Environmental Engineering Reference
In-Depth Information
high pH is generated. Settling ponds are used to remove the solids. Reduction of the pH
below 12 renders the wastewater not hazardous. Water usage has been reduced through
recycling in the plant in a closed loop. Concrete has accounted for up to 40%-50% by
weight of construction and demolition (C&D) waste (Sandler, 2003). More and more of this
waste will be used in road aggregate. Precasting concrete at a central facility can reduce
materials used and wastewater generated.
In the stone, and concrete products industries, more than 530 million tonnes of wastes
were generated in 1993 (USEPA, 1995b). Approximately 96% was recycled, treated, or
recovered for energy, whereas 2.3% was transferred off-site or released to the environ-
ment. Off-site disposal, underground injection, air, land, or water discharge accounted for
2.2% of the waste. The SDC (2002) indicates that the concrete industry wishes to continue
to increase its use of recycled waste and by-product materials involved in concrete manu-
facturing, and thus, by 2030, zero net waste is the objective.
Waste generation and disposal demonstrate the problems of stressors and impacts. For
example, waste production by industry and commerce in England for 1998 to 1999 (DEFRA,
2010) was estimated at 78 million tonnes. This does not include the 294 milllion tonnes
produced by demolition, mining, quarrying, agricultural wastes, construction wastes and
sewage sludge. In the Netherlands, 35 million tonnes more manure is produced than can
be utilized by arable farming (Tirion, 1999).
More than 360,000 tonnes of waste were generated in 1993 by the fabricated metals indus-
try (USEPA, 1995a). According to the Toxic Release Inventory (TRI), approximately 62% of
the waste was either recycled or treated, or the energy was recovered on-site. Another 34%
of the waste was either released to the environment or transferred off-site. Direct releases
by air, water, land or underground injection or disposal accounted for 13.2% of the waste.
13.3 Renewable Geoenvironment Natural Resources
There are two speciic classes of renewable geoenvironment natural resources, namely
living and nonliving. Living renewable natural resources include land and aquatic ani-
mals, forests, native plants, etc., whereas nonliving renewable natural resources include
water and soil. By deinition, renewable natural resources refer to those resources that
have the capability to regenerate, replenish, and renew themselves, either naturally or
with human intervention within a reasonable time period. Sustainability as an objective
requires that full regeneration-replenishment of renewable resources must be obtained.
It is recognized that when consumption (use, exploitation, etc.) exceeds regeneration-
replenishment rate, sustainability of the renewable resource is not obtained. This does not
mean that the renewable resource will not or cannot renew itself. It simply means that the
amount or rate of the resource that is renewed is insuficient to meet the demands placed
on it. In recognition of this, we need to distinguish between (a) unsustainable renew-
able natural resources, i.e., renewable resources that by virtue of circumstances cannot be
fully renewed or replenished, and (b) sustainable renewable natural resources, i.e., renew-
able resources that can be totally regenerated and replenished. When consumption rate is
greater than the rate of regeneration and/or replenishment, etc., the amount or nature of
the particular renewable natural resource will be depleted and may eventually become
extinct. Striking examples of this are overishing and overharvesting of groundwater and
deep-seated aquifers.
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