Biomedical subjects

C P Chu

Publications and source records attributed to C P Chu.

At least 19 recordsLinked to original sources

PubMed2005

Energy demand in sludge dewatering.

This work investigates the energy required to dewater a suspension, i.e., activated sludge dewatered by centrifugation or consolidation. Total energy input to the suspension from the dewatering device, bond strength between adjacent water and solid surface, and intra-cake friction loss were evaluated for original and flocculated sludges. In centrifugal dewatering, most energy input during the initial stage was consumed by overcoming process irreversibility other than intra-cake friction, and, thereby, had a low energy efficiency. To increase centrifuge speed or to flocculate the sludge at optimal flocculant dosage would yield a high-energy input. In the consolidation test, most energy input at the initial stage was consumed in breaking down the bond strength until the moisture content reduced to less than the critical content. During subsequent dewatering stages, friction loss became the dominant source of energy loss. Dewatering sludge with high-energy efficiency is beneficial to optimally operate a dewatering process.

Centrifugation↗

PubMed2005

Size-dependent anaerobic digestion rates of flocculated activated sludge: role of intrafloc mass transfer resistance.

The anaerobic digestion rate for flocculated sludge has been considered to be lower than that of original sludge, particularly in the later stages of digestion; attributed this relatively slower rate to the increased mass transfer resistance for reactants through the large flocs after flocculation. This study confirmed that methane production was retarded by flocculation. The structure of the floc was identified with fluorescence in situ hybridization (FISH) and a confocal laser scanning microscope (CLSM) technique. To verify the mass transfer resistance induced by flocculation, microsensors were applied to assess the response of oxygen concentration distribution inside the flocs that are subjected to sudden changes in ambient oxygen levels. Response time for the electrode at a floc's center was five times greater than the response time in original sludge flocs. Although the effective diffusivity of oxygen in the floc increased by 2.3 times after flocculation, the increased size of the flocculated floc was the major contributor to the total mass transfer resistance to oxygen.

Bacteria, Anaerobic↗

PubMed2005

Comparison of dewaterability and floc structure of synthetic sludge with activated sludge.

This work compared the appearance, dewaterability, floc size, fractal dimensions derived from free-settling test and light-scattering test, and detailed structural information of floc interior including porosity, Sierpinski carpet fractal dimension, and the fractal dimension of the pore boundaries of a synthetic sludge and an activated sludge. The present synthetic sludge could probe the change in filterability and in fractal dimensions extracted from small angle light scattering test and from free-settling test after conditioning, however, failed to reproduce the detailed structural information of sludge flocs. The use of specific synthetic sludge depends on the field of interest. For instance, the present synthetic sludge is not appropriate to simulate the intrafloc transport of solute owing to its incapability to reproduce the detailed floc structure or to its change after conditioning.

Flocculation↗

PubMed2004

Advective flow in a sludge floc.

The interior of sludge floc is highly heterogeneous, while the large pores in the floc control the advective flow. This work for the first time numerically details fluid flow and mass transfer processes in pores of activated sludge floc. The dimensionless permeabilities and mass dispersion coefficients were contoured against pore size ratio and the floc Reynolds number. With a pore size less than 20% of the floc size, the commonly adopted homogeneous model overestimates the floc permeability, and pore velocity is less than 2% of the bulk velocity. This is particularly true for flocs with low porosity. Although the convective flux is low, the dispersive mass transfer rate can be much higher than the diffusional rate, attributable to the strong Taylor dispersion effect. The three-dimensional pore structures in waste activated-sludge floc were identified using confocal laser scanning microscope (CLSM) images. Large pores were used to numerically estimate the permeability and dispersion coefficient for these pores. The permeability and the dispersion coefficient of the tortuous pores can be one order of magnitude lower than those for the equivalent straight pores. Besides the dispersion effect, the pore tortuosity appeared as the most important geometrical factor retarding the advective flow in the sludge pores. In addition, the small side pores connected to the large pore had only a mild effect on the flow process, and can be neglected in analysis.

Journal Article↗

PubMed2004

Bilevel thresholding of floc images.

Frequently encountered problems on bilevel thresholding of floc images include information loss during the image conversion stage, sampling bias owing to spatially inhomogeneous luminous flux over an optical microscope image or among a series of images, thresholding error adopting various algorithms, and resampling errors during three-dimensional reconstruction. Among these steps the choice of thresholding algorithm could yield most of the processing error. Ways to reduce the potential processing errors are discussed.

Journal Article↗

PubMed2004

Bilevel thresholding of sliced image of sludge floc.

This work examined the feasibility of employing various thresholding algorithms to determining the optimal bilevel thresholding value for estimating the geometric parameters of sludge flocs from the microtome sliced images and from the confocal laser scanning microscope images. Morphological information extracted from images depends on the bilevel thresholding value. According to the evaluation on the luminescence-inverted images and fractal curves (quadric Koch curve and Sierpinski carpet), Otsu's method yields more stable performance than other histogram-based algorithms and is chosen to obtain the porosity. The maximum convex perimeter method, however, can probe the shapes and spatial distribution of the pores among the biomass granules in real sludge flocs. A combined algorithm is recommended for probing the sludge floc structure.

Algorithms↗

PubMed2004

Effect of pre-hydrolysis on floc structure.

Morphological changes in flocs were elucidated by small-angle light scattering, free settling tests and microscopic observation to determine the effects of pre-hydrolysis (alkaline treatment and ultrasonication) on two sludges--primary raw sludge from the Malabar Sewage Treatment Plant, Sydney (sludge M) and biological sludge collected at the nitrogen removal unit of St Marys Sewage Treatment Plant in Sydney (sludge S). Ultrasonication or alkaline treatment released a marked amount of insoluble organic matter in a soluble form. The latter treatment was more efficient than the former. Meanwhile, the pre-hydrolyzed flocs had more compact structures than the original ones, as shown by their higher free-settling fractal dimension, lower areal porosity and smaller internal pores. In particular, alkaline treatment yielded flocs with more compact interiors than did ultrasonication. Such detailed structural information could not be elicited by monitoring the change in floc size. The greater resistance to mass transfer of the hydrolyzed flocs thus produced does not reduce the efficiency of subsequent digestion, indicating that the surface reaction rate on the solid surface might have dominated since the pre-hydrolysis steps modified the local chemical environment to promote digestion.

Bioreactors↗

PubMed2004

Structure of conditioned sludge flocs.

Free settling tests, small-angle light scattering, microtome-slicing techniques, and confocal laser scanning microscopy were performed to examine how the cationic flocculation or freezing and thawing affected the floc structure. The floc size, internal pore size, mass fractal dimensions determined from free-settling test or small angle light scattering test, aeral porosity, boundary fractal dimension and Sierpinski carpet fractal dimension of pore boundary from 2D slices, and the volume porosity, compactness, and the pores' box-counting fractal dimension from 3D reconstructed image, were estimated and compared. Cationic flocculation would produce large flocs with internal pores of shape resembling a long "tube" with rough surface. Freezing and thawing would produce flocs with internal pores with lower aspect ratio and a smoother boundary.

Bacteria↗

PubMed2004

Data management using the personal digital assistant in an acute pain service.

Handheld personal digital assistants (PDA) are increasingly being used by physicians for a variety of information and data management purposes. We evaluated a PDA-based data management system for our acute pain service. A structured questionnaire survey was conducted to assess staff experience and attitude towards the paper system before the introduction of the PDA, and three months after introduction of the PDA system. We compared the time taken to conduct the acute pain round before and after the implementation of the PDA. The time saved in data management and the amount of paper saved were estimated. Data from 177 patients with a total of 635 acute pain follow-up visits were entered over a three-month period. User satisfaction, ease of access to drug reference and clinical guidelines were similar between the two systems. The respondents found that the PDA was easy to use but less so than the paper system (P = 0.007), in particular, when accessing a patient's cumulative data (P = 0.007). There was no missed follow-up or data entry with the use of PDA. The time taken to attend follow-up visits was similar for the two systems (Paper: 8.8 +/- 3.2 compared to PDA: 7.0 +/- 2.0 minutes, P = 0.151). The estimated annual amount of paper and time saved in data management was 650 sheets and 130 man-hours respectively. Our experience with the use of the PDA in APS was satisfactory. The PDA system can potentially reduce time and paper use and missed data entry and patient follow-up.

Acute Disease↗

PubMed2003

Producing hydrogen from wastewater sludge by Clostridium bifermentans.

Excess wastewater sludge collected from the recycling stream of an activated sludge process is biomass that contains large quantities of polysaccharides and proteins. However, relevant literature indicates that the bio-conversion of wastewater sludge to hydrogen is limited and therefore not economically feasible. This work examined the anaerobic digestion of wastewater sludge using a clostridium strain isolated from the sludge as inoculum. A much higher hydrogen yield than presented in the literature was obtained. Also, the effects of five pre-treatments-ultrasonication, acidification, sterilization, freezing/thawing and adding methanogenic inhibitor-on the production of hydrogen were examined. Freezing and thawing and sterilization increased the specific hydrogen yield by 1.5-2.5 times to that of untreated sludge, while adding an inhibitor and ultrasonication reduced the hydrogen yield.

Anaerobiosis↗

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

Use of hospitalization and pharmaceutical prescribing data to compare the prevaccination burden of varicella and herpes zoster in Australia.

The aims of the study were to compare the burden of varicella and herpes zoster in Australia. No national surveillance exists for varicella or herpes zoster. We used hospital morbidity data from 1993-9 and pharmaceutical prescribing data from 1995-9. In the financial year 1998/99, there were 4718 hospitalizations for zoster compared to 1991 for varicella. For varicella the mean age of patients was 15 years compared to 69 years for zoster. The mean length of stay in hospital was 4.2 days for varicella and 12.7 days for zoster. Varicella accounted for 8396 (3726 with principal diagnosis varicella) bed days compared to 26 266 (5382 with principal diagnosis of zoster) for zoster. The in-hospital case-fatality rate was 0.4% for varicella and 1% for zoster. In 1999, 59 200 community-based cases of zoster were treated with antivirals. We estimate that 157 266 cases of zoster occurred in the community in 1999, a rate of 830 per 100 000 population. Herpes zoster has a higher burden of disease than varicella, and must be a component of disease surveillance in order to determine the full impact of vaccination on the epidemiology of varicella zoster virus (VZV).

Adolescent↗

PubMed2003

Hydrogen production from wastewater sludge using a Clostridium strain.

Limited data in literature revealed a relatively low hydrogen yield from wastewater sludge, ca. 0.16 mg/g-dried solids, using anaerobic fermentation. We demonstrated in this work a much higher hydrogen yield, around 1.1 mg-H2/g-dried solids using a clostridium strain isolated from the sludge sample. The formed hydrogen would be consumed after passing the peak value at around 30-36 h of fermentation. We examined the effects of employing five different pre-treatments on substrate sludge, but noted no appreciable enhancement in hydrogen yield as commonly expected for methane production. Since a vast amount of organic matters had been released to water after hydrogen fermentation, we externally dosed methanogenic bacteria to the fermented liquor to produce methane. The fermented liquor could produce more methane than the non-fermented sample, indicating that the dosed methanogenic bacteria readily utilized the organic matters derived from the fermentation test.

Bioelectric Energy Sources↗

PubMed2002

Batch gravitational sedimentation of slurries.

We investigated the batch settling behavior of the kaolin slurry and the UK ball clay slurry at various initial solids fractions (phi(0)s) using a computerized axial tomography scanner (CATSCAN). The spatio-temporal evolutions of solids fractions in the consolidating sediments were continuously monitored. Since the interface between the sediment and the supernatant of the investigated slurries was blurred, an averaging procedure was employed to estimate their null-stress solids fractions (phi(g)s). Besides the rather slow settling for the high-phi(0) slurries, the basic settling characteristics resemble each other regardless of whether phi(0)>phi(g) or vice versa. The above-mentioned experimental data reveal that the investigated slurries are neither purely elastic nor purely plastic in rheological behavior. On contrary to most model works a blurred supernatant-sediment interface makes difficulty in the gel point determination. During initial settling the high-phi(0) slurries clearly exhibit a finite yield stress to resist deformation. That is, the slurries are plastic fluids. However, the network structure in the slurries deteriorates gradually in the subsequent settling stage while the final, equilibrated sediment reveals a continuous distribution in solids fraction. Restated, the final sediment possesses as a purely elastic characteristic. The model parameters of theory by Buscall and White were regressed by the dynamic consolidating sediment data, while those by Tiller and Leu were obtained using the final equilibrated sediment data. Calculations from both models reveal that ball clay slurry is more compressible than is the kaolin slurry. The high-phi(S0) slurry would yield the less compressible sediment.

Journal Article↗

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↗

PubMed2001

Using ATP bioluminescence technique for monitoring microbial activity in sludge.

This study demonstrates, for the first time, that the presence of suspended solids in waste-activated sludge interferes with adenosine triphosphate (ATP) bioluminescence tests. The sludge subject to acid/alkaline treatment represented the test sample. Without consideration of the effect of solid concentrations, one would erroneously estimate the density levels of heterotrophic bacteria in the sludge using ATP data. A light blockage model was proposed to evaluate the luminescence reading without the interference of suspended solids.

Adenosine Triphosphate↗