into cellular material that can be removed as
particulate matter. Microbial cellular matter
and assimilated organic matter continue to
undergo aerobic degradation via the follow-
ing endogenous respiratory reaction:
C 2 H 9 O 3 N+4O 2 →
0.2C 3 H 9 O 3 N+4CO 2 +0.8NH 3 +2.4H 2 O
Oxygen is required for these reactions.
After treatment, the microbial suspended
solids are separated from the water by grav-
ity sedimentation. Some of the dissolved
solids and small-suspended solid matter in
the form of colloidal and supracolloidal par-
ticles escape secondary clarification. If the
effluent concentration is too high, the flow
should be filtered before discharge, or clarifi-
cation can be improved by the addition of
flocculating chemicals.
Anaerobic Lagoons
Anaerobic lagoons can be designed with
either a single stage or multiple stages. The
disadvantages of multiple stage lagoons are
increased construction and land costs.
Advantages are:
●There is less floating debris on the sec-
ond and third stages, with a reduction in
clogging of the flushing system or irri-
gation pump.
●The first lagoon, containing a higher
concentration of waste, will not over-
flow.
●An adequate amount of bacteria will be
available for waste treatment.
●The resulting effluent will be treated
more thoroughly.According to Safley et al. (1993), the
lagoon start-up should be planned to mini-
mize the amount of biological stress. Time is
required for the appropriate bacteria to
become established. Because anaerobic bac-
teria are slow growers, it may require a year
or more for a lagoon to become fully mature.
Lagoons should be started up in late spring
or summer to permit bacterial establishment
during the warmer weather. The amount of
waste added should be increased gradually
over 2 to 3 months.
Lagoons will accumulate fluid over time,
due to precipitation, and should have fluid
removed periodically. Typically, 40 to 50% of
the active lagoon volume should remain, and
fluid removal should be done only during
warmer months to ensure that the bacteria
can replenish themselves and will not decline
below an effective level. In multiple-stage
lagoons, the effluent should be removed from
the last stage.
After 10 to 20 years, a lagoon will build up
sludge that should be removed to prevent
biological overloading. Three techniques are
used for sludge removal. The first technique
involves agitation equipment to re-suspend
the sludge and pump it out while the con-
tents are thoroughly mixed. The remaining
sludge will resettle once the agitation is
stopped. The second technique involves the
use of a floating dredge to move across
the lagoon while a pump located on the
dredge pumps the sludge over to another
pump located on the shore. The second
pump either sends the sludge to a holding
tank or applies it to the land. The third tech-
nique is to pump the liquid to a lagoon and
permit the remaining sludge to dry naturally.
This long process may require several
months.
Waste sludges may be produced by both
primary and secondary treatment. These
sludges typically require further stabilization
before final disposal. Anaerobic and aerobic
lagoons are frequently referred to as stabi-
lization ponds. They have been used for
wastewater treatment and sludge stabiliza-
tion. Use of this treatment technique has
increased since the 1950s because of the rel-
atively low capital investment, low operating
costs, and ease of operation. Anaerobic andWaste Product Handling 225