Characterization and evaluation of aerobic granules in sequencing batch reactor

In order to investigate the aerobic granules cultured under alternating aerobic and anoxic conditions, a sequencing batch reactor (SBR) was operated without the presence of a carrier material. Nitrification and denitrification occurred alternately in the SBR operation, with an increased nitrification efficiency of up to 97% and a high chemical oxygen demand (COD) removal efficiency of up to 95%. It was observed that physical characteristics of granule play an important role in the performance of the SBR process. Light microscopy was used to observe the time dependent development of the granules in the SBR. Based on the microscopic observations, some floc-like sludges remained in the form of a mixture with granules for 30 days of operation. Even though various granule sizes had been formed in the reactor after 50 days, the granule sizes were primarily from 1 +/- 0.35 to 1.3 +/- 0.45 mm, rarely exceeding 2 mm. The granules were analyzed by a combination of microelectrodes and fluorescent in situ hybridization (FISH), which provides more detailed information on what happens inside the granules. Based on their results, ammonia oxidizing bacteria (AOB) existed primarily in the upper and middle layers of the granule. Assuming a first-order reaction for nitrification, most of the nitrification is likely to occur from the surface to 300 microm into the granular thickness.     

Microbial community of aerobic granules for ammonium and sulphide removal in a sequencing batch reactor

Aerobic granules for sulphide and ammonium removal were cultivated in a sequencing batch reactor, and the microbial community of the aerobic granules was investigated by denaturing gradient gel electrophoresis. The loading rate increased from 0.15 to 0.9 kg S2? m?3 d?1, and the removal efficiencies of sulphide, chemical oxygen demand, and NH4 +-N were higher than 99, 80, and 98%, respectively. However, sludge settleability became poorer when the loading rate exceeded 0.3 kg S2? m?3 d?1. The denitrifying bacteria in the aerobic granules were Thauera sp., Pseudomonas alcaligenes, and uncultured planctomycetes, indicating that multiple N-removing processes occurred simultaneously in the aerobic granules. These processes could include nitrification and denitrification, aerobic denitrification, and anaerobic ammonia oxidation. Sludge settleability became poorer because of the overgrowth of uncultured Thiothrix sp.     

Influence of aeration intensity on mature aerobic granules in sequencing batch reactor

Aeration intensity is well known as an important factor in the formation of aerobic granules. In this research, two identical lab-scale sequencing batch reactors with aeration intensity of 0.8 (R1) and 0.2 m³/h (R2) were operated to investigate the characteristics and kinetics of matured aerobic granules. Results showed that both aeration intensity conditions induced granulation, but they showed different effects on the characteristics of aerobic granules. Compared with the low aeration intensity (R2), the aerobic granules under the higher aeration intensity (R1) had better physical characteristics and settling ability. However, the observed biomass yield (Y _obs) in R1 [0.673 kg mixed liquor volatile suspended solids (MLVSS)/kg chemical oxygen demand (COD)] was lower than R2 (0.749 kg MLVSS/kg COD). In addition, the maximum specific COD removal rates (q _max) and apparent half rate constant (K) of mature aerobic granular sludge under the two aeration intensities were at a similar level. Therefore, the matured aerobic granule system does not require to be operated in a higher aeration intensity, which will reduce the energy consumption.     

Selection pressure-driven aerobic granulation in a sequencing batch reactor

In recent years, the research on aerobic granulation has been intensive. So far, almost all aerobic granules can form only in sequencing batch reactors (SBR), while the reason is not yet understood. This paper attempts to review the factors involved in aerobic granulation in SBR, including substrate composition, organic loading rate, hydrodynamic shear force, feast-famine regime, feeding strategy, dissolved oxygen, reactor configuration, solids retention time, cycle time, settling time and exchange ratio. The major selection pressures responsible for aerobic granulation are identified as the settling time and exchange ratio. A concept of the minimal settling velocity of bioparticles is proposed; and it is quantitatively demonstrated that the effects of settling time and exchange ratio on aerobic granulation in SBR can be interpreted and unified on the basis of this concept very well. It appears that the formation and characteristics of aerobic granules can be manipulated through properly adjusting either the settling time or the exchange ratio in SBR. Consequently, theoretical and experimental evidence point to the fact that aerobic granulation is a selection pressure-driven cell-to-cell immobilization process.     

Biodegradation and kinetics of aerobic granules under high organic loading rates in sequencing batch reactor

Biodegradation, kinetics, and microbial diversity of aerobic granules were investigated under a high range of organic loading rate 6.0 to 12.0 kg chemical oxygen demand (COD) m⁻³ day⁻¹ in a sequencing batch reactor. The selection and enriching of different bacterial species under different organic loading rates had an important effect on the characteristics and performance of the mature aerobic granules and caused the difference on granular biodegradation and kinetic behaviors. Good granular characteristics and performance were presented at steady state under various organic loading rates. Larger and denser aerobic granules were developed and stabilized at relatively higher organic loading rates with decreased bioactivity in terms of specific oxygen utilization rate and specific growth rate (μ _overall) or solid retention time. The decrease of bioactivity was helpful to maintain granule stability under high organic loading rates and improve reactor operation. The corresponding biokinetic coefficients of endogenous decay rate (k _d), observed yield (Y _obs), and theoretical yield (Y) were measured and calculated in this study. As the increase of organic loading rate, a decreased net sludge production (Y _obs) is associated with an increased solid retention time, while k _d and Y changed insignificantly and can be regarded as constants under different organic loading rates.     

Simulation of wastewater treatment by aerobic granules in a sequencing batch reactor based on cellular automata

In the present paper, aerobic granules were developed in a sequencing batch reactor (SBR) using synthetic wastewater, and 81 % of granular rate was obtained after 15-day cultivation. Aerobic granules have a 96 % BOD removal to the wastewater, and the reactor harbors a mount of biomass including bacteria, fungi and protozoa. In view of the complexity of kinetic behaviors of sludge and biological mechanisms of the granular SBR, a cellular automata model was established to simulate the process of wastewater treatment. The results indicate that the model not only visualized the complex adsorption and degradation process of aerobic granules, but also well described the BOD removal of wastewater and microbial growth in the reactor. Thus, CA model is suitable for simulation of synthetic wastewater treatment. This is the first report about dynamical and visual simulation of treatment process of synthetic wastewater in a granular SBR.     

Formation and long-term stability of nitrifying granules in a sequencing batch reactor

The formation and long-term stability of nitrifying granules in a sequencing batch reactor was investigated in this study. The results showed that nitrifying granules with a size of 240 microm and SVI of 40 ml g(-1) were formed on day 21 at a settling time of 10 min. Maintaining settling time at 15 min from day 57 to 183 did not affect the physical characteristics of sludge and the fraction of suspended floc in the sludge. In addition, nitrifying granules could tolerate the fluctuations of nitrogen loading rate from 0.72 to 1.8 g l(-1)d(-1) during 2 months without the change of physical characteristics. However, it was observed that complete nitrification to nitrate and partial nitrification to nitrite by sludge converted each other corresponding to the change of the influent NH4+-N concentration. Thus, an appropriate method is needed to maintain a stable complete nitrification or partial nitrification under the conditions with changing influent NH4+-N concentrations and nitrogen loading rates.     

Biodegradation of methyl tert-butyl ether as a sole carbon source by aerobic granules cultivated in a sequencing batch reactor

Aerobic granules efficient at degrading methyl tert-butyl ether (MTBE) were successfully developed in a well-mixed sequencing batch reactor (SBR). Treatment efficiency of MTBE in the reactor during the stable operations exceeded 99.8%, and effluent MTBE was consistently below 800 mug/L. The specific MTBE degradation rate was observed to increase with increasing MTBE initial concentrations from 25 to 400 mg/L, peaked at 18.2 mg-MTBE/g-VSS h, and declined with further increases in MTBE concentration as substrate inhibition effects became significant. There was a good fit between these biodegradation data and the Haldane equation (R (2) = 0.976). Microbial community DNA profiling was carried out using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction amplified 16S rDNA. The aerobic granule was found to contain a wide diversity of microorganisms. More than 70% similarity among the samples in the time period examined indicated a highly stable microbial community as the reactor reached the stable operation.     

Growth kinetics of aerobic granules developed in sequencing batch reactors

AIMS: This paper attempts to develop a kinetic model to describe the growth of aerobic granules developed under different operation conditions. METHODS AND RESULTS: A series of experiments were conducted by using four-column sequencing batch reactors to study the formation of aerobic granules under different conditions, e.g. organic loading rates, hydrodynamic shear forces and substrate N/COD ratios. A simple kinetic model based on the Linear Phenomenological Equation was successfully derived to describe the growth of aerobic granules. It was found that the growth of aerobic granules in terms of equilibrium size and size-dependent growth rate were inversely related to shear force imposed to microbial community, while a high organic loading favoured the growth of aerobic granules, leading to a large size granule. The effect of substrate N/COD ratio on the growth kinetics of aerobic granules was realized through change in microbial populations, and enriched nitrifying population in aerobic granules developed at high substrate N/COD ratio resulted in a low overall growth rate of aerobic granules. CONCLUSIONS: The proposed model can provide good prediction for the growth of aerobic granules indicated by the correlation coefficient >0.95. SIGNIFICANCE AND IMPACT OF THE STUDY: The kinetic model proposed could offer a useful tool for studying the growth kinetics of cell-to-cell immobilization process. The study confirmed that the growth of aerobic granules and biofilms are subject to a similar kinetic pattern. This work would also be helpful for better understanding the mechanism of aerobic granulation.     

Variable aeration in sequencing batch reactor with aerobic granular sludge

This study investigated the effects of reduced aeration in famine period on the performance of sequencing batch reactor (SBR) with aerobic granular sludge. Aerobic granules were first cultivated in two SBRs (R1 and R2) with acetate as sole carbon source. From operation day 27, aeration rate in R1 was reduced from 1.66 to 0.55 cm s(-1) from 110 min to the end of each cycle and further reduced from 30 min to the end of each cycle from day 63. R2 as a control was operated with a constant aeration rate of 1.66 cm s(-1) in the whole cycle during the entire experimental period. Results showed that changing trends of SVI, concentration, average size and VSS/SS of biomass with time in R1 and R2 were similar although different aeration modes were adopted. At steady state, SVI of aerobic granules and biomass concentration maintained at about 40 ml g(-1) and 6 g l(-1), respectively. Average size of granules was about 750 microm in R1 while 550 microm in R2. This is the first study to demonstrate that aerobic granular sludge could be stable at reduced aeration rate in famine period during more than 3-month operation. Such an operation strategy with reduced aeration rate will lead to a significant reduction of energy consumption, which makes the aerobic granular sludge technology more competitive over conventional activated sludge process. Furthermore, the stability of aerobic granular system with variable aeration further indicates that the difference of physiology and kinetics of aerobic granule in feast and famine periods results in the different requirements of oxygen and shear stress for the stability of granules, which will deepen the understanding of mechanism of aerobic granulation in sequencing batch reactor.     

Characteristics of aerobic granular sludge in a sequencing batch reactor with variable aeration

Aerobic granules can be used for the treatment of industrial or municipal wastewater, but high aeration rate is required for the stable operation of the granular sludge system. Therefore, the aim of this research was to reduce aeration rate greatly to decrease the energy consumption for the technology of aerobic granules. Based on the characteristics of sequencing batch reactor with distinct feast and famine periods, aeration rate was reduced from 1.66 to 0.55 cm s⁻¹ in the famine period after granules were formed. It was found that the settleability of aerobic granules in reactor R1 with reduced aeration was the same as that of aerobic granules in reactor R2 with constant aeration rate of 1.66 cm s⁻¹. However, the outer morphology of aerobic granules gradually changed from round shape to long shape, and minor population showed certain shift after aeration rate was reduced in the famine period. Since good settleability is the most essential feature of aerobic granules, it can be said that reducing aeration rate in famine period did not influence the stable operation of aerobic granular sludge system. Furthermore, the experimental results indicated that aeration rate in feast period was much more important to the stable operation of aerobic granules than that in famine period.     

Treatment of dairy effluents in an aerobic granular sludge sequencing batch reactor

Aerobic granular sludge can successfully be cultivated in a sequencing batch reactor (SBR) treating dairy wastewater. Attention has to be paid to the fact that suspended solids are always present in the effluent of aerobic granular sludge reactors, making a post-treatment step necessary. Sufficient post-treatment can be achieved through a sedimentation process with a hydraulic retention time of 15–30 min. After complete granulation and the separation of biomass from the effluent, removal efficiencies of 90% COD_total, 80% N_total and 67% P_total can be achieved at a volumetric exchange ratio of 50% and a cycle duration of 8 h. Effluent values stabilize at around 125 mg l^–1 COD_dissolved. The maximum applicable loading rate is nevertheless limited, as the stability of aerobic granules very much depends on the presence of distinct feast and famine conditions and the degradation of real wastewaters shows slower kinetics compared with synthetic wastewaters. As loading rate and volumetric exchange ratio are coupled in an SBR system, the potential of granular sludge for improving process efficiency is also limited.     

Bioaugmentation with a novel alkali-tolerant Pseudomonas strain for alkaline phenol wastewater treatment in sequencing batch reactor

A novel alkali-tolerant strain JY-2, which could utilize phenol as sole source of carbon and energy, was isolated from activated sludge. It was identified as Pseudomonas sp. by 16S rDNA sequencing analysis. The appropriate conditions for strain growth and phenol biodegradation were as follows: pH 8.0–10.0 and temperature 23–30°C. With initial phenol concentrations of 225, 400, 550 and 750 mg/l, the degradation efficiencies were 94.9, 93.3, 89.3 and 48.2% within 40 h at pH 10.0 and 30°C, respectively. The alkaline phenol-containing wastewater treatment augmented with strain JY-2 in sequencing batch reactor (SBR) system was investigated, which suggested that the bioaugmented (BA) system exhibited the better performance for adjusting high pH to neutral value than the non-bioaugmented (non-BA) one. Also, the BA system showed strong abilities for phenol degradation and maintaining good sedimentation coefficient (SV₃₀). The microbial community dynamics of both sequencing batch reactor (SBR) systems were analyzed by Denaturing Gradient Gel Electrophoresis (DGGE) technique, which showed substantial changes between the two systems. This study suggests that it is feasible to treat alkaline phenol-containing wastewater augmented with strain JY-2.     

Formation of aerobic granules by Mg2+ and Al3+ augmentation in sequencing batch airlift reactor at low temperature

Aerobic granules technology (AGS) was difficult to cultivate at low temperature, and the treatment efficiency of domestic sewage was remarkably low because of low temperature, which greatly limits its development and application. AGS formation time significantly decreased for 43 days by adding 19.0 mg/L Mg(2+) and 21.0 mg/L Al(3+), moreover, AGS possessed better simultaneously chemical oxygen demand, NH(4) (+)-N, TP removal efficiencies at low temperature, which the respective removal efficiencies were 85.6, 88.8, and 91.9%. The content of total polysaccharides was 8.23 mg/gMLSS as well as the content of total protein was 8.52 mg/gMLSS, consequently, the total proteins/total polysaccharides ratio was 1.04, which the relatively high protein content induced by Mg(2+) and Al(3+) presented an essential feature for AGS formation. In addition, the affinity among Mg(2+), Al(3+) and -OH may drive the stretching vibration of -OH band which led to the infrared motion of functional groups in AGS and accelerate AGS formation as well.     

An aerobic sequencing batch reactor for 2,4,6-trinitrophenol (picric acid) biodegradation

A bench scale sequencing batch reactor (SBR) was designed and tested for degradation of 2,4,6-trinitrophenol (TNP) or picric acid-contaminated wastewater or groundwater. Under varying temperatures (25, 15 and 10 degrees C) and influent concentrations (40-200 mg/L TNP) a stable biomass was developed that was consistently capable of degrading the explosive compound to below regulatory drinking water limits (0.057 mg/L). The reactor was initially seeded with a nitroaromatic and nitramine degrading isolate Rhodococcus opacus strain JW01. Kinetic growth modeling was conducted revealing micro(max) values at 25, 15 and 10 degrees C of 0.14, 0.08 and 0.04 d(-1), while the modeled K(s) values were 0.68, 1.11 and 1.24 mg/L, respectively. Overall TNP removal efficiency in the SBR was on average > 99.9% over the 2000 hours of operation. Removal of TNP to below drinking water standards, with low residual dissolved carbon and significant release of nitrogen from the parent compound was accomplished.     

Effects of mechanical stress on Anammox granules in a sequencing batch reactor (SBR)

The effect of shear stress on Anammox process was studied in a sequencing batch reactor (SBR). The reactor was operated during 218 days under different stirring speeds (60-250 rpm) in order to expose the system to different shear conditions and to study the stability of the Anammox granules referred to their biological activity and size. The nitrogen loading rate (NLR) fed to the SBR was kept around 0.3g N(L day)(-1). The nitrite (limiting substrate) removal percentage was 98% during most of the operational period. The specific Anammox activity of the biomass was practically constant and around 0.4 g N(g VSSday)(-1) and the average feret diameter of the formed granules was 0.64 mm. Obtained results indicated that stirring speeds up to 180 rpm have no negative effect on the performance of the Anammox process, whereas Anammox activity decreased to 40% when a rotating speed of 250 rpm was tested and the average diameter decreased in 45%, the concentration of solids in the effluent increased to 0.2g TSSL(-1) and nitrite was accumulated in the reactor up to 60 mg NL(-1).     

Nitrifying granules cultivation in a sequencing batch reactor at a low organics-to-total nitrogen ratio in wastewater

It is possible to cultivate aerobic granular sludge at a low organic loading rate and organics-to-total nitrogen (COD/N) ratio in wastewater in the reactor with typical geometry (height/diameter = 2.1, superficial air velocity = 6 mm/s). The noted nitrification efficiency was very high (99%). At the highest applied ammonia load (0.3 ± 0.002 mg NH₄⁺–N g total suspended solids (TSS)⁻¹ day⁻¹, COD/N = 1), the dominating oxidized form of nitrogen was nitrite. Despite a constant aeration in the reactor, denitrification occurred in the structure of granules. Applied molecular techniques allowed the changes in the ammonia-oxidizing bacteria (AOB) community in granular sludge to be tracked. The major factor influencing AOB number and species composition was ammonia load. At the ammonia load of 0.3 ± 0.002 mg NH₄⁺–N g TSS⁻¹ day⁻¹, a highly diverse AOB community covering bacteria belonging to both the Nitrosospira and Nitrosomonas genera accounted for ca. 40% of the total bacteria in the biomass.     

Nitrite accumulation in a sequencing batch reactor during the aerobic phase of biological nitrogen removal

Accumulation of nitrite occurred during the aerobic phase of a sequencing batch reactor (SBR) operating to remove nitrogen from synthetic waste water. Although present, heterotrophic nitrifiers were not involved in the nitrification of the SBR. The activity of autotrophic nitrite oxidizers was reduced in the SBR where free ammonia was the main inhibitor for the nitrite oxidation. Nitrite build-up in the SBR was reduced when the aerobic phase was extended. All the ammonia could be oxidized when the aerobic phase was longer than four hours. The accumulated nitrite and nitrate were removed completely in the post-anoxic phase.