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Biomedical subjects

H Chua

Publications and source records attributed to H Chua.

At least 19 recordsLinked to original sources
PubMed2006

Assessing optimal fermentation type for bio-hydrogen production in continuous-flow acidogenic reactors.

In this study, the optimal fermentation type and the operating conditions of anaerobic process in continuous-flow acidogenic reactors was investigated for the maximization of bio-hydrogen production using mixed cultures. Butyric acid type fermentation occurred at pH>6, propionic acid type fermentation occurred at pH about 5.5 with E(h) (redox potential) >-278mV, and ethanol-type fermentation occurred at pH<4.5. The representative strains of these fermentations were Clostridium sp., Propionibacterium sp. and Bacteriodes sp., respectively. Ethanol fermentation was optimal type by comparing the operating stabilities and hydrogen production capacities between the fermentation types, which remained stable when the organic loading rate (OLR) reached the highest OLR at 86.1kgCOD/m(3)d. The maximum hydrogen production reached up to 14.99L/d.

Bacteria, Anaerobic↗
PubMed2006

Synthesis of PHAs from waster under various C:N ratios.

Polyhydroxyalkanoates (PHAs) production was carried out under various C:N ratios. A ratio of 100 resulted best polymer yield. C-source was an important factor in synthesis. For example, as the ratio of valeric acid (C5) to butyric acid (C4) in N-free medium was increased, the mole fraction of HV in the copolymer increased. When soy waste was used as a C-source a copolymer, a high HV mole fraction (HB:HV, 75:25) was produced while when malt waste was used, a much lower HV mole fraction (HB:HV, 90:10) was generated. It was concluded that activated sludge bacteria could be induced to produce PHAs using food wastes as C-sources and this could be the basis for production of biodegradable plastics.

Alcaligenes↗
PubMed2005

Determination of the optimal and economical biofilter depth in an anaerobic hybrid reactor for treating livestock industrial wastewater.

A laboratory scale anaerobic hybrid reactor (AHR) being comprised of UASB and anaerobic biofilter was used to study the different biofilter depth with corresponding different critical HRT (1) and HRT (2) in treating livestock industrial wastewater, where the critical HRT (1) was defined as the HRT which resulted in the total COD in the effluent of the AHR exceeding in the influent at unsteady state, and the HRT (2) was defined as the HRT which resulted in the total COD in the effluent of the AHR exceeding the quality standard for discharging to sewer (in Hong Kong is Total COD < 1000 mg L1) at steady state. Two formulas expressing the relationship of different biofilter depth in the AHR and it's critical HRT (1) and HRT (2) in treating livestock industrial wastewater were obtained and used to design optimal and economical biofilter depth in a full scale AHR for treating livestock industrial wastewater on site. The performance of the full scale AHR indicated that using the experience formulas to design the optimal and economical biofilter depth in the full scale AHR for treating livestock industrial wastewater was successful. Experimental results also showed that the biofilter in the full scale AHR had not only physical filtration effect, but also had powerful biodegradation capability, furthermore, at unsteady state, the effect of biofilter on pollutant degrading in the full scale AHR was more great.

Anaerobiosis↗
PubMed2005

Evaluation of a novel integrated bioreactor--AOS system for treating oil-containing restaurant wastewater on site in Hong Kong.

AOS system is an anaerobic digestion reactor (A-section, UASB or UBF), oxidation degradation reactor (O-section, aerobic biofilm reactor), and physical sedimentation tank (S-section) 3-in-1 integrated reactor. The compact bioreactor was applied to treat oil-containing restaurant's wastewater on site in Hong Kong. The treatment efficiency was observed at different HRT. Experimental results indicated that the AOS system for treating oil-containing restaurant wastewater on site was feasible when HRT at 0.6 days above. During the running period, the net sludge generation rate of the AOS system was only about 0.08-0.09 g g(-1)removed COD, and the utmost COD specific volumetric removal rate (SVRR) of the system reached 2.77 gL(-1) d(-1). The utmost specific biomass substrate utilization rate (SBSUR) of COD in O-section and A-section reached 1.22 d(-1) and 0.128 d(-1), respectively. In addition, the experiment results showed that the AOS system with a filter in UASB (that is UBF's AOS system) could bear much more great HLR comparing with UASB's AOS and was more efficient for treating oil-containing restaurant's wastewater on site.

Biodegradation, Environmental↗
PubMed2005

Synthesis of polyhydroxyalkanoate (PHA) from excess activated sludge under various oxidation-reduction potentials (ORP) by using acetate and propionate as carbon sources.

Accumulation of poly hydroxyalkanoate (PHA) from excess activated sludge (EAS) was monitored and controlled via the oxidation-reduction potential (ORP) adjusting process. The ORP was adjusted and controlled by only regulating the gas-flow rate pumped into the cultural broth in which sodium acetate (C2) and propionate (C3) were used as carbon sources. Productivity of PHA and the PHA compositions at various C2 to C3 ratios were also investigated. When ORP was maintained at +30 mV, 35% (w/w) of PHA of cell dry weight obtained when C2 was used as sole carbon source. The PHA copolymer, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), accumulated by EAS with different 3-hydroxyvalarate (3HV) molar fractions ranged from 8% to 78.0% when C2 and C3 was used as sole carbon source, By using ORP to monitor and control the fermentation process instead DO meter, the ORP system provided more precise control to the PHA accumulation process from EAS under low dissolved oxygen (DO) concentrations. Adjusting the C2 to C3 ratios in the media could control the composition such as the 3HV/3HB ratios of the PHBV. Furthermore, it might be an effective way to adjust the 3HV molar fractions in PHBV by controlling the DO concentration via the ORP monitoring system. The 3HV molar fractions in the PHBV declined with increasing ORP from -30 mV to +100 mV by adjusting the gas-flow rate (i.e. the DO concentration). It is concluded that the DO plays a very important role in the synthesis of 3HV subunits in PHBV co-polymer from the EAS. Therefore, a hypothetic metabolic model for PHA synthesis from EAS was proposed to try to explain the results in this study.

Acetates↗
PubMed2005

Effects of fatty acids on growth and poly-3-hydroxybutyrate production in bacteria.

The effects of saturated and unsaturated fatty acids (lauric acid, palmitic acid, steric acid, oleic acid, linoleic acid, soybean oil) on Sphaerotilus natans, 0B17 (Pseudomonas sp.), and recombinant Escherichia coli DH5(/pUC19/CAB were studied. Oleic acid enhances Poly-3-hydroxybutyrate (PHB) production in these three bacterial strains, suggesting that the single double bond of the acid activates the polyhydroxylkanoate accumulation enzymatic reaction. Under the effect of lauric acid and linoleic acid, the growth of S. natans and 0B17 were totally inhibited. However, the enhanced PHB accumulation in recombinant E. coli was observed.

Bioreactors↗
PubMed2005

Microbial synthesis and characterization of physiochemical properties of polyhydroxyalkanoates (PHAs) produced by bacteria isolated from activated sludge obtained from the municipal wastewater works in Hong Kong.

The first objective of this study was the measurement of physical properties of P(3HB-co-3HV) copolymers with different (hydroxybutyrate) HB to (hydroxyvalerate) HV ratios produced by Bacillus cereus (TRY2) isolated from activated sludge. The 3HV PHBV copolymers were 0.05, 22.6, 39.2, 54.1, and 69.1 mol%, respectively. The second objective was to study possible waste water treatment and production of PHAs at the same time by B. cereus (TRY2) and Pseudomonas spp. (TOB17) (both were isolated from activated sludge), recombinant Bacillus DH5alpha, and a combination of the above three bacteria. The results were satisfactory; the maximum COD and TOC of the sewage sludge reduced were 53.5% and 67.5%, respectively.

Bacillus cereus↗
PubMed2004

A combined bioprocess for integrated removal of copper and organic pollutant from copper-containing municipal wastewater.

Heavy metal-containing wastewater is difficult to treat by most of the bioprocess due to its toxicity to microorganism in activated sludge. In this study, a combined bioprocess consisting of biosorption section that contained magnetite immobilized Pseudomonas putida 5-x cell as biosorbent followed by sequence batch reactor (SBR) was developed to treat Cu(2+)-containing municipal wastewater. The production techniques of Pseudomonas putida 5-x cell as biosorbent, such as optimal cell harvest period and cell pretreatment techniques were studied. Experimental results showed, considering both cell biomass and cell adsorption capacity to Cu(2+), 36 h is the optimal harvest period in the course of culturing Pseudomonas putida 5-x cells as biosorbent, and 0.1-0.3 mol L(-1) HCl is an optimal cell pretreating eluant to improve Cu(2+) adsorption capacity. The performances of the combined bioprocess for treating Cu(2+) containing wastewater were assessed. Experimental results showed that after treatment by biosorption, the Cu(2+) level in wastewater was reduced to level that did not inhibit COD removal efficiency of subsequent SBR activated sludge process, although it still affected the COD adsorption capacity of activated sludge. In terms of COD removal, the biosorption section was efficient for reducing Cu(2+) concentration to provide biodegradable wastewater for subsequent SBR activated sludge process.

Adsorption↗
PubMed2004

Contribution of cell outer membrane and inner membrane to Cu2+ adsorption by cell envelope of Pseudomonas putida 5-x.

The role of outer and inner membrane in the Cu2+ adsorption process by gram-negative bacterium Pseudomonas putida 5-x, which was isolated from local electroplating effluent with high Cu2+ accumulating capability, was studied. The results indicate that both the outer and inner membrane exhibited high Cu2+ adsorption capacity. Outer and inner membrane contributed about 30-35% and 20-25% parts of adsorption capacity in Cu2+ adsorption by cell envelope of Pseudomonas putida 5-x, respectively. The total contribution of outer and inner membrane to Cu2+ adsorption by cell envelope was much greater than that of peptidoglycan layer. The relatively high phospholipid content in the outer membrane might result in its greater heavy metal ions adsorption capacity. The Cu2+ binding process by the outer and inner membrane of Pseudomonas putida 5-x is the adsorption processes and can be described with Freundlich isotherms.

Adsorption↗
PubMed2003

Role of cell surface components on Cu2+ adsorption by Pseudomonas putida 5-x isolated from electroplating effluent.

A gram-negative bacterium Pseudomonas putida 5-x with high Cu2+ accumulating capability was isolated from electroplating effluent in Kwun Tong, Hong Kong. The pretreated cells without superficial layer-capsule, isolated cell envelopes and the separated peptidoglycan layer materials were obtained from fresh P. putida 5-x cells, their Cu2+ adsorption capacities and properties were compared with that of the fresh cells. Pretreatment by 0.1 mol L(-1) HCl enhanced Cu2+ adsorption capacity due to the degradation of cell superficial layer-capsule of P. putida 5-x cells. Isolated cell envelopes possessed five times more Cu2+ adsorption capacity than that of fresh intact cell. The Cu2+ adsorption of separated peptidoglycan layer materials indicated that the peptidoglycan layer only played 10-15% part of the Cu2+ adsorption capacity, and implied other cell surface components such as outer membrane or inner membrane might play an important role in such high Cu2+ binding of the cell envelopes. The adsorption process of fresh cells, pretreated cells and cell envelopes of P. putida 5-x could be described with Freundlich isotherm, while the adsorption of Cu2+ by separated peptidoglycan layer materials was better described with Langmuir isotherm.

Adsorption↗
PubMed2003

Ni2+ removal and recovery from electroplating effluent by Pseudomonas putida 5-x cell biomass.

Ni2+ and Cu2+ are the major heavy metal ions in electroplating wastewater of Hong Kong. In the present study, Pseudomonas putida 5-x cell biomass was used to remove Ni2+ from electroplating effluent. Ni2+ adsorption capacity of P. putida 5-x cell biomass cultured in sulphate-limiting medium was found to be minimum in early logarithmic growth phase, and maximum of 28.1 mg g(-1) in late stationary growth phase. Pretreated cells by 0.1 mol L(-1) HCl could greatly enhance the Ni2+ adsorption capacity of cell biomass from 28.1 to 36.7 mg g(-1) and had no significant effect on biomass loss. The adsorption process of P. putida 5-x fresh cells and pretreated cell all could be expressed with Freundlich isotherm. TEM analyses indicated that acidic pretreatment degraded the superficial layer-capsule outside of the fresh cell to improve the adsorption capacity of cell to Ni2+. The Ni2+ bound by P. putida 5-x cell biomass could be efficiently recovered using 0.1 mol L(-1) HCl, and the cell biomass could be reused at least five cycles for Ni2+ removal and recovery with 93% above removal efficiency and 98% above recovery rate. Owing to the Cu2+ presented in electroplating wastewater inhibiting Ni2+ adsorption process by P. putida 5-x cell biomass, two-stage biosorption processes should be designed to remove and recover Cu2+ and Ni2+ sequentially from electroplating effluent.

Adsorption↗
PubMed2003

The biodegradation of 1,3-dichlorobenzene by an adapted strain Bacillus cereus PF-11 derived from town-gas industrial effluent.

In the present study, an adapted bacterium PF-11 with high 1,3-dichlorobenzene degradation capability was isolated from town-gas industrial effluent through continuous introducing of N-methyl-N'-nitro-N-nitrosoquanidine (NTG). In suitable condition, a degradation rate of 32 mg L(-1) d(-1) of 1,3-dichlorobenzene was obtained by strain PF-11 with effective chlorion release. Strain PF-11 was tentatively identified as gram-positive Bacillus cereus. The substrate specificity of the strain PF-11 was relatively low, and the degradation rate for different chlorobenzenes was in the order of monochlorobenzene > 1,3-dichlorobenzene > 1,2-dichlorobenzene. Initial oxidation step was molecular oxygen attacking chlorobenzene ring catalyzed by dioxygenase.

Adaptation, Physiological↗
PubMed2003

Bacterial biosorbent for removing and recovering copper from electroplating effluents.

Investigations were carried out to study the removal and recovery of Cu(II) ions from wastewater by Micrococcus sp. The Langmuir isotherm model described very well the equilibrium behavior of copper biosorption, with maximum biosorption capacity (q(max)) reaching 52.1 mg Cu2+/g dry cell at pH 6. Biomass prewashed with sulfuric acid (0.05 mol 1(-1)) and sodium sulfate (1 mol l(-1)) solutions were shown to increase the copper removal capabilities up to 27% and 16%, respectively. Copper uptake by cells was negligible at pH 2.0 and then increased quickly with increasing pH until 6.0. Cells of Micrococcus sp. were immobilized in 2% calcium alginate and 10% polyacrylamide gel beads. A counter-current process comprising a series of immobilized cell reactors was developed for removing and recovering copper from electroplating effluents. This process was capable of producing an effluent at low copper concentration, with only a minimum amount of desorbing agent used. The technique of scanning electron microscopy coupled with X-ray dispersion analysis shows that Cu2+ exchanged with K+ and Ca2+ on the cell wall of Micrococcus sp., thereby suggesting ion exchange as one of the dominant mechanisms of metal biosorption for this bacterial strain.

Adsorption↗
PubMed2001

The degradation of xenobiotic branched carboxylic acids in anaerobic sediment of the Pearl River in Southern China.

Xenobiotic branched carboxylic acids (BCAs) discharged by industries are often persistent in biological wastewater treatment systems and end up in water and sediments. In this study, the degradation of 12 typical BCAs in an anaerobic environment of river sediment was studied in vitro using enrichment shake-flask cultures. The anaerobic consortium taken from the river sediment, comprising BCA-degrading and methane-producing genera, degraded BCAs with tertiary carbons through beta-oxidation, followed by methanogenesis mechanisms. The maximum cell densities in the cultures using BCAs as the sole carbon source ranged between 5.0 and 6.0 x 10(5) cells/ml. The maximum degradation rates were between 5.0 and 8.5 x 10(-3) mmol/h. The consortium could not degrade BCAs with quaternary carbons. The degree of branching at the alpha or beta position along the carbon chain interfered with the beta-oxidation mechanisms. These BCAs would accumulate in the sediment and significantly affect the cycling of organic carbon and nutrients.

Bacteria, Anaerobic↗
PubMed2001

Assessment of heavy metal cations in sediments of Shing Mun River, Hong Kong.

The extent of heavy metal cation contamination in the Shing Mun River has been assessed. Sediment samples were taken at eight strategic locations along the river system. The highest concentrations of copper (Cu, 1.66 mg/g), lead (Pb, 0.354 mg/g), zinc (Zn, 2.2 mg/g) and chromium (Cr, 0.047 mg/g) were found in the Fo Tan Nullah, a major tributary of the Shing Mun River. The highest concentrations of aluminum (114 mg/g) and cadmium (Cd, 0.047 mg/g) were found in the Shing Mun Main River Channel. These contaminated sediments, accumulated over the years on the river bed, could act as secondary sources of pollution to the overlying water column in the river.

Cations↗
PubMed2001

Nutrient release and sediment oxygen demand in a eutrophic land-locked embayment in Hong Kong.

Tolo Harbour is a large eutrophic land-locked estuarine embayment in Hong Kong. The rapid urbanization, commercio-industrial activities and lack of legislative control around the Tolo catchment produced large quantities of untreated or partially treated municipal sewage, agricultural wastes and cottage industrial effluents which were discharged into Tolo Harbour via rivers and watercourses. Control measures were implemented to reduce the external nutrient loading into the harbour since the early 1980s. Nutrient data for the period 1982 to 1997 were analyzed for temporal trends. Over the period of observation, the total inorganic nitrogen and total phosphorus both show an increasing trend, despite a decade of efforts in reducing nutrient loading. The release rates of potentially mobile nitrogen (N) and phosphorus (P) from the sediments collected from Tolo Harbour were determined by N and P release experiments under oxic conditions. The experimental results showed that the sediment released significant amount of nutrients, especially orthophosphates and ammonia nitrogen. The maximum release rates were 15.0 and 206.0 mg/m2/day, respectively. Although the external nutrient loading has been reduced, nutrients could gradually be released back into the water column from the contaminated sediments and delay improvement of the water quality.

Environmental Monitoring↗
PubMed2001

Bleeding from cavernous angiomatosis of the rectum in Klippel-Trenaunay syndrome: report of three cases and literature review.

Klippel-Trenaunay syndrome (KTS) is a congenital vascular anomaly characterized by limb hypertrophy, cutaneous hemangiomas, and varicosities. GI hemorrhage is a potentially serious complication secondary to diffuse hemangiomatous involvement of the gut. We report on three patients with KTS who presented with transfusion-dependent anemia and life-threatening bleeding due to extensive cavernous hemangiomas involving the rectum. Two patients were treated by proctocolectomy and coloanal anastomosis, which preserved anal function while controlling bleeding. The third patient required an abdominoperineal resection because of extensive rectal, perianal, and perineal angiomatosis. The literature on the evaluation and management of GI hemorrhage in KTS, particularly of colorectal origin, is reviewed.

Adult↗