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Biomedical subjects

C S Poon

Publications and source records attributed to C S Poon.

At least 19 recordsLinked to original sources
PubMed2006

Investigation into the stabilization/solidification performance of Portland cement through cement clinker phases.

This research studied the influence of individual heavy metal on the hydration reactions of major cement clinker phases in order to investigate the performance of cement based stabilization/solidification (S/S) system. Tricalcium silicate (C3S) and tricalcium aluminate (C3A) had been mixed with individual heavy metal hydroxide including Zn(OH)2, Pb(OH)2 and Cu(OH)2, respectively. The influences of these heavy metal hydroxides on the hydration of C3S and C3A have been characterized by X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). A mixture of Zn(OH)2, Pb(OH)2 and Cu(OH)2 was blended with Portland cement (PC) and evaluated through compressive strength and dynamic leach test. XRD and DSC-TG data show that all the heavy metal hydroxides (Zn(OH)2, Pb(OH)2 and Cu(OH)2) have detrimental effects on the hydration of C3A, but only Zn(OH)2 does to the C3S at early curing ages which can completely inhibit the hydration of C3S due to the formation of CaO(Zn(OH)2).2H2O. Cu6Al2O8CO(3).12H2O, Pb2Al4O4(CO3)(4).7H2O and Zn6Al2O8CO(3).12H2O are formed in all the samples containing C3A in the presence of metal hydroxides. After adding CaSO4 into C3A, the detrimental effect of heavy metals increases due to the coating effect of both calcium aluminate sulphates and heavy metal aluminate carbonates. The influence of heavy metal hydroxide on the hydration of C3S and C3A can be used to predict the S/S performance of Portland cement.

Absorption↗
PubMed2005

Transfer mechanisms of contaminants in cement-based stabilized/solidified wastes.

Stabilization/solidification (S/S) processes are routinely used for the final treatment of hazardous wastes prior to land disposal. Cement-based binder systems with partial replacement of cement by pulverized fuel ash (PFA) are common. In order to predict the long-term leaching characteristics of S/S wastes, it is important to understand the leaching mechanism. This paper presents experimental results from a study that has investigated the leaching behaviour of contaminants from cement-based S/S waste forms. A novel radial leach test (RLT) has been used to study the migration of heavy metals. The results show that contaminants migrate from the inner core of the S/S waste during leaching to the sample surface and accumulate near the edge of the S/S waste. The degree of accumulation is related to the contaminant species and the Ca(OH)2 content.

Construction Materials↗
PubMed2005

Use of flue gas desulphurisation (FGD) waste and rejected fly ash in waste stabilization/solidification systems.

Stabilization/solidification (S/S) processes have been used as the final treatment step for hazardous wastes prior to land disposal. Fly ash is a by-product of coal-fired power generation; a significant proportion of this material is low-grade, reject material (rFA) that is unsuitable as a cement replacement due to its high carbon content and large particle size (>45 microm). Flue gas desulphurization (FGD) sludge is a by-product from the air pollution control systems used in coal-fired power plants. The objective of this work was to investigate the performance of S/S waste binder systems containing these two waste materials (rFA and FGD). Strength tests show that cement-based waste forms with rFA and FGD replacement were suitable for disposal in landfills. The addition of an appropriate quantity of Ca(OH)2 and FGD reduces the deleterious effect of heavy metals on strength development. Results of TCLP testing and the progressive TCLP test show that cement-rFA-Ca(OH)2 systems with a range of FGD additions can form an effective S/S binder. The Leachability Index indicates that cement-based waste forms with rFA replacement were effective in reducing the mobility of heavy metals.

Calcium Hydroxide↗
PubMed2001

Aberrant expression of p21(WAF1/CIP1) and p27(KIP1) in cervical carcinoma.

An immuno-histochemical study of p21 and p27 expression in cervical carcinoma was performed in 73 patients. Positive p21 and p27 staining was detected in 35.6 and 11% of tumour tissues, respectively. p21 expression was significantly correlated with advanced disease stage and negative human papilloma virus infection whilst positive p27 staining was not correlated with any clinical and pathological parameters studied. Kaplan-Meier estimation indicated that survival might be related to disease stage, tumour grade and p21 expression. Cox regression analysis confirmed that advanced stage disease and poorly differentiated tumour are independent prognostic factors for cervical carcinoma.

Adult↗
PubMed2001

Titration of chaos with added noise.

Deterministic chaos has been implicated in numerous natural and man-made complex phenomena ranging from quantum to astronomical scales and in disciplines as diverse as meteorology, physiology, ecology, and economics. However, the lack of a definitive test of chaos vs. random noise in experimental time series has led to considerable controversy in many fields. Here we propose a numerical titration procedure as a simple "litmus test" for highly sensitive, specific, and robust detection of chaos in short noisy data without the need for intensive surrogate data testing. We show that the controlled addition of white or colored noise to a signal with a preexisting noise floor results in a titration index that: (i) faithfully tracks the onset of deterministic chaos in all standard bifurcation routes to chaos; and (ii) gives a relative measure of chaos intensity. Such reliable detection and quantification of chaos under severe conditions of relatively low signal-to-noise ratio is of great interest, as it may open potential practical ways of identifying, forecasting, and controlling complex behaviors in a wide variety of physical, biomedical, and socioeconomic systems.

Algorithms↗
PubMed2001

Heavy metal speciation and leaching behaviors in cement based solidified/stabilized waste materials.

A circuit board printing factory sludge containing high concentrations of copper, zinc and lead was stabilized and solidified (S/S) with different portions of ordinary Portland cement (OPC) and pulverized fly ash (PFA). The chemical speciation and leaching behavior of heavy metals in these cement-based waste materials were studied by different sequential extraction procedures, standard toxicity characteristic leaching procedure (TCLP) and progressive TCLP tests. The sequential extraction results showed that more than 80% of Cu, Pb and Zn were associated with Fraction 2 (weak acid soluble, extracted with 1M NaOAc at pH 5.0 with a solid to liquid ratio of 1:60). This indicated that the heavy metals could exist in the S/S matrix as metal hydrated phases or metal hydroxides precipitating on the surface of calcium silicate hydrates (C-S-H), PFA and sludge particles. The progressive TCLP test results and MINTEQA2 calculation also showed the importance of Cu and Zn oxides during the leaching process. The leaching behaviors of these metals in the S/S waste materials were mainly controlled by the alkaline nature and acid buffering capacity of the S/S matrix. During the progressive TCLP tests, the alkaline conditions and acid buffering capacity of the matrix decreased with the dissolution of calcium hydroxide and C-S-H, therefore, the leaching of heavy metals in the S/S waste materials increased. The leaching of heavy metals in the S/S materials can be considered as a pH dependent and corresponding metal hydroxide solubility controlled process.

Hydrogen-Ion Concentration↗
PubMed2001

The effect of flow-through leaching on the diffusivity of heavy metals in stabilized/solidified wastes.

The flow-through leaching test is a test method employed to study the leaching behavior of monolithic stabilized/solidified (S/S) hazardous wastes under the condition that the leachate flows through the sample. This method simulates the leaching process of the S/S hazardous waste disposed under a particular landfill condition when the S/S waste is more permeable than its surrounding materials or when the deterioration of the solidified waste form has reached a state that ground water can flow-through the waste via the porosity system of the S/S waste matrix. This paper describes a study on the long-term performance of the cement-based S/S heavy metal wastes using a flow-through leaching test method. Two series of leaching tests with different synthetic heavy metal waste samples were carried out. The S/S samples were made from five types of heavy metals with two kinds of binders. The metals were Pb(2+), Zn(2+), Cu(2+), Ni(2+) (positive ions as nitrates), and Cr(6+) (a negative ion as potassium dichromate), and the binders were type I ordinary portland cement (OPC) and pulverised fuel ash (PFA). The model developed by Godbee and Joy for simulating the leaching behavior was modified to estimate the diffusivity parameter in this study. The results obtained indicate that since the matrix of the solidified waste in a flow-through leaching tests is always being degraded, the values of diffusivities increase continuously during the leaching period. The diffusivity variation range was from 10(-13) to 10(-3)cm(2)/s, and were normally higher than those obtained from other test methods such as ANS 16.1 test and other dynamic leaching tests.

Decontamination↗
PubMed2001

A comparison of waste-reduction practices and new environmental paradigm of rural and urban Chinese citizens.

This paper compares the public attitudes of three southern Chinese cities/towns, namely Guangzhou, Dongguan, and Yuanzhou on waste recycling and avoidance, and the New Environmental Paradigm (NEP). The latter describes the concept of treating the resources and the ecosystems on Earth as things having their own rights rather than being subordinate and subservient to humans. These three places are chosen to represent areas in different stages of urbanization in the Guangdong province. As Hong Kong is also a southern Chinese city, where data of similar nature are available, comparison with Hong Kong is also made. It was found that the support for source separation of household waste in the rural and urban areas in mainland China was greater than that found in Hong Kong. Concerning actual practices on waste separation, about 85% of the respondents in the cities and almost all of the rural household surveyed have the habit of saving up and selling the recyclables. It is estimated that about 11-13% of the household waste was diverted in such a way. This is higher than the estimated 8% household waste recovery rate of Hong Kong. The majority of the respondents in the three surveyed cities have recovered household recyclables in the past but with higher family incomes, it was now less common. On the contrary, the lower income group tended to recover greater portion of their waste for selling to the waste depots. These findings have implications on the future waste management policy formulation in China. Regarding the acceptance of the New Environmental Paradigm, it was found that the rural population scored better than the urban population and they tended to agree more frequently with the NEP. However, the rural population perceives a greater potential for industrial and urban development without dampening environmental quality. It was also found that the NEP scores of the mainland Chinese are higher, in general, than their Hong Kong counterparts as measured in early 1990s. Insufficient public support has often been a concern for source separation programmes in all countries despite the obvious waste management benefits of recycling. This study shows that there is overwhelming support for source separation of waste in Mainland China, whether it is in rural or urban communities, and that most people are already undertaking source separation due to the redemption value of the recyclables. Therefore, for policy-makers, the concern should not be on whether the public knows how to separate the waste but rather on how to motivate them to separate waste for the good of society, and how to maintain an effective market for recyclables.

Adolescent↗
PubMed2001

A systematic study of cement/PFA chemical stabilisation/solidification process for the treatment of heavy metal waste.

The aim of this study is to systematically quantify the physical and chemical properties of the cement based solidified/stabilised heavy metal waste with increasing replacement of cement by PFA. Bulk density and unconfined compressive strength are measured as the physical parameters. The equilibrium extraction tests, sequential chemical tests and dynamic leaching tests are reported as chemical characteristics. The results showed PFA-blended cement-based waste forms have higher porosity and lower strength than the pure cement-based waste forms at experimental curing time. The lower alkalinities of the PFA-blended cement-based waste forms, however, lead to higher leach rates of heavy metals when the waste is exposed to an acidic medium.

Environmental Pollution↗
PubMed2001

Characterisation of municipal solid waste and its recyclable contents of Guangzhou.

Waste characteristics are essential data for waste disposal facilities planning and waste management policy formulation. However, waste composition studies are rarely carried out in mainland Chinese cities and even when it does, the methodologies used are not stringent. A year-long field survey on the physical components of waste and the recyclable in the waste stream has been conducted in Guangzhou to fill the information gap and to provide further experience for waste characterization study in mainland China. It was found that the ash content in the waste stream has decreased considerably. But the proportion of plastic materials in the waste stream has increased and is now comparable to its more urbanized cities. Although this lends support to the recent controls on expanded polystyrene food containers implemented by the Guangzhou environmental protection bureau, more detailed analysis shows that the focus should not only be on disposable food containers, but also on film plastic waste. Furthermore, the abundance of composite materials in the waste stream solicits attention from the waste management authority to step up the monitoring of their generation pattern and to consider imposing control measures.

China↗
PubMed2001

Degradation kinetics of reactive dye by UV/H2O2/US process under continuous mode operation.

Degradation of a dye, C. I . Reactive Red 120, in dyeing waatewater by the process o UV/H2O2/US was studied with a bench-scale reactor under the continuous mode of operation. The effects of dyeing wastewater flow rate and the feeding rate of an oxidant, H2O2, on the color removal efficiency of the process were investigated. The significance of ultrasonic (US) combined with UV irradiation was also investigated and the performances of the process on color removal were evaluated. The results showed that the decoloration process followed a pseudo first-order kinetic model and the UV light is the most significant factor on dye removal. Besides, at higher flow rates, incomplete color removal was observed due to relatively insufficient irradiation time (low degradation rate). In order to achieve a higher degradation rate, the feeding rate of H2O2 should be increased.

Coloring Agents↗