Figure 9.10 Sewage treatment plantDISPOSING OF SOLID WASTES FROM SEWAGE TREATMENT PLANTS
Sewage sludge is mostly water with lesser amounts of solid material removed
from liquid sewage. Sludge that originates from commercial or industrial sources
is usually contaminated with toxic materials that are released into the sewers
from the industrial processes. Elevated concentrations of such materials may
make the sludge unsuitable for agricultural use, and it may then have to be
incinerated or disposed of in a landfill. Environmental issues that result from the
incineration or disposing of sludge in landfills include:
■ Gases that are released from the incineration of sludge contain greenhouse
gases and/or toxins.
■ Landfills that contain sewage sludge may, over time, leach out toxic
compounds into the groundwater.
■ Landfills that contain sewage sludge produce methane, a potent
greenhouse gas.
Biosolids are treated sewage sludge composed of nutrient-rich organic
materials that result from the treatment of domestic sewage. When treated and
processed, biosolids can be recycled and applied as fertilizer to improve and
maintain productive soils and stimulate plant growth.
Environmental issues that could result from using biosolids for agricultural
purposes include:
■ Sewage systems in most industrialized countries mix industrial wastes
with household sewage.
■ Some pharmaceutical drug compounds, birth control chemicals, and
cosmetic ingredients remain in biosolids even after sophisticated removal
treatments. These micropharmaceutical pollutants may leach out and end
up polluting the surface and groundwater sources and ultimately the food
chain.RELEVANT LAWS
NATIONAL ENVIRONMENTAL POLICY ACT (1969): This act required
all federal agencies to prepare environmental impact statements that outline