Pyrolysis of domestic sewage sludge: influence of operational conditions on the product yields using factorial design.

This study aims to investigate a sustainable method for sewage sludge (SS) safe disposal and reuse. The study involved exploring the optimum parameters of thermal treatment of SS by pyrolysis to produce biochar. Based on the analysis of the full factorial design, the effects of pyrolysis conditions: temperature, heating rate, and isothermal time on pyrolysis product yields were evaluated. The average yield of biochar was significantly reduced when the pyrolysis temperature was increased from 300 to 500 °C, while the average yields of bio-oil (BO) and non-condensable gases (NCGs) were increased. The yield of biochar was nearly the same when the heating rate was increased from 5 to 35 °C/min, while the yield of BO was increased and the yield of NCGs was decreased. The average yields of biochar and NCGs were reduced when the isothermal time was increased from 45 to 120 min, while the yield of BO was slightly increased. Factorial design methodology revealed all potential interactions between the variables of the pyrolysis process of SS. To predict pyrolysis product yields, first-order regression models were developed based on the effects' magnitude of the process parameters and their interactions. The models were agreed to the experimental data.

Bench-scale gasification of cedar wood--part II: effect of operational conditions on contaminant release.

Here, we present the evolution profile of tar in the product gas during cedar biomass gasification. We also discuss the evolution of other contaminants (H(2)S, COS, NH(3), HCN, and HCl). The cedar wood was gasified under various operating conditions in a bench-scale externally heated updraft gasifier; this was followed by thermal reforming. Tar levels in the product gas were significantly affected by the operating conditions used. At a gasification temperature of 923 K, there was no clear relation between the evolution of phenolic tar in the product gas as a function of residence time. The evolution of PAH tar at a low gasification temperature was lower than the evolution of phenolic tar. With increasing temperature, the proportion of PAH tar content became significant. At a gasification temperature of 1223 K, increasing the residence time reduced the content of PAH tar owing to a catalytic effect associated with ash generation at high temperatures. Increasing the steam-to-carbon (S/C) ratio under thermal conditions had a slight effect on PAH conversion. However, increasing the equivalence ratio (ER) effectively reduced the tar levels. The conversion of fuel-sulfur and fuel-nitrogen to volatile-sulfur and volatile-nitrogen, respectively, increased with increasing S/C ratio and ER. The evolutions of COS and HCN gases were much smaller than the evolution of H(2)S and NH(3). The evolution of HCl in the product gas decreased slightly with increasing ER. Increasing the S/C ratio decreased the HCl levels in the product gas. The effect of temperature on contaminant levels could not be fully understood due to limited availability of experimental data at various temperatures. We also compare our findings with data in the literature.

Bench-scale gasification of cedar wood--part I: effect of operational conditions on product gas characteristics.

The present study was conducted within the framework of R&D activities on the development of gasification and reforming technologies for energy and chemical recovery from biomass resources. Gasification of the Japanese cedar wood has been investigated under various operating conditions in a bench-scale externally heated updraft gasifier; this was followed by thermal reforming. Parametric tests by varying the residence times, gasification temperatures, equivalence ratios (ERs) and steam-to-carbon (S/C) ratios were performed to determine their effects on the product gas characteristics. Thermodynamic equilibrium calculations were preformed to predict the equilibrium gas composition and compared with the experimental value. We found that the product gas characteristics in terms of the H(2)/CO ratio, CO(2)/CO ratio, and CH(4) and lighter hydrocarbons concentrations are significantly affected by the operating conditions used. Increasing the residence time decreased the CO(2)/CO ratio; however, a nominal effect was noticed on H(2) concentration as a function of the residence time. At sufficient residence time, increasing the temperature led to higher H(2) yields, CO efficiency and higher heating value (HHV) of the product gas. The presence of steam during gasification effectively enhanced the proportion of H(2) in the product gas. However, higher S/C ratio reduced the HHV of the product gas. Increasing the ER from 0 to 0.3 increased the H(2) yields and CO efficiency and decreased the HHV of the product gas. The evolution of CH(4) and lighter hydrocarbons at low gasification temperatures was relatively higher than that at high temperature gasification. The evolution of CH(4) and lighter hydrocarbons at high gasification temperatures hardly varied over the investigated operating conditions.

Degradation of dissolved diazinon pesticide in water using the high frequency of ultrasound wave.

This article aims to apply the ultrasound technique in the field of clean technology to protect environment. The principle of sonochemistry is conducted here to degrade pesticides in simulated industrial wastewater resulted from a factory manufacturing pesticides namely diazinon. Diazinon pesticide selected in this study for degradation under high frequency ultrasound wave. Three different initial concentrations of diazinon (800, 1200, and 1800 ppm), at different solution volumes were investigated in to degrade dissolved diazinon in water. Ultrasound device with 1.7 MHz, and 0.044 cm diameter, was used to study the degradation process. It is found that as the concentration of diazinon increased, the degradation is also increasing, and when the solution volume increases, the ability to degraded pesticides decreases. The experimental results showed an optimum condition achieved for degradation of diazinon at 1200 ppm as initial concentration and 50 ml solution volume. Kinetic modeling applied for the obtained results showed that the degradation of diazinon by high ultrasound frequency wave followed a pseudo-first-order model with apparent rate constant of around of 0.01 s(-1).