Environmental Engineering Reference
In-Depth Information
600 L/GJ for steam injection. Similarly, natural gas ex-
traction can consume up to 300 L/GJ. Nearly all this
water can be recycled, but a higher water to oil ratio (in
Alberta now
>
10 compared to
<
1 in 1970) requires
more energy for pumping. Coal cleaning needs 20-50
L/GJ, oil refining at least twice as much and up to 200
L/GJ. Even the just cited upper rates would result in
global withdrawals well below 100 km
3
, and consump-
tive uses would be less than 10 km
3
. The grand total
of water withdrawn in 2005 by all energy-producing
industries would then be less than 600 km
3
, and the con-
sumptive use would be at most about 100 km
3
, more
likely 60-70 km
3
. In contrast, global water withdrawal
amounted to about 4000 km
3
in 2005, with agriculture
claiming some 70% (WRI 2005).
Energy industries thus claimed less than 15% of all
water withdrawals; their share of consumptive uses can-
not be pinpointed, but it was definitely less than 5% of
all water consumed by agriculture. Lack of reliable infor-
mation precludes calculating many global totals, notably
how much energy is needed to treat the world's drinking
water, pump it, and transport it by pipelines. The energy
cost of drinking water varies widely: some clean supplies
flow to cities by gravity and need little besides ordinary
chlorination; other flows require extensive treatment and
long conveyance. Somewhat smaller but still large ranges
apply to wastewater treatment. Figures available for Cali-
fornia illustrate these spreads, with the energy cost of wa-
ter treatment ranging from essentially zero to 4 kWh/m
3
and wastewater
state. But even then these costs are less than the energy
requirements for desalination. Desalination, most com-
mon in the Middle East (it supplies 70% of Saudi water),
is highly energy-intensive. The theoretical minimum
needed to desalinate normal seawater (3.45% salts) at
25
C is 0.86 kWh/m
3
, but actual processes consume 1
OM more. During the 1990s multistage flash distillation
(the leading process in volume terms) needed 12-24
kWh/m
3
and reverse osmosis required 5-7 kWh/m
3
,
but costs below 4 kWh/m
2
should be possible in the
near future (Encyclopedia of Desalination 2006).
Energy industries are also the source of various forms
of water pollution, ranging from chronic acid mine drain-
age from coal mines (due to oxidation of exposed FeS
2
)
to recurrent catastrophic spills of crude oil from tankers.
Most of these releases have only localized impacts,
and small spills are subject to evaporation, emulsification,
sinking, auto-oxidation, and above all, microbial oxi-
dation. These natural controls are temporarily over-
whelmed only by very large oil spills following tanker
accidents or offshore well blowups. The worst accidents
of the last quarter of the twentieth century were the At-
lantic Express (in 1979, off Tobago, 287,000 t) and ABT
Summer (1991, 1000 km off Angola, 260,000 t).
Because they took place far offshore, they received
much less attention than the third and fourth record
spills: Castillo de Bellver (1981, off Saldanha Bay, South
Africa, 253,000 t) and Amoco Cadiz (1978, Brittany
beaches, 223,000 t of light crude) (ITOPF 2005). The
highly publicized Exxon Valdez spill in Prince William
Sound, Alaska, in 1989 was 37,000 t (not even among
the largest 30 since the 1960s), but it killed as many
as 270,000 water birds (Piper 1993). In contrast, the
Mexican IXTOC 1 well in Bahia de Campeche spilled
as much as 1.4 Mt in 1979-1980. Besides polluting
treatment costing 0.3-1.3 kWh/m
3
(CEC 2005).
National and regional disparities are similarly large.
The total energy cost of water supply and conveyance
is more than three times higher in southern California
(about 3.4 kWh/m
3
) than in the northern part of the
