School of Mechanical Engineering Galit Sasson
School of Mechanical Engineering Seminar
Monday, April 9, 2018 at 14:00
Wolfson Building of Mechanical Engineering, Room 206
Biological NO3- Elimination from Reverse Osmosis Brackish Water Concentrate
Galit Sasson
Student of Prof. Hadas Mamane
Granot reverse osmosis (RO) desalination plant was established as part of the coastal aquifer rehabilitation project. This project aims to remove a natural salinity stain in the aquifer, comprising of chlorides and nitrates, by continuously pumping the saline water. The pumped brackish water is desalinated at Granot resulting in two streams: potable water and concentrated brine. One of the challenges of inland desalination is the terminal solution for brine disposal. At Granot plant the brine is discharged to the sea via a 30 km pipe line. According to Israel oceanographic & limnological research, the disposal of nitrogen rich brine into the Mediterranean Sea shore line, might cause several problems to marine life and sea ecosystem. Therefore, nitrate should be eliminated from the brine before sea disposal. There are many methods to eliminate nitrate but only few remove it terminally. One of these methods is heterotrophic denitrification, a bacterial process done at anoxic condition with an additional carbon source and nitrate as the electron acceptor. Completion of this process results in nitrate transforming to atmospheric nitrogen gas, leaving the treated water. This research is a pilot study aimed to examine the feasibility of denitrification on continuously working Granot RO brine and evaluate process performance and tolerance to possible inhibitors and planned interventions. Six distinctive process performance scenarios were observed throughout the pilot among them, half showed good process performance with complete nitrate and nitrite removal. At the three bad scenarios, complete nitrate removal was depicted yet, nitrite was present at the effluent. All the scenarios ran at lower carbon source (acetic acid) to nitrate ratio (2.1 -2.5 g Ac /g NO3-N) than the theoretical value (3.5 g Ac /g NO3-N). Better denitrification was observed at the higher range of the C:N ratio. Process showed endurance to shutdowns in the RO plant by relatively quick acclimation after reoperation. A sudden slight increase in salinity caused a process deterioration which resolved after the bacteria were acclimated. Dissolved oxygen (DO) concentration above 0.2 g/m3, documented as an inhibition limit, did not shift process from completion. Heterotrophic denitrification was found to be a possible alternative for nitrate elimination from the brine stream.
