Biomedical subjects

J H Tay

Publications and source records attributed to J H Tay.

At least 37 records · Page 2Linked to original sources

PubMed2004

Removal of micro-particles by microbial granules used for aerobic wastewater treatment.

Microbial granules with a diameter from 0.4 mm to 3.0 mm have been produced by fast sedimentation and retention of microbial aggregates in sequencing batch airlift reactors used for model wastewater treatment. The wastewater was with or without addition of calcium salt. The granules were able not only to degrade organic matter but to remove nano- and micro-particles from wastewater due to microchannels and pores in the matrix of the granules. To detect the removal of 0.1 microm, 0.6 pm, 4.2 microm fluorescent microspheres, and cells of Escherichia coli, stained by permeable nucleic acid stain SYTO9, the granules were incubated with these particles. The rate of particle removal and their accumulation in the granules was measured by a Fluoview300 confocal laser scanning microscope (CLSM) (Olympus, Japan); a FACSCalibur flow cytometer (Becton Dickinson, CA, USA), and a fluorescence spectrometer LS-50B (Perkin-Elmer, UK). The release or removal of biological and non-biological particles was analyzed by a flow cytometer after DNA staining. Total number of the particles bigger than 0.1 microm in the reactors was approximately 4 x 10(7) per ml, and 23% of these particles were bacterial cells. The 0.1 microm and 4.2. microm microbeads were accumulated within 250 microm in the upper layer of the microbial granule but externally added cells of Escherichia coli penetrated to the depth of approximately 800 microm in the granules without calcium addition. Microbial granules contained also attached ciliates but accumulation of the particles in protozoan cells was smaller than in the granule matrix. Kinetics of particle sorption was revealed by flow cytometry and fluorescence spectrometry. Almost half of the stained cells of E. coli can be removed by the granules for one hour. The ability of the microbial granules to remove the particles can enhance their function in aerobic treatment of wastewater.

Aerobiosis↗

PubMed2003

Gravitational sedimentation of flocculated waste activated sludge.

The sedimentation characteristics of flocculated wastewater sludge have not been satisfactorily explored using the non-destructive techniques, partially owing to the rather low solid content (ca. 1-2%) commonly noted in the biological sediments. This paper investigated, for the first time, the spatial-temporal gravitational settling characteristics of original and polyelectrolyte flocculated waste activated sludge using Computerized Axial Tomography Scanner. The waste activated sludge possessed a distinct settling characteristic from the kaolin slurries. The waste activated sludges settled more slowly and reached a lower solid fraction in the final sediment than the latter. Flocculation markedly enhanced the settleability of both sludges. Although the maximum achievable solid contents for the kaolin slurries were reduced, flocculation had little effects on the activated sludge. The purely plastic rheological model by Buscall and White (J Chem Soc Faraday Trans 1(83) (1987) 873) interpreted the consolidating sediment data, while the purely elastic model by Tiller and Leu (J. Chin. Inst. Chem. Eng. 11 (1980) 61) described the final equilibrated sediment. Flocculation produced lower yield stress during transient settling, thereby resulting in the more easily consolidated sludge than the original sample. Meanwhile, the flocculated activated sludge was stiffer in the final sediment than in the original sample. The data reported herein are valuable to the theories development for clarifier design and operation.

Flocculation↗

PubMed2003

Using filtrate of waste biosolids to effectively produce bio-hydrogen by anaerobic fermentation.

Waste biosolids collected from sewage works is a biomass containing a vast amount of polysaccharides and proteins, and thus is considered a potential substrate for producing hydrogen using anaerobic fermentation. This work demonstrated, contrary to the common assumption, that the solids phase in waste activated biosolids presents extra nutrients for anaerobes; it in fact prohibits effective bio-hydrogen production. Using filtrate after removal of solids from biosolids produces more hydrogen than using the whole biosolids, with the former reaching a level an order of magnitude higher than the literature results.

Bacteria, Anaerobic↗

PubMed2003

Anaerobic digestion of polyelectrolyte flocculated waste activated sludge.

This work examined how adding one of three polyelectrolyte flocculants (T3052: cationic, T2000: non-ionic, and T1052: anionic) affected the anaerobic digestion of wastewater sludge. Methane production, floc characteristics (morphology and zeta-potential) and process parameters (soluble chemical oxygen demands (SCODs) and reductive potentials) were monitored along the digestion tests. The digestion rates of T2000- and T1052-conditioned sludge resembled that for original sludge. The T3052-flocculated sludge generated methane at a higher rate during the first 6 days of digestion than did the original one. In the following stage, the digestion rate of sludge flocculated with T3052 at dosage exceeding 15 g/kg dried solids declined. For example, at 40 days of digestion the methane production amounts for original, 15 g/kg DS flocculated, and 40 g/kg flocculated sludge were of 136, 105, and 85 g/kg DS, respectively. The role of flocculants could change in different stages of digestion. The dosed polymers had no apparent toxicity to the inoculum used. The changes in SCOD, adenosintriphosphate concentrations, oxidative and reductive potential, and zeta-potentials did not correlate with the noted hindered digestion for T3052-conditioned sludge. Microphotographic observation revealed that the flocs of T3052-conditioned sludge were not only of a large size, but also were resistant to structural deterioration during digestion. Therefore, mass transfer resistance was proposed to account for the hindered digestion efficiency observed for T3052-conditioned sludge.

Anaerobiosis↗

PubMed2003

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.

Bacteria, Aerobic↗

PubMed2003

Characteristics of coagulation-flocculation of humic acid with effective performance of polymeric flocculant and inorganic coagulant.

Ferric chloride and aluminium sulphate as coagulants and positive charged flocculants PDDMAC ((PDDMAC = poly (diallyldimethylammonium chloride) were used for pre-treatment of water and wastewater for removing humic substance prior to RO membrane filtration. It was found that a combination of flocculant and coagulant enhanced the coagulation-flocculation process and humic acid removal. The optimum conditions of coagulation-flocculation were established in reference to the ratio of humic acid and coagulant. Zeta potential and the ratio of E4/E6 were investigated to explore the possible micro-mechanisms of coagulation-flocculation. The ratios of E4/E6 show the molecular size variations using different coagulants and flocculants, which are expected to benefit membrane-fouling control.

Dimethylamines↗

PubMed2003

A submerged tubular ceramic membrane bioreactor for high strength wastewater treatment.

A 4 L submerged tubular ceramic membrane bioreactor (MBR) was applied in laboratory scale to treat 2,400 mg-COD/L high strength wastewater. A prolonged sludge retention time (SRT) of 200 day, in contrast to the conventional SRT of 5 to 15 days, was explored in this study, aiming to reduce substantially the amount of disposed sludge. The MBR system was operated for a period of 142 days in four runs, differentiated by specific oxygen utilization rate (SOUR) and hydraulic retention time (HRT). It was found that the MBR system produced more than 99% of suspended solid reduction. Mixed liquor suspended solids (MLSS) was found to be adversely proportional to HRT, and in general higher than the value from a conventional wastewater treatment plant. A chemical oxygen demand (COD) removal efficiency was achieved as high as 98% in Run 1, when SOUR was in the range of 100-200 mg-O/g-MLVSS/hr. Unexpectedly, the COD removal efficiency in Run 2 to 4 was higher than 92%, on average, where higher HRT and abnormally low SOUR of 20-30 mg-O/g-MLVSS/hr prevailed. It was noted that the ceramic membrane presented a significant soluble nutrient rejection when the microbial metabolism of biological treatment broke down.

Bioreactors↗

PubMed2003

Operational factors of submerged inorganic membrane bioreactor for organic wastewater treatment: sludge concentration and aeration rate.

Various sludge concentrations and aeration rates were evaluated to find the optimal operation condition of a submerged ceramic membrane filtration system. 5.6 g/L of sludge was diluted with water to concentrations of 2.8 g/L and 1.4 g/L, and the three sludge concentrations were compared in terms of titration characteristics such as pressure and filtrate flux. Flux was at the highest value of about 30 L/m2 x hr at 50 kPa when sludge concentration was 1.4 g/L. In contrast, when sludge concentrations increased to 2.8 g/L and 5.6 g/L, the flux at 50 kPa decreased significantly to 18 L/m2 x hr and 10 L/m2 x hr, respectively. It was concluded that the sludge concentration directly affected the filtration efficiency, and low sludge concentration was suitable for improving filtration efficiency. Adjusting the aeration rate from 2 L/min to 4 L/min at 5.6 g/L of sludge and 50 kPa of pressure increased flux from 10 L/m2 x hr to 13 L/m2 x hr. It was obvious that the vigorous aeration improved the filtration efficiency, but the aeration rate did not seem to be high enough to maintain flux lower than critical flux.

Bioreactors↗

PubMed2003

Manufacturing artificial aggregates from industrial sludge and marine clay with addition of sodium salt.

The potential of converting industrial sludge and dredged marine clay into building and construction materials as an alternative to disposal was investigated in this study. The industrial sludge was mixed with marine clay at various compositions and was shaped into round pellets to be used as concrete aggregates. The pellets were then dried and transferred into a high temperature kiln where they were heated at 1,135 degrees C. The artificial aggregates were more porous then the normal granite aggregate. The occurrence of this condition was suspected to be attributed to two factors, viz. the firing temperature and the amount of sodium in the aggregates. To validate this hypothesis, the aggregates with and without added sodium chloride were fired at temperatures of 1,100 and 1, 200 degrees C. Results showed a reduction in the densities of the aggregates with the addition of sodium chloride and the increase in firing temperature.

Aluminum Silicates↗

PubMed2003

Photocatalytic oxidation technology for humic acid removal using a nano-structured TiO2/Fe2O3 catalyst.

A novel TiO2 coated haematite photocatalyst was prepared and used for removal of colored humic acids from wastewater in an UV bubble photocatalytic reactor. XRD analysis confirmed that nano-size anatase crystals of TiO2 were formed after calcination at 480 degrees C. SEM results revealed that nano-size particles of TiO2 were uniformly coated on the surface of Fe2O3 to form a bulk of nano-structured photocatalyst Fe2O3/TiO2. The porous catalyst had a BET surface area of 168 m2/g. Both the color and total organic carbon (TOC) conversion versus the residence time were measured at various conditions. The effects of pH value, catalyst loaded, initial humic acid concentration and reaction temperature on conversion were monitored. The experimental results proved that the photocatalytic oxidation process was not temperature sensitive and the optimum catalyst loading was found to be 0.4 g/l. Degradation and decolorization of humic acids have higher efficiency in acidic medium and at low initial humic acid concentration. The new catalyst was effective in removing TOC at 61.58% and color400 at 93.25% at 180 minutes illumination time and for 20 mg/l neutral humic acid aqueous solution. The kinetic analysis showed thatthe rate of photocatalytic degradation of humic acids obeyed the first order reaction kinetics.

Catalysis↗

PubMed2003

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.

Bacteria, Aerobic↗

PubMed2003

Isolation of naphthalene-degrading bacteria from tropical marine sediments.

Oil pollution is a major environmental concern in many countries, and this has led to a concerted effort in studying the feasibility of using oil-degrading bacteria for bioremediation. Although many oil-degrading bacteria have been isolated from different environments, environmental conditions can impose a selection pressure on the types of bacteria that can reside in a particular environment. This study reports the successful isolation of two indigenous naphthalene-degrading bacteria from oil-contaminated tropical marine sediments by enrichment culture. Strains MN-005 and MN-006 were characterized using an extensive range of biochemical tests. The 16S ribosomal deoxyribonucleic acid (rDNA) sequence analysis was also performed for the two strains. Their naphthalene degradation capabilities were determined using gas chromatography and DAPI counting of bacterial cells. Strains MN-005 and MN-006 are phenotypically and phylogenetically different from each other, and belong to the genera Staphylococcus and Micrococcus, respectively. Strains MN-005 and MN-006 had maximal specific growth rates (micro(max)) of 0.082 +/- 0.008 and 0.30 +/- 0.02 per hour, respectively, and half-saturation constants (K(s)) of 0.79 +/- 0.10 and 2.52 +/- 0.32 mg per litre, respectively. These physiological and growth studies are useful in assessing the potential of these indigenous isolates for in situ or ex situ naphthalene pollutant bioremediation in tropical marine environments.

Biodegradation, Environmental↗

PubMed2003

A comparative study of anaerobic digestion of food waste in a single pass, a leachate recycle and coupled solid/liquid reactors.

A single pass reactor (R1), a leachate recycle reactor (R2) and a coupled solid/liquid bioreactor (R3-Rm) for anaerobic digestion of food waste were comparatively investigated in terms of digestion process and treatment efficiency. The coupled solid/liquid bioreactor is an enhanced two-phase system and distinctive from a traditional two-phase process with an upflow anaerobic sludge blanket (UASB) reactor as the methanogenic phase and a circulation of treated leachate between the acidification and methanogenic phases. In comparison with R1 and R2, R3-Rm enhanced the digestion process and increased the methane content of biogas. 100% of the R3-Rm methane yield was from the methanogenic phase with average methane content of 71%. The significant enhancement was also confirmed by the removal of 79% of total organic carbon (TOC), 60% of volatile solids (VS) and 80% of total COD in 12 days running of R3-Rm. However, no active methane fermentation was detected in R1 and R2 during 60 days operation. The results in this laboratory-scale study show that the rapid accumulation of volatile fatty acids (VFAs) due to the rapid acidification of food waste inhibits the development of effective methane fermentation in single pass and leachate recycle reactors. The coupled solid/liquid bioreactor is more efficient in converting food waste into methane and carbon dioxide.

Bacteria, Anaerobic↗

PubMed2003

Monitoring of microbial diversity by fluorescence in situ hybridization and fluorescence spectrometry.

The goal of the research was the development of a simple method to quantify microbial groups in environmental samples. Fluorescence intensity was measured in the sample before and after whole cell fluorescence in situ hybridization with rRNA-targeted, fluorochrome-labeled oligonucleotide probes. To determine specific and non-specific binding of different oligonucleotide probes the following approaches have been used: (1) incubation of the sample with probes at two different temperatures; (2) hybridization of labeled probe in the presence of unlabeled probe; (3) incubation of the sample with labeled specific probe or labeled nonsense probe. Specific binding (hybridization) of the probe was calculated as the difference between total binding and non-specific binding of the probe. Specific binding was 40-50% of total binding in the environmental samples tested. The ratio of the specific binding of different probes may be used to quantify the ratio of different microbial groups in the environmental samples. This quantification is suitable for the microbiological monitoring of microbial aggregates because it is a simple technique and the results can be measured by a portable fluorometer.

Bacteria↗

PubMed2003

The effect of organic loading rate on the aerobic granulation: the development of shear force theory.

The effect of organic loading rate (OLR) on aerobic granulation was studied by adopting three column-shaped, sequential aerobic sludge blanket reactors (SASBR). The reactors had been fed with laboratory prepared, synthetic dextrose-nutrient broth substrate. Experimental results showed clearly that the formation, characteristics and stability of aerobic granules had a close relationship with the strength of OLR applied. Aerobic granules appeared firstly under the OLR of 4 kg COD x (m3 x day)(-1). The system stabilization was demonstrated by its little-changed amount and morphology of granules. The characteristics of the stabilized granules were: 5.4 mm in mean diameter, 1.29 in roundness, 118 mg O2 x (mg VSS x hr)(-1) in SPOUR. The respective biomass SVI was 50 mL x (g MLVSS)(-1) and the averaged COD removal rate was 95%. Under the OLR of 8 kg COD x (m3 x day)(-1), granules appeared two days later than those for 4 kg COD x (m3 x day)(-1) and they always coexisted with flocs. The formed granule bed was not as compact as that under 4 kg COD x (m3 x day)(-1). There were no granules formed under the OLR of 1 kg COD x (m3 x day)(-1). Instead, flocs with rather loose structure dominated reactor mixed-liquor. The respective SVI's were 65 and 138 mL x (g MLVSS)(-1) under OLR of 8 and 1 kg COD x (m3 x day)(-1). It was proposed that the growth and maintenance of aerobic granules follow the shear force balance theory. Under the OLR of 4 kg COD x (m3 x day)(-1), a balance was reached between the aeration shear force and organic loading rate. Under this favored condition aerobic granules formed quickly and, became stabilized with the experimental parameters remained unchanged.

Bacteria, Aerobic↗

PubMed2003

Semi-continuous anaerobic digestion of food waste using a hybrid anaerobic solid-liquid bioreactor.

A hybrid anaerobic solid-liquid (HASL) bioreactor was developed to enhance food waste conversion. The HASL bioreactor is a modified two-phase anaerobic digestion system with a solid waste reactor and a high-rate anaerobic wastewater reactor, which was a UASB reactor. In this study, the methanogenesis in the UASB reactor was investigated under a semi-continuous operation of the food waste digestion system. The HASL process, including 7 days of start-up and 23 days of semi-continuous operation followed by 6 days of batch operation, was commenced by loading 2.8 kg of shredded food waste. During the semi-continuous operation, 0.2 kg of the same waste was loaded daily. The leachate from acidification phase, i.e., solid waste reactor, remained acidic (pH 4.9-5.5) and high in total VFA (TVFA), 9,500-11,500 mg/L, and COD (8,000-11,800 mg/L) levels. In the methanogenesis phase, i.e., UASB reactor, effective TVFA and COD removals (88 +/- 5% and 85 +/- 7%, respectively) were obtained, while the methane content was 71%. At the end of operation, about 78% of VS added in the HASL bioreactor was removed, while TOC and total COD reductions were 78% and 79%, respectively. The results showed that the use of UASB reactor in the semi-continuous HASL system can enhance the methanogenesis process and increase the methane content in biogas production.

Bacteria, Anaerobic↗

PubMed2002

Size-effect on the physical characteristics of the aerobic granule in a SBR.

Owing to a fast growth rate, aerobic granules display a wide range of sizes, approximately 0.3-5.0 mm in diameter. As the diameter increases, the aerobic granule undergoes serial morphological and physical changes that could cause problems to the reactor operation, a phenomenon which, however, has not been fully studied hitherto. In this study, aerobic granules from a sequencing batch reactor were mechanically separated into various size-categories in order to investigate their physical properties, including sludge volumetric index (SVI), settling velocity (sv), specific surface hydrophobicity, granule strength, total solids, percentage volatile solids and other structural properties. Also, the live and dead biomass distribution was examined under a confocal laser scanning microscope after treatment with nucleic acid viability stains. Regardless of size, the biomass (both live and dead) was densest in the outer layer of the granule, which was about 600+/-50 microm thick. The live cells appeared only in the peripheral zone, while dead biomass spread into the inner zone. The biomass distribution pattern justified the changing physical properties of the granules as they grew bigger. As size increased, the sv, granule total density and biomass density increased but not in parallel with the size increment, while the granule strength, specific surface hydrophobicity and SVI decreased. Nonetheless, beyond a threshold size (4.0 mm diameter), the granules presented peculiar values in those properties, deviating from the initial trends. This was due to both inner and outer structural changes. The physical properties associated significantly with the size factor, for which the correlation coefficients were above 0.67. In view of biological viability and physical properties, the operational size-range suggested for optimal performance and economically effective aerobic SBR granular sludge is a diameter of 1.0-3.0 mm.

Aerobiosis↗

PubMed2002

"Weak" ultrasonic pre-treatment on anaerobic digestion of flocculated activated biosolids.

This study examined how "weak" ultrasonic pre-treatment affects anaerobic digestion of waste biosolids, treated with a cationic polyelectrolyte flocculant. In relation to pre-treatment, the term "weak" used refers to the fact that the total ultrasonic energy input to biosolids is insufficient to fully disrupt its floc structure or the cell walls, as described in the literature. Methane production potential, floc characteristics (size, morphology and zeta-potential) and process parameters (chemical oxygen demands and oxidative-reductive potentials) were monitored, as the digestion was tested. The presence of polyelectrolyte flocculants enhanced methane production within 6 days of digestion (phase I), but inhibited the digestion thereafter (phase II). Following pre-treatment by sonication (0.33 W/mL, 20 min), the methane productions of both original and flocculated biosolids significantly increased. The underlying mechanisms of weak ultrasonic pre-treatment are discussed.

Bacteria, Anaerobic↗