Biomedical subjects

J H Tay

Publications and source records attributed to J H Tay.

At least 55 records · Page 3Linked to original sources

PubMed2002

Characteristics of aerobic granules grown on glucose and acetate in sequential aerobic sludge blanket reactors.

Aerobic granules were cultivated in two column-type sequential aerobic sludge blanket reactors fed with glucose and acetate, respectively. The characteristics of aerobic granules were investigated. Results indicated that the glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density, hydrophobicity, physical strength, microbial activity and storage stability. Substrate component does not seem to be a key factor on the formation of aerobic granules. However, microbial diversity of the granules is closely associated with the carbon sources supplied to the reactors. Compared with the conventional activated sludge flocs, aerobic granules exhibit excellent physical characteristics that would be essential for industrial application. This research provides a complete set of characteristics data of aerobic granules grown on glucose and acetate, which would be useful for further development of aerobic granules-based compact bioreactor for handling high strength organic wastewater.

Aerobiosis↗

PubMed2002

A hybrid two-phase system for anaerobic digestion of food waste.

A hybrid two-phase system, consisting of a solid waste reactor as the acidification reactor and a wastewater reactor, i.e. an upflow anaerobic sludge blanket (UASB) reactor, as the methanogenic reactor, for anaerobic digestion of food waste was investigated. After the pre-acidification stage, COD and total VFA removals in the methanogenic phase were in the ranges of 74-93% and 77-100%, respectively, while leachate COD and total VFA concentrations in the acidification phase decreased by 95% and 97-99%, respectively. Some 99% of the total CH4 generated was from the methanogenic phase with the CH4 content of 68-70%. About 77-79% of TOC, 57-60% of volatile solids and 79-80% of total COD were removed. The results of this laboratory-scale study show that the hybrid two-phase anaerobic batch reactor system is suitable for effective conversion of food waste into CH4 and CO2. The hybrid two-phase system can be further developed into an effective and efficient way to enhance waste stabilization in operating bioreactor landfills.

Bacteria, Anaerobic↗

PubMed2002

Aerobic granulation in sequential sludge blanket reactor.

Aerobic granulation was studied in a column-type of sequential sludge blanket reactor. Reactor was operated 4 hours per cycle under a chemical oxygen demand (COD) loading rate of 6.0 kg/m3/d by using acetate as substrate. Results showed that aerobic granules with a mean diameter of 0.35 mm were observed at cycle 42. With granulation proceeding, the sludge volume index (SVI) value gradually decreased, and to an average value of 50 mL/g at stable granulation period. Observation of granules' microstructure by scanning electron microscopy (SEM) showed that rod bacteria were dominant in granules with lots of cavities presented. An increase in cell hydrophobicity was observed after the appearance of aerobic granules. The cell hydrophobicity of sludge was found to be about 50% higher after granulation. It appears that high hydrophobicity could induce cell attachment and further strengthen cell-cell interaction; cell hydrophobicity might therefore play a major role in the formation of aerobic granules.

Bacteria, Aerobic↗

PubMed2001

Recovery of heavy metals and stabilization of spent hydrotreating catalyst using a glass-ceramic matrix.

Chemical analysis of spent Co/Mo/gamma Al(2)O(3) catalyst revealed the presence of carbon, molybdenum, sulfur, vanadium and cobalt at levels of 16.0, 10.9, 7.3, 4.6 and 4.0 wt.%, respectively. It was found that calcination at 500 degrees C provides an effective solution for the removal of carbon and sulfur and this generates the oxide form of the heavy metals. The removal of these heavy metals can be achieved through a two-stage leaching process. During the first stage, in which concentrated ammonia is used and it has been found that this process can be successful in removing as much as 83% (w/v) Mo. In a second stage, it was found that using 10% (v/v) of sulfuric acid, it was possible to account for up to 77% (w/v) Co and 4% (w/v) Mo removal. Leaching test results indicated that the vanadium present in the heated spent catalyst was almost stabilized but the molybdenum and cobalt were not. The combination of two solid wastes, ladle furnace slag (LFS) and treated residue of spent catalyst, could be used for making a high value-added anorthite glass-ceramic materials. Further leaching tests showed that ceramic glass materials provided a very effective method of Co, Mo and V heavy metals stabilization resulting in a product with a possible commercial value.

Aluminum Silicates↗

PubMed2001

Strategy for minimization of excess sludge production from the activated sludge process.

Increased attention has been given to minimization of sludge production from activated sludge process since environmental regulations are being more and more stringent in relation to excess sludge disposal. In a biological process, the more organic carbon utilized in carbon dioxide production, the fewer sludge produced, and vice versa. This paper, therefore, reviews strategies developed for minimization of excess sludge production, such as oxic-settling-anaerobic process, high dissolved oxygen process, uncoupler-containing activated sludge process, ozonation-combined activated sludge process, control of sludge retention time and biodegradation of sludge in membrane-assisted reactor. In these modified activated sludge processes, excess sludge production can be reduced by 20-100% without significant effect on process efficiency and stability. It is expected that this paper would be helpful for researchers and engineers to develop novel and efficient operation strategy to minimize sludge production from biological systems.

Journal Article↗

PubMed2001

The effects of shear force on the formation, structure and metabolism of aerobic granules.

The effect of shear force on aerobic granulation was studied in four column-type, sequential aerobic sludge blanket reactors. Hydrodynamic turbulence caused by upflow aeration served as the main shear force in the systems. Results showed that aerobic granulation was closely associated with the strength of shear force. Compact and regular aerobic granules were formed in the reactors with a superficial upflow air velocity higher than 1.2 cm s(-1). However, only typical bioflocs were observed in the reactor with a superficial upflow air velocity of 0.3 cm s(-1) during the whole experimental period. The characteristics of the aerobic granules in terms of settling ability, specific gravity, hydrophobicity, polysaccharide and protein content and specific oxygen utilization rate (SOUR) were examined. It was found that the shear force has a positive effect on the production of polysaccharide, SOUR, hydrophobicity of cell surface and specific gravity of granules. The hydrophobicity of granular sludge is much higher than that of bioflocs. Therefore, it appears that hydrophobicity could induce and further strengthen cell-cell interaction and might be the main force for the initiation of granulation. The shear-stimulated production of polysaccharides favors the formation of a stable granular structure. This research provides experimental evidence to show that shear force plays a crucial role in aerobic granulation and further influences the structure and metabolism of granules.

Aerobiosis↗

PubMed2001

The roles of calcium in sludge granulation during UASB reactor start-up.

Six upflow anaerobic sludge blanket (UASB) reactors were concurrently operated for 146 d to examine the effects of calcium on the sludge granulation process during start-up. Introduction of Ca2+ at concentrations from 150 to 300 mg/l enhanced the biomass accumulation and granulation process. The calcium concentration in the granules was nearly proportional to the calcium concentration in the feed, and calcium carbonate was the main calcium precipitate in the granules. The specific activity of granules decreased with increasing influent calcium concentration. The optimum calcium concentration for the granulation was from 150 to 300 mg/l. The addition of low-concentration calcium to the UASB reactors appeared to enhance the three steps of sludge granulation: adsorption, adhesion and multiplication, but it did not lead to a different proliferation of predominant microorganisms in the granules.

Anaerobiosis↗

PubMed2001

Enhanced sludge granulation in upflow anaerobic sludge blanket (UASB) reactors by aluminum chloride.

Two upflow anaerobic sludge blanket (UASB) reactors were concurrently operated for 146 days to examine the effects of aluminum chloride (AlCl3) on the sludge granulation process during start-up. Sludge granulation (defined as that over 10% of granules were larger than 2.0 mm) was achieved in the control reactor (R1) in approximate three months. Introduction of Al3+ at a concentration of 300 mg/l reduced the sludge granulation time by approximate one month. Throughout the experiment the AlCl3-added reactor (R2) had a higher biomass concentration, e.g., 13.8 g-MLVSS/l versus 12.8 g-MLVSS/l on Day 146. Granules became visible earlier in R2 compared with R1 (35 days versus 65 days). The average size of granules from R2 was larger than that from R1. The results demonstrated that AlCl3 enhanced the sludge granulation process in the UASB reactors.

Aluminum Chloride↗

PubMed2001

Optimising the preparation of activated carbon from digested sewage sludge and coconut husk.

Preparation of activated carbon from sewage sludge is a promising way to dispose of sewage sludge as well as to produce a low-cost adsorbent for pollutant removal. This research work aimed to optimise the condition for activated carbon preparation from anaerobically digested sewage sludge with the additive coconut husk. The sewage sludge sample was mixed with the additive coconut husk. The preparation condition variables investigated involved the concentration of the ZnCl2 solutions, heating temperature, dwell time and heating rate in pyrolysis and the mixing ratio of coconut husk to sewage sludge. Surface area, pore size distribution, aqueous phenol adsorption capacity and the production yield of the final products were determined and compared. Experimental results revealed that low concentrations of ZnCl2 solution tended to improve the microporosity of the final product. Heating temperature had a considerable impact on the surface area, pore size distribution and phenol adsorption capacity of the final products, whereas dwell time and heating rate performed comparatively insignificantly. The effect of increasing the mixing ratio of coconut husk to sewage sludge was principally to increase the microporosity of the final products. The activated carbon with the highest BET surface area was produced with the activation of 5 M ZnCl2 solution and, thereafter, pyrolysis at a heating temperature of 500 degrees C for 2 h with a heating rate of 10 degrees C/min. The mixing ratio of 1:4 in terms of coconut husk to sewage sludge based on their dried weights was found to be most cost effective.

Adsorption↗

PubMed2001

A comparative study of anaerobically digested and undigested sewage sludges in preparation of activated carbons.

Disposal of sewage sludge is an increasingly expensive and environmentally sensitive problem throughout the world. Preparation of activated carbon from sewage sludge offers an attractive re-use alternative to the traditional disposal routes. The objective of this research work was to compare anaerobically digested sewage sludge (DS) and undigested sewage sludge (US) as source materials in the preparation of activated carbons. Prior to the preparation the properties of the two types of sewage sludges were determined and compared. Subsequently the sludge samples were activated with 5 M ZnCl2 solution and thereafter pyrolysed at heating temperature of 650 degrees C for 2 h with the heating rate of 15 degrees C/min under a nitrogen atmosphere. The produced activated carbons were characterised by surface area and porosity analysis, CHN elemental composition and ash contents determination, and aqueous phase phenol adsorption tests. The results indicate that in comparison with the DS, the US had a higher carbon content and lower ash content, and accordingly yielded a better activated carbon with a higher BET surface area, pore volume, carbon content and phenol adsorption capacity.

Adsorption↗

PubMed2001

Metabolic response of biofilm to shear stress in fixed-film culture.

AIMS: In a biofilm reactor, detachment force resulting from hydraulic shear is a major factor that determines the formation and structure of steady state biofilm. The metabolic response of biofilm to change in shear stress was therefore investigated. METHODS AND RESULTS: A conventional annular reactor made of PVC was used, in which shearing over the rotating disc surface was strictly defined. Results from the steady state aerobic biofilm reactor showed that the biofilm structure (density and thickness) and metabolic behaviour (growth yield and dehydrogenase activity) were closely related to the shear stress exerted on the biofilm. Smooth, dense and stable biofilm formed at relatively high shear stress. Higher dehydrogenase activity and lower growth yield were obtained when the shear stress was raised. Growth yield was inversely correlated with the catabolic activity of biofilm. The reduced growth yield, together with the enhanced catabolic activity, suggests that a dissociation of catabolism from anabolism would occur at high shear stress. CONCLUSION: Biofilms may respond to shear stress by regulating metabolic pathways associated with the substrate flux flowing between catabolism and anabolism. A biological phenomenon, besides a simple physical effect, is underlying the observed relation between the shear stress and resulting biofilm structure. SIGNIFICANCE AND IMPACT OF THE STUDY: A hypothesis is proposed that the shear-induced energy spilling would be associated with a stimulated proton translocation across the cell membrane, which favours formation of a stronger biofilm. This research may provide a basis for experimental data on biofilm obtained at different shear stresses to be interpreted in relation to energy.

Biofilms↗

PubMed2001

Microscopic observation of aerobic granulation in sequential aerobic sludge blanket reactor.

AIMS: This paper attempts to provide visual evidence of how aerobic granulation evolves in sequential aerobic sludge blanket reactors. METHODS AND RESULTS: A series of experiments were conducted in two column-type sequential aerobic sludge reactors fed with glucose and acetate as sole carbon source, respectively. The evolution of aerobic granulation was monitored using image analysis and optical and scanning electron microscopy. The results indicated that the formation of aerobic granules was a gradual process from seed sludge to compact aggregates, further to granular sludge and finally to mature granules with the sequential operation proceeding. Glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density and microbial activity. However, the microbial diversity of the granules was associated with the carbon source supplied. In this work, an important aerobic starvation phase was identified during sequential operation cycles. It was found that periodical aerobic starvation was an effective trigger for microbial aggregation in the reactor and further strengthened cell-cell interaction to form dense aggregates, which was an essential step of granulation. The periodical starvation-induced aggregates would finally be shaped to granules by hydrodynamic shear and flow. CONCLUSION: Aerobic granules can be formed within 3 weeks in the systems. The periodical starvation and hydrodynamic conditions would play a crucial role in the granulation process. SIGNIFICANCE AND IMPACT OF THE STUDY: Aerobic granules have excellent physical characteristics as compared with conventional activated sludge flocs. This research could be helpful for the development of an aerobic granule-based novel type of reactor for handling high strength organic wastewater.

Aerobiosis↗

PubMed2001

The role of cellular polysaccharides in the formation and stability of aerobic granules.

AIMS: This paper attempts to investigate the role of cellular polysaccharides in the formation and stability of aerobic granules. METHODS AND RESULTS: Three column sequential aerobic sludge blanket reactors (R1, R2 and R3) were operated at a superficial air upflow velocity of 0.3 cm s(-1), 1.2 cm s(-1) and 2.4 cm s(-1), respectively. Aerobic granules appeared at cycle 42 in R2 and R3 with a mean size of 0.37 mm in R2 and 0.35 mm in R3, however, aerobic granulation was not observed in R1. After the formation of aerobic granules, the sludge volume index (SVI) decreased to 55 ml g(-1) in R2 and 46 ml g(-1) in R3. Aerobic granulation was concurrent with a sharp increase of cellular polysaccharides normalized to cellular proteins, which increased from 5.7 to 13.0 mg per mg proteins in R2, and 7.5-13.9 mg per mg protein in R3. The content of polysaccharides in aerobic granules was 2-3 times higher than that in the bioflocci cultivated in R1. The disappearance of aerobic granules in R2 was tightly coupled to a drop in cellular polysaccharides. After the reappearance of bioflocci in R2, the content of cellular polysaccharides were found to be restored to the level observed in R1. CONCLUSION: It appears that the production of cellular polysaccharides could be stimulated by hydrodynamic shear force and contributes to the formation and stability of aerobic granules. SIGNIFICANCE AND IMPACT OF THE STUDY: It is expected that this study would provide useful information for better understanding the mechanisms of aerobic granulation.

Aerobiosis↗

PubMed2001

Factors affecting nitrite build-up in nitrifying biofilm reactor.

Nitrite build-up in a nitrifying biofilm reactor for direct denitrification from the nitrite stage was investigated. At least three factors were found to influence the nitrite build-up: (i) the relative specific growth rates of Nitrosomonas to Nitrobacter, microNs/microNb in the biofilm; (ii) the relative initial ratio between Nitrosomonas and Nitrobacter on the support surface, (Mao)Ns/(Mao)Nb; (iii) the level of free ammonia, particularly at greater than 0.1 mg N/l that can be inhibitory to Nitrobacter. Results showed that without free ammonia inhibition, the first two factors determined the degree of nitrite build-up. The effect of (Mao)Ns and (Mao)Nb on nitrification kinetics were more significant than the specific growth rates of Nitrosomonas and Nitrobacter. By regulating effects of these three factors, extremely high concentrations of nitrite build-up could occur in a biofilm reactor. This offers a potential for achieving direct denitrification through a nitrate shunt.

Ammonia↗

PubMed2001

Preserved granular sludge for inoculation of new UASB reactors.

In this study, granular sludges collected from a mesophilic laboratory-scale UASB reactor were stored for 6 months at 4 degrees C, 24 degrees C (room temperature) and 35 degrees C, respectively. The preservation characteristics of granular sludges (including soluble COD, granular particle size and granular surface morphology) in terms of storage age and temperature were investigated. It was found that 4 degrees C stored UASB granules were more capable of maintaining their granular structures over those stored at 24 degrees C and 35 degrees C. Granulation in UASB reactors seeded with preserved sludge granules reached its post-maturation stage about 40 days ahead of the control, mainly by means of eliminating the embryonic granule formation stage from the granulation process. The results in this study indicated that the preserved granular sludge could be used as an effective inoculum to accelerate new UASB reactor start-up.

Bacteria, Anaerobic↗

PubMed2001

Wastewater treatment and nitrogen removal using submerged filter systems.

The performance of two submerged filter systems: a two filters-in-series system and a single combined filter system, in treating a strong nitrogenous wastewater with nitrogen concentration of 480 mg/L was evaluated. Both systems were equally effective in removing up to 90% of nitrogen and 98% of COD from the wastewater for loading rates up to 5 kg COD/m3.d and 0.5 kg N/m3.d. The second system in which anaerobic, anoxic, and aerobic zones were incorporated in a single filter offers a greater flexibility in treatment in that by repositioning the locations of the aeration point and effluent recycling inlet, the zonal volumes can be altered easily to treat wastewaters with different COD and nitrogen concentrations.

Bacteria, Anaerobic↗

PubMed2001

Removal of color substances using photocatalytic oxidation for membrane filtration processes.

This study aims to remove the color substances, which normally cause difficulties in membrane filtration processes due to fouling using heterogeneous UV/TiO2/H2O2 reactor. It is confirmed that the technique used in this study was effective to remove TOC at 38% and color400 at 89% within 150-min irradiation. The experiment results showed that low concentrations of hydrogen peroxide dosage (less than 0.016 M) to UV/TiO2 system accelerated the TOC and Color400 removal rate from 9% to 38% and 40% to 89% respectively, while over-dosage made this positive effect decline. The humic acid solution treated by photo catalytic oxidation in UV/TiO2/H2O2 reactor did not change the zeta potential on membrane surface and membrane rejection rate.

Coloring Agents↗

PubMed2001

Reuse of industrial sludge as construction aggregates.

Industrial wastewater sludge and dredged marine clay are high volume wastes that needed enormous space at landfill disposal sites. Due to the limitation of land space, there is an urgent need for alternative disposal methods for these two wastes. This study investigates the possibility of using the industrial sludge in combination with marine clay as construction aggregates. Different proportions of sludge and clay were made into round and angular aggregates. It was found that certain mix proportions could provide aggregates of adequate strength, comparable to that of conventional aggregates. Concrete samples cast from the sludge-clay aggregates yield compressive strengths in the range of 31.0 to 39.0 N/mm2. The results showed that the round aggregates of 100% sludge and the crush aggregates of sludge with up to 20% clay produced concrete of compressive strengths which are superior to that of 38.0 N/mm2 for conventional aggregate. The study indicates that the conversion of high volume wastes into construction materials is a potential option for waste management.

Aluminum Silicates↗