Formation Of Aerobic Granules Research Articles

Specific aerobic granules can be developed in a completely mixed tank reactor by bioaugmentation using micro-mycelial pellets of Phanerochaete chrysosporium

Aerobic granules were firstly developed in a completely mixed tank reactor (CMTR) by seeding micro-mycelial pellets (MMPs) of Phanerochaete chrysosporium. During phenol wastewater treatment, sludge granulation rate reached 67 % after 15-day operation. The granules in CMTR are different from aerobic granules described in literature in morphology, and a majority of them are rod-shaped or rodlike sludge besides spherical granules. The polymorphic granules, having no essential difference with aerobic granules previously reported, achieve advantages over conventional activated sludge in settling ability, biomass concentration, density, integrity coefficient and removal ability to phenol wastewater. The optimized parameters for sludge granulation in CMTR including temperature, inoculum quantity, rotary speed and superficial air upflow velocity are 30 °C, 5–7 g/l, 150 rpm, and 0.5 cm/s, respectively. Analysis on sludge granulation mechanism indicates that MMPs not only result in the formation of aerobic granules containing MMPs as nuclei, but also induce the formation of biogranules which do not have MMP at their cores. The work challenges the general belief that the homogenous circular flow pattern of microbial aggregates is necessary for aerobic sludge granulation.

Aerobic Granulation in a Sequencing Batch Reactor for the Treatment of Piggery Wastewater

This study investigated the formation of aerobic granules fed with digested piggery wastewater. After 42 days of cultivation, small yellow granules with mean diameter of 0.4 mm were first observed in the reactor. Scanning electron microscope pictures showed the granules were compact, round structures with clear outer shapes and mainly composed of filamentous bacteria. Maximum chemical oxygen demand and ammonia removal ratios were 90.1 and 91.7%, respectively. The Monod equation, which was used to describe ammonium utilization, yielded a maximum rate of 6.25 mg (g volatile suspended solids)(-1) h(-1). The measurement of extracellular polymeric substances (EPS) content and three-dimensional excitation and emission matrix results showed that the EPS concentration increased during the granulation process. Fluorescence in situ hybridization analysis showed significant amounts of nitrifying bacteria in the aerobic granules. Results in this study provide insights to the treatment of piggery wastewater using aerobic granular sludge.

Modeling and optimization of granulation process of activated sludge in sequencing batch reactors

Aerobic granulation is a promising process for wastewater treatment, but this granulation process is very complicated and is affected by many factors. Thus, a mathematical model to quantitatively describe such a granulation process is highly desired. In this work, by taking into account all of key steps including biomass growth, increase in particle size and density, detachment, breakage and sedimentation, an one-dimensional mathematic model was developed to simulate the granulation process of activated sludge in a sequencing batch reactor (SBR). Discretization methodology was applied by dividing operational time, sedimentation process, size fractions and slices into discretized calculation elements. Model verification and prediction for aerobic granulation process were conducted under four different conditions. Four parameters indicative of granulation progression, including mean radius, biomass discharge ratio, total number, and bioparticle size distribution, were predicted well with the model. An optimum controlling strategy, automatically adjusted of settling time, was also proposed based on this model. Moreover, aerobic granules with a density higher than 120 g VSS/L and radius in a range of 0.4-1.0 mm were predicted to have both high settling velocity and substrate utilization rate, and the corresponding optimum operating conditions were be determined. Experimental results demonstrate that the developed model is appropriate for simulating the formation of aerobic granules in SBRs. These results are useful for designing and optimizing the cultivation and operation of aerobic granule process.

Distribution of Extracellular Polymeric Substances and their Role in Aerobic Granule Formation

This study investigated the quantity and distribution of extracellular polymeric substances (EPS) in aerobic granules. Results showed that EPS play an important role in the formation and stabilisation of granules. The content of EPS significantly increases during the first weeks of biogranulation. An analysis of EPS in the granules revealed that the protein level was 5 times higher than in polysaccharides. The increase of protein content correlated with the growth of cell hydrophobicity (r2 = 0.95). EPS and hydrophobicity are important factors in cell adhesion and formation of granules. The aim of this work was also to determine the distribution of EPS in the granule structure. In situ EPS staining showed that EPS are located mostly in the center of granules and in the subsurface layer. The major components of the EPE matrix are proteins, nucleic acids and β-polysaccharides. These observations confirm the chemical extraction data and indicate that granule formation and stability are dependent on protein content.

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.

Aerobic granulation and nitrogen removal with the effluent of internal circulation reactor in start-up of a pilot-scale sequencing batch reactor

Aerobic granular sludge was successfully cultivated with the effluent of internal circulation (IC) reactor in a pilot-scale sequencing batch reactor (SBR) using activated sludge as seeding sludge. N removal was investigated in the start-up of aerobic granulation process. Initially, the phenomenon of partial nitrification was observed and nitrite accumulation rates (NO(2) (-)-N/NO (x) (-) -N) were between 84.6 and 99.1 %. It was potentially caused by ammonium oxidizing bacteria (AOB) in the seeding activated sludge, high external environmental temperature (~32 °C) and free ammonia (FA) concentration. After 50 days' running, the aerobic granules-based bioreactor demonstrated perfect performance in simultaneous removal of organic matter and ammonia nitrogen, and average removal efficiencies were maintained above 93 and 96 %, respectively. The maximum nitrogen removal efficiency of 83.1 % was achieved after the formation of aerobic granules. The average diameter of mature aerobic granular sludge mostly ranged from 0.5 to 1.0 mm. Furthermore, one typical cyclic test indicated that pH and DO profiles could be used as effective parameters for biological reactions occurring in the aerobic/anoxic process. The obtained results could provide further information on the cultivation of aerobic granular sludge with practical wastewater, especially with regard to nitrogen-rich industrial wastewater.

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.

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.

Bacterial Selection during the Formation of Early-Stage Aerobic Granules in Wastewater Treatment Systems Operated Under Wash-Out Dynamics.

Aerobic granular sludge is attractive for high-rate biological wastewater treatment. Biomass wash-out conditions stimulate the formation of aerobic granules. Deteriorated performances in biomass settling and nutrient removal during start-up have however often been reported. The effect of wash-out dynamics was investigated on bacterial selection, biomass settling behavior, and metabolic activities during the formation of early-stage granules from activated sludge of two wastewater treatment plants (WWTP) over start-up periods of maximum 60 days. Five bubble-column sequencing batch reactors were operated with feast-famine regimes consisting of rapid pulse or slow anaerobic feeding followed by aerobic starvation. Slow-settling fluffy granules were formed when an insufficient superficial air velocity (SAV; 1.8 cm s−1) was applied, when the inoculation sludge was taken from a WWTP removing organic matter only, or when reactors were operated at 30°C. Fast-settling dense granules were obtained with 4.0 cm s−1 SAV, or when the inoculation sludge was taken from a WWTP removing all nutrients biologically. However, only carbon was aerobically removed during start-up. Fluffy granules and dense granules were displaying distinct predominant phylotypes, namely filamentous Burkholderiales affiliates and Zoogloea relatives, respectively. The latter were predominant in dense granules independently from the feeding regime. A combination of insufficient solid retention time and of leakage of acetate into the aeration phase during intensive biomass wash-out was the cause for the proliferation of Zoogloea spp. in dense granules, and for the deterioration of BNR performances. It is however not certain that Zoogloea-like organisms are essential in granule formation. Optimal operation conditions should be elucidated for maintaining a balance between organisms with granulation propensity and nutrient removing organisms in order to form granules with BNR activities in short start-up periods.

Aerobic Granules Formation in Dual-Layer Percolating Filters

Aerobic spherical granules were observed in zeolitic dual-layer intermittent percolating i»?filters i»?treating domestic septic tank effluent. The diameter of the granules ranged from 0.05 to 0.5 mm and when they predominate in the biofilms the mean SVI value was of 54 ml g-1 instead of 232 ml g-1 when they were absent. Flow behavior in these filters was characterized by the dimensionless Reynolds number. The values obtained (40

Effect of the food-to-microorganism (F/M) ratio on the formation and size of aerobic sludge granules

Laboratory experiments were carried out to investigate the effect of the sludge loading, or the food-to-microorganism (F/M) ratio, on the rate of aerobic granulation and the size of the granules in biological wastewater treatment. Four column batch reactors were used with a similar sludge suspended solids (SS) concentration of around 2000mg/L. The reactors were fed with a glucose-based wastewater at different chemical oxygen demand (COD) concentrations, resulting in F/M ratios from 0.3 to 1.1gCOD/gSS-d. A higher F/M ratio appeared to promote faster formation of larger granules and a lower F/M ratio led to slower formation of smaller granules. Upon complete granulation, the granules became rather stable in size, and the mean diameter of the granules in different reactors increased from 1.2 to 4.5mm linearly with the F/M ratio applied. Molecular analysis of the sludge did not show the domination of any particular bacterial species during the granulation process. It is apparent that applying different F/M ratios in different granulation stages, e.g., a higher F/M in the early stage and a reduced F/M in the later stage, can be an effective start-up strategy to facilitate rapid granule formation and sustain small and healthy granules in bioreactors.

The study of membrane fouling in the view of operating conditions and parameters

Aerobic granulation of activated sludge was achieved in a pilot scale column type sequencing batch reactor (SBR) employed for the treatment of pulp and paper industry wastewater containing Adsorbable Organic Halide (AOX) in the range of 15–20 mg/L. Throughout the 780 days of operation the biomass trends to remain in between 7 and 8 g/L MLVSS and SVI reduced to 60–80 mL/g MLSS. After applying different selection pressure the average size of aerobic granule in the SBR was in the range of 2–4 mm. After achieving steady state conditions in the pilot plant, at an organic loading rateof 4.5 kg COD m−3day−1 at 6 h HRT the degradation of AOX was significant and the effluent AOX concentration of below 5 mg/L was achieved. The results achieved in the study exhibit the viability of formation of aerobic granules in pilot scale SBR and maintenance of long-term strength of aerobic granular sludge with a high reduction of AOX in pulp and paper industry wastewater.

Aerobic granulation with low strength wastewater at low aeration rate in A/O/A SBR reactor

The formation of aerobic granules with low organic loading synthetic wastewater (150–200 mg L −1 of influent COD, acetate/propionate = 1/3) at low aeration rate (0.6 cm s −1 of superficial gas velocity) had been investigated in the anaerobic/oxic/anoxic SBR. Aerobic granules with smooth surface and compact structure were successfully obtained after 50 days. However, these aerobic granules were unstable when the d(0.9) of granules increased to more than 1 mm. The results suggested that the aerobic granules with small diameter (smaller than 1000 μm) were more favorable for treating the low substrate loading wastewater at the low aeration rate. The cycle test revealed that most of the influent COD was removed at the anaerobic stage. The effluent concentrations of N–NH 4 + and P–PO 4 3− were lower than 1 mg L −1, and the effluent concentration of nitrate gradually decreased with the granulation. Phosphate accumulating organisms were found to utilize O 2 or NO x − as electron acceptor for phosphorus removal in the study. Simultaneous nitrogen and phosphorus removal occurred inside the granules.

The characteristics and kinetic behaviors of steady-state aerobic gra- nules under different aerobic starvation

A brief review of aerobic granulation shows that the longer aerobic starvation was an important factor in the formation of aerobic granules,but little information could be found currently available on the essential role of aerobic starvation at steady-state aerobic granules.Thus,this study investigated the characteristics and kinetics of mature aerobic granules in SBR,which performed visible differences at aerobic starvation of 1 h,2 h,3 h and 4 h(R1-R4) respectively.Results indicated that the longer starvation was not a key factor on steady-state granular system.All reactors could keep sludge granulation and stable operating,and the COD removal rate of four reactors was above 98%.However,different aerobic starvation showed an obviously effect on the characteristics of aerobic granules.In 35 days,due to the lower starvation,the production yield of extracellular polymeric substance was reduced,but the ratio of polysaccharides to proteins of granules was increased by 6%,and the size granules still increased.Meanwhile,the longer starvation(2 h) would cause overgrowth of filamentous bacteria,thereby weak the physical characteristics and increase the SVI30 value of granules.In addition,kinetic behaviors of mature aerobic granules showed that the maximum specific COD removal rates(qmax) was 0.25-0.29 h?1(R1-R4),those of four reactors kept the similar level.The apparent half rate constant(K) and biomass yield(Y) of granules were 5.39-8.45 mg/L and 0.391-0.746 kgMLVSS/kgCOD in R1-R4,the reactor had a higher COD effluent and biomass yield under the lower starvation.Thus,the steady-state aerobic granules with low aerobic starvation could successfully apply in SBR,thereby save the energy consumption and keep the stability of granular system.

A review on the essential role of substrate on aerobic granulation

Aerobic granulation is a selection pressure-driven cell-to-cell immobilisation process. So far, the essential role of substrates on aerobic granulation has not been well clarified. This paper reviews current studies about aerobic granulation with different substrates. Although substrates do not exert a major selection pressure on aerobic granulation, they will select substrate-related microorganisms and adjust microbial diversity, and further influence the formation, stability, and structure of aerobic granules. Co-substrate cultivation strategy can be adopted to accelerate aerobic granulation and improve the stability and performance of aerobic granules. This paper hopes to provide a platform for developing full-scale aerobic granules based bioreactors.

Aerobic granule formation in a sequencing batch reactor treating newsprint effluent under low phosphate conditions

Pulp and paper mills are under increasing pressure to minimize the discharge of phosphate to receiving waters. We investigated the operation of two laboratory sequencing batch reactors (SBR) under low phosphate conditions over a period of eight months. Performance characteristics in terms of COD and TSS removal were similar to the full-scale mill activated sludge operation, but the floc density and structure was improved. Sludge yield as a result of phosphate limitation was routinely lower than 0.15 kg/kg of COD. Aerobic granule formation was established in one of the SBRs by reducing the settling time from 30 min to 2 min and by increasing stirring shear force. Once established, the brown granules which were 1-2 mm in diameter were stable over five months of operation. Extracellular polymeric substance (EPS) analysis of the granules indicated a higher galactose content and lower mannose content than in conventional flocs. The granules generated more quorum sensing compound (acyl homoserine lactone) than conventional flocs, suggesting that quorum sensing could play a role in granule formation. When compared to the conventional SBR, the aerobic granule SBR performed at a higher organic loading, at faster settling velocity, and without filamentous bulking.

Structural Determination of a Key Exopolysaccharide in Mixed Culture Aerobic Sludge Granules Using NMR Spectroscopy

Nuclear magnetic resonance (NMR) techniques were used to elucidate the structure of an exopolysaccharide material previously revealed to be important in formation of aerobic granules. The 1D NMR spectral data acquired showed that this gel-forming polysaccharide was a major component of granular EPS, while 1D and 2D NMR spectra showed it consisted of eight sugar residues. These were assigned as α-galactose, α-rhamnose, 2-acetoamido-2-deoxy-α-galactopyranuronic acid, β-mannose, β-galactose, β-glucuronate, β-glucosamine, and N-acetyl β-galactosamine. With the exception of 2-acetoamido-2-deoxy-α-galactopyranuronic acid, a highly unusual sugar, their presence was confirmed with high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Carbon and proton shifts were assigned for each sugar. Heteronuclear multiple bond correlation (HMBC) and nuclear Overhauser enhancement spectroscopy (NOESY) were used to identify linkage sites between individual sugar residues. This gel-forming exopolysaccharide appeared to be a highly complex single heteropolysaccharide with a repeat sequence of α-galactose, β-mannose, β-glucosamine, N-acetyl-β-galactosamine, and 2-acetoamido-2-deoxy-α-galactopyranuronic acid. It has a disaccharide branch of β-galactose and β-glucuronic acid attached to 2-acetoamido-2-deoxy-α-galactopyranuronic acid and an α-rhamnose branch attached to α-galactose.

Effect of seed sludge on characteristics and microbial community of aerobic granular sludge

Abstract Aerobic granular sludge was cultivated by using different kinds of seed sludge in sequencing batch airlift reactor. The influence of seed sludge on physical and chemical properties of granular sludge was studied; the microbial community structure was probed by using scanning electron microscope and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that seed sludge played an important role on the formation of aerobic granules. Seed sludge taken from beer wastewater treatment plant (inoculum A) was more suitable for cultivating aerobic granules than that of sludge from municipal wastewater treatment plant (inoculum B). Cultivated with inoculum A, large amount of mature granules formed after 35 days operation, its SVI reached 32.75 mL/g, and SOUR of granular sludge was beyond 1.10 mg/(g·min). By contrast, it needed 56 days obtaining mature granules using inoculum B. DGGE profiles indicated that the dominant microbial species in mature granules were 18 and 11 OTU when inoculum A and B were respectively employed as seed sludge. The sequencing results suggested that dominant species in mature granules cultivated by inoculum A were Paracoccus sp., Devosia hwasunensi, Pseudoxanthomonas sp., while the dominant species were Lactococcus raffinolactis and Pseudomonas sp. in granules developed from inoculum B.

Performance and fouling characteristics in a membrane sequence batch reactor (MSBR) system coupled with aerobic granular sludge

The treatment performances and membrane fouling parameters of a membrane sequencing batch reactor (MSBR) used to treat synthetic wastewater were studied over 300 days. Aerobic granular sludge ranging from 500 to 1000 µm in particle diameter was cultivated after a period of regulation in operating conditions. The MSBR with aerobic granules achieved a high removal efficiency of pollutants. The emergence of aerobic granules in the MSBR system improved the membrane performance, as indicated by the fouling rate being maintained below 0.1 kPa d − 1 when the MLSS concentration was greater than 18 g L − 1 . The change in granule size and improved sludge settleability played an important role in sustaining the membrane permeability. Specifically, the reduced SVI led to a decrease in the supernatant TOC concentration that corresponded to a slower rise in TMP and less membrane fouling. Proteins were the primary components of EPS, while polysaccharides constituted a higher portion in SMP. In addition, the relative hydrophobicity (RH) and zeta potential increased in the sludge, while the protein to carbohydrate ratio (P/C) of both EPS and SMP increased after the formation of aerobic granules. These changes also enhanced the filterability of the mixed liquor.

Three-dimensional excitation emission matrix fluorescence spectroscopy and gel-permeating chromatography to characterize extracellular polymeric substances in aerobic granulation

Three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy and gel-permeating chromatography (GPC) were employed to characterize the extracellular polymeric substances (EPS) in aerobic granulation. EPS matrix in this study was stratified into four fractions: (1) supernatant, (2) slime, (3) loosely bound EPS (LB-EPS), and (4) tightly bound EPS (TB-EPS). The results showed that the dissolved organic carbon was mainly distributed in TB-EPS fraction, and increased with increasing the operating time. The supernatant, slime, and LB-EPS fractions exhibited four fluorescence peaks, an autochthonous signature, unimodal MW distribution and lower molecular weight (MW) (3 < log [MW]<5), whereas the TB-EPS fraction only had two peaks, an allochthonous signature, multiple peaks and higher MW (5 < log [MW]<7). It was deemed that the formation of aerobic granules was correlated with the accumulation of proteins in the TB-EPS fraction. EEM spectroscopy and GPC profiles could be used as appropriate and effective methods to characterize the EPS in aerobic granulation from a micro-view level.