Environmental Engineering Reference
In-Depth Information
instance, for every 22 kg of dry matter ingested, a dairy cow in a lactating state produces 45 kg
of feces and 27 kg of urine totaling 72 kg of manure on “as is basis” (Hart et al., 1997). The
amount of manure produced by an animal is a function of the body weight. A Holstein dairy
cow produces approximately 0.08 kg of manure per kg of body weight per day; therefore, a
typical Holstein weighting 636 kg excretes around 48 kg of wet manure a day (Hubbard and
Lowrance, 1998). When compared with humans, a farm with 2500 dairy cows produces the
same amount of waste as a city with 411,000 people (EPA, 2004).
Beef cattle feedlots produce on average 9,500kg of manure per animal per year (EPA,
2004). In contrast with dairy farms, where the manure is generally handled wet, in feedlots
manure is scraped from the ground at least once a year and handled dry.
Swine generates approximately 8.4 percent of body weight of raw manure per day (Hatfield
et al., 1998); therefore, considering that a finished pig can weight around 114 kg, its produc-
tion of manure reaches 10 kg a day. Swine manure can be handled in a semisolid or liquid state
(Hatfield et al., 1998), the latter being the most common system. Under the liquid manage-
ment practice, manure is washed off the floors and transported via channels or pipes to lagoons
where it undergoes fermentation.
The main solid wastes produced during poultry production are litter from broiler opera-
tions, manure from laying hens, and dead birds (Edwards and Daniel, 1992). After use, litter
contains the original litter material (e.g., straw, wood shavings, saw dust, peanut hull, and rice
hulls) along with manure, feathers, and wasted food. Land application is a common use of
spent poultry litter, but because of its high content of cellulose and low cost, it is also used as
feed for beef cattle.
Dead birds may not seem significant, but a 4-percent mortality rate is normal over the life
cycle of a flock (Edwards and Daniel, 1992); considering that 22.3 × 10
9
kg of live weight
chickens were slaughtered in the United States in 2007 (“Economic data,” n.d.), it translates
into 8.9 × 10
8
kg of dead birds that need disposal, which includes burying, incinerating, render-
ing, and composting (Moore et al., 1998).
Manure is rich in nitrogen, phosphorus, and potassium, and the contents of these three
nutrients depend on the species. In a year, a lactating 636-kg (1400-lb) cow excretes with
manure 136kg (300lb) of nitrogen, 20.45kg (45lb) of phosphorus, and 75kg (165lb) of
potassium (Hart et al., 1997). In intensive animal production farms, the most important appli-
cation of manure is land application for soil fertilization. If this process is done correctly, land
application is one of the best ways to dispose solid waste, recycles nutrients, and avoids the
use of manufactured fertilizers. However, manure, mainly when it is managed in the liquid
state, as happens in dairy and swine production, is heavy, so its application is restricted to the
vicinity of the farm where the manure is produced. This problem is significant in large opera-
tions in which the volume of manure produced normally surpasses the need of nutrients of the
land surrounding the farm. As a consequence, some farms (especially dairy and swine) store
the surplus manure in lagoons, where it undergoes anaerobic fermentation with the subsequent
emissions of atmospheric pollutants, loss of nitrogen, and precipitation of phosphorus. Also,
these lagoons have the potential of leakage, overflow, or rupture with the potential risk of
contaminating surface and subterranean water.
Solid waste from fish farming consists of fecal matter and wasted feed, which in costal
fisheries sinks to the bottom of the ocean near the net pens and in inland freshwater fish farms
to the bottom of ponds. It was believed that in costal fish farms the impact of solid waste was
minimal; however, new evidence shows that the constant release of high biological oxygen
demand material produces oxygen depletion in surrounding waters and nutrient enrichment
that results in algal blooms. Freshwater fish farms need the permanent renewal of water in
ponds to maintain toxic compounds at levels that do not affect the fish. Where regulations do
