Development and Evaluation of an Electrode for the Capacitive Deionization Unit

Abstract

The existing conventional technologies like Reverse Osmosis, EDI(Electro Deionization), membrane filtration and Ultra Violet filtration offer solutions for drinking water, but various factors like capital and operational cost, ease of operation, maintenance and fouling had been the considerable driving factors to judge the techno-economic paradigm while making a technology selection. Also, the increasing demand for augmenting the safe drinking water calls for novel and sustainable breakthrough technologies. The novel and sustainable technology like Capacitive deionization (CDI) could be a potential alternative which works on electrophoretic phenomenon to provide low TDS (Total Dissolved Solids) drinking water. When water passes between a pair of carbon aerogel electrodes, ionic species are held at the charged electrode surfaces and are removed from the solution during the charging the cycle. After the electrodes become saturated with salts or impurities, the electrodes are regenerated by electrical discharge or polarity reversal, allowing the captured ions to be released into a relatively small purge stream. Thus, CDI can be used to deionize or purify water. An effort is also made to study, evaluate and compare conventional RO technology with Existing CDI technology. Batch ion absorption studies on the newly developed electrodes recorded efficiency with ion removal of 140 ppt using 5 pairs of electrodes (32m 2 area) and the SEM images of the developed electrodes indicated good porosity which in turn illustrates the potential absorption capacity of the developed electrodes. The main factors to be considered while developing an ideal electrode are some of the properties like BET(, electrical conductivity, capacitance, mechanical strength. Correlation studies on the comparison with RO and evaluation of the developed electrodes of the CDI were carried out. I. Introduction The desalination of seawater and brackish groundwater to provide fresh drinking water is an established and thriving industry. Desalinisation refers to any of several processes that removes amount of salt and any other minerals present in the saline water. Salt water is desalinated in order to produce fresh water that is suitable for human consumption or irrigation. The most commonly used technologies at present for the desalination process are Thermal Distillation and Reverse Osmosis (RO) filtration. This report will mainly deal with the research conducted for the development of an ideal electrode which is non-polluting, energy efficient, cost effective and electrically conductive, suitable for an industrial sized capacitive deionisation module. Capacitive Deionisation in other terms can be defined as a powerful desalination module which utilises low-pressure non membrane desalination process. Most of the existing industrial scale desalination centres get their energy from the combustion of fossil fuels, thus in effect exchange potable water for CO2 which causes global warming and eventually contributes to the demise of fresh water. As a result, global warming will lead to increase the need for additional desalination. Therefore, it is imperious to find methods to find desalination of water that are more energy efficient. Thus, electrochemical desalination tools like capacitive deionisation have the potential to be such an energy efficient technology. The main objective of this research is to Evaluate a newly developed electrode for electro adsorption studies and its relevance for CDI technology. Capacitive Deionization technology is evaluated by taking in to consideration factors like construction, operation and maintenance costs to that of reverse osmosis and an head on head evaluation is performed. Taking into consideration brackish type feed water the cost of construction can vary accordingly depending upon various factors. Some of the major factors that influence the design development are:-  Capacity of the water to be treated.  Blending of source water with permeate.  Quality of the feed. (TDS and constituents required removal required)  Concentrate disposal.  Pre and post treatment requirements.