Effects of landfill void fraction and moisture content on the formation of aerobic areas in a semi-aerobic bioreactor

The main disposal method for municipal solid waste (MSW), including the growing worldwide volumes of kitchen waste, involves transport to landfills. Because kitchen waste is mainly composed of organic matter and has a high moisture content, large amounts of leachate and landfill gas are generated when it is sent to landfills. Therefore, rapid waste stabilization is essential. In this study, four semi-aerobic bioreactors (named NS, SS, MS, and LS) were established with void fractions of 33.76%, 39.84%, 44.62%, and 41.31%, respectively. The results showed that the void fractions of landfill directly affected the gas flow path. When the landfill void fraction was small (e.g., NS), most airflow traveled directly through the pipeline and minimal airflow entered the waste layer. When the landfill void fraction was large (e.g., MS), air easily entered the waste layer and some air flowed into the gas vent with the landfill gas. As the reaction proceeded, the void fraction gradually decreased due to gravity-induced sedimentation. During the water addition experiment, the voids were occupied by water, leading to formation of an anaerobic area. Among the four bioreactors, only MS had negligible formation of an anaerobic zone in the center. Methane (CH4) generation was detected only at the connection between the gas vent and the leachate collection pipe. A larger void fraction led to formation of a smaller anaerobic zone. The ratio of air flowing in pipeline was lowest in MS. These results indicated that a large void fraction promotes the decomposition of organic matter.

Impact of internal conditions on the gas flow path in semi-aerobic landfill reactors

Despite the continuous development of waste disposal technology, landfill remains a significant means of municipal solid waste disposal around the world. Accelerating the process of waste stabilisation has become a pressing problem. In this study, four indoor landfill reactors were set up. Reactors A and C were semi-aerobic landfills, and in reactors B and D the gas vents were disconnected from the leachate collection pipes. Kitchen waste was the main ingredient of the sample waste (55.46%). The void fractions of reactors C and D were decreased by adding extra gravel. The void fractions were 32.82% and 33.27% in reactors A and B, respectively, whereas those in reactors C and D were about 6% lower. The temperatures of reactors A and B were higher than those of reactors C and D. The temperature peak in reactor A occurred earlier than that in Reactor B. The temperature and gas concentration measurements confirmed that not all the air was discharged directly through the gas vent, and some air passed horizontally through the waste layer of the reactor. It was finally showed that the void fraction and connections in the pipelines inside the landfill reactor affected the gas flow path.

X-ray tube with artificial neural network model as a promising alternative for radioisotope source in radiation based two phase flowmeters

In this paper, X-ray tube is introduced as a potential alternative for radioisotope sources used in radiation based liquid-gas two-phase flowmeters. X-ray tubes have lots of advantages over the radioisotope sources such as having an adjustable emitting photon's energy, being safer from point of view of radiation health physics during the transportation of the source, having ability to generate a high flux photon beam, and etc. The proposed radiation based system in this study composes an X-ray tube with a tube voltage of 150 kV and a 2.5 mm aluminum filter as the radiation source and one sodium iodide crystal as the photon detector. A pipe was positioned between the X-ray tube and the detector. Two main flow regimes of annular and stratified with different void fractions were modelled inside the pipe. Artificial neural network model of multi-layer perceptron (MLP) was also used in this study for analyzing the obtained data. The output spectrum of sodium iodide detector with 150 samples was applied as the input of multi-layer perceptron network and void fraction was considered as its output. The root mean squared error of proposed measuring system was 4.13 which shows the X-ray tube can be implemented as a promising alternative for radioisotope in radiation based two phase flow meters.

Influence of the void fraction and vertical gas vents on the waste decomposition in semi-aerobic landfill: Lab-scale tests

The waste classification has not been carried out worldwide, especially in developing countries. The high content of water in the kitchen waste will definitely affect the amount of air flowing into waste layer from leachate collection pipe. In this experiment, three lab-scale landfill simulation reactors were established. Reactor A and B are semi-aerobic landfill modes, while reactor C has no vertical gas vent. The void fraction in the waste of reactor B was increased by adding gravel serve as part of the waste. The waste sample used in landfill reactor mainly included kitchen waste (58%). The waste decomposition conditions in the landfill were investigated using temperature sensors embedded in the waste, by determining the velocity and gas flow direction and by measuring the volume and composition of leachate produced. The results showed that the void fraction of waste in reactor A and C was 29.79% and 30.86% respectively, and that of waste in reactor B 34.96%. Compared with reactor A, reactor B had its temperature increase earlier. In addition, the temperature distribution in vertical gas vent of the reactor A and B is higher than in the leachate collection pipe. The gas flux of vertical gas vent increased with the temperature of gas vent. Reactor A and B had significantly lower concentration of chemical oxygen demand (COD) and ammonia nitrogen (NH₃⁺-N) than that of reactor C. It was concluded that landfill decomposition can be accelerated by increasing the void fraction in the waste and keeping a vertical gas vent open.

Towards accurate porosity descriptors based on guest-host interactions

For nanoporous materials at the characterization level, geometry-based approaches have become the methods of choice to provide information, often encoded in numerical descriptors, about the pores and the channels of a porous material. Examples of most common descriptors of the latter are pore limiting diameters, accessible surface area and accessible volume. The geometry-based methods exploit hard-sphere approximation for atoms, which (1) reduces costly computations of the interatomic interactions between the probe guest molecule and the porous material framework atoms, (2) effectively exploit applied mathematics methods such as Voronoi decomposition to represent and characterize porosity. In this work, we revisit and quantify the shortcoming of the geometry-based approaches. To do so, we have developed a series of algorithms to calculate pore descriptors such as void fraction, accessible surface area, pore limiting diameters (largest included sphere, and largest free sphere) based on a classical force field model of interactions between the guest and the framework atoms. Our resulting energy-based methods are tested on diverse sets of metal-organic frameworks and zeolite structures and comparisons against results obtained from geometric-based method indicate deviations in the cases for structures with small pore sizes. The method provides both high accuracy and performance making it suitable when screening a large database of materials.