Development Of Aerobic Granules Research Articles

Characterization of aerobic granules formed in an aspartic acid fed sequencing batch reactor under unfavorable hydrodynamic selection conditions

Granules initiation and development is the backbone of aerobic granular sludge technology. Feed composition can notably affect initiation and development of aerobic granules, and yield aerobic granules with distinct microbial community, morphology and structure. This paper reports an unexpected formation of aerobic granules in an aspartic acid fed SBR under unfavorable hydrodynamic selection conditions. Detailed characteristics of these aerobic granules were investigated in terms of morphology, structure, bioactivity and EPS. The results showed that due to the absence of favorable hydrodynamic selection pressure, the formed aerobic granules had an irregular shape with a rough outline and loose internal structure, which was quite different from mature aerobic granules. Bacteria in these aerobic granules were mainly presented in the form of microcolony with calcium and β-polysaccharides responsible for its mechanical stability. The high N/C ratio of aspartic acid enabled the enrichment of significant amount of nitrifiers within aerobic granules and thus resulted in high nitrification activity of these aerobic granules. The negatively charged and hydrophilic aspartic acid also induced the bacteria to secrete more exopolysaccharides for contributing to more neutral and hydrophilic surface of the aerobic granules, which was beneficial for aspartic acid capture. As a result, polysaccharides, rather than proteins, became the major components of EPS in these aerobic granules. This paper provides us a foundation to better understand the granulation potential of proteinaceous substrates that is frequently encountered in industrial wastewaters.

The development of aerobic granules from slaughterhouse wastewater in treating real dyeing wastewater by Sequencing Batch Reactor (SBR)

In this research, the ability of preformed aerobic granules, which were formed in slaughterhouse wastewater, was investigated for treatment of real dyeing wastewater. The percentages of real dyeing wastewater in the influent were increased gradually from 50% to 100% in orders to investigate the ability of granules in treating of real dyeing wastewater. According to outcomes, maximum chemical oxygen demand (COD) elimination was up to 87%, while the best percentage of dye removal was about 42.6%. Due to the toxic effect of dyeing wastewater, 43.3% reduction in the amount of specific oxygen uptake rate (SOUR) was observed after 90 day of operation. Furthermore, when the percentages of real dyeing wastewater increased to 100%, the granules collapsed, which lead to decrement of granular ratio (GR). Granules collapsing led to 86.5%, 49.73% and 40% reduction in GR0.3, GR0.5 and GR1, respectively.

Effect of air flow rate on development of aerobic granules, biomass activity and nitrification efficiency for treating phenol, thiocyanate and ammonium

The impact of air flow rate on aerobic granulation was evaluated for treating toxic multiple pollutants; phenol (400 mg L−1), thiocyanate (100 mg L−1) and ammonia nitrogen (100 mg L−1) by using three lab scale sequencing batch reactors (SBRs) (R1, R2 and R3). Larger granules (2938.67 ± 64.91 μm) with higher biomass concentration (volatile solids of 4.17 ± 0.09 g L−1), higher granule settling velocity (55.56 ± 1.36 m h−1) and lower sludge volume index (35.25 ± 1.71 mL gTSS−1) were observed at optimal air flow rate of 2.5 L min−1 (R2). Confocal laser scanning microscopic images illustrated the extended fluorescence for extracellular polymeric substances in R2. In R2, partial nitrification was achieved. Phenol was completely removed in all the reactors while partial removal of SCN− and no nitrification were observed with a decrease (1.5 L min−1) and an increase (3.5 L min−1) in air flow rates (R1 and R3, respectively). This study provides an experimental contribution to examine the effect of optimal combination of aeration and toxic multiple pollutants, governing characteristics and nitrification efficiency of granules along with SBR performance in an economic way in terms of optimal air supply.

The development of aerobic granules from conventional activated sludge under anaerobic-aerobic cycles and their adaptation for treatment of dyeing wastewater

In the present study aerobic granules were formed from conventional activated sludge under anaerobic-aerobic cycles in synthetic media and subsequently used for treatment of real dyeing wastewater. Mature aerobic granules, characterised by their consumption of loosely bound extracellular polymeric substances (LB-EPS), and with %GR0.3 (percentage of granules with size ⩾0.3mm) that exceeded 80%, were formed after 94days of operation. Scanning electron microscope (SEM) structural analysis of the aerobic granules pointed to the possibility of the occurrence of azo dye decolorisation inside the aerobic granules during the aerobic phase of sequencing batch reactor (SBR) cycle. The presence of statistically meaningful correlations between total EPS, tightly bound EPS (TB-EPS) – including its protein (PN) and carbohydrate (PS) fraction and their ratio (PN/PS) – with %GR0.5 (percentage of granules with size ⩾0.5mm) and SVI30 were identified, with the protein component of TB-EPS having the greatest influence. A hitherto unreported trend of change of EPS during both the anaerobic and aerobic phase and COD during the anaerobic phase was observed. The aerobic granules were successfully adapted to real dyeing wastewater with 73% color removal and 68% COD removal being achieved with a cycle time of 24h and ratio of anaerobic to aerobic period of 3. Measurement of anaerobic and aerobic color removal revealed aerobic dye decolorisation in the anaerobic core of the aerobic granules up to the point where the %GR0.3 was above 50%. However, during the 94days adaptation period, despite the increase in both total EPS and PN/PS ratio in the greater part of SBR operation, %GR0.3 showed a continuous drop from 81% to 31%.

THE IMPACT OF REACTOR HEIGHT/DIAMETER (H/D) RATIO ON AEROBIC GRANULAR SLUDGE (AGS) FORMATION IN SEWAGE

Until now, the development of aerobic granules sludge (AGS) has been extensively reported using sequencing batch reactor (SBR) with reactor height/diameter (H/D) ratio of over 10. This is because the formation process of aerobic granules itself is depending upon the flowing trajectory inside reactor indulge by reactor height and superficial air velocity (SUAV). Thus, this study aims to determine effect of reactor H/D ratio on performance of AGS develop in two SBRS with equal working volume and organic loading rate (OLR). The two SBRs namely as SBR1 and SBR2 had a difference in reactor H/D ratio of 11.3 and 4.4, respectively. At an aeration rate of 4 L/min, SUAV for SBR1 was two time higher than in SBR2, which were 1.33 cm/s and 0.7 cm/s, respectively. Thus, the SBR2 configuration condition seems unfavorable for development of compact aerobic granules. However, it was found that aerobic granules can be developed in both SBRs at an OLR as low as 0.12 kg CODs/m3 d and up to 0.49 kg CODs/m3 d. Mature aerobic granules were successfully developed after 49 and 89 days of formation, for Batch1 AGS and Batch2 AGS, respectively. At stable conditions, the highest CODs removal and SS effluent for Batch1 AGS and Batch2 AGS were more than 80% and below 26 mg/L, respectively. While effluent performance in both reactors was high, analysis on SVI30 indicated that SBR1 produced more sludge than SBR2. Compare to SBR1, at similar settling time of 15 min, SBR2 provide a short settling distance for biomass which was preferable in case of system breakdown due to shock OLR.

Biodegradation of m-cresol by aerobic granules in a sequencing batch reactor

The present study was aimed at the development of aerobic granules in a sequencing batch reactor for the biodegradation of m-cresol. The reactor was started with 100 mg L−1 of m-cresol. Aerobic granules first appeared within 1 month of the start-up of the reactor. The granules were large and strong and had a compact structure. The diameter of stable granules on day 200 was in the range of 1.5–5 mm. The integrity coefficient and density of the granules was found to be 98% and 1046 kg m−3, respectively. The settling velocity of the granules was found to be in the range of 2–6×10−2 m s−1. The aerobic granules were able to degrade m-cresol up to 800 mg L−1 at a removal efficiency of 87%. UV and GC/MS studies confirmed that the biodegradation of m-cresol occurred via catechol via the ortho-cleavage pathway. The specific m-cresol degradation rate in aerobic granules followed the Haldane model for substrate inhibition. A high specific m-cresol degradation rate of up to 0.718 g m-cresol g−1VSS−1d−1 was sustained up to an m-cresol concentration of 400 mg L−1. The higher removal efficiency and good settling characteristics of aerobic granules make the sequencing batch reactor method suitable for enhancing the microorganism potential for biodegradation of inhibitory compounds.

Biodegradation of o-nitrophenol by aerobic granules with glucose as co-substrate

Aerobic granules to treat wastewater containing o-nitrophenol were successfully developed in a sequencing batch reactor (SBR) using activated sludge as inoculum. Stable aerobic granules were obtained with a clearly defined shape and diameters ranging from 2 to 6 mm after 122 days of operation. The integrity coefficient (IC) and granules density was found to be 98% and 1,054 kg m(-3) respectively. After development of aerobic granules, o-nitrophenols were successfully degraded to an efficiency of 78% at a concentration of 70 mg L(-1). GC-MS study revealed that the biodegradation of o-nitrophenol occurred via catechol via nitrobenzene pathway. Specific o-nitrophenol biodegradation rates followed the Haldane model and the associated kinetic parameters were found as follows: V(max) = 3.96 g o-nitrophenol g(-1)VSS(-1)d(-1), K(s) = 198.12 mg L(-1), and K(i) = 31.16 mg L(-1). The aerobic granules proved to be a feasible and effective way to degrade o-nitrophenol containing wastewater.

The effect of organic loading rates and nitrogenous compounds on the aerobic granules developed using low strength wastewater

The changes in microbial morphologies and structures of aerobic granules under different organic loading rates (OLR) and their tolerance toward free ammonia (FA) and free nitrous acid (FNA) were studied in this research. The development of aerobic granules was carried out in 3 stages using sequencing batch reactor, (i) synthetic wastewater with OLR of 1.2kg/m3day, (ii) low strength real domestic wastewater with OLR of 0.13kg/m3day, and (iii) domestic wastewater with added external carbon source to give an OLR of 0.6kg/m3day. It was found that OLR as low as 0.6kg/m3day was able to develop and maintain the integrity of aerobic granules. After a starvation period, aerobic granules were capable to immediately responded to the increase in substrate. Microscopic images showed that different microbial morphologies and structures were found in aerobic granules at the three different stages. The inhibitory studies of FA and FNA on the activity of aerobic granules reveals that FA at a concentration up to 36.9mg NH3-N/L did not inhibit the oxygen uptake rate (OUR) of aerobic granules. However, FNA started to inhibit the OUR at 0.015mg HNO2-N/L and completely stopped the oxygen consumption at around 0.134mg/L HNO2-N/L.

Roles of ATP-dependent N-acylhomoserine lactones (AHLs) and extracellular polymeric substances (EPSs) in aerobic granulation

Aerobic granules which form through a cell-to-cell self-immobilization process have been intensively studied and developed for wastewater biotreatment. However, the microbiological origin of this phenomenon is still largely unknown. This study investigated the possible role of metabolic energy in the development of aerobic granules. Results showed that aerobic granulation was positively related to ATP-dependent N-acylhomoserine lactones (AHLs) and extracellular polymeric substances (EPSs) production. Inhibited ATP synthesis by a chemical uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide, led to significant reduction of AHLs and EPSs production, which in turn prevented aerobic granulation. This study for the first time demonstrated the involvement of ATP-dependent AHLs in aerobic granulation.

Development of aerobic granules in sequencing batch reactor with p-nitrophenol as sole carbon source

The present study was aimed at the development of aerobic granules in sequencing batch reactor (SBR) for the biodegradation of p-nitrophenol (PNP). The reactor was started with 50 mg L−1 of PNP. Aerobic granules first appeared within 1 month of the start up of the reactor. The granules were large and strong and had a compact structure. The diameter of stable granules on day 200 was in the range of 2–3 mm. The integrity coefficient and granule density was found to be 98% and 1,031 kg m−3 respectively. The settling velocity of granules was found to be in the range of 3 × 10−2 to 4 × 10−2m s−1. The aerobic granules were able to degrade PNP up to 700 mg L−1 at a removal efficiency of 87%. Gas chromatography–mass spectrometry studies confirmed that the biodegradation of PNP occurred by an initial oxygenase attack that resulted in the release of nitrite and the accumulation of hydroquinone. The specific PNP degradation rate in aerobic granules followed the Haldane model for substrate inhibition. A high specific PNP degradation rate up to 0.872 g PNP g−1 VSS−1 d−1 was sustained up to PNP concentration of 200 mg L−1. Higher removal efficiency, good settling characteristics of aerobic granules, makes a SBR suitable for enhancing the microorganism potential for biodegradation of inhibitory compounds.

Decolorization and biodegradation of azo dye, reactive blue 59 by aerobic granules

The present study deals with development of aerobic granules from textile wastewater sludge and challenged with different concentration of reactive blue 59 (RB59) to test their dye degradation potential. The granules efficiently degraded reactive blue 59 and also sustained higher dye loading of up to 5.0gl−1. The significant induction of enzymes azoreductase and cytochrome P-450 indicated their prominent role in the dye degradation while genotoxicity studies demonstrated that the biotransformed product of the dye as non-toxic. The microbial community of the textile dyes degrading aerobic sludge granules analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), revealed significantly diverse dye degrading microbial community belonging to alpha-, beta-, and gamma-proteobacteria.

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.

The influence of starvation phase on the properties and the development of aerobic granules

The current study was to evaluate the influence of starvation phase on surface negative charge, relative hydrophobicity, extra-cellular polymer substances (EPS) and the formation mechanism of aerobic granules. Granules with encouraging settling properties occurred in the reactor about 7 days after the inoculation. The surface negative charge decreased from 0.203 to 0.023 meq g VSS −1 and the relative hydrophobicity increased from 28.8 to 60.3% during the granulation period. Concentrations of protein and carbohydrate decreased from 18.0 to 7.1 and 7.0 to 2.9 mg g VSS −1, respectively in the first period. And from day 13, those values were observed in the range of 5.8–8.6 and 2.9–5.6 mg g VSS −1, respectively. The EPS especially protein concentrations well correlated with surface charge and relatively hydrophobicity. It was concluded that a reasonable amount of EPS should be controlled to form and maintain aerobic granules. It was proposed that aerobic granulation was initiated by starvation phase and then enhanced by anaerobic metabolism.

Substrate concentration‐independent aerobic granulation in sequential aerobic sludge blanket reactor

The development of aerobic granules was studied in four column‐type sequential aerobic sludge blanket reactors fed with different substrate concentrations ranging from 500 to 3000 mg l−1 COD. Results showed that aerobic granules successfully formed in all reactors fed with different substrate concentrations, indicating that the formation of aerobic granules is independent of the substrate concentration. The granule size, roundness, compactness, physical strength, as well as cell surface hydrophobicity and cell polysaccharides contents of the cultivated aerobic granules were investigated. It was shown that aerobic granules formed with different substrate concentrations had similar roundness and compactness. However, the size of aerobic granules slightly increased with an increase in substrate concentration, while granule strength decreased with substrate concentration. It was found that there was a significant increase in cell surface hydrophobicity and cell polysaccharides of the aerobic granules compared to that of seed sludge. The high cell surface hydrophobicity and high cell polysaccharides contents were believed to play an important role in the formation of aerobic granules. However, substrate concentration seems not to be a governing factor for the formation of aerobic granules. The results of this study would be useful for developing aerobic granules‐based bioreactor and for better understanding of the mechanism of aerobic granulation. It was also clearly demonstrated that aerobic granules‐based bioreactor would have great potential in the treatment of high‐strength wastewater.

Selection pressure is a driving force of aerobic granulation in sequencing batch reactors

The effect of hydraulic selection pressure on the development of aerobic granules was studied in four column-type sequencing batch reactors (SBRs). The main feature of SBR is cycle of operations, and settling time acts as hydraulic selection pressure imposed on the microorganisms present. Aerobic granules were successfully cultivated in the reactors operated at a settling time less than of 15 min, while only bioflocs appeared in the reactor run at the longest settling time of 20 min. The characteristics of the aerobic granules in terms of settling ability, hydrophobicity, polysaccharide and protein content as well as specific oxygen utilization rate were examined. Results showed that a short settling time could significantly improve the production of cell polysaccharide, cell surface hydrophobicity and microbial activity. These selection pressure-induced microbial changes favour the formation of aerobic granules.

A culture-independent approach for studying microbial diversity in aerobic granules

This study reports the use of ribosomal-based molecular techniques to study the microbial diversity in aerobic granules. Aerobic granules at different growth stages (young, mature and old) were obtained from a laboratory scale sequential aerobic sludge blanket (SASB) bioreactor fed with glucose as the main source of carbon and energy. Deoxyribonucleic acid (DNA) was extracted from the young, mature and old granules. The polymerase chain reaction (PCR) was used to amplify the Eubacterial 16S ribosomal DNA (rDNA) and three clone libraries were constructed, corresponding to each of the three growth stages. The microbial diversity in each clone library was assessed by amplified ribosomal DNA restriction analysis (ARDRA). The results reveal that there was considerable diversity in each clone library and there were variations in microbial diversity among the three different clone libraries. This suggests a shift in the composition of the microbial communities. Microorganisms associated with 5 restriction fragment length polymorphism (RFLP) types (A, B, C, D and E) appear to play an important role in the development of aerobic granules.