טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBen-Dov Tali
SubjectDevelopment of an Electrochemical Process for Regeneration
of Ion Exchange Resins Used for Ammonia Removal in
Industrial Processes
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Ori Lahav
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Ion exchangers are extensively used in industrial processes such as water softening, boron removal within seawater desalination, and removal of ionic species from polluted drinking waters. The main disadvantage of ion-exchange based processes is associated with the need to treat and dispose-of the brine, i.e. the exhausted regeneration solution. This brine is characterized by a high concentration of the removed ion, as well as by a high background counter ion concentration. For example, the brine of the regeneration solution of ammonium (NH4) ion-exchange removal applications contains a high concentration of ammonia, in addition to one (and sometimes even two) orders of magnitude higher sodium ion concentration. Before discharging the brine or when reuse of the regeneration solution is considered, the ammonia must be oxidized to an environmentally-friendly product which is also inert towards the ion exchange process. The common treatment for removing ammonia from brines is biological treatment, which has multiple disadvantages. In this study a different alternative, based on electrochemical oxidation of ammonia directly to nitrogen gas, was examined. This method is appropriate for a wide range of pH values, temperature and ammonia loads. Additionally, the performance of the electrochemical process is insensitive to fluctuations in the ammonia influent concentration, it does not require a start-up period and can be switched on and off at will, which makes it ideal for usage during low electricity (hourly) costs. After the ammonia is electrochemically oxidized the brine can be, in principle, reused as a regeneration solution for many cycles. This study focused on the effects of reusing the regeneration solution on the ion exchange performance (ammonia breakthrough curves and ammonia removal efficiency) and on the electrochemical process. Several alternatives were examined in the work in purpose to allow prolonged reuse of the regeneration solution following the electrochemical oxidation step. One tested alternative was aggressive chemical regeneration of the ion exchanger using a 2N NaCl solution. Another alternative was to replace the ion exchanger and sell it as a fertilizer. A third suggested alternative was to pass the regeneration solution through a NF membrane. The last alternative tested was to use seawater as a single-time regeneration solution and after electrochemical oxidation release it back to the sea. Operational costs associated with all the alternatives were estimated. The second part of the work focused on a case study of a regeneration solution used for removing ammonia from boiler feed water in the petrochemical industry.