Environmental Engineering Reference
In-Depth Information
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Process sidestreams
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Seasonal variations
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Required effluent quality
8.10.1 influent Characteristics
Major factors to consider when evaluating influent characteristics
are the nature and volume of industrial contributions to the system.
Waste characteristics (BOD, solids, pH, metals, toxicity, and tempera-
ture), volume, and discharge pattern (e.g., continuous, slug, daily, weekly)
should be evaluated when determining if a waste will require pretreat-
ment by the industry or adjustments to operational control levels.
8.10.2 industrial Contributors
One or more industrial contributors produce a significant portion
of the plant loading (in many systems). Identifying and characterizing
all industrial contributors is important. Remember that the volume of
waste generated may not be as important as the characteristics of the
waste. Extremely high-strength wastes can result in organic overload-
ing and poor performance because of insufficient nutrient availability.
A second consideration is the presence of materials that even in small
quantities are toxic to the process microorganisms or that create a toxic
condition in the plant effluent or plant sludge. Industrial contributions
to a biological treatment system should be thoroughly characterized
prior to acceptance, monitored frequently, and controlled by either local
ordinance or implementation of a pretreatment program.
8.10.3 Process sidestreams
Process sidestreams
are flows produced in other treatment pro-
cesses that must be returned to the wastewater system for treatment prior
to disposal. Examples of process sidestreams include the following:
•
Thickener
supernatant
• Aerobic and anaerobic digester supernatant
•
Liquids removed by sludge
dewatering processes (filtrate, centrate,
and subnate)
•
Supernatant from heat treatment and
chlorine oxidation sludge
treatment processes
Testing these flows periodically to determine both their quantity
and strength is important. In many treatment systems, a significant
part of the organic or hydraulic loading for the plant is generated by
sidestream flows. The contribution of the plant sidestream flows can
significantly change the operational control levels of the activated
sludge system.
