Effectiveness of the Vertical Gas Ventilation Pipes for Promoting Waste Stabilization in Post-Closure Phase
Abstract: To make inside of
the municipal solid waste (MSW) landfill aerobic as much as possible is thought
to be preferable for promoting waste stabilization, reducing pollutant's load
in leachate, minimizing greenhouse gas emission and shortening
post-closure-care period. In Japan, installation of semi-aerobic landfill
structure has widely spread in order to promote waste stabilization in MSW
landfill from 1980s. In semi-aerobic landfill structure, outlet of main
leachate collection pipe is opened to atmosphere. Heat generated by aerobic
degradation of waste causes natural convection and natural aeration arises from
the outlet of leachate collection pipe to the gas vents. It is so-called stack
effect. This air flow is thought to be effective for purifying leachate flowing
through drainage layer and leachate collection pipes. And it is also thought to
be contributing to expanding aerobic region in waste layer in landfill. Recently,
measures attempting the promotion of waste stabilization are taken at several landfills
at where stabilization of waste delays, in which many vertical gas vents are
newly installed and close structure to semi-aerobic landfill is created.
However, in many cases, thesegas vents are not connected to leachate collection
pipes. Many vertical gas vents are just installed without scientific proof
regarding whether they can contribute for waste stabilization. In this study,
how such installation of gas vents is effective for waste stabilization and aerobization
of waste layer was discussed by numerical analysis. In numerical analysis, heat
transfer, gas movement by pressure, gas diffusion, biological degradation of
organic matter, and heat generation by biodegradation were taken into account.
Simulations were carried out by using the general purpose simulator of finite
element method. Three types of landfill structure were assumed. As the results,
the following information were obtained. In dig-down type landfill,
installation of gas vents has no effect for changing air flow. On the other
hand, in pile-up type landfill, installation of vertical gas vents can accelerate
air invasion and significantly promote waste stabilization, if it has high
permeable horizontal layer.
Author: Yasumasa Tojo ,
Natsuki Kishizawa, Toshihiko Matsuto, Takayuki Matsuo
Journal Code: jpkimiadd150417
