Environmental Engineering Reference
In-Depth Information
TABLEĀ 19.2
Energy Use Comparison
Energy Requirement
(kW hours/day)
System
Activated sludge
125
Aerated wetland
43
Tidal wetland system
27
Note: The comparison is for 200 m 3 /d systems
(approximately 1,000 people at 200 liters per
person per day). All systems are designed to
achieve the same reuse and nitrogen removal
standards.
such as activated sludge, fail completely without power. Semipassive ecotechnology
therefore may be a good choice for regions where power supply is unreliable.
The cost of ecotechnology is favorable when compared to other wastewater tech-
nologies. A rigorous cost analysis is out the scope of this chapter, but consideration
of construction techniques is instructive. The technologies described in this chapter
use shallow, lined excavations, and local soils or aggregates. Designs must adapt to
local materials and construction methods. Operational power requirements are much
less than conventional technology. Land must be available for the treatment system,
typically 0.5 to 5.0 m 2 per person, depending on the type of wetland and design
goals. Assuming land is available at a reasonable price, the capital costs of ecotech-
nologies are competitive with conventional technologies. Lower power requirements
mean that ecotechnology costs less to operate than conventional technologies.
CONCLUSIONS
Wastewater reuse and ecotechnology cover broad intellectual territory. Subjects
germane to this chapter have included Islamic water law, culture, epidemiology,
public policy, parasitology, plankton ecology, and engineering design. Such a
range of relevant subjects is not surprising when considering wastewater reuse in
an ecological context, given that water is an integrating factor for all life and that
ecology is a study of the relationship between living things, their environment, and
each other.
We have seen that cultures react to wastewater reuse both rationally and irratio-
nally. How or if wastewater reuse projects proceed may have little to do with need or
technical merit. Cultural values rule.
How culture will affect choices for wastewater reuse in small towns and villages
near the Iraqi marshes remains to be seen. It does seem clear that the influence
of Islamic law will not hinder development of decentralized reuse projects given
the clear language of the Saudi fatwa on reuse. Rather, if local imams can be per-
suaded that human health is safeguarded, then they actually may assist in developing
 
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