Experimental investigation for treating the RO reject stream through capacitive deionization

Reverse osmosis is the paramount technology substantially contributing to meet the worldwide demand of drinking water with major challenge of reject disposal. Out of several RO reject treatment approaches, capacitive deionization can offer a viable alternative to treat concentrated streams, via application of small voltage (1.0 V) to the fabricated simple wire shaped electrodes coated with micro-porous material. Electrochemical analysis revealed a potentially high specific capacitance of 176.75F/g and a resistance of 4.87 Ω. Influence of initial concentration (500–2500 mg/L), electro sorption time (10–60 min), and stacking (1–5) of the electrodes was observed over the performance of the system to develop optimal parameters in a batch mode via Box-Behnken design. It was analysed that the fabricated electrodes possess maximum sorption capability of 35 mg/g fitting well with R2 value of 0.99 and second order rate kinetics was well fitted. The mechanism for the same was delineated highlighting electrostatic attractions. Moreover, the application of the system was explored by treating the reject from domestic RO systems and high TDS ground water samples. It was observed that monovalent ions had relatively lesser selectivity to the electrode surface as compared to the divalent ions.