NUTRIENTS - Marine Pollution: What Everyone Needs to Know - page 21

The Big Picture

Minimal
Nutrient
Inputs

Excessive
Nutrient Inputs

Sunlight

Sunlight

Algal Bloom

Balanced
Algae Growth

Healthy
Bay Grasses

Reduced
Bay Grasses

Healthy
System

Eutrophic
System

Algae Die-off

Algae
Decomposition

Adequate
Oxygen No/Low

Oxygen

Figure 2.1 Eutrophication (courtesy Chesapeake Bay Program)

the bay. In Latin America, Asia, and Africa, wastewater from
sewage and industry are often untreated and may be the pri-
mary contributors to eutrophication. In addition to nutrients,
wastewater and animal feces also contain harmful microbes
that can be removed by sewage treatment plants. Otherwise,
these microbes released into waterways may cause disease.
This is discussed further in Chapter 10.

How does a sewage treatment plant work?

Sewage treatment removes contaminants from wastewater.
The treatment includes physical, chemical, and biological pro-
cesses to remove physical, chemical, and biological contami-
nants. The objective is to produce an environmentally safe
liquid waste stream (or treated effluent) and a solid waste (or
treated sludge) suitable for disposal or reuse (usually as farm
fertilizer).
Primary treatment involves the physical separation of sol-
ids and liquids. Sewer pipes carry wastewater from homes