sizes of industrial activities. Normally, 80 to 120
gallons per day per permanent resident and 30 to
50 gallons per day per transient and community
labor personnel can be used as a rough volume
estimate for flow.
PATTERNS OF FLOW
The amount of wastewater a treatment plant
receives fluctuates from hour to hour. Changing
seasons also affect the pattern flow. Peak flow of
domestic wastes normally reaches a plant just after
breakfast and for several hours in the early even-
ing. Industrial wastes may reach the plant during
the industrys period of operation. If the industry
has two or three shifts, flow will be more constant.
The size and topography of the area served
by a treatment plant also affects the flow pattern.
Small plants may have large differences between
peak and low flow periods. Larger plants
normally have more uniform rates of flow. The
period of lowest flow is usually between 2400 and
0500 hours. Unusual flow patterns help operating
personnel identify and correct abnormal surges
in flow in the wastewater system.
CHARACTERISTICS OF SEWAGE
Sewage is composed of many materials that
are broken down into three general areas. These
areas are the physical, chemical, and biological
characteristics of wastewater. This section will aid
you in identifying these various characteristics.
The concentrations of most materials in
wastewater are expressed in milligrams per liter
(mg/I) and denote the strength of the wastewater.
The higher the concentration, or mg/I, the higher
the strength. Table 10-1 lists the most important
materials that compose wastewater.
The physical characteristics of wastewater in-
clude those items that can be detected using the
physical senses. They are temperature, color,
odor, and solids.
The temperature of wastewater varies greatly,
depending upon the type of operations being
conducted at your installation. Wide variation in
the wastewater temperature indicates heated or
cooled discharges, often of substantial volume.
They have any one of a number of sources. For
example, decreased temperatures after a snowmelt
or rainfall may indicate serious infiltration.
Changes in wastewater temperatures affect the
settling rates, dissolved oxygen levels, and
biological action. The temperature of wastewater
becomes extremely important in certain
wastewater unit operations such as sedimentation
tanks and recirculating filters.
The color of wastewater containing dissolved
oxygen (DO) is normally gray. Black-colored
wastewater usually accompanied by foul odors,
containing little or no DO, is said to be septic.
Table 10-2 provides wastewater color information.
Table 10-2.Significance of Color in Wastewater
Blood or other industrial wastes or TNT complex
Industrial wastes not pretreated (paints, etc.)
Red or other
Surface runoff into influent, also industrial flows
Septic conditions or industrial flows