1
technical features
ONSITE AND DECENTRALISED
WASTEWATER SYSTEMS
Advances from a decade of research and educational efforts
RL Siegrist, JE McCray, KS Lowe, TY Cath, J Munakata-Marr
ABSTRACT
Throughout the United States and
worldwide, solutions to wastewater
infrastructure need to be effective in
protecting public health and preserving
water quality while also being acceptable,
affordable and sustainable. Onsite and
decentralised systems have the potential
to achieve these goals in rural areas, periurban developments, small towns and
urban centres in larger cities.
These systems have evolved to include
an array of devices and technologies that can
be assembled to achieve varied discharge
or resource recovery and recycling objectives.
New mathematical models and decision
support tools enable proper system selection
and design for a particular application. To
achieve needed advances in the science
and engineering of onsite and decentralised
systems and help assure integration of
the outcomes into practice, research and
educational efforts have been essential.
INTRODUCTION
In the US today, most people have ready
access to safe drinking water and adequate
sanitation as a result of major investments
during the 20th century. The situation is similar
in many other industrialised nations around
the world. As we entered the 21st century,
centralised water treatment plants and piping
networks produced and distributed drinking
water while sewers collected wastewater for
treatment at remote plants.
In the US, centralised water and wastewater
systems were serving about 85% and 75% of
the population, respectively. However, there
were growing concerns about the sustainability
of large centralised systems. In the US, many
of the components of large centralised
systems were at or approaching the end
of their design life spans and rehabilitation
options were often limited and extremely
costly. In addition, some of the potential flaws
in centralised systems were becoming more
apparent. For example, nearly 50% of the safe
drinking water produced is typically wasted
as a result of water distribution losses (~20%)
and clean water use for flushing toilets (~30%).
Centralised systems can also lead to
unplanned urban sprawl, localised water
resource depletion, excess consumption of
chemicals and energy, release of untreated
sewage through leaking sewers and sewer
overflows, and barriers to beneficial recycling
and reuse. As evidenced by recent events in
the US and abroad, centralised systems are
also subject to upsets during natural disasters
and may be targets of terrorist activities.
In contrast to the larger centralised
systems established in urban areas,
private wells and septic systems were
commonly used in rural and suburban
areas. During much of the 20th century,
many viewed these systems as temporary
with a vision that, sooner or later, they
would be replaced by connection to
centralised systems as these systems
were expanded across the US. During this
period, onsite and decentralised wastewater
systems were not designed or implemented
to achieve explicit treatment and reuse
objectives over long-term permanent
use. Not surprisingly, such systems suffered
performance deficiencies ranging from
hydraulic failures to localised contamination
of groundwaters and surface waters.
These deficiencies were attributed
to varied causes including poor system
siting, improper design, faulty installation,
and/or inadequate operation and
maintenance. To support a growing vision
that onsite and decentralised systems were
not temporary, but rather were a permanent
component of a sustainable wastewater
infrastructure, research and educational
initiatives, along with changes in regulatory
requirements, sought to improve the
standard of practice and mitigate many
of the past performance deficiencies
(eg, USEPA, 1997; Siegrist, 2001).
Based on research and development
efforts over the past decade or more,
modern onsite and decentralised systems
have evolved to include a growing array of
approaches, devices and technologies that
can be applied at the development level
up to watershed scale. Ultra low-demand
fixtures or source separation plumbing can
enhance water infrastructure by minimising
water demands and maximising reuse in
buildings and developments spanning rural,
peri-urban and urban areas. Treatment can
be achieved using anaerobic and aerobic
bioreactors, porous media biofilters,
sorbent filters, membrane separation
units, constructed wetlands, soil treatment
units, UV disinfection units and other
technologies. Reuse of reclaimed water
can occur through toilet flushing, landscape
irrigation and other applications.
The vision of onsite and decentralised
systems is still unfolding and the
possibilities for the future are openended. One vision is that as planning
and design of sustainable water and
wastewater infrastructure occurs, onsite and
decentralised systems will be universally
and equitably considered across all scales
of development (e.g., individual buildings,
cluster developments, communities,
watersheds). Any automatic predisposition
towards more centralised infrastructure will
have vanished. Modern infrastructure will
be characterised by low-demand plumbing
systems, treatment of wastewater at or
near the point of generation, reclamation
and reuse of wastewater resources, use of
sensors and monitoring devices to verify
and enhance performance, and remote
process control and system management
to monitor and automatically correct any
system malfunction. Systems will commonly
mimic natural processes to achieve
performance objectives while minimising
water, energy and chemical use, and
enabling beneficial reuse.
A DECADE OF RESEARCH
AND EDUCATIONAL
EFFORTS
Among the research and educational
efforts initiated in the US during the 1990s,
the Small Flows Program was established
at the Colorado School of Mines (CSM)
in Golden, Colorado. Highlights of some
of the research and educational activities
carried out over the past decade are
presented here.
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Table 1. Average daily wastewater flow rates from residential dwellings based
on field monitoring by Lowe et al. (2009) compared to overall averages of two
earlier studies.
Study average flow
(L/day/person)
Reference and study characteristics
Average
Median
Std. Dev.
Lowe et al. (2009) – Building sewer flows measured at
each of 17 houses in Colorado, Minnesota and Florida,
US, in 2008–09
207
171
143
Mayer et al. (1999) – Indoor water usage measured at
each of 1,188 houses in 12 cities in Colorado, California,
Oregon, Washington, Arizona, Florida, US and Ontario,
Canada in the 1990s
262
229
150
USEPA (1980) – Based on multiple studies of water
use or wastewater flows conducted by different
investigators during the 1960s and 1970s
172
151
–
Table 2. Typical domestic wastewater composition determined by Lowe et al. (2009)
and reported in two other published sources that are commonly used for onsite
system design.
Lowe et al. (2009)
USEPA
(2002)
Crites &
Tchobanoglous (1998)
Constituent
Units
Median
Range
Range
Range
TSS
mg/L
232
22–1690
155–330
100–350
Oil & grease
mg/L
50
10–109
–
50–150
cBOD5
mg/L
420
112–1101
155–286
110–400
COD
mg/L
849
139–4584
500–660
250–1000
TOC
mg/L
184
35–738
Not rept.
80–290
Total N
mg-N/L
60
9–240
26–75
20–85
Total P
mg-P/L
10.4
0.2–32
6–12
4–15
Research Highlights Several areas have
been the focus of sustained research activities,
including projects to: 1) determine the flow
and composition of modern onsite wastewater
streams; 2) evaluate the performance
dynamics of bioreactors and biofilters,
including their integration with soil-based
unit operations; 3) evaluate the performance
of decentralised systems utilising membrane
bioreactors; and 4) develop mathematical
models and decision support tools. A short
discussion also highlights considerations
important to achieving performance potential
when systems are implemented under normal
field conditions.
Characterising Flow and Composition
of Onsite Wastewaters Quantitative
understanding of water use and wastewater
characteristics is
important for proper
system selection and
design. Until recently
much of the available
characterisation data
were from studies
completed more
than 20 years ago.
Recent and ongoing
CSM research
projects have been
focused on advanced
characterisation
of modern waste
streams. For example,
Figure 1. Cumulative frequency distribution of total
in one recent CSM
phosphorus loading rates based on wastewater monitoring at
17 residential dwellings in Colorado, Florida, and Minnesota,
project, over 150
which included 24-hour flow-weighted composite sampling
literature sources were
during each season (2008–2009) (Lowe et al., 2009).
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analysed to obtain characterisation data for
conventional constituents, microorganisms
and trace organic compounds in raw
wastewater and septic tank effluent (STE)
from domestic (single and multiple), food,
medical and non-medical sources (Lowe
et al., 2006). Field monitoring was then
completed at 17 domestic sites in three
regions of the US (Lowe et al., 2009).
A specialised apparatus was fabricated
to collect 24-hour composite samples
of raw wastewater and STE during each
season of the year. Analyses were made
for a suite of wastewater parameters (e.g.,
flow, temperature, pH, cBOD5, nutrients,
microorganisms, and trace organic
compounds). Example results are
presented in Tables 1 and 2 and in Figure 1.
Characterisation data for trace organic
compounds have also been obtained
through field monitoring at 30 sites in
Colorado (Conn et al., 2006) in addition to
the 17 sites studied by Lowe et al. (2009).
This research revealed that many organic
compounds could be present in wastewaters
at relatively low but potentially important
concentrations. Organic compounds
associated with consumer product chemicals
(e.g., caffeine, nonylphenols, Triclosan)
routinely occur at low to high levels
depending on the source (e.g., residential
dwellings, restaurants, vs. convenience
stores, etc.) (Conn et al., 2006, Lowe et
al., 2009, Conn et al., 2010a) (Table 3).
Pharmaceuticals, pesticides, and flame
retardants can also occur, but much less
pervasively and typically at much lower
levels (Conn et al., 2010a).
Evaluating Performance of Onsite Unit
Operations and Systems Onsite and
decentralised systems involve unit operations
that can be combined to achieve up to
tertiary treatment levels with disinfection.
Different types of systems can enable
different discharge and reuse options. For
onsite and decentralised applications, flow
and composition can vary widely, usage
can be discontinuous, and the design life
can be undefined but often decades long.
As a result, the dynamics of performance
as affected by design, operation and
environment can be quite complex. Research
carried out at CSM has investigated the
performance of contrasting systems through
laboratory experiments, field-testing at the
Mines Park Test Site located on the CSM
campus, and full-scale systems monitoring.
This work has focused in part on optimising
the level of treatment to be carried out in
a confined unit (e.g., a bioreactor) versus
a natural system operation (e.g., a network
of soil infiltration trenches) (Figure 2).
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technical features
Table 3. Concentrations of trace organic compounds associated with consumer
product chemicals in wastewaters from 30 small residential, commercial and
institutional sources (Conn et al., 2006).
Use
Detection
frequency
Concentration
range (μg/L)
Stimulant
100%
0.5–E 9,300 1
Coprostanol
Animal sterol
100%
0.5–E 7,100
Cholesterol
Animal sterol
100%
0.5–E 2,200
Metal chelation
100%
0.5–1,700
Trace organic compound
Caffeine
Ethylenediaminetetraacetic acid
(EDTA)
4-Methylphenol
Disinfectant
98%
0.5–E 4,500
4-Nonylphenolethoxycarboxylates
(NPEC)
Surf. metabolite
95%
2–320
Nitrilotriacetic acid (NTA)
Metal chelation
82%
0.5–130
4-Nonylphenol (NP)
Surf. metabolite
77%
2–340
4-Nonylphenolethoxylates (NPEO)
Surf. metabolite
75%
2–170
Antimicrobial
agent
68%
0.5–82
5-chloro-2-(2,4-dichlorophenoxy)
phenol (Triclosan)
1
E = estimated value (concentration exceeded maximum value on standard curve).
ST-TFU > ST (Figure
3). The TFU achieved
an average removal
Septic tank w/
efficiency (mg/L) of
effluent screen
90% for carbonaceous
Soil infiltration
Raw
BOD5 (cBOD5), 30% for
dispersal trenches
Wastewater
nitrogen, and >95%
Septic tank
for fecal coliform
w/ Textile biofilter
bacteria. The removal
efficiency of the MBR
Disk
filter
was 99% for cBOD5,
Soil drip
61% for nitrogen,
dispersal lines
Membrane Bioreactor
and 100% for fecal
Figure 2. Schematic of the onsite wastewater system
coliform bacteria. The
components involved in treatment unit research at the
Colorado School of Mines.
dissolved organic
carbon in the effluents
Onsite Treatment in Septic Tanks, Textile
averaged 34, 11, and 6 mg/L for the ST,
Biofilters and Membrane Bioreactors In one
TFU and MBR, respectively. Organic carbon
CSM project, a septic tank, textile biofilter
characterisation studies revealed that in
unit (TFU), and membrane bioreactor (MBR)
addition to reducing the total concentration
were established at the Mines Park Test
of organic matter in the STE, the TFU and
Site and used to treat wastewater from an
MBR transformed the organic matter.The
8-unit apartment building. Based on 16–28
STE contained saturated organic compounds
months of monitoring, the overall effluent
of low to high molecular weight. The TFU
quality produced followed this relative
effluent had a buildup of humic and fulvic
acid material that was more aromatic in
ranking (higher to lower quality): ST-MBR >
character. The organic matter in the MBR
effluent was similar to TFU effluent, but
with more developed humic and fulvic acid
substances. Directly related to the treatment
efficiency achieved, the operational
complexity, maintenance requirements,
energy use and cost were higher for the MBR
compared to the TFU, which was somewhat
higher compared to a ST.
Studies of full-scale operating systems
have also been insightful regarding system
design and performance. For example,
performance data were available for 30
onsite wastewater treatment systems
installed at homes in Colorado (Wren et
al., 2004). These data were evaluated and
a subset of eight systems employing textile
biofilter units was selected for additional
investigation. Field monitoring revealed
a wide variation in the effluent quality
produced for BOD5 (4 to 45 mg/L), TSS
(1 to 83 mg/L), and total N (12 to 136 mg/L).
A virus tracer using bacteriophages revealed
a potential to achieve 99.9% virus removal.
While unit operations and systems can have
potential to produce high quality effluents,
achieving this under field conditions requires
proper design and routine operation and
maintenance.
In another CSM project where trace
organic compounds were characterised
in wastewaters at 30 sites (see Table 3),
additional monitoring was completed to
assess removal in septic tanks, biofilters
and constructed wetlands (Conn et al.,
2006). Removal efficiencies ranged from
<1% to >99%, with the efficiency dependent
on treatment unit removal mechanisms
and the properties of the trace organic
compounds. For example, compared to
anaerobic treatment in a septic tank, aerobic
treatment in a textile biofilter enhanced
the removal of trace organic compounds
that could be aerobically biodegraded.
In a companion project completed at the
Mines Park Test Site, this relationship was
further revealed, as the removal efficiency in
a textile biofilter was generally greater than
in a septic tank (Table 4) (Conn et al., 2010b).
Figure 3. Cumulative frequency distributions for the concentrations of COD, total nitrogen and fecal coliform bacteria in the
effluents produced by a septic tank (STE), textile biofilter (TFU), or membrane bioreactor (MBR).
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technical features
Table 4. Concentrations of trace organic compounds in the effluents from a septic
tank versus a textile biofilter used to treat wastewater from an 8-unit apartment
building (Conn et al., 2010b).
Parameter
Units
Septic tank
effluent
Textile biofilter
effluent
DOC
mg/L
30 (8.4)
16 (4.2)
NH4
mg-N/L
34 (7.5)
3.8 (1.1)
NO3
mg-N/L
0.85 (0.48)
19 (3.8)
Caffeine
μg/L
34 (8.7)
0.87 (0.49)
Ethylenediaminetetraacetic acid (EDTA)
μg/L
24 (1.0)
33 (13)
Nitrilotriacetic acid (NTA)
μg/L
3.7 (2.3)
4.0 (1.9)
4-Nonylphenol
μg/L
3.3 (1.4)
<RL1 of 2
4-Nonylphenolethoxycarboxylates (NPEC)
μg/L
63 (23)
7.3 (3.6)
4-Nonylphenolethoxylates (NPEO)
μg/L
1.6 (0.97)
<RL of 1
5-chloro-2-(2,4-dichlorophenoxy)phenol (Triclosan)
μg/L
9 (3.3)
<RL of 0.2
1
<RL = result was less than the reporting limit based on the methodology used.
Figure 4. Infiltration rate decline (left) and cumulative mass removal over two years
for total N at 60 cm and 120 cm depth below the infiltrative surface (right) (Lowe
and Siegrist, 2008).
Figure 5. Illustration of infiltration rate
loss due to soil clogging with different
effluent qualities applied at 2 or 8 cm/d
(model simulations following Siegrist and
Boyle, 1987, as reported in Van Cuyk et
al., 2005).
Onsite Treatment in Soil Treatment Units
Onsite and decentralised systems often
involve use of soil for wastewater treatment.
In this area, CSM research has focused on
two onsite system approaches: 1) effluent
dispersal into a soil profile using shallow
trenches outfitted with infiltration chambers
(e.g., Van Cuyk et al., 2005; Lowe and
Siegrist, 2008); and 2) effluent dispersal
into the plant rhizosphere using drip tubing
with pressure-compensating emitters (e.g.,
Parzen et al., 2007). In one area of emphasis,
laboratory experiments and field studies
WATER FEBRUARY 2013
revealing the time-dependent and dynamic
interaction of unit hydraulics and purification
processes for conventional pollutants these
studies also provided new insights into the
transformation of organic matter and the
fate of virus and trace organic compounds.
In another project, a replicated factorial
design was employed to evaluate three soil
infiltrative surface architectures (ISA) (open,
gravel-laden or synthetic-stone laden) with
domestic STE applied at two daily hydraulic
loading rates (HLR) (4 or 8 cm/d) (Siegrist
et al., 2005; Lowe and Siegrist, 2008). Pilotscale infiltration trenches were established
in Ascalon sandy loam soils at the Mines
Park Test Site located on the CSM campus.
Based on two years of monitoring, the
effluent infiltration rate declined to very low
levels due to soil clogging at the infiltrative
surface with a time-dependent behaviour
that was consistent with model simulations
(Figure 4). After this period of decline, an
open ISA maintained an infiltration capacity
that was 40% to 80% higher than the other
ISAs tested. Purification of STE in the soil
was very high; the cumulative mass removal
for dissolved organic carbon (DOC), total
N and total P averaged 94%, 42% and 99%,
respectively, while removal of bacteria and
viruses exceeded 99.9%. While there was
no significant difference in purification
based on ISA or HLR, a slight increase in
purification was associated with an increase
in the soil vadose zone depth (e.g., 120 cm
vs. 90 cm below the soil infiltrative surface).
Figure 6. Illustration of relatively
consistent soil pore water concentrations
despite different effluent qualities
applied at 2 or 8 cm/d (20 or 80 L/m2/d)
(Lowe and Siegrist, 2008).
Addition of a treatment unit to produce
effluent of higher quality than typical STE
has the potential to retard soil clogging and
enable application of higher HLRs, resulting
in smaller soil treatment units. Associated
with the treatment unit study described
(e.g., see Figure 3), the three effluents were
applied to replicate pilot-scale infiltration
trenches installed at the Mines Park Test
Site (Van Cuyk et al., 2005). The results of
bromide tracer tests and infiltration rate
measurements made periodically during
operation revealed that some degree of
soil clogging occurred at the soil infiltrative
surface in the sandy loam soil, even with
application of the much higher quality
TFU or MBR effluents (Figure 5).
have quantified the performance effects
of effluent composition, hydraulic loading
rate, and infiltrative surface architecture on
wastewater treatment in sand filter units and
soil infiltration trenches (e.g., Van Cuyk et
al., 2001; Van Cuyk et al., 2004, 2005; Beach
et al. 2005; Siegrist, 2006; Tomaras et al.,
2006; Van Cuyk and Siegrist, 2007; Lowe
and Siegrist, 2008; Tomaras et al., 2009;
McKinley and Siegrist, 2010). In addition to
When comparing system-wide purification
(i.e., ST-soil vs. ST-TFU-soil vs. ST-MBR-soil),
pollutant and pathogen removal efficiencies
were very high. Moreover, soil pore water
concentrations of pollutants (e.g., DOC, N,
P) were consistent across different treatment
systems and soil depths, even although the
applied water qualities were quite different
(Figure 6). The ability of a sandy loam soil to
remove viruses was quite high (e.g., >99.99%
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technical features
PWastewater influent = ~300gal/h (1.14m3/h)
~100 pop. equivalent (based on 70gal/cap/d)
P2 bioreactor tanks each 2,180gal (8.25m³) and
2 membrane tanks each 870gal (3.3m³)
Net flux = 19L/(m2.h) (11.2 g/ft2/d)
PAverage influent concentrations:
• COD = 270–560 mg/L
• sCOD = 110–210 mg/L
• NH4+-N = 24–37 mg/L
• Ortho-P = 8–16 mg/L
• Solids retention time ~45 days
Figure 7. Sequencing Batch Reactor-Membrane Bioreactor system established on the CSM campus and used for
neighbourhood-scale wastewater treatment and water reuse at Mines Park (Cath, 2012).
by 60 cm soil depth), and insensitive to
whether STE, TFU effluent or MBR effluent
had been applied at either 2 or 8 cm/d.
of tailored water reuse for a complex of
apartment buildings on the CSM campus in
Golden, Colorado (Figures 7 and 8).
To understand the fate of trace organic
compounds in a soil treatment unit, a
controlled field experiment was completed
at the Mines Park Test Site. The effluents
from a septic tank or a textile biofilter (Table
4) were applied to the sandy loam soil and
the soil pore water was periodically sampled
at 60, 120, and 240 cm below the soil
infiltrative surface.
For the purposes of this demonstration,
tailored water reuse involves generation
of water with different concentrations
of nitrogen and phosphorus that can be
used directly for plant irrigation. Research
is investigating the effects of tailored
water operations on system performance,
including optimised approaches to control
biological performance, sustain membrane
performance, reduce energy requirements,
and ensure robustness of the system.
Purification of trace organic compounds
(e.g., caffeine, nonylphenols, Triclosan) in
a soil treatment unit principally occurs by
sorption and biodegradation processes.
Achieving high removal efficiency for a
particular organic compound thus depends
on the properties of the compound as well
as the process conditions present in the
soil treatment unit (Conn et al., 2010b).
For example, caffeine and Triclosan in
septic tank or textile filter unit effluents
were completely removed by 60 cm depth
through aerobic biotransformation (Conn
et al., 2010b).
Decentralised Treatment in Membrane
Bioreactors Membrane bioreactors can be
a viable option for wastewater treatment
and water reuse in applications such as
neighbourhoods, high-rise apartment
buildings or commercial developments. At
CSM, a sequencing batch reactor–membrane
bioreactor hybrid system (SBR-MBR) has been
in operation for four years (Henkel et al., 2011;
Cath, 2012; Vuono et al., 2012). The SBR-MBR
was established through the Advanced Water
Technology Center at CSM (www.aqwatec.
com) and is being used in a demonstration
As part of the demonstration, several
operational strategies have been examined
to determine their effects on effluent quality
and energy consumption. Findings
to date have revealed that by altering
operations, tailored water reuse is possible
by controlling the level of N and P removal.
Mathematical Models and Decision Support
Tools Models and Decision Support Tools
can facilitate proper planning and design
of onsite and decentralised systems. In
one area of emphasis at CSM, analytical
and numerical models of varying scope
and complexity have been developed or
refined to aid design of an isolated system
or clusters of soil treatment units, as well
as for assessment of onsite system impacts
at the local, development and watershed
scale (e.g., Beach and McCray, 2003; McCray
et al., 2005; Poeter et al., 2005; Siegrist et
al., 2005; Bumgarner and McCray, 2007;
Heatwole and McCray, 2007; McCray et al.,
2009, 2010; Geza et al., 2009, 2010, 2012).
A prime example of a model that can
be used to predict purification performance
of a soil treatment unit is STUMOD (Soil
Treatment Unit Model) (Geza et al., 2009).
STUMOD was originally developed to
predict the fate and transport of nitrogen
in a soil treatment unit. STUMOD calculates
nitrogen species concentrations with depth
in the soil profile (Figure 9a) and the fraction
of nitrogen remaining with depth (Figure
9b). By repeatedly running STUMOD using
randomly selected values from ranges of
potential input values, the probability that
a certain fraction of the total nitrogen in the
effluent infiltrated will reach a specified soil
depth can be estimated (Figure 9c).
Initial operation: SBR-MBR treatment efficiency:
97% COD removal (15.0 mg/L)
40% PO4 removal (3.4 mg/L PO4)
70% N removal (8.8 mg/L NO3-N)
(expected N removal = 90%)
Optimised operation: SBR-MBR treatment
efficiency:
97% COD removal (15.0 mg/L)
90% PO4 removal (< 1 mg/L PO4)
95% N removal (< 2.0 mg/L NO3-N)
Figure 8. Illustration of the effluent quality from the SBR-MBR at Mines Park
as affected by operational strategy (Henkel et al., 2011; Vuono, 2012).
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technical features
multiple onsite and decentralised systems
on water quality within a watershed where
numerous sources contribute flow, pollutants
and pathogens (McCray et al., 2005; Siegrist
et al., 2005; Lemonds and McCray, 2007;
McCray et al., 2009; Geza et al., 2010).
Concentration of N species with depth (mg-N/L)
Mass per time per footprint area (g-N/m2/day)
Probability distribution that a given removal
will occur under specific conditions (e.g., there
is a 50% probability of 70% nitrogen removal
at 60 cm depth)
Figure 9. STUMOD simulation of nitrogen
fate when 2 cm/d of STE is applied to a
soil treatment unit installed in a sandy
loam soil (Geza et al., 2009, 2010, 2012,
as reported in McCray et al., 2010).
While models such as STUMOD
provide insight into the operation of soil
treatment units and quantitative estimates
of performance as affected by a range of
conditions, numerical models can better
address many complex processes and lesscommon operating conditions. Modellers at
CSM were among the first to use a numerical
model, HYDRUS 2-D (Šimunek et al., 1999)
to examine the relationships between soil
treatment unit design and environmental
conditions and the resulting hydraulic and
purification performance (e.g., Beach and
McCray, 2003; Bumgarner and McCray,
2007; Heatwole and McCray, 2007).
Models can be particularly helpful
to understand the cumulative effects of
WATER FEBRUARY 2013
In a major CSM project, the Watershed
Analysis Risk Management Framework
model (WARMF) as well as the BASINS/
SWAT and MANAGE models were set
up for the Blue River watershed in Summit
County, Colorado (Siegrist et al., 2005).
This watershed contains over 1,000 onsite
wastewater systems and other non-point
and point sources of pollution, and over
600 onsite drinking water wells along with
community wells and surface water supplies.
Compared to urbanised development and
centralised wastewater treatment plant
discharges, onsite wastewater systems were
not a principal source of water pollutants
as determined by: 1) source load mass
balance calculations; 2) model simulation
results; and (3) water quality monitoring
and analysis of spatial and temporal trends.
Moreover, based on WARMF simulations of
different wastewater management scenarios,
extending central sewers and conversion
of onsite systems to a central treatment
plant offered little or no benefit to water
quality protection.
Achieving System Performance Potential
When onsite and decentralised systems are
implemented under normal field conditions
(i.e., not within a research project), the
potential performance based on process
principles and research observations may or
may not be realised. To achieve a system’s
performance potential, the findings of
research such as highlighted earlier – as
well as observations made during field
experiences – have affirmed the need for
proper design and assurance that required
operation and maintenance activities
will occur. Even a simple septic tank unit
operation requires proper design and
periodic removal and proper disposition of
septage. Unit operations and systems that
are implemented to achieve high quality
effluents in a robust and reliable fashion
(e.g., textile biofilters, membrane bioreactors)
have operational complexity (e.g., pumps,
pressurised piping, aerators, chemical feed,
etc.). The more operationally complex a
system is, the greater the need for and extent
of management and oversight to ensure that
the system’s performance potential is actually
realised under normal field conditions.
Education Highlights During the past
decade or more, research – such as
highlighted in this paper – has advanced
the science and technology of onsite
and decentralised systems. However,
research findings do not automatically
yield improvements in practices. Clear and
compelling research findings can certainly
help foster improvements. But improved
practices and advances in applications also
require translation of research findings so
they convey knowledge and know-how to
designers, contractors, regulators, policy
makers and others. This helps ensure that
findings can be adopted into modern
regulations and requirements.
It is also critical that research findings
be incorporated into curriculum for the
education of students who can help catalyse
improvements and advances. Concerning
this latter point, a semester-long course for
seniors and graduate students has been
developed at CSM and routinely delivered
during the past five years. “ESGN460.
Onsite Water Reclamation and Reuse”
is a 15-week long course focused on the
selection, design and implementation
of onsite and decentralised wastewater
systems. A textbook is being prepared
to support delivery of this type of course
and Springer will publish it by early 2014.
ACKNOWLEDGEMENTS
Numerous individuals and organisations
have contributed to the research highlighted
in this paper. The efforts of past and
current students at CSM are gratefully
acknowledged, including: John Albert,
Jennifer Bagdol, Debbie Huntzinger-Beach,
Kathy Conn, Charlotte Dimick, Sarah
Doyle, Kirk Heatwole, Shiloh Kirkland,
Paula Lemonds, Andy Logan, Jim McKinley,
Rebecca Parzen, Tanja Rauch, Nate Rothe,
Kyle Tackett, Mia Tucholke, Dave Vuono,
Ryan Walsh and Abigail Wren.
Current and former research staff and
post-doctoral fellows include: Drs Sheila Van
Cuyk, Mengistu Geza and Jochen Henkel.
Contributing faculty have included the authors
of this paper as well as Drs Jörg Drewes,
Eileen Poeter, John Spear and Geoffrey Thyne.
Program funding has been acquired
through CSM and its Research Foundation,
the USEPA National Decentralised Water
Resources Capacity Development Project,
USGS National Institutes of Water Research,
National Science Foundation, Water
Environment Research Foundation and
Department of Education, along with contracts
and philanthropic grants from private industry.
7
technical features
THE AUTHORS
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