|M.Sc Student||Mejer Anat|
|Subject||Biological Removal of Ammonia Gas from Poultry House|
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Michal Green|
|Dr. Sheldon Tarre|
|Full Thesis text - in Hebrew|
Poultry houses contain ventilation systems that provide appropriate temperature and gaseous ammonia concentration range. The outlet gases can be treated in either a chemical reactor (usually acid scrubber) or biological reactor. Both types of systems are based on ammonia absorption into the liquid phase. In order to maintain a high ammonia absorption rate, the ammonia concentration in the solution must be kept at minimal level by either maintaining low pH (acid scrubber) or conversion to nitrate (biological reactor). Nitrification is carried out by autotrophic bacteria that oxidize ammonia to nitrate. Oxygen and two moles of alkalinity are consumed, in contrast to one mole of alkalinity released during ammonia absorption. Usually, there is no addition of alkalinity and only ammonia absorption contributes to the alkalinity allowing for only 50% nitrification. Consequently, the solution’s ammonia concentration increases and impairs the ammonia absorption process.
Chalk may be used as an inexpensive source of alkalinity. Chalk (CaCO3) dissolution releases alkalinity when a given solution is under saturated with calcium and carbonate ions, typically at low pH. The occurrence of nitrification at low pH allowing for CaCO3 dissolution makes the usage of chalk as a source of alkalinity for biofilters possible.
This research hypothesis is that chalk can be used as a source of alkalinity for the nitrification process in a biological reactor for efficient ammonia removal from the poultry house outlet gas.
During this research project, experiments were conducted in order to examine ammonia absorption, nitrification and chalk dissolution at numerous calcium concentrations.
Based on the results, a combined system was built consisting of two unsaturated flow reactors. The first reactor (scrubber) absorbed ammonia. The absorbing solution trickled into a PAVB (passively aerated vertical flow bed) reactor which comprised of chalk as a carrier for the biomass and as an alkalinity source for nitrification. The outlet solution of the nitrifying reactor was recycled back into the ammonia absorbing reactor. Recirculation rate between the reactors was 50 ml/min, an air residence time of 1 s and inlet gaseous ammonia concentration was 13 mg N/m3 (similar to poultry house emission). Ammonia absorption at all calcium concentrations (4500-11000 mg/l as CaCO3) was about 75%. Nitrification rate was 320-350 mg NH3-N/l/d. Experiments showed that 36-49% of alkalinity for nitrification originated from chalk dissolution. The usage of chalk enabled full nitrification with the consequent of high ammonia absorption efficiency from poultry house gas and at low costs.