TM 5-814-3/AFM 88-11, Volume III
g. Natural wetlands. Although true wetlands occupy only 3 percent of U.S. land surface, these areas offer
great potential for recharging water tables and refurbishing wastewaters. Purposeful utilization of the
ecologically complex habitats is new to modern man, who began to recognize around 1970 that fresh and salt
water marshes, swamps, peat bogs, cypress domes, and strands could provide excellent, very inexpensive
treatment. With proper system management and design, wetlands can treat wastewater without damaging
the existing ecology; in fact, nutrient addition can enhance productivity and increase wildlife and overall
aesthetic value. During cold periods, wetlands cannot handle discharges; therefore, storage in lagoons in
necessary. Loading capacity has been estimated at about 40 persons per acre. Artifical wetlands have been
constructed on sandy soil, using impervious plastic liner. Others have been made of less pervious silt and lined
with clay. Peat bogs have been very successfully used in Minnesota and in Europe. In deep swamps-natural
or artificial-water hyacinth, duckweed, wolffia and other aquatic plants have been used to remove nutrients
from wastewater. Limitations of such vegetational techniques have been placed at 35 oN latitude. (See Sanks
and Asano, 1976.)
h. Subsurface application. Basically, the subsurface systems involve either soil mounds or subsurface
filters (chap 6). Such systems ae used wehre adverse soil conditions exist, such as high water table, relatively
impermeable clay-rich soils, or shallow bedrock.
i. Composting of sludge. Where sufficient, inexpensive biomass is available (such as bark, wood chips,
sawdust or other agricultural wastes), sewage may be directly mixed with organic matter and composted in
open windrows or in a ventilated building. Such processes require a great deal of biomass, but the biomass
may be dried in the sun with mechanical turning and then re-used to soak up more sewage. This systems may
be used only if flows are small. Composting has most successfully been used on sludges from any of the unit
operations discussed in this manual. Composting techniques were developed in China and India in ancient
times, rediscovered in Europe in the 1800s, and recently have been utilized in the U.S. (Singley et al, 1982;
Borchardt et al., 1981; Parr et al., 1982.)
(1) Moisture control. Sludges may be composted without addition of organic matter but are generally
too moist. Some bulky organic matter such as the organic portion of solid waste should be used to blend with
the sludge and chipped media to entrain air and soak up moisture. Moisture content should be kept at around
65-72 percent.
(2) Techniques. The easiest and least expensive composting technique involves using partially dried,
recycled compost, some new "bulking agent," and sludge mixed with a front-end loader or with mechanical
mixers to the correct moisture content. The compost is then windrowed and turned "inside-out, outside-in"
several times at about one month intervals. An even simpler technique involves collecting leaves or other
biomass during the year, piling the bulking agent in windrows, and pouring sludge into a depression shoveled
along the length of the windrow. Such simple techniques and a six-month curing period will assure sufficient
pathogen kill to allow use of the compost on military base shrubs, lawns or parks. A more elaborate scheme
has been developed at Beltsville by USDA. In this system, blowers, aeration pipes and, usually, a roofed
building allow mroe rapid "curing;; and a more continuous sludge processing. By this system, about 2.5 dry
tons of sludge may be composted per acre, including space for the building, office, runoff control and
adequate landscaping. Before any composting technique is used, a belt of trees should be established
surrounding the work area for odor control (which in proper composting is minimal), dust dampening and
seclusion. Partially finished compost combined with fresh sludge has been treated with earthworms, which
stabilize compost even more rapidly. Earthworms may be removed from the compost by drum screening; but
on military posts, their main function would be to speed up sludge stabilization and produce an easily handled,
granular soil amendment from what had previously been a noxious slurry.
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