Landfills as long-term sinks for organic carbon - an important parameter for reduction of global atmospheric CO2 concentrations

Abstract

Increased CO2 concentrations in the atmosphere contribute to global warming and thus
disturbed meteorological balances, It is of great importance to establish carbon accumulating
processes in the urban society, as the natural CO2 balancing processes are insufficient to
compensate for the increasing emissions of carbon dioxide,
Controlled landfills, and different types of landfill bioreactor cells for residual wastes, play a
role as long-term storage for organic carbon, and therefore, if a reliable biogas collection
system is provided, counteract increased atmospheric CO2 concentrations, Landfills thus can
be regarded as the anthropogenic counterpart to natural peatlands and lake sediments,
In a landfill reactor-cell, treating approximately I 00 000 tons of waste per year, and where
the fermentation residues are left in the landfill, a long-lived organic fraction corresponding
to about 45 000 metric tons of carbon dioxide is long-term accumulated each year. This
compensates for the annual carbon dioxide emissions from about 15 000 cars, provided that
each one runs 15 000 km per year with fossil fuel.
During landfilling most of the organic carbon in fossil derived products, like plastics,
synthetic rubber or textiles, a,s.o, will be brought back to long-term accumulation, As these
products only to a very small extent take part in the methane gas production, the landfill gas
(biogas) can be regarded as a true bio fuel. With a modem bioreactor technique almost all
produced biogas can be collected in the extraction system, and emissions of methane to the
atmosphere are minimized. Modem research has also shown that methane emissions from
landfills are at much lower rates than earlier expected, mainly due to efficient gas collection
systems but also to methane oxidizing bacteria in the surface cover layer of the landfill. As a
conclusion, treatment of residual wastes in highly optimised landfill cells creates an
important sink for organic carbon and a preferred "in-situ" stabilization technique before final
landfi 11 ing,