Formation Of Aerobic Granules Research Articles

Rapid biodecolourization of eriochrome black T wastewater by bioaugmented aerobic granules cultivated through a specific method

In this paper, an interesting phenomenon is revealed. Mn 2+ has a significant influence on the morphologies of hypha and mycelium of Phanerochaete sp. HSD, and under the higher Mn 2+ concentration, strain HSD can form very small micro-mycelium pellets (MMPs). Based on this phenomenon, a specific method to cultivate aerobic granules is presented. By seeding MMPs to bioreactor, bioaugmented aerobic granules (BAGs) were cultivated successfully, and granulation rate reached 53 ± 2% on day 15. MMPs result in the formation of aerobic granules containing MMPs as nuclei and also induce the formation of self-immobilized biogranules which do not have the MMP at their core. Furthermore, the feasibility of using BAGs to degrade eriochrome black T (EBT) wastewater is investigated too. The results prove that the treatment of EBT wastewater using BAGs is a feasible and promising way. BAGs not only can tolerate higher EBT loads, but also have better decolourization efficiency compared with conventional sludge and aerobic granules. Furthermore, the introduction of MMPs leads to the appearance of manganese peroxidase (MnP) in reactor, and MnP plays an important role in the treatment process of EBT wastewater.

Formation, physical characteristics and microbial community structure of aerobic granules in a pilot-scale sequencing batch reactor for real wastewater treatment

In this study, aerobic granular sludge was successfully developed in a pilot-scale sequencing batch reactor (SBR) installed on site to treat real wastewater using traditional activated sludge as inoculum. Compared with 1 or 2 months required by lab-scale reactor for aerobic granulation, it took about 400 days for activated sludge to transform into granule-dominant sludge in the pilot-scale SBR on site. Although the sludge in the reactor after 400-day operation was a mixture of flocs and granules with floc ratio ranged from 5 to 30%, sludge volume index with 5min settling (SVI5) always maintained at around 30mL/g. The similar microbial community structures represented by denaturing gradient gel electrophoresis (DGGE) between coexisted flocs and granules in the reactor indicated no strong microbial selection after the granules were dominant in the reactor. Chemical oxygen demand (COD) and NH4+-N removal efficiencies were above 80 and 98%, respectively, after 50-day operation, and the total inorganic N removal efficiency was about 50%. The results in this study demonstrate that it is feasible to form aerobic granules in pilot-scale SBR reactor and maintain the long-term stability of granular sludge with a high influent quality fluctuation. Meanwhile, stable COD and NH4+-N removal efficiencies can be obtained in the reactor.

Energy uncoupling inhibits aerobic granulation

Although aerobic granulation has been intensively studied, the possible mechanism of this cell-to-cell self-immobilization phenomenon still remains unclear. Aerobic granulation in the absence and presence of a chemical uncoupler, 3,3',4',5-tetrachlorosalicylanilide (TCS), which can dissipate the proton gradient and further disrupt ATP synthesis, was investigated. Upon exposure to TCS, precultivated mature aerobic granules underwent disintegration, indicating that the stability and integrity of aerobic granules would be associated with microbial energy metabolism. It was also shown that the formation of aerobic granules in the presence of TCS was completely inhibited as compared with the control free of TCS. These results, for the first time, reveal that aerobic granulation is energy metabolism dependent, and possible reasons are also discussed.

Aerobic granules formation and nutrients removal characteristics in sequencing batch airlift reactor (SBAR) at low temperature

To understand the effect of low temperature on the formation of aerobic granules and their nutrient removal characteristics, an aerobic granular sequencing batch airlift reactor (SBAR) has been operated at 10 °C using a mixed carbon source of glucose and sodium acetate. The results showed that aerobic granules were obtained and that the reactor performed in stable manner under the applied conditions. The granules had a compact structure and a clear out-surface. The average parameters of the granules were: diameter 3.4 mm, wet density 1.036 g mL −1, sludge volume index 37 mL g −1, and settling velocity 18.6–65.1 cm min −1. Nitrite accumulation was observed, with a nitrite accumulation rate (NO 2 −–N/NO x −–N) between 35% and 43% at the beginning of the start-up stage. During the stable stage, NO x was present at a level below the detection limit. However, when the influent COD concentration was halved (resulting in COD/N a reduction of the COD/N from 20:1 to 10:1) nitrite accumulation was observed once more with an effluent nitrite accumulation rate of 94.8%. Phosphorus release was observed in the static feeding phase and also during the initial 20–30 min of the aerobic phase. Neither the low temperature nor adjustment of the COD/P ratio from 100:1 to 25:1 had any influence on the phosphorus removal efficiency under the operating conditions. In the granular reactor with the influent load rates for COD, NH 4 +–N, and PO 4 3−–P of 1.2–2.4, 0.112 and 0.012–0.024 kg m −3 d −1, the respective removal efficiencies at low temperature were 90.6–95.4%, 72.8–82.1% and 95.8–97.9%.

The essential role of filling material in aerobic granular biomass generation in a periodic submerged biofilter

The paper reports the results of a laboratory-scale investigation aimed at evaluating the influence of the filling material of a Sequencing Submerged Biofilter Reactor (SSBR) on granular biomass generation. The results showed that aerobic granular biomass generation was obtained only in the reactor filled with kmt-k1 carrier, since the features of this filling media are such that they generate a bed characterised by rather uniform internal and external small-sized pore volumes able to retain the released biofilm particles. Finally, the aerobic granule formation improved the biomass retention efficiency and reduced the excess sludge production.

Granulation of activated sludge in a pilot-scale sequencing batch reactor for the treatment of low-strength municipal wastewater

Aerobic granulation of activated sludge was achieved in a pilot-scale sequencing batch reactor (SBR) for the treatment of low-strength municipal wastewater (<200 mg L −1 of COD, chemical oxygen demand). The volume exchange ratio and settling time of an SBR were found to be two key factors in the granulation of activated sludge grown on the low-strength municipal wastewater. After operation of 300 days, the mixed liquor suspended solids (MLSS) concentration in the SBR reached 9.5 g L −1 and consisted of approximate 85% granular sludge. The average total COD removal efficiency kept at 90% and NH 4 +-N was almost completely depleted (∼95%) after the formation of aerobic granules. The granules (with a diameter over 0.212 mm) had a diameter ranging from 0.2 to 0.8 mm and had good settling ability with a settling velocity of 18–40 m h −1. Three bacterial morphologies of rod, coccus and filament coexisted in the granules. Mathematical modeling was performed to get insight into this pilot-scale granule-based reactor. The modified IWA activated sludge model No 3 (ASM3) was able to adequately describe the pilot-scale SBR dynamics during its cyclic operation.

Understanding the properties of aerobic sludge granules as hydrogels

Aerobic sludge granules are larger, denser microbial aggregates than activated sludge flocs with a smoother and more regular surface, which facilitates greater wastewater treatment intensity. Factors important in their growth are still poorly understood, which is an impediment to the construction and operation of full-scale aerobic sludge granule processes. Data in this article obtained with granules treating an abattoir wastewater provide evidence that aerobic sludge granules are hydrogels. The results also demonstrate a method for characterizing macromolecular associations. The rheological profile of these granules was found to be analogous with that of typical polymer gels. Water uptake or swelling reflects an equilibrium between granule elastic modulus and osmotic pressure, whereby uptake is increased by reducing solute concentration or the elastic modulus. A weakening of the extracellular polymeric substance (EPS) matrix as demonstrated with mechanical spectroscopy was induced by several environmental factors including temperature, pH and ionic strength. Uniform and elastic deformation was observed at low strain. Enzymatic degradation studies indicate that proteins and alpha-polysaccharides were the major granule structural materials. The aerobic sludge granules in the current study were therefore protein-polysaccharide composite physical hydrogels. While aerobic sludge granules treating an abattoir wastewater are used as a case study, many of the fundamental principles detailed here are relevant to other granulation processes. The paradigm established in this study can potentially be applied to better understand the formation of aerobic sludge granules and thus overcome a hurdle in the acceptance of aerobic sludge granulation as an alternative to more traditional wastewater treatment processes.

Treatment of saline wastewater in SBR aerobic granular reactors

Fish canning effluents characterized by their salt content, up to 30 g NaCl/L, were treated, previously diluted to desired concentration, in a SBR where aerobic granular sludge was produced. The formation of mature aerobic granules occurred after 75 days of operation with 3.4 mm of diameter, SVI of 30 mL/g VSS and density around 60 g VSS/L-granule. Treated organic loading rates were up to 1.72 kg COD/(m3.d) with fully organic matter depletion. Ammonia nitrogen was removed via nitrification-denitrification up to 40% when nitrogen loading rates were of 0.18 kg N/(m3.d). The presence of salt in the treated effluent did not cause a detrimental effect on the operation of the reactor once the aerobic granules were formed.

Formation of aerobic granules and their PHB production at various substrate and ammonium concentrations

Aerobic granular sludge rich in polyhydroxybutyrate (PHB) was cultivated in a sequencing batch reactor (SBR) by seeding anaerobic granular sludge. The PHB content in aerobic granules was investigated and the experimental results reveal that both influent chemical oxygen demand (COD) and ammonium concentrations had a significant effect on the morphological characteristics and the PHB production of the aerobic granular sludge. At a COD and ammonium concentration of 750 mg/L and 8.5 mg/L, respectively, the PHB content of the granules reached 44%, but their poor settling ability, as evidenced by a high sludge volume index, was observed. This was attributed to the outgrowth of filamentous bacteria on the granule surface. However, an increase in the ammonium concentration resulted in an elevated sludge concentration and a decrease in the PHB content in the granules. In this case, the aerobic granular sludge with a regular and compact structure was formed. The results suggest that, through controlling the COD and ammonium concentrations in the influent, the PHB-rich aerobic granular sludge with good settling ability could be cultivated.

Microbial population dynamics during aerobic sludge granulation at different organic loading rates

Laboratory experiments were carried out to investigate the evolution of the bacterial community during aerobic sludge granulation. The experiments were conducted in three 2.4 L sequencing batch reactors (SBRs) that were seeded with activated sludge and fed with glucose-based synthetic wastewater. Three different influent organic concentrations were introduced into the three SBRs, R1, R2 and R3, resulting in chemical oxygen demand (COD) loading rates of 1.5 (R1), 3.0 (R2) and 4.5 (R3) kg/m 3 d, respectively. Changes in bacterial diversity throughout the granulation process were monitored and analysed using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) techniques. The experimental results demonstrate that glucose-fed aerobic granules could be formed without significant presence of filamentous bacteria. Granules formed at different loading rates had different morphology, structural properties and bacterial species. A higher loading rate resulted in faster formation of larger and loose granules, while a lower loading rate resulted in slower formation of smaller and more tightly packed granules. The biomass underwent a dynamic transformation in terms of bacterial species richness and dominance during the granulation process. The reactor with the highest substrate loading rate had the lowest species diversity, while the reactor with the lowest substrate loading rate had the highest species diversity. Different dominant species of β- and γ-Proteobacteria and Flavobacterium within the granule communities from the three different SBRs were confirmed by analysis of 16S rDNA sequences of the PCR products separated by DGGE. It is apparent that a few common bacterial species play an important role in the formation and growth of aerobic granules and help sustain the granular sludge structure in the bioreactors.

Formation of aerobic granules in the presence of a synthetic chelating agent

This paper examines the development of aerobic granular sludge in the presence of a synthetic chelating agent, nitrilotriacetic acid (NTA), in sequencing batch reactors (SBR). The growth of seed sludge at 0.26 mM, 0.52 mM and 1.05 mM of NTA was found to be significantly lower as compared to that in the absence of NTA. Aerobic granulation was significantly enhanced in the three SBRs (R2, R3 and R4), which were fed with 0.26 mM, 0.52 mM and 1.05 mM of NTA as a co-substrate, in comparison to the acetate-alone fed SBR (R1). After 2 months of operation, the mean diameter of the biomass stabilized at 0.35 mm in R1 (acetate alone), as compared to 2.18 mm in R4 (1.05 mM NTA + acetate). NTA degradation was established in SBRs, with almost complete removal during the SBR cycle. Batch experiments also showed efficient degradation of NTA by the aerobic granules.

Formation and characterisation of fungal and bacterial granules under different feeding alkalinity and pH conditions

Laboratory experiments were carried out using two identical bioreactors to investigate the effect of feeding alkalinity and pH on the formation of aerobic sludge granules in wastewater treatment. Both bioreactors, of 2.4 L each in working volume and seeded with activated sludge, were operated as sequencing batch reactors (SBR) and fed at the same rate with a glucose-based synthetic wastewater. The first SBR, with a low alkalinity of 28.7 mg CaCO 3/L in the influent, had a pH of about 3.0 in the reactor and achieved rapid formation of fungi-dominating granules in 1 week. The second SBR, with a high alkalinity of 301 mg CaCO 3/L from the addition of 440 mg NaHCO 3/L to the influent, maintained a reactor pH of around 8.1 and had a slower formation of bacteria-dominating granules, taking about 4 weeks. After granulation, both reactors performed well in organic degradation and sludge–liquid separation. However, according to examinations carried out using scanning electronic microscopy (SEM) and confocal laser scanning microscopy (CLSM), the mature fungal granules with a mean size of 7.0 mm had a loosely packed fluffy structure. Both fungi and extracellular polymeric substances (EPS) were distributed uniformly throughout the granules. The bacterial granules were smaller, with a mean size of 4.8 mm and a compact structure. EPS were distributed throughout and bacteria were mainly situated in the outer layer of the mature granules. Granulation of fungal sludge could be completed more rapidly than bacterial granulation. However, fungal granules were apparently weaker in structure and subject to more breakage and erosion than bacterial granules in aeration turbulence. The results suggest that by controlling the feeding alkalinity and reactor pH, a strategy of species selection can be developed for aerobic sludge granulation at different rates with different microbial communities and structural features.

Formation and microbial community analysis of chloroanilines-degrading aerobic granules in the sequencing airlift bioreactor

This paper investigates a selection-based acclimation strategy for improving the performance and stability of aerobic granules at a high chloroanilines loading. The experiments were conducted in a sequencing airlift bioreactor (SABR) to develop aerobic granules fed with chloroanilines (ClA). The evolution of aerobic granulation was monitored using image analysis and scanning electron microscopy, and PCR-DGGE analysis of microbial community was performed. The sludge granulation was apparently developed by decreased settling time and gradual increased ClA loading to 0.8 kg m(-3) day(-1). A steady-state performance of the granular SABR was reached at last, as evidenced by biomass concentration of 6.3 g l(-1) and constant ClA removal efficiency of 99.9%. The mature granules had a mean size of 1.55 mm, minimal settling velocity of 68.4 m h(-1), specific ClA degradation rate of 0.181 g gVSS(-1) day(-1). Phylogenetic analysis of aerobic ClA-degrading granules confirmed the dominance of beta-, gamma-Proteobacteria and Flavobacteria. The chosen operating strategy involving step increase in ClA loading and enhancement of major selection pressures was successful in cultivating the aerobic ClA-degrading granules. This research could be helpful for improving the stability of aerobic granules via optimizing operating conditions and developing economic feasible full-scale granular bioreactor.

Effects of aeration intensity on formation of phenol-fed aerobic granules and extracellular polymeric substances

Effect of air aeration intensities on granule formation and extracellular polymeric substances content in three identical sequential batch reactors were investigated. The excitation-emission-matrix spectra and multiple staining and confocal laser scanning microscope revealed proteins, polysaccharides, lipids, and humic substances in the sludge and granule samples. Seed sludge flocs were compacted at low aeration rate, with produced extracellular polymeric substances of 50.2-76.7 mg g(-1) of proteins, 50.2-77.3 mg g(-1) carbohydrates and 74 mg g(-1) humic substances. High aeration rate accelerated formation of 1.0-1.5 mm granules with smooth outer surface. The corresponding quantities of extracellular polymeric substances were 309-537 mg g(-1) of proteins, 61-109 mg g(-1) carbohydrates, 49-92 mg g(-1) humic substances, and 49-68 mg g(-1) lipids. Intermediate aeration rate produced 3.0-3.5 mm granules with surface filaments. Reactor failure occurred with overgrowth of filaments, probably owing to the deficiency of nutrient in liquid phase. No correlation was noted between extracellular polymeric substances composition and the proliferation of filamentous microorganisms on granule surface.

Role of extracellular protein in the formation and stability of aerobic granules

The extracellular proteins extracted from the sludge samples had molecular weights in the range of 31.0–97.4 kDa. Several new protein bands were observed with the aerobic granulation. The quantitative data on extracellular polymeric substances (EPS) indicated the secreted extracellular protein contents increased from 49.4 mg g −1 (VSS) in the seed sludge to 148.3 mg g −1 (VSS) in aerobic granules on day 45, while the extracellular polysaccharides remained almost unchanged. The quantitative data on protein was consistent with the sodium dodecyl sulfonate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Sludge surfaces were more hydrophobic and less negatively charged after aerobic granulation than the flocculent seed sludge. The ratio of proteins to polysaccharide within the sludge EPS increased with the granulation from 2.3 to 4.9 corresponding to the changes in the surface properties of the sludge. A more hydrophobic and less negatively charged surface corresponded to a higher ratio of the extracellular proteins to polysaccharides. After the complete aerobic granulation, the increase of the influent COD loads from 4 to 12 g L −1 d −1 was accompanied with a decrease of the secreted extracellular protein in types and contents and an increase of polysaccharide concentration in sludge EPS. A less hydrophobicity of sludge surface was associated with the changes in the composition of EPS. This might explain why the disintegration of granules would occur at the high influent COD loads employed (10 and 12 g L −1 d −1) from a standpoint of microbiological surface properties. It was proposed that that extracellular protein might be strongly involved in the aggregation of suspended flocs into granules, and also associate with the stability of the granules through affecting the surface properties of sludge.

Influence of starvation time on formation and stability of aerobic granules in sequencing batch reactors

Three sequencing batch reactors, R1, R2 and R3, with a 1.5-h, 4-h and 8-h cycle time, respectively, were used to cultivate aerobic granules with the same synthetic wastewater containing 1000 mg l −1 COD. As the initial COD concentrations in the cycles were the same, three different cycle times led to three different starvation times in repeated cycles of the three reactors. It was found that 63 cycles were needed to form granules with the longest starvation time in R3 while it took 256 cycles in R1 with the shortest starvation time. However, as far as the formation time was concerned, granules were formed on day 16 with 1.5-h cycle time while on day 21 with 8-h cycle time, which indicated that a shorter cycle time with a shorter starvation time speeded up the granulation. This was mainly due to the stronger hydraulic selection pressure at shorter cycle time. However, it was found that granules formed with cycle time of 1.5 h were unstable. Fluffy granules with poor settling ability were observed in R1 in the 4th month, which led to the collapse of R1 after 160-day of operation. Granules in R2 and R3 showed good stability during the long-term operation. Therefore, a reasonable starvation time was necessary to maintain the long-term stability of aerobic granules.

Starvation is not a prerequisite for the formation of aerobic granules

Activated sludge with sludge volume index (SVI)(30) of 77 ml g(-1) and SVI(30) of 433 ml g(-1) was inoculated to start up reactors R1 and R2, respectively. In both R1 and R2, cycle time of 1 h and the influent chemical oxygen demand (COD) concentrations of 1,000 mg l(-1) were employed. Initial settling time of 2 min resulted in the loss of a substantial amount of biomass as wash-out and high effluent COD concentrations within the first week of operation. This implied that there was no starvation phase in each cycle of R1 and R2 during the first week of operation. However, aerobic granules with a size above 400 mum formed by day 7. Thus, it was concluded that starvation was not a prerequisite for the formation of aerobic granules. When cycle time was 1 h, the instability of aerobic granules was observed. When cycle time was prolonged to 1.5 h and granular sludge of 200 ml was used to start up reactor R3, the reactor R3 reached steady state within 1 week. SVI, size, and the morphology of granular sludge in R3 remained stable during the 47-day operation, which indicated that prolonged starvation time had positive effects on the stability of aerobic granules.

Performances of a granular sequencing batch reactor (GSBR)

Aerobic granulation in sequencing batch reactors is widely reported in literature and in particular in SBAR (Sequencing batch airlift reactor) configuration, due to the high localised hydrodynamic shear forces that occur in this type of configuration. The aim of this work was to observe the phenomenon of the aerobic granulation and to confirm the excellent removal efficiencies that can be achieved with this technology. In order to do that, a laboratory-scale plant, inoculated with activated sludge collected from a conventional WWTP, was operated for 64 days: 42 days as a SBAR and 22 days as a SBBC (sequencing batch bubble column). The performances of the pilot plant showed excellent organics removal. COD and BOD removal efficiencies were respectively, 93 and 94%; on the contrary, N-removal efficiency was extremely low (5%-45%/o). The granules dimensions increased during the whole experimentation; change of reactor configuration contributed to further improve this aspect. The experimental work confirmed the essential role of hydraulic settling time in the formation of aerobic granules and in the sludge settleability and the need to find an optimum between granule size and oxygen supply to achieve good N-removal efficiency.

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.