metabolic studio’s pilot wetland study treatment
TRANSCRIPT
Metabolic Studio
1745 N Spring St. #4
Los Angeles, CA 90012
(323) 226-1158
Metabolic Studio’s Pilot Wetland Study
Treatment Performance Report (DRAFT) - A Part of the Bending the River Back Into the City
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Metabolic Studio Pilot Wetland Study
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TABLE OF CONTENTS
Page
1. INTRODUCTION ................................................................................................. 1
1.1 Background ............................................................................................. 1
1.2 Water Quality Objective ...................................................................... 2
1.3 Baseline Conditions ................................................................................ 3
1.4 HSSF Wetlands and Design Constraints ............................................ 4
1.5 Study Objectives ..................................................................................... 5
2. TREATMENT PERFORMANCE .......................................................................... 7
2.1 Indicator Bacteria .................................................................................. 7
2.2 Physical and Chemical Water Quality Parameters .................... 10
3. HYDRAULIC RETENTION TIME ....................................................................... 17
4. VEGETATION COVERAGE ............................................................................ 19
5. CAPITAL AND O&M COSTS.......................................................................... 21
5.1 Capital Costs ......................................................................................... 21
5.2 O&M Costs .............................................................................................. 22
5.3 Total Annual Costs ................................................................................ 22
6. CONCLUSIONS ................................................................................................ 24
7. REFERENCES ..................................................................................................... 26
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ii Metabolic Studio Pilot Wetland Study
LIST OF TABLES
Table 1 Mean and Theoretical Hydraulic Retention Time ........................ 17
Table 2 Capital costs for one and three three-tank in-series systems ... 22
Table 3 Annual O&M costs for one and three three-tank in-series
systems ....................................................................................................... 22
Table 4 Annual operating costs for one and three three-tank in-
series systems ............................................................................................ 23
Table 5 Physical and Chemical Water Quality Parameters Measured
in the Field ................................................................................................. 29
Table 6 Physical and Chemical Water Quality Parameters Measured
in the Laboratory ..................................................................................... 30
Table 7 Water Quality Data of Captured Rainwater Stored in
Cisterns Onsite and LAR Water ........................................................... 32
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iii Metabolic Studio Pilot Wetland Study
LIST OF FIGURES
Figure 1 Locations of Bending the River Back into the City, the
wetland site, and grab sampling ......................................................... 2
Figure 2 Total coliform geometric mean concentration for samples
collected at selected locations ........................................................... 7
Figure 3 Fecal coliform geometric mean concentration for samples
collected at selected locations ........................................................... 8
Figure 4 Enterococci geometric mean concentration for samples
collected at selected locations ........................................................... 9
Figure 5 Average total suspended solids at selected locations along
the treatment systems ........................................................................... 11
Figure 6 Average turbidity at selected locations along the
treatment systems ................................................................................... 12
Figure 7 Average conductivity at selected locations along the three
treatment systems ................................................................................... 13
Figure 8 Average oxidation reduction potential (ORP) at selected
locations along the three wetland systems .................................... 14
Figure 9 Average BOD5 at selected locations along the treatment
systems ....................................................................................................... 15
Figure 10 Average nitrate concentration at selected locations along
the three wetland systems ................................................................... 16
Figure 11 RWT effluent concentration for the gravel and clay pellet
wetlands .................................................................................................... 18
Figure 12 Vegetation coverage of individual wetland cells in the three
wetland systems. ..................................................................................... 20
Figure 13 a) Water truck; b) floatable pump .................................................... 33
Figure 14 a) Influent storage 1 at the lower level and fabric filter
installation prior to refilling the storage tanks; b) influent
storage 2 and the intermediate tank ................................................ 33
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iv Metabolic Studio Pilot Wetland Study
Figure 15 The pilot wetland site plan ................................................................... 34
Figure 16 The layout of the wetland plants in each wetland cell. ............. 35
Figure 17 A flow control and recording setup installed at the influent
of the clay pellet wetland, C. ............................................................. 35
Figure 19 An effluent sampling port located at the end of each
wetland cell .............................................................................................. 36
LIST OF APPENDICES
Appendix 1 – Water Quality Results
Appendix 2 – Rainwater Versus LAR Water Quality
Appendix 3 – Materials and Methodology
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Acronyms and Abbreviations
v Metabolic Studio Pilot Wetland Study
BOD5 Five-Day Biochemical Oxygen Demand
BRBC Bending the River Back to the City
COD Chemical Oxygen Demand
CTRS California Toxic Rule Standard
DCT Donald C. Tillman Water Reclamation
Plant
DTLA Downtown Los Angeles
E. coli Escherichia coli
HRT Hydraulic Retention Time
HSSF Horizontal Subsurface Flow
IN Influent
LACDPH Los Angeles County Department of Public
Health
LAG Water Reclamation Plants
LAR Los Angeles River
MCL Maximum Contamination Level
MPN Most Probably Number
NTU Nephelometric Turbidity Units
ORP Oxidation Reduction Potential
PAHs Polycyclic Aromatic Hydrocarbons
PCBs Polychlorinated Biphenyls
PSF Pounds Per Square Foot
RWT Rhodamine WT
TDS Total Dissolved Solids
TOC Total Organic Carbon
TSS Total Suspended Solids
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1 Metabolic Studio Pilot Wetland Study
1. INTRODUCTION
1.1 Background
Water scarcity due to climate change and prolonged droughts in arid
regions has fueled a growing interest in capturing and using stormwater
and dry-weather runoff for non-potable water applications. These
innovative reuse approaches not only help diversify local water resources,
but also help municipalities achieve discharge requirements specified in
National Pollutant Discharge Elimination System (NPDES) Permits meeting
ambient water quality criteria, such as Total Maximum Daily Loads
(TMDLs).
The 48-mile long Los Angeles River (LAR) flows through the heart of
Downtown Los Angeles (DTLA) discharging into the Pacific Ocean via
Queensway Bay in Long Beach. LAR flow in the DTLA area is comprised
primarily of 1) Title 22 recycled water discharges from the Los Angeles-
Glendale (LAG) and Donald C. Tillman (DCT) Water Reclamation Plants,
2) groundwater underflow from the Glendale Narrows and Arroyo Seco
tributary (US Army Corps of Engineers, 2013), and 3) overflows from the
Japanese Garden, Lake Balboa, Bull Creek, and the Sepulveda Basin
Wildlife Area (US Army Corps of Engineers, 2012).
Dry-weather base flow in the LAR that exceeds 72 cubic-feet-per-second
(cfs) is estimated to be greater than 90% of the time in the DTLA area
(Geosyntec Consultants, 2013). Based on a ten-year average discharge
of 62 cfs, combined discharges from the LAG and DCT water reclamation
plants account for over 80% of total dry-weather flow (Geosyntec
Consultants, 2013). Such a unique flow composition makes the LAR water
in the DTLA area relatively clean.
The capture of dry-weather runoff from the LAR to provide non-potable
water for spray irrigation in nearby public parks was proposed in 2013
(Geosyntec Consultants, 2013) as part of the “Bending the River Back to
the City” (BRBC) project – an alternate water use project envisioned by
Metabolic Studio (the Studio). The project site is located two miles
northeast of DTLA between the 110, 5, and 101 freeways (Figure 1). The
proposed project will consist of an inflatable rubber dam within the LAR
channel diverting dry-weather flow to a water wheel. The water wheel lifts
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the water to a treatment and storage system prior to distribution to nearby
parks for spray irrigation. Less than one percent of the diverted flow will be
lifted by the water wheel, while the remaining flow will immediately flow
back into the LAR through a subsurface flow channel.
Figure 1 Locations of Bending the River Back into the City, the wetland site, and grab
sampling
1.2 Water Quality Objective
The Los Angeles County Department of Public Health (LACDPH) sets the
water quality objectives for the use of non-potable water sources within
the County of Los Angeles, including runoff from the LAR, for aboveground
non-potable uses. At the time when BRBC was proposed, Guidelines for
Harvesting Rainwater, Stormwater, & Urban Runoff for Outdoor Non-
Potable Uses (LACDPH, 2011. “2011 Guidelines”) was the effective
guidelines. It stipulated that non-potable water for aboveground outdoor
non-potable uses shall meet the following single sample limits for indicator
bacteria at the point of use when distributed offsite:
• Total coliforms <10,000 CFU/100mL;
• Fecal coliforms <400 CFU/100mL; and
• Enterococcus <104 CFU/100mL.
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It is noted that the above limits are the same as the Marine REC-1 Water
Quality Objectives for the Long Beach City Beaches and Los Angeles River
Estuary (USEPA Region IX, 2012). In February 2016, the 2011 Guidelines were
replaced by “Guidelines for Alternate Water Sources: Indoor and Outdoor
Non-Potable Uses (2016 Guidelines, (LACDPH, 2016)) to make the non-
potable water use requirements consistent with the California Plumbing
Code (LACDPH, 2016). The Tier 3 Standards in the 2016 Guidelines specify
that aboveground non-potable water uses shall meet the following water
quality objectives:
• NSF 350 Standards or Title 22 Recycled Water Quality equivalence
at the point of use;
• All bacterial limits at point of use when distributed off site;
• California Maximum Contamination Levels (MCLs); and
• The California Toxics Rule Standards (CTRS).
It is noted that the total coliform limit of 2 MPN/100mL referenced in the
2016 Guidelines is intended to benchmark performance and reliability of
disinfection. The presence of total coliform is not necessarily associated
with fecal contamination. However, with this major change, disinfection is
expected to be needed as the final treatment step prior to distribution.
1.3 Baseline Conditions
Dry-weather sampling events were performed between July 2012 and
October 2014 to determine concentrations of indicator bacteria and
other contaminants in the LAR water (Geosyntec Consultants, 2015). A
total of 144 parameters listed in the MCLs, REC 1 and 2, CTRS, and Title 22
were analyzed during the first sampling event. These parameters can be
broadly divided into: general chemistry parameters, pesticides, metals,
indicator bacteria, nutrients, organic compounds, polychlorinated
biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs).
Water quality parameters that did not meet the applicable regulatory
limits were selected as “priority parameters” and monitored during the
subsequent 21 sampling events to provide data necessary for treatment
design. These priority parameters were total coliform, fecal coliform,
Escherichia coli (E. coli), enterococcus, specific conductance, turbidity,
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and pH. The results from the first sampling event concluded that LAR water
did not have exceedance concerning pesticides, metals, organic
compounds, PCBs, and PAHs.
1.4 HSSF Wetlands and Design Constraints
Horizontal subsurface flow (HSSF) wetlands have been used for a wide
range of water treatment applications including: nitrogen and phosphate
removal (Tanaka, N., Karunarathna, A.K. & Jindasa, K.B.S.N., 2008),
graywater treatment (Dallas, S. & Ho, G., 2005), highway runoff treatment
(Terzakis, S. et al, 2008), heavy metal removal from acid mine drainage
(Sheoran, A. & Sheoran, V., 2006), and stormwater runoff treatment (Idris,
S.M. et al, 2012). It has been reported that 99% or greater indicator
bacteria reduction is achievable using HSSF wetlands (Kadlec, R.H. &
Wallace, S.D., 2009).
HSSF wetlands are considered as an attractive alternative to other physio-
chemical and biological treatment options. In addition to proven water
quality treatment performance, HSSF wetlands bring added benefits of
greening highly developed urban spaces, creating wildlife habitats,
requiring little energy input, and reducing carbon dioxide (a greenhouse
gas).
The reported treatment performance and benefits above led the Studio
to consider the use of this treatment option to treat LAR water at the BRBC
facilities in early 2014. In a memo prepared by Geosyntec (2014), a
conventional full-scale rectangular HSSF wetland with two 5.5 ft. deep
gravel beds would occupy a footprint of 65,000 square foot. Such a large
footprint was deemed impractical due to the space constraint.
To save space, the Studio subsequently expressed a preference of
installing part of the wetland on top of the Studio’s main building roof. To
accommodate this siting preference, the wetland systems would be
required to meet a loading limit of no more than 150 pounds per square
feet (psf). Also, the shape of the roof selected had a five-sided polygon
(See Figure 1), this would mean that a wetland with a flexible configuration
would be desirable to optimize the use of available space. Given these
constraints, alternative media with lower density than conventional gravel
media and smaller and shallower beds would need to be considered.
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Also, the Studio expressed a preference for using media from sustainable
sources.
In order to demonstrate the feasibility of using a wetland system that
would meet the above criteria, a pilot study was subsequently planned.
During the design phase, a total of 15 alternative media were considered,
including: commercial media products (e.g., Growth Rock, Rockwool,
expanded clay pellets), natural rock minerals (e.g., perlite, pumice,
gravel), and agricultural waste (e.g., wood chips, rice hull, coconut coir).
Three media types, namely gravel, coconut coir, and clay pellets, were
ultimately selected. Gravel was selected because of its frequent use as
wetland media and was recommended in preliminary design proposed
by Geosyntec (2014). Coconut coir was selected as a sustainable and low
density alternative that has been used for HSSF wetlands (Tanaka, N.,
Karunarathna, A.K. & Jindasa, K.B.S.N., 2008). Expanded clay pellets were
selected as an alternative because its density was between gravel and
coconut coir, and they are typically used as a soil substitute in hydroponic
systems. Also, clay was selected by the Studio because they had
experimented their use in other projects.
To accommodate the size and geometry of potential spaces available for
conducting the pilot study, multiple wetland bed configurations using
temporary structures were considered, including high aspect ratio (up to
1:20) rectangular beds with sloped bottoms, elongated rectangular beds
that spiraled down from the top of a circular mount, multiple wetland
beds in-series. Multiple-bed-in-series using rectangular fiberglass tanks
were selected in the end. This option would allow the Studio to construct
the systems using their existing contractor, accommodate the space
limitations at the site, and allow reuse of materials after the pilot study is
complete.
1.5 Study Objectives
To evaluate the performance of HSSF wetland systems for treatment of
dry-weather LAR water, a pilot study (study) was conducted. Three HSSF
wetland treatment systems were designed and built between June and
September 2015. The primary objectives of this study were:
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6 Metabolic Studio Pilot Wetland Study
1. To demonstrate that HSSF wetlands were capable of treating LAR
water to meet 2011 Guidelines for aboveground non-potable water
uses;
2. To evaluate and compare the treatment performance of three
different media types with respect to FIB, turbidity, organics, and
nutrient removal; and
3. To determine the hydraulic retention time (HRT) required to achieve
optimal treatment performance.
Findings from this study will provide the design basis for scale-up. They will
support the use of HSSF wetland systems for treatment of dry-weather
runoff from the LAR and other rivers in similar urban regions for non-potable
water use. These results will also provide data to support the use of wetland
systems for treatment of dry-weather runoff for bacteria TMDL Marine REC-
1 compliance purposes.
The organization of this report is as follows:
Section 2: Treatment Performance
Section 3: Hydraulic Retention Time
Section 4: Capital and O&M Costs
Section 5: Vegetation Coverage
Section 6: Conclusions.
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7 Metabolic Studio Pilot Wetland Study
2. TREATMENT PERFORMANCE
2.1 Indicator Bacteria
Indicator bacteria are the primary biological contaminant of concern in
LAR water in the previous water quality sampling and testing effort as
described in Section 1.3. As such, indicator bacteria in water samples
collected from the LAR, the influent to the wetland systems (IN), and the
effluent of wetland cells 1, 2, 3, 5, 8, and 9, were analyzed. The total
coliform, fecal coliform, and enterococcus results for these locations are
presented in Figures 2-4, respectively.
Note: Error bars represent the standard deviation of the geometric mean of n= 4- 8 samples.
Figure 2 Total coliform geometric mean concentration for samples collected at
selected locations
As shown in Figures 2-4, indicator bacteria concentrations in the LAR water
were variable. Although the geometric mean was below the limits
specified in the 2011 Guidelines and the bacteria TMDL Marine REC-1, their
single sample concentrations did not consistently meet these two
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8 Metabolic Studio Pilot Wetland Study
requirements. For example, total coliform concentrations in the LAR water
samples were measured in the range between 2 and 16,000 MPN/100mL
during the four sampling events performed and one of them exceeded
the 10,000 MPN/100mL limit.
Note: Error bars represent the standard deviation of the geometric mean for n=4-8 samples.
Figure 3 Fecal coliform geometric mean concentration for samples collected at
selected locations
This results showed that total coliform and fecal coliform concentrations in
IN (i.e. wetland influent after storage) were 93% and 87% lower than the
LAR, respectively (Figures 2-3). This suggests that storage of LAR water prior
to treatment provide reductions, although such reductions were not
statically significant based on a t-test (p-value=0.16>0.05 for total coliform;
p-value=0.24>0.05 for fecal coliform). In contrast, a decrease in
enterococcus concentration was not observed after storage. This
observation is consistent with other studies where enterococci have been
shown to be more persistent in aquatic environments compared to
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coliform bacteria (Davies, C.M. et al, 1995;Anderson, K.L., Whitlock, J.E. &
Harwood, V.J., 2005).
Note: Error bars represent the standard deviation of the geometric mean for n=4-8 samples.
Figure 4 Enterococci geometric mean concentration for samples collected at
selected locations
Reduction in total coliform, fecal coliform, and enterococcus
concentrations after one wetland cell treatment was observed. The
percentage reduction ranges were 80-92% (effluent geomean = 3.6 - 10.5
MPN/100mL), 60-70% (effluent geomean = 1-1.3 MPN/100mL), and 88-97%
(effluent geomean = 1.2-4 MPN/100mL) for total coliform, fecal coliform,
and enterococci, respectively. However, these reductions were not
considered to be significant according to a t-test (p-value=0.16 for total
coliform>0.05, p-value=0.24 for fecal coliform >0.05). The t-test results
could have been a result of relatively low IN concentrations, the variability
in the data, and the limited number of samples taken.
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The effect of providing additional treatment (i.e. with longer HRT) after the
first wetland cell with respect to indicator bacteria removal was
evaluated. The data suggest that additional treatment provide little to no
observable bacterial removal benefits for all the three systems. For the
coconut coir wetland, indicator bacteria removal was observed to be
optimal after one cell. For the gravel and clay pellet wetlands, adding two
more wetland cells was shown to provide negligible improvement. It is
worth pointing out that the treatment system was unable to consistently
attain an effluent total coliform concentration of at or below 2
MPN/100mL (i.e. the 2016 Guidelines requirements) during the sampling
period. This is not surprising because total coliform is an environmental
indicator and can be found in surface water and soil. Nevertheless, to
attain the prescribed effluent quality consistency for compliance,
disinfection of effluent after treatment is necessary.
2.2 Physical and Chemical Water Quality Parameters
pH, turbidity, and conductivity were identified as the primary physical and
chemical water quality parameters of concern in the 2015 Report
(Geosyntec Consultants, 2015). These three parameters, in addition to
others listed in Tables 1-2, were characterized through field measurements
and laboratory analysis of grab samples. The results are summarized in
Tables 1-2. LAR water and IN had an average pH of 7.7±1.2 and 7.9 ±0.3,
respectively. The wetland processes buffered the pH to near neutral,
ranging between 6.8±0.1 and 7.0±0.2. These results were consistent with
those reported by other researchers (Kadlec, R.H. & Wallace, S.D., 2009).
Total suspended solids (TSS) and turbidity (a surrogate for TSS) were
measured at the selected locations and the results at these locations are
presented in Figures 5-6, respectively. LAR water contained an average
TSS and turbidity of 18 mg/L and 3 NTU, respectively. Both exceeded the
limits of 10 mg/L TSS and 2 NTU turbidity as stipulated in 2016 Guidelines
(Figure 5). Storage was shown to provide as much as 90% TSS reduction on
average, resulting in an average IN TSS of 1.8 mg/L. All effluent TSS levels
were consistently well-below the 10mg/L TSS. Consistent with the TSS results,
storage provided an average of 80% of turbidity reduction, resulting in an
average IN turbidity of 0.6±0.1 NTU, below the 2 NTU limit (Figure 6). The
reduction was described as significant per a t-test (p-value=0.04<0.05).
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11 Metabolic Studio Pilot Wetland Study
Recognizing the relatively low average IN TSS and turbidity levels, any
additional reduction gained through wetland treatment was expected to
be limited. Both gravel and coconut wetlands were shown to have further
reduced TSS levels consistently to below the detection limit of 0.5 mg/L. It
is noted that detectable levels of TSS were measured in all clay pellet
wetland effluent samples. These average values were maintained at no
more than the average IN TSS level of 1.8 mg/L, thus these were still
considered as low.
Note: Error bars represent the standard deviation of n=4 samples.
Figure 5 Average total suspended solids at selected locations along the treatment
systems
As for turbidity, both gravel and clay pellet wetlands maintained an
average of no more than the IN turbidity of 0.6 NTU. Based on the slight
turbidity increase detected in Cell 2 of the clay pellet wetland and
coupled with the detectable TSS levels in effluent samples in the clay
pellet wetland, the gravel wetland provided more consistent turbidity and
TSS removal in comparison.
It is noted that effluent turbidity levels in other coconut wetland effluent
samples (Cells 2, 3, 5, 8, and 9) rose with the increasing number of wetland
cells (i.e. HRT, see Figure 6). The causes had yet to be investigated, but
media leaching was thought to be one of the main potential causes. Even
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12 Metabolic Studio Pilot Wetland Study
though the average turbidity levels were below the 2 NTU requirements for
all effluent samples, the coconut coir wetland was considered to have the
poorest turbidity removal performance compared to the other two
wetlands.
Note: Error bars represent the standard deviation of n= 4-12 samples.
Figure 6 Average turbidity at selected locations along the treatment systems
Conductivity, a surrogate for measuring total dissolved solids (TDS), was
another contaminant of concern identified in a previous study (see
Section 1.3). High conductivity can be detrimental to plant health and
thus it is prudent to maintain the conductivity level at a reasonable level
based on the end use. The results show that the average LAR conductivity
level was 1,061 µS/cm, above the recommended MCL of 900 µS/cm but
below maximum MCL of 1,600 µS/cm (Figure 7) as specified in the 2016
Guidelines. Slight elevated average IN conductivity (1,122 µS/cm) could
have been a result of evaporation during storage.
Measurable changes in effluent conductivity was observed after the
wetland treatment processes. As shown in Figure 7, conductivity levels in
the gravel and clay pellet wetlands generally followed a similar upward
trend and increased with HRT (cell 9, gravel = 1,312 µS/cm and clay pellet
= 1,256 µS/cm). Conductivity in the coconut coir wetland effluent
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13 Metabolic Studio Pilot Wetland Study
decreased with increasing HRT (cell 9 = 968 µS/cm). This striking difference
between the gravel and clay pellet wetlands (using inorganic siliceous
minerals) and the coconut coir wetland (using organic cellulose materials)
is hypothesized to be stemmed from the biochemical environments in
these media as supported by the oxidation-reduction potential (ORP)
data.
Note: Error bars represent the standard deviation of n=8 samples. MCL = CA Secondary Maximum Contaminant
Levels.
Figure 7 Average conductivity at selected locations along the three treatment systems
The ORP data (Figure 8) showed that the ORP levels in the coconut coir
wetland were much lower than the other two wetlands with an average
of -280 mV were measured at the selected locations. The average effluent
ORP for the gravel and clay pellet wetlands were +16 mV and +41 mV,
respectively. These results suggest that the biochemical conditions in the
coconut coir wetland was highly reduced; while the other two were
slightly oxidized. A reduced environment favors anaerobic processes,
such as metal precipitation, fermentation, and sulfate reduction. The
decrease in conductivity, increase in organics (total organic carbon
(TOC), chemical oxygen demand (COD), and five-day biochemical
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14 Metabolic Studio Pilot Wetland Study
oxygen demand (BOD5)), and reduction in sulfate (see Table 1) with
increase in hydraulic retention time suggest these processes took place in
the coconut coir wetlands.
Note: Error bars represent the standard deviation of n=8 samples.
Figure 8 Average oxidation reduction potential (ORP) at selected locations along the
three wetland systems
Consistent with the difference in the ORP results, similar water quality
changes were not observed in the gravel and clay pellet wetlands. For
example, these two wetlands were shown to provide organics reduction
(TOC, COD, and BOD), while no conductivity reduction was observed.
Elevated effluent conductivity compared to IN, which could be a result of
water loss due to evapotranspiration (Kadlec, R.H. & Wallace, S.D., 2009).
Biodegradable organic concentrations in the LAR and other selected
locations were measured. The average BOD5 levels for LAR and IN were
2.8 mg/L and 1.8 mg/L, respectively, well below limit of 10 mg/L as
specified in the 2016 Guidelines (Figure 9). This shows that storage
provided slight BOD5 reduction. After treatment using two wetland cells,
BOD5 concentrations in both gravel and clay pellet wetlands were
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15 Metabolic Studio Pilot Wetland Study
reduced to below detection limit of 1 mg/L and remained at the same
level after water passed through additional seven wetland cells.
As noted previously, BOD5 concentrations in the coconut wetland were
evaluated with measurements collected from cells 8 and 9 exceeding 10
mg/L. This gave an overall increase of 88% BOD5 at cell 9 compared to IN
(Figure 9). Consistent with the BOD5 results, an ascending trend was also
observed in COD and TOC results. These BOD5 observations suggest that
controlling the HRT in the coconut coir wetland would be crucial to limit
organic increases and long HRT should be avoided.
Note: Error bars represent the standard deviation of n=4 samples.
Figure 9 Average BOD5 at selected locations along the treatment systems
Change in nitrate concentrations was observed in this study. LAR water
contained an average nitrate concentration of 4 mg/L as N which was
below the Secondary MCL limits as specified in the 2016 Guidelines.
Storage did not provide reduction benefits. After two cells of wetland
treatment, 99% of nitrate was removed and the concentration remained
unchanged in increasing in hydraulic retention time as expected (Figure
10).
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16 Metabolic Studio Pilot Wetland Study
Note: Error bars represent the standard deviation of n=4 samples. MCL = California Maximum Contaminant
Levels.
Figure 10 Average nitrate concentration at selected locations along the three wetland
systems
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17 Metabolic Studio Pilot Wetland Study
3. HYDRAULIC RETENTION TIME
The HRT of each treatment system was determined theoretically (void
space divided by flow rate) and empirically (using rhodamine WT (RWT)
dye tracer) (Table 3). The influent flow rate of each treatment system was
set to approximately 0.5 liter per minute (lpm) to attain a theoretical HRT
of one day per cell. The empirical HRT was calculated based on the time
required for the RWT dye to exit the cells.
When calculating the HRT, a RWT mass recovery of at least 80% must be
attained (Headley, T.R. & Kadlec, R.H., 2007). As shown in Table 3, tracer
test results from gravel and clay pellet wetlands met such a requirement.
The RWT masses recovered from these two wetlands were greater than
100%, which could be attributed to evaporation and/or instrumentation
errors (e.g. RWT sensors and flow meters). For the coconut coir wetland,
only 12% of RWT mass was recovered, and thus an empirical HRT for a
typical coconut coir cell could not be determined. The low tracer
recovery could be due to the sorption of RWT onto the organic coconut
coir media (Lin, A.Y.-C. et al, 2003).
Table 1 Mean and Theoretical Hydraulic Retention Time
Tracer Tests Theoretical
HRT, day per
cell
Measured
Mean HRT,
day per cell
Tracer
Volume, mL
Dye
Recovery
Initial Dye
Detection,
hr
Gravel 1.85 1 123% 13.10 0.80
Coconut
coir
Cannot Be
Determined 4 12% 0.83 1.08
Clay
Pellet 1.66 2 112% 6.77 0.93
The normalized effluent RWT concentrations from cell 1 of the gravel and
clay pellet wetlands are shown in Figure 11. The flow of the RWT in these
two cells can be described as dispersed based on the shape of the
curves. Multiple peaks observed in both wetlands suggest the presence
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18 Metabolic Studio Pilot Wetland Study
of multiple flow paths (Levenspiel, O., 1999). This observation is consistent
with the design of the wetland where multiple holes were predrilled into
the PVC pipes placed horizontally across the wetland bed.
Figure 11 RWT effluent concentration for the gravel and clay pellet wetlands
The calculated HRTs for the gravel and the clay pellet cells were 1.85 and
1.66 days per cell, respectively. They were longer than the theoretical
hydraulic retention time of approximately one day per cell. The longer
than expected HRTs could be attributed to the presence of extensive
plant roots in the wetland cells that were not accounted for calculating
the theoretical HRT. Extensive root systems alter flow paths and may
create stagnant zones to impede flow (Kadlec, R.H. & Wallace, S.D., 2009).
Regarding the tracer test performed at the coconut coir cell, a relatively
short RWT detection time of 50 minutes was recorded. This could be a result
of a combination of high hydraulic conductivity of coconut coir (Abad,
M. et al, 2005) and the presence of short circuiting in the cell (Levenspiel,
O., 1999). Despite the relatively short HRT, treatment performance of the
coconut coir wetland for indicator bacteria and nitrate removal did not
seem to be affected and the effluent concentrations were comparable
to the gravel and clay systems (see Section 2).
D R A F T - For Discussion Purposes Only
19 Metabolic Studio Pilot Wetland Study
4. VEGETATION COVERAGE
Plant species selected and planting layout were identical in all the
wetland cells. After one year of operation, vegetation coverage and size
in all the cells are shown in Figure 12. Vegetation coverage and size
variation in the gravel and clay pellet wetlands were similar with the first
cells having the largest plant sizes and densest vegetation coverage;
while the thinnest coverage and smallest plants were found in the last cells
(A9 and C9). Such a decrease in plant size and coverage could have
been a result of geochemical composition variation in the water, but
further analysis would need to be conducted to confirm this.
Vegetation coverage and size change in the coconut coir wetland
system was noticeably different from the other two wetland systems. The
vegetation coverage, size, and coloration changed abruptly in the mid-
section of cell 1. The plant size remained relatively small with little to no
noticeable difference from cells 2 to 9. The small plant size in the coconut
wetland cells could be related to the presence of highly reduced
conditions (i.e. highly negative ORP). It has been reported that such
conditions cause oxygen stress in plants, affecting photosynthetic
activities and plant growth (DeLaune, R., Pezeshki, S. & Pardue, J.,
1990;Bandyopadhyay, B. et al, 1993). Based on the above observations,
using a relatively short HRT would be crucial for maintain plant health, in
addition to controlling effluent organic concentrations (Section 2.2).
D R A F T - For Discussion Purposes Only
20 Metabolic Studio Pilot Wetland Study
Figure 12 Vegetation coverage of individual wetland cells in the three wetland systems.
It is noted that water flow from left (influent) to right (effluent). The white arrow mark the locations where untreated water flows into the wetland systems, while the blue arrows mark effluent discharge points.
c) Clay Pellet Wetland
b) Coconut Coir Wetland
a) Gravel Wetland
C1 C2 C3 C4 C5 C6 C7 C8 C9
B1 B2 B3 B4 B5 B6 B7 B8 B9
A1 A2 A3 A4 A5 A6 A7 A8 A9
D R A F T - For Discussion Purposes Only
21 Metabolic Studio Pilot Wetland Study
5. CAPITAL AND O&M COSTS
The annual capital and O&M costs for deploying these wetland systems
were estimated using the material and O&M costs incurred during the
study. Based on the findings presented in Section 2-3, it was determined
that treatment systems consisting of three cells would be required to
provide sufficient redundancy for both the gravel and clay pellet media.
The option to use coconut coir as a soil medium was excluded due to its
limitation. The BRBC project would provide the water diversion system and
effluent storage at the Studio site, costs for water delivery and storage
were therefore excluded from the cost estimates presented in this section.
5.1 Capital Costs
The capital costs for a single wetland cell and a single treatment system
were estimated for the gravel and clay pellet systems for comparison. The
costs of a single cell were assumed to be comprised of a fiber glass tank,
metal frames for creating an elevation difference between tanks,
plumbing for influent flow distribution and effluent; wetland vegetation,
media; and labor costs for assembly. The costs of a treatment system
include plumbing for influent distribution, effluent collection, and
connections among the wetland cells; pumps for water transfer and flow
distribution; and labor for system installation.
System assembly and installation were assumed to be conducted by a
contractor who would provide all field equipment, and thus equipment
rental was not necessary. The labor rate of $90 per hour per person was
assumed. It was assumed that a total of 90 hours of labor would be
sufficient to assemble a single wetland cell. An additional four hours of
labor effort was required for installation of pumps and other plumbing
work. A total of 61 hours of labor would be needed to install a system (i.e.
one wetland system with three cells). For three systems connected in
parallel with a single inflow, it was assumed that a total of 175 hours of
labor would be required. A 15% contingency was also assumed. Table 4
summarizes the total capital costs for installing one and three three-tank
in-series systems.
D R A F T - For Discussion Purposes Only
22 Metabolic Studio Pilot Wetland Study
Table 2 Capital costs for one and three three-tank in-series systems
Media Total capital Costs,
$/system
One System (up to three
wetland cells)
Gravel $17,000
Clay Pellet $19,000
Three Systems (up to three
wetland cells per system)
Gravel $44,000
Clay Pellet $50,500
5.2 O&M Costs
O&M activities for treatment wetlands typically involve pretreatment
maintenance (e.g., screen filter replacement), pump maintenance,
vegetation trimming, pest control, and routine site walks to ensure that the
treatment system is in good working order. During the study period, algal
fouling in the plumbing system was observed due to the abrupt change
in LAR water quality. As a result, additional cleaning was conducted to
prevent clogging. Also, it was assumed that sweeping would be required
to maintain site cleanliness. Based on the above, approximately 55 hours
of labor per annum were assumed to be necessary to perform these
activities. The O&M cost estimates for one and three three-tank in-series
systems are presented in Table 5. These cost estimates are expressed in
terms of annual costs.
Table 3 Annual O&M costs for one and three three-tank in-series systems
Labor Effort,
hours/year
O&M by Onsite
Staff, $/year
O&M by
Contractor, $/year
One System 88 4,080 4,960
Three Systems 154 7,200 8,740
5.3 Total Annual Costs
The total annual cost to provide a wetland system (gravel or clay pellets)
is presented in Table 6. To calculate the annual operating costs, a useful
lifetime of 15 years for each system and a salvage value of zero at the end
of its lifetime with a uniform rate of depreciation were assumed. The results
D R A F T - For Discussion Purposes Only
23 Metabolic Studio Pilot Wetland Study
show that some economy of scale could be achieved if more systems
were installed. Also, additional cost saving could be provided by retaining
onsite personnel to perform the O&M work.
Table 4 Annual operating costs for one and three three-tank in-series systems
Media O&M by Onsite
Staff, $/year
O&M by Contractor,
$/year
One System (up to
three wetland cells)
Gravel $5,200 $7,900
Clay Pellet $5,400 $8,300
Three Systems (up
to three wetland
cells per system)
Gravel $8,300 $11,700
Clay Pellet $8,500 $12,100
D R A F T - For Discussion Purposes Only
24 Metabolic Studio Pilot Wetland Study
6. CONCLUSIONS
A pilot study was conducted to evaluate the treatment performance of
modular and compact horizontal subsurface flow (HSSF) wetlands for
treatment of Los Angeles River (LAR) dry-weather runoff for aboveground
non-potable uses. Three systems, each with different media types (gravel,
coconut coir, and clay pellets), were tested. Water quality analysis
revealed that LAR water contained levels of indicator bacteria exceeding
both the LACDPH 2011 and 2016 Guidelines for aboveground non-potable
uses. LAR water contained TSS and turbidity levels that exceeded the 2016
Guidelines. Storage of water prior to treatment was shown to reduce total
and fecal coliform, turbidity, TSS, and organics. Turbidity and TSS were
reduced to below the limits specified in the 2016 Guidelines. Storage,
however, did not reduce other contaminants, such as enterococcus,
nitrate, and TDS.
These wetlands reduced and maintained indicator bacteria
concentrations to levels that complied with the 2011 Guidelines
requirements without the use of disinfection. Indicator bacteria
concentrations in effluent had an average of 10 MPN/100mL or lower after
one cell of treatment and it was maintained at approximately the same
levels throughout the treatment processes1. Under the more stringent 2016
Guidelines, disinfection would need to be used to ensure that water
quality objectives for bacteria were consistently met. However, the
wetland systems were effective in reducing organics (e.g. BOD5 and COD)
and nitrate. Based on the water quality results and adding redundancy to
the system, it was determined that three cells per system should be used
in future designs.
Gravel, coconut coir, and clay pellets have different physical
characteristics. Of these three, coconut coir has the lowest density which
makes it a better material for rooftop installation where the weight of the
system is of a concern. However, coconut coir may cause issues including
fine material leaching, dissolved organic concentration increases and
odor when inappropriate HRT is used. On the other hand, gravel has the
highest density which makes it a less desirable material for rooftop
1Bacteria concentrations can fluctuate across a broad range (2MPN/100mL->10,000MPN/100mL), thus the
increases were considered as small from <10 MPN/100mL to <20 MPN/100mL
D R A F T - For Discussion Purposes Only
25 Metabolic Studio Pilot Wetland Study
installation. However, it is the preferred HSSF media compared to clay
pellets due to its lower material cost, easy access, higher material integrity,
and lack of buoyancy.
This study demonstrated that influent storage of LAR water coupled with a
HSSF wetland could be an effective option for the BRBC project. This
wetland design approach can be easily integrated into commercial,
industrial, and residential properties that have stormwater capture
capability to provide alternative water supply for onsite non-potable uses.
Additionally, other larger-scale stormwater capture projects for non-
potable uses during dry weather could also benefit from the treatment
approach evaluated in this pilot study. Further investigation should be
performed to determine the use of this treatment approach beyond LAR
dry-weather flow in urban areas. These capture, treatment, and use
activities can help diversify local water sources and foster greater water
sustainability.
D R A F T - For Discussion Purposes Only
26 Metabolic Studio Pilot Wetland Study
7. REFERENCES
Abad, M., et al, 2005. Physical properties of various coconut coir dusts
compared to peat. HortScience, 40:7:2138.
Anderson, K.L., Whitlock, J.E. & Harwood, V.J., 2005. Persistence and
Differential Survival of Fecal Indicator Bacteria in Subtropical Waters
and Sediments. Applied and Environmental Microbiology, 71:6:3041.
Bandyopadhyay, B., et al, 1993. Influence of soil oxidation-reduction
potential and salinity on nutrition, N-15 uptake, and growth of Spartina
patens. Wetlands, 13:1:10.
Dallas, S. & Ho, G., 2005. Subsurface flow reedbeds using alternative
media for the treatment of domestic greywater in Monteverde, Costa
Rica, Central America. Water Science and Technology, 51:10:119.
Davies, C.M., et al, 1995. Survival of fecal microorganisms in marine and
freshwater sediments. Applied and Environmental Microbiology,
61:5:1888.
DeLaune, R., Pezeshki, S. & Pardue, J., 1990. An oxidation-reduction
buffer for evaluating the physiological response of plants to root
oxygen stress. Environmental and Experimental Botany, 30:2:243.
Geosyntec Consultants, 2013. LA River Water Reuse
Opportunities/Requirements – Irrigation, Los Angeles.
Geosyntec Consultants, 2015. Bending the River Back into the City
Project Water Quality Data Summary Los Angeles, CA
Headley, T.R. & Kadlec, R.H., 2007. Conducting hydraulic tracer studies of
constructed wetlands: a practical guide. Ecohydrology &
hydrobiology, 7:3:269.
Idris, S.M., et al, 2012. Performance of the giant reed (Arundo donax) in
experimental wetlands receiving variable loads of industrial
stormwater. Water, Air, & Soil Pollution, 223:2:549.
Kadlec, R.H. & Wallace, S.D., 2009 (2nd). Treatment wetlands. CRC Press,
Boca Raton, FL.
LACDPH, 2016. Guidelines for Alternate Water Sources: Indoor and
Outdoor Non-Potable Uses.
Levenspiel, O., 1999. Chemical reaction engineering. Industrial &
engineering chemistry research, 38:11:4140.
Lin, A.Y.-C., et al, 2003. Comparison of rhodamine WT and bromide in the
determination of hydraulic characteristics of constructed wetlands.
Ecological Engineering, 20:1:75.
McMillan, 2016. Model S-111/S-112/S-114 Liquid Flow Meters.
<http://www.mcmflow.com/shop/index.php/model-s-111-s-
114.html#prettyPhoto>, September 1.
D R A F T - For Discussion Purposes Only
27 Metabolic Studio Pilot Wetland Study
Sheoran, A. & Sheoran, V., 2006. Heavy metal removal mechanism of
acid mine drainage in wetlands: a critical review. Minerals
engineering, 19:2:105.
Tanaka, N., Karunarathna, A.K. & Jindasa, K.B.S.N., 2008. Effect of
coconut coir-pith supplement on nitrogen and phosphate removal in
subsurface flow wetland microcosms. Chemistry and Ecology, 24:1:15.
Terzakis, S., et al, 2008. Constructed wetlands treating highway runoff in
the central Mediterranean region. Chemosphere, 72:2:141.
US Army Corps of Engineers, 2012. Donald C. Tillman Water Reclamation
Plant Multi-Use Facility Project Sepulveda Dam Basin - Notice of
Preparatin Los Angeles County
US Army Corps of Engineers, 2013. Los Angeles River Ecosystem
Restoration Integrated Feasibility Report, Los Angeles County
USEPA Region IX, 2012. Long Beach City Beaches and Los Angeles River
Estuary Total Maximum Daily Loads for Indicator Bacteria.
D R A F T - For Discussion Purposes Only
28 Metabolic Studio Pilot Wetland Study
APPENDICES
D R A F T - For Discussion Purposes Only
29 Metabolic Studio Pilot Wetland Study
APPENDIX 1- WATER QUALITY RESULTS
Table 5 Physical and Chemical Water Quality Parameters Measured in the Field
Location Water
Quality
Objectiv
e
LAR IN Gravel Coconut Coir Clay Pellets Effluent
Tank
A1 A2 A3 A5 A8 A9 B1 B2 B3 B5 B8 B9 C1 C2 C3 C5 C8 C9
pH 6-8 7.7±1.2 7.9±0.3 7±0.2 6.9±0.2 6.9±0.2 7±0.2 6.9±0.3 6.9±0.4 6.9±0.3 6.8±0.1 6.8±0.1 6.8±0.1 6.9±0.1 6.8±0.1 6.9±0.1 6.8±0.1 6.9±0.1 6.9±0.1 6.9±0.1 6.9±0.3 7.5±0.1
ORP1, mV NA 158
±115
-31±82 5±150 20±168 24±190 28±208 6±210 10±227 -274
±23
-294
±26
-295
±24
-304
±27
-285
±25
-232
±51
42±123 15±121 50±134 63±144 48±154 28±156 -21±108
DO2, mg/L 9.8±0.5 6.3±1.2 0.7±0.3 0.8±0.2 1.5±0.5 1.8±0.3 1.5±1 1.9±1.4 0.4±0.3 0.3±0.1 0.4±0.1 0.3±0.1 0.4±0.1 0.6±0.1 0.9±0.3 1±0.4 1.2±0.3 1.7±0.4 1.9±0.6 1.6±0.3 7.3±0.2
Conduct-
ivity, µS/cm
1,600 1061
±37
1122
±43
1096
±60
1151
±72
1212
±75
1291
±111
1300
±146
1312
±137
1069
±63
1067
±74
1078
±76
1021
±103
980
±52
968
±41
1102
±60
1145
±81
1186
±109
1260
±158
1243
±164
1256
±160
1320
±98
Turbidity,
NTU3
2 2.9±0.8 0.6±0.1 0.5±0.5 0.3±0.1 0.4±0.3 0.2±0.1 0.2±0.1 0.2±0.1 0.6±0.1 0.9±0.3 1.2±0.3 1.4±0.4 1.3±0.2 1.8±0.2 0.3±0.1 0.7±0.9 0.3±0.1 0.2±0 0.3±0.2 0.3±0.2 0.3±0.1
1Oxidation-reduction potential. 2Dissolved oxygen. 3Nephlometric Turbidity Unit. Red fonts indicate exceedance of regulatory limits. The number of measurements taken is n=6
D R A F T - For Discussion Purposes Only
30 Metabolic Studio Pilot Wetland Study
Table 6 Physical and Chemical Water Quality Parameters Measured in the Laboratory
Criteria Gravel Coconut Coir Clay Pellet
Water Quality
Parameters MCL* LAR Influent A2 A8 A9 B2 B8 B9 C2 C8 C9
TOC1, mg/L NA 10.9±9.5 6.6±0.5 5.1±0.1 4.2±0.3 4.5±0.6 6.6±0.6 12.5±1.3 16±3.5 5.1±0.5 4±0.1 4±0.3
BOD52, mg/L 10 2.8±1.3 1.8±1 ND 1.4±0.7 ND 6.2±2.1 13.4±4.6 17.4±6 ND ND 1.3±0.6
COD3, mg/L NA 26±15.3 17.5±3.7 11±8.5 10.3±10.5 8.5±7 29.5±2.5 59.5±12.4 63.8±15.8 9.8±6.2 6.5±3 20.3±14.9
Ammonia, mg/L-N NA 0.2±0.2 0.2±0.1 0.1±0.1 0.1±0 0.1±0 0.1±0 0.1±0.1 0.1±0 0.1±0.1 0.1±0 0.1±0
Nitrate, mg/L-N 10 4.13±1.08 5.03±0.31 0.19±0.15 ND ND ND ND ND 0.05±0.04 ND ND
Nitrite, mg/L-N 1 0.37±0.19 0.43±0.13 ND ND ND ND ND ND ND ND ND
Orthophosphate, mg/L-
P NA
0.35±0.3 0.45±0.38 ND ND ND ND ND ND 0.17±0.08 0.53±0.41 0.36±0.29
Hardness, mg/L-CaCO3 NA 225±17.3 220±8.2 270±8.2 352.5±15 367.5±37.7 230±18.3 202.5±15 200±29.4 257.5±9.6 367.5±42.7 355±37
Arsenic, mg/L 0.01 0.005±0.003 ND ND ND ND 0.004±0.002 0.003±0.001 0.005±0.003 0.004±0.002 0.006±0.002 0.006±0.003
Copper, mg/L 1.0 0.026±0.022 0.01±0.005 0.004±0.002 0.005±0.002 0.007±0.002 ND ND 0.012±0.02 0.008±0.003 0.016±0.003 0.053±0.072
Chromium, mg/L 0.05 ND ND ND ND ND ND ND ND ND 0.002±0.002 ND
Selenium, mg/L 0.05 ND 0.004±0.002 0.004±0.002 ND ND ND ND ND ND ND 0.004±0.003
Zinc, mg/L 5.0 0.06±0.02 0.08±0.02 0.01±0.01 ND 0.01±0 ND ND 0.03±0.04 0.01±0 ND 0.01±0.01
Boron, mg/L 1.0 0.49±0.01 0.47±0 0.5±0.03 0.5±0.08 0.53±0.1 0.43±0.02 0.36±0.04 0.27±0.03 0.52±0.01 0.58±0.06 0.57±0.06
Magnesium, mg/L NA 19.5±0.7 19.7±0.6 20.7±0.6 22.3±0.6 23.7±2.1 19.3±1.2 19.3±1.5 22.3±2.5 21.3±0.6 25.7±1.5 26.3±1.5
Calcium, mg/L NA 54.5±6.4 56.3±2.1 77±1.7 106.7±5.8 113.3±5.8 61.3±3.5 48.3±5.1 39.3±6.7 69.3±2.1 116.7±5.8 106.7±5.8
TSS4, mg/L 10 18±6.1 1.8±1.2 ND ND 0.4±0.4 ND 0.4±0.4 0.5±0.4 1.8±1.9 0.5±0.4 0.4±0.4
*Maximum contamination level requirements for aboveground non-potable uses. 1Total organic carbon. 2Five-day biochemical oxygen demand. 3Chemical oxygen demand. 4Total suspended solids. NA means not
applicable. Red fonts indicate exceedance of regulatory limits. The number of samples collected is n=4
D R A F T - For Discussion Purposes Only
31 Metabolic Studio Pilot Wetland Study
APPENDIX 2 - RAINWATER VERSUS LAR WATER QUALITY
The Studio installed rainwater cisterns to capture runoff generated from
the roof and parking structure onsite during the winter of 2015/2016. In July
2016, the Studio requested Geosyntec to collect water samples from
selected rainwater cisterns across the site to evaluate their water quality.
The water quality results for these cisterns are presented in Table 7 with LAR
water shown as a comparison.
Rainwater stored in the cisterns was less contaminated than the LAR
water. It contained lower levels of dissolved solids (conductivity and
hardness), biodegradable organics (BOD5), nutrients (ammonia, nitrite,
nitrate, orthophosphate), and metals compared to LAR water. In contrast,
zinc concentrations in rainwater were noticeably higher than that
collected from the LAR water. Elevated zinc concentrations in harvested
rainwater could be associated with the roof materials and the deposition
of suspended zinc particulates from vehicles and the environment.
Total suspended solid concentrations were also low. This could be due to
the fact that the water had been stored in the cisterns since early 2016.
This allowed time for solids and particulates to settle. BOD5 concentrations
were below the detection limit of 1 mg/L in harvested rainwater while
COD concentrations ranged from 8 to 23 mg/L. High COD suggests that
organics present were predominately oxidizable organics.
Indicator bacteria levels in rainwater were also measured. Harvested
rainwater contained very low levels of FIB. E. coli counts were below the
detection limit of 1 MPN/100mL, which is also below the 2.2 MPN/100 mL
criterion specified in the NSF standards specified in the 2016 Guidelines.
Low levels of total coliform were found in all tanks except for R4 (the
confluence point) where the total coliform count was measured at 538
MPN/100mL.
D R A F T - For Discussion Purposes Only
32 Metabolic Studio Pilot Wetland Study
Table 7 Water Quality Data of Captured Rainwater Stored in Cisterns Onsite and LAR
Water
Criteria Rain Cistern Locations LAR
Water Quality
Parameters
LACDPH
2016
R1 R2 R3 R4 R5 R6 Avg.
TOC, mg/L NA 2.13 3.10 1.30 4.43 1.20 0.88 10.9
BOD5, mg/L 10 ND ND ND 2.43 ND ND 2.8
COD, mg/L NA 10.33 24.50 13.00 22.67 21.50 8.00 26
Ammonia, mg/L-N NA 0.05 ND ND 0.26 ND ND 0.2
Nitrate, mg/L-N 10 0.51 0.95 ND 0.57 0.73 0.61 4.13
Nitrite, mg/L-N 1 ND ND ND ND ND ND 0.37
Orthophosphate,
mg/L-P NA 0.19 ND ND 0.21 ND ND
0.35
Hardness, mg/L-
CaCO3 NA 48.67 13.50 6.25 9.30 6.35 6.60
225
Arsenic, mg/L 0.01 ND ND ND ND ND ND 0.005
Copper, mg/L 1.0 0.009 0.009 0.006 0.008 0.006 0.007 0.026
Chromium, mg/L 0.05 ND ND ND 0.002 ND ND ND
Selenium, mg/L 0.05 ND ND ND ND ND 0.006 ND
Zinc, mg/L 5.0 0.150 0.195 0.235 0.242 0.230 0.265 0.060
Boron, mg/L 1.0 0.051 0.017 0.008 0.012 0.013 0.012 0.49
TSS4, mg/L 10 2.37 ND ND 2.37 0.68 1.03 18.4
Turbidity, NTU NA 0.67 -- -- 0.37 -- 0.56
Conductivity, µs/cm 900 22.17 -- -- 29.80 -- 32.75 1061
Fecal Coliform,
MPN/100 mL NA ND -- -- ND -- -- 14.6*
Total Coliform,
MPN/100 mL 2.2 1.26 3.58 4.12 537.5 2.79 2.00 251.4*
Enterococcus,
MPN/100 mL NA 1.26 ND ND ND ND 9.64 19.2*
E. Coli, MPN/100 mL 2.2 ND ND ND ND ND ND --
Note: *Geomean values, n = 2 samples.
D R A F T - For Discussion Purposes Only
33 Metabolic Studio Pilot Wetland Study
APPENDIX 3 - MATERIALS AND METHODOLOGY
LAR Water
This pilot study used water extracted from the LAR
at the location shown in Figure 1. Approximately
8,000 gallons of water from the LAR was extracted
and delivered weekly to the site via a water truck
(Figure 13a). The water extraction processes
involved placing a floatable pump directly on top
of the river bank where water was shallower to
prevent the pump from getting washed off (Figure
13b).
Extracted water was stored
in two 5,000-gallon storage
tanks installed in series on
site as an influent water
supply for the wetland
systems. Screening was
provided to prevent large
solids, as well as snails, from
entering the storage tanks
and eventually into the treatment systems (Figure
14a). The 5,000-gallon tank used to store LAR water
prior to distribution to the wetland systems is referred
to as the “influent tank” in this report. Water from the
influent tank was pumped to an elevated 50-gallon
intermediate tank for gravity flow distribution (Figure
14b).
Pilot Wetland Systems
Three pilot wetland systems were deployed (Figure
15). Each wetland system consisted of nine wetland
cells linked together in series. Each cell was a 7.8 ft L
x 3.8 ft W x 3.0 ft D fiberglass tank that had holes pre-set at 8 inches and 4
inches from the top of the edge of the tank on the influent and effluent
Figure 13 a) Water
truck; b) floatable pump
Figure 14 a) Influent
storage 1 at the lower
level and fabric filter
installation prior to
refilling the storage
tanks; b) influent
storage 2 and the
intermediate tank
D R A F T - For Discussion Purposes Only
34 Metabolic Studio Pilot Wetland Study
sides, respectively. The elevation difference between these two holes
created a fixed hydraulic head of 4 inches across the length of each
wetland cell. Individual tanks were connected using one-inch clear
flexible tubing. Influent flowed into standing pipes and was subsequently
distributed over the width of the wetland via a horizontal perforated pipe
that was fixed at the bottom of each wetland cell. Effluent was collected
from another perforated pipe located about 2.5 inches below the soil
surface on center at the other end of each wetland cell. Such an
arrangement allowed for a horizontal upward flow regime within the
wetland cells as well as enhanced aeration between wetland cells.
The first eight cells of the three wetland systems were made of three
different materials: 1) 3/8 gravel (gravel wetland, A); 2) coconut coir dust
mixed with coconut coir pieces (coconut wetland, B); and 3) expanded
clay pellets (clay wetland, C). The ninth cell in the gravel (A9) and the clay
(C9) wetland systems consisted of coarse sand; while the ninth wetland
cell in the coconut wetland (B9) contained coconut coir dust. The site
layout of these three wetland systems is presented in Figure 15.
Figure 15 The pilot wetland site plan
To promote the use of native vegetation, six native Southern California
wetland plant species were selected and planted in each wetland cell.
These plant species were Schoenoplectus californicus (a.k.a. Scirpus
californicus), Schoenoplectus americanus (a.k.a. Scirpus americanus),
Juncus xiphoides, Bidens laevis, Pluchea purpurascens (PP), and Minulus
guttatus (MG). The plants were arranged to enhance aesthetics of the
Sampling Locations
Effluent Tank
Influent Tank
A1A2A3A4A5A6A7A8A9
B1B2B3B4B5B6B7B8B9
C1C2C3C4C5C6C7C8C9 Cin
INT
LAR
EFT
ee ee ee ee ee ee ee ee eenn nn nn nn nn nn nn nn nn
ee ee ee ee ee ee ee ee eenn nn nn nn nn nn nn nn nn
ee ee ee ee ee ee ee ee eenn nn nn nn nn nn nn nn nn
D R A F T - For Discussion Purposes Only
35 Metabolic Studio Pilot Wetland Study
wetlands by planting the larger species in the middle and the dwarf
species along the edge. The layout of the plants is presented in Figure16.
Figure 16 The layout of the wetland plants in each wetland cell.
Flow Rate Control and Recording
Three McMillan S-Series Model S-111
Microturbine Flo-Meters were installed at the
influent of cells 1 of each system to measure
and record flow rates during the study period.
These flow meters were rated to measure low
flow rates in a range of between 0.013 and 10
liters per minute (lpm) with an accuracy of ±
1.0% (McMillan, 2016). Each flow meter was
paired with a Cole-Parmer multi-turn needle tip
valve to allow for precise flow control. Flow
rates were also measured manually on a
weekly basis for comparison. Figure 17 shows
the location of the valve and the flow meter
installed in the three system.
Figure 17 A flow control
and recording setup installed
at the influent of the clay
pellet wetland, C.
D R A F T - For Discussion Purposes Only
36 Metabolic Studio Pilot Wetland Study
Water Quality Sampling and Analysis
Grab samples were collected between May and August, 2016 for
laboratory analysis and onsite measurements. Grab samples to be sent to
a certified laboratory for analysis were preserved in coolers (<4˚C). Water
quality parameters analyzed in the laboratory were FIB (total coliform,
fecal coliform, Escherichia coli, enterococci), organics (five-day
biochemical oxygen demand (BOD), total organic carbon (TOC),
chemical oxygen demand (COD), nutrients (orthophosphate, ammonia,
nitrite, and nitrate), heavy metals that are known to be commonly found
in the LAR (chromium, arsenic, selenium, copper, and
zinc), total suspended solids, boron, and hardness. FIB
analyses were conducted twice weekly, and the
remaining water quality parameters were analyzed
weekly.
Turbidity (La Motte 2020we, Chestertown, MD),
temperature, oxidation-reduction potential (ORP),
conductivity, total dissolved solids, pH (YSI ProDSS, YSI,
Yellow Springs, OH), and chlorophyll (YSI 650MDS, YSI,
Yellow Springs, OH) were measured in the field twice
weekly. The methods used for the onsite
measurements are presented in Appendix 2.
In addition to routine sampling, a suite of one-time
special sampling was conducted after the outbreak of iron bacteria
overgrowth was observed in the first three cells of the clay pellet wetland
systems (C1-3). The water quality parameter suite tested was total iron,
ferric ion, ferrous ion, sulfate, and manganese.
Hydraulic Retention Time and Tracer Tests
The theoretical hydraulic retention time (tHRT) of each cell was calculated
based on the effective porosity (ε) of the media. Both clay pellets and
coconut coir are porous materials. In the calculation, it was assumed that
fine pores in individual media did not contribute to water flow within
individual wetland cell. Presoaked clay pellets and coconut coir was
used. The measured effective porosities of gravel, coconut coir, and clay
Figure 18 An
effluent sampling port
located at the end of
each wetland cell
D R A F T - For Discussion Purposes Only
37 Metabolic Studio Pilot Wetland Study
pellets were 34%, 36%, and 41%, respectively. The porosity data were used
to calculate the operational flow rate to yield a tHRT of one day per cell
using the relationship presented in Equation 1.
Equation 1 Operational flow rate
𝑄 =𝜀𝑉
𝑡𝐻𝑅𝑇
Where Q = operational flow rate
ε = the effective porosity
V = total volume (media + void spaces)
tHRT = theoretical hydraulic retention time
The mean hydraulic retention time in these three systems was measured
by performing rhodamine WT dye (RWT) tracer tests. RWT was selected for
its ease of use, relatively low cost, low adsorptive tendency in siliceous
materials, strong fluorescence, high diffusivity, chemical stability, and
benign character in aquatic environment (Kadlec, R.H. & Wallace, S.D.,
2009). In-situ RWT concentration detection and recording were achieved
using three YSI 6130 RWT sensors that were attached to three YSI 6820
sondes for data collection purposes. These sensors were calibrated by the
vendor according to the procedures specified by the manufacturer.
Prior to the tracer tests, the RWT background concentrations were
measured at Cells 1, 4, and 9 on a 5-minute interval for 24 hours.
Additionally, RWT sorption potential for coconut coir and clay pellet
media was evaluated by mixing the media in containers filled with a
known RWT concentration. The RWT concentrations in each container
were measured after 24 hours to determine the extent of RWT sorption.
Such information was used to adjust the quantity of dye added to the cells
to yield the desirable peak RWT concentration. It was determined that the
volume of the dye volume required were 1 mL, 4mL, and 2mL of 2.5% RWT
for the gravel, coconut coir, and clay pellet cells, respectively.
The RWT concentration change was measured and recorded at end of
the cell outlet. The sensors remained in the cell outlet until the most of the
D R A F T - For Discussion Purposes Only
38 Metabolic Studio Pilot Wetland Study
tracer tail was captured. The data collected from the tracer tests were
used to determine the average cell hydraulic retention time using
Equation 2 below.
Equation 2 Mean hydraulic retention time of tracer in the wetland, t’, mins
𝑡′=∫ 𝐶𝑡 𝑑𝑡
∞
0
∫ 𝐶 𝑑𝑡∞
0
Where t’ = mean hydraulic retention time of tracer in the wetland, min
C = concentration exiting the wetland at time t, µg/L
t = time since addition of tracer pulse to influent port, min
The exit concentration and the time were normalized using Equations 3-5.
Equation 3 Normalized time
𝜃 =𝑡
𝑡′
Where θ = normalized time
Equation 4 Total mass concentration of mass recovered
𝐶𝑁 = ∫ 𝐶𝑑(𝜃) = ∫ 𝐶 𝑑𝑡
∞
0
𝑡′
∞
0
Where CN = total mass concentration of tracer recovered, µg/L
Equation 5 Normalized concentration
𝐸(𝜃) = 𝐶
𝐶𝑁
Where E (θ) = normalized concentration
Capital and O&M Evaluation
Capital and operation and maintenance (O&M) costs are an important
decision factor for technology selection. A common operational
challenge for HSSF wetland systems is clogging from biofouling or solids
accumulation. Improperly designed pretreatment processes often
exacerbate clogging extent and frequency. Remedy for HSSF wetlands
D R A F T - For Discussion Purposes Only
39 Metabolic Studio Pilot Wetland Study
that are clogged with solids are either removing accumulated solids or
replacing the bed. If such maintenance activities are performed
frequently, it will add significant costs to the overall operations. The normal
O&M costs and incidental repair costs are expected to differ for these
three HSSF wetlands. Accordingly, an evaluation of the capital and O&M
costs was conducted based on the experience and lessons learned from
operating these wetland systems.
Rainwater Cisterns
Metabolic Studio installed rainwater cisterns across the property site that
captured and stored roof runoff for irrigation water use during dry weather
seasons. A total of 60,000 gallons were collected from four roof structures
during the previous rainy season. To characterize the water quality of the
stored rainwater, water samples were collected from six locations to
evaluate bacteria, organics, nutrients, and metals. Water quality
parameters tested in the laboratory were identical to those routinely
tested parameters for the pilot wetland study.