Environmental Engineering Reference
In-Depth Information
would not contribute to any emissions near the landfill. Another option is using compressed
landfill gas as a vehicle fuel.
Both combustion and non-combustion energy recovery systems have three basic
components: (1) a gas collection system; (2) a gas processing, treatment, and conversion
system; and (3) a means to transport the gas or final product to the user. Gas is collected from
the landfill by the use of active vents. It is then transported to a central point for processing.
Processing requirements vary, depending on the gas composition and the intended use, but
typically include a series of chemical reactions or filters to remove impurities. For direct use
of landfill gas in boilers, minimal treatment is required. For landfill gas injection into a
natural gas pipeline, extensive treatment is necessary to remove carbon dioxide. At a
minimum, the gas is filtered to remove any particles and water that may be suspended in the
gas stream.
VIII.
C
ASE
S
TUDY
:
C
ALGARY
B
IOCELL
P
ROJECT
A. Introduction
Although landfill disposal is an integral part of waste management, most people identify
sanitary landfills as a key factor in the mis-management of finite resources and as a source of
greenhouse gas emissions. This situation arose because modem landfills have evolved from
open dumping of solid waste. Since 1960s, engineers and scientists have attempted to rectify
the problems with “open dumps”, targeting groundwater contamination by landfill leachate
and waste related aesthetic issues. More recently, attempts have been made to address the
landfill gas issues, including the contribution of landfills towards the global carbon budget
and potentially global warming. The reactive approach followed by landfill engineers has
created collateral problems. For example, the current traditional approach of waste landfilling,
namely the dry-tomb landfilling approach, solves the problem of groundwater contamination
but is counterproductive because of the slow production and atmospheric release of methane
(CH
4
), and loss of resources (e.g. material and space).
So far, the general approach towards solving the solid waste problem has been mostly
piece meal and reactive. Landfills are considered a liability requiring solutions for individual
landfill problems. This reactive approach has ignored the positive aspects of solid waste
including the inherent resource value of the waste. The pessimistic view of waste is “waste is
a liability and requires high level of resources to manage” but the optimistic view of waste is
“waste is a resource in the wrong place and wrong time”.
Recent advances in sanitary landfill technology research have indicated that the operation
of landfills as bioreactors (Reinhart and Townsend, 1998) could be viable. Waste entombment
in a conventional landfill slows down the process of biodegradation by minimizing moisture
entry, whereas, bioreactors speed up the biodegradation process by controlled input of
moisture (i.e., by leachate recirculation) and increased cycling of nutrients and bacterial
populations (Reinhart and Townsend, 1998). The operation of traditional “entombed”
landfills for the sole purpose of controlling groundwater contamination is not sustainable, and
could be counterproductive because of the slow production and atmospheric release of CH
4
and loss of resources (e.g. material and space).
