Computer Simulation On Gas Injection, Generation And Ransport In Aerobic Bioreactor Landfills Under Uasi-Steady-State Condition

In recent years, with industrial and urban development, land forurban construction is getting limited. Many closed unlined landfills areredeveloped to urban construction sites. However, the stabilization ofthese landfills could take ten years or even decades, during which landfillgases will release continuously, such as CH4. It will be very dangerous ifurban construction is conducted above or near it. In last decades, therewere many reports on fires and explosion accidents on such landfills overthe world. In addition, as these landfills are lack of impermeable lining atthe bottom, and no internal landfill gas and leachate guide row collectionsystem are equipped, leachate and landfill gas emissions are leftuncontrolled, which is a threat not only to the environment, but also to thepersonal safety of residents nearby. How to remove the risks associatedwith the unlined landfills, and to conduct a fast and efficient treatment arequite urgent and important. Bioreactor landfill technology, which canaccelerate the decomposition of municipal solid waste, provides a possible solution for closed unlined landfills.The technology of aerobic bioreactor landfill has been applied inAmerica, Italy, Germany, Austria and Canada, but most theoreticalresearches on bioreactor landfill have been focused on anaerobic. Aerobicbioreactor landfill and anaerobic bioreactor landfill are different inbiochemical degradation reaction and the mechanism of gas and moisturetransport. The experience from anaerobic bioreactor landfill cannot beapplied to the design and operation of aerobic bioreactor landfill directly.Moreover, most of anaerobic and aerobic bioreactor landfill technologiesare used on the treatment of sanitary landfills. The unlined landfills inChina will need different consideration in the selection of ventilation flowrate and water injection volume. This work is aimed to investigate the airtransport behaviors in unlined landfill treatment by aerobic technology.The main contents in this article include the following aspects:(1) Based on a comprehensive analysis of the aerobic biochemicaldegradation process in unlined aerobic bioreactor landfills, it can berecognized that the landfill body is composed by particles packed bymechanical crushing and compaction. The reaction unit can be assumedas a spherical particle, which is divided into the central anaerobic zoneand the peripheral aerobic zone. Incorporating the influence of oxygenconcentration, substrate concentration, microbial concentration,temperature and water content, a mechanism model at particle scale for aerobic biochemical degradation reaction is established;(2) Landfill gas transport characteristics in unlined aerobicbioreactor landfills with vertical column wells for gas injection andextraction are studied in detail, and then a three-dimensional massbalance model at practical engineering scale for aerobic landfill gaspressure distribution is established in a cylindrical coordinate system, inwhich both convection and diffusion are considered. Thethree-dimensional mass balance model at practical engineering scale foraerobic landfill gas pressure distribution, the mechanism model at particlescale for aerobic biochemical degradation reaction and the mass balancemodel for moisture distribution at practical engineering scale are coupled,the profile of landfill gas pressure in unlined aerobic bioreactor landfill issolved by gPROMS;(3) With adequate ventilation for biodegradation, the minimumblower load and operation costs for aerobic bioreactor landfill areobtained. When water injection rate is defined under the condition withno leachate across the bottom boundary of landfill, the suitable wellspacing is determined to accelerate the aerobic biochemical degradation.Both of them are able to provide reference for the design and operation ofunlined aerobic bioreactor landfills, and they will facilitate the promotionof the treatment approach.