Experimental Study On EDI Technology Of Heavy Metal Wastewater Treatment

Heavy metal pollution have got more concern, treatment of heavy metal wastewater is becoming stricter, especially for the first class pollutants. Traditional treatment methods of heavy metal wastewater have their advantages, but still there are different degrees of disadvantages like large investment, low effluent quality, prone to secondary pollution, etc., particularly when wastewater concentration is low, restrictions of technology and economy on traditional treatment process lead to difficult purification and recycling simultaneously, it is hard to meet the requirements of wastewater resources. And the current trend of development is how to realize resourceful treatment technology of heavy metal wastewater zero-discharge、 heavy metal recovery and wastewater reuse.Electrodeionization (EDI) is a clean, high-efficient new water treatment technology, which could reuse wastewater via deep remove, recycle heavy metal ions, and then achieve heavy metal wastewater zero-discharge. There are rare reports about the research on EDI treatment of wastewater containing various heavy metal ions. Therefore, this thesis engage in systematic studies on EDI treatment of low concentration wastewater that containing heavy metal.It was using Ni2+and Cr6+heavy metal wastewater to conducted an EDI experiment, improved the EDI device, realized the concentration and recycle of Ni and Cr, and resolved the precipitate of Ni(OH)2. It studied the mechanism of EDI, and the continuous electric regeneration of ion exchange resin produced by H+and OH" ions from water decomposition. Ni2+、Cr6+ions migrate through resin phase、solution phase and membrane phase into concentration chamber by the interaction of potential driving force and concentration difference pressure.It investigated the influence on EDI processing performance from voltage of EDI modules、pH and concentration of Ni2+、Cr6+ions in untreated water, and other operating parameters. There is a suitable voltage range for EDI process which EDI modules could run safely and effectively within it. The higher voltage and severer water decomposition degree, the better removal efficiency of Ni2+、Cr6+ions. When voltage is lower than this range, then electric field driving force is weak and ions removal rate is low, lead to decline of effluent quality; when voltage goes beyond this range, ineffective water decomposition will substantially reduce the current efficiency and increase energy dissipation without significantly enhance ions removal efficiency. A feasible operating voltage can both satisfy the Ni2+、Cr6+expected removal rate and improve its operation economy. Through the experiment, this voltage is set around20V. EDI is proper for low concentration wastewater. When ion concentration is relatively high, there is quite a part of the ions directly migrate across solution phase of ion exchange resin without passing through ion exchange resin phase, this cannot reflect the advantages of EDI deep purification, effluent quality from freshwater compartment will decrease sharply. It was found that the treatment effect is preferable when wastewater Ni2+. Cr6+ion concentration is not more than50mg/L. Wastewater pH has little effect on EDI processing performance. When wastewater pH is lower, ions removal rate increase slightly. While wastewater pH is lower, concentration of H+ions in freshwater compartment is increased, thus enhance the electrical conductivity of solution, and enlarge the current density, add the impetus to ions shift as well, also strengthen regenerative effect from water decomposition and electric, make an minor increase in the treatment effect.This paper researched the characteristics of EDI continuous treatment on heavy metal wastewater. Studies have shown that EDI process can continuous work steadily, Ni2+ion concentration in2#concentration chamber has reached667mg/L, and the concentration multiple is13.3; Cr6+ion concentration in1#concentration chamber is686mg/L and the concentration multiple is13.7. Ni2+、Cr6+ion concentration from effluent is less than0.1mg/L throughout and removal rate is more than99%, there is no penetration of ion exchange resin. EDI continue to work stably in the optimal operating conditions. This shows that EDI can realize heavy metal recycling and wastewater reuse without chemical regenerating resin, realize zero-discharge of heavy metal wastewater. EDI technology is practicable to manage heavy metal wastewater of low concentration.