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Published with funds provided in support of the
STAC through EPA Region III, Chesapeake Bay Program.
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U.S. E.P.A. Region III
information Resource Center
AVAILABLE TECHNOLOGY
FOR THE CONTROL OF NUTRIENT POLLUTION
IN THE CHESAPEAKE BAY WATERSHED
Scientific and Technical Advisory Committee
Chesapeake Bay Program
Compiled by Andrew A. Randall and Clifford W. Randall
Edited by Clifford W. Randall and Elizabeth C. Krome
CRC Publication No. 126
October 1987
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LIST OF ABBREVIATIONS
BMP Best management practice
BOD Biological oxygen demand
CBDB Chesapeake Bay drainage basin
CMAS Completely mixed activated sludge
COD Chemical oxygen demand
CSO Combined sewer overflow
DO Dissolved oxygen
F/S Flocculation/sedimentation
HRF High-rate filtration
mgd million gallons per day
ML Mixed liquor
NURP National Urban Runoff Program
SBR Sequencing batch reactor
SS Suspended solids
TIP Total inorganic phosphorus
TOC Total organic carbon
UCT University of Cape Town
VSS Volatile suspended solids
DISCLAIMER
Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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TABLE OF CONTENTS
I. INTRODUCTION 3
II. AVAILABLE TECHNOLOGY -- OVERVIEW 9
III. FACT SHEETS 12
COMBINED SEWER OVERFLOWS
Collection System Controls
Catchbasins 15
New Sewer Design 16
Sewer Flushing 17
Polymer Injection 18
Flow Routing 19
Fluidic Regulator 20
Hydrobrake 21
Tide Gate 22
Maintenance 23
Inflow/Infiltration Control 24
Sewer Separation 26
Storage
Impoundment 27
In-Receiving Water Storage 28
Treatment
Microscreens 29
Swirl Flow and Helical Bend Regulator/Concentrator 30
High-Rate Filters 32
Flocculation/Sedimentation 34
Screening/Dissolved Air Flotation 36
Activated Carbon Adsorption 38
High-Rate Disinfection 40
NONPOINT SOURCE NUTRIENT CONTROLS
Urban
Porous Pavement 42
Asphalt with Catchbasin 44
On-Line Wet Ponds 45
Off-Line Wet Ponds 47
Extended Detention Dry Ponds 48
Recharge Basins 50
Infiltration Trenches 52
Surface Sanitation/Street Sweeping 53
Marsh Land 54
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NONPOINT SOURCE NUTRIENT CONTROLS (continued)
Agricultural
No-Till Cropland 56
Minimum Tillage 58
BMP's for Fertilizer 59
BMP's for Chemicals 61
Animal Waste Facilities 62
Vegetated Filter Strips 64
Riparian Areas 66
Controlled Drainage 67
Terraces 69
Sod Waterways 71
Cost-Sharing Programs 72
Other Approaches 73
POINT SOURCE NUTRIENT CONTROLS
Land Treatment Systems
Slow-Rate Systems 76
Rapid Infiltration 77
Overland Flow 78
Wetlands 80
Wastewater Treatment Plants
Methanol Denitrification 82
Bardenpho System 84
RBC Denitrification 86
Media Column Denitrification 87
Alternating Aerobic/Anoxic Operation 90
Oxidation Ditch 92
Tertiary Chemical Phosphorus Removal 93
Simultaneous Precipitation 94
The Economics and Performance of Biological Nutrient Removal in
Activated Sludge Systems 96
Phostrip 98
Operationally Modified (Retrofitted) Activated Sludge Systems 101
Anaerobic/Oxic (A/O) and Anaerobic/Anoxic/Oxic (A2/O) 103
Sequencing Batch Reactors 106
University of Cape Town (UCT) 108
Modified Bardenpho Ill
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I. INTRODUCTION
There is a general consensus, reached through
both scientific and subjective evaluation, that the
quality of the Chesapeake Bay aquatic environment is
rapidly deteriorating, and that nutrient enrichment is
the primary cause. The need, then, is for the
implementation of control technology that will reduce
the quantities of nutrients, i.e., nitrogen and
phosphorus, that enter the waters of the Chesapeake
Bay. This report was developed to provide readers
with an overview of the various technologies that
have been used for the control of nutrients from both
point (wastewater treatment plants) and nonpoint
(stormwater runoff, groundwater, etc.) sources of
pollution, and to assist them in the selection of
appropriate technology for particular situations.
Information on anticipated removaJ efficiencies,
potential installational and operational difficulties,
and economics has been provided to facilitate the
selection process. Much of the information contained
in this report was extracted from presentations at the
Available Technology Workshop held by the
Scientific and Technical Advisory Committee
(STAC) in Arlington, VA, on March 13-14, 1986.
Proceedings of this workshop are available from the
Chesapeake Research Consortium for those desiring
more details.
Considerations other than technological and
economic enter into decisions concerning the
implementation of nutrient control technology. For
example, the technology most needed or the efficiency
of nutrient removal required for enrichment control
will vary with the season, the precipitation pattern,
the geographical location of the inputs, and the
limiting nutrient in the affected water body, as well as
other factors. It is important to know whether the
land use of the area is mostly urban, agricultural, or
forested, because land use determines the dominant
source of pollution and the control strategy of choice.
Is the receiving water fresh or saline, free-flowing or
tidal/impounded? How important to the response of
the aquatic system are the nutrient sinks such as
bottom sediments? What is the trophic state of the
aquatic system, i.e., is the purpose of nutrient control
to protect the existing quality of the water or to
restore it to a desired former quality? These
considerations are important and will be discussed
briefly in the following sections of this chapter.
Nutrient Inputs
Nutrient inputs to the bay waters include point
(discrete) and nonpoint (diffuse) sources. Sewage
treatment plants (STP's) represent the major point
source, although industrial wastewaters may be
important in some basins. The extent of urbanization
and the sewered population in the basin compared
with the agricultural activity determine the relative
importance of the point sources in each watershed,
and each river basin accordingly can be classified as
dominated by either point or nonpoint sources.
Nonpoint sources include stormwater runoff from all
types of land use, baseflow to streams (groundwater),
and atmospheric deposition. The importance of the
nonpoint sources is greatly influenced by both land
use and precipitation patterns. The importance of
nonpoint sources increases during wet periods and
decreases during dry periods, and also varies according
to agricultural practices, the extent of construction,
the percentage of impervious area, and erosion-control
practices in effect. The point source contributions
remain relatively constant and therefore tend to have
greater importance during dry seasons, which
generally coincide with the peak growing season.
Combined sewer overflows (CSO's) can be
major sources of nutrient pollution in urban areas
where sewers transport sewage during dry periods and
a mixture of sewage and stormwater runoff during wet
periods. CSO's are technically a combination of
point and nonpoint flows but can generally be treated
as point sources because they are discharged at
specific, identifiable points. Because CSO discharges
are diluted, untreated sewage, they typically contain
higher concentrations of organic matter and nutrients
than either treated point source contributions or
stormwater runoff. The control of CSO's can be
critical to restoration and recovery of water quality in
the affected areas, and appropriate technologies for
their control have been included in this report. CSO's
are particularly significant in the James River directly
below Richmond.
Atmospheric sources also contribute nutrients,
especially nitrogen, to the Chesapeake Bay aquatic
environment. The contributions are particularly
significant in the vicinity of large metropolitan areas
such as Washington and Baltimore. Smullen et al.
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Introduction
Table 1. Bay-wide nutrient loadings (%), March to October.
Phosphorus
Nitrogen
Rainfall condition
Point
Nonpoint
Point
Nonpoint
Dry year
Average year
Wet year
69
61
36
31
39
64
38
33
19
62
67
81
Source: Chesapeake Bay Program, U.S. Environmental Protection Agency (1982).
(1982) have estimated these contributions and
compared them to other sources.
Nutrient Loading
Researchers for the EPA Chesapeake Bay
Program estimated the 1980 nutrient loadings
delivered to the bay from its total drainage basin and
projected the 2000 loadings (Tippie et al. 1983).
They also estimated the relative fractions of loadings
from the point and nonpoint sources and concluded
that on an annual basis most of the nitrogen is
contributed by nonpoint sources, particularly cropland
runoff. They also concluded that point sources,
especially STPs, contribute most of the phosphorus,
except during wet years (Table 1). It has also been
observed that most of the nitrogen entering the bay is
transported from watersheds throughout the bay basin,
while the phosphorus loadings originate nearer the
bay, i.e., below the fall line (Hartigan et al. 1983;
Tippie et al. 1983). The difference is due to the
differing chemical interactions of the phosphorus and
nitrogen compounds as well as the differing sources.
The Chesapeake Bay watershed contains eight
major basins (Table 2). The three largest tributaries of
the bay, the James River, the Potomac River, and the
Susquehanna River, transport most of the phosphorus
(70%) and nitrogen (78%) loads that enter the tidal
waters of the Chesapeake Bay. The James is the
largest contributor of phosphorus (28%); each of the
other two contributes 21%. The Susquehanna
dominates the nitrogen inputs, contributing 40%,
compared with the 24% and 14% contributed by the
Potomac and James, respectively. The West
Chesapeake basin, centered near Baltimore, is the
fourth largest contributor of both nutrients, despite its
comparatively small land area. This small area
contributes 17% of the phosphorus and 11% of the
nitrogen that enters the bay waters.
Tributary Classification
The river basins have been classified by
Hartigan et al. (1983) as point or nonpoint source-
dominated for phosphorus contributions. These
researchers concluded that the point source loads of
phosphorus to the Potomac and James exceed the
nonpoint source loads, but that nonpoint sources
contribute most of the phosphorus from the
Susquehanna basin. In the urbanized Patuxent River
and West Chesapeake basins, the phosphorus loadings
from point sources exceed those from nonpoint
sources, but in the largely rural Rappahannock, York,
and Eastern Shore basins, nonpoint contributions are
always the dominant source.
Nitrogen loadings from the major river basins
are more often dominated by nonpoint sources than
are phosphorus loadings. Nonpoint sources provide
most of the nitrogen inputs to the Susquehanna and
Potomac under all hydrologic conditions. However,
below the fall line, point sources dominate the
nitrogen inputs into the Potomac. Point sources
constitute most of the nitrogen load to the James
River, but nonpoint nitrogen sources become
important in a wet year. In the Patuxent River basin,
point sources of nitrogen are dominant only under dry
conditions, but in the West Chesapeake basin point
sources are always greater. The nitrogen loadings to
the rest of the basins are primarily from nonpoint
sources, as are the phosphorus loadings.
STP's rather than industrial wastewater inputs
contribute most of the point source nutrients in
virtually all cases, and cropland contributes most of
the nonpoint source nutrient load basinwide. This
comparison holds true for both phosphorus and
nitrogen, although the proportion of the nitrogen
contributed by cropland is greater than that of
phosphorus. The importance of cropland reflects both
its relatively high per-acre loadings and the large areas
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Introduction
of the basin devoted to agriculture (Mackiernan,
1984). Other sources of runoff contribute only 11-
12% of the phosphorus load and 6-7% percent of the
nitrogen basinwide. However, urban runoff inputs
can have a significant impact on water quality in
localized areas, and may even be dominant if point
source treatment is highly efficient. Watershed-wide,
the urban runoff loads are small, because only 3% of
the entire basin can be classified as true urban land.
Table 3 is a closer look at nutrient contributions
relative to the type of land use, and it shows that
cropland in general has the highest unit loadings,
measured in pounds per acre per year, for both
nitrogen and phosphorus. Note, however, that the
ranges are very large. The overlap reflects regional
differences in soil type, topography, fanning
practices, and other factors. The most intensive urban
uses can yield more nutrients per unit area than well-
managed, low-tillage cropland on pervious soils
(Mackiernan, 1984).
Point and Nonpoint Source Tradeoffs
The preceding information shows that
technologies for controlling both point and nonpoint
source inputs are needed to reduce nutrient pollution
in the Chesapeake Bay. It also demonstrates that the
importance of the source depends on the nutrient, i.e.,
nitrogen or phosphorus, being controlled, the land use
patterns and cultivation practices in the area of
concern, the season of the year, and year-to-year
climatological variation. Regardless of these factors,
Table 2. Percentages of nitrogen and phosphorus contributions to the Chesapeake Bay by the
eight major basins, by point and nonpoint source, and by dry, average, and wet years (March-
October).
Point sources Cropland
Other
Nonpoint
Basin
Dry Avg. Wet Dry Avg. Wet Dry Avg. Wet Dry Avg. Wet
Susquehanna
Patuxent
Potomac
Rappahannock
York
James
W. Chesapeake
Eastern Shore
10
61
48
17
22
71
85
13
10
49
44
13
13
62
72
10
5
26
28
7
7
43
52
4
-
—
-
—
—
-
—
Total
38 33
19
Susquehanna
Patuxent
Potomac
Rappahannock
York
James
W. Chesapeake
Eastern Shore
24
88
67
47
50
86
93
44
23
83
59
39
35
81
85
40
12
58
34
14
10
63
67
16
Nitrogen
85
43
48
72
77
29
20
83
60 75
Phosphorus
91
66
66
84
87
49
40
92
5
8
8
15
10
9
8
7
4
8
6
9
6
8
8
4
90
39
52
83
78
29
15
87
90
51
55
87
87
38
28
90
95
74
72
93
93
57
48
96
60
10
23
39
44
12
8
50
77
33
50
71
76
29
25
79
62 67 81
17
7
18
22
6
7
7
10
11
9
16
15
14
8
8
5
76
12
33
53
50
14
7
56
77
17
41
61
65
19
15
60
88
42
66
86
90
37
23
84
Total
69 61 36
27 53
12 11 31 39 64
Source: Chesapeake Bay Program, U. S. Environmental Protection Agency (Tippie et al. 1983).
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Introduction
Table 3. Nutrient loading by land-use type in the Chesapeake Basin.
Estimated loading rate (Ibs/acre/yr)
Land use
Percentage in basin
Total nitrogen
Total phosphorus
Cropland
Pasture
Forest
Urban/suburban
15-20
8-12
60-65
3-5
8-18
2-6
0.5-2
4-10
1.5-5
0.3-0.5
0.05-0.1
1-2
Source: Chesapeake Bay Program, U.S. Environmental Protection Agency (1982).
it seems reasonable to assume that nutrient loadings
from point and nonpoint sources are comparable in
biological availability in the Chesapeake Bay
environment and, therefore, cost-effectiveness analysis
can be used for the development of control strategies.
It is commonly stated that nonpoint source
phosphorus is less available than phosphorus in the
effluents of biological wastewater treatment plants.
This is true over the short-term and is applicable to
flowing streams. However, phosphorus bound in
sediments can be solubilized by either anaerobic or
extreme pH conditions, and when solubilized is
readily available for algal growth. The solubilization
of both phosphorus and ammonia from sediments is
an annual seasonal occurrence in estuarine
environments such as the Chesapeake Bay. Thus,
control of enrichment requires that the nutrients be
prevented from entering the water body, and it matters
little on a long-term basis whether the original source
was point or nonpoint. Consequently, control
strategies for long-term water quality goals can be
developed on an economic trade-off basis as presented
and discussed by Kashmanian et al. (1985) and
Shabman and Norris (1986).
Short-term goals are not as amenable to trade-off
strategies because of the seasonal nature of algal
growth. Consider that, if phosphorus is the limiting
nutrient, for every pound of phosphorus available to
them, algae can generate 111 pounds of organic
matter as algal biomass. Also consider that bacteria
will consume 138 pounds of oxygen in the eventual
destruction of the 111 pounds of algal biomass. If
the oxygen is consumed quickly, the level of oxygen
in the water will be seriously depleted, with
undesirable consequences. On the other hand, if the
consumption rate can be slowed or consumption
partially prevented, reaeration will mitigate the
detrimental effects. Thus, the reduction of limiting
nutrient loads during peak growing seasons (when
point sources usually become most significant) can
have a considerably greater impact than reductions
during other seasons.
Limiting Nutrient
The issue of whether nitrogen or phosphorus is
the nutrient limiting algal growth in the Chesapeake
Bay system has been addressed by the Scientific and
Technical Advisory Committee in a previous
publication (STAC 1986). The situation is complex
and depends on the salinity of the water, the season,
and the dynamics of oxygen and nitrate consumption
in the water. In addition there are other perspectives
to consider. Will there be a system response for any
reduction in nutrient inputs? And can technology
reduce either of the principal nutrients enough to slow
the enrichment rate in the system to the desired level?
The two perspectives can be illustrated by a
hypothetical situation (Figure 1). In this scenario,
the current concentration would be considerably
greater than the maximum growth response
concentration. The current concentration would have
to be reduced below the maximum growth response
concentration before any improvement in the system
would be observed. A lesser reduction would result in
no observable response but would move the system
closer to a response point. The figure also shows
that the concentration achievable when all usable
forms of technology had been fully implemented
would unfortunately still exceed the desired
concentration, (the concentration required to achieve
the water quality objectives). Thus the pollution
control effort would fall short of its objective, but
substantial improvement would have been achieved
and the usable life of the system might have been
prolonged.
The technologically achievable concentrations of
both nitrogen and phosphorus in the Chesapeake Bay
are not known. Neither is the desired concentration,
i.e., the goal. These concentrations need to be defined
as soon as possible to avoid hampering restoration
efforts. The decision whether to emphasize nitrogen
or phosphorus controls for long-term purposes can be
considered logically, however, on the basis of the
chemistry and distribution of the two elements.
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Introduction
o
o.
s
o
Maximum Growth Rate
Concentrations
Figure 1. Hypothetical scenario for nutrient control in the Chesapeake Bay.
Controllable vs. Non-Controllable Nutrient
Sources
Nitrogen is a gas and is available in limitless
supply in the atmosphere. In addition, automobile
and other exhausts discharge nitrous oxide compounds
into the atmosphere. Rainwater eventually washes
these compounds out of the atmosphere into streams
and other bodies of water. Nitrogen will adsorb to
soil and sediment particles fairly readily when in the
form of ammonia but will adsorb negligibly in the
nitrate form. Ammonia, however, is invariably
converted to nitrate in an aerobic soil or aquatic
environment through the action of bacteria.
Consequently, nitrates in groundwater are virtually
uncontrollable, and those in stormwater runoff are
very difficult to control. Since most of the nitrogen
inputs are nonpoint, it can be seen that the
controllable fraction is significantly limited.
Phosphorus, by contrast, does not have a
gaseous phase and is very surface-active. That is, it
readily adsorbs to soil and sediment particles and will
stay adsorbed except under extreme pH or reduced
conditions. Thus it is amenable to both point and
nonpoint source controls. Furthermore, most of the
phosphorus inputs are point sources, and point
sources are readily controllable. Thus, for a long-
term control strategy, phosphorus appears to be the
nutrient of choice. This conclusion presupposes that
phosphorus can be reduced sufficiently to make it the
limiting nutrient, even if it were not originally, and
that the resulting phosphorus-controlled system
would have a lesser growth response than a nitrogen-
controlled system, because of the limited nitrogen
controls available.
It should be recognized, however, that
considerable short-term gains in water quality could
be made through nitrogen control during the growing
season, in locations where it is the limiting nutrient.
Because such gains reduce the organic matter
generated in the system and consequently make it
easier to restore the system, a strategy of combined
nitrogen and phosphorus control is recommended.
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Introduction
LIST OF REFERENCES
Hartigan, J., Sutherland, E., Bonucelli, H., Canvacas,
A., Friedman, J., Quasebarth, T., Raffe, K.,
Scott, T., and White, J. (1983) Chesapeake Bay
Basin Model Final Report. Northern Virginia
Planning District Commission, Annandale, VA.
240 pp + appendices.
Kashmanian, R., Downing, D., Jaksch, J., and
Mahesh, P. (1985) Managing Point/Non-Point
Source Loadings: A Cost Effective Approach to
Nutrient Reduction in the Chesapeake Bay.
Proceedings. Estuarine Research Federation
Conference. Durham, NH.
Mackiernan, G. (1985) Sources and Impacts of
Nutrients in the Chesapeake Bay. Land Use and
the Chesapeake Bay. Virginia Cooperative Ex-
tension Service Publication 305-003. pp 1-20.
Scientific and Technical Advisory Committee,
Chesapeake Bay Program (1986). Nutrient
Control in the Chesapeake Bay. Chesapeake
Research Consortium, Inc. 23 pp + appendices.
Shabman, L. and Norris, P. (1986) Coordinating
Point and Non-Point Pollution Control:
Prospects for a Virginia Case Application.
Department of Agricultural Economics,
VPI&SU, Blacksburg, VA. 19 pages.
Smullen, J., Taft, J., and Macknis, J. (1982) Nutrient
and Sediment Loads to the Tidal Chesapeake
Bay System. Chesapeake Bay Program
Technical Studies: A Synthesis. U. S.
Environmental Protection Agency, Washington,
DC. pp 154-219.
Tippie, V., Gillelan, M., Haberman, D., Mackiernan,
G., Macknis, J., and Wells, H. (1983)
Chesapeake Bay: A Framework for Action. U.
S. Environmental Protection Agency,
Philadelphia, PA. 186 pp + appendices.
U.S. EPA (1982) Chesapeake Bay Program Technical
Studies: A Synthesis. G. Macalaster, D.
Barker, and M. Kasper, Eds. U. S.
Environmental Protection Agency, Washington,
DC. 632pp.
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H. AVAILABLE TECHNOLOGY-OVERVIEW
Many technologies and techniques available for
the control of nutrients are appropriate for use in the
Chesapeake Bay Drainage Basin. The fact sheets in
Section III of this paper briefly describe the most
important of these technologies and give cost and
efficiency information whenever possible. Also
included in most fact sheets is a section on the
potential advantages and disadvantages of the system,
followed by a few helpful references for more
information. This is by no means a comprehensive
listing of the sources used.
Some of the technologies or techniques included
in the fact sheets are relatively new or may not have
been extensively researched. Qualitative remarks
regarding efficiencies have been included when found
in the pertinent literature and when no actual data
were available.
The general discussion that follows should serve
as an orientation to the processes described in the fact
sheets.
Control of Combined Sewer Overflows
The technology available for the control and
treatment of combined sewer overflows (CSO's) can
be divided into three major categories: collection
system controls, storage, and treatment.
Collection system controls are management
alternatives for wastewater interception and transport.
Options may be as simple as improved maintenance
or as labor-intensive and costly as sewer separation.
Between these two extremes are a variety of devices,
such as fluidic regulators, and system approaches,such
as remote flow monitoring and control. All of these
methods, with the exception of sewer separation,
allow the maximum use of existing collection
facilities by control and/or enhancement of flow
through the system pipelines.
Storage is the impoundment of wet-weather
flow until conditions permit it to be sent to treatment
facilities. It is the best documented abatement
measure among the technologies presently available.
It is also an essential one because of the high volume
and variability of storm flow. Storage permits
maximum use of existing facilities and is the most
cost-effective way to reduce pollutants. Some storage
facilities may be designed to treat wastewater via
sedimentation or may have other functions such as
dry-weather flow equalization or flood protection.
Detentidn facilities can also provide storage, flow
reduction, and treatment by settling or infiltration.
But even impoundment in and of itself is an effective
way of dealing with stormwater flows.
Treatment technologies specifically directed at
CSO's are confined to physical/chemical processes.
Biological processes, which are dependent on
microorganisms, have difficulties adapting to the
intense flow conditions and shock-load effects of
storm-generated overflows. Because
physical/chemical treatment usually relies on
chemical dosing, which can be varied with changing
conditions, these systems have an inherent flexibility
and are able to cope with runoff from storms.
Physical devices such as swirl regulators and
sedimentation basins remove pollutants more
efficiently when solids concentrations are high.
Also, physical/chemical technologies are well suited
to high-rate applications, which reduces capital costs.
In practice most systems integrate several or all
of these approaches to CSO control. Two common
integrated systems are storage/treatment and dual-use
wet-weather flow/dry weather flow facilities.
Storage/treatment systems use storage to protect the
treatment system, reducing the quantity and
improving the quality of stormwater flows, and
allowing the treatment system to stay within its
operational abilities. Dual-use wet-weather flow/dry-
weather flow facilities are those that can provide
effective treatment under both wet and dry conditions.
High-rate filtration, microscreening, and equalization
basins are just some of the potential technologies
capable of constant use.
Control of Urban Non-Point Source
Pollution
Most of the methods for controlling urban non-
point pollution (often referred to as urban best
management practices or BMP's) are matters of land
management These practices may pertain either to
the source or site of runoff, or to the collection
system of storm drains.
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10
Overview
Source controls are aimed at erosion, runoff
quantity (flooding), and pollutants leaving the sites
where they originate. Control is accomplished in
many ways, ranging from policies concerning use,
storage, and disposal of chemicals to structural
technologies such as porous pavements. Even simple
measures such as erosion control at construction sites
can be very significant. These measures, alone or in
combination, can be effective controlling nutrient and
pollutant transport in runoff, preserving natural
drainage patterns even with new construction,
reducing drainage costs and pollution, and enhancing
aesthetics, groundwater supplies, and flood protection.
Collection system controls for stormwater
systems involve the use of detention, retention, and
infiltration structures. These structures may vary
considerably in design, but most are essentially
basins or ponds that receive and hold collected
stormflow. These basins or ponds are termed either
on-line or off-line, depending on what happens to the
water that comes into each structure. On-line basins
and ponds ultimately discharge part or all of the water
received into local surface waters. Treatment is
usually accomplished by sedimentation in detention
ponds and by biological action in wet ponds. Off-line
basins and ponds rely on infiltration into the
groundwater or evapotranspiration into the
atmosphere and may virtually eliminate pollutants
through these processes.
Many of these techniques can be used in
combination within a single system. For example,
stormwater can be re-used for irrigation, and small
lakes or wet ponds can be used for recreation. In
addition, some of the same strategies used for CSO's
are equally applicable to stormwater systems.
Examples of these are hydrologic-hydraulic design
rationales and new cross-sectional shapes for
pipelines.
Control of Agricultural Nonpoint Source
Pollution
Agricultural best management practices deal
with pollution that originates from either croplands or
pasturelands and farm animal facilities. Cropland
pollution is the result of erosion and transport of
fertilizers and pesticides by stormwater runoff.
Pollutants from pasturelands and animal facilities
result from the presence of animal wastes.
BMP's for croplands can be as simple as more
efficient use of fertilizers and herbicides or as complex
as no-till farming. Measures for animal wastes are
much more structurally intensive, involving
construction of storage or treatment facilities for
manure and necessitating planning in relationship to
surface waters. Improved practices for the land
application of manure in relationship to the season
and local weather are also an important part of
controlling nutrients from animal wastes.
Control of Point Source Pollution
Wastewater treatment plants can operate in a
variety of ways depending on the type of waste being
treated and the degree of removal desired (Table PT-7).
For the control of nutrients the methods used may be
chemical, biological, or both.
Chemical removal is the traditional method of
removing phosphorus from wastewater. The
chemicals may be added during primary treatment,
during activated-sludge treatment, or after routine
treatment in a separate (tertiary) treatment process.
Chemical removal of phosphorus is possible
because orthophosphate, a form of phosphorus that is
soluble and would normally leave in the plant
effluent, will react with chemicals such as alum and
lime to form insoluble compounds. The phosphorus
precipitates out of solution, is settled, and is removed
as waste sludge.
Biological treatment processes rely on the
metabolic processes of microorganisms to remove
nitrogen and/or phosphorus. In the case of nitrogen,
nitrates are recycled into an anoxic zone (oxygen is
not present) where microbes break them down while
using them as an oxygen source to metabolize
organic compounds. Nitrogen is converted to its
elemental form during the process and is released as a
gas. Using nitrates as an oxygen source instead of
discharging them also recovers a significant amount
of aeration energy if influent wastewater is utilized as
the organic food source. For phosphorus removal,
flow is passed through an anaerobic zone (neither
oxygen or nitrates are present). Here microbes store
organics as food, and energy is saved through
microbial anaerobic stabilization for BOD that would
otherwise require aeration. When flow reaches an
aerobic zone the microbes metabolize the stored
organics and store the energy as ATP, which is
partially composed of phosphorus. Thus the
microbes take most of the available phosphorus into
their cells, using it to make ATP. As a result
phosphorus can be removed by removing the
microbes in the form of waste sludge.
Both types of treatment have their advantages
and disadvantages. Reliance on chemicals can add
flexibility to operations since chemical dosages may
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Overview
11
be easily and quickly varied; also, performance can be
more reliably predicted for most wastewaters. The
disadvantages of chemical processes are the large
amounts of sludge and high operating costs.
Biological treatment can be much more energy-
efficient and less expensive to operate; but some
biological systems have high capital costs, and
performance can be upset for a variety of reasons such
as shock-loading or the presence of toxins.
For both processes, retrofit is feasible and may
be cost-effective depending on the conditions and
treatment level needed. For achieving stringent
standards, the use of both chemical and biological
nutrient removal in the same plant may be the most
cost-effective solution.
Control of Atmospheric Pollution
Technology for the control of atmospheric
pollution is confined to source controls. Catalytic
convenors and unleaded gas for automobiles, and
industrial air pollution controls such as packed
columns and electrostatic precipitators are examples
of these technologies. Emission standards and public
policy in general have an obvious effect on the
quantity of pollutants released to the atmosphere and
ultimately contaminating surface waters through
precipitation. Because different technologies and
practices are used to control air pollution, and because
its short-term significance is minor relative to other
pollutant sources for the Chesapeake Bay, no fact
sheets for air pollution technology are included in this
report.
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III. FACT SHEETS
COMBINED SEWER OVERFLOWS
Collection System Controls
Storage
Treatment
NONPOINT SOURCE NUTRIENT CONTROLS
Urban
Agricultural
POINT SOURCE NUTRIENT CONTROLS
Land Treatment Systems
Wastewater Treatment Systems
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COMBINED SEWER OVERFLOWS
COLLECTION SYSTEM CONTROLS
Catchbasins
New Sewer Design
Sewer Flushing
Polymer Injection
Flow Routing
Fluidic Regulator
Hydrobrake
Tide Gate
Maintenance
Inflow/Infiltration Control
Sewer Separation
STORAGE
Impoundment
In-Receiving Water Storage
TREATMENT
Microscreens
Swirl Flow and Helical Bend Regulator/Concentrator
High-Rate Filters
Flocculation/Sedimentation
Screening/Dissolved Air Flotation
Activated Carbon Adsorption
High-Rate Disinfection
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CSO: Collection System Controls 15
CATCHBASINS
Description
Catchbasins are chambers or wells built at the curbline of a street for the
admission of runoff to a sewer or stormwater system. A sump traps sediment
preventing heavy or large solid matter from the street from entering the sewers.
Catchbasins are also relied upon to prevent odor from escaping low-velocity
sewers by providing a water seal. Recently there have been attempts to optimize
configurations, design, and maintenance of basins to enhance removal of solids.
Efficiency
Conventionally designed Catchbasins may not be effective for solids removal.
Infrequently cleaned Catchbasins can actually contribute to pollution when
trapped solids are flushed out. With more frequent cleanings, however, they may
be somewhat more effective. A study in Boston yielded potential removals of
60-97% of solids, 54-88% of BOD, and 10-56% of COD. Addition of inlet
strainers marginally increases pollution removal (maximum of 10%), but these
strainers also accumulate solids during dry weather.
Economics
Maintenance and disposal of accumulated solids constitute the majority of costs
for pollutant removal with catchbasins. Cost studies in Boston concluded that
frequent cleaning (every six months) of catchbasins was very cost-effective
compared with relying on treatment plants, sewer cleaning, in-line storage, and
swirl treatment. With semi-annual cleanings of catchbasins, costs were
$0.0046/lb solids, compared with $0.0391 for an in-line system, and $0.1527
for a system in Saginaw, MI, utilizing swirl facilities. Catchbasins are very
poor, however, for control of nutrients.
Advantages
1. Effectively reduce total pollution.
2. Improved designs may result in higher removal efficiencies.
Disadvantages
1. Poor for nutrient removal.
2. Require frequent cleaning and disposal.
3. Strainers impractical because of maintenance requirements.
4. Lack operational flexibility, and later improvement not feasible.
Useful References
1. Aronson, G. L., Watson, D. S., and Pisano, W. C. (1983). Evaluation of
Catchbasin Performance for Urban Stormwater Pollution Control. USEPA
Report No. EPA-600/2-83-043. NTIS No. PB 83-217-745.
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16 CSO: Collection System Controls
NEW SEWER DESIGN
Description
New design methods avoid some of the inadequacies encountered with older
concepts such as the Rational Method and the Kutter or Manning equations. In-
line storage, steeper slopes, and different cross-sectional shapes for sewers are
also used to control runoff quantity and quality. A major concern is reducing the
"first flush" of pollutants associated with storms.
Efficiency
The Unit Hydrograph Model and the EPA Storm Water Management Model have
predicted peak runoff rates 25-150% greater than values obtained using the
Rational Method. These models calculate storage volume for effective use of
flow control devices. Design of sewers to maintain flushing velocities in dry-
weather flows reduces pollutants in the "first flush". Upstream storage is
effective in reducing overflow events and controlling pollutants.
Economics
Costs of sewer and pumping station installation and power should be compared
with capital and operational costs for conveyance, storage, and treatment of the
first flush that would otherwise result. In a study in Elizabeth, NJ, the least
expensive sewer design for a given treatment level was a combined sewer system
with additional storage provided. Cost of in-line storage vs. basins depends on
site restrictions, but off-line basins tend to be less costly (as little as 30% of the
cost of in-line storage).
Advantages
1. Reduces costs and operational problems at treatment plants.
2. Greatly diminishes overflows and release of untreated wastes.
3. Reduces maintenance problems from sediment buildup.
4. Cost of pollution control by in-system storage and flow control devices is
small compared to the total cost of sewer system.
Disadvantages
1. May not be as cost-effective as alternatives.
2. System performance difficult to alter once constructed.
3. More difficult to construct and difficult to design.
Useful References
1. Kaufman, H. L. (1978). Conventional and Advanced Sewer Design Concepts
for Dual Purpose Flood and Pollution Control. USEPA Report No. EPA-
6QQ/2-78-Q90. NTIS No. PB 285 663.
2. Sonnen, M. (1977). Abatement and Deposition and Scour in Sewers.
USEPA Report No. EPA-6QQ/2-77-212. NTIS No. PB 276 585.
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CSO: Collection System Controls 17
SEWER FLUSHING
Description
Sewer flushing is the use of water to flush deposited solids, preventing
continuous buildup between storms, and facilitating the routing of combined
sewage to treatment.
Efficiency
Flushing can reduce solids deposited in dry weather for small-diameter laterals. A
35-45% removal of organics for segment lengths of more than 1000 ft has been
shown. Daily flushing in one area of Boston reduced overall SS discharge by
7% and BOD by 17.6%. Sewer flushing during dry days is more effective at
removing BOD than SS because the heavier particles tend to resettle
downstream. Generally flushing is more successful with strong sewages.
Economics
When combined with storage, sewer flushing may be cost-effective for BOD
removal. In Boston cost reductions were 7% for flushing and storage as
compared with a CSO storage/treatment and disinfection facility designed for a
one-year storm. Automatic flushing stations were estimated at $100,000 each in
1979, including operations and maintenance costs (20 years at 6.625%).
Advantages
1. Alleviates wet-weather CSO pollution, reduces downstream treatment
requirements.
2. Maintains open flow areas for the pipes in the sewer system.
Disadvantages
1. Must be used with great frequency to remain effective.
2. May not be cost-effective, depending on site conditions, even for existing
sewers.
Useful References
1. Pisano, W. C. (1979). Dry-Weather Deposition and Flushing for Combined
Sewer Overflow Pollution Control. USEPA Report No. EPA-600/2-79-
121
2. Kaufman, H. L., and Fuhsiung, L. (1980). Alternatives for Evaluation of
Sewer Flushing Dorchester Area- Boston. USEPA Report No. EPA-
600/2-80-118. NTIS No. PB 81-142 648.
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18 CSO: Collection System Controls
POLYMER INJECTION
Description
Polymer is injected into combined sewer flow, reducing the resistance of the
water against the pipe walls and greatly increasing the flow capacity of the pipe.
This technique can be used to reduce localized flooding and excessive overflows
for a marginally inadequate line during critical periods.
Efficiency
Up to 144% increases in capacity have been achieved. Polymer concentrations
of 35-100 mg/1 have eliminated surcharges of more than 6 ft Treatment
efficiency is improved because more of the flow reaches the treatment plant.
Economics
Direct cost savings are possible since relief sewer construction can be eliminated.
These savings can be substantial in areas where pre-existing structures make
construction or alterations expensive.
Advantages
1. Flooding and release of untreated flow can be decreased or eliminated without
the expense, delay, and disruption of normal activities associated with
construction.
Disadvantages
1. Does not eliminate problem; requires more operation and maintenance than a
properly designed sewer.
2. Possibility of operator or mechanical error.
3. Ongoing expense.
Useful References
1. Chandler, R. W., and Lewis, W. R. (1977). Control of Sewer Overflows by
Polymer Injection. USEPA Report No. EPA-600/2-77-189. NTIS No. PB
272 654.
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CSO: Collection System Controls 19
FLOW ROUTING
Description
Flow routing maximizes the use of existing sewer capacity to control overflows
and enhance system treatment. Remote monitoring of rainfall and flow levels is
integrated with a centrally computerized console. Control gates installed at
strategic points control passing flow so that existing in-pipe storage may be
used to alleviate peak flows and pollutant overflows.
Efficiency
In Seattle, WA, overflow and pollutant reduction from 12 overflow points
averaged 55-68%. Experimental automatic control eliminated 90% of the
overflow volume. DO has increased by 1-2 mg/1 and coliforms have decreased
50% in the receiving water. In Elizabeth, NJ, the number of overflow events
was reduced by 65%.
Economics
The Seattle system, serving 13,250 acres, cost $400/acre in the mid-1970's. A
specific study for Seattle at the time stated that sewer separation would cost
$10,000/acre. One-half the costs for flow routing were for computers and
software.
Advantages
1. Effective use in Seattle, Minneapolis-St. Paul, and Detroit.
2. Uses existing system, minimizing new construction.
3. Computers are increasingly capable and less expensive.
Disadvantages
1. Site-specific; requires large, flat existing combined system.
Useful References
1. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
J4 859-870.
2. Watt, T. R. (1974). Sewerage System Monitoring and Remote Control.
USEPA Report No. EPA-60Q/2-74-022. NTIS No. PB 242 107.
3. Leiser, C. P. (1974). Computer Management of a Combined Sewer System.
USEPA Report No. EPA-67Q/2-74-Q22. NTIS No. PB 235 717.
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20 CSO: Collection System Controls
FLUIDIC REGULATOR
Description
A fluidic regulator is a self-powered structure in the sewage flow stream and
permanently open flow passages. It has no mechanical moving parts and uses
energy from the sewage flow. Using simple dip-tube sensors, the regulator
diverts flow at a certain level. It is made of non-corrodible materials such as
concrete and stainless steel.
Efficiency
Fluidic regulators can achieve most of the performance of dynamic overflow
regulators and are more reliable in terms of blockages, fouling, and other
problems typical of conventional regulators. Performance may decline outside of
design range.
Economics
Fluidic regulators are estimated to cost 40% more and 50% less than retrofit of
conventional static and conventional dynamic regulators, respectively. For a
new installation the fluidic regulator costs roughly 10% more than a
conventional static unit. Maintenance costs should be less than for conventional
dynamic units.
Advantages
1. Flexibility and performance near that of a dynamic regulator but at lower
cost.
2. Simple, reliable technology with low maintenance requirements.
3. Has been used in Philadelphia, PA.
Disadvantages
1. Limited performance information available.
Useful References
1. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
1& 859-870.
2. Freeman, P. A. (1977). Evaluation of Fluidic Combined Sewer Regulators
Under Municipal Service Conditions, USEPA Report No. EPA - 600/2-77-
071,NTISNo. PB272834.
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CSO: Collection System Controls 21
HYDROBRAKE
Description
A Hydrobrake (a trade-marked name) is a small device that can be used in
stormwater tanks as a flow regulator, as a CSO regulator, or as an upstream off-
line flow attenuator. The Hydrobrake delivers a virtually constant rate of
discharge regardless of head variations, without moving parts or the use of
external energy. Hydrobrakes can be used in conjunction with off-line storage or
catchbasins to reduce overflow events that would cause street and basement
flooding.
Efficiency
Hydrobrake flow rates are substantially lower than those for an orifice of the
same size and operate more independently of head than conventional openings.
Hydrobrakes can dampen "first flush" effects, enhancing use of existing facilities,
as well as alleviating surcharge and basement flooding problems.
Economics
Where surface ponding is possible, Hydrobrake use without off-line storage
structures is most cost-effective. Even with storage structures Hydrobrakes can
be more cost-effective than other alternatives where both surcharging and
overflows are the prevailing problems. The Hydrobrake itself is relatively
inexpensive and can yield large savings for sites where other alternatives are
prohibitive in cost. In Cleveland, inlet control with the Hydrobrake cost $140-
$240/acre drained, or $13,800-$17,700/acre when combined with storage.
Retention combined with pumping would have cost $22,000/acre, according to
calculations in the Cleveland study.
Advantages
1. Has been used in Cleveland, OH, as well as New York and Rochester, NY.
2. Not susceptible to blockage.
3. Reduces sewer surcharge and basement flooding.
4. Minimal maintenance requirements.
Disadvantages
1. Manufacturing and delivery delays for specialty items.
2. Small diameters (below 2 in.) may clog in very filthy waters.
Useful References
1. Matthews, T. M., Pitts, P. D., Jr., Larlham, R. C., and Koogan, J. C.
(1983). Hydrobrakes Regulated Storage System for Stormwater
Management. USEPA Report No. EPA-6QO/2-83-097. NTIS No. PB 84-
110378.
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22 CSO: Collection System Controls
TIDE GATE
Description
A rubber "duck-bill" tide gate has been developed to prevent the many problems
associated with conventional tide gates. The duck-bill gate is a passive device,
requiring no outside energy source, and seals tightly by virtue of its shape and
material. It protects collector sewers and interceptors from the inflow of tidal or
high river-stage waters just as conventional tide gates do.
Efficiency
The duck-bill tide gate is more likely than conventional tide gates to effectively
seal the pipeline, preventing overflows and plant bypassing. The chance of
severe failure is decreased also. The capacity of the system is maintained more
reliably because backflow conditions are less likely.
Economics
The main economic advantages of the duck-bill gates come from increased
reliability over conventional tide gates. Poor performance of tide gates causes
backflows, flood conditions, increased treatment costs, and treatment plant
upsets. Upstream flooding is less likely since the capacity of the system is
better maintained. Maintenance costs may be significantly less.
Advantages
1. Conventional tide gates fail to close tightly (because of debris blockage,
warpage, and corrosion), stick in one position, and need constant regular
maintenance. All of these are expected not to be problems for the "duck
bill" gate.
2. Demonstration has been initiated in New York, NY.
Disadvantages
1. Insufficient use to confirm expected performance or to define potential
problems.
Useful References
1. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
14 859-870.
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CSO: Collection System Controls 23
MAINTENANCE
Description
Maintenance for combined sewer systems consists of removing debris and
repairing hardware so that the existing system will work as it was designed to.
Efficiency
Proper maintenance for CSO systems working in a state of disrepair can yield a
substantial abatement of pollution. Proper maintenance prevents premature
overflows and backwater intrusion due to malfunctioning regulators and tide
gates, improper diversion settings, and partially blocked interceptors.
Maintenance is an absolute necessity for a total system approach to pollution
control, and much of the effectiveness of an entire system can be lost by
neglecting it.
Economics
Some cities have gained high CSO control cost benefits by implementing good
maintenance for their existing systems.
Advantages
1. Substantial improvement for a small investment.
2. Prevents bypassing of treatment plants by sewage leaks into surface waters
upstream in the sewer network.
Disadvantages
1. Existing system may not be sufficient even when operating as designed.
2. Old or improperly designed systems may be difficult to maintain.
Useful References
1. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
1& 859-870.
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24 CSO: Collection System Controls
INFLOW/INFILTRATION CONTROL
Description
Inflow/infiltration techniques include: reduction of inflow from extraneous
sources such as downspouts; rehabilitation of sewers using conventional
methods or new technologies such as Insituform; and impregnation of pipes with
sulfur to increase strength and reduce permeability. Insituform, a polyester fiber
felt tubing, is inserted through a pipeline using water that is then heated, causing
a resin to form a hard impermeable lining. A new installation technique is
trenchless sewer construction, which consists of plowing in solvent-welded
polyvinyl chloride (PVC) pipe on a grade established by a laser unit (much as
underground cables are laid).
Efficiency
Inflow Reduction. Reduction of extraneous sources improves the use of the
sewer system, reducing the quantity of flow that must be treated.
Sewer Rehabilitation. Sewer system rehabilitation is only partially effective
because of migrating leakage and the difficulty of correcting house connections.
Insituform. Insituform provides structural integrity with respect to infiltration
and does not reduce flow area significantly. It is also resistant to corrosion.
Impregnated Concrete Pipe. Impregnated pipe has reduced permeability, which
prevents the deterioration of internal reinforcement. Sulfur-impregnated
nonreinforced pipe approaches the strength of steel-reinforced pipe, with
improved resistance to corrosion.
Trenchless Sewer. There is much less infiltration than with conventional pipe
because PVC resists corrosion, the 600-foot pipe lengths drastically reduce the
number of joints, and these joints are chemically welded.
Economics
Inflow Reduction. In Springfield, IL, it was estimated that the cost of removing
downspouts would be recovered in 16 months from reduced costs of operation
and maintenance.
Sewer Rehabilitation. Costs associated with construction and excavation are
major expenses of conventional rehabilitation and sliplining processes.
Insituform. Insituform does not require excavation or major construction for
either installation or reestablishment of service connections, and it eliminates the
need for grouting.
Impregnated Concrete Pipe. Impregnation can significantly slow the
deterioration of pipelines, reducing costs due to infiltration and maintenance
costs. Sulfur impregnation may save from $0.83 to $2.08 per linear foot for a
27-in diameter pipe.
Trenchless Sewer. The trenchless method could be at least 16% less expensive
than conventional pipe.
Advantages
Inflow Reduction
1. Maximizes effective collection system and treatment capabilities while
preventing overflow pollution.
2. Can greatly reduce complaints of basement flooding.
3. Reduces operation and maintenance load for the sewage system.
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CSO: Collection System Controls 25
Sewer Rehabilitation
1. Has been used in many localities and can reduce infiltration.
Insituform
1. Does not require excavation and extensive construction.
2. Does not impede flow, and may increase it through reduced friction.
3. Fills cracks and gaps, surmounts rubble, and can turn 45° during installation.
4. Resists corrosion.
5. Has been demonstrated in Northbrook, IL, and Hagerstown, MD.
Impregnated Concrete Pipe
1. Permeability can be reduced for a small initial expense, reducing deterioration
and thus maintenance and replacement costs.
2. Strength improved, reducing reinforcement and capital costs.
Trenchless Sewer
1. Infiltration and corrosion greatly reduced.
2. Has been demonstrated successfully at South Bethany Beach, DE.
Disadvantages
Inflow Reduction
1. Initial expense of removing downspouts and illegal connections.
Sewer Rehabilitation
1. Only partially effective because of migrating leaks and difficulties in
correcting house connections.
2. Requires extensive excavation and construction.
Insituform
1. Experience not as extensive as that with conventional techniques.
Impregnated Concrete Pipe
1. May be more difficult to obtain than conventional pipe.
Trenchless Sewer
1. Full-scale experience limited and cost-effectiveness unknown.
Useful References
1. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
1& 859-870.
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26 CSO: Collection System Controls
SEWER SEPARATION
Description
Sewer separation involves the construction of an entirely new system in which
wastewater and runoff flow through separate pipelines.
Efficiency
The effectiveness is limited because sewer separation does not deal with
treatment of stomvwater, a major contributor of pollution.
Economics
Because constructing separate sewers is prohibitively expensive, it has been
largely abandoned. Sewer separation for the US would cost $100 billion, or
three times the cost of alternative control measures. A study conducted for
Seattle calculated a cost of $10,000/acre for sewer separation as opposed to
$400/acre for a remote monitoring, computerized flow-routing system servicing
13,250 acres.
Advantages
1. Eliminates overflow and bypass of sewage after storms.
Disadvantages
1. Extremely expensive.
2. Extremely difficult to install in a developed area.
3. Does not deal with stormwater pollutant control.
Useful References
1. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
16, 859-870.
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CSO: Storage 27
IMPOUNDMENT
Description
Storage containers may include earthen basins, concrete holding tanks, tunnels,
underground and underwater containers, underground "silos," natural and mined
underground and above-ground formations, abandoned facilities, and existing
sewer lines.
Efficiency
Storage facilities may be used effectively for sedimentation, but are mainly
effective in preventing shock loading to receiving waters and/or sewage treatment
plants.
Economics
Storage allows maximum use of existing facilities and usually results in the
lowest cost of any technique for pollutant removal.
Advantages
1. Best documented and most cost-effective technique.
2. Auxiliary functions such as flood protection, sewer relief, flow transmission,
and dry-weather flow equalization.
Disadvantages
1. Cannot deliver a high degree of treatment.
Useful References
1. Field, R., and Struzeski, E. J., (1972). Management and Control of
Combined Sewer Overflows. Joum. Wat. Pollut. Control Fed. 44.2
1393-1415.
2. Field, R. (1975). Urban Runoff Pollution Control- State-of-the-ArL Journ.
of the Environmental Engineering Division. ASCE. 1Q1EEI107-125.
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28 CSO: Storage
IN-RECEIVING WATER STORAGE
Description
CSO or stormwater flow is contained between floating plastic curtains placed
inside an existing body of water such as a lake. When the overflow ends, pumps
automatically start, and the surrounding waterbody enters the compartments and
pushes stormflow back to the first compartment, where it is pumped back to the
plant.
Economics
This storage method is inexpensive because of low-cost materials, absence of
land requirements, and short installation time. Costs could be 5-15% of costs
for a conventional concrete tank.
Efficiency
In three locations in Sweden performance was good. The structure was subjected
to ice and wind loads and did not fail.
Advantages
1. Will soon be demonstrated in Fresh Creek Basin in New York City.
Disadvantages
1. Experience insufficient to show limitations.
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CSO: Treatment 29
MICROSCREENS
Description
The microscreen is a liquid-straining device that utilizes a micro-fabric mesh to
remove suspended solids from passing flow. These machines are manufactured
by several companies, and most consist of a rotating drum covered with a finely
woven fabric of stainless steel. Water flows through the screen, leaving solids
on the inside. The unit is backwashed to remove accumulated debris.
Efficiency
Some demonstrations have yielded SS removals of more than 90% for high-rate
applications. Full-scale studies in Syracuse, NY, achieved about 50% removal
of SS and about 33% removal of BOD, although actual removal depends on the
type of device, screen aperture size, and hydraulic loading rate. Efficiency
decreases as hydraulic loading rate increases. Removal of heavy metals is
inconsistent and often insignificant. Operational problems related to start-up,
cleaning, and achieving design loading rate have been reported for some brands in
many studies of microscreen devices.
Economics
Estimates from the mid-1970's were that microscreen costs 70% more than
ultrafine screens. A study in Syracuse, NY, in the late 1970's indicated that
costs of microscreens are 1.8-3.8 times the costs of the same system using a
swirl flow regulator. It was concluded that swirl regulators were more cost-
effective for the small overflow stations in use during the study.
Advantages
1. Can remove substantial amounts of solids from CSO flow.
2. Demonstrated in Syracuse, NY, and Fort Wayne, IN.
3. Suitable for high-rate loading and treatment
Disadvantages
1. May not be cost-effective for some treatment levels.
2. No removal of dissolved pollutants.
Useful References
1. Drehwing, F. J., Oliver, A. J., MacArthur, D. A., and Moffa, P. E. (1979).
Disinfection Treatment of Combined Sewer Overflows, Syracuse, New
York. USEPA Report No. EPA 600/2-79-134. NTIS No. PB 8-113 459.
2. Drehwing, F. J. (1979). Combined Sewer Overflow Abatement Program,
Rochester, NY - Vol II: Pilot Plant Evaluations. USEPA Report No.
EPA-60Q/2-79-Q3 Ib. NTIS No. PB 80-149-262.
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30 CSO: Treatment
SWIRL FLOW AND HELICAL BEND REGULATOR/SOLIDS
CONCENTRATOR: SWIRL DEGRITTER
Description
A swirl flow concentrator is a simple ring-shaped basin containing a central
circular weir. The weir controls flow passing through the device as well as
causing a "swirl" action that separates liquid from solids. Flow is separated into
a large volume of clear overflow and a low volume of concentrated waste, which
is stored for later purification or sent directly to the wastewater treatment plant
Helical regulators work on similar principles. The swirl is also used as a
degritter for treatment facilities.
Efficiency
Removals of 50% of SS and BOD are possible. Net removal of SS is 19%
greater than with conventional regulators. Treatment efficiency is relatively
constant over a wide range of flow rates.
Table CSO-1. Efficiency of pilot swirl degritter at Denver, CO.
Grit removal (%) at SS removal (%) at
flow rate (gpm) flow rate (gpm)
iiiuucm
SS (mg/1)
100
200
400
15
69.0
100.0
100.0
40
59.8
91.0
99.1
70
54.8
85.7
93.8
15
56.5
66.6
70.4
40
32.5
48.1
54.1
70
13.3
33.3
41.0
Economics
Swirl systems for primary separation are cost-competitive with
flocculation/sedimentation systems. Choice of treatment for CSO's is dependent
on influent quality and the treatment level required. Construction costs of a
swirl system to function as a degritter are about half the costs for a conventional
degritter, and operation and maintenance costs are lower than for conventional
grit chambers.
Advantages
1. Regulates combined sewer flow.
2. Provides high-rate preliminary treatment.
3. Constant treatment efficiency over a wide range of flow rates.
4. Simple annular-shaped construction.
5. Absence of mechanical parts that use energy.
6. Demonstrated use in Syracuse, NY, and Lancaster, PA.
7. Small tankage requirement in comparison with sedimentation.
8. Use on separate storm drains permits treatment of separate sewer lines and
use of smaller storage tanks.
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CSO: Treatment 31
9. Can function during low-flow or dry-weather periods.
10. For degritting the efficiency and lack of moving parts offer economic and
operational advantages over normal degritters.
Disadvantages
1. Operation may not be optimum outside design flow range.
2. Not capable of high levels of treatment.
3. Cannot be modified easily to increase treatment efficiency.
Useful References
1. Drehwing, F. J. (1979). Combined Sewer Overflow Abatement Program,
Rochester, NY - Vol II: Pilot Plant Evaluations. USEPA Report No.
EPA-6QQ/2-79-03 Ib. OTIS No. PB 80-149-262.
2. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
16., 859-870.
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32 CSO: Treatment
HIGH-RATE FILTERS
Description
High-rate filters (HRF) for CSO treatment are usually dual-media, with sand and
anthracite, for example, in a deep column. Accumulated solids on the surface
and in the bed are removed by backwashing. A fine screen precedes the filter to
remove suspended solids.
Efficiency
Almost all settleable solids are removed, so efficiency rises for stronger
influents. Removal is poor for dissolved solids, so efficiency is low for
wastewaters having high percentages of waste in solution. Treatment is
enhanced with chemical addition. Chemical contact time is also a factor in
treatment efficiency. Chemical coagulants can yield phosphate reductions of 85-
97%. In conjunction with primary systems, HRF can provide SS removals of
72-84% without chemicals and 86-92% with chemical addition.
Economics
Capital costs for a HRF plant treating only CSO is 60-65% of the cost of plant
treating both dry- and wet-weather flow. Capital cost estimates for a system
using polyelectrolytes for a flow of 1,000,000 m3 /day was $6,300,000 for
c. 1978. HRF is competitive with sedimentation for CSO and dual-process
treatment, as it requires only 5-7% as much area. For CSO treatment HRF is
competitive with both dissolved-air flotation and microstraining processes.
Table CSO-2. Efficiency of a pilot plant using high-rate filters, at Newton
Creek, NY, when operating at a flux rate of 16 gpm/fL
Parameter Level in influent (mg/1) Removal (%)
SS
BOD
COD
182
136
302
61
41
42
Advantages
1. Smaller area requirements than for conventional sedimentation.
2. Can be enhanced by chemical addition.
3. Designed for high loading rate.
4. Mesh discostrainers can eliminate a sludge-concentrating step.
Disadvantages
1. Does not remove dissolved material.
2. Constant pressure head needed to avoid breakthrough of solids.
3. Backwash sludge must be handled and disposed of.
4. Chlorination of CSO needed to prevent growth on filter media.
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CSO: Treatment 33
Useful References
1. Innerfield, H., and Forndran, A. (1979). Dual Process High-Rate Filtration
of Raw Sanitary Sewage and Combined Sewer Overflows. USEPA Report
No. EPA-6QQ/2-79-Q1S. NTIS No. PB 296 6267AS.
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34 CSO: Treatment
FLOCCULATION/SEDIMENTATION
Description
Chemicals are mixed with incoming wastewater, which is routed to the
flocculation chamber. Here floes of suspended material form because of chemical
action. The floes then settle to the bottom of a sedimentation basin as flow
passes through. Clear overflow leaves the tank, and the bottom layer of
sediment is removed separately.
Efficiency
The efficiency of the flocculation/sedimentation (F/S) process is greatly enhanced
by chemical treatment. Also, influent SS and overflow rate have significant
effects on the percentage of removal. Flocculation/sedimentation tends not to
remove much TKN.
Table CSO-3. Efficiency of removal in a flocculation-sedimentation process at a
pilot plant in Rochester, NY.
Removal (%) of SS at
indicated flow rate (gpd/sq ft)
SS (mg/1)
No chemical treatment
200
500
With polymer treatment
200
500
With alum plus polymer
200
500
800
15.9
60.9
53.1
77.6
78.2
89.3
1500
12.0
59.1
47.6
75.0
75.4
87.9
2000
10.1
58.2
44.9
73.7
74.0
87.2
Removals (%)
BOD5 VSS TIP
21 37 8
37 47 11
61 79 71
Economics
Capital costs will depend largely on tank volume, which is derived from the
quantity of flow treated. Maintenance and operations costs will be mainly for
chemicals and the handling and disposal of sludge. However, the use of
chemicals to enhance treatment can be very cost-effective. F/S systems are cost-
competitive with swirl separator systems, with increasingly stringent treatment
requirements favoring F/S systems.
Advantages
1. Adaptability to automated operation.
2. Rapid startup and shutdown characteristics.
3. Good resistance to shock loads, with chemical use.
4. Flexibility of operations with chemical use.
5. Good phosphorus removals attainable with alum use.
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CSO: Treatment 35
Disadvantages
1. High initial cost (offset by reduced land requirements).
2. High chemical requirements.
3. With chemical use, increased sludge.
4. Can have high maintenance requirements.
5. Requires chemical use to avoid sensitivity to high flows and loadings.
Useful References
1. Drehwing, F. J. (1979). Combined Sewer Overflow Abatement Program,
Rochester, NY - Vol II: Pilot Plant Evaluations. USEPA Report No.
EPA-6QO/2-79-Q3 Ib. NTIS No. PB 80-149-262.
2. Field, R. (1982). An Overview of the U.S. Environmental Agency's Storm
and Combined Sewer Program Collection System Research. Water Res.
16, 859-870.
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36 CSO: Treatment
SCREENING/DISSOLVED AIR FLOTATION
Description
Combined sewer overflow is automatically directed through a small "satellite"
plant containing drum screens to remove suspended solids; then chemicals are
added before the overflow is directed to flotation tanks. Typically at least 20% of
the flow is saturated with air in pressurization tanks before being mixed with the
remaining flow upon entering the flotation tanks. Then microscopic air bubbles
released from the pressurized portion bring suspended particles to the surface,
where they are removed by scrapers. A cleanup cycle after a CSO ensures proper
operation during the next discharge.
Efficiency
Full-scale studies in Racine, WI, in the mid-1970's showed that substantial
removals are possible with this technology.
Table CSO-4. Efficiency of removal in a screening/dissolved air flotation
system in Racine, WI.
Removal (%), mass basis
Parameter - Site 1 Site 2
BOD 62.4 69.5
TOC 60.0 66.6
Suspended solids 67.6 69.8
Volatile suspended solids 73.6 67.3
Total phosphorus 53.2 62.4
Treatment efficiency is usually better for long runs (greater volume) than for
short runs. A smaller drum screen system without air flotation removed 20% of
BOD, 41% of TOC, and 50% of SS.
Economics
Capital costs for full-scale studies in 1974 are shown below.
Table CSO-5. Cost in 1974 dollars of full-scale satellite plant for
screening/dissolved air flotation.
Site
Site 1
Site 2
Site 3
(screen only)
Design flow
(nvVday)
53,500
168,000
14,800
Total Cost ($)/mgd
cost($) treatment capacity
436,599
841,420
25,001
30,900
18,950
6,410
Cost ($)/acre
of CSO area
6,779
2,078
1,613
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CSO: Treatment 37
Maintenance was the major operations cost for full-scrfe application of this
technology because of the labor necessary for site maintenance and cleanup after
an operation. Sludge handling could be expected as a major cost for this
technology but was not included in the studies at Racine. This technology is a
feasible alternative to combined sewer separation, which is prohibitively
expensive, but it can be significantly more expensive than other technologies
presently available for CSO control.
Advantages
1. Reliable.
2. Adaptable to automated operation, rapid startup and shutdown, and high-rate
operation.
3. Resistant to shock load.
Disadvantages
1. Can be cost-intensive for the treatment received.
2. High maintenance and labor costs.
3. Large equipment requirements, complex machinery.
Useful References
1. Meinholz, T. L. (1979). Screening/Flotation Treatment of Combined Sewer
Overflows - Volume II: Full Scale Operation, Racine, WI. USEPA
Report No. EPA-6QQ/2-79-1Q6. NTIS No. PB 80-130-693.
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38 CSO: Treatment
ACTIVATED CARBON ADSORPTION
Description
Wastewater is passed through a filter column with activated carbon media.
Pollutants are adsorbed in the filter bed and removed from the flow. The filter is
cleaned by backwashing. The carbon filters can also be used to polish effluents
from flocculation/sedimentation and high-rate filtration systems, and dry-weather
flows.
Efficiency
Unlike most CSO treatment technologies, activated carbon adsorption removes
significant amounts of dissolved organics. Pilot studies in Rochester, NY,
indicated optimum 6005 removal at detention times of 20-30 minutes (below).
Table CSO-6. Efficiency of activated carbon adsorption in pilot studies in
Rochester, NY.
Influent BOD5
(mg/1)
30
30
30
30
70
70
70
70
Detention time
(min)
13.5
19.3
30.0
45.0
13.5
19.3
30.0
45.0
Flux
(gpm/sq ft)
0.42
0.61
0.94
1.41
0.42
0.61
0.94
1.41
BOD5 removal
(%)
69
76
83
79
92
91
96
88
The addition of carbon adsorption to primary treatment processes can result in an
overall BOD5 removal of 92-98%.
Economics
Because of high costs for carbon adsorption, the Rochester study recommends
limiting application to locations where it is critical to remove dissolved organics
and toxic substances. Capital cost estimates for a flow of one million cubic
meters are $45,000,000, over seven times the estimate for a high-rate filter
system for the same flow. A major portion of this cost is a result of the
construction required for carbon regeneration.
Advantages
1. Effective removal of dissolved organics and toxic substances.
2. Can produce high-quality effluent as a polishing technique.
Disadvantages
1. Cost-effective only where effluent quality is critical and pollutants are present
that cannot be removed by other techniques.
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CSO: Treatment 39
Useful References
1. Drehwing, F. J. (1979). Combined Sewer Overflow Abatement Program,
Rochester, NY - Vol II: Pilot Plant Evaluations. USEPA Report No.
EPA-600/2-79-03 Ib. NTIS No. PB 80-149-262.
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40 CSO: Treatment
HIGH-RATE DISINFECTION
Description
Chemicals for disinfection are added to influent, which is mechanically mixed by
propellers or baffles in a small mixing basin. Ultraviolet (UV) light and
ozonation require different and usually more complex facilities.
Efficiency
High-rate disinfection can achieve large reductions of bacterial populations in
CSO's. In Syracuse CL^ at levels of 12-24 mg/1 achieved 3-4 log reductions of
fecal coliforms and CLC^ at levels of 6-12 mg/1 reduced levels to 200
counts/100 ml during first-flush loadings. UV light is effective but is affected
by turbidity and leaves no residual disinfectant against future contamination.
Ozone is a very rapid oxidant and is also an alternative for disinfection of CSO's.
Economics
High-rate disinfection for CSOs can be more cost-effective than normal
disinfection. Conventional facilities are operationally cost-intensive, whereas
CSO wet-weather facilities are capital-intensive. In pilot studies in Rochester,
NY, CI>2 had a lower overall cost than CLO2 for all trial cases. CLO2 requires
less detention time and mixing but is not cost-effective because of chemical
costs. Sequential use of CI^ and CLO2 does not seem advantageous. Methods
such as ozonation and UV light are too costly in most situations but have
advantages. New research includes a UV pilot study with a contact time of 10
seconds.
Advantages
1. May be more cost-effective than conventional disinfection.
Disadvantages
1. Higher chlorine dosages needed than for conventional treatment
2. Dechlorination of disinfected effluents for high-rate systems may be needed to
protect aquatic life in receiving waters.
3. Possible significant formation of chlorinated organics and other refractory
residuals, which can be a health concern.
4. Lack of reliable, cost-effective, on-site generation processes.
5. Decentralization may increase maintenance problems.
Useful References
1. Drehwing, F. J. (1979). Combined Sewer Overflow Abatement Program,
Rochester, NY - Vol II: Pilot Plant Evaluations. USEPA Report No.
EPA- 600/2-79-03 Ib. NTIS No. PB 80-149-262.
2. Drehwing, F. J., Oliver, A. J., MacArthur, D. A., and Moffa, P. E.
(1979). Disinfection Treatment of Combined Sewer Overflows, Syracuse,
New York. USEPA Report No. EPA 600/2-79-134. NTIS No. PB 8-113
459.
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NONPOINT SOURCE NUTRIENT CONTROLS
URBAN
Porous Pavement
Asphalt with Catchbasins
On-Line Wet Ponds
Off-Line Wet Ponds
Extended Detention Dry Ponds
Recharge Basins
Infiltration Trenches
Surface Sanitation/Street Sweeping
Marsh Land
AGRICULTURAL
No-Till Cropland
Minimum Tillage
BMP's for Fertilizer
BMP's for Chemicals
Animal Waste Facilities
Vegetated Filter Strips
Riparian Areas
Controlled Drainage
Terraces
Sod Waterways
Cost-Sharing Programs
Other Approaches
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42 Nonpoint Source: Urban
POROUS PAVEMENT
Description
Porous asphalt pavement can let water pass through so that runoff can be
temporarily stored in the reservoir base course and allowed to percolate through
the underlying soil. This porosity is gained by exclusion of most of the fine
aggregate from the asphalt mix; the resulting void ratio is much higher than in
the conventional asphalt pavements (16% vs. 2-3%). Typically, porous
pavement consists of five layers: (1) a sub-base of undisturbed existing soil or,
when this does not provide sufficient drainage, an imported or prepared base
course (in some cases auxiliary drainage structures may be needed as well); (2) a
sheet of filter fabric to prevent soil from piping up into the void spaces of the
reservoir course; (3) a reservoir base course of 1-2-inch diameter crushed stone
aggregate; (4) a 2-inch thick layer of 0.5-inch crushed stone aggregate to
stabilize the surface of the reservoir base course; and (5) porous asphalt surface
course designed for specific pavement requirements (usually 2.5 inches is
sufficient).
Efficiency
Porous pavements may reduce peak runoff rates by as much as 83%, and have
been demonstrated to pass the equivalent of 6 feet of water per hour. Because
porous pavements have no outlet as such, and runoff must pass through the soil,
treatment is excellent. Removal of solids, nitrogen, and phosphorus is estimated
at 90-95%.
Economics
Porous pavement may cost 2.5 times as much as conventional pavements, or
only 35% more, depending on the ease of obtaining the asphalt mix. Typical
costs might be $55-60/ton vs. $35/ton for conventional asphalt. Cost-
effectiveness for nutrient removal, in comparison with extended dry ponds and
other BMP's, is good for applications such as commercial shopping centers.
Cost may be significantly lower than for conventional pavements because
structural drainage systems (i.e., curbs, gutters, and stormsewers) can be reduced
or eliminated.
Advantages
1. Provides multiple use of land (parking), and greatly reduces pollutants as well
as quantity of runoff.
2. Not damaged by freeze-thaw cycles.
3. Erosion and flood control on overland flow and channel areas.
4. Natural drainage boundaries can be maintained, eliminating construction of
new collection and delivery systems for runoff.
5. Eliminates standing water on pavement.
6. Conventional paving equipment may be used.
7. Works over tight soil if provided with drainage through pipes.
8. Natural vegetation can be retained, including trees normally removed from
sites of conventional pavement.
9. Groundwater recharge is enhanced.
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Nonpoint Source: Urban 43
10. Porous pavements have significantly higher friction coefficients when wet
than do conventional pavements, and are 15% more resistant to automobile
skids under wet conditions.
Disadvantages
1. Must be maintained by use of a vacuum sweeper and high-pressure hosing
with water two to four times a year to retain permeability.
2. Effectiveness reduced when accumulated snow melts arid when rain falls on a
frozen surface.
3. Existing building codes may require drainage structures not needed for porous
pavement, making construction costs prohibitive.
4. Spilled gasoline penetrates further into porous pavement, breaking down the
asphalt binder to greater depths.
5. Not cost-effective for smaller sites since asphalt plant must be retooled.
6. Possibility of subsurface pollution for some sites, possibly requiring routing
of flow to protect aquifer.
7. More difficult to design.
8. An asphalt temperature of 260° F during installation is important, limiting
the distance of a site from the batch plant.
9. Quality control at the asphalt plant is important so that fine particles are
filtered out properly.
10. Use can be limited by site soil, slope, depth to groundwater, and distance to
drinking wells.
Useful References
1. Diniz, E., Epsey, Hutson & Assoc., Inc., Albuquerque, NM (1980). Porous
Pavement: Phase I - Design and Operational Criteria. USEPA Report No.
EPA-600/2-80-135. NTIS No. PB 81-104 796.
2. Field, R. (1986). The USEPA Office of Research and Development View of
Combined Sewer Overflow Control: Proceedings of Available Technology
Workshop. Scientific and Technical Advisory Committee. Chesapeake Bay
Project. Arlington, VA.
3. Wiegand, C., Schueler, T., Chittenden, W., and Jellick, D. (1986).
Comparative Costs and Cost Effectiveness of Urban Best Management
Practices. Proceedings. Urban Runoff Quality - Impact and Quality
Enhancement Technology, pp 366-380. B. Urbonas andL. Roesner, Eds.
Engineering Foundation Conference. ASCE, 345 East 47th Street, NY,
NY 10017.
4. Crafton, S. (1986). Urban Nonpoint Control BMP's. Personal
Communication. Virginia Soil and Water Conservation Service.
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44 Nonpoint Source: Urban
CONVENTIONAL ASPHALT PAVEMENT WITH
CATCHBASINS (Untried Technology)
Description
Conventional non-porous asphalt is placed over the deep stone sub-base that is
used under porous pavement with inlet grates to channel water into the reservoir
course. Under each inlet grate is a catchbasin with perforated drainpipes to direct
water into the storage area. This arrangement should allow sediment and trash to
settle into the catchbasin rather than clogging void spaces in the storage area.
Advantages
1. May provide the same benefits of quality and quantity control as porous
asphalt, for about half the cost.
Disadvantages
1. Untried technology with no actual cost or performance data.
Useful References
1. Crafton, S. (1986). Urban Nonpoint Control BMP's. Personal
Communication. Virginia Soil and Water Conservation Service.
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Nonpoint Source: Urban 45
ON-LINE WET PONDS or RETENTION BASINS (Quality
improvement, little or no quantity reduction)
Description
Wet ponds are depressions, excavated or natural, which receive runoff. The pond
is permanent, retaining some water year-round. It detains runoff, reduces peak
flows, and (through sedimentation, physical and chemical interactions, and
biological processes) removes suspended and dissolved pollutants, eventually
discharging into surface waters.
Efficiency
The amount of pollutants removed can vary substantially because of site-
specific factors, such as optimum design of the outlet structure and extent of
plant growth. In the table below are influent concentrations and percentage
removals from two wet ponds in the greater Washington, D.C. area, and
maximum removals from nine wet ponds included in the National Urban Runoff
Program.
Table NPT-1. Influent concentrations (mg/1) and percentage removals for wet
ponds in the Washington, DC, area and in nine ponds in the National Urban
Runoff Program.
Westleigh
Parameter
TSS
COD
TN
TP
Influent
concentration
42.0
47.7
2.49
0.33
Removal
87
—
53
70
Burke
Influent
concentration
17.7
39.8
2.12
0.20
Removal
37
—
51
59
NURP
Removal
91
69
60
79
Economics
Large regional or multi-site facilities are favored rather than small on-site
facilities. Small sites cost $500-$ 1500/acre, whereas large multi-site facilities
cost approximately $150-$200/acre to build. Maintenance costs are $60-
$175/acre for small facilities, and $10-$25/acre for large facilities. For wet
ponds roughly 60% of the construction costs will be for excavation, and 20% for
the inlet and outlet structures. Costs can vary substantially on a site-specific
basis.
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46 Nonpoint Source: Uroan
Table NPT-2. Average capital costs for wet detention ponds (based on 13
ponds).
Storage volume (cubic ft.) Construction costs ($)
100,000 56,000
500,000 159,000
1,000,000 249,000
Wet ponds are 27-157% more expensive than dry ponds, and 19-131% more
expensive than extended-detention dry ponds. Lower percentages correspond to
greater acreage and population density.
Advantages
1. Most effective detention practice for water quality control, particularly
nutrient control.
2. Potential for recreation, aesthetic benefits, and water supply.
3. Simple routine maintenance.
4. Economic disadvantage of wet ponds compared with dry ponds declines with
increasing volumes.
Disadvantages
1. Appropriate sites are more limited in urban areas than for dry ponds.
2. The best sites for regional basins are often multi-jurisdictional.
3. Difficulty in establishing adequate and acceptable long-term management
plans.
4. Problems with safety and liability.
5. Wet ponds take 60% more excavation, on the average, than dry ponds of
comparable volume, making them generally more expensive.
Useful References
1. Grizzard, T. J., et. al. (1986). An Evaluation of Stormwater Management
Ponds for the Control of Urban Runoff Pollution. Personal
Communication. VPI&SU, Manassas, VA.
2. Crafton, S. (1986). Urban Nonpoint Control BMP's. Personal
Communication. Virginia Soil and Water Conservation Service.
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Nonpoint Source: Urban 47
OFF-LINE WET PONDS/RETENTION BASINS (Quality and
quantity control)
Description
Off-line wet ponds rely on infiltration and evaporation, rather than discharge to
surface waters, to pass stormwater runoff. These ponds depend on sediment-
nutrient-microorganism interactions for nitrogen and phosphorus removals.
Ponds of this sort have been used to control runoff pollution at highway
interchanges.
Efficiency
Studies in Florida concluded that 99% of the total phosphorus input accumulated
in the sediments and 85-90% of the total nitrogen was removed by
nitrification/denitrification. The studies also found no pollution hazard to nearby
surface or groundwater, and quantity control was frequently 100%.
Economics
Construction and maintenance costs are similar to those of on-line wet ponds,
for an equal volume. However, depending on the infiltration rate of the soil, it
may be necessary to use a greater storage volume if no discharge to surface
waters is sought.
Advantages
1. Flow attenuation, flood and pollution control.
2. Higher removal of metals and nutrients than detention basins.
3. Recharge of groundwater.
4. Simple routine maintenance.
Disadvantages
1. Requires restoration every 10-15 years.
2. May require more excavation than a dry pond.
3. Sites suitable for this type of pond may be unavailable.
Useful References
1. Yousef, Y. A., Thorkild, H. J., Wanielista, M. P., and Tolbert, R. D.
(1986). Nutrient Transformation in Retention/Detention Ponds Receiving
Highway Runoff. Journal Water Pollution Control Federation. 5JL 838-
844.
2. Driscoll, E. D. (1986). Detention and Retention Controls for Urban Runoff.
Urban Runoff Quality - Impact and Quality Enhancement Technology.
Urbonas, B., and Roeser, L. A., Eds.
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48 Nonpoint Source: Urban
EXTENDED-DETENTION DRY PONDS (Quality improvement)
Description
An extended-detention dry pond is similar in construction to a more conventional
peak-shaving flood-control pond, but usually has a modified outlet, such as a
perforated drain that may be covered with gravel, to increase the detention time.
This additional time allows suspended solids and their associated nutrients to be
removed by settling.
Efficiency
Some research indicates a detention period of 40 hours is needed to remove all
paniculate matter. A full-scale study of a pond with an average detention time of
6 hours showed removal of 60% of SS, 40% of COD, 15% of total phosphorus,
30% of TKN, and 85% of lead. Settling column studies done with the influent
of this pond indicated substantial increases in removals with detention times >24
hours, especially with low-turbidity influents. Data from NURP corroborates
these findings, indicating removals >90% for TSS and lead, 65% for total
phosphorus, and 50% for TKN, COD, and BOD.
Economics
Storage volume and cost are closely related for any type of detention pond,
including extended-detention ponds. Cut-fill expenses account for about 50% of
the total cost, and the inlet-outlet structure for a further 33%. Costs can vary
substantially on a site-specific basis.
Table NPT-3. Average capital costs for extended detention ponds (from 40
ponds).
Storage volume (cubic ft.) Construction cost ($)
10,000 6,000
100,000 32,000
500,000 97,000
An extended-detention dry pond will cost 7-11% more than a conventional dry
pond, and 16-57% less than a wet pond, the lower percentages in each case
corresponding to greater acreage and population density.
Advantages
1. Significant improvement in water quality as well as peak-shaving function of
conventional dry ponds.
2. Efficient use of natural topography in conjunction with embankment
construction is often sufficient for extended-detention dry ponds, resulting
in lower excavation costs than might be expected for a wet pond.
3. No discharge of untreated first flush.
4. Greater removal of pollutants than that obtained with conventional dry ponds.
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Disadvantages
1. Trash accumulation (aesthetic and maintenance problem).
2. Longer detention times may keep bottom marshy throughout growing
season, impeding mowing and debris removal.
3. Frequent clogging of small outlet orifices (can be alleviated by use of a stone
filter jacket covering the outlet).
Useful References
1. Wiegand, C., Schueler, T., Chittenden, W., and Jellick, D. (1986).
Comparative Costs and Cost Effectiveness of Urban Best Management
Practices. Proceedings. Urban Runoff Quality - Impact and Quality
Enhancement Technology, pp 366-380. B. Urbonas and L. Roesner, Eds.
Engineering Foundation Conference. ASCE 345 East 47th Street, NY, NY
10017.
2. Crafton, S. (1986). Urban Nonpoint Control BMP's. Personal
Communication. Virginia Soil and Water Conservation Service.
3. Grizzard, T. J., et. al. (1986). An Evaluation of Stormwater Management
Ponds for the Control of Urban Runoff Pollution. Personal
Communication. VPI&SU, Manassas, VA.
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50 Nonpoint Source: Urban
RECHARGE BASINS (Quality and quantity control)
Description
Recharge basins can vary widely in size and depth and are designed for total
retention and recharge of urban stormwater runoff into the groundwater. The
basins, turfed or unturfed, work by retaining run-off and allowing it to percolate
through the soil. The soil acts as a filter, decontaminating the water before it
reaches the water table.
Efficiency
Soil provides a high degree of contaminant removal. A NURP study of roughly
70 basins in the Fresno area concluded that groundwater quality has not been
adversely affected by existing recharge basins, some of which have been in use
20 years. The elimination of runoff discharge to surface waters is high except
for very large storm events, and some basins have pump-out capability to canals
or other basins. Accumulation of contaminants, particularly lead, on surface
soils is significant but with proper maintenance is not considered hazardous
unless the soil is ingested. Runoff in the NURP study had nutrient
concentrations lower than the groundwater. Effectiveness for an industrial
drainage basin is not known.
Economics
Costs should be similar to those for dry basins of the same volume at a given
site, with the additional cost of any recreation facilities constructed. However,
depending on the percolation rate and the degree of removal desired, the volume
required may be greater than that of a dry basin for the same site, since the
recharge basin is not intended to be a flow-through facility. Typical construction
costs range from 1 % to 79% more than for a dry basin at the same site. This
technology can be cost-effective for large volumes of runoff from densely
populated or heavily paved areas typical of large cities.
Advantages
1. Runoff quality and quantity control approaching 100% where percolation
rates are good.
2. Potential use of turfed basins as recreational facilities; inclusion of a shallow
basin in the design makes it possible to keep the recreational area dry
except in large storms.
Disadvantages
1. Accumulation of lead is a potential health hazard for small children who
might accidentally ingest soil.
2. May require significant maintenance after storms, especially for recreational
facilities.
3. Disposal of contaminated soil after maintenance can be expensive, especially
if there are long periods between clean-ups.
4. Possible eventual soil saturation by contaminants.
5. Requires adequate percolation rate to be practicable.
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Nonpoint Source: Urban 51
Useful References
1. Brown and Caldwell, Consulting Engineers. (1984). Fresno Nationwide
Urban Runoff Program. Project Final Report.
2. Wiegand, C, Schueler, T., Chittenden, W.( and Jellick, D. (1986).
Comparative Costs and Cost Effectiveness of Urban Best Management
Practices. Proceedings. Urban Runoff Quality - Impact and Quality
Enhancement Technology, pp 366-380. B. Urbonas and L. Roesner, Eds.
Engineering Foundation Conference. ASCE, 345 East 47th Street, NY,
NY 10017.
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52 Nonpoint Source: Urban
INFILTRATION TRENCH
Description
Infiltration trenches may be unsupported open cuts with side slopes, vertical-
sided trenches with concrete slab cover, or backfilled trenches with coarse
aggregate and perforated pipes where side support is necessary. The trench has
no outlet, and stormwater exfiltrates through the trench walls, being treated as it
moves through the soil, and replenishing the groundwater.
Efficiency
Removal efficiencies should be quite high for phosphorus and nitrogen, as with
any technology that relies on soil infiltration. Also, groundwater quality should
not be adversely affected for normal urban stormwaters.
Economics
Cost is moderate when a small storage volume is needed, but rises rapidly for
larger volumes. Costs are 20% for excavation, 45% for aggregate, and 35% for
the outlet structure (perforated pipeline). An infiltration trench is 95% to 267%
more expensive than a dry pond of equal volume. For many situations this is
the most cost-effective method for either nutrient removal or volume reduction of
stormwater runoff.
Table NPT-4. Average capital costs for infiltration trenches (data from seven
trenches).
Storage volume (cubic ft.) Construction cost ($)
1,000 2,100
5,000 5,900
10,000 9,100
Advantages
1. Recharge of groundwater and overflow reduction.
2. Considerable success with this technology in Florida.
Disadvantages
1. May be less cost-effective than other technologies.
Useful References
1. Wiegand, C., Schueler, T., Chittenden, W., and Jellick, D. (1986).
Comparative Costs and Cost Effectiveness of Urban Best Management
Practices. Proceedings. Urban Runoff Quality - Impact and Quality
Enhancement Technology, pp 366-380. B. Urbonas and L. Roesner, Eds.
Engineering Foundation Conference. ASCE, 345 East 47th Street, NY,
NY 10017.
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SURFACE SANITATION/STREET SWEEPING
Description
Street sweeping is the mechanical removal of rubbish and dirt from road surfaces
and paved areas. This is accomplished by the metal-brushed street sweepers that
are common in the United States, or by newer machines, such as vacuum
sweepers, that use different mechanisms but work in a similar manner.
Efficiency
In a study in San Jose, CA, twice-daily cleanings removed as much as 50% of
total solids and heavy metals. Also, some modern cleaners such as a modified
regenerative-air Tymco street cleaner have shown promise. However, even
intense cleaning fails to control organics and nutrients. Nutrients and heavy
metals are attached to particles sized <50 (Am, which these devices do not remove
well. Neither conventional street sweepers nor vacuum sweepers are adequate for
improving runoff quality.
Economics
If integrated with other methods, street sweeping may reduce city-wide costs. In
a 1977 study about 75% of the costs were for labor, and costs were roughly $14
and one man-hour per curb-mile cleaned.
Advantages
1. Creates a large number of jobs for money spent.
2. Improves paved areas aesthetically, and improves public sanitation and safety.
Disadvantages
1 . Inadequate for control of nutrients and heavy metals in runoff.
2. Effectiveness depends on climatic conditions.
Useful References
1. Pitt, R. (1979). Demonstration of Nonpoint Pollution Abatement Through
Improved Street Cleaning Practices. USEPA Report No. EPA-6QQ/2-79-
NTIS NO. PB 80-108 988.
2. Characterization, Sources, and Control of Urban Runoff by Street and
Sewerage Cleaning. USEPA Report No. Pending.
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54 Nonpoint Source: Urban
MARSH LAND (Wetlands)
Description
A wetland can be any land with water near or above the ground surface,
supporting plants adapted to a saturated root zone. The vegetation,
microorganisms, and soils of natural or constructed wetlands can be utilized to
remove pollutants from wastewater. Distribution is usually done by irrigation
pipelines or sprinklers, which carry pretreated wastewater and deliver it over the
treatment area. Pretreatment, such as screening, biological treatment, and/or
disinfection, is often needed for wetlands application. This method is well suited
to polishing treated effluents. Harvesting is recommended for maximum
performance.
Efficiency
This technology is capable of reliably providing pH neutralization and some
reduction of nutrients, heavy metals, organics, BOD5, COD, SS, and coliform
bacteria. Phosphorus removal depends on vegetative uptake and frequency of
harvesting. Removal of heavy metals depends on plant species present. Proper
operations are dependent on conscientious management
Table NPT-5. Efficiency of wetlands for removal (%) for secondary effluent
treatment (10-day retention).
BODs TSS COD N Total P Coliforms
80-95 29-87 43-87 42-94 CMM 86-99
Economics
This process is cost-competitive with other treatment technologies for small
communities. Construction costs depend on land cost, distance from treatment
facility, design flows, and site conditions. Operation and maintenance costs are
relatively low.
Advantages
1. Vegetation removed can be used for composting or methane production.
2. Enclosed systems possible for small flows.
3. Has been used in at least eight locations in the U.S.
4. Low-cost, low-energy system.
5. Can be combined with overland flow system and chemical addition.
6. Reliable from mechanical and performance standpoints with low operation
requirements.
7. May enhance nutrient-poor wildlife habitat.
8. Recreational and educational opportunities.
Disadvantages
1. Temperature and thus climate is a major limitation on treatment efficiency.
2. Not suitable for treatment of toxic materials, heavy metals, and herbicides.
3. Impractical for large treatment plants because of large land requirements.
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~ Nonpoint Source: Urban 55
• 4. Breeding ground for mosquitoes may be created without proper maintenance.
5. Large land requirement.
16. Pretreatment usually needed.
7. Availability of a suitable wetland site is a major factor in determining cost-
effectiveness.
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Useful References
1. An Emerging Technology: Wetlands Treatment, USEPA pamphlet,
September 1983.
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56 Nonpoint Source: Agricultural
NO-TILL CROPLAND (Erosion/sediment control)
Description
No-till cultivation is the planting of crops in a small slit or a punched hole in
the soil in order to prevent erosion year-round and minimize spring sediment
surges. Normal preparation of the seed bed is not necessary, and cultivation is
usually not necessary during crop production. The practice requires that the
entire undisturbed cover crop or crop residue be left undisturbed on the soil to
reduce runoff and increase infiltration. This practice is effective in dormant
grass, small grains, and row crop residues.
Efficiency
This technique can reduce erosion 75-90%, but without proper maintenance and
fertilization it may result in high loadings of soluble phosphorus during runoff
events. Roughly 90% reduction of sediment loss on loam soil with 8% slope in
continuous corn was measured at the University of Guelph. A separate study
indicated that the no-till method reduces soil loss by 97%, phosphorus by 87%,
and nitrogen by 82%. A third study conducted in 1985 showed 99% reduction of
sediment loss, 95% reduction of phosphorus, 90% reduction of nitrogen, and
57% reduction of runoff.
Economics
The effect of this technique on yields depends on the soil type. A potential loss
of $7.20/acre has been estimated for fine-textured soils. Costs are less, however,
for more favorable soils, and a yield increase of 16% over conventional clean
tillage may result for coarse-textured soils. The cost of herbicides, insecticides,
and fertilizers is greater for this technique than for conventional methods, but
machine fuel requirements are reduced. Labor, fuel, repair, and machine costs can
be reduced by about $24/acre per year in comparison with conventional tillage.
Cost-sharing programs in Virginia may pay for as much as 65% of the capital
costs of adopting no-till farming.
Advantages
1. Reduces runoff, soil erosion, and the associated loss of nitrogen.
2. Crop residues undisturbed on soil surface.
3. -Energy savings from reduced labor requirements.
4. Has been used in the U.S. and Canada, and researched at several universities.
Disadvantages
1. Increased loss of soluble phosphorus.
2. Unsuitable for crops that require complete tillage for disease control (e.g.,
tobacco and peanuts).
3. Increased use of herbicides, insecticides, and fertilizer.
4. Delays soil wanning and drying.
5. Can reduce yields under some conditions.
6. Climatic and soil restrictions.
7. Crop residue can take up applied nitrogen, reducing availability to crop.
8. Top 2 inches of soil may be acidic from nitrogen application to soil.
9. Without residue chemical runoff can be worse than with conventional tillage.
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Nonpoint Source: Agricultural 57
10. Soil compaction can be a problem.
11. Nitrogen transport to groundwater may be increased, since reduced runoff
means increased water soaking through the soil.
Useful References
1. Givens, F. B. (1986). No-Tillage, Fact Sheet. Virginia Division of Soil
and Water Conservation, Richmond, VA.
2. Givens, F. B. (1986). First Annual Report of the Commonwealth of
Virginia Chesapeake Bay Nonpoint Source Control Program. Personal
Communication. Division of Soil and Water Conservation, 203 Governor
Street, Suite 206, Richmond, VA.
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58 Nonpoint Source: Agricultural
MINIMUM TILLAGE
Description
This practice, a variant of no-till cultivation, results in less soil compaction than
no-till. It requires that a minimum of 30% residue cover be left on the soil
surface.
Efficiency
Soil erosion is roughly 50% of that associated with conventional tillage.
Economics
Fuel, labor, repair, and machine costs are approximately $10/acre per year less
than with conventional tillage.
Advantages
1. Reduces runoff, soil erosion, and the associated loss of nitrogen.
2. Crop residues left on soil surface.
3. Energy savings from reduced labor requirements.
4. Has been used in the U.S. and Canada, and researched at several universities.
Disadvantages
1. Increased loss of soluble phosphorus.
2. Unsuitable for some crops.
3. Increased use of herbicides, insecticides, and fertilizer.
4. Delays soil warming and drying.
5. Can reduce yields under some conditions.
6. Climatic and soil restrictions.
7. Crop residue can take up applied nitrogen, reducing availability to crop.
8. Top 2 inches of soil may be acidic from nitrogen application to soil.
9. Without residue chemical runoff can be worse than with conventional tillage.
10. Soil compaction can be a problem.
11. Nitrogen transport to groundwater may be increased, since reduced runoff
means increased water soaking through the soil.
Useful References
1. Givens, F. B. (1986). No-Tillage, Fact Sheet. Virginia Division of Soil
and Water Conservation, Richmond, VA.
2. Givens, F. B. (1986). First Annual Report of the Commonwealth of
Virginia Chesapeake Bay Nonpoint Source Control Program. Personal
Communication. Division of Soil and Water Conservation, 203 Governor
Street, Suite 206, Richmond, VA.
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Nonpoint Source: Agricultural 59
BEST MANAGEMENT PRACTICES FOR FERTILIZER
Description
Fertilizer BMP's are designed to reduce the amount of phosphorus and nitrogen
lost from cropland. These practices can be categorized as dealing with: (1) rates
of application, (2) time and method of application, and (3) retention of nutrients
on application site.
Efficiency
Optimum use prevents excessive fertilizer from being applied to the soil,
reducing the total amount of nutrients available for transfer to surface waters.
For nitrogen, applying fertilizer during the times of maximum uptake can make
a great difference in the total amount of fertilizer required. Nitrogen uptake is
113 Ib/acre during the winter, 142 Ib/acre at planting time, and 153 Ib/acre when
nitrogen is applied as side-dressing. Also, use of nitrification inhibitors can
approximately double the yield for a given amount of fertilizer. Phosphorus loss
is reduced by measures controlling erosion, since phosphorus is absorbed by
soil. Also, soil testing can determine how much phosphorus is needed to
increase crop yields, thus preventing excess applications.
Economics
There are direct cost savings for fertilizer since excess usage is avoided.
Comparison of the cost of fertilizer with the expected price of the crop being
_ produced should determine the application rate that will yield the maximum net
• profit. Below are corn responses to the nitrogen application rates.
Table NPT-6. Response of corn crops to rates of nitrogen application for
different soil types.
Yield (bushels/acre) for indicated soil type
Nitrogen application rate
(Ib/acre)
0
40
80
120
160
200
Congress
101
133
157
176
190
198*
Davidson
65
110
130
140
146*
149
Cecil
35
44
50
54*
56
56
* Optimal rates for a nitrogen cost of $0.25/lb and a corn price of
$2.50/bushel.
Advantages
1. Avoids unnecessary or uneconomical use of fertilizer.
2. Maximum profits.
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Disadvantages |
1. Possible difficulty in accurate assessment of fertilizer needs. .
2. Requires closer supervision. I
Useful References
1. Hawkins, G. W. (1986). Crop Fertilization That Will Reduce Pollution of |
Surface Waters. Land Use and the Chesapeake Bay. Va. Coop. Ext. Svc.,
Publication - No. 305-003. .
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Nonpoint Source: Agricultural 61
BEST MANAGEMENT PRACTICES FOR CHEMICALS
Description
The control of insecticides, fungicides, and nematicides relies on disease and pest
management programs that give farmers the information needed for determining
how much chemical is necessary to avoid crop destruction. For example, the
Virginia Peanut Leafspot Advisory Program is designed so that 85% of the
peanut fields in the state lie within 15 miles of a monitoring station. Leafspot
advisories are issued daily from June 10 until September 25.
Efficiency and Economics
The Virginia Peanut Leafspot Advisory Program saved farmers an estimated $3.6
million in 1983 by reducing the average number of fungicide applications during
the growing season from seven to three. The Predictive Nematode Assay
Program of Virginia discovered that only 49% of the fields to be planted to
peanuts had enough nematodes to threaten production. Only 15% of corn acreage
was found to benefit from nematode control.
Advantages
1. Reduced total use of chemicals.
2. Direct cost savings to farmers.
Disadvantages
1. Requires closer supervision.
Useful References
1. Phipps, P. M. (1986). Managing Fertilizer and Agri-Chemical Use Within
the Bay Watershed: Fungicides, Nematicides, and Insecticides. Land Use
and the Chesapeake Bav. Virginia Cooperative Extension Service,
Publication No. 305-003.
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62 Nonpoint Source: Agricultural
ANIMAL WASTE FACILITIES
Description
Animal waste facilities are designed either for storage and use or for treatment
and disposal. The three components of each system are collection,
transportation, and storage or treatment Collection may be accomplished by
scraping or washing and flushing. It may also include structures with slotted
floors where wastes drop into pits. Transportation varies from system to system
but is usually done with cross conveyors, pumps, wagons, or manure spreaders.
Storage of waste from cattle usually takes two forms: wet systems and dry
systems. Wet storage facilities consist of storage ponds, concrete pits, and
above-ground tanks used alone or in conjunction with dry storage. These
facilities provide storage for several months, conserving nutrients for land
application. A dry storage facility is constructed as a pole barn with retainer
walls and a sloping concrete floor. Wastes are scraped frequently and placed in
the dry stack contained in the barn. Poultry and swine storage facilities are
usually storage ponds or concrete pits. Curbs and gutters are usually needed to
prevent rainfall from entering storage. For treatment and disposal of most
animal wastes either an anaerobic or an aerobic lagoon is used.
Efficiency
A ton of manure contains 3 Ib of phosphorus and 7 Ib of potash, with 70-80%
of these nutrients available to plants. About 30-40% of the nitrogen in manures
is usable by plants during the first year, with the remainder becoming available
over the next several years. With fertilizer practices oriented to reducing nutrient
removal by runoff, manure can be applied without causing excessive pollution.
Anaerobic and aerobic treatment lagoons reduce phosphorus by as much as 90%
and nitrogen by 60-90% through settling and biological breakdown. Sometimes
efficient nutrient control first requires movement of a facility away from a
passing stream.
Economics
Storage systems often require less land area than treatment facilities and can have
low construction costs (storage ponds). Storage facilities require scheduled
maintenance of the structure and equipment, as well as cleaning. Accumulated
solids must be removed every 10-15 years from anaerobic lagoons and more
frequently from aerobic lagoons. In Virginia a farmer can receive 75% ($7,500
maximum) of the cost of an animal waste control facility. In 1985 in Virginia
the average total cost per facility (for 27 farmers) was $17,760.
Advantages
1. Controls contamination of surface water and groundwater.
2. Maximizes fertilizer potential of animal waste.
3. Storage space gives flexibility to disposal schedule.
Disadvantages
1. Clay-lined livestock lagoons operating below design levels can form cracks,
degrading groundwater quality significantly.
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Nonpoint Source: Agricultural 63
2. More expensive than scraping and hauling without storage or treatment
facilities.
Useful References
1. Givens, F. B. (1986). First Annual Report of the Commonwealth of
Virginia Chesapeake Bay Nonpoint Source Control Program. Personal
Communication. Division of Soil and Water Conservation, 203 Governor
Street, Suite 206, Richmond, VA.
2. Collins, E. R., Jr. (1986). Overview of BMP's for Controlling Animal
Wastes. Department of Agricultural Engineering, VPI&SU, Blacksburg,
VA.
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64 Nonpoint Source: Agricultural
VEGETATED FILTER STRIPS (Quality and limited quantity
control)
Description
Vegetated filter strips, or grass swales, are areas of close-growing perennial
grasses or other vegetation intended to filter pollutants from passing runoff.
They may be placed along the shoulders of highways or around the perimeter of
fields and animal operations, and have also been used in surface-mined areas.
Efficiency
Suspended material settles well at the source area/filter interface, but overall
removal efficiency can be much less dramatic. Filter lengths for 90-95%
pollutant reductions in runoff can range from 10 ft to lengths equivalent to the
area upslope from the filter. At least in urban settings, results have been poor.
Economics
Installation costs vary considerably from location to location. Farmers are
usually eligible for cost-sharing programs. Maryland, for example, pays up to
87.5% of the installation cost through the State Agricultural Cost Share
Program. Average annual cost of installation and maintenance in Virginia in
1983 was $51.75/acre. In a 1986 survey in Maryland, costs for clearing averaged
$60.5 I/hour (range, $40-$75/hour), and costs for seeding averaged $435.9 I/acre
(range, $160-$l,750/acre). These costs do not include potential income lost by
having acreage in filter strips instead of crop production.
Advantages
1. Reduces slope length, slows runoff velocity, filters soil from runoff, and
facilitates adsorption of rain.
2. Infiltration reduces pollutant mass and quantity of runoff.
3. Effective if field is sloped uniformly, promoting sheet flow instead of
concentrated flow (often not the case, however).
Disadvantages
1. Data on individual treatment mechanisms insufficient for routine design of
adequate filters.
2. Variable effectiveness for pollution control, especially for soluble pollutants.
3. Ineffective for removing sediment and nutrients under concentrated flow
conditions, which are common with low-density vegetation.
4. Loses effectiveness with time as sediment accumulates in the filter, unless
vegetation grows as fast as sediment accumulates.
5. Does not remove soluble phosphorus effectively, and total phosphorus is not
removed as effectively as sediment.
Useful References
1. Magette, W. L. (1986). Vegetated Filter Strips for Runoff Treatment.
Proceedings of Available Technology Workshop. Scientific and Technical
Advisory Committee. Chesapeake Bay Project. Arlington, VA.
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Nonpoint Source: Agricultural 65
2. Tollner, E. W., Barfield, B J., Haan, C. T., and Kao, To Yo (1976).
Suspended Sediment Filtration Capacity of Simulated Vegetation.
Transactions of the ASAE. 12, 678-682.
3. Grizzard, T.J. (1986). Performance of Urban BMP's. Personal
Communication. Occoquan Watershed Monitoring Laboratory, Manassas,
VA.
4. Scott, C. (1986). Urban Nonpoint Control BMP's. Personal
Communication. Virginia Soil & Water Conservation Service.
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66 Nonpoint Source: Agricultural
RIPARIAN AREAS
Description
Riparian areas are timbered areas of vegetation placed between agricultural fields
and streams that receive runoff.
Efficiency
Subsurface drainage water passing through a heavily vegetated riparian buffer can
lose essentially all of its nitrogen through denitrification. This can be true for
buffer areas as narrow as 50 feet. Studies in North Carolina indicate that riparian
areas are effective traps for sediment and phosphorus as well.
Advantages
1. These areas intact in many locales.
Disadvantages
1. In some locales, particularly near the coast, these areas do not exist.
Useful References
1. Gilliam, J. W., and Skaggs, R. W. (1986). Management of Agricultural
Drainage Water to Minimize Nutrient Inputs to Estuaries and Bays. Land
Use and the Chesapeake Bay. Virginia Cooperative Extension Service,
Publication No. 305-003.
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Nonpoint Source: Agricultural 67
CONTROLLED DRAINAGE
Description
The degree of drainage and the level of the water table for fields with tile drainage
systems or open ditches is controlled by the use of Dashboards. Controlled
drainage may be used for channelized streams as well.
Efficiency
The amount of nitrate-nitrogen reaching surface water from tiled agricultural
fields can be reduced roughly 50% by using controlled drainage. Phosphorus can
be reduced under some conditions but may be slightly increased. The following
results for control of flow in streams are for only one year but look promising.
Table NPT-7. Effects of maximum control (poor subsurface drainage),
intermediate control, and no control (good subsurface drainage) on levels (mg/1)
of nutrients, in a North Carolina study.
Nutrient
Nitrate nitrogen
Total nitrogen
Total phosphorus
Maximum control
3.7
13.6
0.5
Intermediate
15.7
20.0
0.3
No control
32.4
42.1
0.2
Table NPT-8. Concentrations of nutrients (mg/1) in controlled stream.
Nitrate nitrogen
Time
Before control
After control
Entry Exit
1.87 2.67
2.93 2.06
Change (%)
442
-30
Entry
0.02
0.06
Phosphorus
Exit Change (%)
0.06 +200
0.07 +16
Economics
The structures to control drainage represent a capital cost to farmers, but yields
are unaffected or increased by use of these techniques. Water is used more
efficiently and can be conserved for crop production. The system can be used for
subirrigation by pumping water into the ditch and letting the drainage system
distribute the water back through the field. In North Carolina this technology is
included in cost-share programs for agriculture.
Advantages
1. Installation of 21 subirrigation and 100 controlled-drainage systems
(representing 25,000 acres) in the past two years in North Carolina.
2. Expense may be offset partially or entirely by water use benefits.
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68 Nonpoint Source: Agricultural
Disadvantages
1. Limited phosphorus control.
2. Increased surface runoff and peak discharge.
Useful References
1. Gilliam, J. W., and Skaggs, R. W. (1986). Management of Agricultural
Drainage Water to Minimize Nutrient Inputs to Estuaries and Bays. Land
Use and the Chesapeake Bay. Virginia Cooperative Extension Service,
Publication No. 305-003.
2. Gilliam, J. W., and Skaggs, R. W. (1986). Riparian Areas and Water
Management to Control Nonpoint Pollutants. In Effects of Upland and
Shoreline Activities on the Chesapeake Bay. C. Y. Kuo, Ed.
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Nonpoint Source: Agricultural 69
TERRACES
Description
Terraces may be bench terraces or broad-based terraces. Broad terraces are a series
of shallow terraces constructed on gently sloping land at a suitable spacing along
the contour lines. Farm machinery may be used on broad-based terraces. Bench
terraces are nearly level strips or steps. In the U.S. parallel terraces (straight
terraces) are popular.
Efficiency
Terraces shorten slope length and reduce water velocity so that erosion is
controlled. In the U.S. terraces are usually designed to store runoff from a 6-
hour storm of ten-year severity and to drain the water in 36 hours. Once terraces
are established, overtopping does not cause much damage. Terraces can reduce
erosion by 75-90%.
Table NPT-9. Soil losses (kg/hectare) from grass-backslope, tile-outlet terraces
in Iowa.
Location
Eldora
Charles City
Creston
Guthrie Center
Sediment to ponding area
16,390
6,750
35,000
7,020
Soil loss
658
358
689
872
Economics
Terracing is included in cost-sharing programs for agriculture in some states.
This technology has been evaluated as not being cost-effective for phosphorus
removal, and it is much more expensive than practices such as no-till and
fertilizer management.
Advantages
1. Reduces erosion.
2. Reduces nutrient pollution.
3. Increases infiltration.
Disadvantages
1. More labor-intensive.
2. Not cost-effective for phosphorus removal.
Useful References
1. Loehr, R. C. (1984). Pollution Control for Agriculture. 2nd Edition,
Academic Press, Inc.
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70 Nonpoint Source: Agricultural
2. Moldenhauer, W. C, andOnstad,C. A. (1977). Engineering Practices to
Control Erosion. In D. J. Greenland and R. Lai, Eds. Soil Conservation
and Management in the Humid Tropics, p. 87. John Wiley & Sons.
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Nonpoint Source: Agricultural 71
SOD WATERWAYS
Description
A sod waterway is a watercourse with a grass cover.
Efficiency
These waterways reduce runoff velocity and gully erosion. Removal efficiencies
for nutrients are unknown.
Economics
Sod waterways are included in cost-sharing programs for agriculture in some
states.
Advantages
1. Lower initial cost than for underground conduits.
Disadvantages
1. Uses land that could otherwise be used for crops.
2. Necessity of raising planting equipment to cross slows the farmer and
increases the chance of planter malfunction.
3. Maintenance problem as a result of increased herbicide use.
Useful References
1. Loehr, R. C. (1984). Pollution Control for Agriculture. 2nd Edition,
Academic Press, Inc.
2. Moldenhauer, W. C., and Onstad, C. A. (1977). Engineering Practices to
Control Erosion. In D. J. Greenland and R. Lai, Eds. Soil Conservation
and Management in the Humid Tropics, p. 87. John Wiley & Sons.
3. Joint Commission on Rural Reconstruction of Taiwan (1977). Soil
Conservation Handbook.
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72 Nonpoint Source: Agricultural
COST-SHARING PROGRAMS
Reforestation. Stabilization of croplands and pasturelands by planting of trees
can be very effective in reducing erosion. It is included in some cost-sharing
programs in the CBDB.
Strip-Cropping. Strips of perennial grasses, legumes, or hay crops are alternated
with strips of row crops within a field. This approach reduces slope length,
runoff velocity, loss of soil in runoff, and adsorption of rain. Surface runoff can
be reduced by as much as 85%. Strip-cropping is included in some cost-sharing
programs in the CBDB.
Grazing Land Protection. These practices are included in some cost-sharing
programs in the CBDB.
Sediment Retention. Erosion or Water Control Structures. Construction of
these devices is included in some cost-sharing programs in the CBDB.
Permanent Vegetative Cover on Critical Areas. Establishment of this cover is
included in some cost-sharing programs in the CBDB.
Protective Cover for Vegetable Cropland. Establishment of this cover is
included in some cost-sharing programs in the CBDB.
Contour Farming. Contour farming allows water to seep into the soil rather
than running off. EPA studies show that this technique reduces runoff of
suspended solids by 25-50%, dissolved nitrogen by 25-50%, phosphorus by 55-
65%, and pesticides by 20-25%. Cost is typically only a few dollars per acre,
mostly for removal of rocks or hedgerows and land preparation. The practice is
included in some cost-sharing programs in the CBDB.
Diversions. These structures are included in some cost-sharing programs in the
CBDB.
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Nonpoint Source: Agricultural 73
OTHER APPROACHES
Crop Rotation. Crop rotation adds organic matter, reducing production costs.
Fertilizer use is reduced and weeds, disease, and insect cycles are disrupted.
According to calculations by the Uniform Soil Loss Equation, phosphorus
runoff is reduced by 30-75%, and nitrogen runoff by 55-80%.
Innovative Technologies. Aerial seeding of a winter cover crop is one
innovative technology that is being tried in the CBDB. This early seeding
allows the cover crop to germinate before soybeans or corn are harvested. Use of
nitrification inhibitors is another technology, with a cost of about $6/acre. Split
and late application of nitrogen for more effective crop utilization is another
innovative practice that may improve nutrient control.
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POINT SOURCE NUTRIENT CONTROLS
LAND TREATMENT SYSTEMS
Slow-Rate Systems
Rapid Infiltration
Overland Flow
Wetlands
WASTEWATER TREATMENT PLANTS
Methanol Denitrification
Bardenpho System
RBC Denitrification
Media Column Denitrification
Alternating Aerobic/Anoxic Operation
Oxidation Ditch Denitrification
Tertiary Chemical Phosphorus Removal
Simultaneous Precipitation
The Economics and Performance of Biological Nutrient Removal in
Activated Sludge Systems
Phostrip
Operationally Modified (Retrofitted) Activated Sludge Systems
Anaerobic/Oxic (A/O) and Anaerobic/Anoxic/Oxic (A2/O)
Sequencing Batch Reactors
University of Cape Town (UCT)
Modified Bardenpho
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76 Point: Land Treatment
SLOW-RATE SYSTEMS
Description
Slow-rate land treatment is the application to land of partially treated wastewater
to complete water treatment and to supply nutrients for plants. Farmland, areas
such as parks or golf courses, and woodlands may be used. Treatment is
accomplished by natural processes as water infiltrates through soil.
Efficiency
This technique is very reliable and produces a high-quality treated water.
Economics
Operating costs are lower than for conventional treatment systems, and crop sale
can offset some costs, especially if system is run under the direction of an
experienced farmer.
Advantages
1. Conservation of water through use of wastewater for irrigation.
2. Preservation and enlargement of greenbelts and open space.
3. Lower operating costs, better effluent, and lower energy requirements than
conventional treatment methods.
4. Little chemical use and sludge production.
5. Good stability and reliability.
6. Maintenance is straightforward and easily fit into the operation routine.
Disadvantages
1. Requires much more land than rapid infiltration systems or biological
treatment plants.
Useful References
1. Thomas, R. (1986). Land Treatment Systems. Proceedings, Available
Technology Workshop, C. W. Randall, Ed., Scientific and Technical
Advisory Committee, Chesapeake Bay Project. Chesapeake Research
Consortium, Inc.
2. Lussier, D. (1982). Operation and Maintenance Considerations for Land
Treatment Systems. USEPA Report No. EPA-600/s2-82-039.
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77
Point: Land Treatment "
RAPID INFILTRATION
Description
A rapid infiltration system may consist of nothing more than a set of basins in
sandy soil and the means for applying partially treated wastewater to them.
Water is treated as it seeps through the soil where it eventually joins the
groundwater. Where water is scarce, underdrains or recovery wells are sometimes
used to recover and reuse the treated wastewater.
Efficiency
The water quality resulting from this process is better than can be obtained with
most technologies for advanced wastewater treatment.
Economics
Cost is much lower than for other land treatment systems, because much less
land area is needed for a rapid-infiltration system. The distribution system needed
is also simpler.
Advantages
1. Reliable and cost-effective when properly designed and maintained.
2. Smaller land requirement to treat a given flow.
3. Has been used successfully for 40 years in the U.S.; in 1981, 320 rapid
infiltration systems were in use or under construction.
Disadvantages
1. Increased design complexity with less favorable site conditions (such as soil
fines, impermeable lenses in the soil profile, high water table, large cut-
and-fill requirements).
Useful References
1. Thomas, R. (1986). Land Treatment Systems. Proceedings, Available
Technology Workshop, C. W. Randall, Ed., Scientific and Technical
Advisory Committee, Chesapeake Bay Project. Chesapeake Research
Consortium, Inc.
2. Lussier, D. (1982). Operation and Maintenance Considerations for Land
Treatment Systems. USEPA Report No. EPA-600/s2-82-039.
3. U. S. Environmental Protection Agency (1984). Land Treatment: Rapid
Infiltration. Innovative Technology Pamphlet. USEPA, Washington, DC.
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78 Point: Land Treatment
OVERLAND FLOW
Description
Wastewater is allowed to flow as a thin sheet over gently sloped ground that is
covered with dense grass. The wastewater flows 30 to 60 meters and is collected
at the toe of the slope. Preapplication treatment ranges from screening to
secondary treatment.
Efficiency
Overland flow is capable of meeting standards for secondary treatment in the
winter and tertiary treatment in the summer. BOD and total suspended solids
average 10-20 mg/1 and rarely exceed 30 mg/1, even for influents with BOD's
>500 mg/1 and SS's of >250 mg/1. Nitrogen is reduced 70-90% on a total mass
basis, although concentrations may seem high since 20-50% of the water is lost
to evapotranspiration and seepage. Clay soils can provide 40-60% removal of
phosphorus. Phosphorus removal may also be improved by chemical addition.
Bacterial indicators are reduced by 90-99%. At low application rates 80-90%
removals of cadmium, nickel, copper, and zinc have been obtained.
Economics
Small systems in particular will benefit from the low costs and energy-saving
features of this technology. Availability and cost of land will result in greater
economy for small communities.
Advantages
1. Simple, energy-saving operation.
2. Potentially great savings for small communities.
3. May treat raw sewage without sludge production.
4. Can be used to upgrade existing facilities.
5. Considered an alternative technology by the EPA and eligible for financial
incentives.
6. Plots have been used continuously for at least 12 years in some cases.
7. Works on slopes at least from 2%-8%.
Disadvantages
1. Effluent from collecting ponds may be high in algae and other suspended
solids.
2. Removal efficiency may decline with time in service and varies with site
soils.
3. Several months of system conditioning may be needed to attain stable
performance.
4. Start-up and operation in winter may present a formidable design challenge.
Useful References
1. Thomas, R. (1986). Land Treatment Systems. Proceedings, Available
Technology Workshop, C. W. Randall, Ed., Scientific and Technical
Advisory Committee, Chesapeake Bay Project. Chesapeake Research
Consortium, Inc.
2. Lussier, D. (1982). Operation and Maintenance Considerations for Land
Treatment Systems. USEPA Report No. EPA-600/s2-82-039.
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Point: Land Treatment
I
H 3. Thomas, R. (1986). Overland Flow: A Decade of Progress. Proceedings,
Available Technology Workshop, C. W. Randall, Ed., Scientific and
• Technical Advisory Committee, Chesapeake Bay Project Chesapeake
Research Consortium, Inc.
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Point: Land Treatment
WETLANDS
Description
A wetland can be any land with water near or above the ground surface,
supporting plants adapted to a saturated root zone. The vegetation, micro-
organisms, and soils of natural or constructed wetlands can be utilized to remove
pollutants from stormwater runoff. The runoff is diverted into a wetlands area
which has been constructed or modified to contain the flow for a substantial time
(one day or more) without significant short-circuiting. The intent is to
encourage removal of pollutants by infiltration, sediment adsorption, and
biological action. Harvesting is recommended for maximum performance.
Efficiency
This technology is capable of reliably providing pH neutralization and some
reduction of nutrients, heavy metals, organics, BOD5, COD, SS, andcoliform
bacteria. The removals in the following table are for a wastewater treatment
application, but they also illustrate the potential for reduction of non-point
pollution.
Table PT-1. Efficiency of wetlands for removal (%) for secondary effluent
treatment (10-day retention).
BOD5 TSS COD N Total P Coliforms
80-95 29-87 43-87 42-94 0-94 86-99
Phosphorus removal depends on vegetative uptake and frequency of harvesting.
Nitrogen removal occurs by both vegetative uptake and
nitrification/denitrification. Removal of heavy metals depends on plant species
present. Proper operations are dependent on conscientious management.
Economics
The application of wetlands for non-point pollution control is in its infancy, and
few case histories are available. However, several applications have been
recently made and information can be obtained from the Occoquan Watershed
Monitoring Laboratory, Manassas, VA, as well as the U. S. Geological Survey
and Federal Soil and Water Conservation Offices. Construction costs depend on
land cost, design flows, and site conditions. Operation and maintenance costs are
relatively low.
Advantages
1. Vegetation removed can be used for composting or methane production.
2. Has been used in at least eight locations in the U.S. for wastewater
treatment.
3. Low-cost, low-energy, low-maintenance system.
4. May enhance nutrient-poor wildlife habitat.
5. Recreational and educational opportunities.
Disadvantages
1. Temperature and thus climate is a major limitation on treatment efficiency
2. May not be suitable for treatment of toxic materials, heavy metals, and
herbicides.
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Point: Land Treatment 01
3. Breeding ground for mosquitoes may be created without proper maintenance.
4. Large land requirement.
5. Availability of a suitable wetland site is a major factor in determining cost-
effectiveness.
Useful References
1. U. S. Environmental Protection Agency (1983). An Emerging Technology:
Wetland Treatment. Pamphlet, USEPA.
2. Occoquan Watershed Monitoring Laboratory (1987). Evaluation of an
Artificial Wetlands for Urban Stormwater Runoff Pollution Control,
Proposal to the Soil and Water Conservation District. Information from
OWML, Prince William Street, Manassas, VA 22110.
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82
Point: Wastewater Treatment
METHANOL DENITRIFICATION
Description
This is an activated sludge process operated for nitrogen removal. Denitrification
using methanol is accomplished by adding methanol to nitrified mixed liquor in
an anoxic zone (oxygen is not present). In this zone the microbial utilization of
nitrates and nitrites to oxidize carbon releases nitrogen gas. Typically the
denitrification reactor is the third stage of an extended process. In the first stage
the breakdown and assimilation of organics converts organic nitrogen into
ammonium. The second stage is for the nitrification of ammonium to nitrate.
The nitrified effluent of the second stage is then ready for denitrification in the
presence of a carbon source (methanol) and an acclimated biomass (activated
sludge). The three-sludge system as operated by Mullbarger (1971) is shown in
Figure PT-1, along with a description of the various components.
BACKWASH
ALUM
METHANOL ACID POLYMER
_J
WASTE TO SOLIDS HANDLING SYSTEM AND ULTIMATE DISPOSAL
PRIMARY
TREATMENT
(T'jSEOIMENTATION
^~s TANK
HIGH RATE
ACTIVATED SLU03E
S AERATION TANK
SEDIMENTATION
TANK
NITR IFYING
ACTIVATED SLUDGE
(?)AERATION TANK
(5} SEDIMENTATION
^^ TANK
DENiTRIFYINQ
ACTIVATED SLUDGE
§ ANOXIC REACTORS
AERATED CHANNEL
SEDIMENTATION TANK
POST
TREATMENT
§ MIXED MEDIA FILTERS
CHLORINE CONTACT
(TT) POST AERATION
Figure PT-1.
Efficiency
This process can provide excellent removal efficiencies, particularly for nitrogen
(see Table PT-2).
Economics
The costs of this process are almost prohibitive. Retrofit for this method of
nitrification/denitrification in a 1 mgd plant serving roughly 8,300 people would
entail a capital cost of $1,820,000, an increase in operating and maintenance
costs of $260,000, and an increase (100%) of $13.50 a month in the average user
fee. Estimates of costs for 25 facility retrofits in the Virginia tidewater were
$157,100,000 in capital costs, $15,160,000 in increased operating and
maintenance costs, and increases of $5.07 month for the system consumers.
Because the process is so structurally intensive, requiring three separate
processes, and because costs are high for the addition of methanol, sludge
handling, and disposal, neither capital costs nor operating and maintenance costs
will be less prohibitive for new plant construction.
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Point: Wastewater Treatment
Table PT-2. The effluent results of the final four months of the "three sludge"
system test at Manassas, VA.
Parameter
SS
COD
BOD5
Total P
Organic N
NH4-N
NO2-N
NO3-N
Level after final
clarification (mg/1)
2
21
4.0
0.6
1.0
0.0
0.0
0.8
Level after mixed media
filtration (mg/1)
0
16
0.8
0.3
0.8
0.0
0.0
0.7
Advantages
1. High percentage of nitrogen removed.
2. Relatively stable operation.
3. Each process can be separately optimized.
Disadvantages
1. High capital costs and operation and maintenance costs.
2. Large number of unit processes to operate.
3. Chemicals such as methanol are required.
4. The nitrification/denitrification processes are temperature-sensitive.
Useful References
1. U.S. Environmental Protection Agency (1975). Process Design Manual for
Nitrogen Control. Technology Transfer Manual. USEPA, Cincinnati,
OH.
2. Mulbarger, M. C. (1971). The Three Sludge System for Nitrogen and
Phosphorus Removal. Presented at the 44th Annual Conference of the
Water Pollution Control Federation, San Francisco, CA, October, 1971.
3. Report of the Joint Subcommittee Studying The Problems Associated with
Nutrient Enrichment and Related Water Quality Standards in the Waters of
The Commonwealth, S. D. no.16, 1986 session, Virginia General
Assembly.
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84
Point: Wastewater Treatment
BARDENPHO SYSTEM
Description
This is an activated sludge system that has been modified for biological nitrogen
removal using the influent wastewater as the organic carbon source during
denitrification. It can be operated as either a two-reactor or a four-reactor system.
The flow diagram for a four-reactor Bardenpho system is shown in Figure PT-2.
It can also be operated without the secondary anoxic reactor and the reaeration
reactor. Sometimes methanol is added to the secondary anoxic reactor to ensure
near-complete removal of nitrates.
MIXED LIQUOR RECYCLE
WASTE
Figure PT-2.
Efficiency
This technology is capable of near-complete removal of ammonium and nitrate
nitrogen. It can reduce the total nitrogen in a filtered effluent to <3 mg/1 when
four reactors are used, and to about 5 mg/l when only the first two reactors are
used. Efficiency will be affected by low temperatures but can usually be
maintained if the operating sludge age is increased appropriately, except when the
weather is especially severe. The efficiency is also a function of the mixed
liquor recycle rate. For maximum efficiency, a rate of 4x the influent is used.
Economics
The economics depend on the effluent quality desired. For a two-reactor design,
the operating cost can be 20-30% less than that of a completely aerobic activated
sludge system that is nitrifying if the mixed liquor recycle rate is l-2x the
influent rate. This design will generally remove 70-80% of the total nitrogen.
In a four-reactor design, if the recycle rate is 4x the influent rate and methanol is
added for maximum efficiency, the cost of operating can be 50% higher than a
completely aerobic, nitrifying system. See Table PT-7 for more information
about economics of the system relative to other activated sludge systems.
Advantages
1. Very high removals of nitrogen can be achieved.
2. The percentage nitrogen removal can be varied by changing the method of
operation and/or the number of reactors used.
3. The two-reactor system is more economical than a completely mixed aerobic
activated sludge system treating the same wastewater flow.
4. The system can be operated efficiently at any sludge age that achieves a high
level of nitrification, i.e, a high sludge age does not necessarily reduce the
efficiency of nitrogen removal, and frequently will improve it.
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Point: Wastewater Treatment
Disadvantages
1. A mixed liquor recycle system is required.
2. Use of the four-stage system with methanol addition increases both the
capital and the operating costs in comparison with conventional aerobic
activated sludge.
3. Good understanding of the processes is more necessary for this system than
for conventional aerobic activated sludge systems.
4. Chemical addition for denitrification may be required.
5. Mixers are required for the anoxic reactor(s).
6. This type of system has frequently produced a sludge of poor settleability.
Useful References
1. Walsh, T. K., et al. A Review of Biological Phosphorus Removal
Technology, Presented at the Annual Conference of the Water Pollution
Control Federation, October 1983.
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Point: Wastewater Treatment
RBC DENITRIFICATION
Description
A rotating biological contactor (RBC) system is designed so that the rotating
discs are completely submerged in the wastewater. The system is then operated
to develop anoxic conditions in those units, i.e., nitrates are added along with
organic wastewater in the absence of dissolved oxygen. Denitrification depends
on microbes attached to the surfaces of the rotating discs. The submerged RBC's
may be the final step in an RBC system that is both removing BOD and
accomplishing nitrification, or they may be used to denitrify effluent from an
activated sludge or other type of biological system accomplishing nitrification.
Efficiency
This type of system should be very efficient for the removal of nitrogen if it is
properly operated, i.e., it should accomplish near-complete removal of nitrates.
This system has been used by the Radford Army Ammunition Plant, Radford,
VA, to treat two wastewaters simultaneously. The wastewater mixture had a
TOC concentration of 150 mg/1 and a nitrate-nitrogen concentration of 100 mg/1.
Nitrate removal was <95%.
Economics
The operating costs of RBC systems are low compared to activated sludge
systems when both are treating organic wastewater aerobically. However,
denitrification can be used to reduce the power costs for activated sludge, whereas
the power costs for RBC's would increase somewhat in submerged operation.
An actual comparison is not available, but it is believed the activated sludge
system could be operated more economically.
Advantages
1. Existing RBC systems could be easily modified for denitrification.
2. RBC modules can be added to existing biological wastewater treatment plants
of any type to accomplish nitrogen removal.
3. RBC plants can be expanded modularly to handle increased flows.
4. RBC systems usually have a low power requirement.
Disadvantages
1. Submerging RBC units increases their power consumption.
2. Submerging RBC units results in a greater loading on the axle and could
increase the frequency of failure through axle shear.
Useful References
1. Benefield, L., and Randall, C. (1980). Biological Process Design for
Wastewater Treatment, Prentice-Hall, Inc.
2. U. S. Environmental Protection Agency (1975). Process Design Manual for
Nitrogen Control, Technology Transfer Manual. USEPA, Cincinnati, OH.
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Point: Waste-water Treatment
MEDIA COLUMN DENITRIFICATION
Description
Media column denitrification is used to remove nitrogen from either municipal
or industrial wastewaters. A source of organic carbon such as methanol or
settled sewage is added to the nitrified flow, which is subsequently passed
through a column containing a medium, usually sand, activated carbon, or
plastic beads. Denitrification depends on microbes that attach to the surface of
the medium. Other modifications of this technology also exist, such as columns
where the void spaces are filled with nitrogen gas.
Efficiency
Laboratory studies with upflow, packed sand-filled columns yielded average
removals as high as 98.9% for a detention time of 2.5 hours. This corresponded
to a hydraulic loading rate of 8.7 gpd/ft2 surface area and a nitrate loading rate of
0.172 Ibs/day/ft3. High removal rates may also be obtained with columns using
plastic medium or nitrogen gas/particle medium. Removal depends on media
size, loading rate and detention time but is generally efficient and reliable. Jeris
(1974) reported 99% nitrate removal with detention times as low as 6.5 minutes.
Table PT-3 shows data which illustrate the importance of media size, i.e., the
surface area available for microbial attachment. Sand columns also filter
suspended solids, typically removing 55-90%. A schematic of a typical design,
and a flow sheet showing where it might be inserted in the treatment train are
given as Figures PT-3 and PT-4.
Table PT-3. Comparison of nitrate removal rates.
Study
Seidel
Pafford (4)
St. Amant (6)
Tucker etal. (8)
St. Amant (6)
Parkhurst (5)
Tucker et al. (8)
Tucker et al. (8)
Tucker et al. (8)
Tucker etal. (8)
Tucker et al. (8)
Tucker et al. (8)
Jeris (1)
Jeris (1)
Jeris (2)
Jeris (2)
Jeris (2)
Medium, avg. size
1 .5 in. gravel
1.0 in. gravel
1.0 in. gravel
2.36 mm sand
1 .0 in. gravel
1.18 nun act. carbon
2.36 mm sand
2.36 mm act. carbon
2.36 mm sand
2.36 mm sand
2.36 mm sand
2.36 mm sand
1 .7 mm act. carbon
1 .7 mm act. carbon
0.6 mm sand*
0.6 mm sand*
0.6 mm sand*
Type of flow
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Packed
Fluidized
Ruidized
Fluidized
Removal rate
(mg/Vhr)
8.4
18.0
18.0 (avg.)
23.9
24.1 (max.)
25.0
31.6
38.1
39.1
45.8
51.2
54.7
157.1
166.4
196.6
360.0
833.5 (max.)
*Effective size
Economics
Economics can be quite good. Although these systems can be designed to use
methanol, they can also use other carbon sources, including the influent BOD.
Use of other sources will greatly reduce operating costs. Also, much smaller
structural volumes are required than with normal reactors, because higher
concentrations of microbes are possible within the medium.
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88
Point: Wastewater Treatment
RAW WASTEWATER
SECONDARY
^SEDIMENTATION
TANK
ROTOR OR OTHER
AERATION SYSTEM
Figure PT-3.
BACKWASH WATER
TO STORAGE
EFFLUENT TO
CLARIFICATION OR
FILTRATION
Figure PT-4.
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Point: Wastewater Treatment 89
Advantages
1. Very rapid removal of nitrogen is possible because of high biomass
concentrations in the column.
2. Small reactor size reduces capital costs.
Disadvantages
1. Microbial growth may cause floating medium with high losses from system
during upflow operation.
2. Downflow operation may cause clogging.
Useful References
1. Jeris, J. S., "High Rate Denitrification," presented at the 44th Annual
Conference of the Water Pollution Control Federation, San Francisco, CA
(October 1971).
2. Jeris, J. S., and Owens, R. W., "Pilot Scale High Rate Biological
Denitrification at Nassau County, N. Y., Presented at the New York Water
Pollution Control Association Meeting, (January 1974).
3. McCarty. P. L., Beck, L., and St. Amant, P. (1969). "Biological
Denitrification of Wastewaters by Addition of Organic Materials," Proc.
24th Industrial Waste Conference, Purdue University Extension Series,
135, 1271.
4. Pafford, R. J., DeFacco, P., and Teerink, J. R. (1971). "Denitrification by
Anaerobic Filters and Ponds," Water Pollution Control Research Series,
Publication No. 13030 Ely 04/71-8, EPA, Washington, DC.
5. Parkhurst, J.D., Dryden, F. D., McDermott, G. N., and English, J. (1967).
"Pomona Activated Carbon Pilot Plant," Journal of the Water Pollution
Control Federation, 39, R70.
6. St. Amant, P. P., and McCarty, P. L. (1969). "Treatment of High Nitrate
Waters," Journal of the American Water Works Association, 61,42.
7. Seidel, D. F., and Crites, R. W. (1970). "Evaluation of Anaerobic
Denitrification Processes," Journal of the Sanitary Enginering Division,
Proc. A.S.C.E., SA2, 96, 267.
8. Tucker, D. O., Randall, C. W., and King, P. H. (1974). Columnar
Denitrification of a Munitions Manufacturing Wastewater. Proceedings,
29th Annual Purdue Industrial Waste Treatment Conference, Engineering
Extension Series 145, Lafayette, IN. pp.165-175.
9. U. S. Environmental Protection Agency (1975). Process Design Manual for
Nitrogen Control. Technology Transfer Manual. USEPA, Cincinnati,
OH.
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90
Point: Wastewater Treatment
ALTERNATING AEROBIC-ANOXIC OPERATION
Description
Wastewater is treated by this method in a conventional activated-sludge plant
with modified operating procedures. The completely mixed activated-sludge
system is aerated intermittently instead of continuously. This process creates a
cycle of alternating aerobic and anoxic conditions. Conventional oxidation and
stabilization of wastes takes place during the aerobic period, and nitrate is
denitrified to nitrogen gas during the anoxic period.
Efficiency
Use of this technique can greatly enhance removal of total nitrogen, as well as
removal of BOD and possibly suspended solids. Studies conducted at a plant in
Australia yielded the results shown below.
Table PT-4. Efficiency of an alternating aerobic/anoxic system at Brushy Creek
Plant, Australia.
Effluent
Parameter
Flow, m2/day (mgd)
BOD, mg/1
SS, mg/1
TKN, mg/1
NH3-N, mg/1
NO3-N, mg/1
TN, mg/1
TP, mg/1
Influent
5500(1.45)
320
198
63
44
0
63
11
CMAS
Stage
2900(0.77)
15
8.4
19.6
13.7
0
19.6
7.2
AAA*
Stage
2600(0.69)
7
4.4
2.6
0.9
3.0
6.5
8.2
%
Reduction
53
48
87
93
-
67
(14)
*Air on/off = 2.25/2.75 hour
Similar studies at the Yarra Glen plant in Australia produced reductions in BOD
and effluent nitrates in comparison with conventional activated-sludge operation,
plus a 35% energy saving (from 3400 to 2200 kWh/quarter) and a 40% reduction
in the MLVSS concentration for a schedule of 2 hours on/4 hours off instead of
constant aeration. The results are shown in the following table. Data analysis
by Randall (1986) has shown that the optimum on/off ratio is a function of the
organic loading rate.
Economics
This process should result in reduced operational costs with little or no capital
investment. No significant construction is required to adopt this method, and
operational costs are reduced for two reasons. First, energy (aeration)
requirements are reduced by the use of nitrates for BOD stabilization. Second,
less excess sludge is produced because of the reduced efficiency of microbial
growth under anoxic conditions. This reduction in turn lowers sludge handling
and disposal costs, which are major operating expenses.
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Point: Wastewater Treatment
Table PT-5. Alternating aerobic/ anoxic system at Yarra Glen Plant, Australia.
Effluent
Air on/off hours
Parameter (mg/1)
BOD
SS
TKN
NO3-N
MLVSS
Influent
396
76
0
N.A.
CMAS
5
15
25
3980
3/2
7
20
20
3500
2/3
3
15
10
2400
2/4
3
15
7
2400
Reduction (%)
for 2/4 operation
40
0
72
40
NOTE. Flow = 21.2 nv* (3.9 gpm); period of study was July 1983
through April 1984. Total quarterly energy usage was 3400 kWh for CMAS and
2200 kWh for AAA 2/4; this represents a 35% reduction in energy usage.
Advantages
1. Reduced energy requirements.
2. Less excess sludge.
3. Less nitrogen discharged to surface waters.
4. Operational change is simple, requiring little new equipment and no major
structural changes.
Disadvantages
1. Limited full-scale experience in the U.S.
Useful References
1. Ip, S. Y., Bridger, J. S., and Millis, N. F. (1986). Effect of Alternating
Aerobic and Anaerobic Conditions on the Economics of the Activated
Sludge System, Water Science Technology, Vol. 19, Rio, pp. 911-918.
2. Randall, C. W. (1986). Discussion of "Effect of Alternating Aerobic and
Anaerobic Conditions on the Economics of the Activated Sludge System",
Department of Civil Engineering, Virginia Tech University, Blacksburg,
VA. Water Science Technology, Vol. 19, Rio, pp. 919-921.
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92 Point: Wastewater Treatment
OXIDATION DITCH
Description
The oxidation ditch is a variation on the activated-sludge process in which mixed
liquor is recirculated continuously through a closed-loop aeration channel.
Several aeration techniques may be used. Commonly aerators are staged in series
along the aeration channel, subjecting the biomass to a continuing rapid
alternation of aerobic/anoxic conditions. Aeration may also be accomplished at a
single point, where a barrier ' orces iho entire flow past an aerator. This system
permits operation for both a" obi: cV lation of wastes and anoxic denitrification.
Efficiency
The efficiency of oxidation ditches >- removal of BOD and suspended solids is
well documented. Denitrif k alion k also possible with these systems; the
facility (2 mgd) in Carrollwood Vi'!age, FL, had 84% removal of COD and
97.6% removal of nitrogen, and another (8.9 mgd) in Frankfort, KY, had COD
removal of 89% and nitrogen removal of 76%. Both are single-channel systems,
and the removal at Carrollw xxl is 'lone without an anoxic zone. Near-complete
removal of nitrogen and enhanced -emoval of phosphorus can be achieved with
this technology.
Economics
Both capital and operational costs of oxidation ditches are often lower than for
conventional systems. Capital cost savings come from smaller aeration basins,
fewer aerators, and elimination of chemical feeding equipment. Operationally,
aeration requirements are reduced, lowering energy costs. Also, the need for
expensive chemicals such as methanol for denitrification is eliminated.
Advantages
1. Simple process design and operation.
2. Decreased alkalinity consumption.
3. Reduced need for aeration can increase the capacity of an overloaded facility.
4. Very good process stability.
5. Short-circuiting is reduced by design promoting plug-flow.
6. Enhancement possible by adjustment of oxygenation capacity along the ditch
channels, especially in multi-channel ditches, such as the Orbal system.
Disadvantages
1. Construction costs may be high for some systems, particularly for barrier
aeration system.
2. Operation at high sludge age slows the rate of denitrification because it
results in a very low organic carbon concentration in the mixed liquor.
Useful References
1. Huang, Y. C., and Drew, D. M. (1985). Investigation of the Removal of
Organics and Nitrogen in an Oxidation Ditch, Journal Water Pollution
Control Federation, 57:151-156.
2. Rittman, E., and Langeland, E. (1985). Simultaneous Denitrification With
Nitrification in Single-Channel Oxidation Ditches, Journal Water Pollution
Control Federation, 57:300-308.
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Point: Wastewater Treatment 93
TERTIARY CHEMICAL REMOVAL OF PHOSPHORUS
Description
After completion of a conventional activated-sludge process, the secondary
effluent receives additional treatment to remove phosphorus. Typically this
treatment involves the use of a two-step lime reaction, recarbonation, and multi-
media gravity filtration. Tertiary treatment as simple as sand filtration could
also be used after secondary treatment.
Efficiency
Tertiary systems can meet extremely stringent effluent requirements with proper
design and operation. Lime treatment systems at Lake Tahoe, CA, and near
Manassas, VA, routinely achieve effluent phosphorus (TP) levels <0.1 mg/1. A
tertiary lime system is not, however, a guarantee of meeting design effluent
standards. Also efficiency can be adversely affected by equipment failure or by
impractical labor requirements for operation.
Economics
Tertiary treatment often implies both high capital costs and high maintenance
and operational costs. Total operational costs for a tertiary lime treatment
system in Fairfax, VA, with a flow of 19 mgd were $17,148/day. Both capital
and operational costs are directly related to the complexity and number of
processes constructed for tertiary treatment.
Advantages
1. Suited for stringent standards if well designed and operated.
2. Reliability is increased with additional clarifiers.
3. Retrofit is simple.
Disadvantages
1. High capital, operating, and maintenance costs.
2. May require great technical expertise and labor-intensive operation to meet
design effluent standards.
3. High sludge production, and difficulty with sludge disposal.
4. Chance of equipment failure, increasing with complexity.
5. May involve the storage and handling of chemicals such as lime.
Useful References
1. Canham, R., Randall, C., Jenkins, J., and Fry, O. (1981). Full-Scale
Evaluation of By-Product Ferric Chloride For Phosphorus Removal and
Comparison With Two-Stage Lime Treatment, Presented at the Annual
Conference, Water Pollution Control Federation, Detroit, MI.
2. U. S. Environmental Protection Agency (1976). Process Design Manual for
Phosphorus Removal. Technology Transfer Manual, No. EPA 625/1-76-
OOla.
3. Schmidtke, N. (1985). Estimating Sludge Quantities at Wastewater
Treatment Plants Using Metal Salts to Precipitate Phosphorus.
Proceedings, Phosphorus Management Conference, New University of
Lisbon, Portugal, pp. 379-385.
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Point: Wastewater Treatment
SIMULTANEOUS PRECIPITATION
Description
Chemicals are added directly to the activated sludge of a conventional activated
sludge process, usually before the secondary clarifier. These chemicals convert
phosphorus to an insoluble form that is precipitated and removed with waste
sludge.
Efficiency
Removals of 97% were attained with a total phosphorus effluent concentration of
0.36 mg/1 in Fairfax County, VA. Subsequent changes resulted in effluent total
phosphorus concentrations of <0.18 mg/1 based on routine yearly operation.
Most plants in the Great Lakes drainage basin, where this process is used
extensively, achieve an effluent concentration of total phosphorus of <1 mg/1.
Economics
Major costs are sludge handling and chemicals, and additional storage and
distribution systems. Sludge disposal costs in Fairfax County were $40.89/mg.
Retrofitting costs also may involve additional clarifier costs. Conversion of the
Fairfax County plant from a tertiary high lime system resulted in a sludge
reduction of 28% and an operating cost reduction of $25 1 per million gallons.
The cost of retrofitting and operating an activated sludge plant for chemical
phosphorus removal has been thoroughly researched and presented in the report
of McNamee, Porter and Seeley (1986) prepared for the Chesapeake Bay
Program. The following table was excerpted from graphs presented in that
report.
Table PT-6. Cost estimates (thousands of dollars) for retrofitting plants for
phosphorus removal to an effluent level of 1 mg/1.
Influent phosphorus levels
6-10 mg/1 3-6 mg/1
Costs 10 mgd 5 mgd 1 mgd 10 mgd 5 mgd 1 mgd
Capital cost
Alum and polymer/yr
Life cycle/yr*
170
340
350
130
170
185
55
35
40
160
205
220
115
105
115
55
20
25
NOTE. Numbers rounded to nearest multiple of 5.
*(10% capital cost/yr + alum and polymer/yr).
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Point: Wastewater Treatment 95
Advantages
1. Industry by-products such as FeCl3 (pickle liquor) can be used to precipitate
phosphorus at 50-66% the cost of alum or lime.
2. Retrofit feasible, in many cases easy.
Disadvantages
1. Phosphorus removal to 1.0 mg/1 increases sludge mass by an average of 26%
at conventional and 40% at primary activated-sludge plants.
2. Chemical storage, feed, and distribution must be provided for.
Useful References
1. Canham, R., Randall, C., Jenkins, J., and Fry, 0. (1981). Full-Scale
Evaluation of By-Product Ferric Chloride For Phosphorus Removal and
Comparison With Two-Stage Lime Treatment Presented at the Annual
Conference, Water Pollution Control Federation, Detroit, MI.
2. McNamee, Porter and Seeley, Inc. (1986). Retrofitting POTWS for
Phosphorus Removal in the Chesapeake Bay Drainage Area. Report to the
U. S. Environmental Protection Agency, Chesapeake Bay Program,
Annapolis, MD.
3. U. S. Environmental Protection Agency (1976). Process Design Manual for
Phosphorus Removal. Technology Transfer Manual, No. EPA 625/1-76-
OOla.
4. Schmidtke, N. (1985). Estimating Sludge Quantities at Wastewater
Treatment Plants Using Metal Salts to Precipitate Phosphorus.
Proceedings, Phosphorus Management Conference, New University of
Lisbon, Portugal, pp. 379-385.
-------
96 Point: Wastewater Treatment
THE ECONOMICS AND PERFORMANCE OF BIOLOGICAL
NUTRIENT REMOVAL IN ACTIVATED SLUDGE SYSTEMS
Biological nutrient removal, i.e., the removal of nitrogen and phosphorus
from wastewater by biological processes, is both an old and a new technology.
For example, the biochemical pathways responsible for nitrification and
denitrification, i.e., nitrogen removal, have been known for many years and have
frequently been incorporated in designs. However, our concepts concerning the
way these processes can be used are changing rapidly. In the past we generally
thought of them separately and applied them for the specific goals of oxidizing
ammonium and converting nitrates to nitrogen gas. Now there is a growing
realization that the joint use of these processes in single-sludge activated sludge
systems not only will reduce the nitrogen discharged to the receiving water but
also can result in reduced costs of treatment through reductions in the energy,
requirements and sludge processing costs. This realization will inevitably
increase the incorporation of nitrogen removal processes in treatment plant
designs, regardless of the need for nutrient control.
Biological phosphorus removal has been the subject of study for the past
quarter-century, but the mechanisms and pathways, in contrast to those of
nitrogen removal, have only recently been elucidated. In fact, in the 1970's it
was generally accepted by the wastewater treatment profession that excess
biological phosphorus removal, i.e., the incorporation of phosphorus into
bacterial cells in excess of the amount needed for cellular growth, was
impossible. It is now known, however, that excess biological phosphorus
removal is not only possible, but also easily controlled. Moreover, it can
produce an overall treatment system that is both better and more economical than
a conventional aerobic activated sludge system. It is superior in that it is more
stable, produces better quality effluent, and enhances the incorporation of
nitrogen removal into a single-sludge activated sludge system. It is small
wonder, then, that a growing number of experts consider completely aerobic
activated sludge systems as obsolete for most wastewater treatment applications.
The guiding principle is that biological nutrient removal systems should be used
because it is technically, economically, and environmentally responsible to do
so.
The specific advantages of biological nutrient removal in activated sludge
treatment plants can be illustrated by Table PT-7, which compares the relative
costs, energy and chemical needs, and sludge production rates of the various
designs. A conventional, completely aerobic, single-sludge system is used as
the basis for comparison. The factors shown can be multiplied times the
corresponding factor for a conventional, non-nitrifying system to obtain a cost
estimate, etc., for the specific modification. The table also shows what
pollutants each modification is designed to remove.
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Point: Wastewater Treatment
97
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-------
Point: Wastewater Treatment
PHOSTRIP
Description
Return activated sludge is diverted to a sidestream anaerobic phosphorus-
stripping tank where it is held about 10 hours. Phosphorus released in the
stripper passes out in the supernatant, and phosphorus-poor activated sludge is
returned to the aeration tank. The supernatant is collected in a separate tank,
mixed with lime or another coagulant, and sent to the primary sedimentation
tank or to a separate clarifier for sludge separation. Phosphorus is removed in
the waste sludge biomass and as a chemical precipitant. Possible designs for the
process are shown in Figure PT-5.
Efficiency
A typical efficiency for municipal wastewater is 85% removal of phosphorus,
not including additional removal accomplished in other processes in the plant.
Process effluent levels of five full-scale Phostrip plants are shown below, and
the overall performance for a five-month period is shown for the Adrian, MI,
plant.
Table PT-8. Levels of total phosphorus (mg/1) in unfiltered effluent of Phostrip
process at five plants.
Plant location
Lansdale, PA
Adrian, MI
Little Patuxent, MD
Reno-Sparks, NE
Amherst, NY
Actual flow/
design (mgd)
1.5/2.5
5.0/5.4
8.5/15.0
23.0/30.0
17.0/24.0
Standard
0.2
1.0
0.3
0.5
1.0
Total
Average
0.7
1.8
2.0
1.0
1.7
phosphorus
Typical range
0.5-2.0
0.2-3.0
1.5-3.0
0.5-2.0
0.0-3.0
Table PT-9. Levels (g/m3) of TP, BOD, SS, and NH3 nitrogen in effluents of
plant using Phostrip process.
Fluid TP BOD SS NH3N
Raw influent
Primary effluent
Plant effluent
4.5
4.6
0.4
78
7
143
4
16
4
NOTE. Filtered mixed liquor orthophosphate as phosphorus was 0.238 g/nA
Economics
The Phostrip process is designed to reduce chemical costs and the associated
dewatering and disposal costs of chemical sludge. According to a Canadian
study, Phostrip is not cost-competitive with conventional chemical treatment,
for either capital costs or operating and maintenance costs. The capital cost for
Phostrip is usually a greater economic consideration than the operations cost and
is typically independent of influent phosphorus levels. Phostrip will be most
cost-competitive when high phosphorus influent levels are expected. Capital
cost (including hardware costs and the license fee) for Phostrip at Adrian, MI was
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Point: Wastewater Treatment
99
TO PKIMARV
CAMONACEOUS
STAGE EFFLUENT
WASTE
ACTIVATED
SLUDGE
- *»STE LIME SLUDGE
PRIMARY |-
EFFLUENT"
f
f
\ f
£
-\ ,*-
1 , i .-. , CARBONACEOUS
... ... — aj»iInETl"~"*" ST*GI £FFLUENT
RETURN ACTIVATED SLUDGE ^^
P ENRICHED £l2
STRIPPER SUPERNATANT I
X X-\l
TO LAND
APPLICATION
PHOSPHORUS STRIPPE
S SLUDGE
PHOSPHORUS
STRIPPER
^Tt^
w
WA
ACTI
SLU
STE
(ATED
DGE
-i" "• /
ELUTRIATE
^^.
PRIMARY 1 |4]
-r"
LIME
1 ,
c
1 — »-f
L
K
[L--^---'--^
CLARIFIER S'»SE EFFLUENT
RETURN ACTIVATED SLUDGE ~~-^
P ENRICHED
STRIPPER SUPERNATANT
PHOSPMOflUS STRIPPE
} SLUDGE
ELUTRIATE
j.
$
/~\\
PHOSPHORUS
STRIPPER
D>
}
~r
•uz^
WA
»CTH
SLU
^
STE
ATEO
DGE
Figure PT-5.
$1,000,000 for the design flow of 7.0 mgd. Retrofit costs are site-specific and
include construction of a stripper tank, reactor/clarifier, lime-handling facilities,
and the license fee.
Advantages
1. Sludge settles more easily than conventional activated sludges.
2. May aid quick recovery from plant upsets caused by shock loading more than
other activated-sludge systems.
3. Less affected by brief hydraulic surges and varying waste strengths than
conventional activated-sludge systems, or other biological phosphorus-
removal processes.
-------
100 Point: Wastewater Treatment
4. Sludge has higher fertilizer value. Lime sludge may be valuable soil
amendment for acidic soils.
5. Chemical consumption lower than for conventional (chemical) options for
phosphorus removal.
6. Operational flexibility due to sidestream allows treatment at a lower ratio of
:phosphorus than chemical treatment.
Disadvantages
1. Consistent operating technique may be difficult to establish. Requires high
level of operational skills.
2. Extreme sensitivity to operating parameters; requires careful labor- intensive
monitoring.
3. Large requirements for pump, tankage, and sludge elutriation.
4. Lime (chemical usually used) is difficult to handle.
5. Potential odor problem.
6. Not easily compatible with nitrifying system.
7. Lime scaling in the flocculation/clarifier overflow and elutriation lines causes
maintenance difficulties.
8. Susceptible to toxic loads.
9. System start-up difficult.
10. Conflicting needs of activated sludge and Phostrip systems.
1 1 . A proprietary process.
Useful References
1. Tetreault, M., Benedict, A., Kaempfer, C., and Earth, E. (1985). Biological
Phosphorus Removal, A Technology Evaluation. Presented at the Annual
Conference of the Water Pollution Control Federation, Kansas City, MO.
Available from Brown and Caldwell, Inc., Pleasant Hill, CA.
2. Biospherics Incorporated (1986). Phostrip II Process and System
Description, 4928 Wyaconda Road, Rockville, MD 20852.
3. Walsh, T., Behrman, B., Weil, G., and Jones, E. (1983). A Review of
Biological Phosphorus Removal Technology. Presented at the Annual
Conference of the Water Pollution Control Federation, Atlanta, GA.
Available from Metcalf & Eddy, Inc., Boston, MA.
4. McNamee, Porter and Seeley, Inc. (1986). Retrofitting POTWS For
Phosphorus Removal in the Chesapeake Bay Drainage Area, Report to the
U.S. EPA Chesapeake Bay Office, Annapolis, MD.
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Point: Wastewater Treatment
101
OPERATIONALLY MODIFIED ACTIVATED-SLUDGE
PROCESSES (RETROFITS)
Description
This process usually takes place in a long plug-flow reactor, or possibly in two
separate, completely mixed reactors. Basically, an anaerobic zone is created in an
operating activated-sludge system. In a plug-flow reactor this is accomplished
by not aerating the first portion of the tank. Development of an anaerobic zone
allows excess biological phosphorus to be removed. The schematic of such a
modification is shown in Figure PT-6. Existing plants can also be modified for
both nitrogen and phosphorus removal. A schematic for modifications made to
the Hampton Roads Sanitation District's York River Plant is given in Figure
PT-7. The design incorporates operating flexibility by making it possible to
operate the anoxic zones anaerobically or aerobically, as desired.
INFLUENT
i
(UNAERATED)
ANAEROBIC
AEROBIC
RETURN SLUDGE
XcLARIFIER/ EFFLUENT
^v ' *-
*\
/
III!,.
LEGEND:
^ LIQUID STREAM
\\\\- MAIN PHOSPHORUS
REMOVAL PATHWAY
&"• SLUDGE STREAM
Figure PT-6.
NITRATE CYCLE
UNAEHATED
UNAERATED
AERATED
INFLUENT
ANAEROBIC
ANOXC
/EFFLUENT
WASTE ^
^ ZONE 1
PHOSPHORUS
RELEASE
BOD UPTAKE
PHOSPHORUS
BACTERIA
SELECTION
ZONE 2
DENITRIFCATION
BOD UPTAKE
ZONE 3
NITRIFICATION
PHOSPHORUS UPTAKE
Figure PT-7.
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102 Point: Wastewater Treatment
Efficiency
Effluent data for the biological processes of two operationally modified plants are
listed below. Both plants are capable of consistently achieving effluent
phosphorus levels <1 mg/1 under nitrifying conditions without tertiary
treatment.
Table PT-10. Concentrations (mg/1) of total phosphorus, nitrogen, and BOD5
in influents and effluents of two operationally modified activated-sludge plants.
Percentag
Site of
Flow design
(mgd) flow
Reedy Creek
DePere
4.8
3.5
80
49
e Total
phosphorus
Infl.
6.7
5.1
Effl.
0.9
0.3
Total
nitrogen
Infl.
7.0
12.8
Effl.
5.8
8.6
BOD5
Infl.
85
86
Effl.
3
7
Economics
This process should result in enhanced removals of phosphorus and nitrogen
with little capital investment. Reduced sludge production and energy
consumption could also be expected. Two 0.68 million gallon tanks at the York
River plant were modified for phosphorus removal at a cost of approximately
$50,000 to treat 7 mgd of municipal wastewater. Modification costs for both
nitrogen and phosphorus removal were about $110,000. Modifications were
performed by sanitary district personnel.
Advantages
1. Increased removals of phosphorus and nitrogen with modest construction and
hardware investments.
2. Reduced energy costs for aeration.
3. Can be used with tertiary chemical processes for phosphorus removal to
reduce the overall cost of treatment
Disadvantages
1. Favorable BOD5:total phosphorus ratios are required to attain low effluent
concentrations of phosphorus. Ratios of 20:1 or more to the biological
reactor make it possible to obtain effluent TP concentrations <1 mg/1.
2. Total phosphorus concentrations substantially less than 1.0 mg/1 usually
require chemical co-precipitation or tertiary chemical precipitation.
3. Removal of total nitrogen below 6 mg/1 requires tertiary treatment for
effluent suspended solids removals.
Useful References
1. Tetreault, M., Benedict, A., Kaempfer, C. Barth, E. (1985). Biological
Phosphorus Removal - A Technology Evaluation, Presented at the Annual
Conference, Water Pollution Control Federation, Kansas City, MO.
Available from Brown and Caldwell, Inc., Pleasant Hill, CA.
2. Randall, C. (1986). Quarterly Reports, York Rivers STP Nutrient Removal
Project, Chesapeake Bay Initiatives, State Water Control Board of Virginia.
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Point: Wastewater Treatment
103
A/O PROCESS
Description
A typical A/O reactor, when designed only for phosphorus removal, contains an
activated-sludge process with anaerobic and aerobic (oxic) zones. For nitrogen
removal, an anoxic zone is included between the anaerobic and anoxic zones; this
arrangement is known as A2/O process. Detention times may be 1 hour for the
anaerobic and anoxic zones, and 1.8-2.5 hours for the aerobic zone, although
significantly longer detention times can be used (2.1 hours for anaerobic and 7.7
hours for aerobic at Pontiac, MI). The anaerobic zone is located at the influent
end of the reactor; the anoxic and oxic stages follow. The A2 /O process is
identical to the three-stage modified Bardenpho process. Flow diagrams for the
two modifications are shown in Figure PT-8.
1 to 2O (TYPI
Anoxic Recycle (ARCYI 1
1 to2C
*•
*
•
Nitnfttd R«
Anaerobic
Zone
Return Activated Sludge (RAS)
Sludge (WAS)
1 to 2 Q (TYP)
Q
i
cr
•ail
C3
Amarobic
Zone
I
M
4
NrtrrfMd
•>
cz:
cr>
Anoxic
Zone
Biological Raactoi
0.2 t
Racyc
—*
ie (NRCY)
000
' 0 0 O-
000
Aerobic
Zone
o 0.5 Q (TYP)
1
-t
1
\
1
/
Watte Activated
Return Activated Sludge (RAS)
Sludge (WAS)
Figure PT-8.
Efficiency
Only three full-scale A/O plants are currently in operation: in Largo, FL, in
Pontiac, MI, and on the York River, VA. All are retrofitted plug-flow activated-
sludge plants. The Largo plant includes an anoxic zone; the Pontiac plant does
not. The York River plant is equipped for anoxic operation, but has not yet
been operated in that mode. Below are data from one year of operation at the
Largo plant, from two separate periods of 4-6 weeks at the Pontiac plant, and
four months at the York River plant. The York River plant has primary
clarification and filtrate recycle from belt filter presses processing anaerobically
digested sludge.
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104 Point: Wastewater Treatment
Table PT-11. Concentrations (mg/1) of total phosphorus, BOD, and SS in
influent and effluent at two plants using A/O processes.
Total phosphorus
Location, year
Largo, 1981-82
Pontiac, 1984
Pontiac, 1985
York River, 1986
Flow (mgd)
3.2*
2.86
4.28
6.18
Infl.
_
3.7
2.6
9.4
Effl.
1.5-2.5+
0.9
0.7
2.5
BOD
Infl.
—
163
136
200
Effl.
4-8
9.4
11
14
SS
Infl. Effl.
- 10-26
140 7
136 10
201 7
*Design flow.
+Average effluent concentration of phosphorus at the Largo plant in a recent
performance test was 1.85 mg/1; influent concentration was 8.9 mg/1.
A pilot A/O system in Rochester, NY, with influent levels (mg/1) of PO4
phosphorus andNHs nitrogen of 7.5 and 16.9, respectively, achieved effluent
levels of 0.38 and 0.5, respectively.
Economics
Retrofit is easiest in plug-flow activated-sludge plants, but can be adapted to
most types of activated-sludge processes. Capital cost for retrofit is less than for
Phostrip or Bardenpho, because less reactor volume is needed. A Canadian study
concluded that, on the basis of total annual costs, A/O was more cost-effective
than chemical precipitation, whereas Bardenpho, UCT, and Phostrip were not.
Retrofit costs in 1984 for the Pontiac A/O plant totalled $57,000. Sludge-
handling costs are lower than for chemical treatment, because less sludge is
produced. Also, energy savings can be realized since less aeration is necessary,
and the cost of methanol is eliminated where denitrification is used. A/O is a
proprietary process so a licensing fee is necessary. Some estimates claim that,
depending on the size of the plant, life-cycle costs may be 40-45% less than
costs for conventional chemical treatment Whereas capital costs and operating
and maintenance costs for a conventional 10 mgd plant are $5.48 million and
$872,000, respectively, for an A/O plant these costs are $3.81 million and
$322,000.
Advantages
1. Retrofit is relatively easy and often cheaper than for other biological
processes for phosphorus removal.
2. Relatively simple operation.
3. High-phosphorus sludge has fertilizer value.
4. Short hydraulic detention time reduces capital costs for tankage.
5. Nitrification possible with slight reduction in phosphorus removal and no
need for methanol.
6. Fewer clarifiers than multi-stage systems for nitrogen removal.
7. Lower quantities of chemicals used than with conventional techniques; also
lower operating and maintenance costs.
8. Sludge has good settling characteristics, and less is produced than with
chemical treatment
9. Potential energy savings via anaerobic stabilization.
10. High rate stability.
11. Alkalinity is returned to flow by denitrification.
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Point: Wastewater Treatment 105
Disadvantages
1. May be incapable of simultaneously meeting truly stringent nitrogen and
phosphorus standards, even with effluent filters, without chemical treatment
in addition.
2. Requires high BOD:phosphorus ratio to produce sufficient cell mass.
3. High-rate oxygen transfer device may be required in oxic stage because of
short hydraulic retention time.
4. Limited control flexibility.
5. Responses to hydraulic surge and waste strength, and degree of control and
dependability may not be as good as with other biological processes for
nutrient removal.
6. Limited experience with full-scale plants.
7. Cold-temperature nitrification rate governs maximum operating rate of
process.
Useful References
1. Walsh, T. K., et al. A Review of Biological Phosphorus Removal
Technology, Presented at the Annual Conference of the Water Pollution
Control Federation, October, 1983.
2. Randall, C. (1986). Quarterly Report No. 2, York Rivers STP Nutrient
Removal Project, Chesapeake Bay Initiatives, State Water Control Board of
Virginia.
3. McNamee, Porter and Seeley, Inc. (1986). Retrofitting POTWS For
Phosphorus Removal in the Chesapeake Bay Drainage Area, Report to the
U. S. EPA Chesapeake Bay Office, Annapolis, MD.
4. Tracy, K. (1986). Biological Nutrient Removal. Proceedings, Available
Technology Workshop, C. W. Randall, Ed., Scientific and Technical
Advisory Committee, Chesapeake Bay Project, Chesapeake Research
Consortium.
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106 Point: Wastewater Treatment
SEQUENCING BATCH REACTORS
Description
Sequencing batch reactor (SBR) systems consist of aeration basins that receive
primary effluent, typically on an alternating fill-and-draw basis, with the batches
of wastewater being submitted to a cycle of alternating conditions. These
conditions determine the type of treatment that the wastewater receives. After
the treated effluent is removed and the waste sludge drained off, the treatment
cycle is repeated with a new batch. This type of system is easily adaptable to
small (less than 1 mgd) municipal flows, but can be used for larger flows as
well.
Efficiency
Secondary quality effluent should be possible at loadings comparable to
continuous-flow processes. A laboratory-scale SBR operated for the removal of
nitrogen obtained a 94% reduction in ammonia and oxidized nitrogen.
Phosphorus removals of 93% have been obtained. Full-scale operations at
Culver, IN, yielded 88% removal of phosphorus and 89% removal of nitrogen
simultaneously. Average effluent concentrations for the Culver plant were 0.3-
1.7 mg/1 for NH3 nitrogen, 0.4-1.7 mg/1 for NC>3 nitrogen, and 0.3-1.0 mg/1 for
total phosphorus. Effluent nitrogen levels <2 mg/1 have been achieved there
during both summer and winter. Effluent SS and BODs levels of 10 mg/1 are
easily reached.
Economics
Cost data for SBR systems are limited. However, SBR systems should be
highly economical for many small-scale plants. As higher wastewater volume
increases tank size requirements, SBR's will become increasingly expensive and
impracticable for large flows, and other technologies will prove more cost-
effective for nutrient removal. SBR systems operating for nutrient removal can
also save substantial energy through reduced aeration requirements.
Advantages
1. Effluent meeting secondary treatment standards can be produced by an SBR at
loadings comparable with continuous-flow processes.
2. Can be operated with reduced aeration requirements.
3. Nitrification and denitrification can be achieved simultaneously.
4. The environmental conditions of the mixed liquor are easily controlled.
5. Well suited to automation.
6. Biological phosphorus removal is readily achieved.
7. Highly flexible in operation.
Disadvantages
1. Difficulty of operation increases with higher loadings.
2. If flow quantity exceeds the capacity of the system, it may be necessary to
use continuous flow temporarily.
3. Requires duplicate tanks for alternate treatment.
Useful References
1. Irvine, R., Ketchum, L., Breyfogle, R., and Barth, E. (1983). Municipal
Application of Sequencing Batch Treatment. Journal Water Pollution
Control Federation, 55: 484-488.
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Point: Wastewater Treatment 107
2. Palis, J., and Irvine, R. (1985). Nitrogen Removal in a Low Loaded Single
Tank Sequencing Batch Reactor. Journal Water Pollution Control
Federation, 57: 82-86.
3. Manning, J., and Irvine, R. (1985). The Biological Removal of Phosphorus
in a Sequencing Batch Reactor. Journal Water Pollution Control
Federation, 57: 87-93.
4. Irvine, R., Ketchum, L., Arora, M., and Earth, E. (1985). An Organic
Loading Study of Full-Scale Sequencing Batch Reactors. Journal Water
Pollution Control Federation, 57: 847-853.
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108
Point: Wastewater Treatment
UNIVERSITY OF CAPE TOWN (UCT) NUTRIENT REMOVAL
PROCESS
Description
The UCT process consists of three reactors, anaerobic, anoxic, and aerobic, in
sequence. Its modified form includes a second anoxic reactor between the
anaerobic and aerobic reactors. The process is designed to removed both
phosphorus and nitrogen as wastewater flows through. The UCT process differs
from the three-stage modified Bardenpho process or A2/0 process in that the
settled sludge recycle returns to the anoxic reactor for denitrification, with
biomass being recycled out of the anoxic zone to the anaerobic reactor. This
system reduces or excludes nitrates from the anaerobic reactor to enhance excess
biological phosphorus removal. A concept flow diagram is shown in Figure
PT-9. It was originally conceived as a modification to the Modified Bardenpho
EFFLUENT
[-ANAEROBIC-}—ANOXIC —j- AEROBIC *\ I
PHOSPHORUS RICH
WASTE SLUDGE
INFLUENT
WASTEWATER
CLARIFIER
k ANAEROBIC -f
SLUDGE RETURN
AEROBIC -
EFFLUENT
PHOSPHORUS RICH
WASTE SLUDGE
Figure PT-9.
process and was designed with long hydraulic retention times (10-12 hours) and
operated at high sludge ages (20 days). Research demonstrations, however, have
shown that it can be operated very economically as a high-rate system (sludge
age 5-10 days) with a short hydraulic retention time (6 hours). The high-rate
concept was developed through pilot plant studies for the Virginia Initiative
Plant (VIP) at the Hampton Roads Sanitation District's Lamberts Point Plant in
Norfolk, VA. The process schematic for this plant is given in Figure PT-10.
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Point: Wastewater Treatment
109
MIXED LIQUOR RECYCLE (R)
MIXED LIQUOR-NITRATE RECYCLE (A)
Figure PT-10.
Efficiency
This process is capable of high removals of both phosphorus and nitrogen.
Below are some of the results of the high-rate UCT-type Virginia Initiative Plant
pilot study.
Table PT-12. Average levels (mg/1) of BOD, total phosphorus, and total
nitrogen in influent and effluent of Virginia Initiative Plant, 22 July - 18
August 1985.
BOD
Flow Influent Effluent
Total phosphorus
Influent Effluent
Total nitrogen
Influent Effluent
1.8 gpm 132
4.90 0.66
24.17
7.12
The same study showed similar performance under winter conditions for this
process. Effluent phosphorus levels of <1.0 mg/1 and nitrogen levels of <8
mg/1 were achieved with this process under a variety of operating conditions. It
was also demonstrated that this system was capable of producing waste activated
sludge with an average phosphorus content, on a dry weight basis, in excess of
13% over a period of one month.
Economics
A Canadian study concluded that operating and maintenance costs for phosphorus
removal in the UCT system would be less than costs for a chemical system.
Capital costs were substantially higher, however, resulting in higher overall
annual costs than a conventional system for both retrofit and new systems (but
this study was using the original design concept). Nevertheless, because of the
prohibitive capital, operating, and maintenance costs for nitrogen removal by
methanol addition or other conventional methods, the UCT system is probably
more cost-effective than conventional systems for overall nutrient control.
The high-rate VIP modification was developed to satisfy criteria requiring
significant levels of biological nutrient removal at a cost comparable to that of
secondary treatment. To accomplish this goal, the biological system was sized
to provide the same biological reactor volume as required for a conservatively
sized aerobic activated sludge system, but with anaerobic, anoxic, and aerobic
zones. The pilot plant study was very successful and the information obtained
has been used to design a 50 mgd plant. A cost comparison of the VIP nutrient
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110 Point: Wastewater Treatment
removal system, with and without primary treatment, and both conventional
aerobic and pure oxygen activated sludge systems is given in Table PT-13.
Table - PT-13. Present worth analysis of Lamberts Point upgrade and expansion
alternatives, based on construction of a 2.19 nvVsec (50 mgd) treatment plant.
Alternatives
With primary treatment
Present worth
Capital cost
Annual cost
Replacement cost
Salvage
Total
Conventional
activated sludge
$91,120,000
36,953,000
6,972,000
6,480,000
$128,565,000
Ratio of present worth
to conventional activated
sludge alternative 1 .000
High purity
oxygen
$ 95,126,000
37,373,000
7,279,000
6,765,000
$133,013,000
1.035
Nutrient
removal
$ 94,345,000
36,667,000
7,219,000
6,709,000
$131,522,000
1.023
No primary
treatment
Nutrient
removal
$ 91,609,000
40,835,000
7,009,000
6,514,000
$132,939,000
1.034
Advantages
1. Less excess sludge than with conventional activated sludge or chemical
nutrient control.
2. Substantial energy savings with biological removal of both phosphorus and
nitrogen.
3. Little or no need for expensive chemicals such as methanol and lime.
4. Phosphorus removal is probably more stable and less subject to changing
TKN:COD ratios than with modified Bardenpho.
5. Phosphorus removal capability is superior to both modified Bardenpho and
A/O systems.
6. Not a proprietary technology.
Disadvantages
1. May require chemical addition or some form of additional treatment to meet
effluent nitrogen and phosphorus standards below 5 and 0.8 mg/1,
respectively.
2. No full-scale experience in the U.S.
3. May not achieve as complete a denitrification as modified Bardenpho.
Useful References
1. Water Research Commission (1984). Theory, Design and Operation of
Nutrient Removal Activated Sludge Processes, Water Research
Commission, P.O. Box 824, Pretoria, 001, Republic of South Africa.
2. CH2M Hill, Inc. (1987). Final Report, Virginia Initiative Plant Pilot Plant
Program, Hampton Roads Sanitation District, Virginia Beach, VA.
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Point: Wastewater Treatment
111
MODIFIED BARDENPHO (Phoredox)
Description
The modified Bardenpho process is a multi-staged activated-sludge process,
consisting of an anaerobic zone followed by alternating anoxic and aerobic zones,
having a detention period of 12-21 hours. Its purpose is to reduce the effluent
concentrations of both nitrogen and phosphorus to very low levels. Internal
recycle pumps typically run at about 400% of the raw wastewater flow, returning
nitrates from the first aerobic zone to the first anoxic zone for denitrification.
The sequencing of an anaerobic zone before the anoxic and aerobic zones is a
modification of the original Bardenpho process that enhances excess biological
phosphorus removal. A typical process flow diagram is given in Figure PT-11.
MIXED LIQUOR RECYCLE
EFFLUENT
*•
ANAEROBIC PRIMARY AEROBIC
REACTOR ANOXIC REACTOR
REACTOR
SECONDARY REAEftATION
ANOXIC REACTOR
REACTOR
CLARIFIER
SLUDGE RECYCLE
WASTE
Figure PT-11.
Efficiency
The modified Bardenpho process is capable of producing consistently good
effluent quality. In Kelowna, British Columbia, total phosphorus has been
consistently 0.15-0.6 mg/1, with total nitrogen <4 mg/1. Effluent from a 40
mgd plant in South Africa had average total phosphorus concentrations of 0.66
mg/1, and nitrogen concentrations of 2.78 mg/1. Below are data from a seven-
month period for the modified Bardenpho process in Palmetto, FL.
Table PT-14. Concentrations (mg/1) of phosphorus and nitrogen in influent and
effluent of the Palmetto plant using the modified Bardenpho process.
Phosphorus
Nitrogen
Influent Effluent Removal (%) Influent Effluent Removal (%)
6.6
2.1
68
20.3
1.6
92
The process can function with low- or high-strength wastes and in cold climates
with proper design and operation.
Economics
The Bardenpho process will generally have a greater capital cost than chemical
precipitation in retrofit situations, as will most technologies for enhanced
biological phosphorus removal, but operating and maintenance costs will be
lower. There are energy savings because of reduced aeration, and sludge handling
and chemical costs are lower. The cost of methanol for denitrification is also
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112 Point: Wastewater Treatment
eliminated. According to a Canadian study, however, when total annual costs,
including the financing of the capital costs, are compared, the Bardenpho process
is less cost-effective than chemical removal both in retrofit situations and for
new facilities. This is because of the long hydraulic retention times normally
used for design.The economics can be enhanced by combining the process with
chemical treatment. This process is economically favored by stringent
phosphorus and nitrogen standards and elevated chemical costs.
Advantages
1. Produces less sludge than other biological phosphorus removal systems;
sludge has a high fertilizer value.
2. Can reduce total nitrogen to lower levels than for other biological
phosphorus removal systems and shares the advantage that methanol is not
required.
3. Alkalinity return due to denitrification reduces the need for chemical
adjustment of alkalinity in nitrifying portions of the system.
4. Significant operating experience in South Africa and more than 40 plants
worldwide.
5. Requires fewer clarifiers than a multi-stage system for nitrogen removal.
6. Low-rate design maximizes nitrogen removal.
Disadvantages
1. Increased pumping power and maintenance needs due to large internal
recycles.
2. Very strict nitrogen and phosphorus limitations may necessitate chemical
addition.
3. Requires more reactor volume than the A/O process.
4. Primary settling may reduce ability of Bardenpho to remove nitrogen and
phosphorus, because of decreased BOD.
5. A CODrTKN ratio of roughly 12:1 may be needed to achieve good
denitrification.
6. High BOD:phosphorus ratios may be needed for a high degree of phosphorus
removal.
7. Flexible design important for consistent results.
8. Cold-temperature nitrification rate governs maximum operating rate of
process.
Useful References
1. Walsh, T. K., et al. A Review of Biological Phosphorus Removal
Technology, Presented at the Annual Conference of the Water Pollution
Control Federation, October 1983.
2. Oldham, W. (1984). Full-Scale Optimization of Biological Phosphorus
Removal at Kelowna, Canada. Department of Civil Engineering,
University of British Columbia, Vancouver.
3. Oldham, W. (1985). Three Years of Operating Data With the Kelowna
Bardenpho Plant. Department of Civil Engineering, University of British
Columbia. Vancouver, B. C. Canada.
4. Barnard, J. (1982). Design Consideration Regarding Phosphate Removal in
Activated Sludge Plants. Proceedings, IANPR Post Conference Seminar
on Phosphate Removal in Biological Treatment Processes, Pretoria, South
Africa. Available from Pergamon Press, London, England.
-------
SCIENTIFIC AND TECHNICAL ADVISORY COMMITTEE
CHESAPEAKE BAY PROGRAM
Dr. Maurice Lynch, Director
Chesapeake Research Consortium
STAC Chairman
Dr. Archie McDonnell, Director
Environmental Resources Research Institute
Pennsylvania State University
Dr. Louis Sage, Vice President
Environmental Research
Academy of Natural Sciences of Philadelphia
Dr. Ian Morris, Director
Center for Environmental &
Estuarine Studies
University of Maryland
Alternate: Dr. Wayne Bell
Dr. Lamar Harris, Director
Agricultural Experiment Station
University of Maryland
Alternate: Dr. Alan Taylor
Dr. Gordon Smith, Manager
Environmental Programs
Applied Physics Laboratory
The Johns Hopkins University
Dr. Dennis Powers, Acting Director
Chesapeake Bay Institute
The Johns Hopkins University
Dr. Frank O. Perkins, Dean/Director
Virginia Institute of Marine Science
School of Marine Science
College of William & Mary
Dr. Clifford W. Randall
Department of Environmental Engineering
Virginia Polytechnic Institute and
State University
Dr. William Rickards, Director
Virginia Sea Grant College Program
University of Virginia
Dr. William Dunstan, Chairman
Department of Oceanography
Old Dominion University
Dr. Martha Sager
American University
Mr. James Hannaham, Acting Director
Water Resources Research Center
University of the District of Columbia
Dr. A. Jose Jones, Acting Dean
College of Life Sciences
University of District of Columbia
Dr. Wilbert Wilson, Chair
Environmental Science Department
School of Human Ecology
Howard University
Mr. John Woodson
Dr. Robert Lippson
National Marine Fisheries Service
National Oceanic and Atmospheric
Administration
Dr. Aaron Rosenfield, Director
Oxford Laboratory
Northeast Fisheries Center
National Marine Fisheries Service
National Oceanic and Atmospheric
Administration
Dr. Walmar Klassen, Acting Director
Beltsville Agricultural Research Center
Alternates: Dr. Allan Isense
Dr. Jack R. Plimmer
Dr. Richard Jachowski, Chief
Branch of Migratory Bird Research
Patuxent Wildlife Research Center
US Fish and Wildlife Service
Available Technology Subcommittee
Dr. Clifford W. Randall, Co-Chairman
Dr. Archie McDonnell, Co-Chairman
-------
STAC Executive Secretariat
P.O.Box 1120
Gloucester Point, VA 23062-1120
804-642-7150
------- |