Partial Nitrification in an Airlift Activated Sludge Reactor with Experimental and Theoretical Assessments of the pH Gradient inside the Sponge Support Medium (original) (raw)
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The nitrification process of ammonium-rich (100 -1200 mg N/l) synthetic and industrial wastewater with low BODS (100 mg/l) were investigated over a period of 20 months. Five identical bench scales, completely mixed and single-stage activated sludge units were used. Fundamental process and design parameters of nitrification were studied in different phases under steady-state conditions (pH = 7.6, DO 3 mg 02/1, and temperature = 25 oC ± 5 oC). The major objectives of this research include the effects of C/N ratio, sludge age, BOD5 and NH4-N sludge loading, hydraulic loading, process pH and temperature, and finally long periods of anoxic conditions on nitrification process. All experimental data were obtained from averages of steady-state periods (six weeks in duration) for each process variable condition change. During phase one, four reactors (A, B, C and D), treating synthetic wastewater, were operated at the same NH4 volumetric loading (0.26 kg N/m3*d) but at different BOD loading ...
blOl [SOlJl ([ T[(HMOIOdT Nitrification at high ammonia loading rates in an activated sludge unit
Effective nitrification of ammonia at high nitrogen loading rates, up to 7.5 kg N-NH] m-3 d-t was obtained in a nitrifying activated sludge unit working at a hydraulic retention time of 1.3 h and 20°C. Bicarbonate, used as a carbon source for autotrophic microorganisms, allowed maintainance of a system very stable against different shocks due to point deficiencies of oxygen or other accidents. Ammonia conversion to nitrate was normally between 97 and 99.9%. Temporary accumulations of nitrite were quickly transformed into nitrate. The relative low specific conversion rate of the biomass in the reactor (0.5-0.7 g-N-NH4 + g-VSS-t d t) was compensated by the capacity of the unit to retain high concentrations of biomass (up to 15 g-VSS l-t) due to the excellent characteristics of the biomass (Sludge Volume Index of 12 ml g-VSS t; Zone Settling Velocity of 9 m h-l). Present results show that activated sludge units can be operated efficiently as a high-rate nitrifying technology. This well-known, robust and easy to operate technology is a clear alternative to the airlift or fluidised-bed systems, which can be applied for the nitrification of high load wastewater at full scale.
Performance of a nitrifying airlift reactor using granular sludge
Separation and Purification Technology, 2008
Since nitrification is the rate-limiting step in the biological nitrogen removal from wastewater, many studies have been conducted on the immobilization of nitrifying bacteria. A laboratory-scale investigation was conducted to examine the effectiveness of a continuous-flow airlift reactor (ALR) on the granulation of nitrifying sludge and the nitrification efficiency of the reactor after granulation. The results showed that the granular sludge began to appear on day 30 and matured in 75 days. The mature granules had an average diameter of 1.54 mm, settling velocity higher than 82.4 m h −1 and specific gravity of 1.07. The granules cultured in the present study had aerobic ammonia oxidation activity of 13.3 mg NH 4 +-N (g VSS) −1 day −1 and anaerobic ammonium oxidation (ANAMMOX) activity of 3.22 mg NH 4 +-N (g VSS) −1 day −1 , which demonstrated that the nitrifying granules possessed the potential to be used as seed sludge for ANAMMOX and CANON (completely autotrophic nitrogen-removal over nitrite) reactors. After granulation, the ALR exhibited an excellent nitrification performance. It had strong tolerance to influent NH 4 +-N of 1100 mg L −1. When operated at influent NH 4 +-N concentration of 546 mg L −1 , the reactor could remove over 94.4% of ammonium even at a nitrogen loading rate (NLR) of 2.37 f m −3 day −1 with a short hydraulic retention time (HRT) of 5.4 h. With the influent NH 4 +-N concentration of 547 mg L −1 , HRT 6.9 h and NLR of 1.90 kg m −3 day −1 , superior effluent quality could be achieved robustly, with an effluent NH 4 +-N of less than 5 mg L −1 , satisfying the national primary discharging standard of China (GB 8978-1996).
Nitrification in saline wastewater with high ammonia concentration in an activated sludge unit
Water Research, 2002
A nitrifying activated sludge reactor fed with a high salinity medium was operated efficiently at ammonia loading rates between 1 and 4 g NH 4 +-N l À1 d À1. The system became completely inefficient at inlet salt concentrations higher than 525 mM due to the mixed inhibition effect of salts and ammonia. The final product was mainly nitrate although dissolved oxygen limitations caused sporadic ammonia and nitrite accumulations. Specific nitrifying activity decreased due to the saline effect. A set of activity tests showed that in the continuous reactor non-adapted biomass is rather more sensitive than biomass to the saline effect. Physical properties of biomass in the reactor (sludge volumetric index and zone settling velocity) were not affected by the saline concentration, a biomass concentration of 20 gVSS l À1 was achieved.
Nitrification in Powdered‐Activated Carbon‐Activated Sludge Process
Journal of Environmental Engineering, 1987
Powdered activated carbon (PAC) has been added to activated sludge processes over the past 10 years to improve process performance in a variety of ways, including ammonia removal. Improved ammonia removal is a surprising benefit of PAC since it is not adsorbed. Investigators have speculated that PAC adsorbs inhibitory compounds or provides a media for nitrifier growth. To ascertain the mechanism of nitrification enhancement, a series of experiments were performed with adsorbable (aniline, phenol) and nonadsorbable (ethanol) inhibitors. Experimental results show that adsorption of nitrification inhibitors can dramatically improve nitrification rates in unacclimated activated sludge cultures .
Nitrite effect on ammonium and nitrite oxidizing processes in a nitrifying sludge
World Journal of Microbiology and Biotechnology, 2010
Nitrite accumulation can be undesirable in nitrifying reactors used for the biological elimination of nitrogen from wastewaters because the ammonium oxidation process was seen to be inhibited. There is a need to better understand the effects of nitrite on both ammonium and nitrite oxidizing processes. In this paper, the effect of nitrite on the nitrifying activity of a sludge produced in steady-state nitrification was evaluated in batch cultures. At 25 mg N/l of added nitrite, nitrification was successfully carried out. Addition of higher nitrite concentrations to nitrifying cultures (100 and 200 mg N/l) provoked inhibitory effects on the nitrification respiratory process. Nitrite at 100 and 200 mg N/l induced a significant decrease in the values for nitrate yield (-20% and-34%, respectively) and specific rate of nitrate formation (-26% and-67%, respectively), while the ammonium consumption efficiency kept high and the specific rate of ammonium oxidation did not significantly change. This showed that the nitrite oxidizing process was more sensitive to the presence of nitrite than the ammonium oxidizing process. These results showed that as a consequence of nitrite accumulation in nitrification systems, the activity of the nitrite oxidizing bacteria could be more inhibited than that of the ammonium oxidizing bacteria, provoking a higher accumulation of nitrite in the medium.
Stability of a nitrifying activated sludge reactor
Biochemical Engineering Journal, 2007
A nitrifying activated sludge unit operated in stable conditions was subjected to different instability actuations as overloads due to a sudden increase of the inlet ammonia concentration or a quick change of the inflow rate, pH shocks and limitations of dissolved oxygen (DO) concentration. The response of the unit to these different actuations was evaluated. During concentration overloads there were transitory nitrite accumulations but not during hydraulic overloads. However, efficiencies obtained for both kinds of overloads with respect to ammonia oxidation were very similar. The normal efficiency of the system was always restored and biomass was not washed out in spite of the low values of hydraulic retention time (HRT) used. The pH shocks of 9 and 10 had no appreciable effects, but the pH shock of 11 caused an irreversible loss of efficiency of 60%. An increase of the total organic carbon (TOC) in the effluent after this shock showed that biomass underwent a partial lysis. The specific activity of ammonia-oxidizers decreased from 0.6 to 0.3 g NH 4 +-N/(g VSS day) but the nitrite-oxidizing specific activity remained practically constant. Finally, the unit was operated at different DO levels, ammonia being fully oxidized to nitrate at DO levels higher than 1 mg O 2 /L. Different proportions of ammonia and nitrite appeared when the reactor was operated at DO values of 0.4 and 0.6 mg O 2 /L.
Environmental Technology, 2015
A mathematical model was used to evaluate the effect of the aeration pattern and ammonium concentration in a partial nitritation-anammox sequencing batch reactor with granular and flocculent sludge. In the tested conditions, model results indicate that most of the aerobic ammonium oxidation potential would occur in the bulk liquid, with 70% of the ammoniumoxidizing bacteria (AOB) biomass in suspension rather than in granules. The simulated granular sludge consisted predominantly of anammox bacteria with AOB present in the outer layer of the granule (50 μm AOB layer, accounting for 3% of the granule weight). Simulation results indicated that when granules do not contain any AOB, the amount of granular biomass required to achieve the same level of nitrogen removal would strongly increase (in the simulated conditions, by a factor of three) due to anammox inhibition by oxygen. This underlines the importance of a small fraction of AOB present in the granular anammox sludge. The aeration pattern had an important impact on the nitrogen removal: a better performance was suggested for continuous aeration (90% N-removal) than for intermittent aeration (68-84% N-removal). Anammox inhibition during the periods of high oxygen concentration was identified as the main reason for the lower nitrogen removal in the intermittently aerated system. With increasing oxygen concentration, a higher residual (effluent) ammonium concentration was needed to assure nitrite-oxidizing bacteria repression in the system. This study contributes to further understand the complexity of a reactor with both granular and flocculent sludge and the impact of operation conditions on reactor performance.
Wastewater Nitrification in Airlift Biofilm Reactors
Korean Journal of Chemical Engineering, 2002
The nitrifying biofilm was formed on the carriers of granular activated carbon with the diameter of 0.613 mm in the airlift bioreactor of 27.7 L to investigate the influences of temperature and dissolved oxygen concentration on the nitrification rate. The biofilm of 0.140 mm thickness was obtained after the operation of 130 days with the dilution rate higher than the maximum specific growth rate of nitrifying bacteria. As raising alternately air velocity and ammonium loading rate, ammonium oxidation rate increased stepwise up to the maximum value of at the riser air velocity of 6.34 cm/s and the temperature of . The ammonium oxidation rate increased with increasing the dissolved oxygen concentrations, while the nitrite oxidation rates were almost independent from the dissolved oxygen concentration during the early stages of the reactor operation. The biofilm formed at the late phase, however, led the nitrite build-up to disappear and exhibited the nitrite oxidation rates which incre...
Vietnam Journal of Science, Technology and Engineering, 2019
A lab-scale flat sheet membrane bioreactor (MBR) system was used for the treatment of piggery wastewater to produce an effluent with the appropriate ratio of nitrite:ammonia (1:1 to 1:1.3) as a pre-treatment for the anammox process. The feed wastewater, which was the effluent of a biogas digester, contained 253±49 (n=60) mg.l-1 as COD, 231±18 mg.l-1 as N-ammonia, 223±19 mg.l-1 as total Kjeldalh nitrogen (TKN), alkalinity of 1433±153 mg.l-1 as CaCO 3 , and pH=7.5±0.3. This study aimed to determine the suitable hydraulic retention time (HRT) and alkalinity to yield the appropriate influent for the annamox process. The results showed that the suitable effluent of the partial nitrification with ratio of nitrite:ammonia 1.0:1.1 at HRT of 7h30, equivalent to total nitrogen loading of 0.77 kgNm-3 d-1. The nitrite accumulation rate (NAR) was 82% at HRT of 7h30, whereas NAR were 11 and 63% at HRT of 12h30 and 8h45, respectively, due to the high growth of nitrite oxidation bacteria (NOB) at long HRTs. As increasing alkalinity of up to 1600 mg.l-1 and pH of 8.0 at HRT of 8h45, NAR was increased from 63 to 73%, ratio of ammonia:nitrite reduced from 1.0:1.8 to 1.0:1.6 and free ammonia concentration reached to 20.2 mg.l-1 nitrogen. This shows that the increase of alkalinity inhibited strongly NOB.