PhDThis thesis reports an investigation into the hydrogeological and geotechnical properties
of household wastes within the context of sustainable landfilling and, particularly, the
development of a high rate flushing bioreactor.
The design and construction of a large-scale (2-metre diameter) purpose built
compression cell used in the research are described. Tests on a number of different
household waste materials (including pulverised and aged wastes) were undertaken at
varying applied loads up to 600 kPa, equivalent to a 60 metre depth of landfill. Results
of variations in refuse density, stiffness, absorptive capacity, effective porosity and
hydraulic conductivity are reported against average effective stress in the waste. It was
concluded that the hydrogeological properties of household waste vary considerably with
effective stress and, hence, with depth in landfills. For example, the hydraulic
conductivity of crude household waste could reduce by over three orders of magnitude
from approximately lxi O mis to lxi 4 rn/s between placement (with minimal
compaction) and burial to a depth of 60 metres.
The principles of sustainable development are considered and applied to landfilling. The
view that the polluting potential of landfills should be reduced to acceptable levels
within a generation is supported. In most cases this will require that contaminants in the
landfill are removed by introducing water into the site and recirculating and flushing
leachate from it. The feasibility of achieving this with a variety of different leachate
recirculation systems is examined in the light of the findings of the research. A new
module has been written for MODFLOW, the USGS's groundwater flow model, to allow
hydraulic conductivity to vary throughout simulations with effective stress. The altered
code is used to model a grid of leachate abstraction and injection wells to illustrate the
potential for flushing.
It is concluded that changes are needed to current landfill design and operational
practices to enable wastes to be flushed efficiently within landfills. It is argued, in
particular, that there are significant benefits of operating landfills with large saturated
zones.Waste Technical Division of the department of thr Environment and Cleanaway Ltd
