Characteristics Of Aerobic Granules Research Articles

Effect of transient pH variation on microbial activity and physical characteristics of aerobic granules treating 4-chlorophenol

Chlorophenols are inhibitory compounds that can be biodegraded by aerobic granules in discontinuous processes. Many industrial wastewaters are characterized by transient pH variation over time. These pH changes could affect the overall granule structure and microbial activity during the chlorophenol biodegradation. The objective of this research was to evaluate the effects of transient pH variation on the specific degradation rate (q), granule integrity coefficient (IC), and size in sequencing batch reactors treating 4-chlorophenol (4-CP). First, aerobic granules were acclimated for efficient 4-CP degradation (>99%). The acclimated granules consisted of 55.7% of the phyla Proteobacteria and 40.6% of Bacteroidetes. The main bacteria belong to the order Sphingobacteriales (24%), as well as Amaricoccus, Acidovorax, Shinella, Rhizobium, and Flavobacterium, some of which are new genera reported in acclimated granules degrading 4-CP. Then, pH changes were applied to the acclimated aerobic granules, observing that acid pHs decreased to a greater extent the specific degradation rate (67% to 99%) than basic pHs (34% to 80%). These pH changes caused the granule disaggregation but with lower effects on the IC. The effects of pH change were mainly on the microbial activity more than the physical characteristics of aerobic granules degrading 4-CP.

Partial nitrification using aerobic granule continuous-flow reactor: Operations and microbial community

Partial nitrification on ammonia laden wastewater using aerobic granule continuous-flow reactors was studied. Effects of temperature and carbon sources on performance of partial nitrification and characteristics of aerobic granules were reported. High nitrite accumulation ratio (>90%) was observed in all reactors after an acclimation phase of 6 days. Decrease in temperature or inorganic carbon concentration limited nitrite accumulation ratio; while nitrite accumulation was hard to recover once complete nitrification to nitrate was established in granules. The aerobic granules collected at continuous-flow reactor were stronger in strength than the seed granules from sequential batch reactor. Clone libraries revealed that Nitrosomonas europaea and Nitrosomonas sp. were the ammonia-oxidizing bacteria (AOB), whereas Nitrobacter sp. and Nitrospira cf. moscoviensis were nitrite-oxidizing bacteria (NOB). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that temperature and carbon sources shifted the microbial community in granules.

A Review on Aerobic Granular Sludge for Heavy Mental Wastewater Treatment

With the excellent settle ability and high-porosity structure, aerobic granular sludge was regarded as one of the promising biotechnologies in wastewater treatment. Developed about one decade ago, it was exciting research work that explored beyond the limits of aerobic wastewater treatment in eliminating a wide range of pollutants from the aquatic environment. On account of recent researches for removing heavy metals such as Cu (II), Pb (II), Cd (II) and cadmium (VI), a supposition that using aerobic granular sludge as a biosorbent for heavy metals removal from wastewater is put forward. This paper sketches certain correlative characteristics of aerobic granules, including settle ability, extracellular polymeric substance and biological parameters, discussed its feasibility for heavy mental removal, and finally lists a series of preceding studies on treatment of heavy metals by aerobic granular sludge.

Use of Steady-State Biofilm Model to Characterize Aerobic Granular Sludge

In this study, a steady-state biofilm model was utilized to elucidate the aerobic granular sludge process. In order to describe the experiment data using the model, two different sizes of stabilized aerobic granules (with mean diameters of 0.6 mm and 3 mm, respectively) were investigated through the laboratory operations of sequencing batch reactors (SBRs). On the basis of the estimated parameters from experiments, the model was established to describe the biofilm functions in aerobic granules, such as substrate transfer and substrate concentration variations within the granules. In the modeling at different chemical oxygen demand (COD) concentrations (100-1000 mg/L), the biofilm functions were affected by the characteristics of aerobic granules, such as diameter and density. The larger granules modeled higher substrate fluxes (1.8-14 mg/cm(2)-d) and deeper effective film thicknesses (0.18-1.3 cm). The multi-aspect simulation results demonstrated that the substrate either approaches zero in the film (at low concentration) or penetrates the granules (at high concentration). The sum of aerobic granules in the SBRs can be considered as a mass of biofilm, where the substrate approaches zero at sufficient depth. The steady-state biofilm model could be an effective prediction method for optimizing the aerobic granular sludge process.

Effects of Cu2+ on morphological structure, functional groups, and elemental composition of aerobic granular sludge

Aerobic granular sludge (AGS) is shaped by the self-immobilization of microorganisms. In this study, AGS was cultivated successively in a column sequencing batch reactor (SBR) with glucose and sodium acetate as the carbon sources. The shock-loading effects of varying the Cu2+ concentration (0.0, 1.0, 3.0, 5.0, or 10.0 mg/L) on the characteristics of aerobic granules were studied. The results show that Cu2+ has a toxic effect on the aerobic granules. Although the aerobic granules became increasingly loose as the Cu2+ concentration increased from 1.0 to 5.0 mg/L, their structural integrity was largely maintained. However, the aerobic granules disintegrated and their skeletons consisting of internal filamentous bacteria were exposed at the Cu2+ concentration of 10.0 mg/L. The functional groups ‒NH2, ‒OH, ‒COOH, and C‒N reacted with Cu2+. Ca, Fe, and P were the major trace elements observed in the AGS. With an increase in the Cu2+ concentration from 0.0 to 10.0 mg/L, the weight percentages of the essential elements Fe, Ca, Na, and K in the granules decreased from 23.98%, 24.64%, 3.86%, and 3.87% to 14.90%, 13.93%, 0%, and 0%, respectively, whereas the weight percentage of copper increased correspondingly from 0% to 35.43%. Cu2+ was exchanged with the essential metals and chelated by the nitrogen-containing functional groups (–NH2 or C‒N) of the protein. These effects influenced the structural stability of the sludge.

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 m(3)/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.

Treatment of saline wastewater by a sequencing batch reactor with emphasis on aerobic granule formation

The formation and characteristics of aerobic granules in a sequencing batch reactor (SBR), designed to treat saline wastewater, have been investigated in this study. Granule structure was determined using scanning electron microscope (SEM), and polymerase chain reaction (PCR). Granules formed in the reactors were grouped into light brown granules and black granules that looked ‘fluffy’. The first group was more dense than the second group and consequently had a higher settling velocity. The densities of the first and the second group were 0.056 and 0.035g/ml, respectively. While the corresponding settling velocity were 1.35 and 0.97cm/s, respectively. The kinetic coefficients Ks, kd, k and Y in saline substrate (10g NaCl/l) were estimated to be 195mgsCOD/l, 0.025gVSS/gVSSd, 2.29gsCOD/gVSSd and 0.45mgVSS/mgsCOD, respectively. Analysis of granules using 16S rDNA sequences showed that the dominant microbial species was Klebsiella oxitoca. Minerals and the protozoan community in saline substrate facilitated the formation of granules. It was concluded that the fluffy granules are a variation of the light brown granules which are resistant to salt.

Optimal cultivation and characteristics of aerobic granules with typical domestic sewage in an alternating anaerobic/aerobic sequencing batch reactor

The present work investigated some important factors for optimal aerobic granulation using typical domestic sewage as a substrate in a pilot-scale alternating anaerobic/aerobic sequencing batch reactor. High sludge concentration and low sludge loading, for the first time, were used for the reactor start-up. A vast number of small particles appeared on day8. Subsequently, several measures for controlling sludge concentration and sludge loading within an appropriate range were applied to optimize the granulation process. On day 45, complete sludge granulation was achieved. After 60days of operation, the aerobic granules always kept in stable state, with an average diameter of 750μm and the SVI30 of 20–35ml/g. The COD, TN, and TP removal ratios were 92%, 81%, and 85%, respectively. The results demonstrated that it was feasible to form aerobic granules quickly using typical domestic sewage under optimal operation strategies, which was further proved by the results from denaturing gradient gel electrophoresis fingerprint.

A potential explanation for the effect of carbon source on the characteristics of acetate-fed and glucose-fed aerobic granules

This paper proposes a new theory to account for the effect of carbon source on the characteristics of acetate-fed and glucose-fed aerobic granules. It is well known that reactor pH can vary in response to the oxidation of glucose or sodium acetate. As such, the effects associated with the carbon sources may be explained by the changed pH. The proposal was explored by experiments. Aerobic granules were cultivated in three identical sequencing batch reactors (SBRs, R1, R2 and R3), fed with sodium acetate, glucose, glucose and maintained pH at 4.5 - 5.5 (the variation of reactor pH in the oxidation of glucose), 4.5 - 5.5 and 7.5 - 8.5 (the variation of reactor pH in the oxidation of sodium acetate), respectively, and the effects of carbon source and reactor pH on the characteristics of aerobic granules were assessed. The results showed that the characteristics of aerobic granules, including microbial structure, mixed liquor suspended solids (MLSS), sludge volume index (SVI) and nitrification-denitrification, were strongly affected by reactor pH, but were independent with the carbon source supplied. These results fully supported the validity of the new theory. The theory suggests that the cultivation of aerobic granules with glucose or sodium acetate should take more attention to reactor pH rather than carbon source itself. The implications of this theory are discussed with regards to the other common carbon sources as well as better understanding of the mechanisms of aerobic granulation.

Effect of Copper (II) on the Characteristics of Aerobic Granules

Aerobic granules were cultivated successively in column sequencing batch reactor (SBR) with the glucose as carbon source. The effect of copper (II) on the characteristics of aerobic granules was studied. Results showed that the physical, morphology and extracellular polymeric substances (EPS) of aerobic granules were influenced in different degree under different concentrations of copper (II) in sequencing batch reactor (SBR). The appropriate Cu2+ can be adsorbed by the microorganisms in aerobic granules under the functions of chelation and displacement of heavy metals. Under the Cu2+ concentration of 0.5～3.0mg/L, the stable MLSS and better settleable granules with higher S.G. and lower SVI can been attained in the reactors. The sludge can maintain the granules in stable till the Cu2+ concentration increases to 20.0mg/L. The ratios of EPSC/EPN distribute in 6.60～7.01 steadily under the Cu2+ concentration of 0.5～10.0mg/L.However, excess Cu2+ can destroy the metabolism balance of the microorganisms and the protein synthesization and genetic information transportation are baffled. When the Cu2+ concentration increase to 50mg/L, more filamentous appears in the granules and the compact granules change to in disperse. The ratios of EPSC/EPN evidently rise to 7.59 and 7.46 respectively under high Cu2+ concentration of 20.0mg/L and 50.0mg/L. It suggests that the microorganisms try to excreting more EPS and protecting itself from the environmental change.

Characteristics of aerobic granules for biological wastewater treatment

Characteristics of aerobic granules for biological wastewater treatment

Characteristics and stability of aerobic granules cultivated with different starvation time

The characteristics of aerobic granules at steady state and the effects of starvation time on the stability of aerobic granules during the long-term operation were investigated in three sequencing batch reactors (SBRs R1-R3). The SBRs were operated with a cycle time of 1.5, 4.0, and 8.0 h, respectively, which resulted in a starvation time of 0.8, 3.3, and 7.3 h in three reactors, respectively. Results showed that aerobic granules were successfully cultivated in the three reactors, but the granules in R2 with a starvation time of 3.3 h showed the highest density and the best settleability at steady state. It is obvious that the starvation time has an optimum value in terms of settleability of granules. In addition, it was found that the coexistence of a minority of fluffy granules with smooth granules was the potential unstable factor in R1 with a starvation time of 0.8 h at the steady state. The sudden dominance of fluffy granules in R1 after the 160-day operation led to the operation failure of the reactor R1, whereas the granules in R2 with a starvation time of 3.3 h and R3 with a starvation time of 7.3 h showed good stability during the long-term operation. As short starvation time leads to the instability of granules, and long starvation time is not advisable for practical application due to low efficiency, starvation time should be controlled in a reasonable range.

Formation and Hydrodynamic Characteristics of Aerobic Granules in an Activated Sludge System

Development of aerobic granules in the aeration tank of an activated sludge system has been studied. The introduction of activated carbon particles into the aeration tank resulted in the formation of biogranules containing activated carbon as core nuclei. The presence of activated carbon also induced the formation of self-immobilized granules, which did not have any carrier particle at their core. The presence of aerobic granules enhanced the treatment efficiency of the reactor. At an organic loading rate of 32.8 kg COD m−3d−1 and 0.78 h hydraulic retention time (HRT), the reactor showed 96% COD removal efficiency. At an HRT of 0.272 h and organic loading rate of 46.7 kg COD m−3d−1, the reactor outlet COD remained below 100 mg l−1. Settling velocity studies carried out on the biogranules showed that the drag coefficient of biogranules is greater than that of the rigid particle at the same Reynolds number.

Influence of different substrates on the formation and characteristics of aerobic granules in sequencing batch reactors

The effects of different substrates on the aerobic granulation process were studied using laboratory-scale sequencing batch reactors (SBRs). Four parallel granules sequencing batch reactors (GSBR): R 1, R 2, R 3, and R 4 were fed with acetate, glucose, peptone and fecula, respectively. Stable aerobic granules were successfully cultivated in R 1, R 2, R 4, and smaller granules less than 500 μm were formed in R 3. Morphology and the physic-chemical characteristics of aerobic granules fed with different carbon substrates were investigated by the four reactors operated under the same pressure. The aerobic granules in the four reactors were observed and found that peptone was the most stable one due to its good settleability even after a sludge age as short as 10 d. A strong correlation was testified between the characteristics of aerobic granules and the properties of carbon substrates. The stability of aerobic granules was affected by extracellular polymer substances (EPS) derived from microorganism growth during feast time fed with different carbon substrates, and the influence of the property of storage substance was greater than that of its quantity. Optimal carbon substrates, which are helpful in the cultivation and retention of well-settling granules and in the enhancement of the overall ability of the aerobic granules reactors, were found.

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.

Effect of Organic Loading Rate on Aerobic Granulation. II: Characteristics of Aerobic Granules

Four sequential aerobic sludge blanket reactors, Reactors R1, R2, R3, and R4, were operated at organic loading rates (OLRs) of 1, 2, 4, and 8kg chemical oxygen demand (COD)/m3day, respectively. Aer...

Effect of settling time on aerobic granulation in sequencing batch reactor

The essential role of hydraulic settling time in the formation of aerobic granules was studied in four column sequencing batch reactors (R1–R4). Results showed that aerobic granules were successfully cultivated and became dominant only in the R4 operated at the shortest settling time of 5 min, while a mixture of aerobic granules and suspended sludge was observed in R1–R3 run at settling times of 20, 15 and 10 min, respectively. After the steady state was achieved, the respective settling times of R1–R3 was shortened from 20 to 5 min, from 15 to 2 min and from 10 to 1 min; as the result, aerobic granules completely displaced suspended sludge in these three reactors after two-week operation. It was found that cell surface hydrophobicity was improved significantly at short settling times. Analyses of the polyvalent metals contents in aerobic granules showed that the accumulation of calcium in aerobic granules was related to the settling time, however, the total content of iron, magnesium and aluminium in aerobic granules was much pretty lower than the granule calcium content and almost remained constant. It is obvious that a short settling time favours aerobic granulation, and one may expect to manipulate the formation and characteristics of aerobic granules by controlling settling time.

The formation and characteristics of aerobic granules in sequencing batch reactor (SBR) by seeding anaerobic granules

The cultivation of aerobic granules in SBR by seeding anaerobic granular sludge was investigated using acetate-based synthetic wastewater. Morphological variation of granular sludge in the reactor was observed and results revealed that the inoculated anaerobic granules experienced a process of disintegration—recombination—growing up. The disintegrated anaerobic sludge may play a role of nucleus for the granulation of aerobic sludge. The sludge concentration increased for the first 4 weeks, then decreased and reached a stable value of 5 g/l at 60 d with a SVI of 30–40 ml/g. Granular sludge dominated in the reactor and suspended sludge concentration was less than 0.5 g/l at the end of the process. In the inoculated anaerobic granular sludge, spherical bacteria were the main microorganisms, however, rod-shaped and filamentous microorganisms prevailed in the cultivated aerobic granules. This is ready way to cultivate aerobic granules by seeding anaerobic granular sludge.

Elemental compositions and characteristics of aerobic granules cultivated at different substrate N/C ratios.

The effects of the substrate N/C ratios on the formation, elemental compositions and characteristics of aerobic granules were investigated in four sequencing batch reactors. Results showed that aerobic granules could form at substrate N/C ratios ranging from 5/100 to 30/100 and the substrate N/C ratio had a direct and profound effect on the elemental compositions and characteristics of the aerobic granules. Nitrifying populations in aerobic granules were enriched significantly with the increase in the substrate N/C ratio, while the respective ratio of cell oxygen, nitrogen and calcium to cell carbon were also determined by the substrate N/C ratio. It was found that cell hydrophobicity of aerobic granules was inversely related to the ratio of cell oxygen normalized to cell carbon. Since the cell calcium content in aerobic granules developed at different substrate N/C ratios was even lower than that in the seed sludge, it is reasonable to conclude that the cell calcium would not contribute to aerobic granulation. This study probably for the first time demonstrates that the elemental composition, microbial distribution and characteristics of aerobic granules are related to the substrate N/C ratio applied.

Characteristics of Aerobic Granules Grown on Glucose and Acetate in Sequential Aerobic Sludge Blanket Reactors

Aerobic granules were cultivated in two column-type sequential aerobic sludge blanket reactors fed with glucose and acetate, respectively. The characteristics of aerobic granules were investigated. Results indicated that the glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density, hydrophobicity, physical strength, microbial activity and storage stability. Substrate component does not seem to be a key factor on the formation of aerobic granules. However, microbial diversity of the granules is closely associated with the carbon sources supplied to the reactors. Compared with the conventional activated sludge flocs, aerobic granules exhibit excellent physical characteristics that would be essential for industrial application. This research provides a complete set of characteristics data of aerobic granules grown on glucose and acetate, which would be useful for further development of aerobic granules-based compact bioreactor for handling high strength organic wastewater.