vvEPA
United States
Environmental Protection
Agency
Water Engineering
Research Laborat<
Cincinnati OH 45!:
Technology Transfer
Handbook
. --i Information
Cincinnati OH 452§8
EPA/625/6-87/bf7
Retrofitting
POTWs for Phosphorus
Removal in the
Chesapeake Bay
Drainage Basin
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EPA/625/6-87/017
September 1987
Handbook
Retrofitting POTWs for Phosphorus
Removal in the
Chesapeake Bay Drainage Basin
U.S. Environmental Protection Agency
Office of Research and Development
Water Engineering Research Laboratory
Cincinnati, OH 45268
Center for Environmental Research Information
Cincinnati, OH 45268
-------
Notice
This document has been reviewed in accordance with the U.S. Environmental Protection
Agency's peer and administrative review policies and approved for publication. Mention of trade
names or commercial products does not constitute endorsement or recommendation for use.
This document is not intended to be a guidance or support document for a specific regulatory
program. Guidance documents are available from EPA and must be consulted to address
specific regulatory issues.
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Contents
Chapter
Page
1 INTRODUCTION 1
1.1 Purpose 1
1.2 Handbook Organization 1
2 DESCRIPTION OF RETROFIT PHOSPHORUS REMOVAL TECHNOLOGIES 5
2.1 Introduction 5
2.2 Items Common to Most Retrofitting Situations 5
2.2.1 Insolubilization of Phosphorus Compounds 5
2.2.2 Addition of Metallic Salt 6
2.2.3 Addition of Polymer 6
2.2.4 Mixing Requirements 6
2.2.5 Sequence of Chemical and Physical Reactions 7
2.2.6 Importance of Suspended Solids Control 7
2.2.7 Engineering Guidance Provided on General Schematics 7
2.2.8 Sludge Production at Facilities Retrofitted for Phosphorus Removal 7
2.2.9 Sludge Production Related to Different Effluent TP Requirements. 8
2.3 Process Options for Retrofitting Existing CBDB Facilities
to Achieve Phosphorus Control 9
2.3.1 Retrofitting CBDB Facilities with Chemical Control of Phosphorus 9
2.3.2 Retrofitting CBDB Facilities with Biological Control of Phosphorus 16
2.4 References 21
3 SUMMARY OF EXISTING PHOSPHORUS REMOVAL PERFORMANCE DATA 23
3.1 Introduction 23
3.2 Chemical Phosphorus Removal 23
3.2.1 Effect of Application Point on Chemical Use 23
3.2.2 Effect of Effluent Limit on Chemical Use 31
3.2.3 Effect of Chemical Phosphorus Removal on Sludge Generation 31
3.2.4 Effect of Chemical Phosphorus Removal on pH 36
3.2.5 Cost of Chemicals 36
3.3 Biological Phosphorus Removal 38
3.3.1 PhoStrip Process : 38
3.3.2 A/O Process 39
3.4 References 40
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Contents (continued)
Chapter
Page
4 PROCESS DESIGN SYNOPSES FOR RETROFITTING CHEMICAL
PHOSPHORUS REMOVAL 41
Design Synopsis 1: Plug Flow, Complete Mix, and Step Aeration
Activated Sludge Systems 42
Design Synopsis 2: Contact Stabilization Activated Sludge Systems 45
Design Synopsis 3: Pure Oxygen Activated Sludge Systems 48
Design Synopsis 4: Extended Aeration and Oxidation Ditch
Activated Sludge Systems 51
Design Synopsis 5: Two-Stage Nitrification Activated Sludge Systems . 54
Design Synopsis 6: High-Rate Trickling Filter Systems 57
Design Synopsis 7: Standard-Rate Trickling Filter Systems . 60
Design Synopsis 8: RBC Systems 63
Design Synopsis 9: Lagoon Systems 66
5 HARDWARE DESIGN AND O&M CONSIDERATIONS FOR CHEMICAL PHOSPHORUS
REMOVAL IN SMALL TO MEDIUM PLANTS (<10 MGD) 69
5.1 Introduction 69
5.2 Aluminum Compounds 69
5.2.1 Dry Alum 69
5.2.2 Liquid Alum 71
5.2.3 Dry Sodium Aluminate 73
5.2.4 Liquid Sodium Aluminate 75
5.2.5 Aluminum Chloride 76
5.3 Iron Compounds 77
5.3.1 Liquid Ferric Chloride 77
5.3.2 Ferrous Chloride (Waste Pickle Liquor) 79
5.3.3 Ferric Sulfate 79
5.3.4 Ferrous Sulfate 80
5.4 Polyelectrolytes 80
5.4.1 Dry Polymers 80
5.4.2 Liquid Polymers 81
5.5 Design of Chemical Feed Systems 83
5.5.1 Chemical Feed Systems 83
5.5.2 Chemical Feeders 83
5.5.3 Sizing Chemical Feed System Components 86
5.5.4 Optimum Feed Points and Feed Point Flexibility 87
5.5.5 Room Layouts for Chemical Storage, Preparation, and Pumping 87
5.6 Chemical Equipment Suppliers 88
5.7 Staffing Requirements for Chemical Addition 88
5.8 Sludge Considerations 99
5.9 Laboratory Requirements 100
5.10 Safety and OSHA Requirements for Chemical Addition 100
5.10.1 Ferric Chloride - 100
5.10.2 Polymer 102
5.10.3 OSHA Requirements 103
5.11 References • • • 103
IV
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Contents (continued)
Chapter Page
6 PROCESS AND HARDWARE DESIGN CONSIDERATIONS FOR RETROFITTING
ACTIVATED SLUDGE PLANTS WITH BIOLOGICAL PHOSPHORUS REMOVAL .. 105
6.1 Introduction 105
6.2 PhoStrip Process 105
6.2.1 Conditions Prerequisite to PhoStrip Retrofit 105
6.2.2 Design Considerations x. 105
6.2.3 Attainability of Effluent Limits 107
6.2.4 Lime Handling 107
6.3 A/O Process 107
6.3.1 A/O Operating Conditions 108
6.3.2 Design Considerations 108
6.3.3 Attainability of Effluent Limits 109
7 COMPATIBILITY OF CHEMICAL AND BIOLOGICAL PHOSPHORUS REMOVAL
WITH NITROGEN CONTROL 111
7.1 Introduction 111
7.2 Process Considerations for Complying with Dual Nutrient
Control Requirements 111
7.2.1 Control of Process pH Value 111
7.2.2 Biomass Environmental Management 112
7.2.3 Engineering Aspects 112
7.3 Dual Process Removal and Nitrification Processes 113
7.3.1 Chemical Phosphorus Removal and Nitrification 113
7.3.2 Biological Phosphorus Removal and Nitrification 113
7.3.3 Oxygen Requirements for Nitrification 114
7.4 Dual Phosphorus Removal and Nitrogen Removal Processes 114
7.4.1 Phosphorus and Nitrogen Removal with Multi-Stage Biological
Processes Supplemented with Chemicals 114
7.4.2 Phosphorus and Nitrogen Removal with Managed Biological Systems ... 115
7.5 References 120
8 ESTIMATING COSTS FOR CHEMICAL PHOSPHORUS REMOVAL IN THE CBDB . 123
8.1 Introduction 123
8.2 Illustrative Example 125
8.3 References ; : . . 126
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Contents (continued)
Chapter
9 FACTORS AFFECTING IMPLEMENTATION OF PHOSPHORUS REMOVAL
IN THE CBDB
Page
133
9.1 Introduction 133
9.2 Cost to Implement Phosphorus Removal 133
9.3 Comparison of Chemical and Biological Retrofit Systems 133
9.3.1 Effect of Excessive Infiltration/Inflow on Process Selection 133
9.3.2 Process Reliability 133
9.3.3 Potential Technological Advances 134
9.3.4 Impact of License Fees 134
9.3.5 Degree of Operation and Control Difficulty 134
9.3.6 Additional Staffing Requirements 134
9.3.7 Degree of Maintenance Difficulty 135
9.4 Administrative Issues 135
9.4.1 Planning and Construction Period Schedules 135
9.4.2 Operator Training Seminars 135
9.5 References • 135
VI
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Figures
Number
Page
2-1 Sequence of increased liquid/solids separation and phosphorus removal 8
2-2 Importance of effluent TSS on effluent TP 8
2-3 Retroffiting plug flow, step aeration, complete mix, pure oxygen,
and single-stage nitrification activated sludge systems for
chemical phosphorus removal - 11
2-4 Retrofitting extended aeration and oxidation ditch activated
sludge systems for chemical phosphorus removal . 12
2-5 Retrofitting contact stabilization activated sludge systems for
chemical phosphorus removal 13
2-6 Retrofitting two-stage biological nitrification systems for
chemical phosphorus removal 14
2-7 Retrofitting standard-rate trickling filters for chemical
phosphorus removal 15
2-8 Retrofitting high-rate trickling filters for chemical phosphorus removal 16
2-9 Retrofitting RBCs for chemical phosphorus removal 17
2-10 Retrofitting wastewater lagoons for chemical phosphorus removal 18
2-11 Retrofitting plug flow, step aeration, complete mix, and pure
oxygen activated sludge systems with the Phostrip process for
phosphorus removal 19
2-12 Retrofiting plug flow, step aeration, and pure oxygen activated
sludge systems with the A/O process for biological phosphorus removal 20
2-13 Conceptual sequence of reactions in the A/O process 21
3-1 Alum-to-influent TP ratio vs. effluent TP concentration 32
3-2 Ferric iron-to-influent TP ratio vs. effluent TP concentration 32
3-3 Sludge generation rate vs. effluent TP concentration 36
3-4 Sludge generated vs. metal ion-to-influent TP ratio 37
5-1 Dry feed system alternatives 72
5-2 Viscosity of alum solutions 74
5-3 Liquid chemical feed system alternatives for elevated storage 75
5-4 Liquid chemical feed system alternatives for ground storage 75
5-5 Freezing point curve for commercial ferric chloride solutions 77
5-6 Viscosity vs. composition of ferric chloride solutions at various temperatures ... 78
5-7 Manual dry polymer feed system 82
5-8 Automatic dry polymer feed system 82
5-9 Plunger-type metering pump 84
5-10 Diaphragm-type metering pump 84
5-11 Screw feeder 86
5-12 Beam balance-type gravimetric feeder 87
VII
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Figures (continued)
Number Page
5-13
5-13
5-13
5-13
5-13
5-13
5-13
5-13
5-13
5-13
6-1
6-2
7-1
7-2
7-3
7-4
7-5
8-1
8-2
8-3
8-4
8-5
8-6
8-7
8-8
Typical
Typical
Typical
Typical
Typical
Typical
Typical
Typical
Typical
Typical
chemical
chemical
chemical
chemical
chemical
chemical
chemical
chemical
chemical
chemical
system
system
system
system
system
system
system
system
system
system
layout No. 1
layout No. 2
layout No. 3
layout No. 4
layout No. 5
layout No. 6
layout No. 7
layout No. 8
layout No. 9
layout No. 10
Phostrip process flow diagram
A/O process flow diagrams
Multi-stage biological process supplemented with chemicals for
combined nitrogen and phosphorus removal
Schematic of an activated sludge system retrofitted for the
A2/O process
Schematic of an activated sludge system retrofitted for the
Bardenpho process
Schematic of an activated sludge system retrofitted for the
UCT process
Schematic of activated sludge system retrofitted for the
modified Bardenpho process
Estimated chemical phosphorus removal costs for an influent
TP range of 6 -10 mg/l and an effluent TP limitation of 2 mg/l
Estimated chemical phosphorus removal costs for an influent
TP range of 6 -10 mg/l and an effluent TP limitation of 1 mg/l.
Estimated chemical phosphorus removal costs for an influent
P range of 6 -10 mg/l and an effluent TP limitation of 0.5 mg/l
Estimated chemical phosphorus removal costs for an influent
TP range of 6 -10 mg/l and an effluent TP limitation of 0.2 mg/l
Estimated chemical phosphorus removal costs for an influent
TP range of 3 - 6 mg/l and an effluent TP limitation of 2 mg/l.
Estimated chemical phosphorus removal costs for an influent
TP range of 3 - 6 mg/l and an effluent TP limitation of 1 mg/l
Estimated chemical phosphorus removal costs for an influent
TP range of 3 - 6 mg/l and an effluent TP limitation of 0.5 mg/l
Estimated chemical phosphorus removal costs for an influent
TP range of 3 - 6 mg/l and an effluent TP limitation of 0.2 mg/l.
89
90
91
92
93
94
95
96
97
98
106
109
116
117
119
120
121
124
125
126
127
128
129
130
131
VIII
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Tables
Number
Page
1-1
1-2
2-1
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
3-11
3-12
3-13
3-14
3-15
3-16
3-17
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
CBDB Plant Matrix
Summary of Handbook Contents
2
3
Sludge Production With and Without Chemical Addition 9
Phosphorus Removal Performance and Cost Data for Existing
Plug Flow Activated Sludge Plants
Phosphorus Removal Performance and Cost Data for Existing
Complete Mix Activated Sludge Plants
Phosphorus Removal Performance and Cost Data for Existing
Contact Stabilization Activated Sludge Plants
Phosphorus Removal Performance and Cost Data for Existing
Pure Oxygen Activated Sludge Plants
Phosphorus Removal Performance and Cost Data for Existing
Step Aeration Activated Sludge Plants
Phosphorus Removal Performance and Cost Data for Existing
Extended Aeration Activated Sludge Plants
Phosphorus Removal Performance and Cost Data for Existing
Two-Stage Nitrification Activated Sludge Plants
Phosphorus Removal Performance and Cost Data for Existing
High-Rate Trickling Filter Plants
Phosphorus Removal Performance and Cost Data for Existing
Standard-Rate Trickling Filter Plants
Phosphorus Removal Performance and Cost Data for Existing
RBC Plants
Phosphorus Removal Performance and Cost Data for Existing
Oxidation Ditch Plants
Metal lon-to-lnfluent TP Ratio (Weight Basis) for Various Points
of Application
Summary Information on Selected POTWs in the CBDB
Summary Information on Selected POTWs in Michigan
Average Chemical Cost for Phosphorus Removal
Summary of PhoStrip Plant Operating Conditions for Lansdale
and Little Patuxent
Pontiac A/O Wastewater Treatment Facility Performance Data . . .
Available Grades of Dry Alum
Solubility of Alum at Various Temperatures
Dry Alum Suppliers to the Chesapeake Bay Area
Crystallization Temperatures of Liquid Alum
Liquid Alum Suppliers to the Chesapeake Bay Area
Dry Sodium Aluminate Supplier to the Chesapeake Bay Area . .
Liquid Sodium Aluminate Suppliers to the Chesapeake Bay Area
Aluminum Chloride Supplier to the Chesapeake Bay Area
Liquid Ferric Chloride Suppliers to the Chesapeake Bay Area . .
24
25
26
26
27
27
28
28
29
30
30
31
33
34
37
39
40
69
69
71
73
74
76
76
77
78
IX
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Tables (continued)
Number Pa9e
5-10 Ferrous Chloride Supplier to the Chesapeake Bay Area 80
5-11 Properties of Ferric Sulfate 80
5-12 Ferric Sulfate Suppliers to the Chesapeake Bay Area 81
5-13 Ferrous Sulfate Supplier to the Chesapeake Bay Area 81
5-14 Polymer Suppliers to the Chesapeake Bay Area 81
5-15 Types of Chemical Feeders 88
5-16 Dry Chemical Feeder Suppliers 99
5-17 Chemical Feed Pump Suppliers 100
5-18 Polymer Preparation Systems • 101
5-19 Chemical Storage Tanks 101
5-20 Manpower Required to Operate and Maintain Chemical Feed Systems 102
5-21 Comparison of Filter Yields With and Without Alum Addition 102
5-22 Estimated Sampling and Analytical Needs for Phosphorus Removal
by Chemical Addition 103
9-1 Estimated Capital Costs to Retrofit CBDB Plants for Phosphorus Removal Using
Chemical Addition, Arranged by Influent TP, Effluent TP, and Design Flow .... 134
9-2 Estimated Capital Costs to Retrofit CBDB Plants for Phosphorus
Removal Using Chemical Addition; influent TP Range: 6-10 mg/l 135
9-3 Estimated Capital Costs to Retrofit CBDB Plants for Phosphorus
Removal Using Chemical Addition; Influent TP Range: 3 - 6 mg/l . . 136
9-4 Estimated Annual Chemical Costs for Phosphorus Removal 136
9-5 Comparison of Chemical and Biological Retrofit Systems 137
9-6 Estimated Time Periods for Retrofitting an Existing Plant to
Phosphorus Removal 137
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Acknowledgments
Many individuals contributed to the preparation and review of this handbook. Contract
administration was provided by the Center for Environmental Research Information, Cincinnati,
Ohio.
Major Author:
Shin Joh Rang - McNamee, Porter & Seeley, Ann Arbor, Ml
Contributing Authors:
Victor I. Cooperwasser - McNamee, Porter & Seeley, Ann Arbor, Ml
Lucy B. Pugh - McNamee, Porter & Seeley, Ann Arbor, Ml
Edwin F. Earth - BarthTec, Cincinnati, OH
Reviewers:
Walter G. Gilbert - EPA-OIG, Washington, DC
Wen H. Huang - EPA-OMPC, Washington, DC . •
Richard M. Kashmanian - EPA-OPPE, Washington, DC
Richard C. Brenner - EPA-WERL, Cincinnati, OH
Orville E. Macomber - EPA-CERI, Cincinnati, OH
Joseph J. Macknis - EPA-Chesapeake Bay Program, Annapolis, MD
Peter S. Tinsley - Maryland DHMH, Baltimore, MD
Khandu Patel - Maryland DHMH, Baltimore, MD
James F. Smith - North Carolina DEM, Raleigh, NC
Timothy E. Carpenter - Pennsylvania DER, Harrisburg, PA
Richard I. Sedlak - The Soap and Detergent Assoviation, New York, NY
P. Mac Berthouex - University of Wisconsin, Madison, Wl
Ed D. Smith - USDA-CERL, Champaign, IL
Alan E. Pollock - Virginia WCB, Richmond, VA
Contract Project Officer:
Denis J. Lussier - EPA-CERI, Cincinnati, OH
XI
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Chapter 1
Introduction
1.1 Purpose
The states of Maryland, Pennsylvania, and Virginia
have many wastewater treatment facilities that
discharge into the Chesapeake Bay Drainage Basin
(CBDB). For the protection of the ecology of the
Chesapeake Bay, phosphorus removal has been
implemented at selected treatment facilities and
needs to be instituted at a greater number of sites.
This document assesses the technology, economics,
and efficiency of phosphorus removal processes
available for use in the CBDB to achieve required
levels of protection. Since phosphorus removal
requirements in the CBDB vary a great deal with
geographical location, this assessment includes the
feasibility of achieving effluent total phosphorus (TP)
concentrations of 0.2, 0.5, 1, and 2 mg/l. Also
addressed is the impact that a requirement for either
nitrification or nitrogen removal has on phosphorus
removal processes.
The information base for this document includes data
collected from various municipal wastewater
treatment facilities in the United States, particularly
those located in the CBDB and the Great Lakes
Drainage Basin, as well as from other sources.
This document is a reference manual for government
officials, design engineers and plant operators in the
CBDB to assist them in retrofitting existing treatment
plants to remove phosphorus.
This document covers the following broad areas:
1. Chemical phosphorus removal information is
tailored to reflect those factors specific to the
CBDB, i.e., influent phosphorus, effluent
phosphorus, and plant type.
2. Biological phosphorus removal technologies are a
recent development and may be feasible at this
time for retrofitting certain plants in the CBDB.
Biological phosphorus removal discussions and
data are also tailored to reflect conditions specific
to the CBDB.
3. Several plants in the CBDB may require
concurrent phosphorus and nitrogen removal.
Information is presented to enable engineers to
select appropriate phosphorus removal systems
that will be compatible with current or future
nitrogen removal requirements.
4. Data presented correspond to the sizes of plants
and process types found in the CBDB. Influent TP
concentration ranges of 6 to 10 mg/l and 3 to 6
mg/l and effluent TP limits of 2, 1, 0.5, and 0.2
mg/l are considered.
Based on data provided by Virginia, Maryland, and
Pennsylvania environmental agencies, there are 526
municipal wastewater plants discharging to the CBDB
from these three states (144 in Virginia, 219 in
Maryland, and 163 in Pennsylvania). Ninety-nine of
these plants are removing phosphorus (10 in Virginia,
28 in Maryland, and 61 in Pennsylvania). Seventy-
eight plants are achieving nitrification. In addition, a
number of extended aeration plants are known to
nitrify seasonly. A matrix showing the design
capacities and types of these plants is given in Table
1 -1 .
1.2 Handbook Organization
Table 1-2 presents a brief summary of each of the
nine chapters that compose this document.
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Table 1-1. CBDB Plant Matrix
Design Flow (mgd)1
Plant Type
Activated Sludge - Plug Ftaw
Activated Sludge - Complete Mix
Activated Sludge - Contact
Stabilization
Activated Sludge - Pure Oxygen
Activated Sludge - Step Aeration
Activated Sludge - Extended
Aeration
Trickling Filter - High Rate
Trickling Filter - Standard Rate
Rotating Biological Contactors
Combined Trickling Filter-
Activated Sludge
Others*
Total
Grand Total
State
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
VA
MD
PA
< 0.1
.
_
2(1)
46(0)
-
-
-
-
-
-
-
-
-
12(0)
74(0)
9(1)
-
9(0)
-
3(0)
6(0)
2(0)
1 (0)
3(0)
-
-
-
-
16(0)
-
1(1)
32(0)
138 (0)
14(3)
184 (3)
0.1 -1
,
-
18(4)
13(5)
3(0)
-
8(4)
-
-
-
-
-
-
14(0)
17(2)
46(11)
1 (0)
10(0)
-
6(0)
1 (0)
12(3)
3(0)
7(2)
-
1 (0)
-
2(2)
34(0)
-
-
62(0)
48(9)
86 (24)
196 (33)
1 -5
-
-
21 (10)
5(0)
5(4)
1 (0)
4(2)
-
10(5)
-
-
-
-
-
-
2(0)
5(2)
5(1)
6(0)
6(0)
-
-
-
7(6)
1 (0)
1 (1)
-
1 (1)
-
-
5(1)
-
-
24(4)
17(7)
44 (22)
85 (33)
5- 10
2(0)
-
4(3)
3(0)
2(1)
1(1)
-
-
2(2)
-
1 (0)
1 (0)
-
-
-
1 0)
1(0)
1(1)
2(1)
-
-
-
1 (1)
-
-
-
-
- -
1 (D
-
-
-
6(1)
6(5)
11 (8)
23 (14)
> 10
3(0)
-
3(1)
5(1)
4(4)
-
-
-
2(1)
6(0)
2(2)
2(2)
2(1)
"
-
KD
3(1)
-
-
-
-
1 (0)
1 (0)
1 (1)
-
-
-
-
-
3(1)
-
-
20(5)
10(7)
8(4)
38 (16)
Total by
State1
5(0)
-
48(19)
13(1)
70 (15)
2(1)
7(2)
-
22(12)
5(0)
3(3)
3(2)
2(1)
~
-
29 (1)
100 (6)
61 (13)
8(1)
27(1)
-
9(0)
8(0)
23 (10)
6(1)
11 (3)
-
2(1)
*
3(3)
58(2)
-
1 (1)
144 (10)
219 (28)
163 (61)
526 (99)
Grand
Totali
53 (19)
85 (17)
29 (14)
11 (5)
2(1)
190(20)
35(2)
40 (10)
17(4)
5(4)
59(3)
526 (99)
1 Plants already removing phosphorus are indicated in parentheses.
2 Oxidation ditches, lagoons, activated sludge nitrification, Griffith system, overland flow, primary treatment, combined trickling filter-rotating
biological contactors.
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Table 1-2. Summary of Handbook Contents
Chapter Description
1. Introduction
2. Description of Retrofit
Phosphorus Removal
Technologies
3. Summary of Existing
Phosphorus Removal
Performance Data
4. Process Design
Considerations for
Retrofitting Chemical
Phosphorus Removal
5. Hardware Design and
O&M Considerations for
Chemical Phosphorus
Removal in Small to
Medium Plants [< 0.44
m3/s (10 mgd)]
6. Process and Hardware
Design Considerations
for Retrofitting Activated
Sludge Plants with
Biological Phosphorus
Removal
7. Compatibility of
Chemical and Biological
Phosphorus Removal
with Nitrogen Control
8. Cost Estimates for
Chemical Phosphorus
Removal in the CBDB
9. Potential Effects of
Various Implementation
Factors on Phosphorus
Planning in the CBDB
Introduction and guide for using
handbook.
General engineering considerations
for retrofittting plants to remove
phosphorus by chemical addition or
biological uptake.
Tabulation of performance and
costs data from selected plants in
the United States and Canada
Process design synopsis sheets for
chemical addition retrofit for each
process type, plant size, influent
phosphorus range, and effluent
phosphorus limit.
Information on chemical
characteristics, suppliers, and
costs; chemical storage and
feeding; typical chemical feed
system layouts; safety
considerations; and laboratory and
safety requirements.
Detailed analysis and comparison
of the A/O and Phostrip biological
phosphorus removal processes.
The effects of combined
phosphorus and nitrogen control on
the engineering requirements for
retrofitting plants by chemical
addition or biological uptake.
Estimated capital, annual chemical,
and annual chemical plus amortized
chemical system capital cost
graphs for retrofitting plants to
chemical phosphorus removal in
the CBDB.
Broad factors in implementing
phosphorus removal in the CBDB,
including total area-wide costs for
retrofitting (at different influent
phosphorus levels and different
effluent phosphorus limits), a
comparison of key factors affecting
chemical and biological retrofit
systems, impact of license fees,
difficulty of process operation,
additional staffing required, degree
of maintenance difficulty,
implementation schedules,, and
operator training requirements.
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Chapter 2
Description of Retrofit Phosphorus Removal Technologies
2.1 Introduction
A variety of wastewater treatment processes exist in
the CBDB. These facilities range in design complexity
from lagoon systems to various modifications of the
activated sludge process.
Experience gained at numerous treatment plants in
the Great Lakes Drainage Basin between the late
1960s and early 1980s has shown that some degree
of phosphorus removal can be retrofitted into almost
any existing facility. In a specific retrofit situation, the
degree of compliance with a required effluent TP limit
is related to process configuration, organic and
hydraulic loadings, and operator dedication.
This chapter presents a simplified explanation of
phosphorus removal chemistry and discusses general
engineering considerations for retrofitting existing
plants to control effluent phosphorus using either
chemical addition or biological uptake technology. In
some cases where very stringent effluent TP limits
are imposed, it may be cost-effective to utilize a
combination of biological and chemical phosphorus
removal retrofit alternatives. Later in this chapter, a
series of flow diagrams (Figures 2-3 through 2-10)
is given that represents the complete array of existing
suspended growth and fixed film processes in the
CBDB. These figures are schematics that indicate the
location of retrofitted equipment and chemical dosing
points and provide general engineering guidance
related to chemical dosing and clarification
requirements to meet specific effluent TP limits.
Retrofit requirements for each type of treatment
process installed in the CBDB (refer to Chapter 1 for
list of processes) will be addressed in detail later in
this manual. However, several items are common to
most of the engineering decisions necessary for
retrofitting and are discussed in this chapter. Table
9-5 compares key factors affecting chemical and
biological retrofit systems.
2.2 Items Common to Most Retrofitting
Situations
Successful phosphorus control depends on
insolubilization of phosphorus compounds, either by
chemical or biological reactions. Conditioning of the
insoluble floe formed is necessary to promote good
settling properties, and unit processes should be
provided with adequate capacities to ensure efficient
liquid-solids separation.
2.2.7 Insolubilization of Phosphorus Compounds
Raw municipal wastewater contains a mixture of
phosphorus compounds in the organically-bound,
polyphosphate, and orthophosphate forms. The
orthophosphate form is the species that is most
efficiently insolubilized by the various chemicals used
to precipitate phosphorus.
Organic phosphorus compounds can settle out and
be incorporated in the primary sludge or be
biologically converted to the orthophosphate form if
transferred to the secondary portion of the treatment
process. Polyphosphates are soluble compounds that
pass through primary treatment into the secondary
treatment process where biological enzymatic activity
converts them to the orthophosphate form.
Orthophosphates are soluble, and if not insolubilized
by some mechanism, either deliberate or natural, will
pass completely through primary and secondary
processes and appear in the final effluent.
This chemistry has process implications. Since
polyphosphates are not efficiently insolubilized by
metallic salt cations, dosing of raw wastewater for
removal of phosphorus in primary treatment is less
effective than use of metallic salt cations after the
polyphosphates have been converted to
Orthophosphates. The lowest primary effluent TP
concentration that can be practically achieved by
metallic salt addition to raw wastewater is 1.5 to 2
mg/l. Once all forms of phosphorus have been
converted to orthophosphate, the chemical
insolubilization of phosphorus with a metallic salt
cation (M3 + ), or biological incorporation of
phosphorus into biomass, can be viewed as follows:
M3+ + PO43--» MPO4
(2-1)
Enzymes
Biomass + PO43: -» Biomass bound polyphosphates i
(2-2)
-------
In the case of biological insolubilization, the biomass
converts soluble orthophosphate to intracellular
insoluble polyphosphates, which can be removed in
the waste sludge.
2.2.2 Addition of Metallic Salt
Many of the schematics in this chapter show more
than one site of injection of metallic salt into the
wastewater flow. Experience has shown that with
stringent effluent TP limits such as 0.5 mg/l or less, it
is desirable to have multi-point injection capability.
This arrangement is;~caljed split dosing and results in
a lower overall mole ratio of metallic salt cation to
phosphorus, thereby enhancing insolubilization. For
less stringent effluent limits, such as 1 or 2 mg/l TP,
a single injection site may be adequate. In either
case, however, since the capital cost of an additional
pump and piping is small, multi-injection capability
should be considered in any retrofitting plan.
The general practice in split dosing is to apply the
metal salt dose in a ratio of 2:1, divided between the
first and second injection sites, respectively.
Adjustment of this split may be necessary to suit local
circumstances.
In any retrofit flow scheme with a primary clarifier, it is
worthwhile to consider selection of the primary
influent as the first chemical injection site. The
addition of metal salt and polymer in the influent to
the primary clarifier improves the suspended solids
and organic substances capture capability of this
process unit. This approach maximizes primary
sludge production and, if anaerobic digestion of
sludges is practiced, increases total methane
production. In addition, the increased efficiency of
primary clarification reduces the organic load to the
secondary biological process. This can result in less
secondary sludge production and aeration energy
requirements, as well as assist in achieving
nitrification, if desired.
The actual site for chemical injection into the
secondary portion of a treatment process depends on
local conditions of accessibility, turbulence, and the
existing type of treatment process. Dosing points can
be selected at the influent end of the reactor, at the
exit end of the reactor, at intermediate points within
the reactor, between the reactor and final clarifier, or
using various combinations thereof.
As noted above, dosing into the secondary portion of
a treatment process is more efficient than dosing the
primary portion. Not only is it certain that phosphorus
exists as orthophosphate, but the flow and
concentration peaks can be somewhat dampened by
the volumetric dilution afforded by the secondary
reactor tankage.
2.2.3 Addition of Polymer
Most of the schematics in this chapter show the
addition of polymer in combination with metallic salt
addition. Experience has shown that the efficiency of
liquid-solids separation can be enhanced by polymer
addition. However, the application of polymers in
wastewater treatment is more art than science. While
anionic polymers are usually the* most effective
polyelectrolytes in combination with metallic salts, the
actual type, brand, and concentration must be
determined on site. Suppliers are willing to assist in
conducting laboratory jar tests for selection of the
most suitable product.
Deciding on the need for polymer can be guided by
laboratory jar tests. Since the capital cost for polymer
storage and dosing equipment is minimal, however,
polymer addition should be considered in any
retrofitting plan. Provision for polymer addition is
essential if phosphorus removal in the primary portion
of treatment is to be optimized and in cases where an
effluent of 0.5 mg/l TP or less is required. Polymer
addition may not be necessary in cases where
metallic salt is added to the secondary portion of
treatment and/or the effluent TP requirements are 1
or 2 mg/l.
For the most efficient utilization of polymer, some
finite time period must be provided between
introduction of metallic precipitant and addition of
polymer. The insolubilization reaction between
metallic salt and orthophosphate must be completed
before polymer becomes effective. A time lapse of 1
to 5 minutes has been found to be suitable (1).
2.2.4 Mixing Requirements
Maximization of metallic salt and polymer utilization
requires provision for adequate mixing. At the addition
points, conditions for rapid mixing are essential. This
is necessary for several reasons. Contact between
reacting molecules must be provided, and short-
circuiting must be prevented. Also, the chemical
solutions added have a greater density and viscosity
and may be of a different temperature than the
wastewater.
Rapid mix conditions may exist at points of turbulence
caused by hydraulic jumps, aeration apparatus, or
pump impellers. In some cases, if rapid mix
conditions do not exist, in-line static mixers or
impeller-type mixers may have to be retrofitted at
the points of chemical addition.
After rapid mixing of the chemical additives, a short
period of gentle mixing must be provided to allow
newly formed individual floe particles to agglomerate
into a settleable sludge mass. Suitable conditions can
usually be found in exit piping from reactors, entrance
sections of clarifiers, or center wells of clarifiers, if so
equipped. It is seldom necessary to retrofit for slow
mix conditions; hydraulic motion between unit
processes usually suffices. It is important to realize,
however, that agglomeration must occur for
subsequent efficient liquid/solids separation.
-------
References 1 and 2 are excellent discussions of
chemical addition and mixing, respectively.
2.2.5 Sequence of Chemical and Physical
Reactions
The conceptual sequence of reactions shown in
Figure 2-1 summarizes the control points for
ensuring efficient removal of phosphorus by chemical
addition. The initial short period of rapid mix provides
energy to force molecular contact between metallic
ions and orthophosphate ions to form an insoluble
compound, blending to prevent density currents, and
prevention of major short-circuiting. Polymer is then
introduced and blended by rapid mix to contact the
newly formed precipitate and absorb to the particle
surface, thereby enmeshing several particles into
small individual floes. Slow mixing then provides
opportunity for individual floes to adhere and form
larger agglomerates that will settle by gravitational
force in the quiescent zone. The settled sludge,
containing the insolubilized phosphorus, is withdrawn
to sludge handling operations, and the effluent flows
to the next unit operation or is discharged to the
receiving stream.
2.2.6 Importance of Suspended Solids Control
As the final effluent TP compliance level is reduced
from 2 mg/l to 0.5 mg/l or less, it becomes
increasingly important to control effluent suspended
solids. Once phosphorus removal is instituted by
retrofitting secondary treatment processes with
chemical addition or biological phosphorus uptake
capability, the character of these suspended solids
changes. The major objective of phosphorus control
is insolubilization and transfer of the phosphorus into
the sludge mass. Therefore, the phosphorus content
of the sludge increases.
«
Sludges generated from secondary treatment
processes with either chemical addition or biological
uptake for phosphorus control generally contain about
4.5 percent phosphorus on a dry solids basis. This
value compares with the typical 1.5-percent
phosphorus content (dry solids basis) of biological
sludges produced where phosphorus removal is not
practiced.
Figure 2-2 illustrates the critical need to control
effluent suspended solids as the percent phosphorus
in these solids increases due to phosphorus control
practices. In the case of secondary treatment without
phosphorus removal, with only 1.5 percent
phosphorus in the suspended solids, the phosphorus
content of the effluent would be largely in the form of
soluble phosphorus. The contribution to effluent
phosphorus from paniculate matter in this case would
be minor, provided the effluent total suspended solids
(TSS) concentration did not exceed the Federal
secondary treatment standard of 30 mg/l.
To achieve a 1-mg/l TP effluent limit in phosphorus
removal systems with suspended solids containing
4.5 percent phosphorus, however, the effluent TSS
could npt, exceed 22 mg/l. To achieve a 0.5-mg/l TP
effluent limit, the effluent TSS would have to be
limited to 11 mg/l. Of course, any soluble phosphorus
in the effluent would make these suspended solids
concentrations even more restrictive. An effluent limit
of 2 mg/l TP is not likely to be impacted by effluent
TSS concentrations if the Federal secondary
treatment standard of 30 mg/l is achieved.
2.2.7 Engineering Guidance Provided on General
Schematics
The schematics for each type of treatment process
presented provide guidance on polymer dosage,
metallic ion-to-phosphorus mole ratio, and final
clarifier surface overflow rate (SOR) for four different
TP limits. These are approximations to allow initial
assessment of the feasibility of retrofitting a specific
facility to achieve a stated effluent TP limit.
When considering the retrofit of a treatment plant with
either chemical or biological phosphorus removal, it is
unlikely that a TP concentration of 0.5 mg/l or less
could be achieved if the existing final clarifier SOR
exceeds 20 m3/m2/d (500 gpd/sq ft). At SORs above
this level, the final effluent TSS would almost certainly
be greater than the 8 to 11 mg/l range at which
attainment of a 0.5-mg/l TP concentration is
possible. In these cases, provision for additional final
clarifier capacity and/or granular media filtration of the
secondary effluent should be considered in the retrofit
plan.
2.2.8 Sludge Production at Facilities Retrofitted
for Phosphorus Removal
A survey was conducted on 185 Ontario, Canada
wastewater treatment facilities regarding the impact of
chemical addition for phosphorus removal on sludge
quantity (3). The survey showed that to reach an
effluent TP of 1.0 mg/l, sludge mass increased by an
average of 40 percent at primary treatment plants and
26 percent at activated sludge plants. These data are
summarized in Table 2-1. Information is provided on
sludge mass, percent dry solids, and sludge volume
for conventional primary and activated sludge
processes before and after chemical addition.
In another study (4), it was concluded that the
impacts of all types of phosphorus removal processes
on sludge quantity, quality, stabilization, thickening,
dewatering, incineration, and agricultural utilization are
related to site-specific wastewater characteristics
and process options employed and that
generalizations of these impacts are not possible.
A recent technology evaluation (5) contains data for
four full-scale biological phosphorus removal retrofit
projects. Two were PhoStrip processes, and two were
activated sludge processes modified to include an
-------
Figure 2-1. Sequence of increased liquid/solids separation and phosphorus removal.
Insolubilization
Flocculation
Sedimentation
Precipitant, M3 +
Wastewater, PO43-
rr
O
ix
Poll
i
m
«ner
r
O
X
O
J
m
O
X
0
Effluent
h<
Sludge, MPO4
Rapid Mix
dispersion and
reaction
Rapid Mix
dispersion and
reaction
Slow Mix
floe growth
Quiescence
floe settling
1-5 1-5 15-30
Time for each reaction, minutes
60 - 180
4.5% TP in TSS /'
s
f
Rgurs 2-2. Importance of effluent TSS on effluent TP.
TP in Final Effluent
Contributed by TSS, mg/l
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
I I I I I I
05 10 15 20 25 30
Final Effluent TSS, mg/l
anaerobic stage at the head end of the aeration
system. Waste activated sludge production for all four
facilities ranged from 0.7 to 1.0 kg volatile suspended
solids (VSS)/kg total BODs (TBOD) removed. The
high value of 1.0 kg VSS/kg TBOD was noted at a
facility that did not practice primary settling, and this
higher value was attributed to nondegradable volatile
solids. When the PhoStrip process is employed for
biological phosphorus removal, additional solids are
contributed by the lime added to insolubilize
phosphorus released by the biomass in the anaerobic
stripper. This generally equates to about 20 mg/l of
lime, based on influent flow.
2.2.9 S/uc/ge Production Related to Different
Effluent TP Requirements. *
The discussion in the preceding paragraphs concerns
sludge production for facilities achieving compliance
with a 1-mg/l TP requirement. If the requirement
were 2 mg/l TP instead of 1 mg/l, no material
difference in sludge production would be noted in
either the chemical or biological systems. Regardless
of the effluent TP requirement, a certain amount of
chemical precipitant must be added to satisfy the
initial chemical demand of the wastewater. This
demand must be met before efficient insolubilization
of phosphorus occurs. Once the demand is met,
there is not much difference between the amount of
precipitant required to achieve 1 mg/l vs. 2 mg/l TP,
since the ratio of metal ion close to phosphorus
insolubilized is linear in this effluent concentration
range. Effluent concentrations of 1 to 2 mg/l TP are
about the practical limit for biological phosphorus
removal processes.
A requirement for compliance with a 0.5-mg/l or less
TP effluent limit would increase sludge production in
-------
Table 2-1. Sludge Production With and Without Chemical Addition (3)
• Type of Treatment
Dry Solids Produced, kg/1,000 m3
Dry Solids Produced, Ib/Mgal
Dry Solids Content, percent
Sludge Volume, percent of influent flow
Conventional
120
1,000
6.0
0.20
Primary
" Metal Salt Addition2
169
1,410
5.3
0.32
Activated
Conventional
173
1,443
4.5
0.38
Sludge1
Metal Salt Addition2-3
217
1,810
4.2
0.51
1 Primary plus waste activated sludges.
2 Plant influent TP = 7 mg/l; final effluent TP = 1 mg/l.
3 Metal salt added to aerator.
both chemical and biological phosphorus removal
processes compared with a 1- or 2-mg/l effluent
TP requirement. As noted previously, effluent
suspended solids would have to be controlled to near
10 mg/l to reduce effluent TP to this level. The
additional suspended solids captured would result in
increased sludge production and sludge handling
requirements.
Chemical phosphorus removal processes would
require an increase of about 20 percent in metal ion
dose to achieve a 0.5-mg/l or less TP effluent. This
increase would be necessary to ensure efficient
phosphorus insolubilization and to control the
solubility product of the metal phosphate precipitate.
Biological phosphorus removal processes would in all
likelihood require a chemical supplement to achieve a
0.5-mg/l or less TP concentration. Sufficient metal
ion would have to be added to insolubilize 0.5 to 1.5
mg/l TP after the initial chemical demand was met.
This would result in chemical sludge production and
increased total sludge production compared with
achieving a 1- or 2-mg/l TP concentration.
2.3 Process Options for Retrofitting
Existing CBDB Facilities to Achieve
Phosphorus Control
The schematics illustrated in Figures 2-3 through
2-10 indicate that all of the various treatment
processes existing in the CBDB could be retrofitted
for chemical phosphorus control. Only the activated
sludge processes, however, are considered for
retrofitting to biological phosphorus control. Options
for retrofitting to biological phosphorus control are
limited in this document to the PhoStrip and
Anaerobic/Oxic (A/O) processes, as depicted
schematically in Figures 2-11 and 2-12,
respectively.
2.3.1 Retrofitting CBDB Facilities with Chemical
Control of Phosphorus
The following paragraphs and Figures 2-3 through
2-10 provide general guidance for adding chemical
phosphorus control to existing CBDB facilities. In the
following chemical control examples, some form of
iron or aluminum salt is assumed as the source of
metal ion to insolubilize phosphorus. Lime addition to
the full wastewater flow is not recommended to obtain
the TP concentrations needed for compliance in the
CBDB because of the many O&M problems
associated with its handling.
The M3+/lnf. TP mole ratios shown in Figures 2-3
through 2-10 are initial chemical dose guidelines. It
is well recognized that only soluble phosphorus is
actually precipitated by metal salts. Paniculate and
soluble phosphorus taken up biologically do not
consume chemical.
Based on recent and ongoing research (6,7) claims
have been made that the remaining soluble
phosphorus (SP) not taken up biologically reacts with
metal ion at stoichiometric mole ratios of about 1.4 to
1.5 down to residual SP concentrations of 1 to 2 mg/l.
As shown in Figures 2-3 through 2-10, much
higher chemical doses are needed to achieve effluent
TP concentrations of 0.2 or 0.5 mg/l. The
investigators carrying out the above research (6,7)
have developed a model that predicts that chemical
dose is independent of influent phosphorus
concentration in meeting low (<1 mg/l) effluent TP
concentrations. Rather, their theory suggests that any
variability in the ratio between M3+ dose and influent
SP or influent TP required to reach low (< 1 mg/l)
effluent TP concentrations is a function of the initial
pH and alkalinity of the wastewater, microbial activity,
and mode of aeration and not the influent phosphorus
concentration itself.
While the above research studies (6,7) are being
completed and field tests conducted for verification, a
conventional chemical dosing strategy based on
influent TP is used in this document for all four
effluent TP limits considered. In addition to its impact
on the dosing guidance provided in Figures 2-3
through 2-10, this conventional sjtrategy was utilized
in: 1) displaying the chemical phosphorus removal
effluent quality data in Figures 3-1 and 3-2 and the
-------
chemical phosphorus removal sludge production data
in Rgure 3-4; 2) developing the chemical dose
requirements of the design synopses in Chapter 4; 3)
preparing the chemical storage and supply system
layouts in Rgures 5-13 through 5-22; 4) developing
the estimated chemical phosphorus removal cost
curves in Figures 8-1 through 8-8; 5) estimating
chemical phosphorus removal capital costs for
different plant sizes and effluent TP limits in Tables
9-1 through 9-3; and 6) summarizing annual
chemical costs for different effluent TP limits in Table
9-4.
If the above theory (6,7) is confirmed, those portions
of the above figures and tables involving the 0.5-
and 0.2-mg/l effluent TP limits would require
modification.
2.3.1.1 Retrofitting Plug Flow, Step Aeration,
Complete Mix, Pure Oxygen, and Single-Stage
Nitrification Activated Sludge Systems for
Chemical Phosphorus Removal
Rgure 2-3 indicates that all the above activated
sludge process alternatives have basically the same
general flow scheme. Provided that the chemical
dose and effluent clarification guidelines discussed
previously are complied with, each process alternative
has the capability to achieve an effluent TP
concentration of 2, 1, 0.5, or 0.2 mg/l. Considerations
specific to each option are discussed below.
When compliance with an effluent limitation of 0.5
mg/l TP or less is required, a split dose of metal salt
is recommended. Tertiary filtration may also be
necessary. Tertiary filtration is essential, however, to
achieve 0.2 m/L TP. A separate rapid mix and
flocculation basin may be installed between the
secondary reactor and final clarifier to promote more
efficient use of chemicals and to minimize generation
of chemical sludge.
Well-operating plug flow and complete mix systems
should offer no problems for retrofitting other than
finding the optimum dosing points for metal salt and
polymer, if required. Step aeration systems may need
adjustment in the location of primary effluent feed
points into the aeration basin. It may be necessary to
increase wastewater aeration time to ensure the
enzymatic conversion of polyphosphates to
orthophosphates. This would be particularly important
if a 0.5-mg/l TP or less effluent limit had to be
achieved.
Retrofitting single-stage nitrification systems for
chemical phosphorus removal requires evaluation of
two process operating considerations. First, the
chemicals commonly used for phosphorus removal
are acidic. Furthermore, biological nitrification
reactions also produce hydrogen ions. If the
wastewater does not contain enough alkalinity to
neutralize the acidity generated by these two sources,
some provision for pH control will be necessary.
Second, the metal ion side-products and metal
phosphate precipitates formed and occluded into the
activated sludge mass contribute an inert fraction to
the biomass that lowers the volatile content of the
mixed liquor suspended solids (MLSS) below that
normally encountered where mineral addition is not
practiced. Historical wasting schedules for control of
the sludge retention time (SRT) may have to be
altered from usual operational experience at a given
facility to sustain efficient single-stage nitrification.
This usually involves operating at a higher MLSS
concentration so that the overall quantity of volatile
solids under aeration remains equal to or greater than
the prechemical addition level. These two process
considerations will be discussed in more detail in
Chapter 7.
The pH value of the bioreactor mixed liquor is also of
concern in retrofitting pure oxygen activated sludge
systems with chemical phosphorus control. This type
of reactor is typically covered to provide a gas-tight
environment for efficient utilization of oxygen. Since
only the last aeration compartment is normally vented
to the atmosphere, carbon dioxide resulting from
biological oxidation of wastewater constituents is
trapped in solution rather than being continually air
stripped from the reactor. Carbon dioxide in solution
acts as a weak acid and, coupled with the acidic
nature of most chemicals used for phosphorus
control, can result in pH values low enough to inhibit
normal microbiological metabolic reactions.
This coupled pH effect could occur regardless of
where the acidic metal salt was dosed into the
system. If supplemental alkalinity is required, soluble
alkalis such as sodium hydroxide, bicarbonate, or
carbonate should be selected. Lime would not be
recommended due to the possibility of calcium
carbonate scale formation from the reaction of
calcium ions with dissolved carbon dioxide.
2.3.1.2 Retrofitting Extended Aeration and
Oxidation Ditch Activated Sludge Systems for
Chemical Phosphorus Removal
Figure 2-4 illustrates that these two processes have
similar secondary treatment flow schemes and
typically are constructed without primary clarification.
Degritted wastewater flows directly to the activated
sludge bioreactor. Both processes usually are
designed for nominal aeration tank detention times of
20-24 hours. Extended aeration systems are of
conventional aeration tankage design, while oxidation
ditches are constructed in an oval, race-track tank
configuration. The process considerations for
retrofitting chemical phosphorus removal in these
systems are similar to those discussed for single-
stage nitrification. Due to their long aeration times and
high SRTs, these processes usually nitrify under
10
-------
Figure 2-3. Retrofitting plug flow, step aeration, complete mix, pure oxygen, and single-stage nitrification activated sludge
systems for chemical phosphorus removal.
Polymer 'Metering , , •'••••'*•> "*'"••-
Storage Pump ,
1 L
Oegritted
Wastewater
Prjmary
Clarifier
Activated Sludge
Aeration Tank
Return Sludge
Primary Sludge
I --- 1 i --- 1
Metal Salt Metering
Storage Pump
Effluent
Waste Activated
Sludge
Existing
Retrofit
Final
Effluent
TP
mg/l
2
1
0.5
0.2
* at peak sustained
Polymer
Dose
mg/l
0.1 - 0.2
0.1 - 0.2
0.1 - 0.2
0.5 - 1.0
flow
M3+/lnf.TP
Ratio
mole
1.0-1.2
1.2-1.5
1.5-2.0
3.5 - 6.0
Final
Clarifier
SOR"
gpd/sqft
800
600
500
500
Final Effluent
Filtration
Required
No
No
Maybe
Yes
summer conditions. Therefore, pH control can be a
seasonal process problem when acidic metal salts are
added. Supplemental alkalinity may be required during
the summer months.
The usual design and operational parameters for both
processes are low food-to-microorganism (F/M)
loadings, long SRTs, long aeration detention times,
and low biological sludge yields per mass of BOD
removed. These interrelated factors produce a MLSS
that typically has a high inert fraction. Additional inert
material contributed by metal ion addition can result in
MLSS with an even lower volatile fraction. Volatile
fractions below 50 percent can lead to unstable
operation. Sludge wasting schedules may have to be
adjusted to prevent loss of active biomass.
Another operational adjustment that can be
considered for an extended aeration system is
isolation of a portion of the aeration tankage to reduce
aeration detention time. This should result in an
increase in biological sludge yield and help control the
inert-to-volatile ratio of the MLSS. This operational
adjustment may not be possible with an oxidation
ditch system, however, because of the oval
configuration of the aeration tank.
With both processes, the above points become more
critical if a 0.5-mg/l TP or less effluent limit is
required. This criticality arises from the extra metal
ion required and the lack of a primary clarifier to
remove inert solids. If an engineering evaluation
indicates that the buildup of inert material could
become extensive, tertiary media filtration with a
polish dose of metal ion prior to the filter might be
considered to ease the inerts problem. Solids in the
filter backwash should be transferred directly to
sludge processing units and not returned to the
secondary system. A jar test should be conducted to
determine the necessary dosage of chemicals. If the
required dosage is excessive, a separate-stage
tertiary chemical reactor-clarifier is recommended to
achieve an effluent TP concentration of 0.5 mg/l or
less. A pH adjustment system should also be
considered.
11
-------
Figure 2-4. Retrofitting extended aeration and oxidation ditch activated sludge systems for chemical phosphorus removal.
Metal Salt Metering
Storage Pump
i
L_J £?A
Degritted
Wastewater
"T
_4_
Activated Sludge
Aeration Tank
Return Sludge
i—\ i—i
Metering Polymer
Pump Storage
Effluent
Waste Activated
Sludge
Existing
Retrofit
final
Effluent
TP
mgn
2
1
0.5
0.2
* at peak sustained
Polymer
Dose
mg/l
0.1 - 0.2
0.1 - 0.2
0.1 - 0.2
0.5 - 1.0
flow
M3+/mf.TP
Ratio
mole
1.0- 1.2
1.2- 1.5
1.5-2.0
3.5 - 6.0
Final
Clarifier
SOR"
gpd/sqft
800
600
500
500
Final Effluent
Filtration
Required
No
No
Maybe
Yes
2.3.1.3 Retrofitting Contact Stabilization Activated
Sludge Systems for Chemical Phosphorus
Removal
The configuration of the contact stabilization activated
sludge process is shown in Figure 2-5. The major
process consideration for retrofitting contact
stabilization facilities is similar to that for step
aeration. The contact tank usually has a hydraulic
detention time (HOT) of only 30 to 60 minutes for the
main stream primary effluent flow. This may not be
enough HOT to provide for enzymatic conversion of
polyphosphates to orthophosphates. The short
contact time could also restrict the biological
conversion of organic phosphorus compounds to the
orthophosphate form. These items become more
important if the effluent TP compliance level is 0.5
mg/l or less. Laboratory testing could quantify the
aeration HOT necessary for these conversions to
ensure efficient insolubilization of phosphorus. Once
phosphorus has been insolubilized by metal salt
addition and occluded into the mixed liquor biomass,
no resolubilization occurs in the reaeration tank. If
additional aeration HOT is required, the split of
tankage volume between the contact tank and the
sludge reaeration or stabilization tank could be
modified if the plant layout permits.
2.3.1.4 Retrofitting Two-Stage Biological
Nitrification Systems for Chemical Phosphorus
Removal
The schematic provided in Figure 2-6 indicates that
two-stage nitrification facilities offer great flexibility
for metal salt dosing because of the multiple unit
processes employed. Many variations of both
suspended growth and attached growth processes in
different combinations have been utilized for two-
stage nitrification.
To achieve a 1- or 2-mg/l TP effluent
concentration, it may only be necessary to dose one
unit process with metal salt. The primary clarifier or
first-stage carbonaceous reactor would normally be
selected. If the required effluent concentration was
0.5 mg/I TP or less, a polish dose could be provided
at the second-stage nitrification reactor.
The cautions noted previously relative to the
combined effect of metal salt addition and nitrification
12
-------
Figure 2-5. Retrofitting contact stabilization activated sludge systems for chemical phosphorus removal.
Polymer Metering
Storage Pump
Metal Salt Metering
Storage Pump
Existing
Retrofit
Final
Effluent
TP
mg/l
2
1
0.5
0.2
" at peak
Polymer
Dose
mg/l
0.1 - 0.2
0.1 - 0.2
0.1 - 0.2
0.5- 1.0
sustained flow
M3+/inf. TP
Ratio
mole
1.0 - 1.2
1.2 - 1.5
1.5-2.0
3.5 - 6.0
Final
Clarifier
SOR*
gpd/sq ft
800
600
500
500
Final Effluent
Filtration
Required
No
No
Maybe
Yes
on lowering pH should be considered. Second-stage
processes also have very low net cell synthesis.
Therefore, the discussion on retrofitting extended
aeration systems is relevant to the second-stage
nitrification reactor. This implies that only a polish
dose of metal salt be added to second-stage
reactors to avoid a large buildup of inerts in the
MLSS.
2.3.1.5 Retrofitting Standard-Rate Trickling
Filters for Chemical Phosphorus Removal
Standard-rate trickling filters (Figure 2-7) can
achieve the effluent phosphorus concentrations
required in the CBDB. Both rock and plastic media
trickling filters have been retrofitted for phosphorus
removal.
Since flow through a trickling filter is typically more
laminar than turbulent, metal salt is not normally
dosed directly to the filter media. Therefore, it may be
necessary to provide a rapid mix chamber prior to the
secondary clarifier when the metal salt is added after
the filter.
Polymer addition capability is considered necessary
for any trickling filter facility retrofitted for chemical
phosphorus control. If metal salt is dosed to the
primary clarifier, polymer is needed to ensure that a
large amount of inorganic solids does not carry over
to the trickling filter and produce a biofilm with a high
inert solids fraction. Standard-rate filter biomass is
similar to the biomass of an extended aeration
process; i.e., it has a low net cell synthesis and a
long SRT.
If chemical addition to the secondary clarifier is
planned, a critical review should be made of existing
secondary clarifier performance to determine if the
SOR and depth are adequate to handle the increased
solids loading. This is particularly important with older
trickling filter installations that often were equipped
with shallow secondary clarifiers with relatively high
SORs: When existing clarifiers are found inadequate,
consideration should be given to adding new clarifiers
as required.
Typically, trickling filters produce effluents that
contain both sloughed and colloidal solids, and
polymer addition to the secondary clarifier would be
necessary to meet a 0.5-mg/l TP or less effluent
limit.
13
-------
Figure 2-6. Retrofitting two-stage biological nitrification systems for chemical phosphorus removal.
Polymer Metering
Storage Pump
Motal Salt Metering
Storage Pump
Existing
Retrofit
Fina)
Effluent
TP
mg/l
2
1
0.5
0.2
Polymer
Dose
mg/l
0.1 - 0.2
0.1 - 0.2
0.1 - 0.2
0.5 - 1.0
M3+/lnf. TP
Ratio
mole
1.0- 1.2
1.2-1.5
1.5-2.0
3.5 - 6.0
Final
Clarifier
SOR"
gpd/sqft
800
600
500
500
Final Effluent
Filtration
Required
No
No
Maybe
Yes
* at peak sustained flow
2.3.1.6 Retrofitting High-Rate Trickling Filters for
Chemical Phosphorus Removal
The high-rate trickling filter process (Figure 2-8)
represents the most difficult process in the CBDB to
retrofit for chemical phosphorus control. The typical
designs for these systems favor high SORs for both
primary and secondary clarifiers. Additionally, the
trickling filter unit process is designed with a high
hydraulic application rate that leads to a short contact
time of wastewater with the biofilm and incomplete
bio-oxidation of organics. Final effluent from this
process typically is turbid and contains dispersed
suspended solids and undegraded organics.
Conversion of organically-bound phosphorus and
polyphosphates to orthophosphates is limited by the
short contact time. High-rate trickling filter systems
have marginal capability to produce a final effluent of
30 mg/l TBOD and TSS.
Ail of these process characteristics are contrary to
achievement of efficient phosphorus removal. Major
emphasis for retrofitting a high-rate trickling filter has
to be placed on provision of efficient rapid mix and
flocculation capabilities to enhance solids capture. In
all likelihood, stringent effluent phosphorus limits
would also be accompanied by more stringent effluent
BOD requirements, so the retrofit design would also
need to address enhanced organic removal. Polymer
addition capability would also be essential in any
chemical phosphorus removal retrofit of a high-rate
trickling filter system.
To meet a 2-mg/l TP effluent limit, metal salt and
polymer addition to the primary clarifier would be the
preferred choice. This dosing arrangement would
reduce the organic load on the high-rate filter and
provide some improvement in BOD removal.
Attainment of a 1-mg/l TP effluent limit with a high-
rate filter system is questionable due to the limited
solids capture of clarifiers and the presence of
phosphorus forms that are not efficiently insolubilized
by metal ions. A 1-mg/l concentration might be
achieved by adding a second dose of metal salt and
polymer after the high-rate filter, thus improving both
phosphorus and BOD removals above the levels
obtainable with primary clarifier metal salt addition
alone.
14
-------
Figure 2-7. Retrofitting standard-rate trickling filters for chemical phosphorus removal.
Polymer Metering
Storage Pump
Metal Salt Metering
Storage Pump
Existing
Retrofit
Final
Effluent Polymer
TP Dose
mg/l tng/1
2 0.1 - 0.2
1 0.1 - 0.2
0.5 0.1 - 0.2
0.2 0.5-1.0
M3+/inf. TP ,
Ratio
mole
1.0 - 1.2
1.2- 1.5
1.5-2.0
3.5 - 6.0
Final
Clarifier
SOR*
gpd/sq ft
800
600
500
500
Final Effluent
Filtration
Required
No
No
Maybe
Yes
" at peak sustained flow
A 0.5- or 0.2-mg/l TP effluent limit would probably
require construction of a second-stage bioreactor
and clarifier, or expansion of the existing high-rate
trickling filter system to reduce hydraulic and organic
loadings to standard-rate trickling filter loadings.
A phased approach to the attainment of a 0.5- or
0.2-mg/l TP effluent limit with the existing system
could be instituted. After the retrofit for dosing the
primary clarifier was in place to achieve a 2-mg/l TP
effluent concentration, laboratory and pilot testing
could be conducted to provide guidance on the need
for new construction to further reduce phosphorus
levels in the effluent.
2.3.1.7 Retrofitting Rotating Biological Contactors
for Chemical Phosphorus Removal
Retrofitting a rotating biological contactor (RBC)
system for chemical phosphorus removal is shown
schematically in Figure 2-9. A split dose
arrangement is recommended for attainment of a
0.5- or 0.2-mg/l TP effluent limit. Provided that the
chemical dosage and clarification guidelines
discussed previously are adhered to, no major
problems with implementing chemical phosphorus
control should be encountered.
An RBC system is similar to a standard-rate trickling
filter system, and considerations discussed in that
section of this chapter apply to RBC retrofits. Since
the RBC is an attached growth process and shear
forces act on the biofilm during the liquid immersion
portion of the rotational cycle, the effluent can contain
both sloughed and colloidal suspended solids.
Polymer addition to the final clarifier is recommended
to meet a 0.5- or 0.2-mg/l TP effluent limit.
2.3.1.8 Retrofitting Wastewater Lagoons for
Chemical Phosphorus Removal
Figure 2-10 depicts a multi-cell lagoon, with
aeration provided in the first cell, retrofitted for
chemical phosphorus control. Information on
phosphorus removal technology for lagoon systems is
scarce, due in part to the fact that most of these
systems have flows less than 0.04 m3/s (1 mgd) and
many systems of this size are exempt from nutrient
control requirements.
Guidance is not offered in Figure 2-10 for attaining a
0.5-mg/l TP or less effluent limit with a retrofitted
lagoon system. Mixing patterns, stratification, short-
circuiting, algal growth, pH fluctuations, large
15
-------
Rgure 2-8. Retrofitting high-rate trickling fitters for chemical phosphorus removal.
Polymer Metering
Storage Pump
Effluent
Metal Salt Metering
Storage Pump
Existing
Retrofit
Final
Eflluont Polymer
TP Dose
mg/i mg/1
2 0.1 - 0.2
1 0.1 - 0.2
0.5- 0.1 - 0.2
0.2~ 0.5-1.0
M3+/lnf. TP
Ratio
mole
1.0- 1.2
1.2 - 1.5
1.5-2.0
3.5 - 6.0
Final
Clarifier
SOR*
gpd/sqft
800
600
500
500
Final Effluent
Filtration
Required
No
No
Maybe
Yes
• at peak sustained flow
~ major expansion may be necessary
t may be necessary for 0.5 and 0.2 mg/L effluent TP
surface-to-volume ratios, and long hydraulic
retention times (HRTs) combine to indicate that a
simple retrofit could not reliably achieve this
concentration. To meet this limit would probably
require construction of a separate tertiary chemical
treatment system (consisting of a flocculation tank
and a Clarifier) followed by filtration. The same
considerations are also the reason Figure 2-10
shows slightly higher metal salt dosages to achieve a
2- or 1-mg/l TP effluent concentration than
recommended for the other secondary treatment
processes discussed previously.
Because of the large liquid volume of cells in a
lagoon system, mixing of metal salt with wastewater
can be a major process problem. If aeration devices
are present, the turbulence produced during aeration
could be utilized. If a quiescent cell is selected for
chemical dosing, a mixing device must be installed to
ensure adequate mixing of chemical additives and cell
contents.
Polymer addition is not shown in Figure 2-10
because not enough experience has been reported
for a general recommendation to be made. Reference
8 contains several citations on lagoon systems dosed
with metal salt to achieve a 1-mg/l TP effluent
concentration.
2.3.2 Retrofitting CBDB Facilities with Biological
Control of Phosphorus
The following sections and Figures 2-11 and 2-12
provide general guidance for retrofitting selected
suspended growth activated sludge process
configurations at existing facilities in the CBDB with
biological phosphorus control. Two proprietary
processes are considered, the PhoStrip process and
the Anaerobic/Oxic (A/0) process. The PhoStrip
process utilizes a sidestrearn unit operation to
chemically insolubilize phosphorus that has been
stripped or leached from phosphorus-rich biomass.
The A/O process operates as a main stream
biological phosphorus removal process.
These biological phosphorus removal processes are
implemented by maintaining a cyclic exposure of
aeration tank biomass to anaerobic and aerobic
16
-------
Figure 2-9. Retrofitting RBCs for chemical phosphorus removal.
Polymer Metering
Storage Pump
Metal Salt Metering
Storage Pump
Existing
Retrofit
Final
Effluent
TP
mg/l
2
1
0.5
0.2
* at peak sustained
Polymer
Dose
mg/l
0.1 - 0.2
0.1 - 0.2
0.1-0.2
0.5- 1.0
flow
M3+/lnf. TP
Ratio
mole
1.0 - 1.2
1.2- 1.5
1.5-2.0
3.5 - 6.0
Final
Clarifier
SOR*
gpd/sqft
800
600
500
500
Final Effluent
Filtration
Required
No
No
Maybe
Yes
conditions. A period of acclimation is necessary to
allow time for natural selection of microorganisms that
can survive under these conditions. This period can
vary from 2 to 4 weeks for establishment of a
steady-state population.
During the anaerobic cycle, these microorganisms
release intercellular-stored phosphorus to the bulk
liquid while simultaneously sorbing organics. Upon
entering the subsequent aerobic cycle, the same
microorganisms will degrade the sorbed organics and
remove the liberated phosphorus from the bulk liquid
by incorporating it into intercellular granules.
Reference 9 is an excellent discussion of biological
phosphorus removal processes from an engineering
viewpoint. Reference 10 discusses the relationship of
wastewater composition to the feasibility of utilizing a
biological process for phosphorus removal at a
specific site.
2.3.2.1 Retrofitting Activated Sludge Systems for
Biological Phosphorus Removal Using the
PhoStrip Process
Figure 2-11 represents an activated sludge system
that has been retrofitted to include the PhoStrip
process. A portion of the return sludge stream is
subjected to anaerobic conditions in a reactor called
an "anaerobic stripper." The portion of return sludge
sent to the stripper can vary from 15 to 30 percent of
total plant flow. The purpose of the stripper tank is to
provide conditions conducive to release of
intercellular phosphorus from the microorganisms in
the return sludge (phosphorus stripping). Some
modifications of the PhoStrip process employ an
elutriation stream with the stripper operation; this is
not shown in Figure 2-11. The elutriation stream
may be stripper tank recycle, primary effluent,
secondary effluent, lime precipitation tank overflow, or
digester supernatant return. The choice and
magnitude of the elutriation stream is a site-specific
selection based on operational and wastewater
composition criteria. The purpose is to increase the
efficiency of phosphorus stripping (5).
The SRT of the return sludge solids in the stripper
tank can vary from 5 to 20 hours, and the HOT can
vary from 1 to 10 hours. The return sludge solids in
the underflow from the stripper tank, which have now
been partly stripped of intercellular phosphorus, are
returned to the aerobic aeration tank to biologically
17
-------
Figure 2-10. Retrofitting wastewater lagoons for chemical phosphorus removal.
Degritted
Wastowater
i r-ft-
I 1 £._Ji
Metal Salt Metering
Storage Pump
mix (Provide
mixing
chamber)
CelM
Cell 2
Floating
Aerator
Existing
Retrofit
Final
Effluent
TP
mg/1
2
1
M3+/Inf.TP
Ratio
mole
1.2 - 1.5
1.5 - 2.0
insolubilize phosphorus from the main stream flow
and then be recycled back to the anaerobic stripper.
Overflow from the stripper is treated with lime in a
precipitation tank to chemically insolubilize the
stripped phosphorus. Lime dosages of 100 to 150
mg/1 are typically used to increase the pH to 9.0 to
9.5. This equates to about 20 to 25 mg/1 of lime
based on plant influent flow. Some facilities route the
precipitation tank contents directly to the primary
clarifier as shown in Figure 2-11. Once insolubilized
by lime, the phosphorus does not resolubilize in the
primary clarifier. The lime-phosphorus sludge co-
settles with the primary sludge. Other facilities employ
a reactor-clarifier in lieu of a precipitation tank and
route only reactor-clarifier overflow to the primary
clarifier. The underflow lime-phosphorus sludge is
disposed of separately.
As further described in Chapter 6, aeration tank HOT
should be between 4 and 10 hours for effective
PhoStrip operation. Detention time in extended
aeration plants may, therefore, need to be shortened
by blocking a portion of the tankage. This will also
result in a higher organic loading rate, which is
desirable for biological phosphorus removal. On the
other hand, aerobic contact time in the contact
stabilization process may be too short, necessitating
the use of all or a portion of the sludge reaeration
volume as additional contact volume. Typically, this
can be accomplished with minor modifications.
The key process feature that determines the
efficiency of the PhoStrip concept is the differential
phosphorus content of the return sludge solids
entering and leaving the anaerobic stripper. This
differential times the mass of solids passing through
the stripper is equivalent to the amount of phosphorus
removed from the main stream wastewater flow by
cycling a portion of the return sludge through the
stripper.
The other non-effluent outlet for phosphorus in a
PhoStrip process is the waste activated sludge
removed from the system. The phosphorus removed
at a PhoStrip facility, therefore, is accomplished
through a combination of stripping of return sludge
and sludge wasting.
A 0.3- to 0.6-percent quantitative loss in the
phosphorus content of the return sludge volatile solids
entering and leaving the anaerobic stripper when the
aeration tank volatile solids ranged between 3.3 and
4.6 percent phosphorus has been reported (5). A
18
-------
Figure 2-11. Retrofitting plug flow, step aeration, complete mix, and pure oxygen activated sludge systems with the PhoStrip
process for phosphorus removal.
Wastewater
Aeration Tank
Effluent
Return Sludge
(6)
Primary Sludge
i
l
/0>
(2)
(4)
+
_L_
Waste Activated
Sludge
I
III,,
|"[<8)f-»,J»
Existing
Retrofit
Legend
(1) Portion of return sludge going to anaerobic stripper.
(2) Anaerobic stripper tank for leaching of phosphorus.
(3) Stripper tank overflow.
(4) Stripper tank underflow returned to activated sludge aeration tank.
(5) Tank containing lime slurry to precipitate phosphorus leached from return sludge in anaerobic stripper. Lime dose (CaO)
25 mg/l based on plant influent flow.
(6) Insolubilized phosphorus returned to primary clarifier for co-settling with primary sludge.
(7) Lime storage.
(8) Lime slurry tank.
(9) Pump for transfer of lime slurry to phosphorus precipitating tank.
20-
phosphorus mass balance at one facility without
primary clarification showed that 67 percent of the
overall phosphorus removal occurred by operation of
the stripper and lime precipitation and 33 percent was
removed via the waste activated sludge.
The PhoStrip process can achieve 2- and 1-mg/l
TP effluent concentrations without effluent polishing.
A 0.5-mg/l TP effluent concentration is possible
when effluent suspended solids concentrations are
low (5). To achieve an effluent limit of 0.2 mg/l TP
with PhoStrip, filtration and split dosing of chemicals
should be considered.
Because the PhoStrip process utilizes a sidestream
chemical addition unit process, and since key
operational parameters such as return sludge flow
rate through the stripper, elutriation stream quality,
and elutriation stream flow rate can be readily
controlled, effluent phosphorus concentrations are not
as sensitive to influent wastewater composition as are
other biological phosphorus removal approaches.
2.3.2.2 Retrofitting Activated Sludge Systems for
Biological Phosphorus Removal Using the A/O
Process
A schematic of an activated sludge system retrofitted
for biological phosphorus removal employing the A/O
process is presented in Figure 2-12. A critical
design feature of the A/O process is provision of
sequential stages of two different environments for
the biomass to cycle through. Therefore, if an existing
complete mix activated sludge system could not be
retrofitted into a staged reactor by baffling, the A/O
process would not be suitable. Installation of a
chemical backup feed system in an A/O process
retrofit is recommended to ensure that effluent TP
concentrations of 1 and 0.5 mg/l can be consistently
achieved. Due to the high phosphorus content of
effluent solids, consideration of effluent filtration is
also recommended if effluent concentrations of less
than 1 mg/l TP must be obtained.
Retrofit with the A/O process is most easily
accomplished in plug flow activated sludge tanks, but
can also be adapted to most of the other activated
19
-------
Figure 2-12. Retrofitting plug flow, step aeration, and pure oxygen activated sludge systems with the A/O process for
biological phosphorus removal.
Activated Sludge
Aeration Tank
Dognttod
Wastewalor
Anaerobic
Stages1
Oxic
Stages2
Return Sludge
Primary Sludge
Effluent
Waste Activated
Sludge
Metal Salt Motoring
Storage Pump
Existing
Retrofit
Legend
(D
(2)
Mixing by submersible pump or mixers. No DO is present
Conventional aeration devices for achieving satisfactory DO levels.
Final Effluent
TP
Probable Need for
Chemical Addition
mg/1
2
1
0.5
0.2
None
Occasional
Continuous polish dose
Continuous polish dose
sludge flow configurations. The ease of retrofit is
determined by the ability to delineate and convert a
portion of the tankage to an anaerobic stage.
Anaerobic here is defined as the absence of all DO
and oxidized nitrogen, while anoxic refers to the
conditions where DO is low or absent but oxidized
nitrogen is present. Space for construction of retrofit
facilities is normally not required for the A/O process,
and generally an A/O retrofit is more easily
accomplished than a retrofit for PhoStrip.
The A/O process induces a natural selection of
phosphorus-accumulating microorganisms to occur
by providing alternate environments of anaerobic and
aerobic (oxic) conditions. Wastewater and return
sludge are mixed in the anaerobic stage. It is not
necessary to cover this stage if suitable non-
turbulent mixing is provided. For example, mixing can
be accomplished by submersible pumps or impeller
mixers in a manner that does not cause oxygen
transfer from excessive exposure of liquid surface to
air. The HRT of the anaerobic stage can vary from 1
to 2 hours. During this time, soluble phosphorus is
released from the biomass into the bulk liquid and,
concurrently, organic matter (BOD) is sorbed from the
bulk liquid and stored by the biomass.
In the subsequent oxic stage with DO levels of 1 to 2
mg/l, the stored organics are biodegraded and new
cellular growth occurs coincident with transport of
soluble phosphorus into intercellular granules. The
HRT of the oxic stage can vary from 2 to 4 hours.
This sequence of anaerobic and aerobic events is
shown in Figure 2-13. These reactions are common
to all biological phosphorus removal processes.
These processes must be designed and operated to
accommodate the anaerobic sorption of BOD and
release of soluble phosphorus, followed by aerobic
cellular synthesis and phosphorus uptake.
The efficiency of phosphorus removal is affected by
the ratio of soluble BOD5 (SBOD) to SP in the
system influent. A ratio of influent SBOD to SP of 10
20
-------
Figure 2-13. Conceptual sequence of reactions in the A/O process.
SLOTS FOR SCUM TRANSPORT
BETWEEN STAGES
WASTEWATER FEED
f
TO
CLARIFIER
to .15 is necessary to achieve a 1-mg/l TP effluent
concentration with main stream biological phosphorus
removal processes such as A/O (5). To achieve a TP
effluent concentration of 0.5 mg/l, the ratio would
have to be about 20 to 25. The effect of internal
recycle streams, such as digester supernatant, sludge
thickener overflow, and filter press or vacuum filter
filtrates on the influent SBOD-to-SP ratio must also
be considered.
An evaluation of four full-scale biological phosphorus
removal facilities (5) revealed that none of the
facilities practiced anaerobic digestion of sludges.
Chemical treatment of some sludge handling recycle
streams was necessary to prevent previously
removed phosphorus from re-entering the secondary
system and adversely affecting attainment of effluent
phosphorus limitations.
Final clarifier design and operation is important for
biological phosphorus removal processes. A long
sludge blanket residence time in a clarifier can lead to
development of anaerobic conditions in the blanket
and cause leaching of soluble phosphorus from the
phosphorus stored in the biomass granules.
Provisions for rapid sludge removal from the clarifier
and reserve return sludge pumping capacity are
recommended where biological phosphorus removal
is contemplated.
2.4 References
1. Encyclopedia of Chemical Processing and
Design. Flocculation section, p. 184, Edited by
J.J. McKetta. Marcel Dekker, Inc., New York, NY,
and Basel, Switzerland, 1985.
2. Wastewater Engineering: Treatment, Disposal,
Reuse. Revised by G. Tchobanoglous. McGraw-
Hill, New York, NY, 2nd Edition, 1979.
3. Schmidtke, N. Estimating Sludge Quantities at
Wastewater Treatment Plants Using Metal Salts
to Precipitate Phosphorus. Proceedings of the
International Conference: Management Strategies
for Phosphorus in the Environment, Lisbon,
Portugal. Published by Selper Ltd., London,
England, ISBN 0-948411-00-7, 1985.
4. Dick, R. Management of Phosphorus Laden
Sludges. Proceedings of the International
Conference: Management Strategies for
21
-------
Phosphorus in the Environment, Lisbon, Portugal.
Published by Selper Ltd., London, England, ISBN
0-948411-00-7, 1985.
5. Tetreault, M.J., A.H. Benedict, C. Kaempfer, and
E.F. Barth. Biological Phosphorus Removal: A
Technology Evaluation. JWPCF 58:823, 1986.
6. Personal communication from R.I. Sedlak, The
Soap and Detergent Association, New York, NY,
to R.C. Brenner, U.S. EPA, Cincinnati, OH, May
20, 1987.
7. Personal communication from D. Jenkins,
University of California, Berkeley, CA, to S.J.
Kang, McNamee, Porter and Seeley, Ann Arbor,
Ml, July 31, 1987.
8. Design Manual, Municipal Wastewater
Stabilization Ponds. EPA-625/1-83-015,
U.S.EPA, Center for Environmental Research
Information, Cincinnati, OH, October 1983.
9. Summary Report of Workshop on Biological
Phosphorus Removal in Municipal Wastewater
Treatment. Prepared by R.L. Irvine and
Associates, Inc., Sponsored by U.S. EPA, Water
Engineering Research Laboratory, Cincinnati, OH,
Held at Annapolis, MD, September 1982.
10. Evans, B. and P. Crawford. Introduction of
Biological Nutrient Removal in Canada. Presented
at Technology Transfer Seminar on Biological
Phosphorus Removal, Sponsored by Environment
Canada, Burlington, Ontario, Held at Penticton,
British Columbia, Canada, April 1985.
22
-------
Chapter 3
Summary of Existing Phosphorus Removal Performance Data
3.1 introduction
The chemical phosphorus removal performance data
presented in the first part of this chapter represent a
collection of information from 76 wastewater
treatment plants located in the Great Lakes Drainage
Basin, including the states of Michigan, Ohio, Indiana,
Wisconsin, and Minnesota, as well as the Province of
Ontario, Canada. Data from a limited number of plants
in the CBDB are included for comparison: two from
Virginia, two from Maryland, and two from
Pennsylvania. Information from the plants in the Great
Lakes area was obtained from various sources.
These sources include the published literature and
direct contacts in the past and during preparation of
this manual. This data base includes treatment
process sequence and performance information,
methods of phosphorus removal including chemical
dosages and application points, and costs for
chemical usage and overall sludge disposal.
Biological phosphorus removal is relatively new, and
only a few full-scale plants are currently in operation
that employ this technology. Performance of the
PhoStrip and A/O processes is discussed in the last
part of this chapter.
3.2 Chemicai Phosphorus Removal
Performance data for 82 plants that chemically
remove phosphorus are summarized in Tables 3-1
through 3-11. The plants are grouped together by
the type of secondary treatment process employed as
follows:
15 Plug Flow Activated Sludge Systems
15 Complete Mix Activated Sludge Systems
11 Contact Stabilization Activated Sludge Systems
2 Pure Oxygen Activated Sludge Systems
5 Step Aeration Activated Sludge Systems
8 Extended Aeration Activated Sludge Systems
1 Two-Stage Nitrification Activated Sludge
System
4 High-Rate Trickling Filters
10 Standard-Rate Trickling Filters
9 RBCs
2 Oxidation Ditches
Influent TP concentrations ranged from 1.2 to 11.6
mg/l, reflecting the impacts of inflow/infiltration and
industrial inputs, as well as other site-specific
conditions.
Chemicals used included ferric chloride, ferrous
chloride, ferrous sulfate, alum, sodium aluminate, and
lime, as well as a variety of polymers. The effluent TP
permit limits range from 0.2 to 2.0 mg/l. For most of
these plants the limit is 1.0 mg/l. Actual effluent TP
concentrations varied between 0.2 and 2.7 mg/l, with
only eight plants producing average effluent TP
concentrations above 1.0 mg/l.
Chemicals were applied at most plants at a single
location within the treatment system except for a few
that practiced split dosing at two locations. The
principal application point was ahead of the primary
clarifier for 42 percent of the plants, in the secondary
biological process for 39 percent of the plants, and
ahead of the secondary clarifier for 19 percent of the
plants. It should be noted, however, that many of
these plants do have the flexibility to split feed at
multiple locations. Polymer was used in conjunction
with the metal salts in about half of the plants.
Some form of tertiary suspended solids removal was
employed at 29 percent of the plants.
3.2.1 Effect of Application Point on Chemical Use
A review of the plants in Tables 3-1 through 3-11
was made of chemical dosages for various points of
application as expressed by the ratios of metal salts
to influent TP concentrations on a weight basis. A
summary is provided in Table 3-12 for alum, ferric
chloride, and ferrous chloride. Data for other
chemicals are not included due to the limited data
base.
The general trend is that less chemicals are used
when dosed to the secondary process as compared
with the primary process. For those plants that use
polymer, the alum dose does not vary widely with
application point but a definite trend to lower doses
was revealed for ferric chloride the later it was applied
in the treatment sequence. A trend was not evident
for ferrous chloride.
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Table 3-12. Metal lon-to-lnfluent TP Ratio (Weight Basis)
for Various Points of Application
Point of Application"
With Polymer
Alum
Ferric Chloride
Ferrous Chloride
Without Polymer
Alum
Ferric Chloride
Ferrous Chloride
Primary
Clarifier
1.81 (2)
3.95(11)
2.26 (5)
4.01 (2)
2.20 (1)
1.77(4)
Secondary
Biological
Process
1.63(3)
3.02 (3)
3.94 (4)
1.00(1)
2.40 (1)
2.35 (9)
Secondary
Clarifier
2.28 (4)
1.88(4)
1.62(3)
2.07 (5)
1.24(2)
2.13 (6)
* Number of plants are indicated in parentheses.
Impacts of polymer addition on the metal salt dosage
were not shown to be consistent. In some plants, the
metal salt dosage was reduced when polymer was
used. In other plants, however, the metal salt dosage
increased. This is an apparent reflection of site-
specific conditions such as background water
chemistry, plant layout for mixing and flocculation,
settling and control, and plant management operating
strategies.
The above ratios should be examined with caution
since they are based on influent concentration.
Removal of phosphorus does occur in both the
primary clarifier and the biological process; therefore,
ratios calculated on an available phosphorus basis
would be somewhat higher when chemicals are
dosed to the secondary biological process or
secondary clarifier.
3.2.2 Effect of Effluent Limit on Chemical Use
The relationships between metal-to-influent TP
ratio on a weight basis and effluent phosphorus
concentration for aluminum and iron salts for the
plants summarized in Tables 3-1 through 3-11 are
presented in Figures 3-1 and 3-2, respectively.
Data for those plants with tertiary treatment are
distinguished from those with secondary treatment,
and chemical dosage ranges recommended for use in
Chapter 2 are included.
Although some plants achieved low effluent
phosphorus concentrations without tertiary treatment,
higher chemical dosages were generally required to
attain the same results. In both cases, the chemical
dosage increased as the required effluent TP
concentration decreases. Iron-to-influent TP weight
ratios as high as 10 and aluminum-to-influent TP
weight ratios over 4 were needed to achieve effluent
TP concentrations of 0.2 mg/l, while corresponding
ratios to achieve an effluent TP concentration of 1.0
mg/l were down to 4 for iron and 3 for aluminum.
In Table 3-13, expanded performance data for
specific plants in the CBDB are shown. Five plants,
four activated sludge and one trickling filter, used
aluminum salts for two different effluent TP limits:
Upper Allen, PA; Seneca, MD; and, Elizabethtown,
PA, with 2.0 mg/l, and Dale City, VA, and Piscataway,
MD, with 0.2 mg/l. The corresponding A|3 +/influent
TP feed rates (weight basis) were 0.85, 0.8, 2.5,
2.34, and 1.78, respectively. The dosage for the four
activated sludge plants was two to three times more
to reach the 0.2-mg/l TP effluent limit than the 2.0-
mg/l limit. Two trickling filter plants used ferric
chloride: Elizabethtown, PA, with an effluent limit of
2.0 mg/l TP and Little Hunting Creek, VA, with an
effluent limit of 0.2 mg/l TP. The corresponding
Fe3 + /influent TP feed rates (weight basis) were 1.39
and 4.69, respectively. Again, the dosage was over
three times higher to achieve the lower effluent limit
of 0.2 mg/l TP. The Elizabethtown plant added alum
from July 1985 through January 1986, then switched
to ferric chloride in February 1986. Data from one
CBDB plant, Damascus, MD, that does not remove
phosphorus chemically are included in Table 3-13 to
provide baseline information.
Polymer dosage varied from none at Dale City and
Elizabethtown to 2.8 mg/l at Little Hunting Creek and
3.8 mg/l at Piscataway.
3.2.3 Effect of Chemical Phosphorus Removal on
Sludge Generation
Sludge generation resulting from chemical
phosphorus removal was evaluated for selected
plants in the Chesapeake Bay and the Great Lakes
Drainage Basins as shown in Tables 3-13 and 3-
14, respectively. Major contributing factors are the
effluent phosphorus limit as described earlier, dosage
rate, and sludge handling methods at the plant.
The impact on total sludge production when
phosphorus removal chemicals are added to
secondary treatment plants is depicted in Figure 3-3.
Total sludge production is represented as multiples of
mass of raw influent TSS and is plotted against
effluent TP concentration. A marked increase in
sludge production is evident at low effluent TP
concentrations of 0.2 mg/l compared to 0.7 to 2.0
mg/l. The data in Figurer 3-3 suggest that the
quantity of sludge produced will be 2 to 3 times
higher at very low effluent TP concentrations, such as
0.2 mg/l, than at more moderate effluent TP
concentrations. The exact quantity further depends on
the amount of chemicals added for sludge handling.
The type of biological treatment process also impacts
the sludge quantity. The least sludge generation is
expected from an extended aeration process, and the
most is expected from a high-rate activated sludge
process.
31
-------
Figure 3-1. Alum-to-infJuent TP ratio vs. effluent TP concentration.
AI3+/!nfluentTP (weight)
6 r
A Secondary Treatment
• Tertiary Treatment
J I I I
I I
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Effluent TP, mg/l
1.4 1.6 1.8
Figure 3*2. Ferric Iron-to-influent TP ratio vs. effluent TP concentration.
Fe3+/InfluentTP (weight)
10 r- A
J I
A Secondary Treatment
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J I
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1.4 1.6 1.8
32
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35
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Figure 3-3. Sludge generation rate vs. effluent TP concentration.
Sludgo Generation Rate -
Total Sludge Mass/Raw TSS, Ib/lb
4 r—
• Alum - CBDB
A. Ferric - CBDB
A Ferric - Great Lakes
O No Chemicals Added
•
I
I
I
4 6
Effluent TP, mg/l
10
The combined effects of effluent phosphorus
concentration achieved and methods of sludge
handling employed on sludge production is further
illustrated in Figure 3-4. The extended aeration
processes at Upper Allen and Seneca produced low
sludge generation rates (SGRs), defined as total
mass of sludge produced per unit of raw influent TSS
received at the plant, while contact stabilization at
Dale City yielded a high SGR of 2.0. High SGRs of 2
to 3 were noted for plants that use lime stabilization
for sludge conditioning and have low effluent
phosphorus limits.
The treatment/sludge handling scheme having the
least impact on sludge generation with chemical
phosphorus removal was aerobic digestion followed
by land application of liquid sludge in an extended
aeration plant. A good example is Upper Allen, PA,
where alum addition is practiced, with an SGR of
0.36. Land application of anaerobically digested
sludge at Elizabethtown, PA, produced an SGR of 0.9
where ferric chloride was added to this two-stage
trickling filter plant.
The least desirable sludge handling alternative
evaluated was lime stabilization followed by vacuum
filtration. Not only was the quantity of lime necessary
to stabilize sludge excessive, but significant
maintenance problems also existed in plants utilizing
this sludge handling sequence. Piscataway, MD, and
Little Hunting Creek, VA, produced SGRs of 2.32 and
3.2, respectively, using this technology.
Polymer conditioning of sludge in general results in
somewhat lower solids content in the cake, which
means higher handling costs. This alternative,
however, does not increase the sludge quantity
significantly.
3.2.4 Effect of Chemical Phosphorus Removal on
pH
Two major factors contribute to reductions in pH
during wastewater treatment: nitrification and
coagulants such as aluminum and iron salts. Further
description of these phenomena are presented in
Chapter 7.
Low to moderate alkalinity necessitates pH
adjustment in some parts of CBDB where chemical
phosphorus removal is practiced. Examples were
found in Seneca, MD, and Dale City, VA, where
seasonal nitrification is also required. The dosages of
caustic soda at Dale City and sodium hydroxide at
Seneca necessary to prevent unacceptable pH
depression vary with the seasonal nitrification
operation. Other CBDB plants having facilities
necessary to feed caustic chemicals were not
operating these facilities at the time the plants were
studied.
3.2.5 Cost of Chemicals
The cost of phosphorus removal chemicals was
calculated on a pound removed basis and included
the cost of metal salts and polymer (when used).
Average costs were then determined for individual
chemicals with and without polymer use and for
effluent TP concentrations greater or less than 0.5
mg/l. These average costs are presented in Table 3-
15.
36
-------
Figure 3-4. Sludge generated vs. metal ion-to-influent TP ratio.
Sludge Generation Rate -
Total Sludge Mass/Raw TSS, Ib/lb
4 i—
(0.2)
'
Aluminum Salt
Ferric Chloride
Effluent TP Cone.
Dose Ratio Based on Metal Ion/Influent TP
« Dose Ratio Based on Metal Ion/IP Removed
Little Hunting Creek, VA*
TF
Lime Stab.
Filter Press
(0.2) &
Piscataway, MD*
2-Stage AS
Lime Stab.
Filter Press
(0.2)9
Dale City, VA"
Contact Stab.
Chem. Reactor-Clarifier
Aerobic Digestion
Filter Press w/Polymer
Seneca, MD*
Ext. Aeration
Aerobic Dig.
Filter Press
(0.2) •
(0.7)4 Warren, Mr
Lime/Ferric Cond.
Belt Press
Elizabethtown, PA'
(1-7) A
Lansing, Mr
AS
Zimpro
Vac. Filtration
(0.65)A
Elizabethtown, PA*
TF
Anaer. Digestion.
Land Application
(0.9)4
Port Huron. Mr
AS
Lime Stab.
Land Application
(2.0)« Upper Allen. PA"
Ext. Aeration
Aerobic Dig.
Lf nd Applicatiqn
2 3
AI3+/TP or Fe3+/TP (weight)
Table 3-15. Average Ch
Chemical
Alum
Sodium Aluminate
Ferric Chloride
Ferrous Chloride
Ferrous Sulfate
Lime
lemical Cost for Phosphorus Removal (S/lb TP removed)*
Effluent TP > 0.5 mg/l Effluent TP
Without Polymer
1.29 (5)
1.54(1)
0.51 (3)
0.53 (19)
0.33 (4)
0.81 (1)
With Polymer
1.50 (5)
1.40 (1)
1.30(10)
1.02(10)
0.70(1)
0.81 (1)
Without Polymer
1.91 (4)
1.38(1)
0.25(1)
0.10 (3)
-
< 0.5 mg/l
'With Polymer
4.81 (4)
-
, 2.39(8):
0.44 (2)
-
' -
Number of plants indicated in parentheses.
As expected, chemical costs were higher for those
plants achieving effluent TP concentrations less than
0.5 mg/l, with the exception of those plants using
ferrous salts. Alum was 40 percent more expensive
than ferric chloride for plants at which polymer was
not used, and 100 percent more expensive when
used in combination with polymer. Ferrous salts were
used at only a handful of plants achieving effluent
phosphorus concentrations less than 0.5 mg/l, and
the average cost was very low, probably because
37
-------
ferrous iron was available as pickle liquor for the cost
of shipping only.
3.3 Biological Phosphorus Removal
3.3.1 PhoStrip Process
3.3.1.1 PhoStrip Process Performance
Thirteen full-scale plants have been constructed or
retrofitted to the PhoStrip process to date, and a
fourteenth is under construction at Ithaca, NY. Five of
the completed facilities are no longer being operated
with PhoStrip for phosphorus removal. Several have
converted to chemical phosphorus removal, and in
one case the need for phosphorus compliance was
eliminated. Design flow rates for the PhoStrip process
have ranged from 0.04 to 1.3 m3/s (0.9 to 30 mgd).
Most of the plants were designed to achieve effluent
TP concentrations of 1.0 mg/l, although two were
designed for an effluent concentration of less than 0.5
mg/l TP with tertiary filtration.
Rve PhoStrip plants were designed to operate with
pure oxygen aeration, and nine with conventional air
aeration. A variety of activated sludge flow regimes
have been selected for use in conjunction with
PhoStrip, including complete mix, plug flow, contact
stabilization, step aeration, two-stage nitrification,
and high-rate activated sludge. Equalization and
tertiary filtration were incorporated in many of the
PhoStrip treatment sequences. Over half the plants
were designed with more than one anaerobic stripper.
Eight plant designs used one or more reactor*
clarifiors for lime precipitation, while the remaining six
had one or more mixer/flocculators and co-settled
the lime-phosphorus sludge in the primary clarifiers.
Reactor-clarifier overflow was the most frequently
chosen elutriation source, and stripper tank sludge
recycle was provided in five of the plants. Primary
effluent was the elutriation source for two plants.
Performance data are available for four of the eight
PhoStrip plants currently in operation. The four for
which data are not available are Tahoe-Truckee, CA;
Southtowns, NY; Brockton, MA; and Rochester, MN.
Brief descriptions of and performance summaries for
the four operating plants are given below.
Adrian, ML The 0.31-m3/s (7.0-mgd) Adrian
PhoStrip plant has been in operation since 19SO.
PhoStrip was constructed as part of the first-stage
activated sludge system followed by a second-stage
nitrification system. Primary effluent serves as the
elutriate, and lime precipitation is carried out in a
flocculation tank with the lime-phosphorus sludge
co-settled in the primary clarifiers. Secondary
effluent receives tertiary filtration prior to discharge.
Overall, the performance of the PhoStrip process at
Adrian has been good, with average removal
efficiencies for TBOD, TSS, and TP of 95, 97, and 69
percent, respectively, during the period October 1981
through September 1982 without the second-stage
system in operation.
Savage, MD. The Little Patuxent Wastewater
Treatment Plant serving Savage, MD, is a two-
stage, plug flow, activated sludge PhoStrip plant with
two strippers and two reactor-clarifiers. Reactor-
clarifier overflow is used as the elutriate. A 1985 data
summary indicated that for an average flow of 0.39
m3/s (8.8 mgd) and an average influent (to the
PhoStrip process) TP concentration of 8.6 mg/l,
secondary effluent TP averaged 0.8 mg/l while the
filtered effluent averaged 0.4 mg/l. Occasional daily
excursions of the effluent TP above 1.0 mg/l have
been encountered.
Reno-Sparks, NV. The Reno-Sparks Wastewater
Treatment Facility is a single-stage, plug flow,
activated sludge PhoStrip plant with five strippers and
two mixer/flocculators using stripper sludge recycle as
the elutriate. At an average flow of 1.1 m3/s (25.4
mgd) and an average influent TP concentration of
7.25 mg/l, the average effluent TP concentration was
'0.31 mg/l for the period June 1985 through March
1986. Effluent phosphorus excursions above 1.0 mg/l
rarely occurred on a daily basis. It should be noted
that this excellent performance was achieved without
tertiary filtration.
Lansdale, PA. This 0.1-m3/s (2.5-mgd) plant has
no primary. Wastewater flows to an activated
sludge-PhoStrip system for BOD and phosphorus
removal. Reactor-clarifier overflow and secondary
effluent are used to elutriate phosphorus in the
stripper.
Nitrification occurs in a separate-stage activated
sludge system. Waste biological sludges are
combined with the waste chemical sludge from the
PhoStrip process, gravity thickened, stabilized with
lime, and then dewatered or spread on land.
A 1984-1985 data summary indicated average
effluent concentrations of 0.8 mg/l for TP, 3 mg/l for
TBOD and 4 mg/l for TSS were achieved with the
first-stage activated sludge-PhoStrip system. Table
3-16 summarizes typical operating conditions for the
Lansdale and Little Patuxent plants (1).
3.3.1.2 Cost for PhoStrip Process Retrofit
Retrofit costs for the PhoStrip process must be
evaluated on a site-specific basis. Capital costs will
include construction of a stripper tank, reactor-
clarifier or chemical mix/flocculation tank, lime
handling facilities, and associated piping, as well as a
license fee charged for use of the proprietary
process. O&M costs will include energy for pumping
and mixing, lime, and maintenance associated with
operating a lime feed system.
38
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Table 3-16. Summary of PhoStrip Plant Operating Conditions for Lansdale
Lansdale
Parameter
Stripper
SDT, hr
Feed flow rate, percent of mainstream flow
Elutriation flow rate, percent of feed flow
Elutriation rate1, l/g TSS/d
Underflow rate, percent of mainstream flow
Recycle rate, percent of stripper flow
Overflow rate, percent of mainstream flow
Effluent Total P, mg/l
Effluent Ortho P, mg/l
Reactor-Clarifier
Effluent Total P, mg/l
Effluent Ortho P, mg/l
Overflow rate, gpd/sq ft
Lime dosage
mg/l
PH
Activated Sludge Process
F/M, kg TBOD/kg MLVSS/d
MLSS, mg/l .
TP/VSS, percent
SRT, days
. HRT, hr
Return sludge ratio
DO, mg/l :
Sludge production4, kg VSS/kg TBOD
,-•: 1982
20
14
124
0.14
10
0
23
20.6
16.4
• -.
3.6
0.9
1,600
100
9.0:
0.16
1,900
3.3
6.5
46
^•** - :'
0.16
2-3
1.0
and Little Patuxent
Little Patuxent
July 1984
8
22
121
0.72
14
0
35
9.5
7.2
3.9
0.9
1,120
160
9.5
. 0.52.3
2.9502
4.0
3.72.3
2.6
0.32-
1.3
0.7
April 1985
7
34
50
0.25
21
78
31
20.0
17.6
7.2
1.2
840
100
9.5
0.5
2,000
4.6
2.8
3.0
0.57
2-5
"
1 Based on mass of solids in stripper.
2 Estimated from solids balance.
3 Calculated based on estimated MLSS.
4 Based on removed carbonaceous TBOD.
The capital cost for the hardware for the PhoStrip
process at Adrian, Ml, in 1977, was $556,000 for the
design flow of 0.31 m3/s (7.0 mgd). The license fee
was $250,000, making the total cost $806,000. The
license fee amount may not be representative of the
fee that would be charged today. The annual O&M
cost in 1986 was approximately $25,000, of which
$14,800 was for lime, $6,000 for labor, and $4,200
for excess sludge handling and disposal.
3.3.2 A/O Process
3.3.2.1 A/O Process Performance
Two full-scale A/O plants are currently in operation:
Largo, PL, and Pontiac, Ml. Another 13 full-scale
A/O systems are, currently in .design or under
construction with design capacities of 0.13 to 3.1
nr>3/s (3 to 70 mgd). Available data for the Largo and
Pontiac facilities are summarized below.
Largo, FL. The Largo A/O system is a retrofit of a
plug-flow activated sludge plant.designed for a flow
of 0.14 m3/s (3.2 mgd). Anaerobic and aerobic
detention times are 1.5 and 2.6 hours, respectively.
Influent TP averged 8.9 mg/l during the performance
test period, while the effluent TP averaged 1.85 mg/l.
The effluent SP concentration during the same period
averaged 0.51 mg/l. The plant was designed to
achieve an effluent TP of 1.5. mg/l. Sludge handling
consists of aerobic digestion followed by mechanical
dewatering.
Pontiac, Ml. The A/O system in Pontiac is a 0.15-
m3/s (3.5-mgd) retrofit of a plug-flow activated
sludge train. Detention times for the anaerobic and
aerobic stages are longer here, 2.1 and 7.7 hours,
respectively. TP was reduced from an average
influent concentration of 3.7 mg/l to an average
effluent concentration of 0.9 mg/l on a U.S. EPA
demonstration project during a period when
nitrification was being achieved and the main
treatment process was receiving full in-plant recycle
of sidestreams, including anaerobic digester
supernatant. During the 1-year demonstration
project, average effluent TP concentrations exceeded
1 mg/l during only two 2-week periods. The
excursions were attributed to the effect of extremes in
pH caused by industrial discharges. The plant has
been successfully operating for about 2 years with
seasonal nitrification and recycle of anaerobic
digester supernatant. It was shown that only a
fraction of the phosphorus removed biologically was
released into the digester supernatant under
anaerobic conditions. The mechanism by which
phosphorus is trapped in the solids in the digester is
being further studied, but it is currently hypothesized
39
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Toblo 3-17. Pontlac A/O Wastewater Treatment Facility Performance Data
Influent
Effluent
Parameter
Timo Period
Flow, mgd
TBOD, mg/l
TSS, mg/l
TP, mg/l
With Nitrification
10/1/84-11/14/84
2.86
163
140
3.7
Without Nitrification
2/6/85 - 3/31/85
4.28
136
136
2.6
With Nitrification
-
-
9.4
7
0.9
Without Nitrification
-
-
11
10
0.7
that phosphorus is being chemically precipitated in
tho presence of magnesium and ammonia in the
digester to an insoluble compound called magnesium
ammonium phosphate. The average performance of
the Pontiac A/O system is summarized in Table 3-
17 for a 45-day period with nitrification and full in-
plant digester supernatant recycle and a 54-day
period without nitrification, but with full in-plant
digester supernatant recycle.
3.3.2.2 Cost for A/O Process Retrofit
As with PhoStrip, retrofit costs for the A/O process
must be evaluated on a site-specific basis. Capital
costs include construction of baffles to separate the
various stages, removal of existing aeration devices in
anaerobic stages, possible addition of aeration
devices in aerobic stages, and installation of mixers in
anaerobic stages. O&M costs include energy for
internal recycle pumping, if required, and to operate
the mixers. It has been reported that some savings in
aeration power may be realized due to the decreased
aerobic stage organic loading resulting from the BOD
removal that occurs in the anaerobic stages (2).
Retrofit costs (in 1984 dollars) for the Pontiac project
totaled $57,000 for conversion of a 0.15-m3/s
(3.5-mgd) plug flow activated sludge train to an A/0
system. The license fee was waived for Pontiac
because this was a demonstration project.
3.4 References
1. Tetreault, M.J., A.H. Benedict, C. Kaemfer, and
E.F. Barth. Biological Phosphorus Removal: A
Technology Evaluation. JWPCF 58:823, 1986.
2. Brannan, K.P., C.W. Randall, and L.D. Benefield.
The Anaerobic Stabilization of Organics in a
Biological Phosphorus Removal System.
Presented at the 59th Annual Conference, Water
Pollution Control Federation, Los Angeles, CA,
October 1986.
40
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Chapter 4
Process Design Synopses for Retrofitting Chemical Phosphorus Removal
This chapter is primarily directed to the plant designer
who has the task of retrofitting an existing wastewater
treatment plant to phosphorus removal by means of
chemical precipitation. The designer should refer to
the design synopsis that pertains to the plant
category to be retrofitted. This chapter also should be
of interest to plant operators and regulators charged
with reviewing construction grant applications. There
are nine design synopses covering the following plant
categories:
1. Plug Flow, Complete Mix, and Step Aeration
Activated Sludge Systems
2. Contact Stabilization Activated Sludge Systems
3. Pure Oxygen Activated Sludge Systems
4. Extended Aeration and Oxidation Ditch Activated
Sludge Systems
5. Two-Stage Nitrification Activated Sludge
Systems
6. High-Rate Trickling Filter Systems
7. Standard-Rate Trickling Filter Systems
8. RBC Systems
9. Lagoon Systems
Each design synopsis provides information on the
following 12 areas, grouped by required effluent TP
concentration {0.2, 0.5, 1, and 2 mg/l):
1. Chemical dose requirements
2. Points of metal salt addition
3. Points of polymer addition
4. Impact on overall secondary treatment process
performance
5. Impact on sludge settling
6. Impact on sludge quantities and characteristics
7. Impact on sludge thickening
8. Impact on sludge handling/disposal facilities
9. Impact on return sludge and sludge handling
recycle streams
10. Impact of wastewater temperature
11. Effluent polishing requirements
12. Process flexibility recommendations
The choice of chemical for use in phosphorus
removal must be made on a site-specific basis and
will depend primarily on cost and availability. The use
of lime for chemical phosphorus removal is not
recommended due to the many associated problems
in handling.
Metal salt-to-influent TP weight ratios were used as
initial chemical dose guides for the design synopses
in this chapter. Once a facility is in operation and a
data base exists, more precise dosage ratios of metal
salt-to-influent SP can be established for routine
operational control.
41
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Design Synopsis 1:
Plug Flow, Complete Mix, and Step Aeration Activated Sludge Systems
1. Chemical dose requirements:
Required Effluent TP
M3+/lnfluentTP
Ratio (weight) Polymer Dose
mg/l
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/I effluent TP:
Ahead of both primary and secondary clarifiers.
For 1 and 2 mg/l effluent TP:
Ahead of primary or secondary clarifier.
3. Points of polymer addition:
For 0.2 and 0.5 mg/l eff. TP (will be necessary):
Ahead of both primary and secondary clarifiers.
For 1 mg/I eff. TP (will be necessary):
Ahead of primary or secondary clarifier.
For 2 mg/l eff. TP (may be necessary):
Ahead of primary or secondary clarifier.
4. Impact on overall secondary treatment process performance:
When phosphorus removal chemicals are added to the secondary treatment process, metal phosphate
precipitates and other metal ion precipitates are formed and occluded into the activated sludge mass. This
contributes an inert fraction to the MLSS, and wasting schedules for control of SRT may have to be altered.
For 0.2 mg/I effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Sludge settling rates are normally improved when metal salts are added to primary and/or secondary
cfarifiers. Polymer addition is sometimes also necessary in conjunction with metal salt addition to aid in solids
agglomeration and capture and prevent carry-over of inorganic solids to the secondary treatment process or
fine floe particles to the final effluent. Best results are attained when clarifiers are greater than 2.7 m (9 ft)
deep.
For 0.2 and 0.5 mg/I effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
For 1 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
For 2 mg/I effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 m3/m2/d (800 gpd/sq ft).
42
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6. Impact on sludge quantities and characteristics:
When chemicals are added prior to primary clarifiers, sludge yields will increase due to the formation of
insoluble metal hydroxides and the entrapment of BOD and suspended solids onto floes. Primary sludge will,
therefore, contain a greater amount of organic matter since it is captured with the inorganic floes.
Solids production also increases when chemicals are added to the secondary treatment process, but not to
as great an extent. Waste secondary sludge will contain a higher fraction of inert solids than normal.
For 0.2 mg/1 effluent TP:
Increases in sludge production greater than 200 percent can be expected due to the extremely high dosages
of chemicals necessary to achieve this low effluent limit. Actual increases, however, will depend on site-
specific conditions.
For 0.5 mg/1 effluent TP:
Increases in sludge production of 100 to 200 percent have been documented when chemicals are added to
both the primary and secondary treatment processes. Actual increases, however, will depend on site-
specific conditions.
For 1 and 2 mg/1 effluent TP:
Increases in sludge production of 60 to 100 percent have been documented when chemicals are added to
the primary treatment process, and 40 to 60 percent when chemicals are added to the secondary treatment
process. Actual increases, however, will depend on site-specific conditions.
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/1 effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Return activated sludge will contain a higher fraction of inert solids when phosphorus removal chemicals are
used in the secondary treatment process. As a result, higher return sludge rates will normally be required.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may also increase when chemical phosphorus removal is imposed on an existing
treatment plant. This factor needs to be considered in the overall retrofit design and is particularly important if
biological reactor capacity is marginal.
10. Impact of wastewater temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
43
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11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Polymer addition to the primary and secondary clarifiers and tertiary filtration will be required.
For 0.5 mg/l effluent TP:
Polymer addition to the primary and secondary clarifiers will be required. Additional clarifier capacity or
tertiary filtration may be necessary.
For 1 and 2 mg/l effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
® Multiple metal salt and polymer addition points:
« Row equalization:
» Polymer addition:
e Effluent polishing:
necessary
necessary
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/I effluent TP:
» Multiple metal salt and polymer addition points:
e Row equalization:
» Polymer addition:
» Effluent polishing:
For 1 and 2 mg/l effluent TP:
e Multiple metal salt and polymer addition points:
* Flow equalization:
• Polymer addition:
» Effluent polishing:
necessary
may be required
necessary
may be required
recommended
not required
may be required
not required
44
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Design Synopsis 2:
Contact Stabilization Activated Sludge Systems
1. Chemical dose requirements:
Required Effluent TP
M3+/Influent TP
Ratio (weight) Polymer Dose
mg/l
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/l effluent TP:
Ahead of primary clarifier and at end of contact tank.
For 1 and 2 mg/l effluent TP:
Ahead of primary clarifier or at end of contact tank.
3. Points of polymer addition:
For 0.2 and 0.5 mg/l eff. TP (will be necessary):
Ahead of both primary and secondary clarifiers.
For 1 mg/l eff. TP (will be necessary):
Ahead of primary or secondary clarifier.
For 2 mg/l eff. TP (may be necessary):
Ahead of primary or secondary clarifier.
4. Impact on overall secondary treatment process performance:
When phosphorus removal chemicals are added to the secondary treatment process, metal phosphate
precipitates and other metal ion precipitates are formed and occluded into the activated sludge mass. This
contributes an inert fraction to the MLSS, and wasting schedules for control of SRT may have to be altered.
For 0.2 mg/l effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Sludge settling rates are normally improved when metal salts are added to primary and/or secondary
clarifiers. Polymer addition is sometimes also necessary in conjunction with metal salt addition to aid in solids
agglomeration and capture and prevent carry-over of inorganic solids to the secondary treatment process or
fine floe particles to the final effluent. Best results are attained when clarifiers are greater than 2.7 m (9 ft)
deep.
For 0.2 and 0.5 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
For 1 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
For 2 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 m3/m2/d (800 gpd/sq ft).
45
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6. Impact on sludge quantities and characteristics:
When chemicals are added prior to primary clarifiers, sludge yields will increase due to the formation of
insoluble metal hydroxides and the entrapment of BOD and suspended solids onto floes. Primary sludge will,
therefore, contain a greater amount of organic matter since it is captured with the inorganic floes.
Solids production also increases when chemicals are added to the secondary treatment process, but not to
as great an extent. Waste secondary sludge will contain a higher fraction of inert solids than normal.
For 0.2 mg/1 effluent TP:
Increases in sludge production greater than 200 percent can be expected due to the extremely high dosages
of chemicals necessary to achieve this low effluent limit. Actual increases, however, will depend on site-
specific conditions.
For 0.5 mg/I effluent TP:
Increases in sludge production of 100 to 200 percent have been documented when chemicals are added to
both the primary and secondary treatment processes. Actual increases, however, will depend on site-
specific conditions.
For 1 and 2 mg/I effluent TP:
Increases in sludge production of 60 to 100 percent have been documented when chemicals are added to
the primary treatment process, and 40 to 60 percent when chemicals are added to the secondary treatment
process. Actual increases, however, will depend on site-specific conditions.
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/I effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Return activated sludge will contain a higher fraction of inert solids when phosphorus removal chemicals are
used in the secondary treatment process. As a result, higher return sludge rates will normally be required.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may also increase when chemical phosphorus removal is imposed on an existing
treatment plant. This factor needs to be considered in the overall retrofit design and is particularly important if
biological reactor capacity is marginal.
10. Impact of wastewater temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
46
-------
11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Polymer addition to the primary and secondary clarifiers and tertiary filtration will be required.
For 0.5 mg/l effluent TP:
Polymer addition to the primary and secondary clarifiers will be required. Additional clarifier capacity or
tertiary filtration may be necessary.
For 1 and 2 mg/l effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
necessary
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
For 1 and 2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
may be required
recommended
not required
may be required
not required
47
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Design Synopsis 3:
Pure Oxygen Activated Sludge Systems
1. Chemical dose requirements:
Required Edluent TP
M3+/influentTP
Ratio (weight) Polymer Dose
mg/l
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/l effluent TP:
Ahead of both primary and secondary clarifiers.
For 1 and 2 mgil effluent TP:
Ahead of primary or secondary clarifier.
3. Points of polymer addition:
For 0.2 and 0.5 mg/l eff. TP (will be necessary):
Ahead of both primary and secondary clarifiers.
For 1 mg/I eff. TP (will be necessary):
Ahead of primary or secondary clarifier.
For 2 mg/l eff. TP (may be necessary):
Ahead of primary or secondary clarifier.
4. Impact on overall secondary treatment process performance:
With a covered pure oxygen reactor, carbon dioxide resulting from biological oxidation is trapped in solution
rather than being air stripped from the mixed liquor. The chemicals used for phosphorus removal are also
acidic. Depending on wastewater alkalinity, some provision for pH control may be necessary, therefore, to
prevent an unacceptable degree of pH depression and subsequent interference with normal metabolic
reactions.
In addition, when phosphorus removal chemicals are added to the secondary treatment process, metal
phosphate precipitates and other metal ion precipitates are formed and occluded into the, activated sludge
mass. This contributes an inert fraction to the MLSS, and wasting schedules for control of SRT may have to
be altered.
For 0.2 mg/l effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Sludge settling rates are normally improved when metal salts are added to primary and/or secondary
clarifiers. Polymer addition is sometimes also necessary in conjunction with metal salt addition to aid in solids
agglomeration and capture and prevent carry-over of inorganic solids to the secondary treatment process or
fine floe particles to the final effluent. Best results are attained when clarifiers are greater than 2.7 m (9 ft)
deep.
For 0.2 and 0.5 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
48
-------
For 1 mg/1 effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
For 2 mg/1 effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 m3/m2/d (800 gpd/sq ft).
6. Impact on sludge quantities and characteristics:
When chemicals are added prior to primary clarifiers, sludge yields will increase due to the formation of
insoluble metal hydroxides and the entrapment of BOD and suspended solids onto floes. Primary sludge will,
therefore, contain a greater amount of organic matter since it is captured with the inorganic floes.
Solids production also increases when chemicals are added to the secondary treatment process, but not to
as great an extent. Waste secondary sludge will contain a higher fraction of inert solids than normal.
For 0.2 mg/1 effluent TP:
Increases in sludge production greater than 200 percent can be expected due to the extremely high dosages
of chemicals necessary to achieve this low effluent limit. Actual increases, however, will depend on site-
specific conditions.
For 0.5 mg/1 effluent TP:
Increases in sludge production of 100 to 200 percent have been documented when chemicals are added to
both the primary and secondary treatment processes. Actual increases, however, will depend on site-
specific conditions.
For 1 and 2 mg/1 effluent TP:
Increases in sludge production of 60 to 100 percent have been documented when chemicals are added to
the primary treatment process, and 40 to 60 percent when chemicals are added to the secondary treatment
process. Actual increases, however, will depend on site-specific conditions.
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/1 effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Return activated sludge will contain a higher fraction of inert solids when phosphorus removal chemicals are
used in the secondary treatment process. As a result, higher return sludge rates will normally be required.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may also increase when chemical phosphorus removal is imposed on an existing
treatment plant. This factor needs to be considered in the overall retrofit design and is particularly important if
biological reactor capacity is marginal.
49
-------
TO. Impact of wastewater temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Polymer addition to the primary and secondary clarifiers and tertiary filtration will be required.
For 0.5 mg/l effluent TP:
Polymer addition to the primary and secondary clarifiers will be required. Additional clarifier capacity or
tertiary filtration may be necessary.
For 1 and 2 mg/l effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/I effluent TP:
* Multiple metal salt and polymer addition points:
• Row equalization:
• Polymer addition:
• Effluent polishing:
necessary
necessary
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/I effluent TP:
• Multiple metal salt and polymer addition points:
• Row equalization:
* Polymer addition:
• Effluent polishing:
For 1 and 2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Row equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
may be required
recommended
not required
may be required
not required
50
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Design Synopsis 4:
Extended Aeration and Oxidation Ditch Activated Sludge Systems
1. Chemical dose requirements:
Required Effluent TP
M3+/influent TP
Ratio (weight) Polymer Dose
mg/1
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/1 effluent TP:
End of aeration tank and a polish dose to the tertiary filter.
For 1 and 2 mg/1 effluent TP:
End of aeration tank.
3. Points of polymer addition:
For 0.2 mg/1 eff. TP (will be necessary):
Ahead of secondary clarifier and a polish dose to tertiary filter.
For 0.5 mg/1 eff. TP (will be necessary):
Ahead of secondary clarifier.
For 1 and 2 mg/1 eff. TP (may be necessary):
Ahead of secondary clarifier.
4. Impact on overall secondary treatment process performance:
Extended aeration and oxidation ditch systems nitrify during at least part of the year. Acidic hydrogen ions are
a byproduct of the nitrification process. Depending on wastewater alkalinity, some provision for pH control
may be necessary, therefore, to prevent an unacceptable degree of pH depression and subsequent
interference with normal metabolic reactions.
In addition, when phosphorus removal chemicals are added to the secondary treatment process, metal
phosphate precipitates and other metal ion precipitates are formed and occluded into the activated sludge
mass. This contributes an inert fraction to the MLSS, and wasting schedules for control of SRT may-have to
be altered.
For 0.2 mg/1 effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Extended aeration and oxidation ditch systems generally are not preceded by primary clarification. When
metal salts are dosed to or just ahead of secondary clarifiers in these systems, sludge settling rates are
normally enhanced. Polymer addition may also be necessary, however, to agglomerate fine floe particles.
Best results are attained when secondary clarifiers are greater than 2.7 m (9 ft) ddep.
For 0.2 and 0.5 mg/1 effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
51
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For 1 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
For 2 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 m3/m2/d (800 gpd/sq ft).
6. Impact on sludge quantities and characteristics:
Chemicals added to the secondary treatment process will effect an increase in sludge production due to the
formation of insoluble metal hydroxides and phosphates. Waste secondary sludge will contain a higher
fraction of inert solids than normal.
For 0.2 mg/1 effluent TP:
Increases in waste secondary sludge production greater than 200 percent can be expected due to the
extremely high dosages of chemicals necessary to achieve this low effluent limit. Actual increases, however,
will depend on site-specific conditions.
For 0.5 mg/l effluent TP:
Increases in waste secondary sludge production of 100 to 200 percent have been reported when chemicals
are added to the secondary treatment process in a plant that does have primary clarifiers. Actual increases,
however, will depend on site-specific conditions.
For 1 and 2 mg/l eff TP:
Increases in waste secondary sludge production of 40 to 100 percent have been documented when
chemicals are added to the secondary treatment process in a plant that does not have primary clarifiers.
Actual increases, however, will depend on site-specific conditions.
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/l effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Return activated sludge will contain a higher fraction of inert solids when phosphorus removal chemicals are
used in the secondary treatment process. As a result, higher return sludge rates will normally be required.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may also increase when chemical phosphorus removal is imposed on an existing
treatment plant. This factor needs to be considered in the overall retrofit design and is particularly important if
biological reactor capacity is marginal.
52
-------
10. Impact of wastewater temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Tertiary filtration with polish doses of metal salt and polymer to the filter will be necessary.
For 0.5 mg/l effluent TP:
Tertiary filtration with a polish dose of metal salt to the filter may be necessary.
For 1 and 2 mg/l effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
For 1 and 2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
may be required
not required
necessary
may be required
not required
not required
may be required
not required
53
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Design Synopsis 5:
Two-Stage Nitrification Activated Sludge Systems
1. Chemical dose requirements:
Required Effluent TP
M3+/Influent TP
Ratio (weight) Polymer Dose
mg/l
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/l effluent TP:
Ahead of either primary or intermediate clarifier with a polish dose to the second-stage nitrification reactor.
For 1 and 2 mg/l effluent TP:
Ahead of either primary or intermediate clarifier.
3. Points of polymer addition:
For 0.2 and 0.5 mg/l eff. TP (will be necessary):
Ahead of either primary or intermediate clarifier with a polish dose to the second-stage nitrification clarifier.
For 1 and 2 mg/l eff. TP (will be necessary):
Ahead of either primary or intermediate clarifier.
4. Impact on overall secondary treatment process performance:
Acidic hydrogen ions are a byproduct of the nitrification process. Depending on wastewater alkalinity, some
provision for pH control may be necssary, therefore, to prevent an unacceptable degree of pH depression
and subsequent interference with normal metabolic reactions.
In addition, when phosphorus removal chemicals are added to the secondary treatment process, metal
phosphate precipitates and other metal ion precipitates are formed and occluded into the activated sludge
mass. This contributes an inert fraction to the MLSS, and wasting schedules for control of SRT may have to
be altered.
For 0.2 mg/l effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Sludge settling rates are normally improved when metal salts are added to primary and/or secondary
clarifiers. Polymer addition is sometimes also necessary in conjunction with metal salt addition to aid in solids
agglomeration and capture and prevent carry-over of inorganic solids to the secondary treatment process or
fine floe particles to the final effluent. Best results are attained when clarifiers are greater than 2.7 m (9 ft)
deep.
For 0.2 and 0.5 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
For 1 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
54
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For 2 mg/I effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 m-Vm^/d (800 gpd/sq ft).
6. Impact on sludge quantities and characteristics: .
When chemicals are added prior to primary clarifiers, sludge yields will increase due to the formation of
insoluble metal hydroxides and the entrapment of BOD and suspended solids onto floes. Primary sludge will,
therefore, contain a greater amount of organic matter since it is captured with the inorganic floes.
Solids production also increases when chemicals are added to the secondary treatment process, but not to
as great an extent. Waste secondary sludge will contain a higher fraction of inert solids than normal.
For 0.2 mg/I effluent TP:
Increases in sludge production greater than 200 percent can be expected due to the extremely high dosages
of chemicals necessary to achieve this low effluent limit. Actual increases, however, will depend on site-
specific conditions.
For 0.5 mg/I effluent TP:
Increases in sludge production of 100 to 200 percent have been documented when chemicals are added to
both the primary and secondary treatment processes. Actual increases, however, will depend on site-
specific conditions.
For 1 and 2 mg/I effluent TP:
Increases in sludge production of 60 to 100 percent have been documented when chemicals are added to
the primary treatment process, and 40 to 60 percent when chemicals are added to the secondary treatment
process. Actual increases, however, will depend on site-specific conditions,
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/1 effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Return activated sludge will contain a higher fraction of inert solids when phosphorus removal chemicals are
used in the secondary treatment process. As a result, higher return sludge rates will normally be required.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may also increase when chemical phosphorus removal is imposed on an existing
treatment plant. This factor needs to be considered in the overall retrofit design and is particularly important if
biological reactor capacity is marginal.
55
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10. Impact of wastewater temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Metal salt and polymer addition to the second-stage nitrification reactor and second-stage nitrification
clarifior, respectively, will be required. Tertiary filtration will be required.
For 0.5 mg/l effluent TP:
Metal salt and polymer addition to the second-stage nitrification reactor and second-stage nitrification
clarifier, respectively, will be required. Tertiary filtration may be necessary.
For 1 and 2 mg/I effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
For 1 and 2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition*.
• Effluent polishing:
necessary
may be required
necessary
may be required
recommended
not required
may be required
not required
56
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Design Synopsis 6:
High-Rate Trickling Filter Systems
1. Chemical dose requirements:
M3+/Influent TP
Required Effluent TP
Ratio (weight) Polymer Dose
mg/l
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/l effluent TP:
Ahead of both primary and secondary clarifiers, as well as to retrofit bioreactor.
For 1 mg/l effluent TP:
Ahead of both primary and secondary clarifiers.
For 2 mg/l effluent TP:
Ahead of primary clarifier.
3. Points of polymer addition:
For 0.2 and 0.5 mg/l eff. TP (will be necessary):
Ahead of both primary and secondary clarifiers, as well as to retrofit bioreactor.
For 1 mg/l eff. TP (will be necessary):
Ahead of both primary and secondary clarifiers.
For 2 mg/l eff. TP (will be necessary):
Ahead of primary clarifier.
4. Impact on overall secondary treatment process performance:
The trickling filter media should be protected from the effects of metal salts as much as possible. When
these chemicals are added to the primary clarifier, inorganic solids may carry over to the tricking filter. This
may result in the production of a biofilm with a higher inert fraction than desirable and interference with
normal metabolic reactions. Polymer should be used to minimize the carry-over of inorganic solids from the
primary clarifier to the trickling filter.
For 0.2 and 0.5 mg/l effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5 Impact on sludge settling:
Sludge settling rates are normally improved when metal salts are added to primary and/or secondary
clarifiers. Polymer addition is sometimes also necessary in conjunction with metal salt addition to aid in solids
agglomeration and capture and prevent carry-over of inorganic solids, to the secondary treatment process or
fine floe particles to the final effluent. Best results are attained when clarifiers are greater than 2.7 m (9 ft)
deep.
For 0.2 and 0.5 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
For 1 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
57
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For 2 mg/I effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 m3/m2/d (800 gpd/sq ft).
6. Impact on sludge quantities and characteristics:
When chemicals are added prior to primary clarifiers, sludge yields will increase due to the formation of
insoluble metal hydroxides and the entrapment of BOD and suspended solids onto floes. Primary sludge will,
therefore, contain a greater amount of organic matter since it is captured with the inorganic floes.
Solids production also increases when chemicals are added to the secondary treatment process, but not to
as great an extent. Waste secondary sludge will contain a higher fraction of inert solids than normal.
For 0.2 mg/1 effluent TP:
Increases in sludge production greater than 200 percent can be expected due to the extremely high dosages
of chemicals necessary to achieve this low effluent limit. Actual increases, however, will depend on site-
specific conditions.
For 0.5 mg/I effluent TP:
Increases in sludge production of 100 to 200 percent have been documented when chemicals are added to
both the primary and secondary treatment processes. Actual increases, however, will depend on site-
specific conditions.
For 1 and 2 mg/l effluent TP:
Increases in sludge production of 60 to 100 percent have been documented when chemicals are added to
the primary treatment process, and 40 to 60 percent when chemicals are added to the secondary treatment
process. Actual increases, however, will depend on site-specific conditions.
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/I effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Settled sludge from the secondary clarifier is normally not returned to and recycled through a high-rate
trickling filter bioreactor.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may increase when chemical phosphorus removal is imposed on an existing treatment:
plant. This factor needs to be considered in the overall retrofit design and is particularly important if biological
reactor capacity is marginal.
58
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to. Impact of wastewater temperature: «•,'••
Phosphorus removal performance decreases in cold temperatures due to decreased settleability or cnemicai
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Construction of a second-stage bioreactor and clarifier, or expansion of the trickling filter system, as well as
tertiary filtration will be required. Addition of metal salt and polymer both after the trickling filter and to the
second-stage bioreactor, if utilized, will also be required.
For 0.5 mg/l effluent TP:
Construction of a second-stage bioreactor and clarifier, or expansion of the trickling filter system, may be
required. Addition of metal salt and polymer both after the trickling filter and to the second-stage bioreactor,
if utilized, may also be required.
For 1 mg/l effluent TP:
Addition of metal salt and polymer after the trickling filter will be required.
For 2.0 mg/l effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
» Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 and 1 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
For 2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
may be required
recommended
not required
necessary
not required
59
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Design Synopsis 7:
Standard-Rate Trickling Filter Systems
1. Chemical dose requirements:
Required Effluent TP
M3+/infIuentTP
Ratio (weight) Polymer Dose
mg/I
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/I
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/I effluent TP:
Ahead of both primary and secondary clarifiers.
For 1 and 2 mg/I effluent TP:
Ahead of primary or secondary clarifier.
3. Points of polymer addition:
For 0.2 and 0.5 mg/I eff. TP (will be necessary):
Ahead of both primary and secondary clarifiers.
For 1 mg/I eff. TP (will be necessary):
Ahead of primary or secondary clarifier.
For 2 mg/I eff. TP (may be necessary):
Ahead of primary or secondary clarifier.
4. Impact on overall secondary treatment process performance:
The trickling filter media should be protected from the effects of metal salts as much as possible. When
these chemicals are added to the primary clarifier, inorganic solids may carry over to the trickling filter. This
may result in the production of a biofilm with a higher inert fraction than desirable and interference with
normal metabolic reactions. Polymer should be used to minimize the carry-over of inorganic solids from the
primary clarifier to the trickling filter.
For 0.2 and 0.5 mg/I effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Sludge settling rates are normally improved when metal salts are added to primary and/or secondary
clarifiers. Polymer addition is sometimes also necessary in conjunction with metal salt addition to aid in solids
agglomeration and capture and prevent carry-over of inorganic solids to the secondary treatment process or
fine floe particles to the final effluent. Best results are attained when clarifiers are greater than 2.7 m (9 ft)
deep.
For 0.2 and 0.5 mg/I effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
For 1 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
60
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For 2 mg/1 effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 nrvm^/d (800 gpd/sq ft).
6. Impact on sludge quantities and characteristics:
When chemicals are added prior to primary clarifiers, sludge yields will increase due to the formation of
insoluble metal hydroxides and the entrapment of BOD and suspended solids onto floes. Primary sludge will,
therefore, contain a greater amount of organic matter since it is captured with the inorganic floes.
Solids production also increases when chemicals are added to the secondary treatment process, but not to
as great an extent. Waste secondary sludge will contain a higher fraction of inert solids than normal.
For 0.2 mg/1 effluent TP:
Increases in sludge production greater than 200 percent can be expected due to the extremely high dosages
of chemicals necessary to achieve this low effluent limit. Actual increases, however, will depend on site-
specific conditions.
For 0.5 mg/1 effluent TP:
Increases in sludge production of 100 to 200 percent have been documented when chemicals are added to
both the primary and secondary treatment processes. Actual increases, however, will depend on site-
specific conditions.
For 1 and 2 mg/1 effluent TP:
Increases in sludge production of 60 to 100 percent have been documented when chemicals are added to
the primary treatment process, and 40 to 60 percent when chemicals are added to the secondary treatment
process. Actual increases, however, will depend on site-specific conditions.
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/1 effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Settled sludge from the secondary clarifier is normally not returned to and recycled through a standard-rate
trickling filter bioreactor.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may increase when chemical phosphorus removal is imposed on an existing treatment
plant. This factor needs to be considered in the overall retrofit design and is particularly important if biological
reactor capacity is marginal.
61
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10. Impact of wastewater temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
11. Effluent polishing requirements:
For 0.2 mg/I effluent TP:
Polymer addition to the secondary clarifier and tertiary filtration will be required.
For 0.5 mg/I effluent TP:
Polymer addition to the secondary clarifier will be required.
For 1 and 2 mg/1 effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Row equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
For 1 and 2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Row equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
may be required
may be required
not required
necessary
not required
62
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Design Synopsis 8:
RBC Systems
1. Chemical dose requirements:
M3+/lnfluentTP
Required Effluent TP
Ratio (weight) Polymer Dose
mg/l
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/l effluent TP:
Ahead of both primary and secondary clarifiers.
For 1 and 2 mg/l effluent TP:
Ahead of primary or secondary clarifier.
3. Points of polymer addition:
For 0.2 and 0.5 mg/l eff. TP (will be necessary):
Ahead of both primary and secondary clarifiers.
For 1 mg/l eff. TP (will be necessary):
Ahead of primary or secondary clarifier.
For 2 mg/l eff. TP (may be necessary):
Ahead of primary or secondary clarifier.
4. Impact on overall secondary treatment process performance:
The RBC media should be protected from the effects of metal salts as much as possible. When these
chemicals are added to the primary clarifier, inorganic solids may carry over to the RBC media. This may
result in the production of a biofilm with a higher inert fraction than desirable and interference with normal
metabolic reactions. Polymer should be used to minimize the carry-over of inorganic solids from the primary
clarifier to the RBC media.
For 0.2 and 0.5 mg/l effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Sludge settling rates are normally improved when metal salts are added to primary and/or secondary
clarifiers. Polymer addition is sometimes also necessary in conjunction with metal salt addition to aid in solids
agglomeration and capture and prevent carry-over of inorganic solids to the secondary treatment process or
fine floe particles to the final effluent. Best results are attained when clarifiers are greater than 2.7 m (9 ft)
deep.
For 0.2 and 0.5 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 20 m3/m2/d (500 gpd/sq ft).
For 1 mg/l effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 24 m3/m2/d (600 gpd/sq ft).
63
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For 2 mg/I effluent TP:
Secondary clarifier overflow rate at peak sustained flow should not exceed 32 m3/m2/d (800 gpd/sq ft).
6. Impact on sludge quantities and characteristics:
When chemicals are added prior to primary clarifiers, sludge yields will increase due to the formation of
insoluble metal hydroxides and the entrapment of BOD and suspended solids onto floes. Primary sludge will,
therefore, contain a greater amount of organic matter since it is captured with the inorganic floes.
Solids production also increases when chemicals are added to the secondary treatment process, but not to
as great an extent Waste secondary sludge will contain a higher fraction of inert solids than normal.
For 0.2 mg/I effluent TP:
Increases in sludge production greater than 200 percent can be expected due to the extremely high dosages
of chemicals necessary to achieve this low effluent limit. Actual increases, however, will depend on site-
specific conditions.
For 0.5 mg/I effluent TP:
Increases in sludge production of 100 to 200 percent have been documented when chemicals are added to
both the primary and secondary treatment processes. Actual increases, however, will depend on site-
specific conditions.
For 1 and 2 mg/1 effluent TP:
Increases in sludge production of 60 to 100 percent have been documented when chemicals are added to
the primary treatment process, and 40 to 60 percent when chemicals are added to the secondary treatment
process. Actual increases, however, will depend on site-specific conditions.
7. Impact on sludge thickening:
The increased sludge volumes resulting from chemical phosphorus removal will lead to both higher solids and
hydraulic loading rates on gravity and flotation thickeners. Thickener design loading rates may, therefore, be
exceeded in plants that are at or near treatment capacity. Solids capture may decrease when design loading
rates are exceeded.
8. Impact on sludge handling/disposal facilities:
The increase in sludge production may cause the design loading rates of sludge handling/disposal facilities to
be exceeded if the plant is at or near treatment capacity. Under these circumstances, sludge disposal
facilities may not operate correctly and may need to be reviewed and upgraded to handle the additional
quantities and types of sludges generated (e.g., conversion of low-rate digesters to high-rate digesters or
a two-stage digestion system to a single-stage digestion system).
For 0.2 and 0.5 mg/l effluent TP:
Anaerobic sludge digestion may be inhibited due to the high proportion of chemical sludge resulting from high
dosages of chemical. Use of this method of sludge stabilization should be avoided, therefore, if possible,
where very low effluent phosphorus is required.
9. Impact on return sludge and sludge handling recycle streams:
Settled sludge from the secondary clarifier is normally not returned to and recycled through an RBC
bioreactor.
The concentration of certain constituents in sludge handling recycle streams such as nitrogen, phosphorus,
and soluble organics may increase when chemical phosphorus removal is imposed on an existing treatment
plant. This factor needs to be considered in the overall retrofit design and is particularly important if biological
reactor capacity is marginal.
64
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to. Impact of wastewater temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Polymer addition to the secondary clarifier and tertiary filtration will be required.
For 0.5 mg/l effluent TP:
Polymer addition to the secondary clarifier will be required.
For 1 and 2 mg/l effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
9 Flow equalization:
• Polymer addition:
• Effluent polishing:
For 1 and 2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
may be required
necessary
may be required
may be required
not required
necessary
not required
65
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1. Chemical dose requirements:
Design Synopsis 9:
Lagoon Systems
Roquirod Effluent TP
M3+/lnfluentTP
Ratio (weight) Polymer Dose
mg/l
0.2
0.5
1
2
2.0-5.0
1.5-2.0
1.2-1.5
1.0-1.2
mg/l
0.2-1.0
0.1-0.5
0.1-0.2
0.1-0.2
2. Points of metal salt addition:
For 0.2 and 0.5 mg/l effluent TP:
Retrofit tertiary chemical treatment system.
For 1 and 2 mg/I effluent TP:
Ahead of first and last cells; if unaerated, provide mixing chamber.
3. Points of polymer addition:
For 0.2 and 0.5 mg/l eff. TP (may be necessary):
Retrofit tertiary chemical treatment system.
For 1 and 2 tng/1 effluent TP:
Not required.
4. Impact on overall secondary treatment process performance:
Dosing phosphorus removal chemicals directly to the lagoon creates the concern of imparting a high inert
fraction to the active organisms that may decrease the capability for normal metabolic reactions.
For 0.2 and 0.5 mg/l effluent TP:
Process pH must be monitored since high dosages of metal salts can result in depressed pH values.
5. Impact on sludge settling:
Clarifiers are not normally used in a lagoon treatment system.
6. Impact on sludge quantities and characteristics:
Solids separation or effluent clarification is not normally practiced in lagoon treatment systems. If chemicals
are added directly to the lagoon, it is expected that an accumulation of inert solids would eventually occur
that may require removal at some point in time.
7. Impact on sludge thickening:
Thickeners are not normally used in conjunction with lagoon treatment systems.
8. Impact on sludge handling/disposal facilities:
Sludge handling/disposal facilities are not normally necessary for lagoon treatment systems.
9. Impact on return sludge and sludge handling recycle streams:
Return sludge and sludge handling recycle streams are not normally a factor in lagoon treatment systems.
66
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10. Impact of waste water temperature:
Phosphorus removal performance decreases in cold temperatures due to decreased settleability of chemical
floes resulting from greater liquid viscosity and density. Increased chemical dosages and polymer use may be
required.
11. Effluent polishing requirements:
For 0.2 mg/l effluent TP:
Tertiary chemical treatment (consisting of a flocculation tank and a clarifier) and filtration will be necessary.
For 0.5 mg/l effluent TP:
Tertiary chemical treatment (consisting of a flocculation tank and a clarifier) and filtration will likely be
required.
For 1 and 2 mg/l effluent TP:
Effluent polishing should not be necessary.
12. Process flexibility recommendations:
For 0.2 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
not required
may be required
necessary
In addition, pH control instrumentation and dosing of pH neutralizing chemicals may be required.
For 0.5 mg/l effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
For 1 and 2 mgll effluent TP:
• Multiple metal salt and polymer addition points:
• Flow equalization:
• Polymer addition:
• Effluent polishing:
necessary
not required
may be required
necessary
necessary
not required
not required
not required
67
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Chapters
Hardware Design and O&M Considerations for
Chemical Phosphorus Removal in Small to Medium Plants (< 10 mgd)
5.1 Introduction
This chapter presents information on the
characteristics and properties of chemicals used for
phosphorus removal, suppliers of chemicals to the
Chesapeake Bay area, chemical costs for the
Chesapeake Bay area, chemical storage and feeding
facilities, typical chemical addition system layouts,
staffing requirements and sampling and analytical
needs for chemical addition, and safety precautions
and OSHA requirements for chemical addition. This
information has been derived from extensive
experience with the design and operation of chemical
addition systems in the Great Lakes region.
Modifications have been incorporated, where
appropriate, to make the information relevant to
treatment plants in the CBDB.
The intent of this chapter is to assist engineers in the
CBDB to design efficient site-specific chemical feed
systems without "reinventing the wheel." It is also
anticipated that the information contained in this
chapter will aid plant operators in the CBDB to
minimize problems associated with chemical addition
operational continuity and system maintenance,
thereby reducing downtime, waste of chemicals, and
sludge handling difficulties.
5.2 Aluminum Compounds
The principal aluminum compounds that are
commercially available and suitable for phosphorus
precipitation are alum and sodium aluminate. Both are
available in either liquid or dry forms. Alum is acidic in
nature, while sodium aluminate is alkaline. This may
be an important factor in choosing between them.
Aluminum chloride should also be considered and is
discussed herein.
5.2.1 Dry Alum
5.2.1.1 Properties and Availability
The commercial dry alum most used in wastewater
treatment has the approximate chemical formula
[Al2(SO4)3«14H20] and a molecular weight of 594.
The pH varies between 3.0 and 3.5 in aqueous alum
solutions having concentrations between 1 and 10
percent. Commercially available grades and their
corresponding bulk densities and angles of repose
are given in Table 5-1.
Table 5-1. Available Grades of Dry Alum
Grade Bulk Density Angle of Repose
Lump
Ground
Rice
Powdered
Ib/cu ft
62 -68
60-71
57-61
38 -45
0
varies
43
38
65
Each grade has a minimum aluminum content of 17
percent, expressed as A^Oa- This corresponds to a
9-percent concentration as aluminum. Viscosity and
solution crystallization temperatures are included in
the subsequent section on liquid alum.
The solubility of commercial dry alum at various
temperatures is listed in Table 5-2.
Table 5-2. Solubility of Alum at Various Temperatures
Temperature Solubility
°F
32
50
68
86
104
Ib/gal
6.03
6.56
7.28
8.45
10.16
Dry alum is not corrosive unless it absorbs moisture
from the air, such as during prolonged exposure to
humid atmospheres. Therefore, precautions should be
taken to ensure storage space is free of moisture.
Alum is typically shipped in 45-kg (100-lb) bags or
in bulk (minimum of 18,150 kg or 40,000 Ib) by truck.
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Bag shipments may be ordered on wood pallets.
Information on suppliers of dry alum to the
Chesapeake Bay area is given in Table 5-3.
5.2.1.2 General Design Considerations
Utilities usually use ground and rice alum because of
their superior flow characteristics. These grades have
less tendency to lump or arch in storage and,
therefore, provide more consistent feeding qualities.
Hopper agitation is seldom required with these
grades, and, in fact, may be detrimental to feeding by
causing packing of the contents of the bin.
Alum dust is present in the ground grade and will
cause minor irritation of eyes and respiratory tract. A
respirator will protect against alum dust. Alum dust
should be thoroughly flushed from the eyes
immediately and washed from the skin with water.
Gloves should be worn to protect the hands. Because
of minor irritation in handling and the possibility of
alum dust causing rusting of adjacent machinery, dust
removal equipment is desirable.
5.2.1.3 Storage
A typical storage and feeding system for dry alum is
shown in Figure 5-1. Bulk alum can be stored in
mild steel or concrete bins with dust collector vents
located in, above, or adjacent to the equipment room.
Recommended storage capacity is about 30 days.
Dry alum in bulk can be transferred with screw
conveyors, pneumatic conveyors, or bucket elevators
made of mild steel. Pneumatic conveyor elbows
should have a reinforced backing to withstand
abrasion.
Bags and drums of alum should be stored in a dry
location. Bag or drum loaded hoppers should have
storage capacity for 8 hours at the nominal maximum
feed rate so personnel are not required to charge the
hopper more than once per shift. Converging hopper
sections should have a minimum wall slope of 60° to
prevent arching.
Bulk storage hoppers should have a discharge bin
gate so feeding equipment may be isolated for
servicing. The bin gate should be followed by a
flexible connection and a transition hopper chute or a
hopper that acts as a conditioning chamber over the
feeder.
5.2,1.4 Feeding Equipment
The feed system includes all components required for
preparation of the chemical solution. Capacities and
configurations should be selected to fulfill individual
system requirements. Three basic types of chemical
feed equipment are used: volumetric, belt gravimetric,
and loss-in-weight gravimetric. Volumetric feeders
are usually used where low initial cost and lower
delivery capacities are the basis of selection.
Volumetric feeder mechanisms are usually exposed to
corrosive vapors from the dissolving chamber.
Manufacturers normally control this problem by use of
an electric heater to keep the feeder housing dry or
by using plastic components in the exposed areas.
Volumetric dry feeders are generally of the screw
type. Two designs of screw feed mechanism are
available. Both allow even withdrawal across the
bottom of the feeder hopper to prevent dead zones.
One screw design is the variable pitch type with the
pitch expanding evenly to the discharge point. The
second screw design is the constant pitch-
reciprocating type. This type has each half of the
screw turned in opposite directions so the turning and
reciprocating motion alternately fills one half of the
screw while the other half is discharging. The variable
pitch screw has one point of discharge, while the
constant pitch-reciprocating screw has two points of
discharge, one at each end of the screw. The
accuracy of volumetric feeders is influenced by the
character of material being fed and ranges between 1
percent for free-flowing materials to 7 percent for
cohesive materials. This accuracy is volumetric and is
not related to accuracy by weight (gravimetric).
Where the greatest accuracy and more economical
use of chemical is desired, the loss-in- weight type
feeder should be selected. This feeder is suited to
low and medium feed rates with a maximum of
approximately 1,500 kg (4,000 lb)/h. The unit consists
of a material hopper and feeding mechanism mounted
on enclosed scales. Continuous comparison of actual
hopper weight with set hopper weight prevents
cumulative errors. Accuracy of the loss-in-weight
feeder is near 1 percent by weight of the set rate.
Belt-type gravimetric feeders span the capacity
ranges of volumetric and loss-in-weight feeders
and can be sized for most applications in watewater
treatment. Initial expense falls between that for the
volumetric feeder and the loss-in-weight feeder.
Belt-type gravimetric feeders consist of a basic belt
feeder incorporating a weighing and control system.
Feed rates can be varied by changing either the
weight per unit length of belt, belt speed, or both.
Controllers in general use are mechanical, pneumatic,
electric, and mechanical-vibrating. Accuracy
specified for belt-type gravimetric feeders should be
within 1 percent of the set rate. This equipment
normally includes mild steel hoppers, stainless steel
mechanism components, and rubber surfaced feed
belts.
Because alum solution is corrosive, dissolving or
solution chambers should be constructed of type 316
stainless steel, fiberglass reinforced plastic (FRP), or
plastics (polyvinyl chloride, polyethylene,
polypropylene, and similar materials). Dissolvers
should be sized for preparation of the desired solution
strength. The most dilute solution strength usually
recommended is 0.06 kg of alum/I (0.5 Ib/gal) of
water, or a 6-percent solution. The dissolving
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Table 5-3. Dry Alum Suppliers to the Chesapeake Bay Area
Name _ . Address
Telephone
1986 Price Quotations*
Manley-Regan Chemicals
Delta Chemicals
Coyne Chemicals
East Emmaus Street
P. O. Box 391
Middletown, PA 17057
12601 Cannery Avenue
Baltimore, MD 21226
3015 State Road
Croyden, PA 19020
(717)994-7471
(301)354-0100
(215) 785-3000
100-lb bags:
20 bags-$16.75/100 Ib
50 bags - $15.50/100 Ib
100 bags-$14.90/100 Ib
100-lb bags:
400 bags (minimum order)
$185/ton ($9.25/100 Ib)
40,000-lb hopper truck:
$165/ton ($8.25/100 Ib)
100-Jb bags:
100 bags-$14.60/100 Ib
240 bags - $12.10/100 Ib
40,000-lb hopper truck:
$242Aon ($12.10/100 Ib)
1 Call for applicable freight charges, if any. Generally, prices include freight up to varying distances from the point of manufacture.
chamber is designed for a minimum detention time of
5 minutes at the maximum feed rate. Because
excessive dilution may be detrimental to coagulation,
eductors or float valves that would ordinarily be used
ahead of centrifugal pumps are not recommended.
Dissolvers should be equipped with water meters and
mechanical mixers so the water-to-alum ratio may
be properly established and controlled.
5.2.1.5 Piping and Accessories
Pipe made FRP or plastic is recommended for alum
solution. Care must be taken to provide adequate
support for these piping systems, with close attention
given to spans between supports so objectionable
deflection will not occur. Lined steel pipe is generally
tougher and more rigid, but the cost of providing a
near perfect lining may detract from its suitability.
Solution flow by gravity to the point of discharge is
desirable. When pumping is necessary, little or no
dilution is required. When metering pumps or
proportioning weir tanks are used, return of excess
flow to a holding tank'should be considered. Metering
pumps are discussed in the section on liquid alum.
Valves used in solution lines should be plastic, type
316 stainless steel, or rubber-lined iron or steel.
5.2.1.6 Pacing and Control
Volumetric and gravimetric feeders are usually
adaptable to operation from any standard instrument
control and pacing signals. When solution must be
pumped, consideration should be given to the use of
holding tanks between the dry feed system and feed
pumps; solution water supply should be controlled to
prevent excessive dilution. The dry feeders may be
started and stopped from tank level probes. Variable
control metering pumps can transfer alum stock
solution to the point of application without further
dilution.
Means should be provided for calibration of chemical
feeders. Volumetric feeders may be mounted on
platform scales. Belt feeders should include a sample
chute and box to check actual delivery with set
delivery.
Gravimetric feeders are usually furnished with
totalizers only. Remote instrumentation is frequently
used with gravimetric equipment, but seldom used
with volumetric equipment.
5.2.2 Liquid Alum
5.2.2.1 Properties and Availability
Liquid alum is shipped in insulated tank cars or
trucks. During the winter, it is heated prior to
shipment so crystallization will not occur during
transit. Liquid alum is shipped at a solution strength of
about 4.37 percent as aluminum, about 8.3 percent
as AI2O3, or 49 percent as A12(SO4)3»14H2O. This
solution has a density of 1.33 kg/I (11.1 Ib/gal) at
60 °F and contains about 0.65 kg of dry alum/I (5.4
Ib/gal) of liquid, or 17 percent A^Oa. This solution will
begin to crystallize at 30°F and crystallizes at 18°F.
Crystallization temperatures of other solution
strengths are given in Table 5-4. The viscosity of
various alum solutions is given in Figure 5-2.
Liquid alum is typically delivered in truck lots of
11,400 to 18,900 I (3,000 to 5,000 gal). Information
on suppliers of liquid alum to the Chesapeake Bay
area is presented in Table 5-5.
Since liquid alum is an intermediate compound in
production of dry alum, the liquid form costs less.
However, liquid alum costs more to transport since it
is nearly half water by weight. Therefore, a cost
tradeoff point can be established when exact
chemical costs and local freight rates are determined.
Liquid alum will generally be more economical than
71
-------
Figure 5-1. Dry feed system alternatives.
Dust
Collector
Fill Pipe
(Pneumatic)
Dust
Collector
Screen
with
Breaker
Flexible
Connection
Bag
/Fill
Day Hopper for
Dry Chemical
from Bags
or Drums
LL
Alternative Supplies Depending on Storage
JU
Control Solenoid
Valve Valve
Water
Supply
Pump to. Application
___€>
dry alum if the point of use is within 100 miles of the
manufacturing plant; ease of handling, storing, and
feeding liquid alum extend its practical transport limit
to 200 miles or more.
5.2.2.2 General Design Considerations
Bulk unloading facilities usually must be provided at
the treatment plant. Railroad tank cars are
constructed for top unloading and, therefore, require
an air supply system and flexible connectors to
pneumatically displace the alum from the car. U.S.
Department of Transportation regulations concerning
chemical tank car unloading should be observed.
Tank truck unloading is usually accomplished by
gravity or by a truck-mounted pump.
No particular industrial hazards are encountered in
handling liquid alum. However, a face shield and
gloves should be worn around leaking equipment.
The eyes or skin should be flushed and washed upon
contact with liquid alum. Liquid alum becomes very
slick upon evaporation, and, therefore, spillage should
be avoided.
5.2.2.3 Storage
Liquid alum is stored without dilution at the shipping
concentration. Storage tanks may be open if indoors,
but must be closed and vented if outdoors. Outdoor
tanks should also be heated, if necessary, to keep
the temperature above 25° F to prevent crystallization.
Storage tanks should be constructed of type 316
stainless steel, FRP, steel lined with rubber, polyvinyl
chloride, or lead; see subsequent section for details.
Liquid alum can be stored indefinitely without
deterioration.
Storage tanks should be sized according to maximum
feed rate, shipping time required, and quantity of
72
-------
Table 5-4. Crystallization Temperatures of Liquid Alum
Temperature of Crystallization
percent
5.19
6.42
6.67
6.91
7.16
7.40
7.66
7.92
8.19
8.46
8.74
°F
26
21
19
17
15
13
12
14
17
20
28
shipment. Tanks should generally be sized for 1-1/2
times the quantity of shipments. A 10-day to 2-
week supply should be provided to allow for
unforeseen snipping delays.
5.2.2.4 Feeding Equipment
Various types of gravity or pressure feeding and
metering units are available. Figures 5-3 and 5-4
illustrate commonly-used feed systems. The
rotodip-type feeder or rotameter is often used for
gravity feed and the metering pump for pressure feed
systems.
The pressure or head available at the point of
application frequently determines the feeding system
to be used. The rotodip feeder can be supplied from
overhead storage by gravity with the use of an
internal level control valve, as shown in Figure 5-3.
It may also be supplied by a centrifugal pump. The
latter arrangement requires an excess flow return line
to the storage tank, as indicated in Figure 5-4.
Centrifugal pumps should be direct-connected but
not close-coupled because of possible leakage into
the motor, and should be constructed of type 316
stainless steel, FRP, or plastic.
Metering pumps currently available allow a wide range
of capacity compared with the rotodip and rotameter
systems. Hydraulic diaphragm-type pumps are
preferable to other type pumps and should be
protected with an internal or external relief valve. A
backpressure valve is usually required in the pump
discharge to provide efficient check valve action.
Materials of construction for feeding equipment
should be as recommended by the manufacturer for
the service but, depending on the type of system, will
generally include type 316 stainless steel, FRP,
plastics, and rubbber.
5.2.2.5 Piping and Accessories
Piping systems for liquid alum should be constructed
of FRP, plastics (subject to temperature limits), type
316 stainless steel, or lead. Piping and valves used
for alum solutions are also discussed in the preceding
section on dry alum.
5.2.2.6 Pacing and Control
The feeding systems described above are volumetric,
and the feeders generally available can be adapted to
receive standard instrument pacing signals. The
signals can be used to vary motor speed, variable-
speed transmission setting, stroke speed, and stroke
length, where applicable. A totalizer is usually
furnished with a rotodip feeder, and remote
instruments are available. Instrumentation is rarely
used with rotameters and metering pumps.
5.2.3 Dry Sodium Aluminate
5.2.3.1 Properties and Availability
Dry sodium aluminate, Na2Al2O4, is shipped in 23-
kg (50-lb) bags and has a bulk density ranging from
640 to 800 kg/m.3 (40 to 50 Ib/cu ft). The AI2C>3
content ranges from 41 to 46 percent. Dry sodium
aluminate is noncorrosive, and the pH of a 1-percent
solution is about 11.9. Manufacturers should be
consulted for more precise specifications of their
product.
Dry sodium aluminate is available in the Chesapeake
Bay area from the supplier listed in Table 5-6.
5.2.3.2 General Design Considerations
Requirements for dry sodium aluminate feed systems
are generally similar to those for dry aluminum
sulfate. Dry sodium aluminate is not available in bulk
quantities. Therefore, the small, day-type hoppers
with manual filling arrangements as shown in Figure
5-1 are used. Precautionary measures for handling
sodium aluminate are similar to those for strong
alkalies, such as caustic soda. Contact with skin,
eyes, and clothing should be avoided. Aluminate dust
or solution spray should not be breathed.
5.2.3.3 Storage
Dry sodium aluminate is stored as received, in bags,
and at optimum conditions of 60 to 90°F; the
recommended storage limit is 6 months. Hopper
material of mild steel is completely adequate. This
chemical may or may not be free flowing, depending
on the manufacturer and grade used. Therefore,
hopper agitation may be required. Sodium aluminate
deteriorates on exposure to the atmosphere, and care
should be taken to avoid tearing of bags.
5.2.3.4 Feeding Equipment
Materials of construction for dissolving chambers may
be mild steel or stainless steel, and selection may be
influenced by conformity with adjacent equipment.
Equipment similar to that shown in Figure 5-1 is
applicable. Standard practice for the free-flowing
grade of sodium aluminate calls for dissolvers sized
for 0.06 kg/I (0.5 Ib/gal) or 6-percent solution
73
-------
Flflure 5-2. Viscosity of alum solutions (courtesy of Allied Chemical Co.).
0.1
30
100
Temperature, °F
150
220
Table 5-5. Liquid Alum Suppliers to the Chesapeake Bay Area
Name Address Telephone
1986 Price Quotations*
Mantoy-Rogan Chemicals
Delta Chemicals
Coyne Chemicals
East Emmaus Street
P. O. Box 391
Middleton, PA 17057
12601 Cannery Avenue
Baltimore, MD 21226
3015 State Road
Croyden, PA 19020
(717)944-7471 $l45/ton of dry alum.
A 4,600-gal tank truck contains 25,000
Ib(i2.5 ton) of dry alum.
Cost per truck - $1,813.
Cost per gal - $0.40
(301) 354-0100 $l45/ton of dry alum.
(215) 785-3000 $l33/ton of dry alum.
Call for applicable freight charges, if any. Generally, prices include freight up to varying distances from the point of manufacture.
strength with a dissolver detention time of 5 minutes
at the maximum feed rate.
After dissolving dry sodium aluminate in the
preparation of batch solutions, agitation should be
minimized or eliminated to prevent deterioration of the
solution. Air agitation is not recommended, and
solution tanks should be covered to prevent
carbonation of the solution.
74
-------
Figure 5-3. Liquid chemical feed system alternatives for
elevated storage.
Figure 5-4. Liquid chemical feed system alternatives for
ground storage.
Elevated
Chemical
Storage
Tank
(gravity ±
feed) T
Rotary Dipper Feeder
a. Rotary dipper feeder
Recirculation
Ground
Chemical
Storage
Tank
JS
r
.
Rotary Dipper
Feeder
To Process
(gravity
feed)
a. Rotary dipper feeder
Elevated
Chemical
Storage
Tank
Rotameter (or mag meter)
Control
Valve
l_I>s<-l
t->vl
To Process
(gravity |
feed)
Rotameter (or Mag Meter)
b. Rotameter with control valve
Control
Valve
I—Xh-
To Process
(pressure
feed)
Elevated
Chemical
Storage
Tank
Relief
Valve
X Back
T Valve
1 i^, ^i
(*3 ^
v .TV
Pressure
To Procesd
(pressure ±
fp,aH\ T
Centrifugal Feed Pump
b. Centrifugal pump with rotameter and control valve
Relief
Valve
Metering Pump
c. Metering pump
Ground
Chemical
Storage
Tank
,
i
_IS)
M t ' D
c. Metering pump
Back Pressure A
Valve
To Process
(pressure
feed)
5.2.3.5 Piping and Accessories
Materials for piping and transporting dry sodium
aluminate solution may be mild steel, iron, type 304
stainless steel, concrete, or plastics. The use of
copper, copper alloys, and rubber should be avoided.
5.2.3.6 Pacing and Control
Pacing and control fundamentals are similar to those
described for dry alum. The amount of dilution is not
a consideration in the use of sodium aluminate.
Therefore, the use of float valves to satisfy centrifugal
pump suction and the use of eductors are
permissible.
5.2.4 Liquid Sodium Aluminate
5.2.4.1 Properties and Availability
Liquid sodium aluminate is available in the
Chesapeake Bay area from the suppliers listed in
Table 5-7. There is considerable variety in the
composition of liquid sodium-aluminate from the
manufacturers listed. The A^Oa content varies from
4.9 to 26.7 percent. The lower solution strengths are
usually more expensive because of the cost of
transporting the solution water. Because of the variety
of solution strengths available, the manufacturers
should be contacted for more specific information on
density, viscosity, and cost. Liquid sodium aluminate
75
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Tablo 5-6. Dry Sodium Alumlnate Supplier to the Chesapeake Bay Area
Name Address Telephone
1986 Price Quotations
Nalco Chemical
170 Forbes Road
Braintree, MA 02184
(617) 944-7471
50-lb bags:
120 bags or less - $0.50/lb
> 120 bags - $0.45/lb
Freight not included.
Table 5-7. Liquid Sodium Aluminate Suppliers to the Chesapeake Bay Area
Name Address Telephone
1986 Price Quotations*
Nalco Chemical
2901 Butterfield Road
Oak Brook, IL 60521
Vinings Chemicals
Coyno Chemicals
P. O. Box 773
Richboro. PA 18954
3015 State Road
Croyden, PA 19020
(312) 887-7500 Nalco " 1" (12.8 Ib/gal):
12-59 30-gal drums - $0.45/lb
> 59 30-gal drums - $0.36/lb
Bulk, 3,000-gal tank truck - $0.20/lb
Nalco "2" (12.1 Ib/gal):
12-59 30-gal drums - $0.38/lb
>59 30-gal drums - $0.34/lb
Bulk, 3,000-gal tank truck - $0.l8/lb
(215) 322-5871 Vinings "45":
$0.20/lb in drums
$0.l4/lb in tank trucks
Vinings "38":
$0.i95/lb in drums
$0.135/lb in tank trucks
(215) 785-3000 Vinings "38":
$0.l65/lb in tank trucks
(Coyne does not supply Vinings "45" due to
freezing problems.)
" Call (or applicable freight charges, if any. Generally, prices include freight up to varying distances from the point of manufacture.
is typically available in 114-1 (30-gal) drums and
11,400-1 (3,000-gal) tank trucks.
5.2.4.2 General Design Considerations
Because of the alkaline nature of liquid sodium
aluminate, it should not be used in contact with brass,
copper, aluminum, or rubber. Liquid sodium aluminate
is a strong alkali, and the same precautions should be
exercised in handling it as in handling caustic soda.
5.2.4.3 Storage
Liquid sodium aluminate is usually stored at the
shipping concentration, either in the shipping drums
or in mild steel tanks. Storage tanks may be located
indoors or outdoors; however, outdoor tanks should
be provided with facilities for indirect heating. The
maximum recommended length of storage is 2 to 3
months. Bulk shipments can be unloaded by gravity,
pumping, or air pressure. If air is used, however, it
should first be passed through lime-caustic soda
breathers to remove carbon dioxide. To avoid this,
some treatment plants do not allow shipments to be
air unloaded. Steam injection facilities are required at
the unloading site.
5,2.4.4 Feeding Equipment
Feeding equipment and systems as described for
liquid alum generally apply to liquid sodium aluminate
except with changes of requirements regarding
dilution and materials of construction as described
above.
Liquid sodium aluminate may be fed at shipping
strength or diluted to a stable 5- to 10-percent
solution. Stable solutions are prepared by direct
addition of low hardness water and mild agitation. Air
agitation is not recommended.
5.2.4.5 Piping and Accessories
Piping requirements are the same as previously
indicated for solutions of dry sodium aluminate.
5.2.4.6 Pacing and Control
System pacing and control requirements are the
same as described for liquid alum.
5.2.5 Aluminum Chloride
Aluminum chloride is available in the Chesapeake Bay
area from the supplier listed in Table 5-8.
Much of the aluminum chloride produced is in the
form of semi-pure anhydrous crystals with an off-
white color. This product is derived from direct
chlorination of scrap aluminum and has a molecular
weight of 133.3 and purities near 99 percent. In some
instances, purities may drop to 96 percent, which is
76
-------
Table 5-8. Aluminum Chloride Supplier to the Chesapeake Bay Area
Name Address Telephone
1986 Price Quotations*
Pearsall Chemical
Div. of Witco Corp.
P. O. Box 42817
Houston, TX 77242
(800)231-3452 Bulk:
40,000 Ib - $0.48/lb delivered
50-lb bags:
< 100 bags-$0.61/Ib
100-479 bags - $0.60/lb
FOB Philipsburg, NJ
>479 bags - $0.59/lb delivered
* Call for applicable freight charges, if any. Generally, prices include freight up to varying distances from the point of manufacture.
satisfactory for wastewater treatment if analysis
shows other compounds present are acceptable.
Another solid form is produced by crystallization from
hydrochloric acid in the form of a hexahydrate, in
which six molecules of water attach to each molecule
of aluminum chloride.
Containers for shipping and storing should be similar
to those used for dry and liquid alum. Handling and
feeding requirements are also similar to those used
with alum. Designers should check with local
producers for further details.
5.3 Iron Compounds
The principal iron compounds that are commercially
available and suitable for phosphorus precipitation
are liquid ferric chloride, ferrous chloride (waste pickle
liquor), ferric sulfate, and ferrous sulfate.
5.3.7 Liquid Ferric Chloride
5.3.1.1 Properties and Availability
Liquid ferric chloride is a corrosive, dark brown, oily-
appearing solution having a typical unit weight
between 1.3 and 1.5 kg/I (11.2 and 12.4 Ib/gal), or 35
to 45 percent FeCla. The ferric chloride content of
these solutions is 0.47 to 0.67 kg/I (3.95 to 5.58
Ib/gal). Shipping concentrations vary from summer to
winter due to the relatively high crystallization
temperature of the more concentrated solutions as
shown in Figure 5-5. The pH of a 1-percent
solution is 2.0.
The molecular weight of ferric chloride is 162.22.
Viscosities of ferric chloride solutions at various
temperatures are presented in Figure 5-6.
Liquid ferric chloride is shipped in 11,400- to
15,100-1 (3000- to 4,000-ga!) bulk truckload lots.
Information on suppliers of liquid ferric chloride to the
Chesapeake Bay area are provided in Table 5-9.
Tank trucks are normally unloaded pneumatically, and
operating procedures must be closely followed to
avoid spills and accidents. The safety vent cap and
assembly (painted red) should be removed prior to
Figure 5-5. Freezing point curve for commercial ferric
chloride solutions.
Temperature, °F
80 i—
60
40
20
-20
Water Utility Grade
-40
I
J
20 30 40
Percent by Weight in Water
50
opening the unloading connection to depressurize the
tank truck.
5.3.1.2 General Design Consideration
Ferric chloride solutions are corrosive to many
common materials and cause stains that are difficult
to remove. Areas subject to staining should be
protected with resistant paint or rubber mats.
Normal precautions should be employed when
cleaning ferric chloride handling equipment. Workmen
should wear rubber gloves, a rubber apron,, and
goggles or a face shield. If ferric chloride comes in
contact with the eyes or skin, flush with copious
quantities of running water and call a physician. If
ferric chloride is ingested, induce vomiting and call a
physician.
5.3.1.3 Storage
Ferric chloride solution can be stored as shipped.
Storage tanks should have a free vent or vacuum
relief valve. Tanks may be constructed of FRP,
77
-------
Figure 5-6. Viscosity vs. composition of ferric chloride solutions at various temperatures.
100i
80
60
50
40
30
20
| 15
« 10
> 8
I 6
£
1
(Absolute Viscosity) = (Kinematic Viscosity) x (Density)
Centipoises = Centistokes x Gm/cc
I^.-*T
10
20
30
i, percent
40
50
Table 5-9. Liquid Ferric Chloride Suppliers to the Chesapeake Bay Area
Name Address Telephone
1986 Price Quotations"
Mantoy-Rogan Chemicals
Coyne Chemicals
East Emmaus Street
P. O. Box 391
Middletown, PA 17057
3015 State Road
Croyden, PA 19020
(717)994-7471 $235/ton
A 4,600-gal tank truck contains 17,204
Ib of Fe3 + (@ 3.74 Ib/gal). Tank Truck is,
therefore, $235/ton x 8.6 tons * 4,600
gal = $0.44/gal.
(215) 785-3000 32-percent Fea+ - $222/dry ton.
Call for applicable freight charges, if any. Generally, prices include freight up to varying distances from the point of manufacture.
rubber-lined steel, or plastic-lined steel. Resin
impregnated carbon or graphite are also suitable
materials for storage containers.
It may be necessary in most instances to house liquid
ferric chloride tanks in heated areas or provide tank
heaters or insulation to prevent crystallization. Ferric
chloride can be stored for long periods of time without
deterioration. The total storage capacity should be
1-1/2 times the largest anticipated shipment and
should provide at least a 10-day to 2-week supply
of the chemical at the design average dose.
78
-------
15.3.1.4 Feeding Equipment
Feeding equipment and systems described for liquid
alum generally apply to ferric chloride except for
materials of construction and the use of glass tube
rotameters.
It may not be desirable to dilute the ferric chloride
solution from its shipping concentration to a weaker
feed solution because of possible hydrolysis. Ferric
chloride solutions may be transferred from
underground storage to day tanks with impervious
graphite or rubber-lined, self-priming centrifugal
pumps having Teflon rotary and stationary seals.
Because of a tendency for liquid ferric chloride to
stain or deposit, glass tube rotameters should not be
used for metering this solution. Rotodip feeders and
diaphragm metering pumps are often used for ferric
chloride and should be constructed of materials such
as rubber-lined steel and plastics.
5.3.1.5 Piping and Accessories
Materials for piping and transporting ferric chloride
should be rubber or Saran-lined steel, hard rubber,
FRP, or plastics. Valving should consist of rubber-
or resin-lined diaphragm valves, Saran-lined valves
with Teflon diaphragms, rubber sleeved pinch-type
valves, or plastic ball valves. Gasket material for large
openings such as manholes in storage tanks should
be soft rubber; all other gaskets should be graphite-
impregnated blue asbestos, Teflon, or vinyl.
5.3.1.6 Pacing and Control
System pacing and control requirements are similar to
those discussed previously for liquid alum.
5.3.2 Ferrous Chloride (Waste Pickle Liquor)
5.3.2.1 Properties and Availability
Ferrous chloride, FeCIa, is available as a liquid in the
form of waste pickle liquor from steel processing. The
liquor weighs between 1.2 and 1.3 kg/I (9.9 and 10.4
Ib/gal) and contains 20 to 25 percent ferrous chloride
or about 10 percent available iron. A 22-percent
solution of ferrous chloride will crystallize at a
temperature of -4°F. The molecular weight of
ferrous chloride is 126.76. Free acid in waste pickle
liquor can vary from 1 to 10 percent and usually
averages about 1.0 to 1.5 percent. Ferrous chloride is
slightly less corrosive than ferric chloride.
Ferrous chloride is available in the Chesapeake Bay
area in 15,100-1 (4000-gal) truckload lots from the
supplier listed in Table 5-10.
5.3.2.2 General Design Considerations
Since ferrous chloride or waste pickle liquor may not
be available on a continuous basis, storage and
feeding equipment should be suitable for handling
ferric chloride. Therefore, the ferric chloride section
should be referred to for storage and handling details.
5.3.3 Ferric Sulfate
5.3.3.1 Properties and Availability
Ferric sulfate, Fe2(SO4)3«H2O, is marketed as a dry,
partially hydrated product with seven water
molecules. Typical properties are presented in Table
5-11.
Ferric sulfate is typically shipped in 45-kg (100-lb)
moisture-proof paper bags. Ferric sulfate is available
in the Cheapeake Bay area from the suppliers given
in Table 5-12.
General precautions should be observed when
handling ferric sulfate, such as wearing goggles and
dust masks, and areas of the body that come in
contact with the dust or vapor should be washed
promptly.
5.3.3.2 General Design Considerations
Aeration of ferric sulfate should be held to a minimum
because of the hygroscopic nature of the material,
particularly in damp atmosperes. Mixing of ferric
sulfate and quicklime in conveying and dust vent
systems should be avoided as caking and excessive
heating can result. The presence of ferric sulfate and
lime in combination has been known to destroy cloth
bags in pneumatic unloading devices. Because ferric
sulfate in the presence of moisture will stain,
precautions similar to those discussed for ferric
chloride should be observed.
5.3.3.3 Storage
Ferric sulfate is usually stored in the dry state in the
shipping bags.
5.3.3.4 Feeding Equipment
Feed solutions are usually made up at a water-to-
chemica! ratio of 2:1 to 8:1 (on a weight basis) with
the usual ratio being 4:1 with a 20-minute detention
time. Care must be taken not to dilute ferric sulfate
solutions to less than 1 percent to prevent hydrolysis
and deposition of ferric hydroxide. Ferric sulfate is
actively corrosive in solution, and dissolving and
transporting equipment should be fabricated of type
316 stainless steel, rubber, plastics, ceramics, or
lead.
Dry feeding requirements are similar to those for dry
alum except that belt feeders are rarely used because
of their open-type construction. Closed construction,
as found in the volumetric and loss-in-weight type
feeders, generally exposes a minimum of operating
components to the vapor and thereby minimizes
maintenance. A water jet vapor remover should be
provided at the dissolver to protect both the
machinery and operator.
79
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Table 5-10. Ferrous Chloride Supplier to the Chesapeake Bay Area
Address Telephone
1986 Price Quotations
Byproducts Management
1150 Junction
Schereville, IN 46375
(219)322-2560 $0.26/lb of Fe2 + = $0.31/gal
4,800-gal truck = 48,000 Ib/truck @ 12
percent Fe2 + == 5,760 IbFe2*/truck =
$l,500/truck.
Prices include delivery to Chesapeake
Bay area.
Table 5-11. Properties of Ferric Sulfate
Molecular Weight
Bu!k Density, Ib/cu ft
Water Soluble Iron as Fe3+. percent
Water Soluble Fe3 +, percent
Insdubtes Total, percent
Free Acid, percent
Moisture © 105°C, percent
526
56-60
21.5
19.5
2.0
2.5
2.0
5.3.3.5 Pipe and Accessories
Piping systems for ferric sulfate should be FRP,
plastics, type 316 stainless steel, rubber, glass, or
ceramics.
5.3.4.2 General Design Considerations
The granular form of ferrrous sulfate has the best
feeding characteristics, and gravimetric or volumetric
feeding equipment may be used.
The optimum chemical-to-water ratio for
continuous dissolving is 0.06 kg/I (0.5 Ib/gal), or a 65-
percent solution with a detention time of 5 minutes in
the dissolving tank. Mechanical agitation should be
provided in the dissolver to assure complete solution.
Lead, rubber, iron, plastics, and type 304 stainless
steel can be used as construction materials for
handling solutions of ferrous sulfate.
Storage, feeding, and transporting systems probably
should be suitable for handling ferric sulfate as an
alternative to ferrous sulfate.
5.3.3.6 Pacing and Control
System pacing and control
discussed for dry alum.
5.3.4 Ferrous Sulfate
5.3.4.1 Properties and Availability
Ferrous sulfate or copperas is a byproduct of steel
pickling and is produced as granules, crystals,
powder, and lumps. The most common commercial
form of ferrous sulfate is FeSO4»7H20 with a
molecular weight of 278 and containing 55 to 58
percent FeSO4 and 20 to 21 percent Fe. The product
has a bulk density of 990 to 1,060 kg/m3 (62 to 66
Ib/cu ft). When dissolved, ferrous sulfate is acidic.
The composition of ferrous sulfate may be quite
variable and should be established by consulting the
nearest manufacturers.
Ferrous sulfate is available in bags and in the
Chesapeake Bay area in 18,200-1 (4,800-gal)
truckload lots from the supplier given in Table 5-13.
Dry ferrous sulfate cakes at storage temperatures
above 68° F, is efflorescent in dry air, and oxidizes
and hydrates further in moist air.
General precautions similar to those for ferric sulfate
with respect to dust and handling acidic solutions
should be observed when working with ferrous
'sulfate. Mixing quicklime and ferrous sulfate produces
high temperatures and the possibility of fire.
are the same as 5.4 Polyelectrolytes
5.4.1 Dry Polymers
5.4.1.1 Properties and Availability
Types of polymers vary widely in characteristics.
Manufacturers should be consulted for properties,
availability, and cost of the polymer being considered.
Some polymer suppliers available to the Chesapeake
Bay area are given in Table 5-14.
5.4.1.2 General Design Considerations
Dry polymer and water must be blended and mixed to
obtain a recommended solution for efficient action.
Solution concentrations vary from a fraction of a
percent to 1 percent or more. Preparation of the
stock solution involves wetting of the dry material
and usually an aging period prior to application.
Solutions can be very viscous, and close attention
should be paid to piping size and length and pump
selections. Metered solution is usually diluted just
prior to injection into the process to obtain better
dispersion at the point of application.
5.4.1.3 Storage
General practice for storage of bagged dry chemicals
should be observed. The bags should be stored in a
dry, cool, low humidity area and used in proper
rotation, i.e., first in, first out. Solutions are generally
stored in type 316 stainless steel, FRP, or plastic-
lined tanks.
80
-------
Table 5-12. Ferric Suifate Suppliers to the Chesapeake Bay Area
Name Address Telephone
1986 Price Quotations*
Manley-Regan Chemicals
Coyne Chemicals
East Emmaus Street
P. O. Box 391
Middletown, PA 17057
3015 State Road
Croydon, PA 19020
(717) 994-7471
(215)785-3000
100-lb bags:
20 bags - $15.30/100 Ib
60 bags-$14.05/100 Ib
100 bags - $13.55/100 Ib
$19.75/100 Ib
* Call for applicable freight charges, if any. Generally, prices include freight up to varying distances from the point of manufacture.
Table 5-13. Ferrous Suifate Supplier to the Chesapeake Bay Area
Name Address Telephone
1986 Price Quotations
Byproducts Management
1150 Junction
Schereville, IN 46375
(219) 322-2560 $0.3l/lb of Fe2 + = $0.20/gal
4,800-gal truck = 48,000 Ib/truck @ 6.5
percent Fe2* = 3,120 Ib Pe2*/truck =
$970Aruck.
Prices include delivery to Chesapeake
Bay area
Table 5-14. Polymer Suppliers to the Chesapeake Bay Area
Name
Pollu-Tech
Nalco
Hercules
Calgon
American Cyanimid
Dow
DuBois Chemicals
Div. W. R. Grace and Co.
Address
853 2nd Street Pike
Brownstone 2
Suite B-200
Richboro, PA 18954
2901 Butterfield
Oakbrook, IL 60521
910 Market Street
Wilmington, DE 19899
P. O. Box 1346
Pittsburgh, PA 15230
Berdan Avenue
Wayne, NJ 07470
1603 Santa Rosa Road
Richmond, VA 23288
3630 E. Kemper Road
Sharonville, OH 45241
Telephone
(215)357-1821
(312) 887-7500
(302) 575-6500
(412) 777-8000
(201)831-2000
(904) 288-1601
(513) 762-6000
1986 Price Quotations
Prices vary widely depending on the
nature of the product and amount required.
Prices typically range from $1.00 to
$3.00/lb. Call for freight charges.
5.4.1.4 Feeding Equipment
Two types of systems are frequently combined to
feed polymers. The solution preparation system
includes a manual or automatic blending system with
the polymer dispensed by hand or by a dry feeder to
a wetting jet and then to a mixing-aging tank at a
controlled ratio. The aged polymer is transported to a
holding tank where metering pumps or rotodip
feeders dispense the polymer to the process. A
schematic of such a system is shown in Figure 5-7.
It is generally advisable to keep the holding or storage
time of polymer solutions to a minimum, 1 to 3 days
or less, to prevent deterioration of the product.
5.4.1.5 Piping and Accessories
Selection must be made after determination of the
polymer; however, type 316 stainless steel or plastics
are generally used.
5.4.1.6 Pacing and Control
Controls as described for liquid alum apply to the
control of dispensing feeders for polymer solutions.
The solution preparation system may be an automatic
batching system, as illustrated by the schematic in
Figure 5-8, that fills the holding tank with aged
polymer as required by level probes. Such a system
is usually provided only at large plants. Unitized
solution preparation units are available, but have a
limited capacity.
5.4.2 Liquid Polymers
5.4.2.1 Properties and Availability
As with dry polymers, a wide variety of products
exists and manufacturers should be consulted for
specific information. See Table 5-14 for Chesapeake
Bay area suppliers.
81
-------
Figure 5-7. Manual dry polymer feed system.
Hose
Eductor
1
Y
1
ft"
ii
1 1
!!>
n
n
n
n
/
\
\
Scale
Relief
Valve
Point of
Application
Metering
Backpressure
Valve
Figure 5-8. Automatic dry polymer feed system.
Solenoid
Valve
Hot
Water
Pressure
Regulator
Dispenser
Control
Valve
Point of
Application
Solution
Feeders
Transfer Pumpl I
T'
Mixing-Aging
Tank
Level
Probe
Holding
Tank
82
-------
5.4.2.2 General Design Considerations
Liquid systems differ from the dry systems only in the
equipment to blend the polymer with water to prepare
the solution. Liquid solution preparation is usually a
hand-batching operation with manual filling of a
mixing-aging tank with water and polymer.
5.4.2.3 Feeding Equipment
Liquid polymers need no aging, and simple dilution is
the only requirement for feeding. The dosage of liquid
polymers may be accurately controlled by metering
pumps or rotodip feeders.
The remainder of the feed system is generally the
same as described for dry polymers.
5.5 Design of Chemical Feed Systems
5.5.1 Chemical Feed Systems
Chemical feed systems must be flexibly designed to
provide for a high degree of reliability in view of the
many contingencies that may affect their operation.
Thorough wastewater characterization in terms of flow
extremes and chemical requirements should precede
the design of the chemical feed system. The design
of the chemical feed system must take into account
the form of each chemical desired for feeding, the
particular physical and chemical characteristics of the
chemical, maximum waste flows, and the operational
reliability of the feeding devices.
The capacity of a chemical feed system is an
important consideration in both storage and feeding.
Storage capacity design must take into account the
advantage of quantity purchase vs. the disadvantage
of construction cost and chemical deterioration with
time. Potential delivery delays and chemical use rates
are necessary factors in the total picture. Storage
tanks or bins for solid chemicals must be designed
with proper consideration of the angle of repose of
the chemical and its necessary environmental
requirements, such as temperature and humidity. Size
and slope of feeding lines are important along with
their materials of construction with respect to the
corrosiveness of the chemicals.
5.5.2 Chemical Feeders
The chemicals added to wastewater to remove
phosphorus are either in liquid or solid form: Those in
solid form are usually converted to solution or slurry
form prior to introduction into the wastewater stream;
however, some chemicals are fed in a dry form. In
either case, some type of solids feeder is usually
required. Chemical feeders are available in a variety
of types because of wide ranges in chemical
characteristics, feed rates, and degree of accuracy
required. Liquid feeding is somewhat more restrictive,
depending mainly on liquid volume and viscosity.
Chemical feeders must accommodate the minimum
and maximum feeding rates required. Manually
controlled feeders typically have a range of 20:1, but
this range can be increased to about 100:1 with dual
control systems. Chemical feeder control can be
manual, automatically proportioned to flow, dependent
on some form of process feedback, or a combination
of any two of these. More sophisticated control
systems are feasible if proper sensors are available. If
manual control systems are specified with the
possibility of future automation, the feeders selected
should be amenable to this conversion with a
minimum of expense. An example would be a feeder
with an external motor that could easily be replaced
with a variable speed motor or drive when automation
is installed. Standby or backup units should be
included for each type of feeder used. Reliability
calculations will be necessary in larger plants with a
greater multiplicity of these units. Points of chemical
addition and piping to them should be capable of
handling all possible changes in dosing patterns to
provide proper flexibility of operation. Designed
flexibility in hoppers, tanks, chemical feeders, and
solution lines is the key to maximum benefits at least
cost.
5.5.2.1 Liquid Feeders
Liquid feeders are generally furnished in the form of
metering pumps or orifices. Usually these metering
pumps are of the positive displacement variety,
plunger type, or diaphragm type. The choice of liquid
feeder is highly dependent on the viscosity,
corrosivity, solubility, suction and discharge heads,
and internal pressure-relief requirements. Some
examples are shown in Figures 5-9 and 5-10. In
some cases, control valves and rotameters may be all
that is required. In other cases, such as polymer
feeding, progressive cavity pumps are used with
appropriate controls. More complete descriptions of
liquid feeder requirements can be found in the
literature and in manufacturer's catalogs.
5.5.2.2 Dry Feeders
Solids characteristics vary greatly, and the choice of
feeder must be considered carefully, particularly in
the smaller-sized facility where a single feeder may
be used for more than one chemical. Generally,
provisions should be made to keep all chemicals cool
and dry. Dryness is very important, as hygroscopic
(water absorbing) chemicals may become lumpy,
viscous, or even rock hard; other chemicals with less
affinity for water may become sticky from moisture on
the paniculate surfaces, causing increased arching in
hoppers. In either case, moisture will affect the
density of the chemical and may result in under-
feed. Dust removal equipment should be used at
shoveling locations, bucket elevators, hoppers, and
feeders for neatness, corrosion prevention, and safety
reasons. Collected chemical dust may often be
reused.
The simplest method for feeding solid chemicals is by
hand. Chemicals may be preweighed or simply
83
-------
Figure 5-9. Plunger-type metering pump (courtesy of Wallace & Tiernan).
Discharge Valve
Plunger
Suction Valve
Figure 5-10. Diaphragm-type metering pump (courtesy of Wallace & Tiernan).
Rale ol Feed Indicator
Anti-Syphon Valve
4
Discharge Valve
Diaphrag
Head and Front Cover
•
Suction Valve
Reservoir Chamber
Return Spring
Stroke-Adjustment Shalt
Ball Bearing
Push Rod
Eccentric Needling
Bearing
Ball Bearing
Aluminum Housing
Input Shaft and Worm
Fiber Glass Base
Gear Driven
Oil Pump
84
-------
shoveled or poured by the bagful into a dissolving
tank. This method is limited to very small wastewater
plants, or to chemicals used in very weak solutions.
Also, dry chemicals can be drawn into the dissolving
tank by means of an eductor.
Because of the many factors, such as moisture
content, grades, and compressibility, that can affect
chemical density (weight-to-volume ratio),
volumetric feeding of solids is normally restricted to
smaller wastewater plants, specific types of chemicals
that are reliably constant in composition, and low
rates of feed. Within these restrictions, several
volumetric types are available. Accuracy of feed is
usually limited to plus or minus 2 percent by weight,
but may be as high as plus or minus 5 percent.
One type of volumetric dry feeder uses a continuous
belt of specific width moving from under the hopper
to the dissolving tank. A mechanical gate mechanism
regulates the depth of material on the belt, and the
rate of feed is governed by the speed of the belt
and/or the height of the gate opening. The hopper
normally is equipped with a vibratory mechanism to
reduce arching. This type of feeder is not suited for
easily fluidized chemicals.
Another type employs a screw or helix from the
bottom of the hopper through a tube opening slightly
larger than the diameter of the screw or helix. Rate of
feed is governed by the speed of the screw or helix
rotation. Some screw-type designs are self-
cleaning, while others are subject to clogging. A
typical screw feeder is shown in Figure 5-11.
Most remaining types of volumetric feeders generally
fall into the positive displacement category. All
designs incorporate some form of moving cavity of'a
specific or variable size. In operation, the chemical
falls by gravity into the cavity and is more or less fully
enclosed and separated from the hopper's feed. The
size of the cavity and the rate at which the cavity
moves and is discharged govern the amount of
material fed. One unique design is the progressive
cavity metering pump, a non-reciprocating type.
Positive displacement feeders often utilize air injection
to enhance flowability of the chemical.
The basic drawback of volumetric feeder design, its
inability to compensate for changes in the density of
materials, can be overcome by including a gravimetric
or loss-in-weight controller. This modification
allows for weighing of the chemical as it is fed. The
beam balance type, shown in Figure 5-12, measures
the actual mass of chemical. This is considerably
more accurate, particularly over a long period of time,
than the less common spring-loaded gravimetric
designs. Gravimetric feeders are used where feed
accuracy of about plus or minus 1 percent is required
for economy (as in large-scale operations) or when
chemicals are used in small, precise quantities. It
should be noted, however, that even gravimetric
feeders cannot compensate for weight added to the
chemical by excess moisture. Many volumetric
feeders can be converted to a loss-in-weight
function by placing the entire feeder on a platform
scale .that is tared to neutralize the weight of the
feeder.
Good housekeeping and the need for accurate feed
rates dictate that the gravimetric feeder be shut down
and thoroughly cleaned on a regular basis. Although
many of these feeders have automatic or semi-
automatic devices that compensate to some degree
for accumulated solids on the weighing mechanism,
accuracy is affected, particularly on humid days when
hygroscopic chemicals are fed. In some cases, built-
up chemicals can actually jam the equipment.
5.5.2.3 Dissoivers
Most feeders, regardless of type, discharge their
material to a small dissolving tank that is equipped
with a nozzle system and/or mechanical agitator
depending on the solubility of the chemical being fed.
Solid chemicals, such as polymers, can be carefully
spread into a vortex spray or washdown jet of water
immediately before entering the dissolver. It is
essential that the surface of each particle become
thoroughly wetted before entering the feed tank to
ensure accurate dispersal and to avoid clumping,
settling, or floating.
A dissolver for a dry chemical feeder is unlike a
chemical feeding mechanism, which by simple
adjustment and change of speed can vary its output
tenfold. The dissolver must be designed for the job to
be done. A dissolver suitable for a rate of 4.5 kg (10
lb)/hr may not be suitable for dissolving at a rate of 45
kg (100 lb)/hr. As a general rule, dissolvers may be
oversized, but dissolvers for commercial ferric sulfate
do not perform well if greatly oversized due to a
hydrolysis reaction with water.
It is essential that specifications for dry chemical
feeders include specifications on dissolver capacity. A
number of factors need to be considered in designing
dissolvers of proper capacity. These include detention
times and water requirements, as well as other
factors specific to individual chemicals.
The capacity of a dissolver is based on detention
time, which is directly related to the wettability (or rate
of solution) of the chemical. Therefore, the dissolver
must be large enough to provide the necessary
detention for both the chemical and the water at the
maximum rate of feed. At lower rates of feed, the
strength of solution or suspension leaving the
dissolver will be less, but the detention time will be
approximately the same unless the water supply to
the dissolver is reduced. When the water supply to
any dissolver is controlled for the purpose of forming
a constant strength solution, mixing within the
85
-------
Figure 5-11. Screw feeder (courtesy of Wallace & Tiernan).
Control Box
Motor
Optional
Hopper
Hopper Agitating Plate
Goar Reducer
Agitator
Rotating Feed Screw
Optional Feeder
Downspout and Tank
dissolver must be accomplished by mechanical
means because sufficient power will not be available
from the mixing jets at low rates of flow. Hot water
dissolvers are also available to minimize the required
tankage.
5.5.2.4 Chemical Feeders Summary
The foregoing descriptions give some indication of
the wide variety of materials that may be handled.
Because of this variety, a facility may contain any
number of different types of feeders with combined or
multiple materials capability. Ancillary equipment to
the feeder also varies according to the material to be
handled. Liquid feeders encompass a limited number
of design principles that account for density and
viscosity ranges. Solids feeders, relatively speaking,
vary considerably due to the wide range of physical
and chemical characteristics, feed rates, and the
degree of precision and repeatability required. Table
5-15 describes several types of chemical feeders
commonly used in wastewater treatment.
5.5.3 Sizing Chemical Feed System Components
Components of the chemical feed system must be
sized so that chemicals can be applied at the required
rates and so that manpower required to receive,
transfer, and mix chemicals is kept to a minimum.
The chemical feed system consists of storage tanks
or bins, day tanks or hoppers, liquid or dry feeders,
and the necessary transfer systems.
Chemical storage facilities are sized so that a
capacity equal to approximately 30 days of storage is
available at average chemical rates of application.
Chapter 4 provides details on chemical usage rate
calculations. Bulk facilities for smaller plants must
have a capacity great enough to hold 1-1/2 times
the minimum shipment of chemical.
At smaller wastewater plants where chemicals are
mixed in a batch, or with polymer systems, day tanks
are normally provided. Day tanks act as aging vessels
for polymer systems and allow the operator to visually
judge the amount of chemical fed during a shift or
24-hour period. Day tanks are typically sized to hold
a 24-hour supply of chemical at the maximum rate
of chemical application.
At larger wastewater plants where dry chemicals can
be stored in bulk, hoppers are usually located above
86
-------
Figure 5-12. Beam balance-type gravimetric feeder (courtesy of Wallace & Tiernan).
Vertical Gate
Flexures
Traction
Roll
Weighbelt
i^ Counter
Weights »iBeam
Idler Roll-' / ,*
-**, | £^3
"^^••4 ~--J
the dry chemical feeders to provide a continuous
supply of chemical to the feeder. The chemical
hopper is generally a part of the bulk storage bin. If
the bulk storage bin cannot be located above the dry
chemical feeders, it may be necessary to provide a
day hopper with a pneumatic conveying system to
transfer dry chemical from bulk storage to the day
hopper. The day hopper should be large enough to
hold a minimum of 8 hours of chemical at maximum
feed rates. A 24-hour capacity at the rate of
maximum supply is preferable. Smaller dry feeders
and dissolvers typically have integral hoppers large
enough to hold 1-1/2 bags of chemical.
Both liquid and dry feeders must be sized so that
they are capable of delivering both the maximum and
minimum chemical dosages. In some cases, it may
be necessary to provide multiple pumps or feeders to
span the required chemical feed rates.
5.5.4 Optimum Feed Points and Feed Point
Flexibility
Phosphorus removal chemicals can be added at
many different points in the wastewater treatment
process. It is best to design feed point flexibility into
the chemical feed system. Provisions should be made
to feed chemicals ahead of primary clarification as
well as ahead of secondary clarification. With the
required pipework in place, the necessary feed point
or combination of feed points can be used to attain
the desired level of treatment in the most efficient
manner.
Addition of metal salts ahead of primary clarification
typically results in a greater usage of chemical than
would be the case if added ahead of or to the
secondary system. Suspended solids and BOD
reduction in primary clarification are enhanced with
the addition of metal salts. This enhanced
performance leads to the production of greater
volumes of primary sludge, but also improves the
treatment process efficiency by reducing the load to
the secondary system.
Metal salts added ahead of or to the secondary
system can be utilized more efficiently, particularly
with the activated sludge process. With addition
ahead of or to the secondary system, final clarifier
performance is improved and, in the case of the
activated sludge process, a large fraction of the metal
salt is returned to the head of the aeration tank with
the return sludge. See Chapter 2 for a more detailed
discussion of chemical feed application points.
5.5.5 Room Layouts for Chemical Storage,
Preparation, and Pumping
Typical room layouts for storage, solution preparation,
and pumping of ferric chloride and polymer are
87
-------
Table 5-15. Types of Chemical Feeders
Type of Feeder
Limitations
Use
Capacity
Range
D»y Feeder:
Volumetric
Oscillating plate
Oscillating throat (universal)
Rotating disc
Rotating cylinder (star) -
Screw
Ribbon
Belt
Gravimetric
Continuous-belt and scale
Loss in weight
Solution Feeder.
Nonoositive Displacement
Decanter (lowering pipe)
Orifice
Rotameter (calibrated valve)
Positive Displacement
Rotating dipper
Proportioning Pump
Diaphragm
Piston
Any material, granules or powder.
Any material, any particle size.
Most materials including NaF, granules, or powder
Any material;, granules or powder.
Dry, free-flowing material, powder or granular.
Dry, free-flowing material, powder, granular, or lumps.
Dry, free-flowing material up to 1.5-in size, powder or
granular.
Dry, free-flowing, granular material or floodable material.
Most materials, powder, granular, or lumps.
Most solutions or light slurries.
Most solutions.
Clear solutions.
Loss in weight (tank control valve) Most solutions.
Most solutions or slurries.
Most solutions, special unit for 5-percent slurries.*
Most solutions, light slurries.
cu ft/hr
0.01 - 35
0.002 -100
0.01 - 1.0
8 - 2,000
or
7.2 - 300
0.05 - 18
0.002-0.16
0.1 - 3,000
0.02 to 2
0.02 to 80
0.01 to 10
0.16 to 5
0.005 to 0.16
or
0.01 to 20
0.002 to 0.20
0.1 to 30
0.00+to 0.15
0.01 to 170
40 to 1
40101
20101
10101
or
100 to 1
20101
10 to 1
10101
or
100 to 1
100 to 1
100 to1
100 to 1
10 to 1
10to1
30to1
100 to 1
100 to 1
20to1
" Uses special heads and valves for slurries.
presented in Figures 5-13 through 5-22. The
figures cover the range of 0.004 to 0.44 m3/s (0.1 to
10 mgd); 6 to 10 mg/l and 3 to 6 mg/l influent TP; and
0.2, 0.5, 1.0, and 2.0 mg/l effluent TP. These layouts
are suitable for conceptual design applications and
observe all regulatory requirements.
(Note: For alum, the storage volume requirements are
approximately 50 percent more than for ferric
chloride. However, due to standard storage tank
sizes, this does not always translate into larger tank
requirements. Also, an anti-siphon leg should be
installed downstream of the feed pump for alum or
ferric chloride when the application point is below the
level of the day tank.)
As indicated previously in Chapter 2, a theoretical
model being developed from research currently in
progress (1,2) predicts that metal ion dose
requirements to attain low effluent TP concentrations
of <1 mg/l are independent of influent TP
concentration. Published data confirming this model
are lacking at this time. In the absence of such data,
the room layouts in Figures 5-13 through 5-22
were developed on the basis of conventional metal
ion-to-influent TP dose relationships for all four
effluent TP limitations considered in this document. If
the above theory (1,2) is eventually verified, separate
room layouts would not be appropriate for the 0.5-
and 0.2-mg/l TP effluent limits. Accordingly, a
portion of Figure 5-13 (0.2-mg/l effluent TP limit at
influent TP of 3-6 mg/l and plant flow of 1 mgd)
would become identical to Figure 5-15 (0.2-mg/l
effluent TP limit at influent TP of 6-10 mg/l and plant
flow of 1 mgd). Similarly, Figure 5-16 (0.5-mg/l
effluent TP limit at influent TP of 3-6 mg/l and plant
flow of 5 mgd) would become identical to Figure 5-
19 (0.5-mg/l effluent TP limit at influent TP of 6-10
mg/l and plant flow of 5 mgd).
5.6 Chemical Equipment Suppliers
The various manufacturers and local Chesapeake Bay
Area representatives of chemical feed equipment (dry
chemical feeders, chemical feed pumps, polymer
preparation systems, and chemical storage tanks) are
listed in Tables 5-16 through 5-19.
5.7 Staffing Requirements for Chemical
Addition
A treatment plant that is retrofitted to remove
phosphorus by chemical addition will require
additional man-hours to operate and maintain the
88
-------
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Table 5-16. Dry Chemical Feeder Suppliers
Name
Main Office
Chesapeake Bay Area Representative
BIF, a unit of General
Signal
1600 Division Road ,*
West Warwick, Rl 02893
(401)885-1000
Wallace & Tiernan Div.
Pennwalt Corp.
25 Main Street
Belleville, NJ 07109
(201) 759-8000
T. E. Byerly Co., Inc.
262 M Cedar Lane
Suite 5
Vienna, VA 22180
(703) 849-8170
Pyrz Water Supply Co., Inc.
P. O. Box 1271
43 Becker Road
North Wales, PA 19454
(215)699-9550
Tri-Star
300 Vine Street
P. O. Box 255
Middletown, PA 17057
(717)944-1234
Wallace & Tiernan
The Woods, Suite 511
985 Old Eagle School Road
Wayne, PA 19087
(215)687-4930
Wallace & Tiernan
Suite 210
11501 Georgia Road
Wheaton, MD 20902
(301)933-2110
chemical feed systems. Plants that use ferric chloride
rather than alum will require more man-hours due to
the corrosiveness of ferric chloride. The approximate
number of man-hours required per year to operate
and maintain chemical feed systems for different size
plants up to 0.44 m,3/s (10 mgd) are summarized in
Table 5-20.
5.8 Sludge Considerations
The application of metallic salts at various points in a
wastewater treatment plant creates new and
additional sludges. Depending on the point of
chemical addition, increased amounts of primary
and/or secondary sludges will be generated. The ratio
of primary to secondary sludge will be affected by
chemical usage. For example, if a mineral salt is
added to the primary settling tank, floe production and
solids capture will increase; since more primary
sludge will be produced, the primary sludge-to-
secondary sludge ratio will increase. The additional
solids loading resulting from chemical sludges must
be considered in the design of sludge handling and
treatment facilities. Metallic salts usage can result in
as much as a 200-percent increase in sludge solids
for disposal over that produced in strict biological
treatment, depending on dosage and feed points.
Sludges generated in wastewater treatment
processes to which phosphorus removal chemicals
are added may be handled and disposed of by any of
the conventional methods. However, sludge
conditioning characteristics will change according to
the chemical content of the sludge. The gelatinous
properties of aluminum hydroxide floe result in
somewhat lower filter yields when alum is present in a
sludge. A typical comparison is presented in Table
5-21, where total sludge production and filter yields
are given for a conventional activated sludge process
operating with a) no chemical treatment and b) alum
addition to the aeration tanks.
As shown in Table 5-21, the use of alum may result
in a 50-percent increase in sludge solids produced
per volume of wastewater treated. The use of ferric
chloride or other iron salts will result in a similar
increase in sludge solids as discussed in Chapter 3.
Dewaterability as measured by vacuum filter yield is
typically lower with alum sludge as compared to ferric
chloride sludge. Other data indicate no significant
handling or conditioning problems for sludges from
processes incorporating ferric chloride.
The handling of sludges containing products of
chemical coagulation poses no special problems. The
design engineer must be aware, however, of the
greater solids production that results from chemical
usage and the impact of the greater solids loading on
handling and conditioning unit processes. The varying
characteristics of the different chemical sludges also
are a factor in the design of conditioning equipment.
Laboratory filterability tests can be useful in this
respect.
99
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Table 5-17. Chemical Feed Pump Suppliers
Name Main Office
Chesapeake Bay Area Representative
BIF, a unit of General
Signal
1600 Division Road
West Warwick, Rl 02893
(401) 885-1000
Wallaco & Tiernan Div.
PonnwaH Corp,
25 Main Street
Belleville, NJ 07109
(201) 759-8000
Robbins & Meyers
409 Plymouth Road
Plymouth, Ml 48170
(313) 459-4336
Milton Roy Co,
Flow Control Division
203 Ivyland Road
Ivyland, PA 18974
(215)441-0800
T. E. Byerly Co., Inc.
262 M Cedar Lane
Suite 5
Vienna, VA 22180
(703)849-8170
Pyrz Water Supply Co., Inc.
P. O. Box 1271
43 Becker Road
North Wales, PA 19454
(215) 699-9550
Tri-Star
300 Vine Street
P. O. Box 25S
Middletown, PA 17057
(717)944-1234
Wallace & Tiernan
The Woods, Suite 511
985 Old Eagle School Road
Wayne, PA 19087
(215)687-4930
Wallace & Tiernan
Suite 210
11501 Georgia Road
Wheaton, MO 20902
(301)933-2110
Robbins & Meyers
102 North Main, Suite 101
Bell Aire, MD 21014-3542
(301)879-9566
Robbins & Meyers
108 WillowbrooK Lane
West Chester, PA 19382-5592
(215)693-2331
Geiger Pump
8851 Kelso Drive
Baltimore, MD 21221
(301)682-2600
Milton Roy Pumps
2500 Maryland Avenue
Willow Grove, PA 19090
(215)657-7770
5.9 Laboratory Requirements
The estimated sampling and analytical needs for
phosphorus removal by chemical addition to
mainstream processes are shown in Table 5-22.
5.10 Safety and OSHA Requirements for
Chemical Addition
5.10.1 Ferric Chloride
5.10.1.1 General
Common sense safety precautions should be
observed around storage tanks. Washing of
contaminated areas from spills that occur at delivery
time is recommended. Brown stains occur rapidly
following a spillage. Containment walls around the
tanks will confine the tank contents in case of
leakage. Containment areas should be kept clean and
dewatered at all times.
Ferric chloride is a reddish-brown solution varying in
strength from 35 to 45 percent, by weight, depending
on time of shipment. Precautions for handling the
chemical should be followed as given below. Water
hoses, emergency showers, and eye washes should
be located within 15 m (50 ft) of the ferric chloride
unloading station and storage tank(s) and near the
ferric chloride pumps.
The following discussion also applies to ferrous
chloride and ferrous sulfate.
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Table 5-18. Polymer Preparation Systems
Name
Main Office
Chesapeake Bay Area Representative
BIF, a unit of General
Signal
1600 Division Road
West Warwick, Rl 02893
(401)885-1000
Wallace & Tiernan Div.
Pennwalt Corp.
25 Main Street
Belleville, NJ 07109
(201)759-8000
Stranco "Polyblend"
P. O. Box 389
Bradley, IL 60915-0389
(815)932-8154
T. E. Byerly Co., Inc.
262 M Cedar Lane
Suite 5
Vienna, VA22180
(703) 849-8170
Pyrz Water Supply Co., Inc.
P. O. Box 1271
43 Becker Road
North Wales, PA 19454
(215)699-9550
Tri-Star
300 Vine Street
P. O. Box 255
Middletown, PA 17057
(717)944-1234
Wallace & Tiernan
The Woods, Suite 511
985 Old Eagle School Road
Wayne, PA 19087
(215)687-4930
Wallace & Tiernan
Suite 210
11501 Georgia Road
Wheaton, MD 20902
(301)933-2110
Heyward, Inc.
717 East Blvd.
Charlotte, NC 28203
(704) 372-5805
Riordan Materials Corp.
1413 Ormsby Place
Crofton, MD21114
(301)858-0609
Table 5-19. Chemical Storage Tanks
Name
Main Office
Chesapeake Bay Area Representative
Owens - Corning
Fiberglas
Fiberglas Tower
Toledo, OH 43659
(419) 248-7000
Process Equipment Corp.
500 Reed Street
fielding, Ml 48809
(616)794-1230
900 W. Valley Road
Suite 1101
Wayne, PA 19087
(215)688-9306
7501 Forbes Blvd.
Suite 102
Seabrook, MD 20770
(301)390-6900
Rodem, Inc.
5095 Crookshank Road
Cincinnati, OH 45238
(513) 922-6140
Whitney Packaging, Inc.
50 Kearny Road
Needham, MA 02194
(617)444-5050
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Table 5-20. Manpower Required to Operate and Maintain Chemical Feed Systems
Alum (man-hr/yr)
Plant Design
Flow (mgd)
< 0.1
0.1 - 1.0
1 -5
5-10
Operation
150 - 300
300 - 460
460-1,100
1,100-1,700
Maintenance
50 - 100
100 - 140
140 - 360
360 - 540
Total
200 - 400
400 - 600
600- 1,460
1,460-2,240
Operation
110 -220
220 - 320
320 - 800
800 - 1,200
Maintenance
35 - 70
70 - 100
100 - 250
250 - 380
Total
145 - 290
290 - 420
420 - 1,050
1,050 - 1,580
Table S-21. Comparison of Filter Yields With and Without
Alum Addition
Metal Salt
None
Alum
Dose
mg/l
-
150
Feed
Sludge
% solids
6.2
5.7
Sludge
Solids
Produced
tons/Mgal
0.8
1.2
Vacuum
Filter
Yield
Ib/hr/sq ft
5.2
4.6
5.10.1.2 Precautions for Handling Ferric Chloride.
1. Protective Equipment for Eyes. Wear suitable eye
protection such as chemical worker's goggles or
their equivalent. All emergency showers and eye
washes should be tested once a day.
2. Hazards to Eyes. Eyes contaminated with ferric
chloride may rapidly become irritated; prolonged or
permanent impairment of vision or even total loss
of sight may occur. Dilution of ferric cloride to 20
percent or less tends to reduce the intensity of
effect Tests indicate that such concentrations
may cause mild conjunctiva! irritation and possibly
some transient corneal injury.
3. First Aid for Eye Contact. In cases of splashes of
liquid ferric chloride into the eyes, flush
immediately and thoroughly with large amounts of
water for 20 to 30 minutes and then rinse with a
weak solution of sodium bicarbonate or boric acid.
Consult a physician, preferably an eye specialist,
immediately. Chemical burns to the eye must be
treated promptly. Repeatedly flooding the eye with
water within seconds after contact with a chemical
is the most effective way to prevent permanent
damage. In the opinion of medical experts, if a
victim can reach an eyewash station within 10 to
15 seconds, his chances of recovering with no
permanent damage to the eyes are excellent. After
15 seconds, the chances of recovery decline
rapidly.
4. Protective Equipment for Skin. Most people are
not sensitive to ferric chloride and need wear only
regular work clothing with whatever protection is
desired to minimize staining, e.g., rubber or plastic
sleeves, apron, and gloves. Since ferric chloride
deteriorates leather rapidly, people working with
ferric chloride should wear rubber shoes or regular
work shoes with rubber soles and heels and
waterproofed leather uppers.
5. Hazard to Skin. When in contact with the skin,
ferric chloride solution may cause blistering and
superficial burns unless washed off promptly.
Such contact will also stain the skin. Repeated
prolonged skin contact with strong solutions may
cause superficial burns, especially if confined to
the skin as might occur when contaminated
clothing or shoes are worn.
6. First Aid for Skin Contact. Remove contaminated
clothing and wash affected skin with soap and
plenty of water until the wash water is essentially
colorless. A physician should be consulted if any
irritation or injury to the skin develops.
7. Ingestion Hazard. If large amounts of ferric
chloride are swallowed, it may cause burns to the
mucous membranes and severe irritation of the
gastrointestinal tract.
8. First Aid for Ingestion. If large amounts of ferric
chloride are swallowed, a physician should be
called immediately. While the physician is on the
way, the patient should be induced to vomit.
9. Spills. Spills should be neutralized with caustic
soda or lime and the areas flushed with water.
Adequate diking and drainage should be provided
at unloading and storage areas to prevent spills or
leaks from harming surrounding equipment and
facilities. To prevent spills and splashing, tank cars
and trucks containing ferric chloride solution
should never be moved unless all openings are
secured and lines drained arid disconnected.
5.10.2 Polymer
There are so many types of polymers on the market
that the operator should obtain complete instructions
from the supplier as to the safe handling of the
particular brand product being used. Polymers can be
purchased in either liquid or dry powder form and in
various size containers.
In general, polymers are not considered to be toxic,
but it is well to avoid unnecessary contact with either
102
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Table 5-22. Estimated Sampling and Analytical Needs for Phosphorus Removal by Chemical Addition
Measurement Plant Size ^m9d^ Test Frecluency Location of Sample Method of Sample
pH
Alkalinity
TSS
TBOD
Jar Test
Total Solids
Total Solidsi
Flowi
Total R1.2
Prtho P1
All
All
All
All
All
> 1
< 1
All
All
All
1/day
2/week
1/day
1/day
Spot Check
1/week
3/week
Record Continuously
3/week
3/week
Clarifier Influent
Clarifier Effluent
Clarifier Influent
Plant Effluent
Clarifier Influent
Clarifier Effluent
Clarifier Influent
Clarifier Effluent
Clarifier Influent
Sludge Underflow
Sludge Underflow
Sludge Underflow
Clarifier Influent
Clarifier Effluent
Plant Effluent
Clarifier Influent
Plant Effluent
24-hr Composite
24-hr Composite
24 -hr Composite
24-hr Composite
24-hr Composite
Grab Composite
Grab Composite
Record Continuously
24-hr Composite
24-hr Composite
Reason for Test
Process Control
Recordkeeping/Permit
Compliance
Recordkeeping/Permit
Compliance
Process Control
Recordkeeping/Permit
Compliance
Process Control
Recordkeeping/Permit
Compliance
Process Control
Cost Control
Process Control
Process Control
Process Control
Process Control
Recordkeeping/Permit
Compliance
Process Control
Recordkeeping/Permit
Compliance
1 Suggested minimum.
2 Or as prescribed by permit
the powder or liquid. Goggles, gloves, and aprons
should be used to protect the skin and eyes. The use
of a face mask when handling the powder should be
required.
Anionic polyelectrolytes have a low acute oral toxicity.
Eye contact with either the undiluted or diluted
material may result in mild transistory irritation. The
materials are not irritating to the skin.
Polymers, when in solution, are highly viscous and,
therefore, very slippery and dangerous to foot traffic if
allowed to spill.
Handling polymers should cause no health problems
if reasonable care, good housekeeping, and personal
cleanliness are practiced to avoid skin and eye
contact.
5.70.3 OSHA Requirements
Detailed state OSHA requirements may vary between
the Chesapeake Bay area states. However, as a
minimum, the following guidelines are recommended.
1. Provide a water hose, eyewash, and shower within
15m (50 ft) of any hazardous chemical unloading,
storage, and feed area.
2. Provide a spill containment dike around each
storage tank. The dike containment volume should
be equal to at least 150 percent of the volume of
the storage tank.
3. Provide a means for removing water or chemicals
from within each containment dike.
4. Provide a 15-cm (6-in) high concrete curb
around all chemical feed areas for containment of
spillage.
5. Provide splash guards at all pumps.
6. Provide spray shields under all hazardous
chemical piping crossing walkways or passage
ways.
5.11 References
1. Personal communication from R.I. Sedlak, The
Soap and Detergent Association, New York, NY,
to R.C. Brenner, U.S. EPA, Cincinnati, OH, May
20, 1987.
2. Personal communication from D. Jenkins,
University of California, Berkeley, CA, to S.J.
Kang, McNamee, Porter and Seeley, Ann Arbor,
Ml, July 31, 1987.
103
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Chapter 6
Process and Hardware Design Considerations for
Retrofitting Activated Sludge Plants with Biological Phosphorus Removal
6.1 Introduction
As discussed in Chapters 2 and 3, two proprietary
processes are considered in this manual for
retrofitting selected suspended growth activated
sludge systems with biological phosphorus removal:
the PhoStrip process and the A/O (anaerobic/oxic)
process. Although the major mechanism for removing
phosphorus with these processes is biological, the
PhoStrip process employs a sidestream to chemically
precipitate biologically removed phosphorus, while the
A/O process is a mainstream process where
phosphorus is removed in the waste activated sludge.
Both processes can be retrofitted only to activated
sludge systems, including plug flow, complete mix,
contact stabilization, pure oxygen, step aeration,
extended aeration, and two-stage nitrification
configurations. Activated sludge is alternately cycled
through an anaerobic stage where phosphorus is
released and an aerobic stage where phosphorus-
stripped biomass takes up phosphorus at an
increased rate. Biological phosphorus removal is most
applicable for treatment of wastewaters with relatively
low (3-6 mg/l) influent TP concentrations. The
probability that chemical polishing will be required
becomes greater with higher influent TP
concentrations.
Activated sludge plants retrofitted with biological
phosphorus removal may experience improved
settling characteristics and suspended solids
removals resulting from the anaerobic/aerobic cycling
of activated sludge. Additional process design and
operating considerations are presented below for
each process.
6.2 PhoStrip Process
Retrofit with the PhoStrip process can be
accomplished for any of the commonly used activated
sludge flow regimes given an adequate site for
construction of a stripper tank, a precipitation tank or
reactor-clarifier for chemical precipitation, and lime
handling facilities. The PhoStrip process is owned and
marketed by Biospherics Incorporated, 4928
Wyaconda Rd.,
770-7700.
Rockville, MD 20852-2496, (301)
6.2.1 Conditions Prerequisite to PhoStrip Retrofit
The conditions listed below indicate the operating
ranges experienced to date for PhoStrip systems and
should be considered prerequisite operating
conditions for retrofit.
Influent TBOD = 70 to 300 mg/l
Influent TP = 3 to 10 mg/l
Secondary clarifier oxidized nitrogen = 3 to 30 mg/l
Wastewater temperature = 10to30°C
Aeration tank HOT = 4 to 10 hr
MLSS = 600 to 5,000 mg/l
F/M loading = 0.1 to 0.5 g TBOD/g MLVSS/d
If a PhoStrip retrofit is being considered for a plant
where operating conditions within the range presented
above cannot be achieved, a pilot study is warranted
prior to full-scale design and construction.
6.2.2 Design Considerations
A generic PhoStrip process schematic including key
sidestream flow rates and other information is
presented in Figure 6-1. For plants that are not
operating at primary clarifier design capacity, a
chemical precipitation tank can be substituted for the
reactor-clarifier, the contents of which would go to
the primary clarifier.
As shown in Figure 6-1, the range for the direct
return activated sludge rate (0.2 to 0.5 times the
influent flow rate) is that normally observed for
activated sludge plants. In addition, return sludge is
cycled through the stripper tank at 0.15 to 0.3 times
the influent flow rate. Anaerobic conditions are
maintained in the stripper tank, with a detention
normally between 8 and 12 hours. It is here that
phosphorus is released in a soluble form for
subsequent chemical precipitation. A longer anaerobic
stripper detention time is required when oxidized
nitrogen is present. This is because denitrifying
microorganisms that convert nitrate nitrogen to
nitrogen and oxygen under anaerobic conditions
compete with microorganisms responsible for
105
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Figure 6-1. PhoStrip process flow diagram.
Influent (Q) ^ Primary
Direct Sludge Recycle
(0.2 - 0.5 Q)
Primary Sludge
Effluent
Waste Activated
Sludge
Phosphorus-
Enriched Sludge
(0.15 -0.3Q)
Supernatant
(0.1 - 0.2 Q)
Stripper Underflow
(0.1 - 0.2 Q)
Anaerobic
Phosphorus Stripper
(HRT = 8-12 hr)
Chemical Sludge
Elutriation from any of:
(a) Stripper Underflow Recycle
(b) Primary Effluent
(c) Reactor-Clarifier Supernatant
phosphorus removal for the readily biodegradable
substrate. In addition, it has been theorized that
nitrate nitrogen acts as a terminal electron acceptor
for phosphate-accumulating bacteria. As a result,
sufficient anaerobic contact time must be provided for
denitrification, i.e., removal of nitrate nitrogen, to be
carried to completion first and then be followed by
phosphorus release.
The volume of the stripper tank is determined by the
sludge flow into the stripper and the required
anaerobic detention time. The stripper SOR, typically
selected in accordance with gravity thickener designs
at 16 to 24 m3/m2/d (400 to 600 gpd/sq ft),
determines the stripper surface area. The stripper
volume divided by the surface area determines the
sludge blanket depth, and normally 0.9 to 1.2 m (3 to
4 ft) is added to the depth for supernatant storage.
Phosphorus release is encouraged in the stripper tank
by the elutriation of the sludge with a stream low in
phosphorus content such as primary effluent,
secondary effluent, or lime precipitation tank overflow.
The elutriation flow rate is normally 50 to 100 percent
of the stripper feed rate. Stripper tank underflow
recycle or digester supernatant recycle can also be
used as elutriate sources. The higher organic content
of these streams encourages phosphorus release. As
stated in Chapter 2, the choice and magnitude of the
elutriation stream is a site-specific selection based
on operational and wastewater composition criteria.
The underflow rate from the stripper tank typically
amounts to 0.1 to 0.2 times the plant influent flow
rate, and the sludge solids in this stream can double
in concentration through the stripper's thickening
function. The phosphorus-poor biomass in the
underflow from the stripper tank is returned to the
activated sludge aeration tank to insolubilize primary
effluent phosphorus via the process of enhanced or
"luxury" biological uptake. F/M loading rates used are
typical of most activated sludge processes and can
range from 0.1 to 0.5 kg TBOD/kg MLVSS/d,
although it is noted that increased organic loadings
lead to greater phosphorus removal through the
waste activated sludge resulting from increased
sludge yields.
Supernatant from the anaerobic stripper tank carries
high SP concentrations in the range of 15 to 100 mg/l
and flows continuously to the chemical precipitation
tank at a rate of 0.1 to 0.2 times the plant influent
flow. Here the phosphorus is chemically insolubilized
with lime at dosages of 100 to 200 mg/l to maintain a
pH of 9.0 to 9.5. These dosages amount to 20 to 30
mg/l of lime based on plant influent flow. It is noted
that lime becomes a much more economical chemical
for use in phosphorus precipitation when the
phosphorus stream is concentrated than iron or
aluminum based salts due to the differences in
stoichiometries between those salts. Lime dosage is
in general independent of phosphorus concentration
106
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and depends primarily on the alkalinity of the water,
since it will first react with alkalinity to precipitate
CaCOa and then precipitate phosphorus. Iron and
aluminum salts must be applied on roughly an equal
molar basis to phosphorus; therefore, the same
amount would be necessary whether the stream was
small in flow and concentrated in phosphorus or high
in flow and less concentrated.
Where sufficient primary clarifier capacity exists, the
contents of the chemical precipitation tank (used in
lieu of a reactor-clarifier) can be routed there for
co-settling with primary sludge. Alternately, the
precipitation tank contents can be clarified separately
with only clarifier overflow from the operation routed
to the primary clarifier. A typically-used chemical
precipitation clarifier overflow rate is approximately 50
m3/m2/d (1,200 gpd/sq ft). The lime-phosphorus
sludge is generally disposed of separately with this
option.
A variation of the PhoStrip process called PhoStrip II
was recently unveiled, but to date has not been used
in a full-scale application. PhoStrip II makes use of a
prestripper tank with 30 minutes of detention where
return sludge and a BOD source are mixed. This
mixture then flows to a down-sized stripper tank with
4 to 8 hours of detention where elutriation is not
required. Other design parameters are similar to the
original PhoStrip process.
6.2.3 Attainability of Effluent Limits
Effluent limits of 2 and 1 mg/l TP can be reliably
attained using the PhoStrip process. An effluent TP
limit of 0.5 mg/l can be met if effluent suspended
solids are reliably controlled, but tertiary filtration may
be necessary. Achieving an effluent limit of 0.2 mg/l
TP may require a tertiary chemical polishing step in
addition to tertiary filtration. Provisions for metal salt
addition to the aerator as well as just prior to filtration
should also be made for achieving a 0.2-mg/l TP
effluent limit.
6.2.4 Lime Handling
Lime used for the PhoStrip process is available in
two forms: quicklime (CaO) or hydrated lime
[Ca(OH)2]. Quicklime contains about 90 percent CaO
and must first be hydrated or slaked to the Ca(OH)2
form prior to application to the wastewater. Hydrated
lime, a dry powder, has already been slaked and
contains 72 to 74 percent CaO and 23 to 24 percent
water of hydration. Slaking refers to the process of
adding water to quicklime to produce hydrated lime.
Lime is available in bulk by rail or truck, or in bags. In
general, bagged hydrated lime is recommended for
applications requiring less than 450 kg (1,000 lb)/d.
This would be the case for PhoStrip retrofits of less
than 0.18 m3/s (4 mgd). In bulk, hydrated lime is
recommended for applications up to 2,700 to 3,600
kg (6,000 to 8,000 lb)/d, or PhoStrip retrofits up to 1
m3/s (24 mgd). Thus, quicklime and associated
slaking equipment would be cost-effective only for
very large retrofit applications.
Storage areas for both bulk and bagged lime must be
kept covered and dry. Hydrated lime may be stored
for up to 1 year, while quicklime should not be stored
more than 3 months. Lime bags can be stacked 20
high, or higher when pallets are used. Bulk storage of
lime is usually done in conventional steel or concrete
bins and silos with conical bottoms. Hydrated lime
does not flow as well as quicklime, and tall storage
bins with height-to-diameter ratios of 2.5 to 4 are
recommended. Vibrating bin bottoms or discharge
chutes can help prevent arching or bridging of the
lime.
Lime is normally added to water to form a slurry prior
to being applied to the wastewater. For small
applications, bagged hydrated lime can be added
manually to a batch mixing tank to form a slurry for
feeding to the chemical precipitation tank. Bulk
hydrated lime is fed with a dry chemical feeder to a
batch or continuous mixing tank for subsequent feed
to the chemical precipitation tank. Bulk quicklime
must be fed to a slaker, where it is first hydrated. It is
then further diluted in a separate tank prior to
application. Gravimetric dry chemical feeders are
somewhat more costly than the volumetric type, but
offer several advantages and are the preferred
choice.
Diaphragm pumps, progressive cavity pumps, or
dipper wheel feeders are used to feed the lime
solution, typically at a concentration of 5 percent. A
recommended maximum solution concentration is 1
kg lime to 17 I water (1 Ib to 2 gal water), and the
solution tank detention time should be 5 minutes.
Scaling is a major problem in pumps, pipes, and
valves. Piping distances should be minimized, and
flow should be by gravity. Sodium
hexametaphosphate can be added to dilution water
and polymers can be used to inhibit scale formation.
Troughs and channels or flexible hose are preferred
to rigid pipe for slurry transport. Provisions for acid
flushing and the use of "pigs" should be made for
lime slurry lines.
6.3 A/O Process
Although the A/O process is most easily retrofitted to
plug flow activated sludge tanks, it can also be
adapted to most of the activated sludge flow regimes.
The ease of retrofit is determined by the ability to
delineate and convert a portion of the aeration
tankage to an anaerobic zone. Anaerobic here is
defined as the absence of all DO and oxidized
nitrogen, while anoxic refers to the conditions where
DO is low or absent but oxidized nitrogen is present.
Space for construction of retrofit facilities is normally
107
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not required for the A/O process, and generally an
A/O retrofit is more easily accomplished than a retrofit
for PhoStrip. The A/O process is owned and
marketed by Air Products and Chemicals, Inc., P.O.
Box 538, Allentown, PA 18105, (215) 481-4911.
6.3.1 AlO Operating Conditions
The ratio of influent SBOD to SP should be greater
than 10 to achieve an effluent TP concentration of
1-2 mg/l, and highe. ratios are desirable since they
are more conducive in achieving the release of
phosphorus in the anaerobic stage. This minimum
ratio is necessary to provide sufficient readily
biodegradable substrate, to produce enough cell
mass to trigger the phosphorus release/uptake
mechanisms, and to ensure the absence of
exogenous electron acceptors in the anerobic stage.
Additional operating conditions are as follow:
Wastewater temperature = 10 to 30°C
Anaerobic detention time = 1 to 2 hr
Anoxic (when requried) detention time = 1 hr
Aerobic detention time = 2.5 hr without
nitrification, 6 hr with
nitrification
MLSS = 2,000 mg/l in the summer; 3,500 mg/l in
the winter
F/M loading = 0.15 to 0.6 kg TBOD/kg MLVSS /d
If an A/O retrofit is being considered for a plant where
operating conditions within the ranges presented
cannot be achieved, a pilot study is warranted prior to
full-scale design and construction.
6.3.2 Design Considerations
Generic A/O flow diagrams for the cases without and
with nitrification are illustrated in Figure 6-2. An
anoxic stage is normally required after the anaerobic
and prior to the aerobic stages when nitrification is a
process consideration. A flow scheme consisting of
anaerobic, anoxic, and aerobic stages in series is
generally referred to as the A2/O process, a
modification of the basic A/0 process designed to
remove nitrogen and/or mitigate the negative effects
of nitrification on biological phosphorus release in the
anaerobic stage.
In the A2/O scheme, some method of low-head
pumping is required to recycle mixed liquor at a rate
of approximately 100 percent of the influent flow rate
from the last aerobic stage to the first anoxic stage.
The anoxic stage serves to denitrify the oxidized
nitrogen, thereby preventing competition with the
microorganisms responsible for phosphorus leaching
in the anaerobic stage. While the internal recycle
does not prevent nitrate nitrogen from entering the
anaerobic stage, it does reduce the nitrate
concentration in the return sludge stream.
The A/O process has not been operated with
nitrification on a full-scale basis at total detention
times less than 8 hours, although studies are
currently underway at lower detention times. If
sufficient total detention time is available, existing
tankage can be retrofitted with baffles to delineate the
anaerobic, aerobic, and, if necessary, anoxic stages.
It is desirable to maintain plug flow as much as
possible to ensure good contact of microorganisms
with substrate. For this reason, three anaerobic
stages, four aerobic stages, and, if necessary, three
anoxic stages are normally used. The exact
configuration is a site-specific consideration. Excess
tankage may be available at some plants such as
those employing the extended aeration process. In
these cases, a portion of the tankage may be blocked
off and taken out of service.
A variety of baffle materials are available including
concrete, different types of woods and plyboard, and
plastic coated fabrics. Open slots should be left at the
bottom of these baffles to allow movement of mixed
liquor. Where there are several baffles in sequence,
the slots should be constructed at alternating corners
to enhance plug flow. In addition, slots should be
provided at the top of each baffle to prevent the
buildup of scum.
Aeration devices in the anaerobic and anoxic stages
must be removed or prevented from operating since it
is extremely important that air not be introduced to
these stages. Aeration capacity in the remaining
aerobic stages may be insufficient, especially in
extended aeration type systems where long detention
times are being retrofitted to shorter ones. In these
cases, aeration devices can be moved from
anaerobic stages to aerobic stages when possible, or
auxiliary aeration may be required. Oxygen demand in
the aerobic stages is similar to that for conventional
activated sludge, or 1.5 kg Oa/kg TBOD removed. DO
concentrations in excess of 2 mg/l should be
maintained at all times in the aerobic stages.
Some form of mixing is required in the anaerobic and
anoxic stages. The mixing must be such that oxygen
transfer through excessive exposure of liquid surface
to air is minimized. Submersible pumps can be used
in smaller tanks or stages. Vertical mechanical mixers
are appropriate where the stage length and width
dimensions are similar and the depth is shallow, since
excessive shaft vibration can occur when the shaft is
long. For stages that are much longer than they are
wide, or for large, deep stages, side-mounted
submerged propeller-type mixers are desirable. The
goal of the mixing is simply to maintain the MLSS in
suspension with less than a 10-percent variation in
concentration. Mixing power requirements in the
anaerobic and anoxic zones can be estimated at 20
kW/1,000 m3 (0.75 hp/1,000 cu ft), although this
depends heavily on tank configuration.
The return activated sludge rate is typically between
20 and 75 percent of the influent flow rate. When
108
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Figure 6-2. A/O process flow diagrams.
Influent
1 -- - »-
L
Anaerobic
Stages
Oxic
Stages
J Fin
"H Clari
Sludge Recycle
1
Effluent
Primary Sludge
Waste Activated Sludge
(Phosphorus-Rich)
A/O Schematic for Phosphorus Removal Without Nitrification
Influent
Primary Sludge
1 A
L
Anaerobic
Stages
Anoxic
Stages
Oxic
Stages
iJ Fin
*l Clari
Sludge Recycle
^
Effluent
Waste Activated Sludge
(Phosphorus-Rich)
A/O Schematic for Phosphorus Removal With Nitrification
operating at the lower end of this range, it is
important that appropriate waiving be provided to
accurately control return sludge rates for proportional
pacing with low influent flows. The sludge blanket
depth in the secondary clarifier should be maintained
at less than 0.6 m (2 ft) to prevent development of
anaerobic conditions and subsequent leakage of
phosphorus into the secondary effluent. Secondary
clarifier SORs can range between 24 and 26 m3/m2/d
(600 and 650 gpd/ sq ft).
The organic loading rate is an important consideration
in successful operation of the A/O process. Higher
organic loading rates result in higher sludge yields
and, therefore, greater removals of phosphorus since
the only exit for phosphorus in the A/O process is
through the waste activated sludge. Although higher
rates have been successfully used, the recommended
volumetric organic loading rate for concurrent
nitrification is 0.15 kg TBOD/kg MLVSS/d or 0.08 kg
SBOD/kg MLVSS/d. Higher volumetric organic loading
rates up to 0.6 kg TBOD/kg MLVSS/d may be applied
when nitrification is not required.
When the method of sludge handling includes
anaerobic digestion or other operations where the
sludge is subjected to anaerobic conditions, at least a
portion of the biologically-removed phosphorus will
be released in a soluble form. This can then find its
way back to the influent of the plant through recycle
streams.
The effects of recycle streams such as digester
supernatant, sludge thickener overflow, and filter
press or vacuum filter filtrates on mainstream process
operation and performance must also be carefully
considered. These streams may carry a large loading
of phosphorus back to the influent and may upset the
required influent BOD-to-phosphorus ratio.
Segregation of the recycle streams may be necessary
in extreme cases.
6.3.3 Attainability of Effluent Limits
An effluent limit of 2 mg/l TP should be attainable for
most wastewaters where an A/O retrofit is used. An
effluent limit of 1 mg/l TP could be attainable most of
the time with the A/O process and perhaps all of the
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time at some locations. However, a backup feed
system for dosing selected chemicals to the aerobic
zone is recommended for any necessary polishing.
In achieving effluent limits of 0.5 mg/l TP or less, the
influent SBOD-to-SP ratio becomes more
important, with a desired ratio of 20 to 25. Provisions
for chemical polishing in the aerobic zone would be
necessary to achieve an effluent TP concentration of
0.5 mg/l, and a tertiary chemical polishing stage plus
tertiary filtration would be required to achieve an
effluent TP concentration of 0.2 mg/l.
110
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Chapter 7
Compatibility of Chemical and Biological Phosphorus Removal with Nitrogen Control
7.1 introduction
At some locations in the CBDB, there may be a need
to simultaneously control both nitrogen and
phosphorus in municipal effluents. Nitrogen control
requirements may be contingent on several
environmental impacts: provision for nitrification for
protection of the receiving water from ammonium
nitrogen oxidation demand, protection of aquatic life
from ammonia nitrogen toxicity, nitrogen removal to
prevent eutrophication of the receiving water, and/or
control of health hazards due to nitrate ions.
Requirements for dual nutrient control, i.e.,
phosphorus removal and nitrification or nitrogen
removal, can greatly affect the biological, chemical,
and engineering considerations of retrofitting
wastewater treatment facilities.
7.2 Process Considerations for
Complying with Dual Nutrient Control
Requirements
When a chemical or biological phosphorus removal
process must be modified to also include nitrogen
control, the impact of side reactions must be carefully
evaluated. Topics discussed in the following sections
are essential considerations for all dual nutrient
control processes.
7.2.1 Control of Process pH Value
Currently, all nutrient control processes are either
biological processes supplemented by chemical
additions or specially managed biological processes.
Therefore, control of process pH in the range of 6.0
to 8.0 is necessary to protect biomass from the toxic
effects of hydrogen ions.
As noted in Chapter 2, metallic salts used for
chemical removal of phosphorus are acidic in nature.
This acidity is due to the hydrolysis of metal ions
when added to water. For example, when aluminum
sulfate is added to wastewater the following reaction
occurs:
AI2(SO4)3 + 6H2O -» 2 AI(OH)3 + 3H2SO4 (7-1)
The sulfuric acid produced by this reaction consumes
a portion of the alkalinity of the wastewater. If
Equation 7-1 is calculated on the basis of aluminum,
the acid produced is equivalent to 5.6 mg/l of calcium
carbonate alkalinity for each 1 mg/l of aluminum
added to the wastewater.
Similar calculations for ferric salts show that each 1
mg/l of ferric ion dosed to wastewater will consume
2.5 mg/l of calcium carbonate alkalinity. If the source
of metallic precipitant selected for phosphorus
removal is waste pickle liquor in the form of ferrous
sulfate or ferric chloride, it should be noted that these
products may also contain free acid, which will also
consume alkalinity in addition to the metal hydrolysis
reaction.
When a nitrified effluent must be produced, the
biological conversion of ammonium nitrogen to nitrate
nitrogen can also deplete alkalinity. The conversion is
a sequential two-step biological oxidation
accomplished by two specialized microorganisms;
however, the overall nitrification reaction can be
viewed as follows:
NH4+ + 2C-2
+ H2O + 2H + (7-2)
Calculated on a nitrogen basis, for each 1 mg/l of
ammonium nitrogen converted to nitrate nitrogen, the
amount of hydrogen ions produced will consume 7.1
mg/l of calcium carbonate alkalinity. This depletion
can be severe. If, for instance, 20 mg/l of ammonium
nitrogen were oxidized, the calcium carbonate
alkalinity would be reduced by 142 mg/|. As a rule of
thumb, if a wastewater has a carbonate/bicarbonate
buffer system with a pH value between 7.0 and 8.5,
the concentration of ammonium nitrogen that can be
oxidized before the pH value decreases below 6.0 is
about 0.1 of the wastewater calcium carbonate
alkalinity.
Another important reaction must be taken into
account if a denitrification process is instituted for
nitrogen removal requirements. Biological
denitrification is a very complex series of biochemical
reactions; however, for process control purposes, the
reaction can be considered to occur as follows:
O2 + 0.5 N2 + OH' (7-3)
For each nitrate ion converted to nitrogen gas, one
hydrogen ion is consumed and one hydroxyl ion is
111
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produced. This has the overall effect of increasing the
alkalinity of the wastewater. For each 1 mg/l of nitrate
nitrogen converted to nitrogen gas, 3.5 mg/l of
calcium carbonate alkalinity will be produced. In
certain process configurations, this alkalinity
production can partially offset the alkalinity depleting
reaction of nitrification and assist in maintaining
control of process pH.
7.2.2 8/omass Environmental Management
The discussion of biological phosphorus removal in
Chapter 2 describes the different environments that
the biomass of these processes must cycle through
for proper population selection. These environments
must be managed to be anaerobic, anoxic, and
aerobic.
When nitrification or nitrification/denitrification is
coupled with biological phosphorus removal, it
becomes necessary to further define these
environments as follows:
1. An anaerobic stage should not contain DO, and
nitrate should not be present.
2. An anoxic stage should not contain DO, but
should contain nitrate.
3. An aerobic stage should contain at least 1 mg/l
DO and may contain nitrate. -
It has been found that the presence of DO or nitrate
in the anaerobic stage of a biological phosphorus
removal process will inhibit the release of intercellular
phosphorus. As long as either of these is present, the
microorganisms will utilize these oxygen resources to
oxidize organics instead of sorbing organics and
releasing phosphorus. Thus, phosphorus uptake in
the subsequent aerobic stage may be prevented.
If a PhoStrip or A/O process must also be retrofitted
to produce a nitrified effluent, the nitrate content of
the return sludge flow into the side stream stripper
tank or main stream anaerobic stage, respectively,
would have to be taken into account to allow
adequate HRT for oxygen resources to be consumed
and phosphorus release to occur.
For nitrogen removal processes, anoxic stages are
provided for biological denitrification, which transforms
nitrate nitrogen into nitrogen gas. The microorganisms
performing this transformation are facultative
organisms that can metabolize substrate using either
DO or oxygen from the nitrate radical. If both DO and
nitrate are present, the microorganisms will
preferentially use DO. Therefore, to ensure efficient
denitrification, an anoxic stage must be operated to
exclude DO.
Aerobic stages are incorporated into all dual nutrient
control processes for provision of the proper
environmental conditions for oxidation of organics and
nitrification.
If a phosphorus removal process, either biological
combined with chemical or biological by itself, must
also achieve nitrification or nitrogen removal via
denitrification, the dominant design and operational
considerations become the selection of SRT and
management of the several environments the
biomass must cycle through to foster population
selection and achieve effluent limitations.
7.2.3 Engineering Aspects
Dual nutrient control processes offer situations in
which attention to engineering aspects of design and
operation becomes critical. Consideration should be
given to the following:
1. Reactor recycle flows
2. Mixing devices
3. Baffling between reactor stages
4. Clarifier mass loading
5. Reuse of oxygen contained in the nitrate radical
All processes combining dual biological phosphorus
removal and denitrification for nitrogen removal entail
recycling flows between various reactor stages. While
these can be low-head pumping operations, the
magnitude of recycle flows can be up to four times
the influent flow. Power requirements for these
recycle flows should be evaluated as an operational
cost. Recycles between reactor stages with different
environmental conditions can interfere with attainment
of proper reactor stage performance such as
introducing DO from an aerobic stage into an anoxic
stage. Also, the effect of the magnitude of recycle
flows on substrate residence time must be evaluated.
Mixing devices for anaerobic and anoxic stages can
be submerged pumps, impeller mixers, or very coarse
bubble, low volume aeration devices. The basic
design requirement is supplying enough power to
keep the biomass in suspension, yet not creating a
turbulent surface that will cause oxygen transfer to
occur. Typically, the power required to maintain
biomass in suspension is about 20 kW/1,000 m3 of
tank volume (0.75 hp/1,000 cu ft) for mechanical
devices and about 25 m3 air/1,000 m3 of tank volume
(25 cu ft/1,000 cu ft) for aeration devices.
Baffling between reactor stages is necessary to
maintain proper environmental conditions in each
stage and to prevent short circuiting. Baffle walls can
be constructed from concrete, treated wood, or heavy
duty plastic curtains. Material selection should be
based on site-specific details such as cost, duration
of the retrofit operation, and effluent requirements.
Generally, a retrofit for dual nutrient control processes
places a greater solids load on an existing final
clarifier. Either a chemical or biological phosphorus
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removal process that must also achieve nitrogen
control requires operating at a greater SRT. Chemical
and biological phosphorus removal processes can be
operated at SRTs of 3 to 4 days, irrespective of
temperature considerations. However, nitrification or
denitrification requires SRTs of 6 to 8 days for
summer conditions and 15 to 20 days under winter
conditions. This equates to a greater mass of mixed
liquor in the reactor that must cycle through the final
clarifier. The flux loading on the clarifier floor should
not exceed 120 kg/m2/d (25 Ib/sq ft/d).
Inspection of Equation 7-3 indicates that during
biological denitrification, not only is alkalinity
produced, but oxygen is liberated from the nitrate
radical. Depending on the process configuration
selected for retrofit and the facility's operational staff
capability, this liberated oxygen can be a resource.
The theoretical calculation for Equation 7-3 shows
that 67 percent of the oxygen in the nitrate radical
could be recovered for use in bio-oxidation of
organics in wastewater. The following equation can
be used as a first approximation of the magnitude of
this recovered oxygen:
(mg/l NOa'-N x 4.5 x 8.3 x mgd x 0.67 x $/wire hp-
hr) T Ib Oa/wire hp-hr (aeration efficiency) = $/d
(7-4)
In Equation 7-4, the value of 4.5 is the oxygen factor
for oxidation of ammonium nitrogen to nitrate
nitrogen.
For a 0.48-m3/s (5-mgd) facility that recovered 15
mg/l of nitrate oxygen with an oxygen transfer
efficiency of 1.0 kg Oa/kWh (1.65 Ib/wire hp-hr) and
an electrical energy cost of $0.10/kWh ($0.075/wire
hp-hr), the theoretical value of the recovered oxygen
would be $85/day. This, of course, would be offset
by efficiency factors due to process configuration,
recycle pumping costs, and additional operating
attention for process control. At larger facilities that
are required to nitrify or denitrify, this source of
oxygen should be evaluated in early retrofit decisions.
7.3 Dual Process Removal and
Nitrification Processes
Aside from the items noted in the previous sections,
mating of phosphorus removal with nitrification
requires consideration of HRT, SRT, the F/M loading
rate, and oxygen supply.
7.3.7 Chemical Phosphorus Removal and
Nitrification
Combined activated sludge-chemical phosphorus
removal processes that also achieve nitrification were
shown previously in Figures 2-3 and 2-6. One-
and two-stage systems for nitrification have been
employed. The choice between the configurations
should be based on wastewater temperature and
wastewater quality. A requirement for wintertime
nitrification favors a two-stage system to reduce the
total reactor detention time deriving from the ability to
maintain a long SRT in the second stage. A two-
stage system should also be selected if the organic
content of the wastewater is high. The first-stage
reactor reduces the organic loading to the nitrification
stage, allowing attainment of the proper SRT to
achieve nitrification in that stage.
In retrofit situations, spare aeration tankage or baffling
of tankage may allow implementation of two-stage
treatment. Existing secondary clarifier capacity may
be the limiting factor in this decision.
If nitrification is required only during the summer
months and the wastewater is of usual municipal
organic strength, the retrofit choice would typically be
single-stage nitrification. Reference 1 contains many
examples of dual chemical phosphorus removal and
nitrification employing a variety of options.
7.3.2 Biological Phosphorus Removal and
Nitrification
Flow diagrams of biological phosphorus removal
utilizing the PhoStrip and A/O processes were
presented previously in Figures 2-11 and 2-12,
respectively. Achieving nitrification with these
processes in a retrofit situation depends on the
temperature and organic loading at which the facility
has to nitrify. At cold temperatures, both processes
require a significant increase in SRT. Since the A/O
process depends on sludge wasting as the
phosphorus removal mechanism, it can be impacted
by changes in SRT. The PhoStrip process, with a
sidestream chemical operation, would not be
impacted to as great an extent.
High organic loads would favor the A/O process,
since this process depends on removal of
phosphorus by cellular synthesis. However, the
organic load could not be so great as to prevent
achieving an SRT suitable for nitrification.
Reference 2 describes a full-scale PhoStrip process
that produced a nitrified effluent during the summer of
1984. The F/M loading was 0.16 kg TBOD/kg
MLVSS/d, an SRT of 7 days was maintained, and the
aerator HRT was 4.6 hours.
This same reference provides data for two full-scale
facilities utilizing a process configuration similar to the
A/O process. Nitrification was achieved in the
summer of 1984. Winter nitrification capability was not
monitored. Based on the aerobic portion of the
bioreactors, the HRT varied between 6 and 15 hours
and the F/M loading between 0.12 and 0.33 kg
TBOD/kg MLVSS/d. The SRT, based on total reactor
volume, ranged from 7 to 11 days.
Reference 3 reports on the full-scale demonstration
of a facility retrofitted for the A/O process to achieve
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biological phosphorus removal and nitrification. This
northern facility has a seasonal permit that requires
the monthly average values of effluent ammonium
nitrogen and TP never to exceed 3.2 and 1 mg/l,
respectively. The ammonium nitrogen limitation
applies from May 1 through September 30. Process
loadings and operational parameters were not
provided, but the facility was meeting the permit
limitations.
The influence of nitrate nitrogen in the anaerobic
stages and the anaerobic stripper, as discussed
previously, was evident at all four of these facilities. A
direct relationship was noted between SP and nitrate
nitrogen concentrations in the plant effluents.
Increases in nitrate nitrogen were followed by
increases in SP. At 10 mg/l of nitrate nitrogen, the SP
content of the effluents was approximately 0.5 mg/l.
7.3.3 Oxygen Requirements for Nitrification
When either a biological-chemical or biological
phosphorus removal process must also be retrofitted
to achieve nitrification, oxygen supply capability must
bo considered. Calculation of the consumption of
oxygen by biological nitrification, as given previously
in Equation 7-2, shows that for each 1 mg of
ammonium nitrogen oxidized to nitrate nitrogen, 4.5
mg of oxygen will be required. This is in addition to
the oxygen demand for carbonaceous oxidation and
the oxygen required for meeting the endogenous
demand of biomass.
In a retrofit situation, the anticipated peak oxygen
requirement anticipated from these combined
demands should be evaluated against the capability of
the existing aeration system to transfer this amount of
oxygen.
7.4 Dual Phosphorus Removal and
Nitrogen Removal Processes
If a facility must remove both phosphorus and
nitrogen to meet effluent requirements, the retrofit
decisions will have to be carefully tailored to the
numerical limits imposed. Numerous process options
are available for controlling both nitrogen and
phosphorus with a wide spectrum of overall
efficiencies. An effluent specification that had
stringent limits, such as 0.2 mg/l TP and 3 mg/l total
nitrogen, would dictate consideration of a multi-stage
biological process supplemented with chemical
additions. A less stringent effluent requirement, such
as 2 mg/l TP and 10 mg/l total nitrogen, would lead to
consideration of managed biological systems.
Between these two extremes are numerous options
that could be evaluated.
To effectively remove both phosphorus and nitrogen,
any process must be operated to control a series of
transformations. As discussed in Chapter 2, influent
phosphorus forms must be converted to
orthophosphate for efficient insolubilization by
chemicals or incorporation into cellular material.
For nitrogen removal to occur, the various unoxidized
forms of nitrogen in the influent must first be
transformed into nitrate nitrogen. Then, conditions
must be arranged for biological denitrification to
convert the nitrate nitrogen to nitrogen gas. For this
conversion, microorganisms utilize hydrogen bound in
organic materials to combine with oxygen from the
nitrate radical. This is an oxidation/reduction reaction
with water, carbon dioxide, nitrogen gas, and hydroxyl
ions as end products. Using methanol as an example
of organic matter, the reaction is:
6NO3" + 5CH3OH -» 7H2O + 5CO2 + 3N2 + 6OH'
(7-5)
The velocity of this reaction is dependent on the type
of organic substrate provided. Materials such as
methanol are very soluble in wastewater and readily
utilized by acclimated denitrifying organisms. In
addition, the chemical is available in pure form and
can be dosed into a denitrification process in a known
ratio to nitrate nitrogen.
Managed biological processes depend on different
types of organics. Some utilize organics (BOD)
present in influent wastewater; others rely on organics
liberated by endogenous hydrolysis of cellular
organics present in biomass. The quality and quantity
of these organics are largely unknown and can be
highly variable. The extent of biological utilization of
these materials is also subject to variability.
Generally, these types of organics have slower
reaction velocities than materials such as methanol.
However, no implicit cost is associated with these
in-plant sources of organics.
The trade-off that must be evaluated between
externally added materials like methanol and in-plant
organics is the cost of chemical and dosing
equipment for the former vs. biological reactor size
and recycle pumping costs for the latter, coupled with
the effluent total nitrogen residual and degree of
compliance required. Retrofitting for removal of both
nitrogen and phosphorus at any facility that was near
design hydraulic and organic loadings, no matter
which option was chosen, would no doubt involve
capital construction.
7.4.1 Phosphorus and Nitrogen Removal with
Multi-Stage Biological Processes Supplemented
with Chemicals
Many examples of multi-stage, chemically-assisted
processes are provided in References 1 and 4. The
data base for this technology is well established from
both design and operational standpoints. The array of
process options is large because various
combinations of suspended and attached growth
biological processes, operated in series, have been
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constructed. The most complex are systems with
separate reactors for carbonaceous oxidation,
nitrification, and denitrification, each with its own
clarifier. Other configurations combine carbonaceous
oxidation and nitrification in a single reactor and have
a separate stage for denitrification. The denitrification
reactor has been designed both as a post-
denitrification and a pre-denitrification process. In
some systems, where an attached growth process is
included in the design, the provision for clarification
after this process may not be necessary.
Such a diversity of process options exists for these
systems that recitation of all possibilities is not
possible. One example will be discussed to illustrate
this control technology. Reference 5 provides data on
two municipal facilities that were designed and
operated to comply with final effluent limitations of 5
mg/l TBOD, 5 mg/l TSS, 1 mg/l TP, and 3 mg/l total
nitrogen. Both employ multi-stage treatment. A
schematic of one of the facilities is given in Figure
7-1 .
Influent flow of 0.09 m3/s (2 mgd) is degritted and
routed to a flow equalization tank. Plant personnel
consider equalization an essential feature to
stabilizing downstream HRT, SORs, chemical
dosages, and filter application rates. Flow is pumped
at a constant rate to the first-stage, complete mix
activated sludge-clarifier system. This is a
carbonaceous oxidation process that reduces the
organic load on subsequent processes. Metal salt is
dosed to the first-stage reactor to insolubilize the
major fraction of influent phosphorus, which is
removed in the waste activated sludge.
Second-stage rotating biological contactors provide
attached growth nitrification of the first-stage
activated sludge effluent. Since the organic load to
the contactors is very low and nitrifiers have a low net
cell yield, there is little solids production in this unit
operation and, therefore, no need to provide
clarification.
Nitrified effluent passes to a third-stage, plug flow,
suspended growth denitrification reactor that receives
a dose of methanol in proportion to the nitrate
nitrogen content. Mixing is provided by submerged,
low-speed impeller mixers to prevent turbulence.
Nitrogen is removed as nitrogen gas by the
denitrification reaction. Any nitrogen gas bubbles
adhering to sludge particles are scrubbed from the
reactor flow as it passes through a flash aeration
chamber. A small dose of metal salt is added to this
chamber to insolubilize any remaining SP, which is
then removed via the third-stage waste sludge
stream.
At the final clarifier, polymer dosing capability is
provided on an as-needed basis in the event that
sludge settleability problems are encountered. The
clarifier overflow is further polished by dual media,
gravity flow filters to ensure compliance with the
stringent effluent standards.
Waste activated sludge and waste denitrification
sludges are digested aerobically. Decanting is done
on a batch basis. Insolubilized metal phosphate,
precipitated in the sludges, does not resolubilize
during aerobic digestion. After conditioning, the
digested sludge is applied to agricultural land.
On a yearly basis, using monthly average data, the
facility achieves compliance with the 1-mg/l TP
limitation 90 percent of the time and complies with
the 3-mg/l total nitrogen requirement 95 percent of
the time.
7.4.2 Phosphorus and Nitrogen Removal with
Managed Biological Systems
Currently, no large reservoir of full-scale operational
experience is available with biological processes that
cycle biomass through managed environments to
achieve both nitrogen and phosphorus removal to
meet prescribed effluent limitations.
Reference 3 states that three full-scale facilities
(Lansdale, PA; Reedy Creek, FL; and DePere, Wl)
practicing dual biological phosphorus removal and
nitrification did exhibit significant degrees of overall
nitrogen removal. This was attributed to unintentional
denitrification of nitrate nitrogen in recycle streams
entering anaerobic zones of the processes.
A large number of process configurations have been
evaluated for biological phosphorus and nitrogen
removal, many only in laboratory or pilot-scale
studies. The three that have received considerable
attention in the United States are the
Anaerobic/Anoxic/Oxic (A2O) process, the Bardenpho
process, and a modified PhoStrip process. These
processes will be presented and discussed in
subsequent sections.
As noted in Chapter 2, for biological phosphorus
removal, the wastewater should have a SBOD-to-
SP ratio of at least 10 to 15. With the dual process
approach, incorporating denitrification, the ratio of
TBOD to total Kjeldahl nitrogen (TKN) also becomes
important. Reference 6 recommends that the ratio of
TBOD to TKN be 5 to 10. It is important with
managed nutrient control processes, which are not
provided with supplemental organic compounds, that
the influent wastewater contain enough organic matter
to enable the denitrification reaction between nitrate
and organics to occur. If the TBOD-to-TKN ratio
were lower, greater concentrations of nitrate nitrogen
would appear in the final effluent.
It should be noted in the following process flow
diagrams that all of these dual control systems
recover some of the oxygen contained in the nitrate
115
-------
Figure 7-1. Multi-stage biological process supplemented with chemicals for combined nitrogen and phosphorus removal.
Metal Salt Motet
Storage Purr
i__j"'i
Dogrittod
Wastowater ^
Eq.
— \
— \
Flow
jalizc
Methanol
infl Storage! 1 , v
p i__j W
_w/lRt-PtaOp 1 fel fSlnrifier \ *,
I AS y l 7 "
/ >
ition T
2nd-
Stage
RBC
!
t
3rd-Stage
Suspended
Growth
Denitrification
Poly
Stor<
Return Slu
ner. , __
aae i i j
i i "
•*
Flash j,
Aeration *"
d_ge
f
i
/^
» Final
V Clarifier
^-—r---'
Return
Sludge
[_ ^3?t?_?Jyf!9§ Streams
To Head
Works •
Decant
Wastewater
Sludge
Chemicals
Digested
Sludge
- To Land
Final
Effluent
radical via recycle of internal streams into an anoxic
stage. Also important to note is the fact that the last
reactor stage in all these systems is an aerobic (oxic)
stage where nitrification occurs. Theoretically, this
indicates that unless high internal recycle rates and
extensive baffling are employed along with long
HRTs, these systems cannot achieve as low a final
effluent nitrate nitrogen content as a multi-stage
system with a chemically supplemented terminal
denitrification reactor.
Both biological nitrification and biological denitrification
transformations are affected by wastewater
temperature. Data on temperature coefficients for
multi-stage systems from pilot- and full-scale
studies are included in Reference 1. However,
temperature data for dual biological systems in a
variety of options are not extensive.
In dual biological phosphorus and nitrogen removal
applications, the biomass has to be managed to
balance two opposing microbial population selection
objectives. Biological phosphorus removal is
dependent on excess sludge production by a group of
organisms that can survive extremes of DO
concentration. Increased rates of sludge production
are favored by a short SRT.
Since denitrification must be preceded by nitrification,
conditions for survival of nitrifiers must be provided.
These organisms require an aerobic environment and
have a low growth rate, which mandates a long SRT.
At the present time, due to the lack of a large data
base on the influence of wastewater quality and
component ratios, the magnitude of internal recycle
streams necessary to achieve a given effluent
residual, temperature effects on dual processes, and
the need to balance SRT, it is recommended that any
retrofit for these systems be guided by pilot plant
studies.
7.4.2.7 Phosphorus and Nitrogen Removal with
the A2/O Process
The A2/O process configuration is presented in Figure
7-2. It is similar to the A/O process (Figure 2-12),
except that an anoxic stage is inserted between the
anaerobic stage and the oxic stage.
The system must be designed and operated to obtain
phosphorus leaching in the anaerobic stage and
subsequent biological cellular uptake in the following
aerobic stage. The SRT of the biomass must be
selected to ensure a steady-state population of
nitrifiers at the design temperature. The detention
time of the aerobic stage must be sufficient to
accomplish nitrification and organic oxidation in this,
the only aerated portion of the process.
116
-------
Figure 7-2. Schematic of an activated sludge system retrofitted for the A2/O process.
Polymer Me
Storage P
i — -i ^^
1 ' (
1 !•--»
1 1 f~*
i 1 t
Degritted
Wastewater
'
i i ."
i r f
i 1 L.
tering
jmp
J
t
A
^/ Pfjnfiarv i h^
k. V Clar
i
Primary i
-\
ifier I *
r
Sludge
L
Anaerobic
Stage
Anoxic
Stage
Return Sludge
Recycle
Aerob
Stag
'
ic i J Final \ Effluent ^
rl Clarifier 1 w
" ^^~\
'
TF
Waste
Activated
Sludge
Final
Effluent
TP
mg/l
2
1
0.5
0.2
Probable Need
for
Chemical Addition
None
Occasional
Continuous polish dose
Continuous polish dose
Final
Clarifier
SOR"
gpf/sq ft
800
600
500
500
* at peak sustained flow
Approximate final nitrogen concentrations (mg/l):
Organic-N:
NH4-N:
NO2-N:
NO3-N:
3.5
1
0.1
6
Nitrified mixed liquor is recycled to the anoxic stage
where biological denitrification occurs in response to
organics (BOD) entering this stage from the
anaerobic stage. By recycling mixed liquor from the
aerobic to the anoxic stage for denitrification, the
negative influence of nitrate nitrogen on phosphorus
leaching in the anaerobic stage is somewhat
alleviated, as only nitrate contained in the return
sludge enters the anaerobic stage. Thus, in the A2/0
process, denitrification can occur in both the anoxic
and anaerobic stages.
The influent to the anaerobic stage must contain
organics for two purposes: first, to serve as substrate
to be sorbed by the phosphorus-accumulating
organisms, and, second, to serve as organic
substrate for anaerobic stage denitrification of return
sludge nitrate, which in turn reduces the negative
influence of nitrate on phosphorus leaching. Enough
organic material must pass through the anaerobic
stage to the anoxic stage, however, so that reduction
of nitrate in the recycle mixed liquor is not inhibited.
Consideration may be given to bypassing all or a
portion of the raw wastewater around the primary
Clarifier to increase the organic concentration entering
the anaerobic stage if the influent wastewater has a
low organic content.
Depending on the magnitude of the two recycle
streams, the A2/O process recovers some fraction of
the oxygen content of the nitrate radical. Additionally,
the denitrification reactions in the anaerobic and
anoxic stages will create alkalinity to help offset
downstream alkalinity loss due to nitrification and
metal salt addition, if required.
Operational control must be utilized to manage
reactor influent organic concentration, select the rates
of the two recycle streams, and maintain proper
environmental conditions within each stage and
appropriate sludge wasting schedules. It should be
noted that as the magnitude of these internal recycles
increases, the more closely the bioreactor
approaches a complete mix process, with increasing
loss of environmental control of the separate stages.
The effect of in-plant recycles, such as sludge
processing and handling supernatants or filtrates,
needs to be evaluated regarding their impact on
organic, phosphorus, and nitrogen loadings received
by the bioreactor.
117
-------
To achieve an effluent TP concentration of 2 mg/l
with the A2/O process, metal salt addition would
probably not be needed. To achieve 1 mg/l might
require occasional polish dosing. To achieve 0.5 or
0.2 mg/l would probably require continuous polish
dosing.
7.4.2.2 Phosphorus and Nitrogen Removal with
the Bardenpho Process
Inspection of Figure 7-3 shows that the Bardenpho
process has a similar configuration to the A2/O
process; however, it is segmented into a greater
number of stages.
The lead stage is an anaerobic stage where
phosphorus leaching from the microorganisms must
occur. This is followed by four alternate stages that
are managed to provide anoxic and aerobic
environments. The first anoxic stage is the site of the
major denitrification reaction. In the first aerobic
stage, biological phosphorus cellular uptake, oxidation
of ammonium nitrogen, and oxidation of organics
occur.
The subsequent anoxic and aerobic stages are
essentially polishing stages to provide low effluent
residual total nitrogen and efficient organic removal.
Any denitrification occurring in the second anoxic
stage is due to the endogenous oxygen demand of
the mixed liquor since there is no direct input of
organics to this stage. Thus, three locations exist in
the Bardenpho system where denitrification can
occur: the anaerobic, first anoxic, and second anoxic
stages. Nitrification and organic oxidation can occur in
the two aerobic stages.
As with the A2/O process, the Bardenpho process
has an interstage recycle between the first aerobic
and anoxic stages for denitrification and reduction of
the influence of nitrate nitrogen on phosphorus
leaching in the anaerobic stage. The anaerobic stage
receives only nitrate contained in the return sludge.
The highly baffled configuration approaching plug flow
and the presence of the two internal recycles are
conducive to the reuse of oxygen from the nitrate
radical. Operating and environmental constraints for
managing biological phosphorus and nitrogen removal
discussed in the section for the A2/O process apply
equally well to the Bardenpho process. Likewise, the
influence of in-plant recycle streams must be
evaluated.
Some descriptions of the Bardenpho process label
the first stage in the process a fermentation zone
instead of an anaerobic stage. In reality, the biological
transformations that occur in this reactor, whether
labeled fermentation zone or anaerobic stage, are the
same. The fermentation zone concept originated at
facilities where the wastewater was weak in organic
content. The purpose of this fermentation zone was
to provide an anaerobic operation where particulate
organics in influent wastewater could be hydrolyzed
(fermented) to short-chain fatty acids, such as
acetate (7). As previously discussed, soluble organics
must be present in the initial anaerobic stage for
sorption by the phosphorus-accumulating
microorganisms.
The need for the presence of short-chain fatty acids
in the anaerobic stage of all biological phosphorus
uptake processes, not just the Bardenpho process,
has been established (7). Various operational
approaches have been applied to ensure that these
materials are present. These include
1. adding increments of primary sludge to the
anaerobic stage (8),
2. recycling in-plant streams such as thickener
overflow to the anaerobic stage (9),
3. infrequent mixing of the anaerobic stage to allow
sludge deposition and subsequent hydrolysis of
the sludge (10),
4. provision of an off-line fermentation reactor for
biological hydrolysis of primary sludge to produce
fatty acids to be dosed into the anaerobic stage
(11), and
5. addition of anaerobic digester supernatant to the
anaerobic stage (2).
For the Bardenpho process, Figure 7-3 indicates
that attainment of an effluent TP concentration of 1
mg/l may require an occasional supplemental dose of
a metal salt and that a continuous polish dose of
metal salt will probably be required to attain an
effluent TP concentration of 0.5 mg/l or less.
Attainment of an effluent total nitrogen concentration
of 1.5 mg/l has been reported for a 0.07-m3/s (1.7-
mgd) municipal facility. The effluent TP concentration
was 3 mg/l (10).
7.4.2.3 Phosphorus and Nitrogen Removal with
the University of Capetown (UCT) Process
The UCT process was developed at the University of
Capetown, Capetown, South Africa (12). A flow
schematic is given in Figure 7-4. There are currently
no known installations of the UCT process in the
United States.
The process is akin to the A2/O and Bardenpho
processes. However, two interstage recycles are
incorporated in the process flowsheet instead of one.
As with the A2/O and Bardenpho processes, mixed
liquor is recycled from the aerobic stage to the anoxic
stage, but to protect the anaerobic stage from nitrate
inhibition of phosphorus leaching, an engineering
modification was made. Return sludge is directed into
the anoxic stage instead of the anaerobic stage and
118
-------
Figure 7-3. Schematic of an activated sludge system retrofitted for the Bardenpho process.
Polymer Metering
Storage Pump
[._.( 1.
i /~v
_j t—i
Degritted
Wastewater
Anaerobic
Stage
i Recycle
Anoxic
Stage
Aerobic
Stage
Anoxic
Stage
Aerobic
Stage
Return Sludge
Primary Sludge
Effluent
Waste
Activated
Sludge
I 1 L 1
Metal Salt Metering
Storage Pump
Existing
Retrofit
Final
Effluent
TP
mg/l
2
1
0.5
0.2
* at peak
Probable Need
for
Chemical Addition
None
Occasional
Continuous polish dose
Continuous polish dose
sustained flow
Final
Clarifier
SOR*
gpf/sq ft
800
600
500
500
Approximate final
Organic-N:
NH4-N:
NO2-N:
NO3-N:
nitrogen concentrations (mg/l):
3.5
1
0.1
5
then mixed liquor from the anoxic stage is recycled to
the anaerobic stage.
In evaluating this process for possible retrofit
applications, careful consideration should be given to
the detention times of the various stages since a high
degree of recycling within the reactor could greatly
alter the maintenance of proper stage environmental
conditions and substrate utilization rates.
Metal salt addition would probably not be needed to
achieve an effluent TP concentration of 2 mg/l. To
achieve 1 mg/l might require occasional dosing. To
achieve 0.5 or 0.2 mg/l would require a continuous
polish dose.
7,4.2.4 Phosphorus and Nitrogen Removal with
the Modified PhoStrip Process
A modification of the PhoStrip process that provides
for biological denitrification of the nitrate nitrogen
contained in the return sludge flow is discussed in
Reference 13. This modification is presented
schematically in Figure 7-5.
The modification retains all the features of the original
PhoStrip process as previously described. For
implementing removal of nitrogen, the main stream
activated sludge system would have to be operated to
achieve nitrification. The nitrate in the return sludge
flow is directed to an anoxic reactor ahead of the
anaerobic stripper tank.
The denitrification rate is dependent on the hydrolysis
of organics due to endogenous respiration since a
nitrified return sludge stream has very little soluble
organics present. Consideration could be given to
providing a bypass line to introduce primary effluent
directly into the anoxic reactor to increase the
denitrification rate.
The anoxic reactor is sized larger than the quantity of
flow required for the anaerobic stripping of return
sludge for phosphorus removal. A portion of the
anoxic denitrified flow is routed directly back to the
aeration tank. Denitrification of the return sludge flow
in this modification also serves to protect the
anaerobic stripper phosphorus leaching reaction from
the inhibiting action of nitrate.
Theoretically, Figure 7-5 indicates that the
denitrification removal capability of this modification
would be limited to the percentage of return sludge
119
-------
Figure 7-4. Schematic of an activated sludge system retrofitted for the UCT process.
Polymer Metering
Storage Pump
Degritted
Wastewater
_wi Primary
^ Clarifier
xRecycle 1 I ^ Recycle 2]
Anaerobic
Stage
Anoxic
Stage
Aerobic
Stage
Return Sludge
Primary Sludge
l-O-
E«luent
Waste
Activated
Sludge
; 1 /—\
Metal Salt Metering
Storage Pump
Existing
Retrofit
Final
Effluent
TP
mg/l
2
1
0.5
0.2
Probable Need
for
Chemical Addition
None
Occasional
Continuous polish dose
Continuous polish dose
Final
Clarifier
SOR'
. gpf/sq ft
800
600
500
500
* at peak sustained flow
Approximate final nitrogen concentrations (mg/l):
Organic-N:
NH4-N:
NO2-N:
NO3-N:
3.5
1
0.1
5
flow. For instance, if the return flow were 50 percent
of the influent plant flow, the amount of nitrate
nitrogen that could be denitrified would be 0.5/1.5, or
33 percent. However, it has been reported (13) that a
pilot plant operated in this mode denitrified 70 percent
of the nitrate nitrogen present. The incremental
removal was attributed to coincidental denitrification in
the nitrifying activated sludge system. This agrees
rather well with results presented elsewhere (2),
where a full-scale PhoStrip plant producing a nitrified
effluent with no anoxic reactor achieved an overall
nitrogen removal of 31 percent.
Currently, there are no known U.S. installations of the
PhoStrip process modified for biological denitrification.
Since the PhoStrip process is a sidestream process,
there is no apparent reason that it should not be
compatible with a variety of mainstream biological
denitrification processes.
Metal salt addition would probably not be needed to
achieve effluent TP concentrations of 2, 1 or 0.5 mg/l.
To achieve 0.2 mg/l, an occasional polish dose might
be required.
7.5 References
1. Process Design Manual for Nitrogen Control.
U.S. EPA, Technology Transfer, Cincinnati, OH,
October 1975.
2. Tetreault, M.J., A.H. Benedict, C. Kaempfer, and
E. F. Barth. Biological Phosphorus Removal: A
Technology Evaluation. JWPCF 58:823, 1986.
3. Kang, S.J., P.J. Horvatin, and L. Briscoe. Full-
Scale Biological Phosphorus Removal Using A/0
Process in a Cold Climate. Proceedings of the
International Conference: Management Strategies
for Phosphorus in the Environment, Lisbon,
Portugal. Published by Selper, Ltd., London,
England, ISBN 0-948411-00-7, 1985.
4. Wastewater Engineering: Treatment, Disposal,
Reuse. Revised by George Tchnobanoglous.
McGraw-Hill Book Company, New York, NY,
2nd Edition, 1979.
5. T. Comfort and L. Good. Nitrogen and
Phosphorus Control by Two Facilities in Florida.
120
-------
Figure 7-5. Schematic of activated sludge system retrofitted for the modified Bardenpho process.
Degritted
Wastewater
• Nitrifying
Activated Sludge
Aeration tank
Effluent
Return Sludge
(2a)
(7)
Primary Sludge
.., (6)
(3)
J r — n (1)
J i i4-i_'.
"•T (2) !
(5)
Waste Activated
Sludge
i --- 1
i i
_
i / i
—
Existing
Retrofit
Legend
(1) Portion of return sludge going to anoxic tank.
(2) Anoxic tank for return sludge flow
(2a) Portion of denitrified return sludge flow.
(3) Anaerobic stripper tank for leaching of phosphorus.
(4) Stripper tank overflow.
(5) Stripper tank underflow returned to activated sludge aeration tank.
(6) Tank containing lime slurry to precipitate phosphorus leached from return sludge in anaerobic stripper.
Lime dose (CaO) = 20-25 mg/l based on plant flow
(7) Insolubilized phosphorus returned to primary for co-settling with primary sludge.
(8) Lime storage.
(9) Lime slurry tank.
(10) Pump for transfer of lime slurry to phosphorus precipitating tank.
Final
Effluent
TP
mg/l
2
1
0.5
0.2
* at peak
Probable Need
for
Chemical Addition
None
None
None
Occasional
sustained flow
Final
Clarifier
SOR"
gpf/sq ft
800
600
500
500
Approximate final
Organic-N:
NH4-N:
NO2-N:
NO3-N:
nitrogen concentrations (mg/l):
3.5
1
0.1
6
EPA-600/2-79-075, NTIS No. PB80-118813,
U.S. EPA, Cincinnati, OH, July 1979.
6. Evans, B. and P. Crawford. Introduction of
Biological Nutrient Removal in Canada. Presented
at Technology Transfer Seminar on Biological
Phosphorus Removal, Sponsored by Environment
Canada, Burlington, Ontario, Held at Penticton,
British Columbia, Canada, April 1985.
7. Summary Report of Workshop on Biological
Phosphorus Removal in Municipal Wastewater
Treatment. Prepared by R. L. Irvine and
Associates, Inc., Sponsored by U.S. EPA, Water
Engineering Research Laboratory, Cincinnati, OH,
Held at Annapolis, MD, September 1982.
8. Stensel, D., N. Sakakibara, D.R. Refling, and
C.R. Burdick. Performance of First U.S. Full-
Scale Bardenpho Facility. Presented at
International Seminar on Control of Nutrients in
Municipal Wastewater Effluents, Sponsored by
U.S. EPA, Cincinnati, OH, Held at San Diego, CA,
September 1980.
9. Barnard, J. Activated Primary Tanks for
Phosphate Removal. Water-South Africa,
10:121, 1984.
10. Nasr, S. and K. Knickerbocker. Biological Nutrient
Removal - Payson, Arizona. Presented at the
58th Annual Conference of the Water Pollution
121
-------
Control Federation, Kansas City, MO, October
1985.
11. Seyen, J., P. LeFlohic, G.M. Faup, M. Meganck,
and J.C. Block. A Separate Acetate Producing
Reactor to Improve Biological Phosphorus
Removal. Proceedings of the International
Conference: Managment Strategies for
Phosphorus in the Environment, Lisbon, Portugal.
Published by Selper, Ltd., London, England, ISBN
0-948411-00-7, 1985.
12. Siebritz, I.P., G. Ekama, and G.vR. Marais. A
Parametric Model for Biological Excess
Phosphorus Removal. Presented at IAWPR Post
Conference on Phosphate Removal in Biological
Treatment Processes, Pretoria, South Africa, April
5, 1982.
13. Match, L.C. and R.F. Drnevich. PhoStrip; A
Biological-Chemical System for Removing
Phosphorus. Advances in Water and Wastewater
Treatment: Biological Nutrient Removal, Edited by
M. Wanielista and W.W. Eckenfelder, Jr., Ann
Arbor Science Publishers, Inc., Ann Arbor, Ml,
1978.
122
-------
Chapters
Estimating Costs for Chemical Phosphorus Removal in the CBDB
8.1 Introduction
This chapter contains cost data sheets (Figures 8-1
through 8-8) that summarize the estimated capital,
annual alum and polymer, and total annual costs to
retrofit existing treatment plants in the CBDB to
achieve phosphorus removal by means of chemical
treatment. These are incremental costs over and
above the current costs to build and operate plants in
the CBDB. The costs of pH instrumentation and
controls, additional clarification capacity, increased
sludge conditioning and handling capacities, additional
building space for housing chemicals and chemical
feed equipment, and effluent filtration are not
included. The need for these items will be dictated by
site-specific conditions such as present capacities of
unit processes, wastewater quality, the existing
sludge handling scheme, the phosphorus removal
option selected, and applicable effluent limitations,
among others.
Depending on the degree of excess sludge handling
capacity available at a specific treatment plant and
the type of sludge handling and disposal methods in
use, only minor increases in capital and O&M costs
may be necessary to process and dispose of the
greater quantities of sludge resulting from chemical
phosphorus removal. Conversely, if a plant is already
operating at or near its existing sludge handling
capacity and new sludge handling and disposal
facilities must be built to accommodate the increased
amounts of sludge produced, significant expenditures
may be required.
Since the need for additional sludge handling capacity
must be determined on a case-by-case basis,
generalized cost estimates associated with increased
sludge production resulting from chemical phosphorus
removal could be misleading. For this reason, cost
estimates to retrofit existing plants to chemical
phosphorus removal are limited in this chapter to
capital and O&M requirements directly related to the
storage and feeding of chemicals.
The chemical retrofit costs summarized in Figures
8-1 through 8-8 apply to all of the treatment plant
categories found in the CBDB except wastewater
lagoons. These categories include:
plug flow activated sludge,
step aeration activated sludge,
complete mix activated sludge,
contact stabilization activated sludge,
pure oxygen activated sludge,
single-stage nitrifying activated sludge,
two-stage nitrifying activated sludge,
extended aeration,
oxidation ditches,
standard-rate trickling filters,
high-rate trickling filters, and
RBCs.
Four of the cost data sheets (Figures 8-1 through
8-4), one for each of the effluent TP limitations (2,
1, 0.5, and 0.2 mg/l) considered in this manual, were
developed for an influent TP concentration range of 6
to 10 mg/l. The other four cost data sheets (Figures
8-5 through 8-8) were developed for the same
effluent TP limitations, but an influent TP
concentration range of 3 to 6 mg/l.
Eighteen of the operating plants included in Tables
3-1 through 3-13 use alum for chemical
phosphorus removal. For nine of these 18, the annual
chemical costs of alum and polymer fall within the
appropriate ranges of theoretical annual alum and
polymer costs shown in Figures 8-1 through 8-8.
The annual chemical costs for the other nine plants
are less than those predicted by these figures. These
comparisons indicate that an inherent conservatism is
built into a theoretical stoichiometric dosing approach.
The annual chemical cost curves presented in this
chapter, therefore, should represent an adequate
chemicals O&M budget for chemical phosphorus
removal planning purposes for virtually all conceivable
wastewater characteristics and influent conditions
based on current chemical pricing structures.
In meeting 0.5- and 0.2-mg/l TP effluent limitations,
it is realized that substantial additional costs could be
involved in providing for improved effluent suspended
solids removals. This is particularly true for high-rate
trickling filters, which also might require additional
biological reactor capacity to effectively insolubilize
phosphorus to low effluent levels. Estimating average
incremental costs for these site- and situation-
specific requirements is impractical and beyond the
123
-------
Figure 8-1. Estimated chemical phosphorus removal costs for an influent TP range of 6 - 10 mg/l and an effluent TP
limitation of 2 mg/l.
Annual Alum and Polymer Cost
Total Annual Cost*
10 I 1 1 T
100,000 200,000
$/year
300,000
100,000 200,000
$/year
300,000
1 Sum ol the annual alum and polymer cost and the amortized chemical system capital cost. Costs associated with sludge treatment and
disposal are not included.
Plant
Size
mgd
< o.i
0.1 -1
> i -5
>5 -10
Chemical System
Capital Cost
$
34,000
54,000
130,000
170,000
scope of this handbook. Rather, the designer is
advised to carefully evaluate the potential impact of
effluent polishing on the total cost of any anticipated
retrofit project.
As indicated previously in Chapter 2, a theoretical
model being developed from research currently in
progress (1,2) predicts that metal ion dose
requirements to attain low effluent TP concentrations
of <1 mg/l are independent of influent TP
concentration. Published data confirming this model
are lacking at this time. In the absence of such data,
the cost curves presented in this chapter are based
on conventional metal ion-to-influent TP dose
relationships for all four effluent TP limitations
considered in this document. If the above theory (1,2)
is eventually verified, Rgure 8-3 (0.5-mg/l effluent
TP limit at influent TP of 6-10 mg/l) and Figure 8-7
(0.5-mg/l effluent TP limit at influent TP of 3-6
mg/l) would appropriately be merged into one figure
as would Figure 8-4 (0.2-mg/l effluent TP limit at
influent TP of 6-10 mg/l) and Figure 8-8 (0.2-mg/l
effluent TP limit at influent TP of 3-6 mg/l)
Estimated costs for retrofitting existing plants using
biological phosphorus removal processes are not
provided in this manual because each retrofit must be
uniquely designed and the necessary modifications
can range from minimal to considerable. Usually, no
significant net increase is experienced in operation
and maintenance costs when a biological phosphorus
removal system is installed. License fees are required
for some biological phosphorus removal processes.
The amount of the fees is determined on a case-
124
-------
Figure 8-2. Estimated chemical phosphorus removal costs for an influent TP range of 6 - 10 mg/1 and an effluent TP
limitation of 1 mg/l.
Annual Alum and Polymer Cost
Total Annual Cosf
150,000 300,000
$/year
450,000
150,000 300,000
$/year
450,000
Sum of the annual alum and polymer cost and the amortized chemical system capital cost. Costs associated with sludge treatment and
disposal are not included.
Plant
Size
mgd
< 0.1
0.1 -1
> 1 -5
>5 -10
Chemical System
Capital Cost
$
34,000
54,000
130,000
170,000
by-case basis by the process patent holders. These
fees can sometimes be substantial and may preclude
the use of a specific process.
8.2 Illustrative Example
Figures 8-1 through 8-8 each contain a graph
showing a range of annual alum and polymer costs as
a function of plant size, a graph showing a range of
total annual costs as a function of plant size, and a
tabulation of estimated capital costs for four plant size
ranges. For example, Figure 8-1 presents the cost
data for chemical phosphorus removal for an influent
TP concentration of 6 to 10 mg/l and an effluent TP
limitation of 2. mg/l. To estimate the capital, annual
alum and polymer, and total annual costs for a 0.18-
m3/s (4-mgd) plant with these influent and effluent
conditions, the reader would proceed as follows:
Using the capital cost tabulation, the capital cost to
retrofit any plant between 0.04 and 0.18 m3/s (1 and
5 mgd) is approximately $130,000. This cost includes
construction, engineering, legal, and administrative
fees, and contingencies. This cost is for the chemical
storage, feed, and distribution system only.
Moving to the first graph, the annual alum and
polymer cost would range between $100,000 and
$125,000 per year. As noted in Chapter 3, the cost
of ferric chloride or ferrous chloride would be lower
than the cost of alum. Therefore, the costs presented
here are conservative.
125
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Figure 8-3. Estimated chemical phosphorus removal costs for an influent TP range of 6 - 10 mg/l and an effluent TP
limitation of 0.5 mg/l.
Annual Alum and Polymer Cost
Total Annual Cost*
200,000 400,000
$/year
600,000
200,000 400,000
$/year
600,000
' Sum of the annual alum and polymer cost and the amortized chemical system capital cost. Costs associated with sludge treatment and
disposal are not included.
Plant
Size
mgd
< 0.1
0.1 -1
> 1 -5
>5-10
Chemical System
Capital Cost
$
34,000
54,000
145,000
170,000
The second graph shows the estimated total annual
cost. This graph is based on an assumed annual
capital cost of 10 percent (based on 8 percent
interest over a 20-year period) of the original capital
cost ($13,000 in this case) plus the annual alum and
polymer cost range ($100,000 to $125,000 in this
case). In this example, the estimated total annual cost
would range between $113,000 and $138,000 per
year.
8.3 References
1. Personal communication from R.I. Sedlak, The
Soap and Detergent Association, New York, NY,
to R.C. Brenner, U.S. EPA, Cincinnati, OH, May
20, 1987.
2. Personal communication from D. Jenkins,
University of California, Berkeley, CA, to S.J.
Kang, McNamee, Porter and Seeley, Ann Arbor,
Ml, July 31, 1987.
126
-------
Figure 8-4. Estimated chemical phosphorus removal costs for an influent TP range of 6 - 10 mg/l and an effluent TP
limitation of 0.2 mg/l.
Annual Alum and Polymer Cost
Total Annual Cost"
400,000 800,000 1,200,000
$/year
400,000 800,000 1,200,000
$/year
Sum of the annual alum and polymer cost and the amortized chemical system capital cost Costs associated with sludge treatment and
disposal are not included.
Plant Chemical System
Size Capital Cost
mgd
< 0.1
0.1 -1
> 1 -5
>5-10
$
41,000
87,000
185,000
200,000
127
-------
Figure 8-5. Estimated chemical phosphorus removal costs for an influent TP range of 3 - 6 mg/l and an effluent TP limitation
of 2 mg/l.
Annual Alum and Polymer Cost
Total Annual Cosf
60,000 120,000 180,000
$/year
60,000 120,000 180,000
$/year
Sum of the annual alum and polymer cost and the amortized chemical system capital cost. Costs associated with sludge treatment and
disposal are not included.
Plant Chemical System
Size Capital Cost
mgd
< 0.1
0.1 -1
> 1 -5
>5-10
34,000
54,000
115,000
160,000
128
-------
Figure 8-6. Estimated chemical phosphorus removal costs for an influent TP range of 3 - 6 mg/l and an effluent TP limitation
of 1 mg/l.
Annual Alum and Polymer Cost
Total Annual Cost*
80,000 160,000
$/year
240,000
80,000 160,000
$/year
240,000
Sum of the annual alum and polymer cost and the amortized chemical system capital cost Costs associated with sludge treatment and
disposal are not included.
Plant
Size
mgd
< 0.1
0.1 -1
> 1 -5
>5 - 10
Chemical System
Capital Cost
34,000
54,000
115,000
160,000
129
-------
Figure 8-7. Estimated chemical phosphorus removal costs for an influent TP range of 3 - 6 mg/l and an effluent TP limitation
of 0.5 mg/l.
Annual Alum and Polymer Cost
Total Annual Cost*
100,000 200,000
$/year
300,000
100,000 200,000 300,000
$/year
1 Sum of the annual alum and polymer cost and the amortized chemical system capital cost. Costs associated with sludge treatment and
disposal are not included.
Plant
Size
mgd
< O.i
0.1 -1
> i -5
>5 - 10
Chemical System
Capital Cost
$
34,000
54,000
120,000
170,000
130
-------
Figure 8-8. Estimated chemical phosphorus removal costs for an influent TP range of 3 - 6 mg/l and an effluent TP limitation
of 0.2 mg/l.
Annual Alum and Polymer Cost
Total Annual Cost
250,000 500,000 750,000
$/year
250,000 500,000 750,000
$/year
Sum of the annual alum and polymer cost and the amortized chemical system capital cost. Costs associated with sludge treatment and
disposal are not included.
Plant Chemical System
Size Capital Cost
mgd
< 0.1
0.1 -1
> 1 - 5
>5 - 10
. $
41,000
79,000
185,000
200,000
131
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Chapter 9
Factors Affecting Implementation of Phosphorus Removal in the CBDB
9.1 Introduction
The purpose of this chapter is to assist Chesapeake
Bay Area government officials in visualizing the broad
factors involved in implementing a comprehensive
program of phosphorus removal in the CBDB.
9.2 Cost to Implement Phosphorus
Removal
Based on the estimated costs to remove phosphorus
by chemical addition given in Chapter 8, the
approximate capital costs to retrofit CBDB plants
based on size, influent phosphorus concentration
range, and effluent phosphorus requirement are
summarized in Table 9-1. To put these capital costs
in perspective, the approximate costs of constructing
secondary treatment plants (without phosphorus
removal) are also given. The total costs to retrofit all
429 plants in the CBDB that are currently not
practicing phosphorus removal for the four effluent TP
limits considered in this manual are given in Tables
9-2 and 9-3 for the influent TP concentration
ranges of 6 to 10 and 3 to 6 mg/l, respectively. These
costs are for the chemical storage, feed, and piping
systems only. They do not include the costs for pH
control, additional plant capacity or sludge handling
equipment, increased sludge disposal quantities, or
effluent polishing.
Table 9-2 indicates that the total capital cost for
chemical storage and feed to retrofit these 429 plants
would be approximately $29,000,000 for an influent
TP concentration range of 6 to 10 mg/l and effluent
TP limitations of 2, 1, or 0.5 mg/l. For an effluent TP
limitation of 0.2-mg/l, the cost increases
approximately 35 percent to $39,000,000. For influent
TP concentrations of 3 to 6 mg/l, the estimated
capital costs are approximately 5 percent less than
those for an influent TP in the range of 6 to 10 mg/l.
O&M cost totals are not shown because they must be
calculated for each individual plant size in the CBDB
matrix. This can be done by using the annual
chemical cost range chart presented in Table 9-4.
As indicated previously in Chapter 2, a theoretical
model being developed from research currently in
progress (1,2) predicts that metal ion dose
requirements to attain low effluent TP concentrations
of <1 mg/l are independent of influent TP
concentration. Published data confirming this model
are lacking at this time. In the absence of such data,
the tabular summaries of estimated capital costs and
estimated annual chemical costs for chemical
phosphorus removal given in this chapter are based
on conventional metal ion-to-influent TP dose
ratios for all four effluent TP limitations considered in
this document. If this theory (1,2) is eventually
verified, the estimated capital costs to achieve 0.5-
and 0.2-mg/l effluent TP concentrations in Table 9-
1 would become the same for both the 6-10 and 3-
6 mg/l influent TP ranges. Similarly, the estimated
capital costs in the 0.5- and 0.2-mg/l effluent TP
columns in Tables 9-2 and 9-3 would become
identical. Finally, no distinction between the annual
chemical costs for the 0.5- and 0.2-mg/l effluent
TP limits in Table 9-4 would be appropriate for the
two influent TP ranges.
Capital and O&M costs for necessary sludge handling
improvements will vary depending on the amount of
sludge handling capacity available at each plant, the
types of sludge treatment and handling processes in
use, and the plant location (urban versus rural), which
generally dictates the methods of sludge disposal that
can be considered.
9.3 Comparison of Chemical and
Biological Retrofit Systems
Table 9-5 summarizes the major differences
between chemical and biological phosphorus removal
retrofit systems.
9.3.7 Effect of Excessive Infiltration/Inflow on
Process Selection
Excessive infiltration/inflow has no major effect on the
design of chemical retrofit systems. However, it can
seriously affect biological retrofit systems (e.g., larger
tank sizes may be required) and must be factored
into the overall design.
9.3.2 Process Reliability
Chemical treatment is a very reliable process for
phosphorus removal. It is estimated that wastewater
133
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Table 9-1. Estimated Capital Costs to Retrofit CBDB Plants for Phosphorus Removal Using Chemical Addition, Arranged by
Influent TP, Effluent TP, and Design Flow1
Effluent TP
Plant Size
2.0 mg/l
1.0 mg/l
0.5 mg/l
0.2 mg/l
$
$
Influent TP: 6-1 0 mo/1
< 0.1 mgd
0.1 - 1 mgd
> 1 -Smgd
> 5 -10 mgd
> 10mfld2
Intluofil TP: 3-6 mg/l
< 0.1 mgd
0.1 - 1 mgd
> 1 -Smgd
> 5 -10 mgd
> 10 mgd2
34,000
54,000
130,000
170,000
213,000
34,000
34,000
115,000
160,000
200.000
34,000
54,000
130,000
170,000
213,000
34,000
54,000
115,000
160,000
200,000
34,000
54,000
145,000
170,000
213,000
34,000
54,000
120,000
170,000
213,000
41,000
87,000
185,000
200,000
250,000
41,000
79,000
185,000
200,000
250,000
1 To put these capital costs in perspective, the approximate capital and annual O&M costs for conventional secondary treatment plants
without phosphorus removal utilizing the activated sludge process, vacuum filter sludge dewatering, and landfilling of dewatered sludge
are (3):
Design Flow Capital Cost
0.1 mgd $2,400.000 ($65,750/Mgal)
1 mgd $8,000,000 ($21,920/Mgal)
5 mgd $18,600,000 ($lO,l90/Mgal)
10 mgd $29,300,000 ($8,030/Mgal)
Annual O&M Cost
$200,000 ($5,480/Mgal)
$700,000 ($1,920/Mgal)
$1,500,000 ($820/Mgal)
$3,000,000 ($820/Mgal)
2Sfnce plant sizes over 10 mgd are not listed in this table, capital cost estimates of 25 percent above the 5-10 mgd estimates are assumed
across the board.
treatment plants utilizing chemical addition for
phosphorus removal achieve their effluent TP limits
90 percent of the time.
A sufficient data base is not available to judge long-
term reliability of biological phosphorus removal at
this time. Chemical feed equipment for backup dosing
and/or effluent polishing can be installed to enhance
reliability.
9.3.3 Potential Technological Advances
Technological advances can be expected to occur in
the next several years in the area of biological
phosphorus removal. The emerging
processes/concepts include:
• A/O and A2/O
• PhoStrip II
• Bardenpho
• Magnesium ammonia phosphate precipitation
during anaerobic digestion
• European technology using managed biological
systems for nutrient control. Investigators in
Denmark, Germany, Austria, and Japan are
working with a variety of process options.
• Metal salt dose requirements and optimum dosage
points to polish effluent TP concentrations to 0.5
mg/l and below in conjunction with biological
phosphorus removal processes.
9.3.4 Impact of License Fees
Certain biological phosphorus removal processes
require the payment of a license fee. The amount of
the fee, which can be substantial, is determined on a
case-by-case basis by the process patent holders.
It is recommended that municipalities considering
these technologies negotiate license fees prior to
embarking on rigorous retrofit planning and design.
9.3.5 Degree of Operation and Control Difficulty
Biological phosphorus removal processes are
generally more difficult to operate and control than
chemical phosphorus removal processes. The degree
of difficulty can be significant. Operations must be
adjusted to account for 1) temperature effects on the
biological activity of a complex sludge biomass, 2) the
ratio of influent BOD to phosphorus, 3) internal
recycle flows, 4) sludge removal rates from
secondary clarifiers, and 5) the phosphorus content of
in-plant recycle streams.
9.3.6 Additional Staffing Requirements
The estimated ranges of man-hours required per
year to operate and maintain a ferric chloride or alum
feed system were given previously in Table 5-20 as
a function of plant size. These man-hours can be
converted to numbers of personnel by dividing by
1,500. For example, from the chart, a maximum of
134
-------
Table 9-2. Estimated Capital Costs to Retrofit CBDB Plants for Phosphorus Removal Using Chemical Addition; Influent TP
Range: 6 - 10 mg/l
Plant Size
mgd
< 0.1
0.1 - 1
> 1 -5
> 5- 10
> 10
Total
Grand Total
State
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
No. of Plants Not
Currently Practicing -
Phosphorus Removal
32
138
11
181
62
39
62
163
21
10
22
53
5
1
3
g
16
3
4
23
136
191
102
429
2.0 or 1.0
$1,000
1,088
4,692
374
6,154
3,348
2,106
3,348
8,802
2,730
1,300
2,860
6,890
850
170
510
1,530
3,408
639
852
4,89,9
11,424
8,907
7,944
28,275
Effluent TP (mg/l)
0.5
$1,000
1,088
4,692
374
6,154
3,348
2,106
3,348
8,802
3,045
1,450
3,190
7,685
850
170
510
1,530
3,408
639
852
4,899
11,739
9,057
8,274
29,070
0.2
$1,000
1,312
5,658
451
7,421
5,394
3,393
5,394
14,181
3,885
1,850
4,070
9,805
1,000
200
600
1,800
4,000
750
1,000
5,750
15,591
11,851
11,515
38,957
1,580 man-hours per year is required to operate and
maintain an alum feed system for a plant in the 0.22
to 0.4 m3/s (5 to 10 mgd) range. This equates to
about one additional staff person.
Additional staff time will also be required to operate
and maintain biological phosphorus removal systems.
However, due to the newness of this technology,
additional staff time has not been quantified.
9.3.7 Degree of Maintenance Difficulty
Chemical feed systems will typically require a higher
degree of maintenance than biological phosphorus
removal systems. Chemical feed systems require
maintenance at the storage, makeup, and distribution
points of the system, and sophisticated
instrumentation maintenance for larger systems may
be necessary. The maintenance problems are
compounded when corrosive chemicals like ferric
chloride must be handled. Maintenance on biological
phosphorus removal systems should be limited to the
tank mixers and recycle pumps, which is relatively
simple, safe, and inexpensive to provide.
9.4 Administrative issues
9.4.1 Planning and Construction Period
Schedules
The estimated time periods necessary to retrofit a
wastewater treatment plant for phosphorus removal
are shown in Table 9-6. The times shown are from
the initiation of design through plant startup.
9.4.2 Operator Training Seminars
It is recommended that each state in the CBDB
conduct operator training seminars for phosphorus
removal. These seminars should be conducted at
least twice a year at a central location. In addition,
plant designers should make personnel available to
conduct operator training sessions at each plant
retrofitted. These sessions should cover the theory
and operation of the phosphorus removal system to
be used. Individual site training should begin a few
months prior to, and be repeated after, plant startup.
9.5 References
1. Personal communication from R.I. Sedlak, The
Soap and Detergent Association, New York, NY,
to R.C. Brenner, U.S. EPA, Cincinnati, OH, May
20, 1987.
2. Personal communication from D. Jenkins,
University of California, Berkeley, CA, to S.J.
Rang, McNamee, Porter and Seeley, Ann Arbor,
Ml, July 31, 1987.
3. DeWolf, G., P. Murin, J. Jarvis, and M. Kelly. The
Cost Digest: Cost Summaries of Selected
Environmental Control Technologies. EPA-
600/8-84-010, U.S. EPA, Washington, DC,
October, 1984.
135
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Table 9-3.
Estimated Capital Costs to Retrofit CBDB Plants for Phosphorus Removal Using Chemical Addition; Influent TP
Rango: 3-6 mg/l
No. of Plants Not
Effluent TP (mg/l)
Plant Size
mod
< 0.1
0.1 • 1
> 1 -5
> 5- 10
> 10
Total
Grand Total
State
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
Total
VA
MD
PA
Currently Practicing —
Phosphorus Removal
32
138
11
181
62
39
62
163
21
10
22
53
5
1
3
9
16
3
4
23
136
191
102
429
2.0 or 1.0
$1,000
1,088
4,692
374
6,154
3,348
2,106
3,348
8,802
2,415
1,150
2,530
6,095
800
160
480
1,440
3,200
600
800
4,600
10,851
8,708
7.532
27,091
0.5
$1,000
1,088
4,692
374
6,154
3,348
2,106
3,348
8,802
2,520
1,200
2,640
6,360
850
170
510
1,530
3,408
639
852
4,899
11,214
8,807
7,724
27,745
0.2
$1,000
1,312
5,658
451
7,421
4,898
3,081
4,898
12,877
3,885
1,850
4,070
9,805
1,000
200
600
1,800
4,000
750
1,000
5,750
15.095
11,539
11,019
37,653
Tablo 9-4.
Influent TP
Estimated Annual Chemical Costs for
Phosphorus Removal
Effluent TP
Limitation
Annual
Chemical Cost
6-10
3-6
mg/I
2
1
0.5
0.2
2
1
0.5
0.2
$/Mgal
68 - 84
82 -104
102 -142
137 - 350
42-52
50-64
62-88
83 - 217
136
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Table 9-5 Comparison of Chemical and Biological Retrofit Systems
Items Chemical System
Biological System
Attainable Effluent TP
Concentration
Amenable Unit Processes
Reliability
Costs
Sludge Quantities
Operator Training
Additional Staffing
Requirements
Infiltration/Inflow
Potential Technical
Advantages
0.2 mg/l
All secondary treatment processes can be retrofitted.
Reliable, proven technology.
High O&M in terms of chemical and sludge handling,
more difficult to maintain.
A considerable amount of chemical sludge is
produced for which additional sludge handling facilities
may be required.
Relatively simple to operate. Some training will be
required for operation of chemical feed pumps and
systems.
An additional person may be required depending on
the size of the plant.
No major effect on retrofit design.
None anticipated.
1.0 mg/l (0.5 mg/l or less requires chemical addition).
Amenable only to activated sludge-type secondary
processes.
Long-term reliability not proven.
Little or no excess sludge produced, low O&M costs.
Payment of license fee may be required,
Sludge quantities will increase only slightly with the
A/O and PhoStrip processes.
More difficult to operate and control. Some training
will be required for monitoring and chemical feed
system operation for the PhoStrip process.
For the PhoStrip process, an additional person may
be required depending on the size of the plant
Additional staff should not be necessary for the A/O
process.
Can significantly affect retrofit design.
Several anticipated.
Table 9-6. Estimated Time Periods for Retrofitting an
Existing Plant to Phosphorus Removal
Design, Plans,
Plant Size
mgd
< 0.1
0.1 - 1
> 1 -5
> 5- 10
> 10
& Specs
months
3
4
6
8
10
Construction
months
6
8
12
18
24
Startup
months
1
i
3
4
6
Total
months
10
13
21
30
40
137
U.S. GOVERNMENT PRINTING OFFICE: 1987— 7 «f 8 - 1 2 1 / S7Q31
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