|M.Sc Student||Shulman Marina|
|Subject||Characterization of Nitrogen Removal in Single-Stage|
Partial Nitritation/Anammox Process Fed with
Synthetic Medium and Reject Water
from Thermophilic Anaerobic...
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Carlos Dosoretz|
|Dr. Isam Sabbah|
Anaerobic ammonium oxidation (anammox) processes have gained popularity worldwide to treat nitrogen rich streams following sludge digestion and dewatering. For the first time, a single stage partial nitritation/anammox process with granular biomass based on a sequential batch reactor (SBR) of 26 liters volume was run to study the feasibility of nitrogen removal from the reject water of the thermophilic sludge digestion plant at the Shafdan wastewater treatment plant (WWTP). The aim of this research was to determine and understand the changes in nitrogen removal performance under different operational conditions and their direct and indirect effect on the autotrophic nitrogen removal population, tracked by a combination of analytical chemistry and microbiological methods. The targeted dissolved oxygen (DO) concentration to maintain aerobic nitritation was 0.3 mg/L. Excess aeration leads to nitrite oxidation (nitratation) by nitrite oxidizing bacteria (NOB).
Within the frame
of the research, two consecutive runs were performed: Run#1
duration of 500 days and Run#2 with
a duration of 138
days. Run#1 started at a load of 1 2 0 mg-N/L/day, with specific activity around 150 mg-N/gVSS/d
operating with synthetic wastewater. The reactor operation was stable over the
period. When feed was shifted to 20% diluted reject water around day 300,
solids in the feed, despite filtration, deteriorated the settling properties of
the granules and within 40 days significant washout took place. Specific
anammox activity measured by Oxitop and NGS analyses evidenced that population
within the reactor shifted, with prevalence of thermophilic anaerobes and
denitrifying proceeding from the anaerobic digestion stage. Based on mass
balances and stoichiometry calculations, specific activities of each population
were calculated. The ammonium oxidizing bacteria (AOB) responsible for partial
nitritation appeared most affected. Increased aeration to encourage the AOB
enhanced development of NOB, leading to complete nitrification.
In Run#2, after 40 days of steady operation feed with synthetic wastewater at a load of 350 mg-N/L/d, approx. 80% nitrogen removal efficiency was achieved with a specific activity of 100 and 7 0 mg-N/gVSS/d for AOB and anammox respectively, and NOB ≤20 mg-N/gVSS/d. The reactor was then gradually exposed (5%, 10%, 20%, 25%) to reject water of controlled suspended solids quality (300 mg/L). In general terms, increase in organic matter led to a gradual shift of biomass with increase of heterotrophs and decrease of Planctomycetes, as evidenced by NGS and FISH analyses and specific activity by Oxitop. The DO electrode showed a value of 0 during two runs thus not allowing it to be used as a control parameter, leading to increased development of NOB population.
Concluding, a process of partial nitritation/anammox can be adapted to treatment of the reject water after thermophilic digestion; however, strict separation of suspended solids is required along with pretreatment to decrease COD content and reduce ammonia load. The SBR system studied appeared extremely sensitive to the presence of suspended solids carried on with the reject water, which changed the settling properties of the granules. In order to reduce the sensitivity of the system to the presence of suspended solids in the feed, mechanical separation is required to preserve the granules.