Proportions Of Ammonia Oxidizing Bacteria Research Articles

Effects of salinity on pollutant removal and bacterial community in a partially saturated vertical flow constructed wetland

This study investigated the influence of salinity on pollutant removal and bacterial community within a partially saturated vertical flow constructed wetland (PS-VFCW). High removal rates of NH4+-N (88.29 ± 4.97–100 ± 0%), total inorganic nitrogen (TIN) (50.00 ± 7.21–62.81 ± 7.21%) and COD (91.08 ± 2.66–100 ± 0%) were achieved at 0.4–2.4% salinity levels. The removal of ammonia, TIN and organic matter occurred mainly in unsaturated zone. Salt-adaptable microbes became the dominant bacteria with salinity elevated. The proportion of ammonia-oxidizing bacteria (AOB) in the 0–5 cm depth layer (unsaturated zone) decreased obviously as the salinity increased to 2.4%. Nitrite-oxidizing bacteria (NOB) in the 0–5 cm depth layer showed a decreasing trend with elevated salinity. Denitrifying bacteria (DNB) in the 0–5 cm depth layer maintained high abundance (27.70–53.60%) at 0.4–2.4% salinity levels. At 2.4% salinity, AOB, NOB and DNB were observed in the unsaturated zones and saturated zones, and showed higher abundance in the unsaturated zone.

Performances and microbial characteristics of granular sludge for autotrophic nitrogen removal from synthetic and mainstream domestic sewage

The completely autotrophic nitrogen removal over nitrite (CANON) process is an important component of energy self-sufficient sewage treatment plants, and the use of aerobic granular sludge is a profitable choice for the CANON process. In this study, the performance and microbial characteristics of CANON granular sludge were investigated for treating synthetic and mainstream domestic sewage. The average nitrogen removal rate (NRR) was 3.22 kg N m−3 d−1 during the high-rate operating period with high MLSS (4.09 g L−1) and DO (∼1.0 mg L−1) for treating synthetic sewage. When the influent was mainstream sewage, the average NRR was 1.11 kg N m−3 d−1. The effluent nitrate concentration was very low, and nitrate build-up was not found. High-throughput pyrosequencing results indicated that, Nitrosomonas and Candidatus Brocadia were the dominant genus in ammonia oxidizing bacteria (AOB) and anaerobic AOB (AAOB), respectively. The proportions of AOB and AAOB decreased during mainstream sewage treatment, but the reactor maintained good performance. The results confirmed the feasibility of using CANON granular sludge for treating mainstream sewage.

Effect of Two-Stage Aeration on Nitrogen Removal Performance of Aerobic Granular Sludge

Four mini experiments were conducted at different conditions. The heterotrophic microorganisms on the aerobic granular sludge surface consumed organic compounds at the initial stage of aeration. The denitrification rate and the efficiency of NO2--N and NO3--N removal were relatively low. Therefore, under the normal temperature conditions (20-23℃), aerobic granular sludge sequencing batch reactor (SBR) was operated in the two-stage aeration mode(first in low aeration then in high aeration mode). The low aeration time were carried out at 1, 2 and 3 hours stages respectively, and the characteristics of the granular sludge and its effects on microorganisms were analyzed by scanning electron microscopy (SEM) and fluorescence in situ hybridization (FISH) technique. The results show that the increase in the aerobic granular sludge (AGS) particle size improved the denitrification capacity; the denitrification rate of NO2--N was the highest at low aeration mode with 2 h and reached 9.66 mg·(g·h)-1. The accumulation rate of nitrite increased to 77.84% and the total nitrogen removal rate to 70%. The bacterial count inside the granular sludge increased and they were mainly cocci, bacillus, and ellipsoidal bacteria. Moreover, the proportion of ammonia-oxidizing bacteria in total bacterial count increased from 13.70% to 15.40%. Therefore, the two-stage aeration process achieved shortened simultaneous nitrification and denitrification processes and showed a good denitrification performance.

The effect of dissolved oxygen concentration (DO) on oxygen diffusion and bacterial community structure in moving bed sequencing batch reactor (MBSBR)

The effect of dissolved oxygen concentration (DO) on simultaneous nitrification and denitrification was studied in a moving bed sequencing batch reactor (MBSBR) by microelectrode measurements and by real-time PCR. In this system, the biofilm grew on polyurethane foam carriers used to treat municipal sewage at five DO concentrations (1.5, 2.5, 3.5, 4.5 and 5.5 mg/L). The results indicated that the MBSBR exhibited good removal of chemical oxygen demand (92.43%) and nitrogen (83.73%) when DO concentration was 2.5 mg/L. Increasing the oxygen concentration in the reactor was inhibitory to denitrification. Microelectrode measurements showed that the thickness of oxygen penetration increased from 1.2 to 2.6 mm when the DO concentration (from 1.5 mg/L to 5.5 mg/L) in the system increased. Oxygen diffusion was not significantly limited by the boundary layer surrounding the carrier and had the largest slope when DO concentration was 2.5 mg/L. The real-time PCR analysis indicated that the amount of the ammonia-oxidizing bacteria and nitrite-oxidizing bacteria increased slowly as DO concentration increased. The proportions of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, as a percentage of the total bacteria, were low with average values of 0.063% and 0.67%, respectively. When the DO concentration was 2.5 mg/L, oxygen diffusion was optimal and ensured the optimal bacterial community structure and activity; under these conditions, the MBSBR was efficient for total inorganic nitrogen removal. Changing the DO concentration could alter the aerobic zone and the bacterial community structure in the biofilm, directly influencing the simultaneous nitrification and denitrification activity in MBSBRs.

Nitrogen-removal performance and community structure of nitrifying bacteria under different aeration modes in an oxidation ditch

Oxidation-ditch operation modes were simulated using sequencing batch reactors (SBRs) with alternate stirring and aerating. The nitrogen-removal efficiencies and nitrifying characteristics of two aeration modes, point aeration and step aeration, were investigated. Under the same air-supply capacity, oxygen dissolved more efficiently in the system with point aeration, forming a larger aerobic zone. The nitrifying effects were similar in point aeration and step aeration, where the average removal efficiencies of NH4+-N were 98% and 96%, respectively. When the proportion of anoxic and oxic zones was 1, the average removal efficiencies of total nitrogen (TN) were 45% and 66% under point aeration and step aeration, respectively. Step aeration was more beneficial to both anoxic denitrification and simultaneous nitrification and denitrification (SND). The maximum specific ammonia-uptake rates (AUR) of point aeration and step aeration were 4.7 and 4.9 mg NH4+-N/(gMLVSS h), respectively, while the maximum specific nitrite-uptake rates (NUR) of the two systems were 7.4 and 5.3 mg NO2−-N/(gMLVSS h), respectively. The proportions of ammonia-oxidizing bacteria (AOB) to all bacteria were 5.1% under point aeration and 7.0% under step aeration, and the proportions of nitrite-oxidizing bacteria (NOB) reached 6.5% and 9.0% under point and step aeration, respectively. The dominant genera of AOB and NOB were Nitrosococcus and Nitrospira, which accounted for 90% and 91%, respectively, under point aeration, and the diversity of nitrifying bacteria was lower than under step aeration. Point aeration was selective of nitrifying bacteria. The abundance of NOB was greater than that of AOB in both of the operation modes, and complete transformation of NH4+-N to NO3−-N was observed without NO2−-N accumulation.

Effects of hydraulic retention time on nitrification activities and population dynamics of a conventional activated sludge system

The effects of hydraulic retention time (HRT) on the nitrification activities and population dynamics of a conventional activated sludge system fed with synthetic inorganic wastewater were investigated over a period of 260 days. When the HRT was gradually decreased from 30 to 5 h, the specific ammonium-oxidizing rates (SAOR) varied between 0.32 and 0.45 kg NH 4 + -N (kg mixed liquor suspended solids (MLSS)·d)−1, and the specific nitrate-forming rates (SNFR) increased from 0.11 to 0.50 kg NO 3 − -N (kg MLSS·d)−1, showing that the decrease in HRT led to a significant increase in the nitrite oxidation activity. According to fluorescence in situ hybridization (FISH) analysis results, the proportion of ammonia-oxidizing bacteria (AOBs) among the total bacteria decreased from 33% to 15% with the decrease in HRT, whereas the fraction of nitrite-oxidizing bacteria (NOBs), particularly the fast-growing Nitrobacter sp., increased significantly (from 4% to 15% for NOBs and from 1.5% to 10.6% for Nitrobacter sp.) with the decrease in HRT, which was in accordance with the changes in SNFR. A short HRT favored the relative growth of NOBs, particularly the fast-growing Nitrobacter sp., in the conventional activated sludge system.

Microbial population structure changes in a suspended carrier biofilm reactor

The changes of microbial population structure in biofilm caused by variations of COD/NHNH4(+)-N ratio in influent were investigated in a suspended carrier biofilm reactor (SCBR). When COD/NHNH4(+)-N was 10, the highest COD removal reached was about 73.8 per cent, whereas the highest NH4(+)-N removal, about 55.9 per cent, was reached when COD/NH4(+)-N was 5. By using fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) observation, it was found that the thickness of the biofilm formed on the carrier was about 80 to 120 microm, and ammonia-oxidizing bacteria (AOB) and nitrifying bacteria existed mainly in the upper layer about 20 to 30 microm. The results of the quinone profile analysis showed that when the COD/NH4(+)-N increased, the microbial diversity (DQ) increased, while the proportions of AOB and nitrifying bacteria in the biofilm communities decreased.