Infrastructure Models for Ecological Wastewater Management - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 401

TABLE 20.1
Wastewater Infrastructure Models

Planning and
Organization Capacity

Most Suitable Infrastructure
Scale Typical Population Density

Centralized systems (“The Big
Pipe”)

High Regional

Clustered systems
(decentralized)

Medium Local

Low Family Single-home systems

the population density and/or organizational capacity of a community, as summa-
rized in Table 20.1.
In many areas of the world, a high population density is not synonymous with
the ability to plan and organize infrastructure on a regional scale. In these cases, the
ability of governments to plan and organize is a much more important determinant in
the selection of appropriate wastewater infrastructure than population density. The
existence of government agencies does not ensure that effective planning and orga-
nization do, in fact, occur. For the purpose of this chapter, it is important to define
the concept of institutional capacity. “Institutional capacity” is defined as the ability
for an organization to develop a plan and to provide effective implementation of that
plan . The importance of organizational and planning capacity in technology selec-
tion is key in understanding why so many wastewater technology transfers between
developed and developing countries fail.
Determining the scale at which the wastewater infrastructure will operate is
significant because each of the three infrastructure models is embodied by unique
technologies, and there is very limited technology crossover between the three mod-
els. By selecting the scale level, planners determine the range of technology options
that will be available to the engineers who construct the infrastructure (Wallace et
al. 2005).
A theoretical framework for wastewater management has been developed for
Zimbabwe (Nhapi, Gijzen, and Siebel 2003), but is applicable to many regions of the
globe, including Iraq. This framework summarizes the effects of population density,
effluent reuse, level of treatment, and appropriate technology options, as shown in
Figure 20.1.
In reviewing Figure 20.1, it can be seen that as the treatment level increases, there
is a cascade from property level (single-home) systems up to large-scale centralized
treatment systems (lower right quadrant). As the scale level increases, there is gener-
ally an increase in population density, with an upward cascade from low-density to
high-density areas. The technologies used for wastewater management (lower left
quadrant) cascade upward from simple graywater/blackwater systems (implemented
at the single-home level) up to large-scale advanced treatment systems (employing
biological nutrient removal [BNR]). As the scope and complexity of the infrastruc-
ture change, the end use of treated effluent also changes (upper left quadrant), cas-