Environmental Engineering Reference
In-Depth Information
FIGURE 19.4
A package treatment system located in a U.S. residential neighborhood.
There is an aesthetic clash with the neighborhood. Landscaped berms or a thick screen of
trees may be able to visually remove this facility from adjacent sightlines. Photo courtesy of
North American Wetland Engineering, LLC.
and soils. All of these issues can be successfully addressed by competent engineer-
ing design informed by science and knowledge of local conditions.
Obligate internal pathogens cause the diseases of concern to wastewater reuse.
For these organisms, direct human-to-human infection is not the mode of trans-
mission. For most waterborne pathogens, human waste must leave the body of one
person and be ingested by another. Infection depends upon ingestion of a life cycle
stage that lives outside of the human and is shed to the environment in urine or feces
(Figure 19.5). Additionally, there are other diseases, such as schistosomiasis, that
enter the human host through the skin via direct contact with wastewater contami-
nated with human urine or feces (WHO 1993).
Wastewater treatment for reuse must interrupt the pathogen or parasite life cycle
to eliminate it from its host population in the intermediate to long term. To achieve
that goal with irrigation reuse, wastewater must meet recognized standards of treat-
ment. Irrigation reuse places treated wastewater in soils. A high degree of disin-
fection occurs as wastewater percolates through soils (EPA 1981). A well-managed
irrigation reuse program also can interrupt the potential flow of pathogens into local
surface waters, resulting in additional public health benefits. Additionally, there are
effective management practices to minimize potential contamination of food crops
irrigated with treated wastewater (WHO 1989).
One potential disadvantage of irrigation reuse comes from salt. Wastewater is
more saline than the original freshwater sources. Some soils with high clay content
may be vulnerable to irrigation with slightly saline water without periodic flushing
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