applications, reaching 15 mg g–1 when operating using CaCl2 solutions instead of NaCl. This study represents a great example of the water–energy–food nexus in the framework of the circular economy.

Asymmetric Membrane Capacitive Deionization Using Anion-Exchange Membranes Based on Quaternized Polymer Blends

“…During each adsorption/desorption cycle a conductivity drop is observed during the charging step (1.2 V), followed by an increase in conductivity during short-circuiting (0.0 V). These results are consistent with regeneration profiles found in batch-mode MCDI configurations, 51 , 53 , 54 indicating that membranes can maintain the characteristic desalination performance over repeated cycles. Analogous behavior was observed for the Q0, Q5, and Q10 membranes; shown in Figures S10–S12 , respectively.…”

Food‐processing wastes

“…The use of sugarcane bagasse fly ash (SCBFA) was studied by Lado, Zornitta, Vazquez, Malverdi, and Ruotolo (2019) as a precursor for activated carbon production for treatment of sugarcane ethanol biowaste. SCBFA was found to provide a positive impact of large surface areas, good combination of micro‐ and mesopores, and the presence of surface functional groups on specific capacitances.…”

Theoretical Analysis of Constant Voltage Mode Membrane Capacitive Deionization for Water Softening

“…Capacitive deionization (CDI) removes charged particles in solution by attracting them toward the oppositely charged porous electrodes and temporarily holding them in the electric double layer (EDL) formed near the electrodes’ surface [ 8 , 9 ]. CDI is applicable to water softening due to the preferential electrosorption of divalent hardness ions over monovalent ions [ 10 , 11 ] and the technology has been investigated for softening brackish waters [ 12 , 13 , 14 , 15 , 16 , 17 , 18 ].…”