Environmental Engineering Reference
In-Depth Information
primarily with fertilizer use. Nitrogen contamination of groundwater from animal
waste has been linked to both grazing animals and to land application of wastewater
from Confined Animal Feeding Operation (CAFO) lagoons [20, 24-28].
9.1.2 Phosphorus
Phosphorus is of environmental concern because excess amounts in surface water
bodies may cause eutrophication. Phosphate (PO
4
-P) is a soluble agricultural chem-
ical that may be moved from point of application by surface runoff or move out
of the soil surface with percolation. In general, PO
4
-P is considered to be of con-
cern primarily for surface runoff since it binds to Fe, Al or Ca in the soil depending
on pH and is not readily leachable. Soluble PO
4
-P and PO
4
-P associated with sed-
iment in surface runoff have been found to vary linearly with P application rate
[29]. Low concentrations of dissolved PO
4
-P have been found in runoff from deep
incorporation of fertilizers [30]. Movement of PO
4
-P through the soil profile varies
with soil texture. For nonsandy soils, the leaching of PO
4
-P with percolating water
is extremely low or undetectable. The PO
4
-P content of percolate from non-sandy
soils can be within an order of magnitude of 0.1 mg L
-1
[31]. Numerous investiga-
tors [31-34], however, have shown that in very sandy soils, PO
4
-P will move down
the profile to a considerable depth (>1.0 m). On the basis of diffusion studies, Olsen
and Watanabe [35] concluded that there was an eight-times greater risk of PO
4
-P
pollution of groundwater from sands than from clays. The contribution of P from
animal wastes can represent a significant fraction of the P circulating in agricultural
systems. Where fecal matter is deposited into farm ponds or streams the direct effect
may be noticeable.
9.1.3 Wastewater Lagoons
A number of methods have been designed to handle animal wastes from CAFOs.
Most systems involve primary treatment in wastewater lagoons for settling of solids
and loss of gases by volatilization. Anaerobic treatment systems (lagoons) are used
widely for practical treatment and storage of swine manure [36, 37]. These lagoons
are typically earthen and rely on bacteria to stabilize organic material [38]. Lagoons
are relatively simple to operate and maintain, and are relatively inexpensive com-
pared with other treatment methods [39]. Dairy operations may use a two lagoon
system with aerators commonly used in the second lagoon. Animal wastewater
lagoons are extreme examples of contaminated surface water bodies.
Aquaculture operations for production of fish or shrimp may also produce
wastewater. The water in the ponds must be periodically replaced to avoid dis-
ease, low O
2
, algae, and/or pH problems associated with the accumulation of waste.
Organic solids, mainly generated from feed residue and fish excreta, are the primary
pollutants to be removed from an aquaculture effluent or in a recirculating aqua-
culture system [40]. These solids can become an additional source of O
2
demand,
