TM 5-814-3/AFM 88-11, Volume III
j. Land spreading of sludges. Soil biota are capable of stabilizing most organic wastes, including oily
sludges. Today, only about 25 percent of sludges are spread on land; even less are composted. However, the
organic materials in sludges are beneficial in restoring fertility to soils disturbed by mining, gravel operations
or poor agricultural practices. There are, however, some major limitations. Concentrated sludges (if not
composted or otherwise stabilized) placed on land should be immediately covered to prevent odor production
and insect breeding.. Sludges can be sliced or injected into soil or into stubble, using special equipment. Deep
snow and deep frost will stop land spreading operations. Although heavy metals concentrations in some city
or industrial sludges hae prevented their agricultural use, this limitation should not apply to waste sludges
on military posts. Particularly useful for design of sludge land disposal is EPA Report 625/1-77-008. (See
also Seabloom et al., 1978.)
15-9. Nitrification.
a. Process description. Nitrification occurs in two steps: first NH4+ is converted to NO2G by
Nitrosomonas bacteria; then the NO2G is converted to NO3G by Nitrobacter bacteria. This process is limited
by the relatively slow growth rate of Nitrosomonas. The following discussion is mainly applicable to activated
sludge processes and nitrification. Additional information may be found in EPA Process Design Manual for
Nitrogen Control.
b. Single-stage nitrification. When nitrification utilizing the activated sludge process is designed as a
single stage, a longer detention time (12 to 24 hours as compared with the usual 2 to 8 hours) is necessary
in the aeration basin in order to provide an effective microbial population. This is interpreted in terms of
"mean solids residence time" (SRT), which is defined as the amount of mixed-liquor, volatile suspended solids
under aeration (in pounds) divided by the sum of suspended solids wasted and suspended solids lost in the
effluent (in pounds per day). The mean solids residence time will be maintained at 10 to 20 days or longer,
depending on the temperature; in terms of hydraulic detention time, 12 to 24 hours is typical. Temperature
has a significant effect on the nitrification reaction rate, which approximately doubles for every 10oC rise in
temperature between 6oC and 25oC. A minimum dissolved oxygen level of 1.0 milligrams per liter is sufficient
for nitrification. However, since dissolved oxygen concentration is a critical parameter, the aeration system
will be designed to provide a residual dissolved oxygen of 2.0 milligrams per liter and pH 8.5, using lime
addition if necessary. The optimum pH has been reported to be 8.4. Lime requirements will vary with the
temperature and must be determined for each case. Nitrification consumes approximately 7.5 milligrams per
liter of alkalinity per milligram per liter ammonia nitrogen oxidized.
(1) Effect of toxic substances. Nitrification can be inhibited by certain toxic substances, such as
halogen-substituted phenolic compounds, thiourea and its derivatives, halogenated solvents, heavy metals,
cyanides, phenol, and cresol. These, however, are usually associated with industrial wastes. (Table 10-4 gives
information on materials that inhibit nitrification.)
(2) Design criteria for single-stage nitrification in activated sludge, extended aeration processes.
The design of single-stage nitrification systems will provide for:
(a) Increased aeration tank capacity and additional aeration to maintain dissolved oxygen level at 2.0
milligrams per liter;
(b) A hydraulic detention time of 12 to 24 hours;
(c) Sludge handling equipment suited to light, poorly compacted sludge, with recycle capacity of 150
percent of average flow;
(d) Food-to-micro-organism ratio of less than 0.25 pounds biochemical oxygen demand per pound
mixed liquor, volatile suspended solids;
(e) Sludge retention time during winter conditions in excess of 20 days; and
(f) Lime feeding equipment to provide alkalinity at a rate of 7.5 milligrams per liter per milligram per
liter of ammonia oxidized, and a pH between 8.0 and 8.5.
15-19
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