Environmental Engineering Reference
In-Depth Information
Figure 6.1 Waste management hierarchy.
treatment plants. This system should be transformed into a less energy-consuming alter-
native, requiring less transportation, on-site treatment facilities, utilizing the waste at
the highest possible level of waste hierarchy, without mixing and diluting it, with as
little emission of CO 2 and toxic materials as possible, using the waste as much as pos-
sible in its original form. Emissions from waste management may be considerable, e.g.
CO 2 from composting, CO 2 ,N 2 O and particulate matter from incineration, CH 4 from
landfilling and anaerobic digestion, toxic emissions from recycling. When assessing the
environmental efficiency of a waste treatment technology, not only the risk reduction
for waste, but also the risk posed by the emitted material during waste treatment must
be considered.
Waste treatment at the site of generation has many advantages such as reuse,
recycling or energy recovery without mixing and transporting the originally sepa-
rated wastes, avoiding secondary contamination, and dilution of the utilizable waste
material. The concentrated nutrient content of runoffs (e.g., nutrient containing agri-
cultural runoffs) can be utilized for producing high-quality products (e.g., wetland
plants, reed), instead of having the microbial cell mass growing in the wastewater
treatment plant which, in addition, is loaded with persistent contaminants. To effi-
ciently utilize wastewaters, they should be controlled at the place of their origin, and
their mixing with other wastewaters or surface runoffs must be avoided.
Recovering and recycling wastes may help to conserve the normal element cycles
in the global ecosystem and thus avoid unacceptable deficiencies or surpluses in the
regular element flows. Waste utilization on soil—an old concept in a new perspective—
may kill two birds with one stone: utilizing the nutrients and organic matter contained
in the waste to increase fertility and humus content of soils. Wastes able to amend soil
texture will increase soil quality and prevent low stability, compaction, or erodabil-
ity. Most wastes contain large amounts of nutrient, which has no benefit or is even
disadvantageous at the wrong place (i.e., in surface waters), but beneficial if streamed
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