Environmental Engineering Reference
In-Depth Information
of tropical corn in summer (both for silage). These systems were investigated at
field scale under a pivot irrigation system and in replicated small plots, and included
comparisons between manure and commercial fertilizer that was applied at rates
based on soil tests following each crop. Newton et al. [49] showed that dairy lagoon
wastewater could be successfully used for triple cropping systems including both
cropland and winter grazing of pasture.
Hubbard et al. [56] showed that vegetated buffer systems can effectively assim-
ilate N from swine lagoon wastewater. In a study on replicated 30X4 m plots they
tested three different vegetated buffer treatments at two different wastewater rates.
The treatments were (1) 10 m grass buffer draining into 20 m existing riparian zone
vegetation; (2) 20 m grass buffer draining into 10 m existing riparian zone vegeta-
tion; and (3) 10 m grass buffer draining into 20 m maidencane (
Panicum hematomon
Schult 'Halifax'). The wastewater, which contained an average N concentration of
160 mg L
-1
N was applied to the plots either once per week (1285 L plot
-1
)or
twice per week (2570 L plot
-1
). Nitrogen concentrations in surface runoff and shal-
low groundwater increased over time at the top ends of the plots but showed little
increase at the bottom ends of the plots. Overall, all three vegetative treatments were
successful in assimilating N from the wastewater. In a similar study, but at the farm
scale with highly contaminated wastewater from the anaerobic lagoon of a com-
mercial hog farm, Hubbard et al. [57] found that NO
3
-N concentrations in shallow
groundwater 20-30 m downslope from the overland flow application point were still
near background levels after five years of wastewater application.
9.2.2 Constructed Wetlands
Another method of treating contaminated surface waters is by using constructed
wetlands. Constructed wetlands, that is, the integrated physical, chemical, and
biological processes that occur in the substratum soil (or gravel)-water-plant ecosys-
tem, have grown in popularity for wastewater treatment since the early 1970s
[58]. During the past three decades, constructed wetlands have been used to treat
municipal wastewater, acid mine drainage, industrial wastewater, agricultural and
storm runoff, and effluent from livestock operations [41, 42]. Their advantages
include moderate capital costs, very low energy consumption and maintenance
requirements, and benefits of increased wildlife habitat [59]. Many researchers have
demonstrated that natural treatment systems can remove significant amounts of SS,
organic matter (OM), N, P, trace elements, and microorganisms (including algae)
from wastewater [60-63].
Lin et al. [41] used a pilot-scale wastewater treatment system consisting of free
water surface (FWS) and subsurface flow (SSF) constructed wetlands arranged in
series for treatment of aquaculture wastewater. Their study was conducted to exam-
ine system start-up phenomena and to evaluate system performance in removing
inorganic N and P from aquaculture wastewater under various hydraulic loading
rates (1.8-13.5 cm day
-1
). They found excellent N removals. The efficiencies were
86-98% for NH
4
-N and 95-95% for total inorganic nitrogen (TIN) and removal
