A team of French scientists comprising biologists, chemists and geologists have got together to study landfill sites. They are evolving a new method to make landfills safer and leak-proof
THE team analysing the disposal of
wastes in landfills is doing pioneering
work in that it has not just identified the
types of waste being dumped but even
segregated the waste, allocating them it)
sparate landfills. The waste in these
landfills undergoes decomposition by
fermentation. The process of decomposition varies in different landfills
because bacterial activity may require
the fermentation process to be either
aerobic or anaerobic in nature.
In an aerobic landfill, a first layer of
waste is spread on the ground and oxidied by micro-organistins before
decomposition takes place. The fermentation process in the culture medium
raises the temperature to roughly 65-
85C which sterilises the layer by killing
organisms like Salmonella typhosa,
Escherichia coli and 13mcclia arborat us.
After about 90 days, the temperature
decreases to 40'( ' and the process slows
down as it ages. I lie process is completcd when carbondioxide bubbles at,
noticed on the surface of the waste. SiN
months later , the landfill is ready for the
second waste layer. Oxygenation whi,l)
is crucial to the Success of the operation
is supplied by running landfill roller
drums Which grind and mix the waste.
In an anaerobic landfill site, fermentation takes place in the absence of oxygen. There are two methods in use to
prevent the entry of oxygen. The first
one involves the spread of a layer of
waste to a thickness of two in which prevents oxygen front reaching the core of
the dump. The other one reduces
organic Molecules through hydrolysis
into amino acids and sugar while bacterial action leads to the formation of
organic acids. The end-result of the
process is the release of hydrogen, oxygen and digester gas. A tontic of waste
produces 200-400 cu in of digester gas,
which can be used as fuel. I he bales of
waste used are also being tested to find
the efficacy of the process.
To prevent waste juices like lixivium
from escaping and polluting surrounding waterbodics, the landfill sites in
sonic countries are lined with leak-proof plastic film. The French scientists
are trying out the use of 50 m x 50 in
bins, the first of which has a leak-proof
seal made of 60 cm of thick compacted
clay. The other three bins are secured
with either a high density polyethylene
membrane, s 'vnthetic film or bentonite
(very pure clay)-based textile. The bins
ate equipped with a pumping system
which retrieves the liquids for further
analysis. The temperature, pressure and
movement of the tested membranes are
recorded with the help of sensors which
are placed at various locations on the
site. The objective of this experiment is
to develop membranes with optimum
performance levels and understand the
evolution of a landfill site.
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