cess, and the design and operation of a soil-based
MODELING
land treatment facility must consider these effects.
Land treatment of wastewater is one of the earli-
Types
est bioremediation techniques. The goal of the re-
Many early models were primarily research ori-
search preceding WASTEN was to understand how
ented. Although model development and testing
various soil conditions interact with processes,
is still an active area for research, a number of de-
thereby enabling advantageous manipulation of
sign or management models have been spawned
soil conditions.
from earlier research programs. Management or
operational models range from complex to fairly
simple. Generally there is a compromise between
History
For early man, waste disposal was simple and
the two extremes. More complex models require
without alternatives. In areas of sufficiently low
more input data and user knowledge and, being
population density, slight alterations of the earli-
numerically complex, require more computer
est disposal methods may still suffice. However,
power and time to operate. Relatively simple mod-
as man became less nomadic and population cen-
els require less input data, less operator knowl-
ters developed, sanitation and health problems as-
edge and less computing capabilities, but their out-
sociated with ineffective waste disposal became
put has less information about variations with soil
more urgent. Land application to treat collected
depth. Safeguards are incorporated to prevent
wastes and wastewater has been practiced for
grossly erroneous output.
many years, and there are documented accounts
of wastewater and sludge applications to soil dur-
WASTEN
ing the 16th century (Wierzbicki 1977, Iskandar
WASTEN is a dynamic simulation model de-
1978). Pound and Crites (1975) cited currently op-
veloped at the Cold Regions Research and Engi-
erational systems in the United States that were
neering Laboratory by CRREL researchers and co-
started in approximately 1900.
operating scientists (Selim and Iskandar 1981).
Early practices of waste and wastewater appli-
Originally developed as a research tool, WASTEN
cation to soil were driven by the need to dispose
incorporates a number of features not usually in-
of wastes. Although many soils have considerable
cluded in management-focused models. However,
natural capacity to treat wastes, little attention was
the increased capabilities and availability of com-
given to operation or management. In the mid-
puters has enabled the use of WASTEN for design,
1970s, research focused on identifying and under-
operation and management. In addition to the ini-
tial concentrations and distributions of NH4-N
standing the controlling processes and their inter-
actions. The inherent complexity of the overall
gen) in the soil profile, wastewater application fac-
process of soil-based remediation became increas-
tors that can be input into WASTEN include the
ingly apparent. Although useful empirical data
rate of application, the duration of application, the
could be obtained, the number of uncontrollable
NH4-N and NO3-N concentrations and the waste-
factors operating at any specific site or time made
water application schedule or cycling. WASTEN
a strictly empirical approach intractable. To ad-
can account for plant uptake, evapotranspiration,
dress these issues, modeling was incorporated into
rainfall, soil layers and leaching. Nitrogen trans-
the research programs.
Nitrogen
Wastewater
Denitrified
N
K2
NH4-N in Immobilized
KD
K1
NH4 -N in
NH3-N in
and Exchangeable
Solution Phase
Solution Phase
Phases
Plant
Uptake
Figure 1. Nitrogen transformation processes considered in the nitrogen
submodel. (After Selim and Iskandar 1981.)
2
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