Displaying publications 1 - 20 of 44 in total

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  1. Teh YY, Lee KT, Chen WH, Lin SC, Sheen HK, Tan IS
    Bioresour Technol, 2017 Dec;246:20-27.
    PMID: 28781203 DOI: 10.1016/j.biortech.2017.07.101
    This study aims to produce biochar and sugars from a macroalga Eucheuma denticulatum using dilute sulfuric acid hydrolysis along with microwave-assisted heating. The reactions were operated at sulfuric acid concentrations of 0.1 and 0.2M, reaction temperatures of 150-170°C and a heating time of 10min. Compared to the raw macroalga, biochar qualities were improved with increased carbon content and lower ash and moisture contents. The calorific value of the biochar could be intensified up to 45%, and 39% of energy yield was recovered. Apart from producing biochar, the highest total reducing sugars were 51.47g/L (74.84% yield) along with a low by-product 5-HMF of 0.20g/L, when the biomass was treated under the optimum conditions at 160°C with 0.1M H2SO4. Thus, this study demonstrated that macroalgae could be potentially used as biomass feedstock under microwave-assisted acid hydrolysis for the production of biofuel and value-added products.
  2. Yu KL, Lau BF, Show PL, Ong HC, Ling TC, Chen WH, et al.
    Bioresour Technol, 2017 Dec;246:2-11.
    PMID: 28844690 DOI: 10.1016/j.biortech.2017.08.009
    Algal biomass is known as a promising sustainable feedstock for the production of biofuels and other valuable products. However, since last decade, massive amount of interests have turned to converting algal biomass into biochar. Due to their high nutrient content and ion-exchange capacity, algal biochars can be used as soil amendment for agriculture purposes or adsorbents in wastewater treatment for the removal of organic or inorganic pollutants. This review describes the conventional (e.g., slow and microwave-assisted pyrolysis) and newly developed (e.g., hydrothermal carbonization and torrefaction) methods used for the synthesis of algae-based biochars. The characterization of algal biochar and a comparison between algal biochar with biochar produced from other feedstocks are also presented. This review aims to provide updated information on the development of algal biochar in terms of the production methods and the characterization of its physical and chemical properties to justify and to expand their potential applications.
  3. Chen WH, Hsu HJ, Kumar G, Budzianowski WM, Ong HC
    Bioresour Technol, 2017 Dec;246:12-19.
    PMID: 28803060 DOI: 10.1016/j.biortech.2017.07.184
    This study focuses on the biochar formation and torrefaction performance of sugarcane bagasse, and they are predicted using the bilinear interpolation (BLI), inverse distance weighting (IDW) interpolation, and regression analysis. It is found that the biomass torrefied at 275°C for 60min or at 300°C for 30min or longer is appropriate to produce biochar as alternative fuel to coal with low carbon footprint, but the energy yield from the torrefaction at 300°C is too low. From the biochar yield, enhancement factor of HHV, and energy yield, the results suggest that the three methods are all feasible for predicting the performance, especially for the enhancement factor. The power parameter of unity in the IDW method provides the best predictions and the error is below 5%. The second order in regression analysis gives a more reasonable approach than the first order, and is recommended for the predictions.
  4. Lee XJ, Show PL, Katsuda T, Chen WH, Chang JS
    Bioresour Technol, 2018 Dec;269:489-502.
    PMID: 30172460 DOI: 10.1016/j.biortech.2018.08.090
    Membrane bioreactor (MBR) is regarded as the state-of-the-art technology in separation processes. Surface modification techniques play a critical role in improving the conventional membrane system which is mostly hydrophobic in nature. The hydrophobic nature of membranes is known to cause fouling, resulting in high maintenance costs and shorter lifespan of MBR. Thus, surface grafting aims to improve the hydrophilicity of bio-based membrane systems. This review describes the major surface grafting techniques currently used in membranes, including photo induced grafting, plasma treatment and plasma induced grafting, radiation induced grafting, thermal induced grafting and ozone induced grafting. The advantages and disadvantages of each method is discussed along with their parametric studies. The potential applications of MBR are very promising, but some integral membrane properties could be a major challenge that hinders its wider reach. The fouling issue could be resolved with the surface grafting techniques to achieve better performance of MBRs.
  5. Mak CY, Lin JG, Chen WH, Ng CA, Bashir MJK
    Water Sci Technol, 2019 May;79(10):1860-1867.
    PMID: 31294702 DOI: 10.2166/wst.2019.188
    The application of the anammox process has great potential in treating nitrogen-rich wastewater. The presence of Fe (II) is expected to affect the growth and activity of anammox bacteria. Short-term (acute) and long-term effects (chronic) of Fe (II) on anammox activity were investigated. In the short-term study, results demonstrated that the optimum concentration of Fe (II) that could be added to anammox is 0.08 mM, at which specific anammox activity (SAA) improved by 60% compared to the control assay, 0.00 mM. The inhibition concentration, IC50, of Fe (II) was found to be 0.192 mM. Kinetics of anammox specific growth rate were estimated based on results of the batch test and evaluated with Han-Levenspiel's substrate inhibition kinetics model. The optimum concentration and IC50 of Fe (II) predicted by the Han-Levenspiel model was similar to the batch test, with values of 0.07 mM and 0.20 mM, respectively. The long-term effect of Fe (II) on the performance of a sequencing batch reactor (SBR) was evaluated. Results showed that an appropriate Fe (II) addition enhanced anammox activity, achieving 85% NH4+-N and 96% NO2--N removal efficiency when 0.08 mM of Fe (II) was added. Quantitative polymerase chain reaction (qPCR) was adopted to detect and identify the anammox bacteria.
  6. Itliong JN, Villagracia ARC, Moreno JLV, Rojas KIM, Bernardo GPO, David MY, et al.
    Bioresour Technol, 2019 May;279:181-188.
    PMID: 30731357 DOI: 10.1016/j.biortech.2019.01.109
    This study aimed to investigate the transport mechanisms of ions during forward-osmosis-driven (FO-driven) dewatering of microalgae using molecular dynamics (MD) simulations. The dynamical and structural properties of ions in FO systems of varying NaCl or MgCl2 draw solution (DS) concentrations were calculated and correlated. Results indicate that FO systems with higher DS concentration caused ions to have lower hydration numbers and higher coordination numbers leading to lower diffusion coefficients. The higher hydration number of Mg2+ ions resulted in significantly lower ionic permeability as compared to Na+ ions at all concentrations (p = 0.002). The simulations also revealed that higher DS concentrations led to higher accumulation of ions in the membrane. This study provides insights on the proper selection of DS for FO systems.
  7. Tan CH, Show PL, Ling TC, Nagarajan D, Lee DJ, Chen WH, et al.
    Bioresour Technol, 2019 Aug;285:121331.
    PMID: 30999192 DOI: 10.1016/j.biortech.2019.121331
    Third generation biofuels, also known as microalgal biofuels, are promising alternatives to fossil fuels. One attractive option is microalgal biodiesel as a replacement for diesel fuel. Chlamydomonas sp. Tai-03 was previously optimized for maximal lipid production for biodiesel generation, achieving biomass growth and productivity of 3.48 ± 0.04 g/L and 0.43 ± 0.01 g/L/d, with lipid content and productivity of 28.6 ± 1.41% and 124.1 ± 7.57 mg/L/d. In this study, further optimization using 5% CO2 concentration and semi-batch operation with 25% medium replacement ratio, enhanced the biomass growth and productivity to 4.15 ± 0.12 g/L and 1.23 ± 0.02 g/L/d, with lipid content and productivity of 19.4 ± 2.0% and 239.6 ± 24.8 mg/L/d. The major fatty acid methyl esters (FAMEs) were palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2). These short-chain FAMEs combined with high growth make Chlamydomonas sp. Tai-03 a suitable candidate for biodiesel synthesis.
  8. Yew GY, Chew KW, Malek MA, Ho YC, Chen WH, Ling TC, et al.
    Biotechnol Biofuels, 2019;12:252.
    PMID: 31666807 DOI: 10.1186/s13068-019-1591-8
    Background: The extraction of lipids from microalgae requires a pretreatment process to break the cell wall and subsequent extraction processes to obtain the lipids for biofuels production. The multistep operation tends to incur high costs and are energy intensive due to longer process operations. This research work applies the combination of radicals from hydrogen peroxide with an organic solvent as a chemical pretreatment method for disrupting the cell wall of microalgae and simultaneously extracting lipids from the biomass in a one-step biphasic solution.

    Result: Several parameters which can affect the biphasic system were analyzed: contact time, volume of solvent, volume ratio, type of organic solvent, biomass amount and concentration of solvents, to extract the highest amount of lipids from microalgae. The results were optimized and up to 83.5% of lipid recovery yield and 94.6% of enhancement was successfully achieved. The results obtain from GC-FID were similar to the analysis of triglyceride lipid standard.

    Conclusion: The profound hybrid biphasic system shows great potential to radically disrupt the cell wall of microalgae and instantaneously extract lipids in a single-step approach. The lipids extracted were tested to for its comparability to biodiesel performance.

  9. Sankaran R, Parra Cruz RA, Pakalapati H, Show PL, Ling TC, Chen WH, et al.
    Bioresour Technol, 2020 Feb;298:122476.
    PMID: 31810736 DOI: 10.1016/j.biortech.2019.122476
    Microalgal and lignocellulosic biomass is the most sumptuous renewable bioresource raw material existing on earth. Recently, the bioconversion of biomass into biofuels have received significant attention replacing fossil fuels. Pretreatment of biomass is a critical process in the conversion due to the nature and structure of the biomass cell wall that is complex. Although green technologies for biofuel production are advancing, the productivity and yield from these techniques are low. Over the past years, various pretreatment techniques have been developed and successfully employed to improve the technology. This paper presents an in-depth review of the recent advancement of pretreatment methods focusing on microalgal and lignocellulosic biomass. The technological approaches involving physical, chemical, biological and other latest pretreatment methods are reviewed.
  10. Lin BJ, Chen WH, Lin YY, Chang JS, Farooq A, Singh Y, et al.
    Bioresour Technol, 2020 Apr;301:122774.
    PMID: 31954973 DOI: 10.1016/j.biortech.2020.122774
    The thermal characteristics of Actinobacillus succinogenes (AS) from pyrolysis, torrefaction, and combustion are analyzed to evaluate the potential of this biomass as a renewable fuel. AS pyrolysis can be classified into four stages, and its main decomposition zone is at 200-500 °C. The solid yield of AS after 60 min torrefaction is over 60 wt%, and the torrefaction severity index map indicates that a high torrefaction temperature with a short duration has a more profound influence on its decomposition. The Py-GC/MS analysis of AS suggests that the volatile products from 500 °C pyrolysis are similar to microalgae-derived pyrolysis bio-oils. The combustibility index (S) of AS is 4.07 × 10-7 which is much higher than that of lignite coal (0.39 × 10-7) and bituminous coal (0.18 × 10-7), and close to those of biochar and bio-oil. The obtained results are conducive to the development of microorganisms as fuel to achieve a circular bioeconomy.
  11. Khoo KS, Chew KW, Yew GY, Leong WH, Chai YH, Show PL, et al.
    Bioresour Technol, 2020 May;304:122996.
    PMID: 32115347 DOI: 10.1016/j.biortech.2020.122996
    The world energy system faces two major challenges: the requirement for more energy and less carbon. It is important to address biofuels production as an alternative to the usage of fossil fuel by utilizing microalgae as the potential feedstock. Yet, the commercialization of microalgae remains contentious caused by factors relating to the life cycle assessment and feasibility of microalgae-based biofuels. This present review starts with an introduction to the benefits of microalgae, followed by intensive elaboration on microalgae cultivation parameters. Subsequently, the fundamental principle along with the advantages and disadvantages of various pretreatment techniques of microalgae were reviewed. In addition, the conventional and recent advances in lipid extraction techniques from microalgae were comprehensively evaluated. Comparative analysis regard to the gaps from previous studies was discussed point-by-point in each section. The effort presented in this review will provide an insight for future researches dealing with microalgae-biofuel production on downstream processing.
  12. Wong WY, Lim S, Pang YL, Shuit SH, Chen WH, Lee KT
    Sci Total Environ, 2020 Jul 20;727:138534.
    PMID: 32334218 DOI: 10.1016/j.scitotenv.2020.138534
    Interest in biodiesel research has escalated over the years due to dwindling fossil fuel reserves. The implementation of a carbon-based solid acid catalyst in biodiesel production eradicates the separation problems associated with homogeneous catalysis. However, its application in the glycerol-free interesterification process for biodiesel production is still rarely being studied in the literature. In this study, novel environmentally benign catalysts were prepared from oil palm empty fruit bunch (OPEFB) derived activated carbon (AC) which is sustainable and low cost via direct sulfonation using concentrated sulfuric acid. The effects of synthesizing variables such as carbonization and sulfonation temperatures with different holding times towards the fatty acid methyl ester (FAME) yield in interesterification reaction with oleic acid and methyl acetate were investigated in detail. It was found that the optimum carbonization temperature and duration together with sulfonation temperature and duration were 600 °C, 3 h, 100 °C and 6 h, respectively. The catalyst possessed an amorphous structure with a high total acid density of 9.0 mmol NaOH g-1 due to the well-developed porous framework structure of the carbon support. Under these optimum conditions, the OPEFB derived solid acid catalyst recorded an excellent catalytic activity of 50.5% methyl oleate yield at 100 °C after 8 h with 50:1 methyl acetate to oleic acid molar ratio and 10 wt% catalyst dosage. The heterogeneous acid catalyst derived from OPEFB had shown promising properties that made them highly suitable for cost-effective and environmental-friendly glycerol-free biodiesel production.
  13. Wan Mahari WA, Nam WL, Sonne C, Peng W, Phang XY, Liew RK, et al.
    Bioresour Technol, 2020 Sep;312:123572.
    PMID: 32470829 DOI: 10.1016/j.biortech.2020.123572
    Microwave vacuum pyrolysis of palm kernel shell was examined to produce engineered biochar for application as additive in agriculture application. The pyrolysis approach, performed at 750 W of microwave power, produced higher yield of porous biochar (28 wt%) with high surface area (270 cm2/g) compared to the yield obtained by conventional approach (<23 wt%). Addition of the porous biochar in mushroom substrate showed increased moisture content (99%) compared to the substrate without biochar (96%). The mushroom substrate added with biochar (150 g) was optimal in shortening formation, growth, and full colonization of the mycelium within one month. Using 2.5% of the biochar in mushroom substrate desirably maintained the optimum pH level (6.8-7) during the mycelium colonization period, leading to high mycelium growth (up to 91%) and mushroom yield (up to 280 g). The engineered biochar shows great potential as moisture retention and neutralizing agent in mushroom cultivation.
  14. Wu Y, Ge S, Xia C, Cai L, Mei C, Sonne C, et al.
    Bioresour Technol, 2020 Oct;313:123675.
    PMID: 32563796 DOI: 10.1016/j.biortech.2020.123675
    An innovative approach was developed by incorporating high-pressure CO2 into the separate hydrolysis-fermentation of aspen leftover branches, aiming to enhance the bioethanol production efficiency. The high-pressure CO2 significantly increased the 72-h enzymatic hydrolysis yield of converting aspen into glucose from 53.8% to 82.9%. The hydrolysis process was performed with low enzyme loading (10 FPU g-1 glucan) with the aim of reducing the cost of fuel bioethanol production. The ethanol yield from fermentation of the hydrolyzed glucose using yeast (Saccharomyces cerevisiae) was 8.7 g L-1, showing increment of 10% compared with the glucose control. Techno-economic analysis indicated that the energy consumption of fuel bioethanol production from aspen branch chips was reduced by 35% and the production cost was cut 44% to 0.615 USD L-1, when 68 atm CO2 was introduced into the process. These results furtherly emphasized the low carbon footprint of this sustainable energy production approach.
  15. Ang TN, Young BR, Taylor M, Burrell R, Aroua MK, Chen WH, et al.
    Chemosphere, 2020 Dec;260:127496.
    PMID: 32659541 DOI: 10.1016/j.chemosphere.2020.127496
    Activated carbons have been reported to be useful for adsorptive removal of the volatile anaesthetic sevoflurane from a vapour stream. The surface functionalities on activated carbons could be modified through aqueous oxidation using oxidising solutions to enhance the sevoflurane adsorption. In this study, an attempt to oxidise the surface of a commercial activated carbon to improve its adsorption capacity for sevoflurane was conducted using 6 mol/L nitric acid, 2 mol/L ammonium persulfate, and 30 wt per cent (wt%) of hydrogen peroxide (H2O2). The adsorption tests at fixed conditions (bed depth: 10 cm, inlet concentration: 528 mg/L, and flow rate: 3 L/min) revealed that H2O2 oxidation gave desirable sevoflurane adsorption (0.510 ± 0.005 mg/m2). A parametric study was conducted with H2O2 to investigate the effect of oxidation conditions to the changes in surface oxygen functionalities by varying the concentration, oxidation duration, and temperature, and the Conductor-like Screening Model for Real Solvents (COSMO-RS) was applied to predict the interactions between oxygen functionalities and sevoflurane. The H2O2 oxidation incorporated varying degrees of both surface oxygen functionalities with hydrogen bond (HB) acceptor and HB donor characters under the studied conditions. Oxidised samples with enriched oxygen functionalities with HB acceptor character and fewer HB donor character exhibited better adsorption capacity for sevoflurane. The presence of a high amount of oxygen functional groups with HB donor character adversely affected the sevoflurane adsorption despite the enrichment of oxygen functional groups with HB acceptor character that have a higher tendency to adsorb sevoflurane.
  16. Wan Mahari WA, Peng W, Nam WL, Yang H, Lee XY, Lee YK, et al.
    J Hazard Mater, 2020 12 05;400:123156.
    PMID: 32574879 DOI: 10.1016/j.jhazmat.2020.123156
    A review of valorization of oyster mushroom species and waste generated in the mushroom cultivation is presented, with a focus on the cultivation and valorization techniques, conditions, current research status and particularly the hazard mitigation and value-added recovery of the waste mushroom substrate (WMS) - an abundant waste in mushroom cultivation industry. Based on the studies reviewed, the production rate of the present mushroom industry is inadequate to meet market demands. There is a need for the development of new mushroom cultivation methods that can guarantee an increase in mushroom productivity and quality (nutritional and medicinal properties). This review shows that the cylindrical baglog cultivation method is more advantageous compared with the wood tray cultivation method to improve the mushroom yield and cost efficiency. Approximately 5 kg of potentially hazardous WMS (spreading diseases in mushroom farm) is generated for production of 1 kg of mushroom. This encourages various valorization of WMS for use in agricultural and energy conversion applications, mainly as biocompost, plant growing media, and bioenergy. The use of WMS as biofertilizer has shown desirable performance compared to conventional chemical fertilizer, whilst the use of WMS as energy feedstock could produce cleaner bioenergy sources compared to conventional fuels.
  17. Chen WH, Cheng CL, Lee KT, Lam SS, Ong HC, Ok YS, et al.
    Chemosphere, 2021 May;271:129510.
    PMID: 33434827 DOI: 10.1016/j.chemosphere.2020.129510
    Zeolite socony mobil-5 (ZSM-5) is a common catalyst used for biomass pyrolysis. Nevertheless, the quantitative information on the catalytic behavior of ZSM-5 on biomass pyrolysis is absent so far. This study focuses on the catalytic pyrolysis phenomena and mechanisms of biomass wastes using ZSM-5 via thermogravimetric analyzer and pyrolysis-gas chromatography/mass spectrometry, with particular emphasis on catalytic level identification and aromatic hydrocarbons (AHs) formation. Two biomass wastes of sawdust and sorghum distillery residue (SDR) are investigated, while four biomass-to-catalyst ratios are considered. The analysis suggests that biomass waste pyrolysis processes can be divided into three zones, proceeding from a heat-transfer dominant zone (zone 1) to catalysis dominant zones (zones 2 and 3). The indicators of the intensity of difference (IOD), catalytic effective area, catalytic index (CI), and aromatic enhancement index are conducted to measure the catalytic effect of ZSM-5 on biomass waste pyrolysis and AHs formation. The maximum IOD occurs in zone 2, showing the highest intensity of the catalytic effect. The CI values of the two biomass wastes increase with increasing the biomass-to-catalyst ratio. However, there exists a threshold for sawdust pyrolysis, indicating a limit for the catalytic effect on sawdust. The higher the catalyst addition, the higher the AHs proportion in the vapor stream. When the biomass-to-catalyst ratio is 1/10, AHs formation is intensified significantly, especially for sawdust. Overall, the indexes conducted in the present study can provide useful measures to identify the catalytic pyrolysis dynamics and levels.
  18. Chen WH, Chang CM, Mutuku JK, Lam SS, Lee WJ
    Environ Res, 2021 06;197:110975.
    PMID: 33689824 DOI: 10.1016/j.envres.2021.110975
    The deposition phenomenon of microparticle and SAR-CoV-2 laced bioaerosol in human airways is studied by Taguchi methods and response surface methodology (RSM). The data used herein is obtained from simulations of airflow dynamics and deposition fractions of drug particle aerosols in the downstream airways of asthma patients using computational fluid dynamics (CFD) and discrete particle motion (DPM). Three main parameters, including airflow rate, drug dose, and particle size, affecting aerosol deposition in the lungs of asthma patients are examined. The highest deposition fraction (DF) is obtained at the flow rate of 45 L min-1, the drug dose of 200 μg·puff-1, and the particle diameter of 5 μm. The optimized combination of levels for the three parameters for maximum drug deposition is performed via the Taguchi method. The importance of the influencing factors rank as particle size > drug dose > flow rate. RSM reveals that the combination of 30 L min-1, 5 μm, 200 μg·puff- has the highest deposition fraction. In part, this research also studied the deposition of bioaerosols contaminated with the SAR-CoV-2 virus, and their lowest DF is 1.15%. The low DF of bioaerosols reduces the probability of the SAR-CoV-2 virus transmission.
  19. Leong YK, Chew KW, Chen WH, Chang JS, Show PL
    Trends Plant Sci, 2021 07;26(7):729-740.
    PMID: 33461869 DOI: 10.1016/j.tplants.2020.12.010
    Given their advantages of high photosynthetic efficiency and non-competition with land-based crops, algae, that are carbon-hungry and sunlight-driven microbial factories, are a promising solution to resolve energy crisis, food security, and pollution problems. The ability to recycle nutrient and CO2 fixation from waste sources makes algae a valuable feedstock for biofuels, food and feeds, biochemicals, and biomaterials. Innovative technologies such as the bicarbonate-based integrated carbon capture and algae production system (BICCAPS), integrated algal bioenergy carbon capture and storage (BECCS), as well as ocean macroalgal afforestation (OMA), can be used to realize a low-carbon algal bioeconomy. We review how algae can be applied in the framework of integrated low-carbon circular bioeconomy models, focusing on sustainable biofuels, low-carbon feedstocks, carbon capture, and advances in algal biotechnology.
  20. Dharmaraj S, Ashokkumar V, Pandiyan R, Halimatul Munawaroh HS, Chew KW, Chen WH, et al.
    Chemosphere, 2021 Jul;275:130092.
    PMID: 33984908 DOI: 10.1016/j.chemosphere.2021.130092
    COVID-19 has led to the enormous rise of medical wastes throughout the world, and these have mainly been generated from hospitals, clinics, and other healthcare establishments. This creates an additional challenge in medical waste management, particularly in developing countries. Improper managing of medical waste may have serious public health issues and a significant impact on the environment. There are currently three disinfection technologies, namely incineration, chemical and physical processes, that are available to treat COVID-19 medical waste (CMW). This study focuses on thermochemical process, particularly pyrolysis process to treat the medical waste. Pyrolysis is a process that utilizes the thermal instability of organic components in medical waste to convert them into valuable products. Besides, the technique is environmentally friendly, more efficient and cost-effective, requires less landfill capacity, and causes lower pollution. The current pandemic situation generates a large amount of plastic medical wastes, which mainly consists of polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and nylon. These plastic wastes can be converted into valuable energy products like oil, gas and char through pyrolysis process. This review provides detailed information about CMW handling, treatment, valuable product generation, and proper discharge into the open environment.
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