טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKeisar Itay Moshe
SubjectDenitrification of High Nitrate Concentration in
a Pressurized Hydrogen-Based Reactor
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Green Michal
Dr. Tarre Sheldon
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Intensive use of fertilizers is the main source for groundwater contamination by nitrate (NO3-) observed worldwide. Nitrate concentrations exceeding the Israeli standard of 70 mg/L (16 mg NO3--N/L) is the main reason for closing wells in the coastal aquifer. Physicochemical treatment techniques, such as reverse osmosis, ion exchange and electro-dialysis, are effective techniques for removing nitrates. However, the main disadvantage of all physicochemical treatment techniques is the production of large amounts of waste brine, containing high concentrations of nitrate, chlorides and other ions, with concentrations of up to 10 times that of the source groundwater. Disposal of these concentrates to either the sewerage system or to water bodies is a major problem.

This research investigates a new method to treat brines containing high concentrations of nitrate using biological denitrification, the reduction of nitrate to nitrogen gas. The reactor system presented here is based on an innovative reactor developed at the Technion for typical polluted groundwater ~25 mg NO3--N/L where a closed pressurized vessel for biological denitrification is used with hydrogen gas as the electron donor. The reactor’s main advantages are efficient delivery and usage of hydrogen gas with no need for gas purging resulting from nitrogen gas buildup from denitrification. During continuous operation a gas-liquid equilibrium is established in the reactor according to Henry’s law and excess N2 gas is carried out by the effluent in dissolved form. Since the nitrogen gas pressure that develops in the head-space of a closed reactor is proportional to the nitrate concentration removed during denitrification, applying this technique for wastewaters with high concentrations of nitrate will result in extremely high pressures in the reactor.

In order to overcome this problem, a degassing unit connected to the pressurized reactor via liquid recirculation and open to the atmosphere was investigated. The hypothesis of this research was that enough excess dissolved nitrogen gas would be released to the atmosphere as water recirculated through the degassing unit to prevent nitrogen gas buildup in the reactor.

The research objectives were:

1) Prove the ability of the degassing unit to release enough excess nitrogen to maintain a steady state gas equilibrium in the reactor.

2) Characterize the degassing unit and the mechanisms that govern it.

3) Investigate the parameters and conditions required to achieve steady state.

4) Determine maximal denitrification rates and the limiting conditions in the reactor,

5) Maximize hydrogen utilization and investigate the parameters influencing it.

6) Investigate the influence of salinity on reactor performance and microbial population.

7) Develop a model for determining optimal operational conditions of the system.