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  1. Lau EV, Gan S, Ng HK
    Bull Environ Contam Toxicol, 2012 May;88(5):741-6.
    PMID: 22297628 DOI: 10.1007/s00128-012-0527-9
    The concentrations of polycyclic aromatic hydrocarbons (PAHs) in soil samples were measured at five different sites within Klang Valley, Malaysia. The results showed that the total concentrations of the fourteen priority PAHs ranged from 64 to 155 μg/kg. Irrespective of the land use, all the measured soil PAH concentrations in this study were significantly lower than that found in soil samples in temperate regions. The profile of PAHs in the soils was dominated by the LMW PAHs. The PAHs in Klang Valley soils originated from pyrogenic sources, with a combination of petroleum and biomass combustion in vehicles, industries and non-point sources.
  2. Gan S, Lau EV, Ng HK
    J Hazard Mater, 2009 Dec 30;172(2-3):532-49.
    PMID: 19700241 DOI: 10.1016/j.jhazmat.2009.07.118
    Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic micropollutants which are resistant to environmental degradation due to their highly hydrophobic nature. Concerns over their adverse health effects have resulted in extensive studies on the remediation of soils contaminated with PAHs. This paper aims to provide a review of the remediation technologies specifically for PAH-contaminated soils. The technologies discussed here include solvent extraction, bioremediation, phytoremediation, chemical oxidation, photocatalytic degradation, electrokinetic remediation, thermal treatment and integrated remediation technologies. For each of these, the theories are discussed in conjunction with comparative evaluation of studies reported in the specialised literature.
  3. Lim MW, Lau EV, Poh PE
    Mar Pollut Bull, 2016 Aug 15;109(1):14-45.
    PMID: 27267117 DOI: 10.1016/j.marpolbul.2016.04.023
    Oil spills result in negative impacts on the environment, economy and society. Due to tidal and waves actions, the oil spillage affects the shorelines by adhering to the soil, making it difficult for immediate cleaning of the soil. As shoreline clean-up is the most costly component of a response operation, there is a need for effective oil remediation technologies. This paper provides a review on the remediation technologies for soil contaminated with various types of oil, including diesel, crude oil, petroleum, lubricating oil, bitumen and bunker oil. The methods discussed include solvent extraction, bioremediation, phytoremediation, chemical oxidation, electrokinetic remediation, thermal technologies, ultrasonication, flotation and integrated remediation technologies. Each of these technologies was discussed, and associated with their advantages, disadvantages, advancements and future work in detail. Nonetheless, it is important to note that no single remediation technology is considered the best solution for the remediation of oil contaminated soil.

    CAPSULE: This review provides a comprehensive literature on the various remediation technologies studied in the removal of different oil types from soil.

  4. Lau EV, Gan S, Ng HK
    Int J Anal Chem, 2010;2010:398381.
    PMID: 20396670 DOI: 10.1155/2010/398381
    This paper aims to provide a review of the analytical extraction techniques for polycyclic aromatic hydrocarbons (PAHs) in soils. The extraction technologies described here include Soxhlet extraction, ultrasonic and mechanical agitation, accelerated solvent extraction, supercritical and subcritical fluid extraction, microwave-assisted extraction, solid phase extraction and microextraction, thermal desorption and flash pyrolysis, as well as fluidised-bed extraction. The influencing factors in the extraction of PAHs from soil such as temperature, type of solvent, soil moisture, and other soil characteristics are also discussed. The paper concludes with a review of the models used to describe the kinetics of PAH desorption from soils during solvent extraction.
  5. Chew EK, Lee KY, Lau EV
    J Colloid Interface Sci, 2017 Nov 15;506:452-459.
    PMID: 28755640 DOI: 10.1016/j.jcis.2017.07.078
    HYPOTHESIS: The effects of varying carbon chain lengths (CCLs) and concentrations of aqueous solutions of imidazolium based ionic liquids on bubble particle attachment (BPA) will provide a better understanding in catering for the varying degrees of surface activities in the application of the flotation technology. The general trends of this study should also be applicable to homologous series of other cationic surfactants and ionic liquids.

    EXPERIMENTS: Zeta potentials of small air bubbles and bunker oil drops dispersed in aqueous solutions of n-methylimidazolium chloride ionic liquids (n=0, 2, 3, 6, 8, 10, 12) of concentrations ranging from 1000PPM to 8000PPM, as were interfacial tensions of these solutions with bunker oil (180cst) and contact angles made by air bubbles at interfaces between these solutions and thin layers of bunker oil on flat solid surfaces were investigated. Finally, interparticle forces analysis using the Derjaguin-Landau, Verwey-Overbeek (DLVO) theory is also included.

    FINDINGS: Analysis using the DLVO theory showed attractive forces between the oil particles and micro-bubbles are significantly more prevalent in short CCLs solutions of imidazolium-based ILs in low concentrations, namely [C0mim][Cl] and [C2mim][Cl] at a maximum zeta potential difference of 75.3mV. The results from CA measurements follows similarly whereby low concentrations of ILs with short CCLs were in favor for the bubble-particle attachment process with angles ranging between 93.95° for [C0mim][Cl] and 97.28° for [C2mim][Cl]. IFT which is important in reducing coalescence for the preferential BPA process to occur in flotation decreases with an increase of CCL and concentration of IL.

  6. Lau EV, Gan S, Ng HK, Poh PE
    Environ Pollut, 2014 Jan;184:640-9.
    PMID: 24100092 DOI: 10.1016/j.envpol.2013.09.010
    Polycyclic aromatic hydrocarbons (PAHs) in soil have been recognised as a serious health and environmental issue due to their carcinogenic, mutagenic and teratogenic properties. One of the commonly employed soil remediation techniques to clean up such contamination is soil washing or solvent extraction. The main factor which governs the efficiency of this process is the solubility of PAHs in the extraction agent. Past field-scale soil washing treatments for PAH-contaminated soil have mainly employed organic solvents or water which is either toxic and costly or inefficient in removing higher molecular weight PAHs. Thus, the present article aims to provide a review and discussion of the alternative extraction agents that have been studied, including surfactants, biosurfactants, microemulsions, natural surfactants, cyclodextrins, vegetable oil and solution with solid phase particles. These extraction agents have been found to remove PAHs from soil at percentages ranging from 47 to 100% for various PAHs.
  7. Oh KS, Poh PE, Chong MN, Chan ES, Lau EV, Saint CP
    Carbohydr Polym, 2016 Sep 05;148:161-70.
    PMID: 27185127 DOI: 10.1016/j.carbpol.2016.04.039
    Polyelectrolyte-complex bilayer membrane (PCBM) was fabricated using biodegradable chitosan and alginate polymers for subsequent application in the treatment of bathroom greywater. In this study, the properties of PCBMs were studied and it was found that the formation of polyelectrolyte network reduced the molecular weight cut-off (MWCO) from 242kDa in chitosan membrane to 2.71kDa in PCBM. The decrease in MWCO of PCBM results in better greywater treatment efficiency, subsequently demonstrated in a greywater filtration study where treated greywater effluent met the household reclaimed water standard of <2 NTU turbidity and <30ppm total suspended solids (TSS). In addition, a further 20% improvement in chemical oxygen demand (COD) removal was achieved as compared to a single layer chitosan membrane. Results from this study show that the biodegradable PCBM is a potential membrane material in producing clean treated greywater for non-potable applications.
  8. Mak NL, Ooi EH, Lau EV, Ooi ET, Pamidi N, Foo JJ, et al.
    Comput Methods Programs Biomed, 2022 Dec;227:107195.
    PMID: 36323179 DOI: 10.1016/j.cmpb.2022.107195
    BACKGROUND AND OBJECTIVES: Thermochemical ablation (TCA) is a thermal ablation technique involving the injection of acid and base, either sequentially or simultaneously, into the target tissue. TCA remains at the conceptual stage with existing studies unable to provide recommendations on the optimum injection rate, and reagent concentration and volume. Limitations in current experimental methodology have prevented proper elucidation of the thermochemical processes inside the tissue during TCA. Nevertheless, the computational TCA framework developed recently by Mak et al. [Mak et al., Computers in Biology and Medicine, 2022, 145:105494] has opened new avenues in the development of TCA. Specifically, a recommended safe dosage is imperative in driving TCA research beyond the conceptual stage.

    METHODS: The aforesaid computational TCA framework for sequential injection was applied and adapted to simulate TCA with simultaneous injection of acid and base at equimolar and equivolume. The developed framework, which describes the flow of acid and base, their neutralisation, the rise in tissue temperature and the formation of thermal damage, was solved numerically using the finite element method. The framework will be used to investigate the effects of injection rate, reagent concentration, volume and type (weak/strong acid-base combination) on temperature rise and thermal coagulation formation.

    RESULTS: A higher injection rate resulted in higher temperature rise and larger thermal coagulation. Reagent concentration of 7500 mol/m3 was found to be optimum in producing considerable thermal coagulation without the risk of tissue overheating. Thermal coagulation volume was found to be consistently larger than the total volume of acid and base injected into the tissue, which is beneficial as it reduces the risk of chemical burn injury. Three multivariate second-order polynomials that express the targeted coagulation volume as functions of injection rate and reagent volume, for the weak-weak, weak-strong and strong-strong acid-base combinations were also derived based on the simulated data.

    CONCLUSIONS: A guideline for a safe and effective implementation of TCA with simultaneous injection of acid and base was recommended based on the numerical results of the computational model developed. The guideline correlates the coagulation volume with the reagent volume and injection rate, and may be used by clinicians in determining the safe dosage of reagents and optimum injection rate to achieve a desired thermal coagulation volume during TCA.

  9. Mak NL, Ng WH, Ooi EH, Lau EV, Pamidi N, Foo JJ, et al.
    Comput Methods Programs Biomed, 2024 Jan;243:107866.
    PMID: 37865059 DOI: 10.1016/j.cmpb.2023.107866
    BACKGROUND AND OBJECTIVES: Thermochemical ablation (TCA) is a cancer treatment that utilises the heat released from the neutralisation of acid and base to raise tissue temperature to levels sufficient to induce thermal coagulation. Computational studies have demonstrated that the coagulation volume produced by sequential injection is smaller than that with simultaneous injection. By injecting the reagents in an ensuing manner, the region of contact between acid and base is limited to a thin contact layer sandwiched between the distribution of acid and base. It is hypothesised that increasing the frequency of acid-base injections into the tissue by shortening the injection interval for each reagent can increase the effective area of contact between acid and base, thereby intensifying neutralisation and the exothermic heat released into the tissue.

    METHODS: To verify this hypothesis, a computational model was developed to simulate the thermochemical processes involved during TCA with sequential injection. Four major processes that take place during TCA were considered, i.e., the flow of acid and base, their neutralisation, the release of exothermic heat and the formation of thermal damage inside the tissue. Equimolar acid and base at 7.5 M was injected into the tissue intermittently. Six injection intervals, namely 3, 6, 15, 20, 30 and 60 s were investigated.

    RESULTS: Shortening of the injection interval led to the enlargement of coagulation volume. If one considers only the coagulation volume as the determining factor, then a 15 s injection interval was found to be optimum. Conversely, if one places priority on safety, then a 3 s injection interval would result in the lowest amount of reagent residue inside the tissue after treatment. With a 3 s injection interval, the coagulation volume was found to be larger than that of simultaneous injection with the same treatment parameters. Not only that, the volume also surpassed that of radiofrequency ablation (RFA); a conventional thermal ablation technique commonly used for liver cancer treatment.

    CONCLUSION: The numerical results verified the hypothesis that shortening the injection interval will lead to the formation of larger thermal coagulation zone during TCA with sequential injection. More importantly, a 3 s injection interval was found to be optimum for both efficacy (large coagulation volume) and safety (least amount of reagent residue).

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