Efficient desalination system for brackish water incorporating biomass-derived porous material

• With the green motive to re-use agro-waste, the walnut shell powder was calcined (WSAC). • Surface modifications of WSAC was done to explore the desalting RO Reject. • FeCu@Nanoparticles electrodes revealed the best desalination performance with 89.8% removal. • The economics of the system was evaluated revealing the least energy consumed system of 0.5 kWh m −3 . • Treating real RO reject samples from commercial and domestic drinking water systems and groundwater sample. Capacitive deionization (CDI) is a recent advancement to monitor massive reverse osmosis (RO) reject concentrate. With the conventional material activated carbon developed from biomass, surface modifications and composite materials have improved surface properties. Therefore, with the green motive to re-use agro-waste, the walnut shell powder was calcined (WSAC), which was modified with potassium hydroxide (K-WSAC), incorporated with iron nanoparticles (Fe@Nanoparticle) and iron-copper nanoparticles (FeCu@Nanoparticle) for fabricating CDI electrodes. Developed electrodes were electrochemically characterized, revealing the specific capacitance of 97.5 F/g and implemented for deionizing the RO concentrate. The FeCu@Nanoparticles electrodes showed the best desalination performance of 89.8% removal with an initial concentration of 1000 ppm at an electro-sorption time of 20 min exhibiting a salt sorption rate of 1.21 mg/g min. The economics of the system was evaluated, revealing the least energy consumed system of 0.5 kWh m −3 . FeCu@Nanoparticles electrodes were implemented to treat real samples from commercial and domestic drinking water systems and groundwater samples, resulting in positive outcomes. Therefore, the investigation revealed that WSAC based electrodes resulted in the development of an excellent desalination system.