Application Of Electro-electrodialysis In Organic Acids Treatment

Organic acids are closely related to human production and life,and are widely used in food,medical and daily chemicals.Phenol is a kind of phenolic organic acid and also one of the common water pollutants.Wastewater containing phenol is released from a broad range of industries,such as coal gasification,tanning,oil refineries,and paint manufacturing,which has pose a crucial threat to the environment and human health.It has been listed as one of the key hazardous wastewaters to be solved.Tartaric acid is a dicarboxylic organic acid,which is widely used in the pharmaceutical,food,electroplating,and tanning industries.At present,the production of tartaric acid is still based on the separation from its salt solution.The traditional separation method of tartaric acid requires to go through precipitation,acidification,ion exchange,concentration and crystallization.The whole process is long and consume a large amount of acid,so it is likely to produce waste liquid pollution.Therefore,it is urgent to find a new technology to separate the organic acids.Electro-electrodialysis(EED)process can be applied to the treatment of organic acids.With a direct electrical potential applied,OH~-generated in the cathode compartment by water splitting and phenol was converted into phenoxide ions.Then it could be remove driven by voltage.For the acidification of tartaric acid,H~+ formed on the surface of anode could complete the acidification of tartrate to tartaric acid.In this paper,the application of EED in the treatment of saline phenol wastewater and tartrate acidification is discussed.The application of EED process for removing phenol in the model wastewater was investigated firstly.The influence of applied voltage,sodium sulfate and phenol concentrations on the separation performance and energy consumption of the EED process was studied.More than 90%of the phenol could be removed by EED process,illustrating the feasibility of this process.The specific energy consumption for phenol removal was primarily influenced by the concentration and characteristics of the competitive anions,such as sulfate and hydroxyl ions in the feed solution.An increase of phenol concentration reduced the specific energy consumption,while a higher salt concentration resulted in higher energy consumption.The EED process is more energy efficient for treating wastewater with low salt concentrations and high phenol concentrations.These results can significantly enhance the application potential of this emerging separation process.The acidification of potassium tartrate to produce tartaric acid through two-chamber EED and three-chamber EED process was compared.The effect of current density on the production of tartaric acid by EED process was studied.The conversion ratio of tartaric acid increased with the increase of current density.The competitive migration of potassium ion and hydroxyl ion through cation-exchange membrane was the key factor affecting the acidification in two-chamber EED process.While the migration of tartrate ion influenced the three-chamber EED process significantly.Three-chamber EED process obtained higher purity and concentration of tartaric acid than the two-chamber EED process.The conversion ratio of tartaric acid reached over 98%after 120 min running at 5 mA/cm~2 in the three-chamber EED process.Owing to their lower resistance of the membrane stack,the specific energy consumption in two-chamber EED process was lower than that of three-chamber EED process.