Biogas combustion characteristics under varying carbon dioxide dilution and hydrogen enrichment

This study investigates the combustion characteristics of four different types of gaseous fuels namely methane (CH4), biogas, simulated biogas with varying carbon dioxide (CO2) content and hydrogen enriched biogas under atmospheric condition. Flammability, laminar burning velocity and flame stability of each fuel are among the combustion characteristics investigated using spherical flame method. Measurement of these parameters is important to explain the effects of CO2 and hydrogen on biogas combustion which are still lacking in literature. CH4 flammability range was found to be within the equivalence ratio of 0.7 to 1.3 with peak laminar burning velocity at approximately 36 cm/s which agrees well with previous findings. For biogas, flammability range narrows to equivalence ratio range of 0.6 to 0.9 with a peak laminar burning velocity of around 24 cm/s. For simulated biogas, as CO2 content increased, the flammability range tended to become narrower with appreciable decrease in laminar burning velocity. Peak laminar burning velocity value steadily decreased to 21%, 34% and 45% as CO2 content was increased from 20% to 40% and 50% respectively. CO2 could slow down the reactions that produce radicals important for CH4 dissociation. It could also modify mass and thermal diffusion pattern as indicated by the corresponding changes in Markstein length. For hydrogen enriched biogas, the flammability limits widened to the leaner side from equivalence ratio of 0.4 to 0.9 for 30% and 40% enrichment. Both flame speed and laminar burning velocity were enhanced with hydrogen enrichment especially at 30% and 40% which led to significant increase in maximum laminar burning velocity to 52 % and 88 % respectively. Flame appeared to become less stable under leaner conditions as supported by the occurrence of buoyancy and mild cellularity at the equivalence ratio of 0.4 and 0.5 under 30% and 40% hydrogen enrichment. Simulation revealed dramatic increase in H radical at 30% hydrogen enrichment onwards. These observations imply the significance of hydrogen on biogas combustion both on laminar burning velocity and flame stability

Flame propagation and burning rates of methane-air in a closed combustion vessel

The propagation and burning rates of methane-air mixtures were investigated at initial atmospheric pressure with temperature range of 298-302K and equivalence ratio range of 0.8 to 1.3. Experiments were performed in a cylindrical constant volume combustion chamber where the mixture is ignited by centrally located electrodes. The images of spherically expanding flame were observed and recorded using schlieren photography technique with high speed camera system. Analysis of the flame area yield flame radii and further burning rates in term of outwardly flame speed propagation can be calculated. Results shows that smooth spherical flames were observed throughout the flame propagation for all equivalence ratios. The fastest flame propagation was recorded at equivalence ratio 1.0 and 1.2. In addition, flame speed of each equivalence ratio exhibits small fluctuation probably arising from acoustic disturbance. This disturbance becomes more apparent at higher equivalence ratio

Prevalence of antibiotic resistance bacteria in aquaculture sources in Johor, Malaysia

The intensive use of antibiotics in aquaculture results in the proliferation of antibiotic. In this study, antibiotic resistant bacteria from six different aquaculture sources (pond of Fisheries Research Institute (FRI), and rivers of Kukup, Pulai, Pendas Laut, Sungai Melayu and Kong Kong) were isolated. These isolates were tested for antibiotic resistance against seven antibiotics via the disc diffusion method. Finally, phenotypic and genotypic identification via 16S rRNA sequencing and phylogenetic analysis were carried out. The results show that 58 out of 118 bacterial isolates are resistant to multiple antibiotics. The highest isolate resistance was observed towards rifampicin (89.66%), followed by ampicillin (79.31%) and sulfafurazole (67.24%). The isolates with multiple antibiotic resistant (MAR) index values with more than 20% were sub-jected to 16S rRNA gene sequencing. The majority of the bacterial strains exhibit multiple antibiotic resistance, indicating that they were isolated from highly contaminated sources based on the tested water qualities profiles, which showed the high level of turbidity and total dissolved solid (TDS) in most sampling sites with the high num-ber of MAR bacteria obtained

Hydrolysis of liquid pineapple waste by invertase immobilized in PVA-alginate matrix

A thorough investigation of sucrose hydrolysis by invertaseimmobilized in recently developed PVA–alginate beads was performed. The developed PVA–alginate bead is distinguished by the treatment with sodium sulfate solution. The performance of invertaseimmobilized in PVA–alginatematrix beads in terms of leakage, reusability, ideal temperature and pH and kinetic parameters Km and Vmax was investigated. Results revealed that the ideal temperature and pH for the immobilizedinvertase are 50 °C and 4 respectively. The apparent Km of each bead is relatively lower than that of the free enzyme with the value of 4.7 × 10-5 mM and 2.849 × 10-5 mM for 12PVA–5BA and 12PVA–7BA, respectively. An increase in Vmax was also observed with the value of 2281.02 U mg-1 enzyme and 2281.02 U mg-1 enzyme for 12PVA–5BA and 12PVA–7BA, respectively. The reusability of the beads and its storage period were also investigated and were found to be 14 cycles and 60 days, respectively. Finally, the beads with the best performance (12PVA–5BA) were used to hydrolyze liquidpineapplewaste. The production yield of glucose was about 745% in 3 h in the hydrolysis of the liquidpineapplewaste

Immobilization of Baker's yeast invertase in PVA-alginate matrix using innovative immobilization technique

This paper presents an innovative technique of immobilizing Baker's yeast invertase using polyvinyl alcohol (PVA)-alginate matrix. Previous immobilization technique was improved by adding treatment solutions such as boric acid and sodium sulphate. PVA-alginate beads with four different compositions were investigated in terms of enzyme activity within the beads, immobilization yield, diffusion coefficient and also chemical and mechanical stability. The enzyme activity within the beads was also compared with the free enzyme activity. Finally, the microstructure of the beads was analyzed using SEM. Amongst others, the results revealed that the fabricated beads remained insoluble in aqueous solution owing to the innovative technique. In addition, beads produced from 12% (w/v) PVA concentration and 5% (w/v) boric acid possess at least 10% higher enzyme activity while those produced from 12% (w/v) PVA concentration and 7% (w/v) boric acid have at least 28% higher mechanical stability compared to the other formulations

Optimization of L(+) lactic acid production from solid pineapple waste (SPW) by Rhizopus oryzae NRRL 395

Solid pineapple waste (SPW) is one of the most abundant agricultural wastes found in the tropic region. Improper management could lead to deposition of such waste in the environment causing other problems. Optimized bioconversion into value added products using potent microorganism could be an option to manage SPW. In this study, Rhizopus oryzae NRRL 395 was used to convert SPW to L(+) lactic acid through solid-state fermentation (SSF). The lactic acid production, reducing sugar utilization and by-product formation were studied using central composite design (CCD) after screening step using 2 level Factorial Design (2LFD). Studied parameters include moisture content (45 to 85% w/w), incubation time (0 to 7 days), temperature (25 to 45 °C), pH (4 to 8), and inoculum size (1 × 105 to 1 × 109 spores/g). During 2LFD, the highest lactic acid concentration obtained was 84.85 mg/g under the condition of 60% w/w of moisture content, 3 days of incubation, 35 °C, pH of 7 and 1 × 107 spores/g. Based on the condition suggested by CCD, the maximum lactic acid concentration of 103.69 mg/g was obtained with the following optimized SSF conditions: 67.53% w/w of moisture content, 3 days of incubation, temperature of 32.2 °C, pH of 5.6, and inoculum size of 1 × 107 spores/g. Graphic Abstract: [Figure not available: see fulltext.]

Immobilization of Candida rugosa lipase in PVA-Alginate-sulfate beads for waste cooking oil treatment

Hydrolysis of waste cooking oil (WCO) using immobilized Candida rugosa lipase (CRL) was studied. PVA-Alginate-Sulfate beads were used to immobilize CRL. During the transesterification process, three parameters were considered: pH, temperature and enzyme concentration. The degree of hydrolysis as well as the rate of the hydrolysis were also determined. The morphology of the beads was analyzed using Fourier Emission Scanning Electron Microscopy (FESEM). It was found that the operating conditions, pH = 7.00, temperature = 50°C, and bead loading of 8 g, were most favourable for the hydrolysis of WCO by immobilized CRL to yield maximum fatty acid production and hydrolysis conversion. It was also found that the rate of hydrolysis by immobilized CRL is higher than that of free enzyme which is 96.50% and 68.75%, respectivel

Optimization of biodiesel production from palm oil mill effluent using lipase immobilized in PVA-alginate-sulfate beads

In this study, production of biodiesel from palm oil mill effluent (POME) using immobilized Candida rugosa lipase was optimized using Box-Behnken design (BBD) of response surface methodology (RSM). The optimized parameters chosen were methanol/POME ratio, reaction time, weight of the immobilized beads and agitation speed. The highest yield of both palmitic acid methyl esters (PAME) and oleic acid methyl ester (OAME) was obtained at the following optimum conditions; agitation speed (300 rpm), oil/methanol molar ratio (1:6), incubation period (5 h) and weight of the immobilized beads weight (2 g). The important fuel properties of the biodiesel such as flash point, kinematic viscosity, water and sediment and copper strip corrosion were evaluated according to the American Society for Testing of Materials (ASTM D6751) and European Standard (EN 14214) and were found to be in good agreement with the standard quality and specification

Potential use of liquid pinapple waste for bioethanol production by immobilized bakers' yeast

Bioethanol is the most extensively used biofuel for transportation in the world. Nowadays, researchers are focusing in producing bioethanol from crops and agricultural wastes. Malaysia contributes to 1% of world pineapple production which corresponds to an enormous amount of waste generation per year. Utilization of waste from pineapple processing industry for bioethanol production could help to reduce potential environmental issues. In this study, Bakers' yeast (Saccharomyces cerevisiae) was immobilized in modified PVA-alginate beads to produce bioethanol from liquid pineapple waste. The results revealed that by using 10 % (w/v) of the immobilized cells highest overall productivity of 0.0752 g/L/h and maximum production of 5.4179 g/L of bioethanol could be achieved. Although its maximum productivity of immobilized yeast was 0.0752 g/L/h which appreciably lower than that of the free cells, this deficiency is balanced by its overall productivity which is almost 50 % higher compared to that of free cells