An active-fire based burned area mapping algorithm for the MODIS sensor

We present an automated method for mapping burned areas using 500-m Moderate Resolution Imaging Spectroradiometer (MODIS) imagery coupled with 1-km MODIS active fire observations. The algorithm applies dynamic thresholds to composite imagery generated from a burn-sensitive vegetation index and a measure of temporal texture. Cumulative active fire maps are used to guide the selection of burned and unburned training samples. An accuracy assessment for three geographically diverse regions (central Siberia, the western United States, and southern Africa) was performed using high resolution burned area maps derived from Landsat imagery. Mapped burned areas were accurate to within approximately 10% in all regions except the high-tree-cover sub-region of southern Africa, where the MODIS burn maps underestimated the area burned by 41%. We estimate the minimum detectable burn size for reliable detection by our algorithm to be on the order of 120 ha.     

Performance evaluation of a pilot scale vortexing fluidized bed combustor

To understand vortexing fluidized bed combustor (VFBC) performances, an investigation was carried out in a 0.45 m diameter and 4.45 m height pilot scale VFBC. Rice husks, corn, and soybean were used as the biomass feedstock and silica sand serving as the bed material. The bubbling bed temperature was controlled by using water injected into the bed. The experimental results show that the excess air ratio is the dominant factor for combustion efficiency. The in-bed combustion proportion increases with the primary air flow rate and bed temperature, and decreases with the volatile/fixed carbon ratio. The stability constant is proposed to describe the inertia characteristics of the vortexing fluidized bed combustor. The experimental results indicate that the stability of the VFBC increases with bed weight and primary air flow rate, but decreases with bed temperature.     

Effects of controlling parameters on production of hydrogen by catalytic steam gasification of biomass at low temperatures

Low temperature catalytic steam gasification of biomass is being investigated around the world as an environmentally friendly alternative to the existing techniques for hydrogen production. The aim of the present investigation was to gain a fundamental understanding about the catalytic steam gasification of some species under low temperature conditions. The research, in particular, focused on the role and relative importance of controlling parameters, such as reaction temperature and the heating rate on the composition of the products. It was found that higher temperatures and steam flow rates increased the gas yield. A relatively low reaction temperature of 600 °C and a high steam content of about 90% showed the strongest tendency for maximising the hydrogen production.     

Modelling anaerobic biomass growth kinetics with a substrate threshold concentration

Many bacteria have been observed to stop growing below a certain substrate threshold concentration. In this study, a modification of the Monod kinetics expression has been proposed to take into account this substrate threshold concentration observed in bacterial growth. Besides the threshold concentration no additional parameters have been added to the kinetic expression and so, only the substrate threshold concentration and the half-saturation constant have to be estimated for model calibration purposes. Furthermore, for parameter estimation purposes, practical identifiability of this new function has been studied and the results have been satisfactory. The new model has been applied, as an example, to a simple anaerobic model to simulate the competition for hydrogen between sulphate reducers and methanogens in a thermophilic methanol-fed bioreactor. Oscillatory behaviour and mathematical instabilities have been avoided by using the proposed model. Parameter sensitivities have also been calculated along the simulation period in order to investigate the importance of hydrogen threshold concentration parameters.     

Particulate matter and carbon monoxide in highland Guatemala: indoor and outdoor levels from traditional and improved wood stoves and gas stoves

Area 22-h average carbon monoxide (CO), total suspended particulates (TSP), particles less than 10 microns in diameter (PM10), and particles less than 2.5 microns in diameter (PM2.5) measurements were made in three test homes of highland rural Guatemala in kitchens, bedrooms, and outdoors on a longitudinal basis, i.e. before and after introduction of potential exposure-reducing interventions. Four cookstove conditions were studied sequentially: background (no stove in use); traditional open woodstove, improved woodstove with flue (plancha), and bottled-gas (LPG) stove. With nine observations each, kitchen PM2.5 levels were 56 micrograms/m3 under background conditions, 528 micrograms/m3 for open fire conditions, 96 micrograms/m3 for plancha conditions, and 57 micrograms/m3 for gas stove conditions. Corresponding PM10/TSP levels were 173/174, 717/836, 210/276, 186/218 micrograms/m3. Corresponding CO levels were 0.2, 5.9, 1.4, 1.2 ppm. Comparisons with other studies in the area indicate that the reductions in indoor concentrations achieved by improved wood-burning stoves deteriorate with stove age. Mother and child personal CO and PM2.5 measurements for each stove condition demonstrate the same trend as area measurements, but with less differentiation.     

Biosorption of mercury from aqueous solutions by powdered leaves of castor tree (Ricinus communis L.)

A new biosorbent produced from castor leaves powder [Ricinus communis L.] was used to remove mercury(II) from aqueous solutions. The initial mercury concentrations, contact time and initial pH were evaluated. The ability of castor leaves to remove mercury at various pH (2-8) was studied. The maximum capacity (Qmax) of biomass was found to be 37.2mg Hg(II)/g at pH 5.5. Biosorption equilibrium was established in approximately 1h. The equilibrium data were described well by Langmuir and Freundlich models. The adsorbed mercury on biomass was desorbed using 10 ml of 4M HCl solution. The biomass could be reused for other biosorption assays. The ability of biomass to adsorb mercury(II) in a column was investigated. These studies consider the possibility of using leaves of castor tree as an inexpensive adsorbent for the removal of Hg(II) from contaminated chemical and mining industry wastewaters. It is also suggested that the dried biomass might be simply kept and used in a very low cost metal ion removal system.     

Reduction in personal exposures to particulate matter and carbon monoxide as a result of the installation of a Patsari improved cook stove in Michoacan Mexico

The impact of an improved wood burning stove (Patsari) in reducing personal exposures and indoor concentrations of particulate matter (PM(2.5)) and carbon monoxide (CO) was evaluated in 60 homes in a rural community of Michoacan, Mexico. Average PM(2.5) 24-h personal exposure was 0.29 mg/m(3) and mean 48-h kitchen concentration was 1.269 mg/m(3) for participating women using the traditional open fire (fogon). If these concentrations are typical of rural conditions in Mexico, a large fraction of the population is chronically exposed to levels of pollution far higher than ambient concentrations found by the Mexican government to be harmful to human health. Installation of an improved Patsari stove in these homes resulted in 74% reduction in median 48-h PM(2.5) concentrations in kitchens and 35% reduction in median 24-h PM(2.5) personal exposures. Corresponding reductions in CO were 77% and 78% for median 48-h kitchen concentrations and median 24-h personal exposures, respectively. The relationship between reductions in median kitchen concentrations and reductions in median personal exposures not only changed for different pollutants, but also differed between traditional and improved stove type, and by stove adoption category. If these reductions are typical, significant bias in the relationship between reductions in particle concentrations and reductions in health impacts may result, if reductions in kitchen concentrations are used as a proxy for personal exposure reductions when evaluating stove interventions. In addition, personal exposure reductions for CO may not reflect similar reductions for PM(2.5). This implies that PM(2.5) personal exposure measurements should be collected or indoor measurements should be combined with better time-activity estimates, which would more accurately reflect the contributions of indoor concentrations to personal exposures. PRACTICAL IMPLICATIONS: Installation of improved cookstoves may result in significant reductions in indoor concentrations of carbon monoxide and fine particulate matter (PM(2.5)), with concurrent but lower reductions in personal exposures. Significant errors may result if reductions in kitchen concentrations are used as a proxy for personal exposure reductions when evaluating stove interventions in epidemiological investigations. Similarly, time microenvironment activity models in these rural homes do not provide robust estimates of individual exposures due to the large spatial heterogeneity in pollutant concentrations and the lack of resolution of time activity diaries to capture movement through these microenvironments.     

Model for biomass char combustion in the riser of a dual fluidized bed gasification unit: Part II — Model validation and parameter variation

The two-phase combustion model for biomass char combustion in a riser of a dual fluidized bed gasification unit that has been presented in part I is validated using the data obtained from the 8 MWth dual fluidized bed reactor at Guessing/Austria. The model is capable of calculating the average temperatures in all zones, the gas phase composition, solid hold up, char feed rates and air ratio. The model predictions for the temperature profile along the riser and for the exiting gas composition are in good agreement with the measured values. The simulation results show that the residual char from the gasifier is only partly converted in the riser for char particles larger than 0.6 mm. Un-combusted char is circulated back into the gasification reactor. Parameter variations show that the exact location where additional liquid fuels are introduced in the middle zone of the riser does not affect the global behaviour of the combustion reactor. Based on the simulation results it is proposed that external supply of char (additional) may be a very effective method for reducing producer gas recycling to the riser, which is currently necessary to obtain the desired gasification temperatures.     

Coupled Effects of Small-Scale Turbulence and Phytoplankton Biomass in a Small Stratified Lake

Recent laboratory studies demonstrated that small-scale fluid motion mediates phytoplankton physiological responses. We have investigated to what extent the laboratory studies are consistent with field measurements in a small stratified lake. We propose the rate of energy dissipation and corresponding Kolmogorov velocity are important scaling variables that describe the enhanced algal growth and the uptake of nutrients in a moving fluid under laboratory and field conditions. The ratio of nutrient flux to an alga in a moving fluid versus the nutrient flux in a stagnant fluid (Sherwood number) is quantified by the ratio of advective nutrient transport to molecular diffusion of a nutrient (Péclet number, PeK). The advective transport of nutrients is described by the layer-averaged Kolmogorov velocity (K). An enhanced algal growth due to fluid motion is proposed over the Péclet number range 6.7>PeK>1.3, with the maximal growth at PeK = 2.9. Field measurements recorded by a microstructure profiler demonstrated encouraging agreement between laboratory and field findings. The current mechanistic models of phytoplankton population dynamics could consider the proposed Péclet number with redefined characteristic velocity scale (K) in the formulation of subgrid scale closure fluxes on nutrient uptake and growth rate. Furthermore, the laboratory and field results presented in this study are intended to motivate researchers to question the validity of standard laboratory biotoxicity protocols and to modify existing procedures in the examination of effluent toxicity in the environment by including the fluid motion.     

The continuous self stirred tank reactor: measurement of the cracking kinetics of biomass pyrolysis vapours

The continuous self stirred tank reactor is a well known suitable device for studying the kinetics of high-temperature gas phase reactions. Temperature and composition are uniform at any point of the reactor, and for a given residence time, it is easy to calculate the values of kinetic constants from a very simple mathematical model. The aim of the present paper is to report the first experimental results obtained on the thermal cracking of vapours produced by the pyrolysis of biomass. The experiments are carried out between 836 and 1303 K and under mean residence times ranging from 0.3 to 0.5 s. The calculated activation energy and preexponential factor are in good agreement with those obtained by other authors operating in more usual devices, but needing the solving of more sophisticated models.