Biomedical subjects

J-H Tay

Publications and source records attributed to J-H Tay.

18 recordsLinked to original sources

PubMed2005

Relationship between size and mass transfer resistance in aerobic granules.

AIMS: To investigate the size effect of aerobic granules on mass transfer efficiency by introducing the effective factor and the modified Thiele modulus. METHODS AND RESULTS: Batch experiments of aerobic granules with different sizes were conducted to study the size effect of granules on mass transfer resistance. Results showed that both specific substrate removal and biomass growth rates were size dependent, i.e. reduced rates were observed at big sizes. It was found that the diffusion resistance described by the effective factor and the Thiele modulus increased with the increase of the size of aerobic granules. CONCLUSIONS: The effective factor should be controlled at values higher than 0.44 and the Thiele modulus lower than 1.05 for efficient mass transfer in aerobic granules. SIGNIFICANCE AND IMPACT OF THE STUDY: Based on the coupled effective factor and Thiele modulus, an operation guidance including granule radius, kinetics of biomass and environmental conditions could be proposed for stable aerobic granulation.

Aerobiosis↗

PubMed2004

The use of sewage sludge and horticultural waste to develop artificial soil for plant cultivation in Singapore.

Greenhouse pot experiments were performed with Ipomoea aquatica (Kang Kong) to evaluate artificial soil produced from poor fertility subsoil, horticultural compost, and sewage sludge. The addition of horticultural compost and sewage sludge to subsoil substantially improved plant growth, improved the physical properties of subsoil and enriched subsoil by essential nutrients for plants. The effect was enhanced when the two ingredients were added to subsoil together. The highest yield of biomass of I. aquatica was observed in artificial soil prepared by mixing subsoil with 4% (wet weight/wet weight) of horticultural compost and 2% (dry weight/wet weight) of sewage sludge. The contents of heavy metals in plants, grown in the artificial soil, were significantly lower than toxic levels. The artificial soil could be recommended for urban landscaping and gardening in Singapore.

Conservation of Natural Resources↗

PubMed2004

Bacteriological examination of ballast water in Singapore Harbour by flow cytometry with FISH.

In this study the concentrations of total bacteria, enterobacteria, Vibrio spp., and E. coli have been compared for ballast water samples taken from ships in Singapore Harbour. The cell concentrations were enumerated using FISH and flow cytometry. The data were highly variable, reflecting the many influences upon ballast water as it is utilized in the shipping industry. The concentration of bacterial species was determined as a proportion of the total concentration of cells for the ballast water sampled. For the ballast water sampled these concentrations were 0.67-39.55% for eubacteria, 0-2.46% for enterobacteria, 0.18-35.82% for Vibrio spp., and 0-2.46% for E. coli. Using FISH and flow cytometry, an informative determination of the bacterial hazards of ship ballast water can be made.

Bacteria↗

PubMed2004

Microbiological monitoring in the biodegradation of sewage sludge and food waste.

AIM: To study the microbiology of intensive, in-vessel biodegradation of a mixture of sewage sludge and vegetable food waste. METHODS AND RESULTS: The biodegradation was performed in a closed reactor with the addition of a starter culture of Bacillus thermoamylovorans SW25 under conditions of controlled aeration, stirring, pH and temperature (60 degrees C). The content of viable bacterial cells, determined by flow cytometry, increased from 5 x 108 g-1 of dry matter to 61 x 108 g-1 for 6 days of the process and then dropped to the initial value at the end of the process. The reductions of organic matter, 16S rRNA of methanogens and coenzyme F420 fluorescence during 10 days of the treatment were 67, 54 and 87% of the initial values, respectively. The biodegradability of the organic matter decreased during the 10 days of the treatment from 3.8 to 1.3 mg CO2 g-1 of organic matter per day. The treatment of sewage sludge and food waste at 60 degrees C did not remove enterobacteria, which are the agents of intestinal infections, from the material. The percentage of viable enterobacterial cells, determined by fluorescent in situ hybridization (FISH) with Enterobacteriaceae-specific oligonucleotide probe and flow cytometry, varied from 1 to 14% of the viable bacterial cells. CONCLUSIONS: The mixture of sewage sludge and food waste can be degraded by the aerobic thermophilic bacteria; the starter culture of Bacillus thermoamylovorans SW25 can be used to perform this process; and enterobacteria can survive under treatment of sewage sludge and food waste at 60 degrees C for 13 days. SIGNIFICANCE AND IMPACT OF THE STUDY: The results show that FISH with an oligonucleotide probe can be used to study not only the growth but also the degradation of biomass. Obtained results could be used to design the bioconversion of sewage sludge and food waste into organic fertilizer.

Bacillus↗

PubMed2004

Growth kinetics of aerobic granules developed in sequencing batch reactors.

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

Aerobiosis↗

PubMed2004

The effect of hydraulic retention time on the stability of aerobically grown microbial granules.

AIMS: The aim of this study is to evaluate the effect of hydraulic retention time (HRT) on the development of aerobically grown microbial granules. METHODS AND RESULTS: Five column-shaped sequential aerobic sludge blanket reactors (SASBRs) were seeded with aerobically grown microbial granules and operated in a cyclic mode at different HRTs. At the shortest HRT of 1 h, the strong hydraulic pressure triggered biomass washout and led to reactor failure. At the longest HRT of 24 h, which represented the weakest hydraulic selection in this study, aerobic granules were gradually substituted by bioflocs because of the lower frequency of volumetric exchange. Within the optimum range of HRTs from 2 to 12 h, however, aerobic granules became stabilized in the presence of adequate hydraulic selection in the reactors, with good mixed liquor volatile suspended solids (MLVSS) retention, high volumetric chemical oxygen demand (COD) removal, low sludge volume index (SVI) values, good effluent quality, low sludge production rate, stronger and more compact structures, high cell hydrophobicity and high ratios of extracellular polysaccharides (PS) to extracellular proteins (PN). CONCLUSIONS: HRTs between 2 and 12 h provided the hydraulic selection pressures favourable for the formation and maintenance of stable aerobic granules with good settleability and activity. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first systematic study on the effect of HRT on heterotrophic aerobic granules. The results of the investigation are useful in understanding how aerobic granules can be applied for wastewater treatment.

Aerobiosis↗

PubMed2003

A thermodynamic interpretation of cell hydrophobicity in aerobic granulation.

Aerobic granulation can be regarded as a microorganism-to-microorganism self-immobilization process, in which cell hydrophobicity could be a decisive parameter in determining the microorganism-to-microorganism interaction and structural compactness of aerobic granules. This study looked into the thermodynamic interpretation of cell hydrophobicity in aerobic granulation; and a model that correlates microbial interaction and relative cell hydrophobicity defined as the ratio of cell hydrophobicity over cell hydrophilicity was derived. This model describes how cell hydrophobic and hydrophilic interactions affect aerobic granulation and offers deep insights into the thermodynamic mechanisms of microbial aggregation. The model prediction was in good agreement with experimental data. Results showed that aerobic granulation was a function of cell hydrophobicity over cell hydrophilicity, i.e. a high cell hydrophobicity strongly favors microbial aggregation and results in a more compact structure.

Aerobiosis↗

PubMed2003

Changes in structure, activity and metabolism of aerobic granules as a microbial response to high phenol loading.

Four column-type sequential aerobic sludge blanket reactors were fed with phenol as the sole carbon and energy source and operated at loading rates of 1.0, 1.5, 2.0 and 2.5 kg phenol m(-3) day(-1). The results indicated that phenol loading exerted a profound influence on the structure, activity and metabolism of the aerobic granules. Compact granules with good settling ability were maintained at loadings up to 2.0 kg phenol m(-3) day(-1), and structurally weakened granules with enhanced production of extracellular polymers and proteins and significantly lower hydrophobicities were observed at the highest loading of 2.5 kg phenol m(-3) day(-1). Specific oxygen uptake rate, catechol 2,3-dioxygenase (C23O) and catechol 1,2-dioxygenase (C12O) activities peaked at a loading of 2.0 kg phenol m(-3) day(-1), and declined thereafter. Granules degraded phenol completely in all four reactors, mainly through the meta cleavage pathway as C23O activities were significantly higher than C12O activities. At the highest loading applied, the anabolism and catabolism of microorganisms were regulated such that phenol degradation proceeded exclusively via the meta pathway, apparently to produce more energy for overstimulation of protein production against phenol toxicity. This work contributes to a better understanding of the ability of aerobic granules to handle high-strength industrial wastewaters containing chemicals that are normally inhibitory to microbial growth.

Aerobiosis↗

PubMed2003

Development and characteristics of phosphorus-accumulating microbial granules in sequencing batch reactors.

Phosphorus (P)-accumulating microbial granules were developed at different substrate P/chemical oxygen demand (COD) ratios in the range of 1/100 to 10/100 by weight in sequencing batch reactors. The soluble COD and PO4-P profiles showed that the granules had typical P-accumulating characteristics, with concomitant uptake of soluble organic carbon and the release of phosphate in the anaerobic stage, followed by rapid phosphate uptake in the aerobic stage. The size of P-accumulating granules exhibited a decreasing trend with the increase in substrate P/COD ratio, while the structure of the granules became more compact and denser as the substrate P/COD ratio increased. The P uptake by granules fell within the range of 1.9% to 9.3% by weight, which is comparable with uptake obtained in conventional enhanced biological phosphorus removal (EBPR) processes. It was further found that low aerobic respirometric activity of granules in terms of specific oxygen utilization rate favors P uptake by granules. The results presented would be useful for the further development of a novel granule-based EBPR technology.

Bacteria, Aerobic↗

PubMed2003

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.

Bacteria↗

PubMed2003

Importance of Gram-positive naphthalene-degrading bacteria in oil-contaminated tropical marine sediments.

AIMS: The aim of this study was to isolate, characterize and evaluate the importance of naphthalene-degrading bacterial strains from oil-contaminated tropical marine sediments. METHODS AND RESULTS: Three Gram-positive naphthalene-degrading bacteria were isolated from oil-contaminated tropical intertidal marine sediments by direct isolation or enrichment using naphthalene as the sole source of carbon and energy. Bacillus naphthovorans strain MN-003 can also grow on benzene, toluene, xylene and diesel fuel while Micrococcus sp. str. MN-006 can also grow on benzene. Staphylococcus sp. str. MN-005 can only degrade naphthalene and was not able to use the other aromatic hydrocarbons tested. Strain MN-003 possessed the highest maximal specific growth rate with naphthalene as sole carbon source. An enrichment culture fed with naphthalene as sole carbon source exhibited a significant increase in the relative abundances of the three isolates after 21 days of incubation. The three isolates constituted greater than 69% of the culturable naphthalene-degrading microbial community. Strain MN-003 outcompeted and dominated the other two isolates in competition studies involving batch cultures inoculated with equal cell densities of the three isolates and incubated with between 1 and 10 mg l-1 of naphthalene. CONCLUSIONS: Three Gram-positive naphthalene-degrading bacteria were successfully isolated from oil-contaminated tropical marine sediments. Gram-positive bacteria might play an important role in naphthalene degradation in the highly variable environment of oil-contaminated tropical intertidal marine sediments. Among the three isolates, strain MN-003 has the highest maximal specific growth rate when grown on naphthalene, and outgrew the other two isolates in competition experiments. SIGNIFICANCE AND IMPACT OF THE STUDY: This research will aid in the development of bioremediation schemes for oil-contaminated marine environments. Strain MN-003 could potentially be exploited in such schemes.

Bacillus↗

PubMed2003

Biomass and porosity profiles in microbial granules used for aerobic wastewater treatment.

AIMS: To obtain biomass and porosity profiles for aerobically grown granules of different diameters and to determine a suitable range of granule diameters for application in wastewater treatment. METHODS AND RESULTS: Microbial granules were cultivated in an aerobic granulated sludge reactor with model wastewaters containing acetate, or ethanol plus acetate, or glucose as the main carbon source. Granules were formed by retaining microbial aggregates using a settling time of 2 min. Sampled granules had diameters ranging from 0.45 to 3 mm. Microbial biomass in the granules was detected with the nucleic acid stain SYTO 9 and confocal laser scanning microscopy. The thickness of the microbial biomass layer was proportional to the granule diameter, and had a maximum value of 0.8 mm. The thickness of the microbial biomass layer correlated with the penetration depth of 0.1 microm fluorescent beads into the granule. CONCLUSIONS: The microbial biomass and porosity studies suggest that aerobically grown microbial granules should have diameters less than a critical diameter of 0.5 mm, if deployed for wastewater treatment applications. This critical diameter is based on the assumption that whole granules should have a porous biomass-filled matrix. SIGNIFICANCE AND IMPACT OF THE STUDY: This work could contribute to the development of aerobic granulation technology for effective biological wastewater treatment.

Aerobiosis↗

PubMed2002

Presence of anaerobic bacteroides in aerobically grown microbial granules.

Microbial granules were grown in a column-type sequential aerobic sludge blanket reactor inoculated with activated sludge flocs taken from a wastewater treatment plant and containing a medium with glucose as the main carbon source. The reactor selected for granules that could settle rapidly by employing a short settling time of 2 min. Matured granules with diameters between 2 and 3 micro m were examined for anaerobic bacteria as their presence can signal the onset of diffusion limitation problems that can potentially diminish granule stability due to the bacterial production of fermentation gases and organic acids under anaerobic conditions. To detect the anaerobes in the granules, clones were constructed from 16S rRNA PCR amplicons. Two sequence types associated with a strict anaerobe Bacteroides spp. were identified from these clones. Fluorescence in situ hybridization (FISH) followed by confocal laser scanning microscopy (CLSM) demonstrated that cells of Bacteroides spp. were concentrated at a depth of approximately 800 micro m below the surface of the granule. Cell enumeration using flow cytometry showed that the percentage of labeled cells of Bacteroides spp. compared to total bacterial cells in the granules was 0.56%. This is the first study to use a suite of culture-independent techniques to report the presence of a defined species of anaerobic bacteria in aerobically grown microbial granules.

Aerobiosis↗

PubMed2002

Hydraulic selection pressure-induced nitrifying granulation in sequencing batch reactors.

The effect of hydraulic selection pressure on the development of nitrifying granules was investigated in four column-type sequencing batch reactors (SBR). The nature of SBR is cycle operation, thus SBR cycle time can serve as a main hydraulic selection pressure imposed on the microbial community in the system. No nitrifying granulation was observed in the SBR operated at the longest cycle time of 24 h, due to a very weak hydraulic selection pressure, while the washout of nitrifying sludge was found in the SBR run at the shortest cycle time of 3 h, and led to a failure of nitrifying granulation. Excellent nitrifying granules with a mean diameter of 0.25 mm and specific gravity of 1.014 were developed in a SBR operated at cycle times of 6 h and 12 h, respectively. The results further showed that a short cycle time would stimulate microbial activity, production of cell polysaccharides and also improve the cell hydrophobicity. These hydraulic selection pressure-induced microbial changes favour the formation of nitrifying granules. This work, probably for the first time, shows that nitrifying granules can be developed at a proper hydraulic selection pressure in terms of SBR cycle time. Nitrifying granulation is a novel biotechnology which has a great potential for wastewater nitrification.

Bacteria↗

PubMed2002

Specific layers in aerobically grown microbial granules.

AIMS: To determine the optimal size of aerobically grown granules for wastewater treatment by measuring specific layers within the granules. METHODS AND RESULTS: A variety of biological layers were detected by oligonucleotide probes, specific fluorochromes, and fluorescent microspheres. The channels in the granule matrix penetrated to depths of 900 microm. A layer of obligate anaerobic bacteria was detected at a depth of 800 microm below the granule surface. Dead cells were also observed in the granule interior. CONCLUSIONS: Aerobically grown granules contained layers of aerobic and anaerobic micro-organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: The optimal diameter of the aerobic granule is less than 1600 microm. This is twice the distance from the granule surface to the anaerobic layer. This approach can be used to optimize the thickness of other microbial aggregates such as flocs, colonies and biofilms.

Aerobiosis↗

PubMed2002

High organic loading influences the physical characteristics of aerobic sludge granules.

AIMS: The effect of high organic loading rate (OLR) on the physical characteristics of aerobic granules was studied. METHODS AND RESULTS: Two column-type sequential aerobic sludge blanket reactors were fed with either glucose or acetate as the main carbon source, and the OLR was gradually raised from 6 to 9, 12 and 15 kg chemical oxygen demand (COD) m(-3) d(-1). Glucose-fed granules could sustain the maximum OLR tested. At a low OLR, these granules exhibited a loose fluffy morphology dominated by filamentous bacteria. At higher OLRs, these granules became irregularly shaped, with folds, crevices and depressions. In contrast, acetate-fed granules had a compact spherical morphology at OLRs of 6 and 9 kg COD m(-3) d(-1), with better settling and strength characteristics than glucose-fed granules at similar OLRs. However, acetate-fed granules could not sustain high OLRs and disintegrated when the OLR reached 9 kg COD m(-3) d(-1). CONCLUSIONS: The compact regular microstructure of the acetate-fed granules appeared to limit mass transfer of nutrients at an OLR of 9 kg COD m(-3) d(-1). The looser filamentous microstructure of the glucose-fed granules and the subsequent irregular morphology delayed the onset of diffusion limitation and allowed significantly higher OLRs to be attained. SIGNIFICNACE AND IMPACT OF THE STUDY: High organic loading rates are possible with aerobic granules. This research would be helpful in the development of aerobic granule-based systems for high-strength wastewaters.

Acetic Acid↗

PubMed2002

Aggregation of immobilized activated sludge cells into aerobically grown microbial granules for the aerobic biodegradation of phenol.

AIMS: The aim of this study is to evaluate the utility of aerobically grown microbial granules for the biological treatment of phenol-containing wastewater. METHODS AND RESULTS: A column-type sequential aerobic sludge blanket reactor was inoculated with activated sludge and fed with phenol as the sole carbon source, at a rate of 1.5 g phenol l-1 d-1. Aerobically grown microbial granules first appeared on day 9 of reactor operation and quickly grew to displace the seed flocs as the dominant form of biomass in the reactor. These granules were compact and regular in appearance, and consisted of bacterial rods and cocci and fungi embedded in an extracellular polymeric matrix. The granules had a mean size of 0.52 mm, a sludge volume index of 40 ml g-1 and a specific oxygen utilization rate of 110 mg oxygen g VSS-1 h-1 (VSS stands for volatile suspended solids). Specific phenol degradation rates increased with phenol concentration from 0 to 500 mg phenol l-1, peaked at 1.4 g phenol g VSS-1 d-1, and declined with further increases in phenol concentration as substrate inhibition effects became important. CONCLUSIONS: Aerobically grown microbial granules were successfully cultivated in a reactor maintained at a loading rate of 1.5 g phenol l-1 d-1. The granules exhibited a high tolerance towards phenol. Significant rates of phenol degradation were attained at phenol concentrations as high as 2 g l-1. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study to demonstrate the ability of aerobically grown microbial granules to degrade phenol. These granules appear to represent an excellent immobilization strategy for microorganisms to biologically remove phenol and other toxic chemicals in high-strength industrial wastewaters.

Aerobiosis↗

PubMed2002

Aerobic granules: a novel zinc biosorbent.

AIMS: Aerobic granules are aggregates with a compact and porous microbial structure. In view of the potential use of aerobic granules as biosorbents for Zn(II) removal from industrial wastewater, this study investigated the effects of initial Zn(II) and aerobic granule concentrations on the kinetics of Zn(II) biosorption on the aerobic granule surface. METHODS AND RESULTS: Acetate-fed aerobic granules with a mean diameter of 1.0 mm were used as biosorbents. Results showed that the kinetics of Zn(II) biosorption on the aerobic granule surface were related to both initial Zn(II) and granule concentrations. It was found that the real driving force for Zn(II) biosorption on the aerobic granule surface could be described by the ratio of initial Zn(II) concentration (Co) to initial granule concentration (Xo), rather than individual Co or Xo. The Co/Xo ratio provides a unified basis for interpretation of the biosorption data obtained under different initial conditions. The maximum biosorption capacity of Zn(II) by aerobic granules was 270 mg g(-1). CONCLUSIONS: It appears that the aerobic granule can be used as an effective biosorbent for efficient removal of Zn(II) or other types of heavy metals from industrial wastewater. SIGNIFICANCE AND IMPACT OF THE STUDY: This study could lead to the development of a novel granular biosorbent for the removal of heavy metals from wastewater. A simple and compact aerobic granule-based biosorber could be expected.

Absorption↗