|M.Sc Student||Amara Ronza|
|Subject||Complementary Treatment for Ion Exchange and Bioregeneration|
System to Remove Nitrates from
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Michal Green|
|Dr. Sheldon Tarre|
|Full Thesis text - in Hebrew|
The rehabilitation of nitrate-contaminated wells is essential to increase limited water resources. Treating these wells with well-known physico-chemical methods is problematic due to the stricter regulations regarding discharge of brines from such processes to sewers. This study investigates a combined physico-chemical/biological system for nitrate removal with minimal brine waste. The system consists of ion exchange for removal of nitrate and biological denitrification to regenerate the spent brine carried out in a sequential batch reactor. The proposed research work is focused on reducing the organic matter in the regenerant by post-treatment in order to achieve long-term sustainable system operation.
Residual DOM can cause problems of bacterial regrowth in ion exchange columns, bacterial contamination in the product water, and can react with disinfectants to form harmful disinfection by-products. This study will investigate two alternatives for post-treatment: 1) Membrane bio-reactor with granular activated carbon, and 2) ozonation with bio-granular activated carbon.
The first alternative treatment worked under conditions of pH=9.5 since the release of alkalinity in SBR due to denitrification without pH adjustment. pH adjustment was not made to maximize chemical precipitation in the SBR to reduce the potential of membrane fouling in MBR. In the second alternative, the SBR was corrected to pH=8, since this alternative did not include membrane filtration and lower pH is generally recognized as more effective for ozonation.
Results: The product water quality matched the drinking water standards with nitrate concentration (less than 10ppm), zero turbidity and (DOC 1-2ppm). Denitrification of the brine regenerant in SBR was shown to be completed within 6-8 hours. The DOC concentration of the SBR effluent was 100ppm, turbidity (600nm) varied according to the two alternative treatment schemes, 1)turbidity of 0.35 (MBR), 2)turbidity less than 0.1 (ozonation). This was evident in SBR effluent TSS and VSS values that were between 20 and 40ppm in the first alternative and 20ppm in the second one.
Ozonation was found to significantly improve turbidity of the regenerant brine to nearly zero as in the MBR, but DOC and TSS remained the same. Denitrified regenerant brine VSS was lower, oxidized by ozonation. This changed the effluent’s physico-chemical characteristics generating a small amount of foam easily removed from the ozonation reactor. TSS and DOC values were similar for the two alternatives (50ppm to DOC, 20-40ppm TSS). In contrast to ozonation, solids and larger dissolved matter accumulated in the MBR reactor (150 liters), resulting in higher brine waste volumes, frequent clogging of the membranes and the lack of reliability of the system.
In summary, ozonation combined with BGAC allows for system operation without constant supervision with minimal brine waste. However, there is potential for growth of bacteria in the ion exchange columns and contamination of the product water, due to residual DOC and the presence of bacteria in the BGAC reactor. This requires careful IX column disinfection between service and regeneration cycles to ensure process safety.