TM 5-814-8
nomics and several other factors which must be
can take place at either the end of the
wastage
considered.
react cycle or after the settling cycle, prior to
draw off of the effluent. If required, a higher
6-3. Physical and Chemical
Waste-
wastage concentration can be obtained through
water Treatment Processes
draw off of the settled solids. Effluent quality can
be considered essentially equal to conventional
a. Introduction. Physical and chemical pro-
treatment, with its benefits being seen mainly
cesses may be categorized as treatment for the
with smaller sytems requiring a relatively low
removal pollutants not readily removable or
flow of wastewater for treatment.
unremovable by conventional biological treatment
(3) Sequencing batch reactors. The sequenc-
processes. These pollutants may include sus-
ing batch reactor system ( SBR) uses two or more
pended solids, BOD (usually less than 10 to 15
tanks with various functions operating in a se-
mg/L), refractory organics, heavy metals and
quence. The typical treatment cycle consists of
inorganic salts. In domestic wastewater treat-
the same steps as a single batch activated sludge
ment, a physical-chemical process may be re-
treatment system, fill, react, settle, draw, and
quired as tertiary treatment to meet stringent
idle. The tanks fill in sequence in a multiple tank
permit applications. In industrial applications,
system, allowing for a joint reactor-clarifier unit.
physical-chemical treatment is frequently used as
As with the batch activated sludge system,
a pretreatment process in addition to its use as a
sludge wastage can occur from each reactor dur-
tertiary process. The primary physical-chemical
ing either the react or settle mode. Vitrification
processes included in this manual are:
and dentrification are possible through system
--Activated carbon adsorption.
modifications. The SBR system is capable of
Chemical oxidation.
meeting effluent requirements, with operational
Solids removal (clarification, precipitation).
and maintenance cost roughly equal to, and initial
Each of the treatment alternatives above, as well
cost less than or equal to conventional systems
as, other less common physical chemical processes
(74).
are discussed in this section.
(4) Septic system with recirculating sand fil-
b. Activated carbon adsorption.
ters. A septic system with a recirculating sand
(1) Description. Carbon adsorption removes
filter utilizes a conventional septic or Imhoff tank
m a n y soluble organic materials. However, some
with a sand filter instead of a tile field (166). The
organics are biodegradable, but not adsorbable.
system also includes a recirculation tank which
These will remain in the effluent from physical-
chemical systems. While carbon adsorption is
receives effluent from the septic system as well as
used in physical-chemical secondary treatment
underflow from the sand filter. Effluent from the
systems, its most significant application is as
recirculator tank is pumped to the filter on a time
part of an advanced wastewater treatment sys-
basis. Float controls may also be required to keep
tem employing numerous schemes for additional
the recirculation tank from overflowing. The pur-
constituent removal or as part of a system
pose of the recirculation tank is to keep the sand
treating an industrial wastewater stream.
filter wetted at all times. This system eliminates
(2) Applications. Carbon adsorption has been
the odor problem common with intermittent fil-
adequately demonstrated in numerous pilot and
ters. This system is applicable for small domestic
full scale facilities as a system which can achieve
facilities, recreational areas, etc.
a high degree of organic removal to satisfy water
(5) Overland flow. This technique is the con-
quality standards. The carbon adsorption process
trolled discharge, by spraying or other means, of
can be readily controlled and designed to achieve
effluent onto the land with a large portion of the
various degrees of organic removal efficiency.
wastewater appearing as run-off. Soils suited to
This feature makes it unique as an advanced
overland flow are clays and clay silts with limited
wastewater treatment step. The activated carbon
drainability. The land for an overland flow treat-
system is utilized to treat certain industrial
ment site should have a moderate slope.
process wastewaters from military installations
e. Biological system comparisons. Table 64
including munitions wastes.
provides a comparison of the key wastewater
(3) Design considerations. Both the powdered
treatment processes which must be considered for
and granular forms of activated carbon can be
pollution control programs at military installa-
used. However, powdered carbon currently cannot
tions. These comparisons include major equip-
be justified economically due to problems associ-
ment required, preliminary treatment steps, re-
ated with regeneration of the material; thus, the
moval efficiency, resource consumption, eco-
present state-of-the-art in activated carbon
6-14
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