Environmental risk of waste and its management - Environmental Deterioration and Contamination: Problems and their Management - page 153

The environmental impacts to be taken into account during the LCA were the
following:

- Methane production : Transport to disposal site, impacts of waste disposal, and
methane use;
- Composting : Transport to the composting facility, transport to agricultural fields,
contaminant content (toxic metals);

- Incineration for cement production : Transportation to cement works for heat

production.

Calculating with the local conditions, distances, material requirement, and emis-
sions, composting was the best from the point of view of acid rain and eutrophication,
but incineration for clinker production proved to be the best from the point of view of
raw material need, global warming, ozone depletion, and smog, due to the substitution
of conventional energy sources and the proximity of the wastewater treatment plant
and the cement works.
The final and most decisive argument for the use of this sewage sludge for clinker
production is its toxic metal content, which may cause unacceptable load on soil
over the long term. The risk of every toxic metal contained in the waste was calcu-
lated according to the site-specific quantitative risk assessment procedure for chemical
substances regulated by REACH (2006).
With regard to biowastes and by-products, further options in addition to com-
posting, methane production and incineration should be considered. This includes
direct application of the waste/by-product on agricultural fields or wastelands. Another
option is pyrolysis, which represents a rather high level in waste hierarchy. Pyroly-
sis is the thermochemical decomposition of organic materials at high temperatures
in the absence of oxygen. The products of pyrolysis mainly include gas, some liq-
uid and a solid residue rich in carbon, called char. Char from biomass is also called
biochar. Pyrolysis which mostly leaves the residue in the form of carbon is called car-
bonization. Biochar is the black component of “ terra preta '', the black soil of the
Amazon basin artificially created by the ancient people of the Amazon from waste
and char.
Biochar is used to improve soil texture and support a healthy soil ecosystem. It is
capable of sorbing and retaining macro-, mezo- and micronutrients and releasing them
proportionally. From a hygiene perspective, biochar is safe as compared to manure as
it is disinfected at high temperature. Biochar is also considered for carbon sequestra-
tion since it is able to store carbon within the soil over the long term as shown by
terra preta .
As concerns the composition and material content of wastes, most of them can
be used to replace the missing soil components responsible for soil deterioration. Sim-
plified, one may say: what has been extracted by plants and removed by the harvest
should be returned to the soil, including macro- meso- and microelements. It must be
understood that chemical fertilizers cannot complement soil properly. The long-term
exploitation of soil nutrients results in increasing depletion and an overall shortage
of some meso- and micronutrients. The result is poor quality of food crops with low
nutritional value and subsequent human deficiency diseases. The same applies for
soil organic matter (humus) content. Soils world-wide are suffering from nutrient and