City of Chattanooga Urban Stormwater Retrofit
By
Britt Faucette,
Mo Minkara,
Fatima Cardoso
According to the
EPA, sediment, oil, grease, nutrients, bacteria, and heavy metals are some of
the typical pollutants found in urban and suburban stormwater runoff originating
from parking lots, roadways, lawns and gardens, pet waste, and roof shingles
(EPA 2003). These pollutants are carried into streams, rivers, and lakes,
causing severe degradation of drinking and recreational water supplies, as well
as the water quality necessary to support aquatic life.
In April 2007, the
city of Chattanooga, TN, implemented field-scale testing of FilterSoxx as a
low-impact development (LID) practice to evaluate their performance in urban
runoff pollution filtration applications. Several bench-scale experiments had
been conducted to quantify the performance of Filtrexx FilterSoxx on the removal
of these common urban and suburban stormwater pollutants, including fine
sediments (clay and silt), petroleum hydrocarbons, phosphorus, nitrogen (N),
bacteria (total coliform and E.
coli), and heavy metals (copper,
cadmium, chromium, nickel, lead, and zinc). These experiments indicated
considerable removal efficiencies: 65 and 66% for clay and silt particulates,
respectively; 84, 99, and 43% for motor oil, diesel fuel, and gasoline,
respectively; between 14 and 28% for soluble phosphorus; 15% for ammonium
nitrogen; 71 and 73% for total coliforms and E.
coli, respectively; and between
37 and 71% for heavy metals.
However,
field-scale testing of LID integrated management practices, such as Filtrexx
FilterSoxx, is necessary to augment and validate these bench-scale research
studies. Chattanooga’s Water Quality Program has been monitoring the
practicality and performance of retrofitting existing stormwater systems by
installing a Filtrexx FilterCell across a stormwater outfall draining 5.5 acres
of the city’s service vehicle parking and processing facility (Figure 1). The
outfall is known as City Wide Services (CWS) stormwater outfall #2 (Figure
2).
Quarterly
stormwater-quality sampling and analysis is currently being conducted by the
city’s Water Quality Program and is scheduled to run annually in perpetuity
according to the city’s National Pollutant Discharge Elimination System (NPDES)
stormwater permit. Stormwater pollutants analyzed include total suspended solids
(TSS); oil and grease; chemical oxygen demand (COD); ammonium-N
(NH4-N); organic-N; total Kjeldahl-N (TKN); metals (arsenic,
beryllium, cadmium, chromium, copper, lead, nickel, and zinc); hardness; and
specific organic pollutants. Table 1 shows the results for COD, TSS, and oil and
grease in effluent from outfall #2 before and after the
retrofit.
Degradation of
Petroleum Hydrocarbons From Stormwater With Compost
Although compost
filter media has been shown to remove petroleum hydrocarbons from stormwater,
thereby reducing their migration to and pollution of surface waters, what is the
eventual fate of this pollutant within the compost filter
media?
The benefit of
compost is that it can naturally provide 1) a high diversity of microorganisms,
including hydrocarbon-degrading microorganisms, and 2) an optimum environment
for these microorganisms to thrive. Hydrocarbon-degrading microorganisms require
an environmental habitat that has a sufficient and sustainable source of water
and air, mild ambient temperature, and a moderate pH. Compost provides a habitat
that supplies each of these abiotic (environmental) factors. At optimum levels,
these environmental factors provide the energy and metabolic resources that
create a widely diverse group of beneficial microorganisms that will reproduce
rapidly. While these degrader microorganisms increase their populations, they
also work rapidly and effectively to degrade organic compounds, including
petroleum hydrocarbons, for food (from carbon) to sustain their growth pattern.
Additionally, it is often the humus content of compost (six times higher in
mature compost than in typical soils) that catalyzes the degradation process of
organic compounds and contaminants (Stevenson 1994 and EPA
1998).
 |
Figure 2. CWS outfall #2 after Filtrexx FilterCell
installation |
Under optimum
environmental conditions, petroleum concentrations in soil have been reduced
from 196 to 10 mg kg-1 and from 2,109 to 195 mg kg-1 over
a one-year period (Mohn 2001). Thomassin-Lacroix et al. (2002) found that under
favorable environmental conditions, diesel fuel was degraded from 2.9 to 0.5 mg
g-1 in 65 days, and at a rate of 90 µg per gram of soil per day for
14 days. Petroleum contaminated soils amended with compost exhibited degradation
rates of 375 mg kg-1 per day compared to only 40 mg kg-1
per day without compost (Stegmann et al. 1991 and Hupe et al. 1996). At the rate
exhibited by the compost amended soil, typical petroleum
hydrocarbon-contaminated soils (the normal range is between 5,000 and 20,000 mg
kg-1) would be completely degraded in 14 to 60 days (EPA 1998).
According to the EPA (1998), compost has been shown to degrade the following
contaminants under controlled conditions and/or in field research programs:
petroleum hydrocarbons (gasoline, diesel fuel, jet fuel, oil, and grease);
polynuclear aromatic hydrocarbons (wood preservatives, refinery wastes, and coal
gasification wastes); pesticides (herbicides and insecticides); and explosives
(TNT, RDX, and nitrocellulose).
 |
 |
| Additional views of CWS outfall #2 after installation |
Specific Fate of
Hydrocarbons After Degradation by Microorganisms
In an experiment by
Hupe et al. (1996), 59% of hydrocarbons was converted to CO2, 4% was
volatilized, 4% was converted into the biomass of the microorganisms, 8% was
extractable (in its original form), and 24% was bound to residue. The fraction
that bonds with the residue often is incorporated into the core structure of the
humic materials, making it relatively bio-unavailable for decades and even
centuries (Stevenson 1994 and EPA 1998).
Bacteria and fungi
are the primary agents for degradation of organic contaminants in soil
(Alexander 1994), and increasing the diversity, population, and community
structure can accelerate the degradation of the contaminants (Cole et al. 1994).
Microbial diversity and population density are greatly increased by the addition
of compost, compared to fertile, productive soils; therefore, bioremediation
takes far less time with compost than under natural conditions (Cole et al. 1994
and EPA 1998). Normal bacteria populations in fertile soils are approximately 26
million per gram of dry soil, while in compost bacteria, populations are
approximately 417 million per gram of dry compost. Similarly, fungi populations
in fertile soils are approximately 28,000 per gram of dry soil, and
approximately 155,000 per gram for dry compost (Cole 1976 and Cole et al. 1994).
Additionally, microbial activity in mature compost can be nearly 40 times
greater in compost than in soil (EPA 1998). It is no surprise that
hydrocarbon-degrading microorganisms are often isolated from compost and used to
inoculate in situ bioremediation projects (Civilini et al. 1996 and Castaldi et
al. 1995).
Author's Bio: Britt Faucette, Ph.D., CPESC, LEED AP, is an ecologist and director of Research and Technical Services with Filtrexx International in Decatur, GA.
Author's Bio: Mo Minkara, Ph.D., P.E., is the water quality manager for the city of Chattanooga, TN.
Author's Bio: Fatima Cardoso is a research assistant with Filtrexx International in Grafton, OH.
May 2009
City of Chattanooga Urban Stormwater Retrofit
By
Britt Faucette,
Mo Minkara,
Fatima Cardoso
According to the
EPA, sediment, oil, grease, nutrients, bacteria, and heavy metals are some of
the typical pollutants found in urban and suburban stormwater runoff originating
from parking lots, roadways, lawns and gardens, pet waste, and roof shingles
(EPA 2003). These pollutants are carried into streams, rivers, and lakes,
causing severe degradation of drinking and recreational water supplies, as well
as the water quality necessary to support aquatic life.
In April 2007, the
city of Chattanooga, TN, implemented field-scale testing of FilterSoxx as a
low-impact development (LID) practice to evaluate their performance in urban
runoff pollution filtration applications. Several bench-scale experiments had
been conducted to quantify the performance of Filtrexx FilterSoxx on the removal
of these common urban and suburban stormwater pollutants, including fine
sediments (clay and silt), petroleum hydrocarbons, phosphorus, nitrogen (N),
bacteria (total coliform and E.
coli), and heavy metals (copper,
cadmium, chromium, nickel, lead, and zinc). These experiments indicated
considerable removal efficiencies: 65 and 66% for clay and silt particulates,
respectively; 84, 99, and 43% for motor oil, diesel fuel, and gasoline,
respectively; between 14 and 28% for soluble phosphorus; 15% for ammonium
nitrogen; 71 and 73% for total coliforms and E.
coli, respectively; and between
37 and 71% for heavy metals.
However,
field-scale testing of LID integrated management practices, such as Filtrexx
FilterSoxx, is necessary to augment and validate these bench-scale research
studies. Chattanooga’s Water Quality Program has been monitoring the
practicality and performance of retrofitting existing stormwater systems by
installing a Filtrexx FilterCell across a stormwater outfall draining 5.5 acres
of the city’s service vehicle parking and processing facility (Figure 1). The
outfall is known as City Wide Services (CWS) stormwater outfall #2 (Figure
2).
Quarterly
stormwater-quality sampling and analysis is currently being conducted by the
city’s Water Quality Program and is scheduled to run annually in perpetuity
according to the city’s National Pollutant Discharge Elimination System (NPDES)
stormwater permit. Stormwater pollutants analyzed include total suspended solids
(TSS); oil and grease; chemical oxygen demand (COD); ammonium-N
(NH4-N); organic-N; total Kjeldahl-N (TKN); metals (arsenic,
beryllium, cadmium, chromium, copper, lead, nickel, and zinc); hardness; and
specific organic pollutants. Table 1 shows the results for COD, TSS, and oil and
grease in effluent from outfall #2 before and after the
retrofit.
Degradation of
Petroleum Hydrocarbons From Stormwater With Compost
Although compost
filter media has been shown to remove petroleum hydrocarbons from stormwater,
thereby reducing their migration to and pollution of surface waters, what is the
eventual fate of this pollutant within the compost filter
media?
The benefit of
compost is that it can naturally provide 1) a high diversity of microorganisms,
including hydrocarbon-degrading microorganisms, and 2) an optimum environment
for these microorganisms to thrive. Hydrocarbon-degrading microorganisms require
an environmental habitat that has a sufficient and sustainable source of water
and air, mild ambient temperature, and a moderate pH. Compost provides a habitat
that supplies each of these abiotic (environmental) factors. At optimum levels,
these environmental factors provide the energy and metabolic resources that
create a widely diverse group of beneficial microorganisms that will reproduce
rapidly. While these degrader microorganisms increase their populations, they
also work rapidly and effectively to degrade organic compounds, including
petroleum hydrocarbons, for food (from carbon) to sustain their growth pattern.
Additionally, it is often the humus content of compost (six times higher in
mature compost than in typical soils) that catalyzes the degradation process of
organic compounds and contaminants (Stevenson 1994 and EPA
1998).
|
Figure 2. CWS outfall #2 after Filtrexx FilterCell
installation |
Under optimum
environmental conditions, petroleum concentrations in soil have been reduced
from 196 to 10 mg kg-1 and from 2,109 to 195 mg kg-1 over
a one-year period (Mohn 2001). Thomassin-Lacroix et al. (2002) found that under
favorable environmental conditions, diesel fuel was degraded from 2.9 to 0.5 mg
g-1 in 65 days, and at a rate of 90 µg per gram of soil per day for
14 days. Petroleum contaminated soils amended with compost exhibited degradation
rates of 375 mg kg-1 per day compared to only 40 mg kg-1
per day without compost (Stegmann et al. 1991 and Hupe et al. 1996). At the rate
exhibited by the compost amended soil, typical petroleum
hydrocarbon-contaminated soils (the normal range is between 5,000 and 20,000 mg
kg-1) would be completely degraded in 14 to 60 days (EPA 1998).
According to the EPA (1998), compost has been shown to degrade the following
contaminants under controlled conditions and/or in field research programs:
petroleum hydrocarbons (gasoline, diesel fuel, jet fuel, oil, and grease);
polynuclear aromatic hydrocarbons (wood preservatives, refinery wastes, and coal
gasification wastes); pesticides (herbicides and insecticides); and explosives
(TNT, RDX, and nitrocellulose).
|
|
| Additional views of CWS outfall #2 after installation |
Specific Fate of
Hydrocarbons After Degradation by Microorganisms
In an experiment by
Hupe et al. (1996), 59% of hydrocarbons was converted to CO2, 4% was
volatilized, 4% was converted into the biomass of the microorganisms, 8% was
extractable (in its original form), and 24% was bound to residue. The fraction
that bonds with the residue often is incorporated into the core structure of the
humic materials, making it relatively bio-unavailable for decades and even
centuries (Stevenson 1994 and EPA 1998).
Bacteria and fungi
are the primary agents for degradation of organic contaminants in soil
(Alexander 1994), and increasing the diversity, population, and community
structure can accelerate the degradation of the contaminants (Cole et al. 1994).
Microbial diversity and population density are greatly increased by the addition
of compost, compared to fertile, productive soils; therefore, bioremediation
takes far less time with compost than under natural conditions (Cole et al. 1994
and EPA 1998). Normal bacteria populations in fertile soils are approximately 26
million per gram of dry soil, while in compost bacteria, populations are
approximately 417 million per gram of dry compost. Similarly, fungi populations
in fertile soils are approximately 28,000 per gram of dry soil, and
approximately 155,000 per gram for dry compost (Cole 1976 and Cole et al. 1994).
Additionally, microbial activity in mature compost can be nearly 40 times
greater in compost than in soil (EPA 1998). It is no surprise that
hydrocarbon-degrading microorganisms are often isolated from compost and used to
inoculate in situ bioremediation projects (Civilini et al. 1996 and Castaldi et
al. 1995).