EPA-R2-73-122
„„-, Environmental Protection Technology Series
July 1973
Evaluation Of Treatment
For Urban Wastewater Reuse
Office of Research and Developement
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
1. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-R2-73-122
July 1973
EVALUATION OF TREATMENT FOR
URBAN WASTEWATER REUSE
by
K. D. Linstedt
E. R. Bennett
University of Colorado
Boulder, Colorado 80302
Grant #17080 D01
Project Officer
Edwin F. Earth
U.S. Environmental Protection Agency
National Environmental Research Center
Cincinnati, Ohio 45268
for the
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $2.10
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EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and
Monitoring, Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
ii
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ABSTRACT
This study was undertaken to evaluate the efficacy of
combining biological nitrification with each of two modes of
chemical clarification for production of a water suitable for
specific industrial reuse applications.
For this purpose, a 7200 gpd pilot plant was constructed,
operated and analyzed. The nitrifying activated sludge system
was operated to identify the effect of variations in detention
time, loading, and temperature on the performance of the system,
In the temperature range of 5-30°C, a maximum nitrification
rate was observed to occur at about 25°C. Variations in BOD,
COD, and ammonia loadings were investigated over a wide range,
with complete nitrification observed for loadings at or below
the following levels: 0.4 #BOD5/#MLSS/DAY; 1.4 #COD/#MLSS/DAY ;
and 0.16 #NH3-N/#MLSS/DAY. The oxygen demand for ammonia
oxidation by nitrification was determined to be 4.6
In the conventional clarification system, low doses of
lime or alum were shown to be effective in removing greater
than 95% of the BOD, turbidity, and suspended solids from the
nitrified secondary effluent . Efficient phosphorus removals
necessitated higher lime and alum additions of 300 mg/1, and
100—150 in0" ^1 res^ec t i vel'*7 . A.t the hirrheT" litre closes ?~ two-
fold reduction in bacterial organisms was achieved. Specific
heavy metals were removed through both alum and lime additions.
With either coagulant chemical, practical rapid sand filter
runs of 16 hours were observed to be possible .
Similar removal results were obtained with alum in a high-
rate clarification flow system with direct dual-media filtra-
tion of alum flocculated wastewater. Filter runs of 5-6 hours
could be realized.
This report was submitted in fulfillment of Project Number
17080 - DOI, under sponsorship of the Office of Research and
Monitoring, Environmental Protection Agency, by the University
of Colorado, Boulder, Colorado.
iii
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Experimental Pilot Plant 7
V Analytical Methods 19
V
VI Biological Nitrification 25
VII Conventional Clarification 47
VIII High Rate Clarification 91
IX Acknowledgements 133
X References 135
v
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FIGURES
Number E^LI.
1. Pilot Plant Flow Schematic 8
2. Hydraulic Profile - Denver Reuse Pilot Plant Study 9
3. Nitrification Aeration and Clarification Units 11
4. Vertical Adjusting Weir - Chemical Settling 12
Tank Unit
5. Effect of Temperature on Nitrification From
Bench Scale Studies 33
6. Sludge Volume Index as a Function of Temperature
For The Bench Scale Studies Utilizing A Four
Hour Detention Time 35
7. Effect of BOD Loading on Nitrification From
Bench Scale Studies 36
8. Ammonia Oxidation as a Function of BOD Loading
Factor 37
9. Ammonia Oxidation,as a Function of the COD
Loading Factor 39
10. Ammonia Oxidation as a Function of the Ammonia
Loading Factor 40
11. Extent of Biological Nitrification as a Function
of Reaction Time 43
12. Residual Phosphate as a Function of Flocculation
Detention Time 50
13. Residual Phosphate as a Function of Mixing Intensity 51
14. pH in Flocculation Reactor as a Function of Lime
Dose 52
15. Turbidity Removals with Lime Addition 53
16, Suspended Solids Removal with Lime Additions 54
17. BOD Removal with Lime Addition 55
VI
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FIGURES
Dumber Page
18. COD Removal with Lime Addition 57
19. Ortho- Phosphate Removals with Lime Additions 58
20. Total Phosphate Removal with Lime Additions 60
21. Turbidity Removal Efficiency After Lime Treatment
and Filtration 61
22. Suspended Solids Removal Efficiency After Lime
Treatment and Filtration 62
23. BOD Removal Efficiency After Lime Treatment
and Filtration 63
24. COD Removal Efficiency after Lime Treatment
and Filtration 64
25. Phosphate Removal Efficiency with Lime 55
26. Effect of Lime Sludge Recycle on the Removal
01 Total Phosphate with Lime 66
27. Coliform Removal With Lime Additions 67
28. Fecal Coliform Removals With Lime Additions 69
29. Fecal Streptococcus Removals With Lime Addition 70
30. Monthly Variations in Iron Concentration 71
31. Monthly Variations in Copper Concentration 72
32. Monthly Variations in Manganese Concentration 73
33. Monthly Variations in Chromium Concentration 74
34. Monthly Variations in Lead Concentration 75
35. Monthly Variations in Zinc Concentration 76
36. Monthly Variation in Molybdenum Concentration 77
37. Monthly Variation in Aluminum Ion Concentration 78
38. Monthly Variations in Cadmium Concentration 79
Vll
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FIGURES
Number
Page
39. Waste Sludge Production (Tons/MG) as a Function
of Lime Dose 81
40. Headless as a Function of Solids Capture in a
Rapid Sand Filter 83
41. Turbidity Removal With Alum in the Alum Clarifier
System 84
42. BOD Removal With Alum in the Alum Clarifier
System 86
43. COD Removal With Alum in the Alum Clarifier
System 87
44. Ortho— Phosphate Removal With Alum in the Alum
Clarifier System 88
45. Total Phosphate Removal With Alum in the Alum
Clarifier System 89
46, pH Optimization for the Alum System 97
47. Ortho-Phosphate Removal With Alum 98
48. Total Phosphorus Removal With Alum 100
49. Total Phosphate Removal as a Function of Al/PO,
Molar Ratio 101
50. Turbidity Removal With Alum 102
51. Suspended Solids Removal With Alum 104
52. COD Removal With Alum Additions 105
53. BOD Removal With Alum 106
54. Residual Pollutional Parameters as a Function
of Alum Dose 1Q7
55. Influent and Effluent Iron Concentrations ^9
56. Influent and Effluent Copper Concentrations HO
57. Influent and Effluent Manganese Concentrations m
58. Influent and Effluent Chromium Concentration -,-12
viii
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FIGURES
Number Page
59. Influent and Effluent Lead Concentration 113
60. Influent and Effluent 'Zinc Concentration 114
61. Influent and Effluent Cadmium Concentration 115
62. Influent and Effluent Molybdenum Concentrations 116
63. Influent and Effluent Aluminum Concentration 117
64. Total Coliform Removal History With Alum 119
65. Fecal Coliform Removal History With Alum 120
66. Fecal Streptococcus Removal History With Alum 121
67. Filter Headloss as a Function of Suspended Solids
Captured (2.39 gpm/Ft.2) 123
68. Filter Headloss as a Function of Suspended Solids
Captured (3.0 gpm/Ft.2) 124
69. Filter Headloss as a Function of Suspended Solids
Captured (3.8 gpm/Ft.2) 125
70. Filter Headloss as a Function of Suspended Solids
Captured (5.0 gpm/Ft.2) 126
71. Filter Headloss as a Function of Suspended Solids
Captured (5.7 gpm/Ft.2) 127
72. Filter Headloss as a Function of Suspended Solids
Captured and Flowrate 128
73. Headloss as a Function of Flowrate for Clear
Water Flowing Through the Dual-Media Filter 130
ix
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TABLES
Numbers Page
I Rapid Sand Filter Composition 16
II Dual-Media Filter Composition 17
III Nitrification Design Parameters 31
IV Comparison of BOD Loading Data 38
V Oxygen Utilization for Nitrification 45
VI Trace Metal Removals 80
VII Average Trace Metal Influent and Effluent
Concentrations 118
VIII Alum Dose vs. Percent Reduction of Total Coliforms 122
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I. CONCLUSIONS
It was demonstrated in this pilot plant investigation that
complete conversion of ammonia to nitrate can be achieved through
biochemical oxidation in a second-stage activated sludge type
system.
The nitrification reaction rate is quite predictable with a
reaction rate constant of 0.16. #NH3/#MLSS/DAY and aeration require-
ments of 4.6 #02/#NH3~N. It appears that the rate of reaction is
not proportional to the ammonia concentration, but proceeds at
a constant rate until all of the NH4 is converted to N03~- With
the relatively rapid rate of ammonia conversion, and a high organism
level it should be possible to remove the second-stage BOD from
secondary effluents in a comparatively small tertiary activated
sludge unit.
The rate of nitrification is temperature dependent, with a
maximum rate at about 25°C.
The settleability of the nitrifying sludge improves with
increasing temperature in the range of 5-30°C.
Acclimation of nitrifying activated sludge is considerably
more difficult than in a carbonaceous system. In this study,
the acclimation time was reduced somewhat by seeding the aeration
system with aerobically digested activated sludge.
In the tertiary nitrification system, the sludge has a very
high biomass fraction. This sludge is relatively light, resulting
in a pinpoint floe carry-over problem. With the solids loss
resulting from this carry-over, coupled to the long generation
time of the nitrifying organisms, it was not possible in this
study to achieve a net sludge growth. Therefore, in plant appli-
cations of nitrifying activated sludge systems it may be necessary
to provide for enhancement of the flocculation in the biological
system, or to maintain a supplemental source of nitrifying organisms.
In the chemical clarification studies utilizing sedimentation-
filtration treatment it was shown that moderate Ca(OH)9 additions
of 100 mg/£, with corresponding pH levels of 8.0-9.5, produce a
clear effluent with a high degree of suspended solids and BOD
removal. Higher lime doses of 200-300 mg/£ (pH>11.0) are necessary
to reduce the total phosphate level below 1 mg/-l. At these higher
lime doses the residual COD can be reduced to about 20 mg/£ as a
limit.
The effectiveness of lime in reducing the concentration of
bacterial organisms increases with dose and pH. At lime doses of
400 mg/£, fecal coliform, fecal streptococcus, and total coliform
concentrations can be reduced by two orders of magnitude utilizing
conventional clarification without chlorination.
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Lime is effective in precipitating some heavy metals from
secondary effluent. The concentrations of iron, manganese, chromium
and zinc are reduced in lime treatment, while copper, lead, molyb-
denum, aluminum, and cadmium are not significantly precipitated at
the trace concentrations found in wastewater.
At typical suspended solids levels of 5 mg/
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II. RECOMMENDATIONS
From the results obtained in this and other research, it is
evident that chemical clarification with or without filtration
holds considerable promise for upgrading existing wastewater
effluents at a comparatively low cost. With addition of moderate
doses of alum or lime, a clear product can readily be produced
having a BOD,, of less than 5 mg/t. This system also has capability
for phosphorus removal through the simple manipulation of the
applied chemical dose. The choice between alum and lime should
be considered in the context of each specific operational and
sludge disposal situation, since these criteria will likely dic-
tate the economic practicality of the system. The use of this
technology should be strongly encouraged for improved water pol-
lution control and increased opportunities for beneficial succes-
sive use of products from such plants.
Further, for potential high-level successive use applications,
including potable use, the studies elaborated in this and other
reports should be extended to evaluate the role of the nitrification
and chemical clarification systems as pre-treatment to subsequent
carbon and ion removal units. This and alternate process trains
should be evaluated in the context of successive potable use as
well as for their water pollution control potential, since there
appears to be increasing pressure developing for general application
of the reuse concept. Necessarily, the evaluation for potable
reuse potential must be much more extensive than that required by
water pollution control criteria.
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III. INTRODUCTION
Water pollution and its control are of great concern with
the increasing quantities and continually changing character
of water pollutants. Suspended solids, refractory organics,
nutrients, and inorganic salts are discharged to receiving
streams in ever increasing quantities. Simultaneously, the
streams are being overwhelmed by the higher load of biologi-
cally degradeable pollutants. The 85 to 90 percent BOD removal
attainable by conventional waste treatment practices is becom-
ing inadequate for maintenance of aesthetically acceptable con-
ditions in many receiving streams.
Associated v/ith the indicated degradation of water quality
is a reduction of suitable supply water, since the usefulness
of a stream for supply purposes is closely related to the stream
quality. Renovation and successive use of wastewater offer one
means of alleviating both the water pollution and water supply
problems.
Successive use is particularly attractive in many of the
arid western cities, where legal constraints and water develop-
ment costs make new sources of raw water increasingly difficult
to acquire. For cities on the eastern slope of the Rocky Moun-
tains, source water is presently transported through the Conti-
V» £1 T> 4- O ~l T*\ -iTT-t^O. /^1j->1T(C»^-*-i--ij^\-i-» <->_/JL^— Oi.lU,J.J. JL. W W
miles and involve complex networks of tunnels, canals, conduits,
and reservoirs. Thus, this area has many of the characteristics
of a good location for initiation of large scale fresh water -
renovated water tradeoffs for satisfying industrial needs.
In this context, the objective of this study has been to
evaluate the technical feasibility of several treatment proces-
ses for upgrading wastewater quality to the point that it is
available for certain industrial reuse applications. Specific
processes included in this initial phase of evaluation were
biological nitrification, and chemxcal clarification utilizing
either conventional or high-rate filtration. For these treat-
ment systems, data have been collected to assess the practical-
ity of upgrading secondary effluent at the Metropolitan Denver
Wastewater Treatment Plant to a quality level which is accept-
able in selected industrial water applications. Specifically,
the aim was to: 1) define the reasonable ranges of these para-
meters which control the biological nitrification activated
sludge process in order to identify the practical limits of the
important operating variables; and, 2) to determine the optimum
dose, pH, mixing, and filtration conditions for achieving sus-
pended solids and phosphate removals in both the conventional
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and high-rate clarification systems. In the fulfillment of
these goals, a 7200 gpd pilot plant was developed, operated,
and analyzed.
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IV. EXPERIMENTAL PILOT PLANT
INTRODUCTION
The 5 gpm pilot plant utilized in these studies was con-
structed on the site of the Metropolitan Denver Sewage Disposal
District Treatment Plant. The units included in this plant are
shown in the simplified flow schematic of Figure 1. As indi-
cated in the Figure, the 5 gpm influent flow consisted of second-
ary effluent from a municipal activated sludge plant. This
influent was initially subjected to biological nitrification for
oxidation of the ammonia nitrogen form to nitrate ion. Follow-
ing nitrification, the flow was divided into two streams for
subsequent clarification treatment. One of the systems had pro-
vision for several operations which are similar to conventional
water treatment operations. These included chemical addition,
rapid mix, flocculation, clarification, and filtration. A
parallel treatment sequence was designed as a high-rate water
clarification system. This treatment system incorporated chemi-
cal addition, rapid mix, flocculation, polyelectrolyte addition,
and dual-media filtration, following the initial biological
nitrification process.
Flov; in the plant v/ns gravity from the nitrification unit
to the filter inflow. Pumps were provided to overcome the
hydraulic head-loss on the filters. This hydraulic profile
for the system is indicated in Figure 2.
PILOT PLANT DESCRIPTION
The pilot plant influent was obtained from the Parshall
flume preceding the chlorination basin at the Metro Denver Plant.
The waste was pumped with a Teel 1P555 screw type pump driven
with a variable speed pulley by a ^ H.P. electric motor. The
plant influent flow was transported through 3/4" PVC pipe to
the Denver Water Department effluent pumping station in which
the pilot plant was located. The line entered the building
where the pipe enlarged to 1^". At this point there was a 5"
globe valve sample cock for sample removal. In subsequent dis-
cussions of the system this point is referenced as sample point
No. 1. Subsequent to this point the system piping was 2" sched-
ule 80 PVC unless otherwise noted. Following the sample cock
the flow passed through a 2" PVC globe valve and into the nitri-
fication tank.
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Pump
Sample Point
Number
NITRIFICATION
ACTIVATED
SLUDGE
DUAL
MEDIA
BACKWASH " \ FILTER
1) S.P.
ELECTROLYTE
PILOT PLANT FLOW SCHEMATIC
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15'
vo
NITRIFICATION
TANK
Figure 2
HYDRAULIC PROFILE
15'
10'
floor
EFFLUENT
TANK
5'-
FILTER
0' J
DENVER REUSE PILOT 1>HNT STUDY
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As indicated, the first unit operation in the Pilot Plant
series was a biological nitrification system. It consisted of
a typical activated sludge system including an aeration tank
followed by a clarifier. Two different aeration systems were
used in different parts of the study. The primary system con-
sisted of a three compartment unit having a total volume of
145 ft3. It is shown in Figure 3 with the nitrification
clarifier. At the design flow rate of 5 gpm, these system
components had detention times of 3 hours, and 70 minutes,
respectively. The second aeration system consisted of a series
of six tanks of 50 gallon capacities.
The primary nitrification aeration tank was constructed
of 3/16" steel plate 4'6" square by 7'7" deep. The tank was
baffled into 3 sections by steel plates extending from top to
bottom. Flow entered at the bottom of the tank and the first
baffle had an opening at the top just below the minimum water
level to provide for the discharge from the first pass. Like-
wise, the second baffle had an opening at the bottom, with the
flow directed up and over the overflow weir at the end of the
third pass. The outlet weir was a V-notch weir which extended
along one side of the tank and was 12" deep by 2" wide. The
weir height was adjustable over a range of approximately +20%
of the design detention time of the tank. The weir assembly
is shown in Figure 4. From the overflow weir a 2" wire rein-
~F /•> v» /~»o /"^l -FTo-v-iV\~!o V» r\c— o /-l-iY»o/-»4-ar1 -f- V* o -r\w r\ t~* o i W W*— fcO *J JL.J.OH C-V> t*. .*-.!_ U O -*- J..1 j:^
through the side of the tank. The mixed liquor in the nitri-
fication tank was aerated by six Chicago Pump Precision saran
wrapped tube diffussors supplied by the Metro Denver Sewage
Treatment Plant. Air was supplied at 16 cfm by a Roots Moxair
1702-162 rotary compressor driven by a 2 H.P. motor. In this
aeration unit, effluent from the Metro Denver Plant was sub-
jected to aeration with a bacterial activated sludge having a
predominance of Nitrosomonas and Nitrobacter.
Following the three hour aeration period, the suspended
biological solids passed into a clarifier where the biological
solids were removed from the liquid stream and the nitrified
effluent was discharged through an overflow weir. The settled
bacterial solids were continuously recycled into the influent
of the aeration unit to provide a constant nitrifying bacterial
population for steady-state bacterial nitrification. From the
aeration tank the process flow passed into the biological clari-
fier. A 2" PVC globe valve and a ^" sample cock were provided
between the aeration tank and the clarifier.
It was found necessary to provide piping within the clari-
fier to impart a radial component to the flow in order to
10
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Figure 3
NITRIFICATION AERATION AND CLARIFICATION UNITS
11
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INFLUENT
X
SLUDGE
Figure 4
VERTICAL ADJUSTING WEIR - CHEMICAL SETTLING TANK UNIT
12
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minimize short circuiting and scouring. For the same reason,
the line from the aeration basin to the clarifier was vented
to the atmosphere to provide for removal of entrained air.
Sludge removed from the process stream by the clarifier
•was recycled to the influent of the nitrification tank by a
small centrifugal pump coupled to a 3/4" rubber hose. Recycle
flow was controlled by incorporating a valved recycle loop
between the pump intake and discharge.
The biological clarifier was 4'0" square on top and the
sides extended vertically downward 2'8". Below this depth
the walls formed an inverted pyramid and extended another 3'8"
to the apex. As with the other system tanks, the construction
material was 3/16" steel plate. A 4' V-notch overflow weir
was located along the center line of the tank. From the weir a
2" flexible hose carried the liquid discharge to a fitting in
the side of the tank.
The effluent from the biological system was subjected to
chemical treatment for removal of suspended solids, phosphates,
and selected organic and inorganic constituents. As indicated
earlier, this was achieved in one of two parallel clarification
systems, conventional and high-rate, by splitting the biologi-
cal clarifier effluent into two flow streams. The conventional
system incorporated j-acixi oics ^or coagulant addition, rapid
mixing, flocculation, settling, and rapid sand filtration.
Provision was made for adding either lime or alum coagulant to
the nitrified influent.
The coagulant was rapidly dispersed throughout the water
volume in a rapid mix tank having a one minute hydraulic deten-
tion time. This tank was 8" wide, 14" long and 19|" deep with
four vertical baffles. The first three baffles had space on
alternate ends for development of an end-around flow pattern.
The final baffle extended entirely across the tank width with
a vertical adjustment to control head and detention within the
tank. The flow passed over this baffle and into the outlet
line.
Following rapid mix, the flow in the conventional system
was again split into parallel systems prior to flocculation and
settling. This was done to maximize operational flexibility
within the plant. The discharge from the rapid mix tank flowed
to a tee where the flow was divided between each of the dupli-
cate slow mix-clarifier systems. Each side of the tee was fitted
with a 2" globe valve for isolation of the individual systems.
The flow rate distribution between the two systems was controlled
13
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by adjusting the weir height in each of the parallel floccu-
lation tanks.
The slow mix tanks were built of 3/16" steel plate. They
were 2'4" by 2'0" on top and 3'4" deep to provide a 30 minute
hydraulic detention at design flow. Each tank had a V-notch
overflow weir similar to that in the biological clarifier ex-
cept that they were only 2'4" long. Each tank was stirred by
a four bladed paddle with the blades being 2|" by 22" long and
located 7 inches from the axis of the stirrer to the center of
the paddle. The speed of the stirrer was variable over the
range 8-33 rpm. Flow over the weir passed through flexible
tubing and out of the tank through a fitting on the side. In
each system, the slow mix tank effluent passed through 2" PVC
to the chemical clarifier. These clarifiers were similar in
operation to the bio-clarifiers. Each clarifier was 3'0"
square on top and had an overall height of 4'8-|". Chemical
sludge removed from the process flow was pumped to a holding
tank on a batch basis and then pumped out for disposal.
Following chemical clarification, facilities were provided
for recarbonation of the effluent. In this operation, carbon
dioxide or mineral acid was added to lower the pH and stabilize
the water prior to applying it to a filter. This was done to
prevent calcium carbonate encrustation of the filter media.
The recarbonation tank was 2T x 2'4" x 3'4".
The parallel chemical treatment system employed high rate
clarification and included units for coagulant addition, rapid
mixing, flocculation, polymer addition, and direct dual-media
filtration. The system was identical to the conventional system
through the slow mix step except that parallel slow mix units
were not provided. From the slow mix tank the flow entered the
intake to the filter pumps.
The filter pumps were Teel 1P555 screw type positive dis-
placement pumps. They were driven by variable speed motors
using belt drives. As with the nitrifier sludge recycle, these
pumps were equipped with a recycle loop to provide control over
the filter loading rates. There were two pumps installed with
adequate piping to permit simultaneous pumping from each of
two tanks, onto either of the two filters.
From the filter pump the process water flowed through 3/4"
rubber hose to either the rapid sand or dual media filters.
The rapid sand filter was 13| in. inside diameter and 6'0" tall.
A plexiglass window was installed on the side of the filter which
extended from 6" below the top. At each end of the filter there
14
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was a £" x 34" flange to which -4" endplates were secured.
These endplates contained the fittings necessary for loading,
discharging and backwashing the filters. A filter head loss
fitting was provided on the side of each filter 1'6" down
from the top of the filter. There were 7 £" x |" x 13-|" annu-
lar rings welded to the inside of each filter starting at 6"
above the bottom and placed every 4" upward. These were in-
cluded to minimize the wall effects within the filters. There
were two perforated baffles 3" apart in the bottom of each
filter. Effluent flowed through a threaded fitting on the
bottom of the filter and into an effluent holding tank from
which it was pumped from the plant. The dual-media filter
construction was identical to that of the rapid sand filter
except that it was 8" inside diameter. The gradations of
filter media within these two filters are shown in Tables I
and II.
15
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TABLE I
RAPID SAND FILTER COMPOSITION
Diameter 14" I.D.
Layer
Depth
24"
21 IT
2
ill!
i"
Material
Filter Sand
Coarse Sand
Coarse Sand
Gravel
Grave 1
Gravel
Gravel
Characteristics
E.S.
All passed
All retained
All passed
All retained
All passed
All retained
All passed
All retained
A 1 1 t^.-.
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TABLE II
DUAL-MEDIA FILTER COMPOSITION
Diameter 8 1/8" I.D.
Layer
Depth
16"
8"
2"
2"
2"
1*"
Material
Anthrafilt
Characteristics
Filter Sand
Coarse Sand
Coarse Sand
Fine Gravel
Gravel
Gravel
S.G.
Porosity
E.S.
U.C.
All passed
All retained
E.S.
All passed
All retained
All passed
All retained
All passed
All retained
All passed
All retained
All passed
All retained
All passed
All retained
1.55
.45 - .55
.90 mm - 1.0 mm
1.7
#12 U.S.S. Sieve
#30 U.S.S. Sieve
.40 mm - .45 mm
#30 U.S.S. Sieve
#50 U.S.S. Sieve
#16 U.S.S. Sieve
#30 U.S.S. Sieve
# 8 U.S.S. Sieve
#16 U.S.S. Sieve
# 4 U.S.S. Sieve
# 8 U.S.S. Sieve
1/4" Sq. Sieve
# 4 U.S.S. Sieve
1/2" Sq. Sieve
1/4" Sq. Sieve
17
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V. ANALYTICAL METHODS
INTRODUCTION
The process waters of the pilot plant were routinely
analyzed for each of the following constituents:
Alkalinity
Aluminum
Calcium
Bacteriological Parameters (coliforms, fecal coliforms,
fecal streptococcus)
Hardness
Nitrogen, Ammonia
Nitrogen, Nitrate
Nitrogen, Organic
Oxygen, Dissolved (D.O.)
Oxygen Demand, Biochemical (BOD)
Oxygen Demand, Chemical (COD)
PH
Phosphate, Ortho-
Phosphate, Total
Residue, Total Volatile & Fixed
Residue, {Suspended (Nonf Alterable) , Volatile, & Fixed
Trace Metals (iron, copper, manganese, chromium, lead,
zinc, cadmium, molybdenum)
Turbidity
In addition, certain of the above analyses were performed on
biological and chemical sludges as well as waste, and recycle
streams .
Samples were collected hourly at each sampling point in
the system and composited over each run. BOD samples were re-
frigerated prior to preparing them for incubation. Samples for
ammonia, organic nitrogen, nitrate, phosphate, alkalinity,
calcium, and total hardness were preserved by adding 40 mg of
HgCl2 to each liter of sample. Samples for COD and aluminum
analyses were preserved with 2 ml. /liter of concentrated
All of the techniques used in the analyses of pilot plant
samples were exactly as described in the 12th and 13th Edition of
Standard Methods for the Examination of Water and Wastewater (1)(2)
except as noted below.
19
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ALKALINITY
Alkalinity determinations were performed by potentiometric
titration using a Radiometer Automatic Titrator. This apparatus
titrated each sample and traced the titration curve. This curve
indicated the volumes of acid titrant necessary to reach pH 8.3
and 4.5, respectively. Alkalinity was calculated from this in-
formation as in the standard colorimetric or potentiometric
tests described in the 13th Edition of Standard Methods. The
use of the automatic titrator removed errors due to the differ-
ent perception of end-point color change among different individ-
uals .
BACTERIOLOGICAL ANALYSES
Tests were run for coliforms, fecal coliforms, and fecal
streptococcol bacteria. The analyses were performed by the Denver
Water Department laboratories using the Membrane Filter Technique
described in the 13th Edition of Standard Methods.
CALCIUM
The EDTA titriometric method was used as descriheH in thn
13th Edition of Standard Methods. The modification of section
3a. was practiced as all calcium samples were previously titrated
in the course of the alkalinity determination and then heated to
incipient boiling for 30 minutes.
HARDNESS
This analysis was performed by the EDTA titrimetric method
described in the 13th Edition of Standard Methods (No. 122.B.).
NITROGEN, AMMONIA
This test was performed as described in the 13th Edition
of Standard Methods (No. 212).
NITROGEN, NITRATE
The Brucine Method presented in the 12th Edition of Standard
Methods (p. 198-200) was used without modification except that
samples were pretreated by centrifugation to remove suspended
matter.
20
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NITROGEN, ORGANIC
This analysis was performed exactly as described in the
13th Edition of Standard Methods (No. 215). The samples tested
were the same as those previously used for the ammonia deter-
mination.
OXYGEN, DISSOLVED
Dissolved oxygen was determined both by the azide modifi-
cation of the lodometric Method as described in the 13th Edition
of Standard Methods (No. 218.B), and by the Membrane Electrode
Method (No. 218.F). For the membrane electrode method a Yellow
Springs Instrument Co. Model 54 dissolved oxygen meter was used.
This meter was calibrated with the lodometric D.O. determination.
OXYGEN DEMAND, BIOCHEMICAL
This analysis was performed as described in the 13th Edition
of Standard Methods (No. 219). All D.O. values were determined
by the lodometric method.
OXYGEN DEMAND, CHEMICAL
COD analyses were performed by the method described in the
13th Edition of Standard Methods (No. 220).
pH
Commercial pH meters were used with regular standardization
against commercial buffer preparations.
PHOSPHATE, ORTHO-
The phosphate analysis was modified somewhat to give better
performance at the combination of high turbidity and color, and
low phosphate concentrations found at some points in the plant.
For low levels of phosphate characteristic of the effluent
streams of the pilot plant the Stannous Chloride Method was used
(Standard Methods, 13th Edition, No. 223.E). The modification
consisted of the inclusion of separate blanks for each sample
to eliminate effects of color and turbidity on the colorimetric
determinati on.
21
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Initially, each sample was homogenized by vigorous stirring
in a blender for 5 minutes. After homogenization, a 25.0 or
50.0 ml. sample was pipetted into a clean 100 ml. volumetric
flask. The samples were neutralized to the phenolpthalein end-
point and then diluted to 100.0 ml. with de-ionized water. Us-
ing a pipet, 50.0 ml. of sample was drawn off and placed in a
clean, dry erlenmeyer flask. Ammonium molybdate solution (S.M.
13th Edition, No. 223.E.3.c) was then added to each of the
samples in the erlenmeyer flasks. Strong acid solution was
added to the corresponsing sample in the volumetric flask (Stan-
dard Methods, 13th Edition, No. 223.E.3.b). Stannous chloride
reagent was added to all of the samples in the volumetric flask
(Standard Methods, 13th Edition, No. 223.E.3.d). Thus, the
samples in the volumetric flasks served as individual blanks
for each sample. No color development occured as no ammonium
molybdate was present. Stannous chloride reagent was added to
each of the samples in the erlenmeyer flasks at intervals of
one minute. After 11 minutes of development time, the transmit-
tance of each sample was read against its corresponding blank.
In this way 11 samples could be run simultaneously. It should
be noted that the sample size after dilution was 50 ml. neces-
sitating only one-half the prescribed volume of reagents (2.0
ml. of ammonium molybdate and strong acid, and 0.25 ml. of
stannous chloride).
For higher phosphate levels an identical procedure was used,
employing the Aminonapthylsulfonic Acid Method as described in
the 12th Edition of Standard Methods (p. 231-234). The only
difference between the two methods, other than the difference
in reagents, was the shorter color development time of five
minutes.
PHOSPHATE, TOTAL
The Persulfate Digestion Method was used (13th Edition of
Standard Methods, No. 223.C.Ill) to release phosphates from com-
bination with organic matter. This digestion was integrated in-
to the orthophosphate determination in the following manner.
After samples were placed in the volumetric flasks and neutra-
lized to the phenolpthalein end point, 0.75 grams of potassium
persulfate was added to each sample. The samples were heated
to incipient boiling for 105 minutes. After digestion, the
samples were cooled and titrated with 3N NaOH to the pink color
of phenolpthalein. The pink color was removed with dropwise
addition of strong acid. The samples were then diluted to 100
ml. and analyzed just as for orthophosphate.
22
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RESIDUE, TOTAL - VOLATILE AND FIXED
This analysis was performed exactly as described in the
13th Edition of Standard Methods (No. 224 a & B) .
RESIDUE, SUSPENDED (NONFILTERABLE) , VOLATILE AND FIXED
A modified method for the analysis of suspended solids
was used to obtain consistent, accurate, and rapid analyses.
The analysis was similar to commonly used methods except that
in the sample filtration a composite filter mat was used. This
mat was composed of a glass fiber disk overlain with coarse
asbestos .
To prepare the filter crucible, asbestos (medium fiber,
acid washed) was placed in a beaker and washed thoroughly un-
til only the coarse fibers remained. This asbestos was then
washed in distilled or de-ionized water for 15 minutes and
stored in a distilled water suspension.
The crucible used was a Gooch type Coors No. 4 or equiva-
lent. The glass disk was 2.4 cm. in diameter, Reeve Angel
#934AH or equivalent. The disk was placed in the bottom of the
w-l-WAl WCIO
the crucible, suspending libers with distilled water during the
addition. This was continued until a 1/16-1/8" asbestos mat
was developed. The edges were tamped and the mats were allowed
to dry prior to firing the crucibles at 600°C for 20 minutes.
The fired crucibles were cooled and stored in a dissicator for
subsequent use .
The samples were introduced in such a way as to keep the
mat submerged during filtration. Care was taken to avoid dis-
turbing the mat during sample filtration. After sample filtra-
tion, the sample container was triple rinsed with de-ionized
water and the filter mat was rinsed with 10 ml. of de-ionized
water.
The crucibles were dryed at 103° in a mechanical convection
oven until the weight loss was negligible. After drying, the
crucible was. placed in a dessicator and cooled before weighing.
Ignition of the crucible for determination of volatile and fixed
solids was accomplished as described in the 13th Edition of
Standard Methods (No. 224 D) . Calculation of results for both
total suspended solids, and the volatile and fixed fractions was
performed as described in Standard Methods.
23
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TRACE METALS
The Denver Water Department laboratories provided heavy
metal analyses for each of the following metals:
Iron
Manganese
Copper
Chromium
Lead
Zinc
Cadmium
Molybdenum
Mercury
The analytical technique used in each case was the Atomic Ab-
sorption Spectrophotometry Method. A Varian Techtron AA5 was
employed with analytical procedures outlined in Analysis of
Trace Elements in Natural Waters by Atomic Absorption^Spectro-
photometry(3).
TURBIDITY
Turbidity measurements were made with a. Hellige Turhidi-
moter. "
24
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VI. BIOLOGICAL NITRIFICATION
INTRODUCTION
Nitrogen compounds are recognized as significant consti-
tuents in natural waters because of their demonstrated role
as eutrophic stimulants, and for their toxic properties with
respect to fish and humans. Since wastewaters provide a signif
icant source of the undesirable aqueous nitrogen, removal of
nitrogen compounds is indicated for tertiary treatment of waste
waters. In this water renovation study, conversion of the
corrosive ammonia form nitrogen to the nitrate form was con-
sidered sufficient for the specific first-stage) application of
wastewater reuse for industrial purposes. In this context, the
major purpose of this phase of the research program was to
evaluate the important design parameters for biological nitri-
fication. As indicated, nitrification is necessary for indus-
trial reuse because of the corrosive nature of ammonia. In a
solution of ammonia complexants containing free available
oxygen, copper corrodes rapidly with the formation of the com-
plex Cu(NH3)4+l" ion. The rate of corrosion is directly re-
lated to the amount of ammonia present in the water. Ammonia
also causes season cracking in brass. It has been shown that
an ammonia concentration of 30 ppm in steam condensate leads
cracking in stressed brass (4 ). The oxidized form of ammonia
is the nitrate ion (N0o~) which is stable and does not react
in a corrosive manner with pipes, fittings, and process machinery.
A subsequent investigation must address the problem of complete
nitrogen removal when higher level reuse applications are con-
sidered .
AEROBIC OXIDATION
In the biological nitrification process, ammonia is oxi-
dized to nitrate by autotrophic bacteria. These bacteria fix
carbon dioxide as a source of carbon for cell material, and
obtain energy from the process by oxidizing inorganic substrates
Two groups of autotrophic bacteria are distinguished in nitri-
fication and each is responsible for a specific phase of the
process. The group Nitrosomonas oxidizes ammonia to nitrites.
The group Nitrobacter oxidizes nitrites to nitrates. The two
step process is expressed as follows:
Nitrosomonas: NH+ + 1 . 5 0 - N0~ + 2H+ + HO
Nitrobacter: N0~ + 0.5
25
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As indicated by Stankewich (5), the stoichiometric de-
mand for oxygen would be 4.57 Ibs. Oo/lb. NH3-N. However,
as was shown theoretically and experimentally by Stankewich
some of the ammonia is taken up in cell synthesis thereby
reducing the oxygen requirement to approximately 4.33 Ib.
0?/lb. NHo-N. With a very short sludge age the oxygen re-
quirement would be less, and should range between 4.0 and
4.6.
One gram of substrate metabolized by the autotrophs
provides the following energy yield ( 6) :
Nitrosomonas: ammonia - nitrite + 2 kcal/gram
Nitrobacter: nitrite - nitrate +0.3 kcal/gram
The ammonium compound metabolized by the autotrophic nitrifier
provides energy to the microorganism through an electron trans-
fer system coordinated by coenzymes found in the microbial
cell. The electron transfer system involves the removal of
hydrogen during metabolism with the effect that the ammonium
compound is oxidized. The best indicator of the expenditure
of biological energy is the oxygen utilized under aerobic
conditions. Oxygen is used to regenerate DPN + H2 (coenzyme
diphoRphonyridine nucleotide with attached hydrogens) and
aiiu~uGni3. is oxiuizGu ciccoruing ^o L.AS proceeding ecjus-uxon Vy'ini
subsequent removal of hydrogen by DPN. The oxygen uptake is
then a function of both the hydrogen removal and the ammonia
oxidation, two major sources of biological energy.
As has been implied, a source of free oxygen is required
in such a bacterial system. This is generally achieved in an
aeration tank where the biomass and the wastewater are mixed
and aerated by air bubbles from a compressed air source.
Nitrification in Secondary Sewage Treatment Plants
In conventional sewage treatment heterotrophic bacteria
oxidize organic carbon and receive both food and energy from
this source. The heterotrophs of the conventional activated
sludge treatment grow at a much faster rate than the auto-
trophic nitrifiers. This is significant since the growth
rate of a bacterial group has a predominant effect on the
ratio of that group to the total bacterial population in a
mixed culture such as encountered in the sewage treatment pro-
cess. For steady state conditions at a particular biomass
concentration and feed rate containing sufficient food a fast
26
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growing type of bacteria, such as the heterotrophs, will pre-
dominate over the slow growing types. This is particularly
true for relatively short activated sludge aeration periods
since the excess cells produced must be wasted in order to
keep a constant biomass concentration in the aeration tank.
The slow growing nitrifying bacteria will be wasted along with
the heterotrophs, with the result that the nitrifiers will
rarely develop a sufficient number in the aeration tank for
significant ammonia oxidation. If, however, the aeration
time is increased, two things occur. First, the nitrifiers
have a longer period of time in which to reproduce so that
their numbers increase if enough substrate ammonia is present.
Second, the endogenous phase which develops for the hetero-
trophs permits ammonia oxidation by the nitrifying bacteria.
A recent study of nitrogen balances on five existing activated
sludge and trickling filter sewage treatment plants has shown
that nitrification can and does occur to varying degrees in
conventional plants (7). The observed oxidation was erratic
and did not correlate to carbon or suspended solids removals.
The study also showed that partial denitrification accompanied
biological nitrification.
Two-Stage Activated Sludge
Another means of limiting heterotrophic growth and main-
taining nitrifiers in a system is to keep the influent food
to the activated sludge in a ratio which constrains the meta-
bolic activity of the heterotrophs to the endogenous phase
throughout the aeration period. This can be done by using a
tertiary activated sludge system acclimated for biological
nitrification (5) (8). This principle is applied in the pilot
plant studies described in this report. The majority of the
organic constituents in the influent to the experimental system
have been oxidized in the preceding secondary treatment so that
the incoming food concentration is low. In this situation, the
nitrifiers continuously circulate in the system with little net
growth, and oxidize all of the wastewater ammonia provided they
have adequate detention and oxygen. Earth, Brenner and Lewis
(8) have shown such a system to produce about 90% nitrification,
PROCESS CONTROL PARAMETERS
Previous investigations have identified several important
parameters in the design and control of nitrification process
operation. Included among the most significant of these
27
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parameters are the mixed liquor solids concentration, organic
and substrate loadings, sludge settling characteristics,
reaction time, recycle rates, temperature, pH, and oxygen
utilization coefficients. These variables were studied in
this investigation for the specific purpose of applying the
results to the Denver situation.
Mixed Liquor Suspended Solids
The aeration tank contains a mixture of suspended and dis-
solved solids. The dissolved solids include soluble organic
and inorganic compounds, and consist mostly of salts. The
suspended solids are made up of a suspension of bacteria and
solid inorganic and organic particles in the mixed liquor. The
volatile fraction of the suspended solids is that portion that
volatilizes after exposure to 600°C temperatures. This includes
most organic substances which would make up the active bacterial
mass. The percent of volatile solids in activated sludge is
usually from 70 to 80 percent. The concentration of MLSS in
the aeration tank determines the organic loading rate when the
wastewater flow and strength is constant.
Organic and Substrate Loading
The organic load is expressed as Ib. BOD per day per Ib.
mixed liquor suspended solids. This loading parameter together
with the reaction time has been shown to directly effect the effi-
ciency of the nitrification process. As was mentioned, when
the carbonaceous content of the influent becomes large for a
unit of time, the growth of heterotrophic bacteria increases
to a point where wasting of sludge becomes necessary. It is
at this point that the nitrifying autotrophs are lost to the
system. The substrate load, in this case ammonia, is given in
the same terms, as the organic load, Ib. NH3 per day per Ib.
MLSS. The loading values can be controlled through hydraulic
loading or by variation of the MLSS.
Settling Characteristics
The settling characteristics of biological sludges are
typically represented by the Sludge Volume Index or SVI . The
Sludge Volume Index is an indication of the density of the
sludge. The SVI is defined as the volume occupied by the sludge
fraction in one liter of mixed liquor after 30 minutes of set-
tling, divided by the dry weight concentration of the sludge.
28
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The SVI has inverse dimensions of density (ml/gm). Values of
SVI from 50 to 100 indicate a good settling sludge, while
values over 200 indicate that the sludge is light, bulked, and
hard to settle .
Recycle Rate
Recycling of suspended solids from the clarifier back to
the aeration tank serves to hold the bacteria in the system,
thereby providing a means of controlling the MLSS concentration.
If it is assumed that there is negligible net growth of bacteria
in the system, and the recycle sludge concentration is one per-
cent, the sludge recycle ratio can be related to the SVI and
MLSS by the following equation:
R _ 1
Q 100 _
SVI «7oMLSS
In this relationship, R is the recycle flow rate, and % MLSS is
the dry weight percent of suspended solids in the mixed liquor.
Oxygen Utilization Coefficient
The oxygen utilization coefficient, micro-liters of oxygen
per mg of MLSS per hour, expresses the oxygen requirements of
a unit of biomass. This value can be found for a range of sub-
strate loadings, temperatures, pH values, and other conditions.
The oxygen utilization rate is essential in design to provide
adequate aeration facilities. During actual plant operation
the air flow rate can be controlled by the operator to give the
proper dissolved oxygen levels at minimum compressor power costs
Reaction Time and Overflow Rate
Due to the design of the pilot plant in this study, it
was not possible to vary the hydraulic load without proportion-
ally varying the organic load for a constant MLSS concentration.
This was true because the organic contents of the influent did
not vary markedly from day to day. Increasing the hydraulic
load decreased the available reaction time for bacterial sub-
strate oxidation. Since flow into the plant was fairly con-
stant, the effect of increasing the hydraulic load could be
achieved by reducing the size of the units. By use of several
sectioned units in series, it was possible to study several
detention times concurrently.
29
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Hydraulic load also effects the settling capabilities in
the clarifier and in many cases the settling characteristics
of the sludge. Although guidelines have been established for
overflow rates of clarifiers, they do not apply consistently
to situations involving activated sludge variations. The
conditions in the aeration tank determine the settling charac-
teristics of the sludge, but the hydraulics of the clarifier
need to be carefully controlled to make use of any positive
settling characteristics possessed by the sludge. Common de-
sign criteria require that overflow rates on activated sludge
clarifiers not exceed 800 gpd/sq. ft. for average daily flow.
Since nitrifying sludge nourished by secondary effluent may
have somewhat different characteristics than conventional
activated sludge, the maximum overflow rate may have to be
decreased for good settling. The values of the parameters
for which the nitrification system was designed are shown
in Table III.
EXPERIMENTAL PROGRAM
The nitrification studies included both bench scale and
pilot plant investigations. The bench scale studies were made
initially to provide direction in the operation of the pilot
p]ant. These laboratory invest! gat. ions involved batch fed
four liter reactors. Parameters investigated in this work in-
cluded detention time, oxygen uptake rates, loading variations,
and the effects of variable temperatures on the performance of
the nitrification system. A wide range of temperatures was
studied in the bench scale tests because of the difficulty in
varying this parameter at the pilot plant scale.
After initiation of the pilot plant studies, the plant was
operated on a continuous basis with composite sampling of the
influent and effluent streams three days each week. The in-
fluent and effluent samples were analyzed for BOD5, COD, NH4-N,
organic nitrogen, N02-N, N03-N, turbidity, total solids, TSS,
VSS. Additionally, the mixed liquor was sampled and analyzed
for MLSS, MLVSS, pH, D.O., temperature, and SVI.
Two different aeration systems were used in this study to
permit evaluation of a wide range of reaction times. One system
incorporated six 50 gallon reactors in series. Through analyses
of the effluent from each vessel in this series detention times
of 12-72 minutes were evaluated at full flow. The other aera-
tion system consisted of a single baffled 900 gallon tank. By
adjusting the height of the discharge weir in this tank reaction
30
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TABLE III
NITRIFICATION DESIGN PARAMETERS
Parameter or Dimension
Design Flow
Aeration Tank Detention Time
Aeration Tank Volume
Clarifier Detention Time
Clarifier Overflow Rate
Recycle Capacity
*for one 55 gallon drum reactor
Value
5 gallons per minute
0.2-3.6 hours
7-145 cubic feet
1.6 hours
450 gallons per day per sq. ft
100 per cent
31
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times of 2-3.6 hours were investigated. Longer detention
times were possible through diversion of a portion of the
inflow. Coupled to these reaction time variations, the
MLSS concentration was varied from 200-4000 mg/1 in incre-
ments of approximately 500 mg/1. In this way, the effect of
BOD5, COD, and nitrogen loading rates could be assessed.
Aeration was provided with diffused air to maintain a
dissolved oxygen concentration of 2 mg/1 or greater. Other
investigators have found that this level is sufficient with
no substantial improvement in process performance at higher
levels (5)(9)(10)(11)(12)(13)(14)(15). Likewise, the system
pH was consistently in an acceptable range for nitrification.
The pilot plant influent ranged between 6.8-7.8, with the
majority of flows in the range 7.1-7.4. This is consistent
with the optimum environmental conditions established by
other investigators for Nitrosomonas and Nitrobacter (5)(9)
(16)(17)(18)(19)(20).
Start-up of the nitrifying activated sludge unit required
an extended period for growth of a nitrifying culture. To
expedite this process, the units in this study were initially
seeded with a sludge taken from aerobic digesters at the
Metropolitan Denver Wastewater Treatment Plant. This sludge
had received approximately eight days of digestion after being
wasted from the secondary process. With this seed sludge,
the pilot plant normally developed full nitrification capability
within about one week. Using no seed material Mechalas, Allen
and Matyskiela (21) found that 6-8 days of acclimation was re-
quired before complete nitrification was achieved in their sub-
merged ring unit. Haug and McCarty (16) reported an acclima-
tion time requirement of four months in the submerged filter
configuration.
EXPERIMENTAL RESULTS
Temperature Effects
The initial bench scale studies were made to establish the ef-
fects of variable temperature on the rate and degree of nitrifica-
tion. Active cultures of nitrifying activated sludge seed were
obtained from an extended aeration treatment plant. Trickling
filter effluent was used as the substrate in the four liter fill
and draw units. The temperature effects on nitrification at a con-
stant loading rate are shown in Figure 5. From these data it can
be noted that for acclimated organisms at an average MLSS concen-
tration of 780 mg/1, with reaction times between 4 and 8 hours,
nitrification was nearly complete over the entire 5-30°C temperature
32
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100-,
80-
60-
40-
20
2 hr. D.T
860 KLSS
10
15
20
25
30
TEMPERATURE °C
Figure 5
EFFECT OF TEMPERATURE ON NITRIFICATION FROM BENCH SCALE STUDIES
33
-------
range. With a 2 hour detention time, the nitrification effi-
ciency decreased markedly. The maximum efficiency of about
80% was achieved between 20-25°C. A similar efficiency maxi-
mum was reported by Sawyer and Rohlich (22). Other authors
have observed similar increases in nitrification rates for
temperatures up to 25°C (9) (16) .
The effect of aeration temperature on sludge settleability
was also investigated in this study. Using the SVI as an in-
dicator of the sludge settling characteristics, it can be seen
in Figure 6 that the settleability improved with increasing
temperatures. Sawyer reported a somewhat similar result (23).
BOD Loading
Preliminary bench scale studies were also run to assess
the effect of BOD loading on the efficiency of the nitrifica-
tion process. The results of this early investigation are
summarized in Figure 7. These results were confirmed by the
pilot plant data presented in Figure 8. The scatter of pilot
plant data on this figure apparently occurred because of the
relatively frequent changes in loading conditions with the re-
sult that organism acclimation was not always complete. It can
up to a BOL»5 biomass loading of approximately 0.4
There are also indications from this plant data that the load-
ing rate might be extended slightly higher with experience in
operation. Several other investigators have found the maxi-
mum loading rate to be in a similar range as shown in Table IV.
COD Loading
The degree of ammonia nitrification as a function of the
COD loading is indicated by the data in Figure 9. The ten-
dencies identified in the previous BOD loading curve are also
evident for COD. The maximum COD loading for complete ammonia
conversion appears to be approximately 1.4 #COD/#MLSS/day.
This is in general agreement with Mechalas, Allen, and Matyskiela
(21) who found that nitrification efficiency was not adversely
affected below a load factor of 1.1 #COD/#MLVSS/day.
Ammonia Loading
The ammonia oxidation as a function of the ammonia loading
factor is shown in Figure 10. It can be noted that a loading
of 0.16 #NH4-N/#MLSS/day was found to be the upper limit for
34
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200-
x 150-
w
w
I
w
SO-
10' 15 20
TEMPERATURE °C
25
30
Figure 6
SLUDGE VOLUME INDEX AS A FUNCTION OF TEMPERATURE FOR THE
BENCH SCALE STUDIES UTILIZING A FOUR HOUR
DETENTION TIME
35
-------
100 i
80
60 -
k-t
Oi
EH
S 40
W
o
(K
W -
p, ^o
0.1
—I— 1—
0.2 0.3
0.*4
0.5
0.6 0.7
£_BOD/day
# MLSS
Figure 7
EFFECT OF BOD LOADING ON NITRIFICATION FROM BENCH SCALE STUDIES
36
-------
g
X
o
W
O
OJ
w
4 o
40
30 "
20
10 -I
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
# MLSS
Figure 8
AMMONIA OXIDATION AS A FUNCTION OF BOD LOADING FACTOR
37
-------
TABLE IV.
Comparison of BOD Loading Data
Maximum Minimum
#BOD/DAY Sludge
FMLST3" *~ Age-Days Reference Comments
0.3-0.4 3-4 (10) Operated at 2800 mg/1 MLSS
and a D.T. of 8 hours.
0.25-0.33 4 (24)
0.25-0.35 - (25)
0.28-0.4 5 (5) Pure Oxygen
38
-------
g COD/day
# MLSS
AMMONIA OXIDATION AS A FUNCTION OF THE COD LOADING FACTOR
39
-------
100 .
Q
w
X
o
•z.
O
•z.
M
O
W
O.
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
# NH3-N/day
# MLSS
Figure 10
AMMONIA OXIDATION AS A FUNCTION OF AMMONIA LOADING FACTOR
FROM PILOT PLANT STUDIES
40
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complete oxidation. For activated sludge containing approxi-
mately 82 percent volatile matter this would be equivalent to
8 mg NH3/Hr/g. MLVSS. This value is slightly higher than the
value of 7.7 determined by Wild, Sawyer, and McMahon (9),
and 5.2 established by Mechalas, Allen, and Matyskiela (2l).
Sludge Settling
The activated sludge clarifier used in this study was de-
signed with an overflow rate of 450 gpd/Ft2. Even at this
relatively low loading rate some solids carry-over was experi-
enced. The nitrifying sludge is very light, due to the fact
that it contains a very high fraction of bacterial mass with
very little inert weighting matter. For this reason, it appears
that very low overflow rates will be necessary in design of
nitrification system clarifiers.
Because of the difficulties in scaling down clarifiers to
pilot plant size, it was not possible to develop quantitative
settling tank design criteria. In general, the settling tank
performance was satisfactory, although pinpoint floe did com-
monly carry-over at a suspended solids level of 30-40 mg/1. It
was noted that carry-over was less pronounced in the pilot
clarifier at MLSS concentrations above 2000 mg/1, In this
range, a blanket formed in the lower portion of the clarifier
which improved the solids capture opportunity. During most
of the study, there was a very gradual reduction in the MLSS
concentration due to the outflow in the clarifier effluent.
This necessitated periodic supplementation of the nitrifying
sludge with solids from the Denver aerobic digestion units. Jar
tests were made with several polyelectrolyte compounds added
to the inflow to aid in capturing the pinpoint floe. None of
these was effective within the reasonable economic dose limits.
Reaction Time
The data developed with the six 50 gallon aeration tanks
was used to establish the relationship between the extent of am-
monia nitrification and detention time. The six units were
operated in series with the settling tank at the end of the
series and the return sludge pumped back to the first tank.
The water accompanying the return sludge was completely nitri-
fied thereby introducing a substantial amount of nitrate in the
first tank. For this reason it was necessary to subtract the
recycle nitrate values from overall nitrate conversion values
41
-------
in each vessel. The results of this analysis are shown in
Figure n. It can be noted that the rate of oxidation is
nearly linear indicating that this rate is essentially in-
dependent of ammonia concentration. This observation was
also presented by Wild, et al (9 ).
A theoretical analysis of the effect of ammonia level on
reaction rate can be developed from a biological kinetics point
of view using the Michaelis-Menten equation:
v - VS/(K + S)
where v is the reaction velocity, Vm is the maximum rate at
which the reaction can occur, Km is the Michaelis constant and
S is the substrate concentration. Michaelis constants are
available (12) for the nitrification reactions. The Nitroso-
monas step is the rate controlling reaction and has a reported
value of Km of 0.8 ppm at 20°C. Using this value, the reaction
velocity can be calculated at different substrate levels.
S (mg/1) v
5 0.86 Vm
10 0.93 V«
iii
15 0.95 V
m
It can be seen from this approach that the reaction rate should
be nearly constant and becomes only slightly reduced at lower
substrate levels. Although the Michaelis-Menten equation should
be used very cautiously with mixed cultures and sequential reac-
tions of the nitrification process, the analysis does give some
insight into the question.
It can also be noted from the data that there is a very
close correlation between rate of nitrification and the reactor
organism content, represented by the MLSS concentration. The
average inflow ammonia concentration during this test series
was 18.3 mg/1. Using this value with the data in Figure 11, a
nitrification rate of 0.16 Ib. NH3/lb. MLSS is calculated from
the following relationship:
18.3 mg/1 NH3-N x 1440 min./day Ib. NHL-N
4000 mg/1 MLSS x 40 min. DT= °-16 Ib. MLSS day
42
-------
O V
w
K
O
O
o
< "S
g O
w •-!
o o
W 0
100 -
80-
60 -
40-
20 -
200 me/1 MLSS
I
20
I
40
I
60
I
80
0 20 40 60 80 100
BIOLOGICAL REACTION TIME (minutes)
Figure 11
EXTENT OF BIOLOGICAL NITRIFICATION AS A FUNCTION OF REACTION TIME
FROM PILOT PLANT STUDIES
43
-------
This is based on complete nitrification in 40 minutes at
4000 mg/1, or in 100 minutes at 1600.mg/1.
The reaction can be approximated by the equation of the
slope of the lines on the plot:
% oxidation = Kt
where; t = detention time in minutes = tank volume/inflow rate
K is shown to be directly proportional to MLSS and is assumed
to be inversly proportional to ammonia concentration. There-
fore :
a . , . . MLSS x t (min)
% oxidation =
87 x NH3-NTmg7l)
which can be rearranged to yield:
least detention time (hr.) = 15° x NVN (mg/l}
at 100% oxidation MLS3
The above equations represent severe over-simplifications but
can serve as a basis for making rough approximations of aera-
tion tank sizes operating in the 15°C temperature range.
Oxygen Utilization
The oxygen requirement of the nitrifying sludge was deter-
mined by making oxygen probe measurements of the rate of oxygen
depletion in the mixed liquor from each of the six 50 gallon
reactors. Samples of the mixed liquor were collected in BOD
bottles and saturated with oxygen by injecting pure oxygen into
the bottles. Following this sample preparation the dissolved
oxygen concentrations in the bottles were measured and recorded
at 30 second intervals. Results of these analyses are presented
in Table V. From these measurements the oxygen utilization was
found to be 0.91 #02/day/#MLSS. As shown in the table, ammonia
measurements were also made on the influent to each tank and it
was found that ammonia oxidation was complete at the end of the
third reactor. Oxygen utilization values for endogeneous respi-
ration were determined from measurements of oxygen utilization
in the last three reactors. This value was found to be 0.18
#02/day/rrMLSS. The difference between these two utilization
ratesj-epresents the oxygen utilization for nitrification of
0.7J rr02/day/f?MLSS. Based on the ammonia conversion value of
0.16 #NH3-N/day/#MLSS presented earlier, the oxygen demand for
ammonia oxidation by nitrification was calculated to be 4 6
44
-------
TABLE V
Oxygen Utilization for Nitrification
Reactor
Ave. D.O. Depletion (mg/1/30 sec.)
Influent NH3~N (with 120% recycle)
MLSS
MLVSS
1
1.0
6.0
3252
2478
2
0.93
3.8
3132
2348
3
0.50/0.2
2.9
2972
2166
4
0.2
0
3154
2332
5
0.2
0
2971
2174
6
0.17
0
3144
2330
-------
#C>2/#NH3-N. This compares very closely with the stoichiometric
quantity of 4.57 #C>2/#NH3-N indicated by Stankewich (5 ).
Several qualitative observations can be made from the long
term pilot plant operation. The nitrifying sludge was consider-
ably more difficult to develop than normal secondary activated
sludge. It did not settle as well and could be lost by gradual
attrition. A source of sludge make-up from an aerobic digester
is convenient and may be even necessary for continued long term
operation.
In the oxidation of carbonaceous matter.in the secondary
process of activated sludge treatment the rate of oxidation
changes throughout the oxidation period as the more easily
assimilated materials are oxidized and only the more resistant
materials remain. Complete oxidation never occurs because some
of the carbonaceous compounds in sewage are too resistant to be
oxidized within a reasonable treatment time. With nitrifying
activated sludge, only a single substrate is involved. For this
reason the rate of oxidation is nearly constant as long as the
ammonia feed source exists and the extent of oxidation is com-
plete if an adequate reaction time is provided.
46
-------
VII. CONVENTIONAL CLARIFICATION
INTRODUCTION
Treatment systems employing chemical addition, floccula-
tion, sedimentation, and filtration have long been used in the
water supply field for removing suspended matter from raw water
supply sources. Relatively recently this same treatment se-
quence has been adapted to problems of wastewater treatment.
In this context, the impetus has developed from a recognized
need to reduce the discharge of phosphorus to natural water-
courses because of its demonstrated role in promoting excessive
algal growth. Chemical precipitation has proven to be an effec-
tive means of accomplishing the desired phosphorus removals.
Accompanying the concentration reduction of this algal nutrient,
other classes of pollutants have also been removed in varying
degrees. Thus, this type of treatment sequence has shown good
potential for upgrading wastewater discharges to a quality level
which will permit some levels of water reuse.
Conventional aluminum and iron coagulants, as well as lime,
have been shown to be effective as chemical additives for up-
grading wastewater effluent quality in this conventional clari-
fication sequence. Of these coagulants, lime ha.3 received the
most attention because of the potential for chemical recovery
through recalcining of the lime sludge.
Lime reacts with the bicarbonate alkalinity in wastewater
to form the calcium carbonate precipitate. It also reacts with
orthophosphate to precipitate hydroxylapatite according to the
following reaction:
5 Ca++ + 4 OH" + 3 HP04 - Ca5
-------
EXPERIMENTAL RESULTS
Lime Precipitation
Throughout the chemical clarification studies, the expressed
aim was to evaluate those parameters of particular importance in
the design and operation of a plant scale system. In this re-
gard, the following system variables were evaluated over a rela-
tively broad range with subsequent analysis of the impact on the
plant effectiveness:
1) lime dose
2) pH
3) flocculation intensity
4) flocculation detention time
5) filter loading rates
6) chemical sludge recycle.
Of course, parameters (1) and (2) above are interdependent and
they relate to the optimal chemical environment within the system
for removal of the constituents which were considered to be of
most importance in this study. These included: phosphate, BOD,
COD, solids, turbidity, bacteria, and heavy metals. Aside from
item number 6, the other major system variables relate to va.ria-
Lions GO. pnysicciju. CGmponon cs wimj-n
In the daily pilot plant evaluation, one-liter samples were
composited over a four-hour period beginning after the system
had reached equilibrium. The points sampled were 1) the pilot
plant influent, 2) the bioclarifier effluent, 3) the clarifier
effluent, 4) the recarbonation discharge, and 5) the filter ef-
fluent. While the samples were being composited, solids analysis
(including suspended solids, suspended volatile solids, total
solids, and total volatile solids), pH and temperature measure-
ments, and turbidity determinations were made on samples from
the five sample points. During the run, filter headless measure-
ments were recorded for the rapid sand filter. These were con-
tinued throughout the filter run or until headloss reached 14.5
feet, which was the limit for the system. Samples for trace
metal and bacterial analyses were also collected during this
time and later analyzed by the laboratory of the Denver Water
Board .
The first set of studies was developed to define the im-
pact of variations in the flocculator operation on the effec-
tiveness of the clarification system. Both flocculation time
and intensity were varied over the range permitted by the plant
design. For the detention time studies, the mixing time was
48
-------
varied between 34-50 minutes while other plant variables were
held constant. In the narrow range of detention times pro-
vided in this design there did not appear to be any significant
difference in the plant performance. The consistency of per-
formance is indicated in Figure 12, where total phosphates are
plotted as a function of mixing time. Similar behavior was
observed with the other wastewater constituents.
The mixing intensity in the flocculation basin was also
studied under controlled conditions to isolate the effects of
mixing rate variations on the clarification system performance.
By varying the impeller speed in the flocculation basin, the
mixing intensity, represented by G, was investigated over the
range 11-50 fps/ft. As shown in Figure 13, which is a plot
of total phosphate vs. mixing intensity, G, variations of the
flocculation intensity did not seem to alter the plant effec-
tiveness in removing phosphates from wastewater.
Because of the strong pH dependence which has been shown
for lime precipitation, one of the early studies was designed
to evaluate the variation of pH with lime dose for the waste-
water under investigation. The results of this portion of the
pilot plant study are summarized in Figure 14. The lime dose
variation covered the range of 0-600 mg/1 Ca(OH)2, with a cor-
responding variation in the wastewater pH following clarifica-
tion of 7.1 to 11.7. With the alkalinity in this wastev/ater
(250 mg/1) it was possible to achieve pH 11 at a moderate
hydrated lime dose of approximately 275 mg/1. This is a desir-
able operational level because of the formation of gelatinous
Mg(OH)2 precipitate which aids in sweeping the fine precipitates
from suspension.
Accompanying the variation in pH observed for variable
lime doses was a significant variation in the effectiveness of
lime clarification for removing the polluting constituents in
wastewater. Data collected on turbidity and suspended solids
reductions indicated that lime precipitation was very effective
in reducing the concentration of particulate matter in waste-
water. As shown in Figures 15 and 16, addition of 50 mg/1 or
more of lime with subsequent sedimentation and filtration re-
sulted in significant reduction of the concentration of these
constituents. More specifically, the turbidity was reduced
from an average concentration of 17.5 mg/1 SiC>2 to a level of
consistently less than 3 mg/1. Likewise, the suspended solids
were reduced from highly variable concentrations in the range
10-110 mg/1 to consistently less than 1 mg/1. These levels of
residual particulates are consistent with those reported by
other authors using lime in somewhat similar clarification
systems (28)(29). It should be noted from the figures that
49
-------
6 '
o
Pi
W
E-
0,
CO
§
D
Q
M
CO
w
o:
4 -
30
e Point 3
o Point 5
a
a
e
e
a
o
a
o
a
o
o
o
o
a
40
DETENTION TIME (minutes)
50
Figure 12
RESIDUAL PHOSPHATE AS A FUNCTION OF FLOCCULATION DETENTION TIME
WITH - 300 mg/1 LIME
-50
-------
5 -
3 4 4
w
0,
CO
o
g
OT
W
o:
3 •
2 -
1 .
0 Point 3
Point 5
o
o
o
o
o
o
o
o
c°
o
o
e
10 20 30 40
MIXING INTENSITY (G) fps/ft
Figure 13
RESIDUAL PHOSPHATE AS A FUNCTION OF MIXING INTENSITY
WITH ~ 300 mg/1 LIME
50
51
-------
pH
12
11-
10-
9-
200 400
Ca(OH)2
600
Figure 14
pH IN FLOCCULATION REACTOR AS A FUNCTION OF LIME DOSE
52
-------
40'
o Cone. pt. 2
Cone. pt. 3
+ Cone. pt. 5
30-
O
CO
\
E
H
1-1
Q
a
201
10-^
O 0
100 200 300 400
Ca(OH)2 added (mg/1)
Figure 15
TURBIDITY REMOVALS WITH LIME ADDITION
500
53
-------
80 -
70
60 -
M 50 -
s
Vl
Q
W
ft
w
30-
20 _
10 -
o Cone, pt. 2
& Cone, pt. 3
4 Cone. pt. 5
o o
0 o
o
o
eo
e
o e
A VR*- 3
^4. A } Da
ata
100 ' 260 ' 360 ' 4do ' sdo
Ca(OH)2 added (mg/1)
Figure 16
SUSPE.VDED SOLIDS REMOVAL WITH LIME ADDITIONS
54
-------
while most of the solids mass is removed in the settling system,
the filter serves to remove approximately 50% of the solids in
the clarifier over-flow and assures that a consistent high
quality product is delivered in spite of any periodic solids
carry-over which might occur in the settling system.
The response of BOD in the wastewater effluent to the lime
dose applied in the clarification system is shown in Figure 17.
BOD concentrations in the influent to the clarification system
were seen to vary over a wide range because of the variable be-
havior of the preceding biological nitrification system. Actual
influent concentrations varied between 35-130 mg/1. With
hydrated lime doses as low as 50 mg/1 the BOD levels in the
clarifier effluent were consistently reduced to 5 mg/1 or less.
The effective BOD removals at relatively low lime doses show a
close correlation to the preceding curve regarding the behavior
of suspended solids, and indicate that nearly all of the BOD
discharged from the biological nitrification system is in the
suspended form. At lime doses above 50 mg/1 the BOD in the
filter effluent was consistently below 5 mg/1, in spite of the
fact that the BOD in the influent to the clarification system
was highly variable.
Lime precipitation of those constituents contributing to
COD was not as complete as in the case of ROD. This is shown
in Figure IS which relates influent and effluent COD levels to
the applied lime dose. During the period of this study, the
COD concentrations influent to the lime system varied from 25
through 175 mg/1. As with the BOD concentration, a significant
reduction in COD was noted at lime doses of less than 100 mg/1.
However, for COD the observed reduction amounted to about
65-75% as compared to 90-95% for BOD. This difference in effec-
tiveness reflects the fact that a substantial fraction of the
COD in nitrified secondary effluent is contributed by soluble
organic species. Additional treatment, such as carbon adsorp-
tion, is indicated for removing this fraction of the COD.
Phosphorus analyses were performed to identify both the
ortho- and total phosphate concentration variations through the
system. The orthophosphate concentrations in the nitrification
clarifier effluent varied over the period of study from 8 mg/1
PO4 to 32 mg/1 PO4. A corresponding variation in total influent
phosphorus was observed in the concentration range of 10-39 mg/1
total phosphate. As shown in Figure 19, the orthophosphate con-
centration was reduced from the average influent of 22 mg/1 P04
to an effluent value of 4.5-5 mg/1 P04 at a lime dose of 100 mg/1,
55
-------
170 -.
160 -
150
140 -
130 ~
120 -
110 -
100 -
» 904
70 -
60 _
50 _
40 -
30 -
20 -
10 -
o Cone. pt. 2
* Cone. pt. 3
+ Cone. pi. 5
0
0
ill II \ i \ \ i r
. 3 Dita
pt. 5 Data
100
200 300 400
Ca(OH)2 added (mi;/l)
500
BOD REMOVAL WITH LIME ADDITIONS
56
-------
160 -
o Cone. pt. 2
A Cone, pt. 3
+ Cone. pt. 5
140 -
120 -
100 -^
00
x
to
E
60 \
O
(J
60 _
40 -
20 -
O
c
200 360 400 500
Ca(OH)2 added (mg/1)
Figure 18
COD REMOVAL WITH LIME ADDITION
57
-------
Oi
en
o
p<
o
35
f-1
g
o Cone, pt. 2
A Cone, pt. 3
+ Cone. pt. 5
50 _,
40 -
100
200
300
400
500
Ca(OH)2 added (mg/1)
Figure_19
OKTHO-PHOSPHATE REMOVALS WITH LIME ADDITIONS
58
-------
and to a lower value of about 1 mg/1 P04 for lime doses of
300 mg/1 and greater. Likewise, for total phosphates, an
reduction, from an average of 25 mg/1 P04 to about 5 mg/1 PC>4,
was observed with a lime addition of 100 mg/1 to the system.
Above lime doses of 300 mg/1 the residual total phosphate con-
centration was consistently below the level of 1 mg/1 P04.
The close correlation between the phosphorus levels after set-
tling and filtration is likely associated with the highly effi-
cient sludge blanket clarification which was designed into the
settling units of the pilot plant. As indicated by Jenkins (3),
it would be expected that in a plant scale clarifier, sufficient
phosphate precipitate would carry-over to necessitate subsequent
filtration for consistent high level phosphorus removals.
The 80% reduction of total phosphate at the 100 mg/1 lime
dose, corresponding to a pH of about 9.5, confirms on pilot
scale the appreciable removals predicted by Schmid and McKinney
(27), in a somewhat different treatment context. Removals at
this level may be significant in the sense of upgrading exist-
ing wastewater treatment plants, since substantial phosphorus
is removed at this dose together with essentially all of the
suspended particulates and BOD.
The efficiencies of removal for the major wastewater con-
stituents are shown graphically in Figures 21 through 25. From
tV* £> «—« f± f~» 1 1 T*T T £1 t~1 -1 -4* "1 f"» CVTT *t f3 f^ ^ "t- -f- V> r* ~t~ -f- V» t~\ w* r-yl—« ~t~ t~* "1 f~f V*"4 •/* "1 /-»«•>>-» -4- >-l /Tl •**» *"» f~\ »•» *f* f\ *-!•£!
iA»—O^ V^ CijL V «~ t> J.I. ^.O >~'VjLClC:.LAU V/Jklc^ti^ CAJ.1^ 111 WO I* O-*-£^H-t--l--l-'-'ClJ.J.l' ^j'-'.L <^>^^J.wCC^V^
removals are realized for all the constituents at a lime dose
of 100 mg/1 or less. Doses above this level serve to minimize
the absolute quantities of residual pollutants.
In an effort to reduce the lime dose requirement for effect-
ing high level phosphate removals, a sludge recycle mode was
established to provide nucleation sites for improving the effi-
ciency of lime utilization. In this operational mode, variable
fractions of the chemical sludge blowdown were recycled back to
the system ahead of the rapid mix unit. For the most effective
case, with 50% recycle in the sludge system, the phosphorus re-
movals are compared to the conventional operating mode in Figure
26. While the recycle removals at low lime dose are consistently
on the low side of the residual phosphate envelope, the pilot
plant data do not appear to show a highly significant deviation
from the results developed in the conventional mode of operation
at the phosphorus removal levels that are generally considered
desirable. Thus, on a plant scale, it is questionable if the
recycle mode is justified.
Throughout the entire lime clarification study, weekly
samples were taken at various points in the conventional clari-
fication system for analysis of the concentration of coliforms,
fecal coliforms, and fecal streptococcus. The data from these
59
-------
bo
E
f-c
s
1
o Cone. pt. 2
A Cone. pt. 3
+ Cone. pt. 5
50.
40
30-
20 -
o " o
o %
O CO
o «>
o o 00°
4-'
'A A-T- " A . A4-
TtTTii J^A A 4-AA A^
200
300
400
500
Ca(OH)2 added (mg/1)
Figure_20
TOTAL PHOSPHATE REMOVAL WITH LIME ADDITIONS
60
-------
SH
g
W
o
(4
E£
Q
W
ffl
100 -i
80 -
60 -
40-
20 ~
1
100
_C Q_
I
200
(
300
400
500
Ca(OH)2 added (mg/1)
TURBIDITY REMOVAL EFFICIENCY AFTER LIME TREATMENT AND FILTRATION
61
-------
CJ
w
w
OS
CO
D
o
CO
D
w
w
o,
CO
100 _
80 _
60
40 ~
20 -
1
100
200 300
Ca(OH)2 added (mg/1)
1
400
500
SUSPENDED SOLIDS REMOVAL EFFICIENCY AFTER LIME TREATMENT AND
FILTRATION
62
-------
100 •
80 -
w
»-l
o
£ 60
fa
,j
1
H 40
§
20 -
.0° 60
1
100
o o
o
1
260
300
1
400
1
500
Ca(OH)2 added (mg/1)
Figure 23
BOD REMOVAL EFFICIENCY AFTER LIME TREATMENT AND FILTRATION
63
-------
100 -
80 "
s
S 60 -
O
n
w
o 40 -
s
K
Q
O
O
20 -
0
o
oo 0 o o o o
o (• °
/O ° ° 0 ° ° °
o y o
/
/•
/°
/
3
0 100 200 300 400 500
Ca(OH)2 added (mg/1)
Figure 24
COD REMOVAL EFFICIENCY AFTER LIME TREATMENT AND FILTRATION
64
-------
c Ortho Phosphate
A Total Phosphate
Q
W
I
W
K
W
I
8
W
Pk
100
80
60-
4 A .S^V^SteS*-^ . 4
** J/4J • • »•
o
A
A ' - A
20'
100
200
300
400
500
Ca(OH)2 added (mg/1)
Figure 25
PHOSPHATE REMOVAL EFFICIENCY WITH LIME
65
-------
0 With Recycle
+• Without Recycle
20 - f
til
w
H
X
W
ft
<
io
100 200 300 400 • 500 600
Ca(OH)2 Added (mg/1)
£igure_26
EFFECT OF LIME SLUDGE RECYCLE ON THE REMOVAL OF TOTAL
PHOSPHATE WITH LIME
66
-------
o
o
«
w
s
•J
8
io
IO
O O
IO
lo
o Cone. pt. 2
A Cone. pt. 3
-f Cone. pt. 5
. 3 & 5
10*1
10
100 200 300 400
Ca(OH)2 added (mg/1)
Figure 27
COHFORM REMOVAL WITH LIME ADDITIONS
500
67
-------
analyses have been reviewed with respect to the applied lime
dose, as shown in Figure 27 for the total coliform concentration
While there is considerable scatter in the data, there does ap-
pear to be a definite proportional tendency between the applied
lime dose and the removal of coliform organisms. This is
consistent with the laboratory observations of several authors
who have noted that the degree of effectiveness of lime in
destroying bacterial organisms is a function of the pH developed
within the system (31) (32) (33) . At lime doses of about 400
mg/1, corresponding to pH values of approximately 11.5, there
was a greater than two-fold reduction in coliform removals with-
in the system. Similar trends were observed for the fecal coli-
forms and fecal streptococcus as shown in Figures 28 and 29.
Trace metal analyses were conducted during the study period
for iron, copper, manganese, chromium, lead, zinc, cadmium, and
molybdenum by the quality control laboratory of the Denver Water
Department. In these studies, all analyses were made by atomic
adsorption methods as discussed in the 12th Edition of Standard
Methods.
The data are summarized in Figures 30 through 38, where
the temporal variations of both influent and effluent concentra-
tions are plotted for each of the elements. From the average
influent and effluent concentrations presented in Table VI, it
can be seen that the concentrations of Zn, Cr, Mn, Cu, Cd, and ,
Fe were reduced somewhat by the lime treatment, while the con-
centrations of Al, Mo, and Pb were not significantly affected
at the levels encountered in the secondary effluent investigated
in these studies. Above a lime dose of about 100 mg/1 there
did not appear to be any significant dose dependence on the de-
gree of removal for the elements which were investigated.
Sludge Production and Thickening
One of the important considerations in the successful
utilization of lime for tertiary treatment of wastewater is
the quantity and character of sludge requiring disposal. To
characterize the sludge generated in this study, the solids
collected in the clarifier were blown down and analyzed for
volume, solids concentration, and thickening behavior. From
these analyses, data were developed which yielded information
on the quantity of sludge requiring disposal for a given lime
dose. This data is summarized in Figure 39. From this curve,
it can be seen that there is a linear relationship between the
applied lime dose and the quantity of sludge requiring disposal.
The slope of this curve for the wastewater treated in these
studies was 0.56 tons/M.G./100 mg Ca(OH>2 added per liter. Of
this quantity the volatile solids comprised approximately 10-15%.
68
-------
10
10
o
o
s.
o
CM
n
8
§
10
3-
io
2J
10 •
4*
A-}-
« Influent cone. pt2
A Effluent cone. pt3
+ Effluent cone. pt5
pt. 3 & 5
Data
0 100 200 300 400
Ca(OH)2 added (mg/1)
Figure 28
FECAL COLIFORM REMOVALS WITH LIME ADDITIONS
500
69
-------
o
o
,o5-
10
10'
H
K
w 10 -
I
1 -
3 t
*• +
oInfluent Cone. pt. 2
A Effluent COnc. pt. 3
^Effluent Gone. pt. 5
100 200 300 400
Ca(OH)2 added (mg/1)
Figure 29
FECAL STREPTOCOCCUS REMOVALS WITH LIME ADDITION
pt. 3 & 5
Data
500
70
-------
WJ
10° -
10
-2
Influent Cone. pt. 1
Effluent Cone. pt. 5
ave.
inf.
+ + -t-
ave.
eff.
r r T r ' ' > > i >
2 3 4 5 6 7 8 9 10 11 12
MONTH
Figure 30
MONTHLY VARIATIONS IN IRON CONCENTRATION
71
-------
o Cone. pt. 1
4 Cone. pt. 5
!?
K
S5
s -1
5
o
t-t-
0.01
•f +
ave. inf.
o 4-
+ 4-
+ 4-
.ave. eff.
o -f-
2345678
MONTH
T 1 I 1
9 10 11 12
Figunre_31
MONTHLY VARIATIONS IN COPPER CONCENTRATION
72
-------
•*" Influent Cone. pt. 1
A Effluent Cone, pt. 5
0.1 J
4-
4- ,4- + •»"«-
ave. inf.
AA
A A
A
ave. eff.
1 0.01 -J
v_^ ."•
w
CO
w
<
g
A A
0.001
A
A
A AA
2345
678
MONTH
9 10 11 12
Figure 32
MONTHLY VARIATIONS IN MANGANESE CONCENTRATION
73
-------
10
-1
.4 Influent Cone. pt. 1
A Effluent Cone. pt. 5
to
E
4- . 4-
4- 4-
Average
iniiucnt
S3
O
£& AA 4 4A A
4-Average
4- Eff'luent
4- 6 A
+• A A A
4-4-A
10~JH 1 1 1 i 1 r- \ 1 1 1
23456789 10 11
MONTH
Figure 33
MONTHLY VARIATION IN CHROMIUM CONCENTRATION
74
-------
1.0-
Q
S
•-3
0.01'
-f- Influent Cone, pt. 1
A Effluent Cone, pt. 5
4-
ave. inf.
A " A A A A
-A
A A
ave. eff.
A-A
A A
2 3 4 5 6 7 8 9 10 11 12
MONTH
Figure 34
MONTHLY VARIATIONS IN LEAD CONCENTRATION
75
-------
•J" Influent Cone, pt. 1
A Effluent Cone, pt. 5
1.0-
4-
A A 4-
ave. inf.
0.11
0.01
4-
A
A -r
. _,A
4.4-
A
"ve. eff.
A A
A
AA A
I I I
2345678 9 10 11 12
MONTH
Figure 35
MONTHLY VARIATIONS IN ZINC CONCENTRATIONS
76
-------
W
§
1.0 _
0.1 -
0.01
•+• Influent Cone, pt. 1
A Effluent Cone. pt. 5
ave. inf.
avc. cff.
34567 8 9 10 11 12
MONTH
Figure 36
MONTHLY VARIATION IN MOLYBDENUM CONCENTRATION
77
-------
W)
E-
i.o _
o.i
influent Cone. pt. 1
Effluent Cone, pt. 5
A ave. inf.
\ ave. eff.
A
•t-
8
12
i
9 10 11
MONTH
Figure 37
MONTHLY VARIATION IN ALUMINUM ION CONCENTRATION
78
-------
A .Influent Cone, pt. 1
+ Effluent Cone. pt. 5
0.005'
0.004 '
0.003-
60
e
Q
s
0.002 •
0.001-
+AA4 A A A
+ +A 4
Average Influent
Average Effluent
1 2 3 ' 4 ^ ^5 •? ' 8 ' 9 ' 10 ' 11'12 '
MONTH
Figure 38
MONTHLY VARIATIONS IN CADMIUM CONCENTRATION
79
-------
Table VI
Trace Metal Removals
Metal
Aluminum
Molybdenum
Zinc
Lead
Chromium
Manganese
Copper
Iron
Cadmium
Average Influent
Concentration
Point 1
(mg/liter)
1.110
0.057
0.141
0.040
0.0115
0.065
0.046
0.356
0.0025
Average Effluent
Concentration
Point 5
(mg/liter)
1.120
0.055
0.065
0.030
0.0045
0.013
0.032
0.097
0.0021
80
-------
w
s
O
l-l
B
Q
O
W
CO
w
tH
CO
g
2.4
2.2
2.0
1.8
1.6-
1.4
1.2
1.0'
0.8-
0.6'
0.4-
0.2-
0.0
—I 1 1 1 1
100 200 300 400 500
Ca(OH)2 added (mg/1)
Figure 39
WASTE SLUDGE PRODUCTION (TONS/MG) AS A FUNCTION OF LIME DOSE
81
-------
Solids concentrations in the sludge blowdown were typi-
cally between 1 and 4%. These concentrations could be approxi-
mately doubled with two hours of quiescent settling. This
concentration would be expected to increase further in a gravity
thickening device which incorporated some form of mixing.
Filter Headless
Since the rate of development of filter headless is very
important to the operation and economics of filtration, several
extended filtration runs were made on the lime treated clarifier
effluent. These runs provided an indication of the practical
length of filter runs at each of several loading rates. The
data from these experiments are plotted in Figure 40 with filter
headloss as a function of the grams of solids removed on the
filter per cubic foot of filter bed depth. The abscissa unit
was chosen to normalize for the influence of variable influent
suspended solids. As expected, the rate of headloss develop-
ment increased as the hydraulic loading on the filter was in-
creased from 1.4 to 2.1 gpm/ft2. At the 2.1 gpm/ft2 loading rate,
the filter headloss reached 8 ft. at a total solids loading of
about 13 grams per cubic foot. For typical suspended solids
levels of 5 mg/1 in the clarifier overflow, this represents a
filter run of about 16 hours, assuming that all of these solids
are removed on the filter. This definitely represents a practi-
cal operating range.
Alum Dose Variation
For purposes of comparing the effectiveness of alum and
lime in the conventional clarification system, a series of
studies was performed utilizing alum as the chemical additive.
In these studies the slow mix detention time was maintained at
48 minutes, the flocculation intensity was constant at 19 rpm,
and the pH was maintained in the range 5.5-6. The alum dose was
varied, together with the filter loading rates, and determina-
tions were made to define the extent of removal for turbidity,
suspended solids, BOD, COD, and the phosphate forms. Addition-
ally, the effect of variable dosing and filter loading rates
was analyzed for the impact on the rate of development of filter
headloss.
The effectiveness of tertiary alum treatment in clarifying
nitrified secondary effluent is graphically demonstrated in
Figure 41. With alum addition followed by settling, the waste-
water turbidity was reduced from an influent value of 13.5 mg/1
82
-------
o
-------
CM
O
01
a
tt
E
26
24-]
22
20-}
18
16
14.
12.
TO-
&•
6-
4.
o Cone, pt. 2
A Cone, pt. 3
+ Cone, pt. 5
100 200
ALUM added (rag/1)
300
Figure 41
TURBIDITY REMOVAL WITH ALUM IN THE ALUM CLARIFIER SYSTEM
84
-------
Si02 to about 2.5 mg/1 Si02 at an alum dose of only 50 mg/1.
With subsequent rapid sand filtration the turbidity was re-
duced further to less than 1 mg/1. At higher alum doses, up
to 300 mg/1, the filter effluent showed an additional slight
improvement. However, at this level the filter experienced
increased solids loadings as indicated by the increase in tur-
bidity from the sedimentation unit. Thus, operation at these
high alum levels for turbidity removal would adversely affect
the length of filter runs.
Accompanying the removal of suspended particles, alum
provided a significant reduction in the wastewater BOD. At
alum doses as low as 50 mg/1, the filter effluent BOD was re-
duced to less than 2 mg/1. This level is consistent with the
BOD concentration attainable utilizing lime in the conventional
clarification system, and confirms that the majority of BOD
contributing organics in nitrified secondary effluent are in
the suspended form. Likewise, the removal of COD followed the
pattern established in lime treatment. It was possible to re-
duce the filter effluent COD to about 20 mg/1 at an alum dose
of approximately 50 mg/1. Higher alum doses did not signifi-
cantly improve the removal of this constituent. Thus, as
shown in the lime clarification data, chemical treatment with-
out carbon adsorption was limited to approximately 65-75% COD
reductions for the wastewater treated in this investigation.
Alum was also effective in reducing the concentration of
phosphate in wastewater. This is shown in Figures 44, and 45,
respectively. Approximately 80% of the ortho- and total phos-
phate species were precipitated from the clarifier effluent at
an alum dose of 150 mg/1. Filtration of this settled product
water reduced the average phosphate concentrations to less than
1 mg/1. At alum doses above 150 mg/1, there was little addi-
tional improvement in the degree of phosphorus removal. These
alum dose requirements are in close agreement with the data
developed in the pilot plant experiences at the Bay Park Sewage
Treatment Plant in Nassau County, New York (50,51). Likewise,
the phosphorus levels attainable in the product water are of
the same order of magnitude. The importance of filtration in
realizing the full potential of phosphate precipitation is
clearly indicated by the results of this study. For the experi-
mental system used in this investigation it was difficult to
control some discharge of phosphate solids in the clarifier
overflow.
85
-------
oConc. pt. 2
a Cone. pt• 3
4'Cone. Pit. 5
X-N
r-t
to
E
w
^
o
m
110 •
100 •
90 •
80 -
70 .
60 .
0
0
0
&
i
I
1 A
50-1
40 .
30 '
20 •
10 '
0
1
'
I
1 V/l A
M * A
^ 1 t T - I"
100 200 300
ALUM added (mg/1)
Figure 12
BOD REMOVAL WITH ALUM IV THE ALUM CLARIFIER SYSTEM
86
-------
°Conc. pt. 2
A Cone. pt. 3
4-Conc. pt. 5
IH
bO
Q
O
0
no •
100 •
90 '
80 "
70 '
60 '
50 "
40 -
30 '
20 *
10 '
0
»
&
0
0
1" o
.
*
i . .
4-
H-
0 100 200 300
ALUM added (mg/1)
Figure 43
COD REMOVAL WITH ALUM IN THE ALUM CLARIFIER SYSTEM
87
-------
O Cotic. pt. 2
A Cone, pt. 3
+ Cone. pt. 5
200 300
Alum added (mg/1)
Figure 44
ORTHO-PHOSPHATE REMOVAL WITH ALUM IN THE ALUM CLARIFIER SYSTEM
88
-------
O Cone. pt. 2
A Cone. pt. 3
+ Cone. pt. 5
in
a
W
v.
I
0 100 200 300
ALUM added (mg/1)
Figure 45
TOTAL PHOSPHATE REMOVAL WITH ALUM IN THE ALUM CLARIFIER SYSTEM
89
-------
VIII. HIGH RATE CLARIFICATION
INTRODUCTION
An alternative system of advanced wastewater clarification
treatment is the direct dosing of chemically-treated wastewater
onto dual-media filters. Unlike the conventional AWT process
lineup, this alternative system eliminates the sedimentation
step and provides for the coagulated wastewater to be processed
directly onto the dual-media filter (36). Most of the research
which has been conducted on this type of system has been in the
treatment of potable water supplies. Conley and Hsiung (37)
have reported on experiences with some of the numerous water
treatment plants employing direct multi-media filtration of
coagulated water. They report one case with 12-hour filter runs
at a hydraulic loading of 5 gpm/ft2 with chemical addition of
32 mg/1 alum, and 0.2 mg/1 polymer. In this system 25 units
of turbidity were applied directly to the filter without prior
flocculation or settling. Filtered water turbidities ranged
from 0.2 to 0.4 Jackson Turbidity Units.
The concept of using direct, dual-media filtration for
clarification of chemically coagulated secondary wastewater
effluents is a fairly new idea. The operation appears to have
potential for the following reasons: 1) Significant cost and
space savings may result from elimination of the chemical clari-
fier, 2) Continued development of a more ideal coarse-to-fine
filter media will allow higher filter efficiencies, 3) Constant-
ly improving automated backwash equipment can easily handle the
necessary chore of more frequent backwash operations under the
higher filter solids loading conditions inherent in direct fil-
tration, and 4) The process is a versatile one—if only solids
removal is desired, low chemical doses can be used to coagulate
the solids which can then be removed from the liquid stream on
the mixed-media filter. If additional treatment is desired,
such as for phosphate removal, higher chemical doses will be
required to form a phosphate precipitate, and either filter
loading rates must be decreased or, alternatively, an inter-
mediate settling operation must be employed to handle the in-
creased chemical floe production.
Common problems which have been encountered in direct, dual-
media filtration relate to the difficulty of achieving economi-
cally long filter runs under the inherently high solids load
coming onto the filter. Generally, filter runs will be shorter
than those when an intermediate sedimentation step is provided,
and, as a result, more backwash wastewater will be generated.
91
-------
However, there would probably be an equal amount of waste
solids to dispose of if a combination sedimentation-filtra- ?(
tion system were employed, so that solids disposal in a
system using direct dual-media filtration should not be an
unusually difficult problem.
For direct-dosing filter operations, the length of fil-
ter run and the rate of filter headless development are
usually directly related to the filter loading rate. As men-
tioned earlier, Conley and Hsiung (37) have found that filter
loading rates of 5 gpm/ft2 produced filter runs of 12 hours
using 32 mg/1 alum and 0.2 mg/1 polymer as a filter aid on raw
water treated for potable use. Slechta and Gulp (38) found
that loading rates of 5 gpm/ft2 with an alum dose of 200 mg/1
produced filter runs ranging from 2 to 8 hours when treating
secondary effluent at the Lake Tahoe plant. The filter load-
ing rate will, of course, be dependent to a large degree upon
the quality of the wastewater being filtered, as well as the
size of the media employed in the filter.
Organic polymers have contributed greatly to the effective-
ness of direct dual-media filtration by acting to strengthen
the weak chemical floe produced by the alum coagulation step.
Higher filter flow rates are thus possible without shearing the
fragile floe out of the filter bed. The us XT?. 1 polymer dose
when used as a filter aid is about 0.1 mg/1 (39)(40).
The process of direct filtration of alum-coagulated waste-
water relies on the characteristic of the alum coagulant to
undergo hydrolysis and then precipitate the solids and phos-
phates contained in the wastewater (41) . The mechanism for sur-
face charge reduction and subsequent agglomeration of suspended
colloidal solids has been previously mentioned, but the mechan-
ism for phosphate removal is still rather obscure. Despite
considerable research, the basic chemistry of the phosphate
reaction with Al(III) cations is quite unclear and the accumu-
lated data has often been directly contradictory. To illustrate,
Lea, Rolich, and Katz (42) presented data supporting the view
that phosphate is removed by adsorption on precipitating alumi-
num hydroxides. However, Stumm (43), Cole and Jackson (44),
Recht and Ghassemi (45), and Farrell, Salotto, Dean, and Tolliver
(46), have all concluded that removal of phosphate takes place
primarily by means of a chemical reaction rather than by adsorp-
tion. In general, it appears that adsorption on hydrated oxides
appears to play a significant role along with the chemical for-
mation of an insoluble particle in the removal of phosphate by alum
Clearly, further research is needed to give a true definition
of the mechanism for phosphate removal using alum as a coagulant.
92
-------
The literature also shows considerable disagreement among
researchers concerning the kinetics and stoichiometry of the
cation-phosphate reactions, as well as the effect of various
parameters such as pH and ionic character of the wastewater
on the removal of phosphate. Various researchers (39), (43),
(47), have indicated that with proper pH conditions, and low
cation-to-phosphate ratios, the chemical reaction for Al(III)
cations with ortho-phosphate is
Al(III)
H2PO~
A1PO
2H
+
provided that adequate reaction time 'is provided. In practice,
however, far more than the stoichiometric amount of Al(III) is
required for complete precipitation of ortho-phosphates. Recht
and Ghassemi (45) have indicated that amounts of Al(III) in
excess of stoichiometric requirements can be satisfactorily
explained in terms of the occurrence of competing reactions,
such as
6HC0
2A1(OH).
6C0
3S0
and the dispersion of metal-PO^ precipitate into extremely fine
and often non-settleable colloidal particles. The required ex-
cess of Al(III) is thought to be due.to the fact that hydrolysis
products of Al(TTT) and not. the Al (III) species alone are in-
volved Hi one pi'Gcipi La.L.G j.GonnaL.ion . rxccoi~*ai.ng oo oGiiOn anu
Hannah (40), these hydrolysis products may be transient mono-
meric species such as [Al(1^0)4(OH)g]+1 or more complex poly-
nuclear species such as [Al8(OH)9rJ ^ or
+4
H
O
(H20)4A1;
'0'
H
Positively charged hydroxy-aluminum polymers are also indi-
cated by Hsu (48), and Yuan and Hsu (49) to be the species account-
ing for the precipitation of phosphate. These authors have stated
that this precipitation process is greatly influenced by the ratio
of phosphate to aluminum and also by the nature and concentration
of foreign components present. The precipitation will be either
93
-------
aided or hindered, depending on whether there are just enough
foreign anions to help the P04 anions neutralize the positive r
hydrozy-aluminum polymers, or whether there are so many foreign
anions present that competition exists between them and P04.
Recht and Ghassemi (45) also showed that an approximate linear
relationship exists between the residual ortho-phosphate concen-
tration and the Al/Ortho-P04 molar ratio up to a ratio of about
1:1 in a pure ortho-phosphate solution at a pH of 6.0. Their
work indicated that 1.4 moles of Al(III) are required to pre-
cipitate one mole of P04. This linear relationship at fairly
low A1/P04 molar ratios suggests the occurrence of a chemical
reaction which is dependent on the molar quantities in solution.
EXPERIMENTAL PROGRAM
The objectives of the pilot plant study on the high rate
clarification system were to determine the optimum chemical
doses and operating conditions for two situations: 1) clarifi-
cation only, and 2) clarification plus high PO4 removal. In
each case various constituent concentrations were monitored
(COD, BOD, bacteria, trace metals) to determine the overall
effectiveness of each treatment case. It has been shown that
the chemical doses required for solids removal are lower than
those necessary for P04 removal (50). Thus, it is important to
determine the relative doses required so that efficient plant
operation can be maintained under various required effluent
qualities. For production of a reusable water, the required
advanced waste treatment plant effluent quality may indicate a
low ammonia content (provided by a nitrification unit, for
example) and very low suspended solids content. In this case,
a lower alum dose will be required to coagulate and remove the
solid particles than would be necessary for P04 removal.
RESULTS
As with the conventional clarification system, one-liter
samples were composited over a four hour period after equili-
bration of the system. For the high rate system, the points
sampled were 1) the pilot plant influent, 2) the bio-clarifier
effluent, and 3) the filter effluent. Analysis of these samples
included the same range of variables evaluated for the conven-
tional system.
The wastewater feed to the alum system consisted of
effluent from the Denver Sewage Treatment Plant which had
been nitrified in the preceding pilot plant unit. This waste-
water feed displayed widely fluctuating constituent concentra-
tions. Since this was a pilot plant study and the emphasis
94
-------
was on simulating a full-scale operation, the chemical doses
were held constant for the length of each run and no attempt
was made to measure the changing influent and pace the chemi-
cals accordingly. Because of this, the results show the type
of variation that might be more characteristic of plant scale
operations than the controlled uniform input research studies.
Flocculating Characteristics
One of the initial investigations in the high rate system
was an analysis of the effect of slow mix paddle speed and
detention time on the removal efficiency of the dual-media
filter. Mixing speeds of 7 rpm, 15 rpm, and 23 rpm were in-
vestigated over a period of several weeks. A careful study of
the data showed that, although the physical appearance of the
chemical floe was quite different at the various mixing speeds
(large floe at low speeds, small floe at high speeds), the
phosphate, suspended solids, COD, BOD, and turbidity removals
were not significantly affected by changes in the slow mix
paddle speed within the range of 7 to 23 rpm. The 7 rpm paddle
speed allowed for larger floe particle formation due to the
lower mixing intensity, but in the transmission to and through
the filter the large, weak floe particles were reduced to a
much smaller size. This floe was similar to the floe produced
in the slow mix unit at the higher mixing intensities.
The slow mix detention time varied from 4 minutes to 60
minutes, and an analysis of the data gathered at the different
detention times suggests that the various detention times neither
.aided nor hindered the removal of pollution constituent concen-
trations over the detention time range that was studied. How-
ever, it is clear that if the same results can be achieved at
4 minutes detention time as those at 60 minutes detention time,
then a much smaller slow mix unit can be utilized in the treat-
ment process for the shorter detention time. In fact, Conley
and Hsiung (37), and Slechta and Gulp (38) have reported that
the best clarification and phosphate removal may be achieved
with partically no flocculation period, other than that which
may occur during the subsequent filtering process itself. At
the South Lake Tahoe facility, Slechta and Gulp (38) simply
added the alum coagulating chemical directly to the filter in-
fluent thereby forming a "micro" floe which effectively removed
suspended solids and phosphates.
95
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pH Variation
A wastewater parameter in the high rate clarification pro-
cess which is very important to the system success is the pH.
There have been several discrepancies reported in the litera-
ture for the optimum pH of aluminum phosphate precipitation.
Lea, Rolich, and Katz (42) have reported an optimum pH range
of 7.1-7.7, while Cohen and Hannah (40) indicated a pH range
of 5.5-7.8. Recht and Ghassemi (45), and Leckie and Stumm (5l)
confirmed the middle of this latter pH range with optimums of
pH 6.0 and 6.3, respectively. Of course, the precise optimum
for phosphate removal will vary somewhat with the actual chemi-
cal constituents comprising the wastewater. Data are shown in
Figure 46 for the pH investigation which covered a pH range
from 3.0 to 8.7. It can be seen from these results that the
optimum pH for alum treatment at the pilot plant covers the
range of 5.0-6.0. The residual suspended solids and BOD levels
remain quite low throughout the lower pH range, but begin to
rise above a pH of about 6. This reduction in removal effi-
ciency is attributable to the less efficient coagulation at
the higher pH values. Figure 46 includes only those alum doses
for which the Al/PO^ molar ratio is greater than 1.0. This
was done to reduce the direct, linear effect that relatively
low mole concentrations of aluminum have on phosphate removal
(46).
Alum Dose Variation
The removals of phosphates, suspended solids, COD, BOD, and
turbidity as they vary with the applied alum dose are shown in
Figures 47 through 54. When it was found that the slow mix
paddle speed and detention time were not major parameters in
the alum system, data at all paddle speeds and detention times
were included in these plots of alum dose vs. constituent re-
siduals .
Presented in Figure 47 is a plot of ortho-phosphate removal
vs. alum dose. It can be seen from this curve that about 120
mg/1 alum is required to lower the residual ortho-phosphate to
one mg/1. This corresponds to approximately 96% ortho-phosphate
removal. Also shown on Figure 47 are the results of jar tests
which were conducted on Denver Metro secondary effluent at the
beginning of the study. The jar test results and the pilot
plant results are in close agreement, although the jar tests
incorporated 30 minutes of settling while the pilot plant flow
underwent direct dual-media filtration to remove the accumulated
chemical floe.
96
-------
Total PO..
Suspc-nded Solids
•o
CS
w
<
£
w
o
p
£-•
fcc
VI
Q
O
w
g
CO
12 -
10
6 "
2 -
pH
Figure 46
pH OPTIMIZATION FOR THE HIGH RATE ALUM SYSTEM
97
-------
X
tn
W
EH
o
p,
O
OS
O
25
£> Jar Test Results
o Pilot Plant Data
20 k-
15
0 100 200
ALUM DOSE (mg/1)
Figure 47
OkTHO-PHOSPHATE REMOVAL WITH ALUM
300
98
-------
Figure 48 represents data on total phosphate residual vs.
alum dose. Data points include residuals from dual-media fil-
tration alone, as well as residuals from combined dual-media
and membrane filtration. As shown by the curve, for a particu-
lar filter run, the dual-media filtered effluent generally con-
tained slightly more residual total phosphate than the mem-
brane - filtered sample. The agreement between the two curves
is an indication, however, that the dual-media filter actually
retained nearly all of the insoluble phosphate in the waste-
water. The definition of insoluble phosphate for this purpose
is that which will not pass a 0.45 micron membrane filter.
From Figure 48 it can be seen that a dose of about 120
mg/1 alum was required to consistently produce a residual total
phosphate level of about one mg/1. It should be noted that an
increase in the alum dose from 110 mg/1 to 200 mg/1, an in-
crease of 82%, increased total phosphate removal by only 5%.
The scatter of data in Figures 47 and 48 is primarily due
to the variation in phosphate concentrations entering the high
rate system. These variations arise from fluctuations in soluble
phosphorus levels and the significant amounts of organic biomass
containing phosphorus which periodically passed through the
nitrification clarifier and into the alum system. These varia-
tions have caused the total phosphate concentrations to range
J?__ TO O -. /n J- ~ O O O ~ /T ,,, .: 4- U "v- «-!--£•> —r* f~r^ ^-C O O O «~ /~\ .-> ~
J-J. Ulll 1^. . ^ J"fe/ -L LU •-»->*<-> lilg/ -L , W-LUii O.U. a V fci ttgc U>J- £J*J . u Ilig/ J_ H.S
P04.
In Figure 49 the residual total phosphate data from Figure
48 has been plotted against the A1/PC>4 molar ratio. In this
plot the wide-ranging influent phosphate concentrations can be
accounted for by ratioing them with the particular alum dose
for that day. This appears to be a valid way of comparing phos-
phate removals at various initial phosphate concentrations when
using low doses of alum. At low alum doses the chemical nature
of the aluminum-phosphate reaction predominates and the alum
requirement corresponds much more closely to stoichiometric re-
lationships than it does at higher alum doses (46).
It is indicated in Figure 50 that turbidity in the final
filtered effluent was reduced to approximately 0.5 mg/1 Si02
by addition of an alum dose of 50 mg/1. Influent turbidities
ranged from 0.4 mg/1 to 49 mg/1 as Si02. This represents an
overall turbidity removal of about 97% with both dual-media and
rapid sand filtration. These removal efficiencies did not im-
prove significantly above an applied alum dose of 50-60 mg/1.
99
-------
w
P<
CO
§
e,
CO
w
B;
o Dual-Media Filtered
X Membrane Filtered
Dual-Media
50
100 150
ALUM DOSE (mg/1)
200
Figure 48
TOTAL PHOSPHOROUS REMOVAL WITH ALUM
100
-------
20
o Dual-Media, Filtered
Figure 49
TOTAL PHOSPHATE REMOVAL AS A FUNCTION OF A1/P04 MOLAR RATIO
101
-------
20
15
w
CQ
K
X Upflow - Rapid Sand
O Downflow - Dual Media
150
ALUM added (mg/1)
200
TURBIDITY REMOVAL WITH ALUM
102
-------
Suspended solids removal is shown in Figure 51 as a func-
tion of alum dose. During the testing period the influent
suspended solids at point two in the alum system averaged 41
mg/1, with a high of 108 mg/1 and a low of 8 mg/1. A much lower
alum dose was required for effective clarification than was re-
quired for phosphate removal, as only about 50-60 mg/1 alum was
necessary to achieve a suspended solids residual of less than
one mg/1. During a portion of the study, the alum-coagulated
wastewater was filtered through the rapid sand filter at the
pilot plant in both upflow and downflow operational modes.
Suspended solids removal was quite good at all times (< 1 mg/1
residual) as shown by the "x" data points in Figure 51.
The high rate clarification system was effective in remov-
ing the suspended fraction of the COD. The COD influent ranged
from 28.8 mg/1 to 174 mg/1, with an average of 78.3 mg/1. The
average residual COD shown in Figure 52, was about 20 mg/1,
representing the soluble refractory organics. The applied alum
dose did not appear to significantly affect COD removal at alum
doses of greater than 50 mg/1. Results indicate that about
75% of the COD had been removed at an alum dose of 50-60 mg/1.
Again, data for COD removal by rapid sand filtration is similar
to that from dual-media filtration.
BOD is another parameter which varied widely in the alum
system influent, ranging from a high of 159 mg/1 to a low of
3.5 mg/1. Figure 53 indicates that reductions to 2 mg/1 BOD
were achieved at alum doses as low as 50-60 mg/1. Increasing
the alum dose above this amount did not produce significant
improvements in removal. Filtration through dual-media and
rapid sand produced almost identical results - removals of
about 98%.
The last graph in this series, Figure 54, combines the phos
-------
20 -
w
OT
O
o
CO
Q
w
g
g
OT
W
w
15
o Downflow through dual-media
X Upflow through rapid sand
10 „
150
200
SUSPENDED SOLIDS REMOVAL WITH ALUM
104
-------
80
60
§
o
CO
w
K
40
20
X Upflow through rapid sand
° Downflow through dual media
50
100 150
ALUM DOSE (mg/1)
200
Figure 52
COD REMOVAL WITH ALUM ADDITIONS
105
-------
40
30
x Upflow through rapid sand
o Downflow through dual media
x.
to
e
20
Q
10
O I O
50 100 150
ALUM DOSE (mg/1)
Figure 53
BOD REMOVAL WITH ALUM
200
106
-------
to
E
Q
>H
a
3
•D
C
to
•
CO
v
o
d,
I
Q
C
m
Q
8
g
Q
40 -i
35.
30-
25 -
20 -
15 -
10 .
50
100
150
flLUM added (mg/1)
Figure 54
RESIDUAL POLLUTIONAL PARAMETERS AS A FUNCTION OF ALUM DOSE
IN THE HIGH RATE SYSTEM
107
-------
Trace Metal Removals
As performed for the conventional system, trace metal
analyses were conducted for iron, copper, manganese, chromium,
lead, zinc, cadmium, and molybdenum by the laboratory of the
Denver Water Board. All analyses were conducted by atomic ab-
sorption methods given in the 12th edition of Standard Methods.
Figures 55 through 63 illustrate the influent and effluent
concentrations for each of the trace metals during the testing
period. It is shown on the figures that molybdenum, cadmium,
zinc, and lead were not significantly affected by alum treat-
ment while some removal was observed for the other trace metals
as indicated by the separation of the influent and effluent
average concentration lines on each graph. An exception to
the above statement is shown in Figure 56, where the copper con-
centration consistently increased in passing through the alum
system. This is thought to be due to the fact that the aeration
pipes in the nitrification unit prior to the alum system were
made of copper, which, under corrosive conditions, naturally
acted to increase the concentration of copper in the surround-
ing wastewater. Other sources of copper initially in the alum
system were several valves and hose connections, which were
replaced late in the study. This may explain the decreasing
copper residual concentrations in the latter months of the pro-
ject. For copper, as well as for all other trace metals, an
analysis of the daily results, with widely varying alum doses,
suggested that the trace metal removal did not vary as a func-
tion of applied alum dose. Large differences in residual trace
metal concentrations were often noted for the same alum dose
application.
(.
Figure 61 reveals that the cadmium concentration in the
effluent was consistently reduced to 0.002 mg/1 which, as seen
from the graph, was the limit of detection for cadmium by the
atomic absorption method for this series of tests.
Table VIII represents average influent and effluent concen-
trations for each of the trace metals.
Bacteriological Analyses
The Water Laboratory of the Denver Water Board monitored
coliforms, fecal coliforms, and fecal streptococcus on a weekly
basis throughout the duration of the pilot alum study. The
variation of influent and effluent bacterial concentration with
time is shown in Figures 64, 65, and 66. Generally, a reduction
in coliforms of greater than 97% was achieved by alum treatment
irrespective of the alum dose. This is indicated with selected
data included in Table IX.
108
-------
0.8 -
O
O
Influent Cone. pt. 1
Average
Influent,
Average Effluent
INFLUENT AND EFFLUENT IRON
CONCENTRATIONS
109
-------
Influent Cone. pt. 1
O
H
8
I
Effluent Cone. pt. 5
Average
Kffluent
20 30
WEEKS
Figure 56
INFLUENT AND EFFLUENT COPPER CONCENTRATIONS
110
-------
Influent C°nc. pt. 1
to
E
O
g
w
8
w
OT
W
1
0.10 -
0.09 -
Average
Influent
0.00 -Q- re 20-
WEEKS
Figure 57
INFLUENT AND EFFLUENT MANGANESE CONCENTRATIONS
111
-------
to
o
KH
E-
O
O
O
p
n
£S
O
O
0.05
0.04
Influent Con. pt. 1
0.01
0.00
\_7
Average
.. Effluent
0 -10 20 30
WEEKS
Figure 58
INFLUENT AND EFFLUENT CHROMIUM CONCENTRATION
112
-------
0.10 -
Influent Cone. pt. 1
U)
E
o
W
o
o
a
I
Effluent
Cone. pt. 5
Average
Influent
WE>KS
Figure 59
INFLUENT AND EFFLUENT LEAD CONCENTRATION
113
-------
5S
O
W
O
S5
O
O
X
0.40 -
Influent Cone, pt. 1
Effluent Cone. pt. 5
Average
Effluent
0.00
30
Figure 60
INFLUENT AND EFFLUENT ZINC CONCENTRATION
114
-------
tc
E
O
H
•<
oj
0.005
0.004
0.003
o
O
o
0.002
0.001
0.001
Effluent
Cone, pt. 5
I
10 20
WEEKS
Influent Cone. pt. 1
Average
Influent
30
Figure 61
INFLUENT AND EFFLUENT CADMIUM CONCENTRATION
115
-------
0.1-1 -
to
E
S
W
5
o
0.12
0.10 -
0.08 -
0.06 -
0.04
0.02
0.00
Influent
Cone. pi. 1
\_
Effluent
Cone. pt. 5
Average Effluent
10 20
WEEKS
30
Figure 62
INFLUENT AND EFFLUENT MOLYBDENUM CONCENTRATIONS
116
-------
4.0 -
•v
to
o
H
O
o
o
Effluent
Cone. pt.
3.0 -
2.0
0.0
Average
Influent
10
WEEKS
Figure 63
INFLUENT AND EFFLUENT ALUMINUM CONCENTRATION
T n f I 11 o n t
117
-------
Table VII
Average Trace Metal
Influent and Effluent Concentrations
Average
Average
Metal
Iron
Copper
Manganese
Chromium
Lead
Zinc
Cadmium
Molybdenum
Aluminum
Influent
Cone . mg/1
.285
.042
.067
-013
.033
.129
.0026
.005
1.124
Effluent
Cone . mg/1
.162
.081
.046
.006
.027
.130
.0021
.050
2.233
Average
% Removal
43.2
+ 92.8
31.3
53.8
18.2
+ 0.8
19.2
13.8
+ 98.7
118
-------
o Influent Cone, pt.2
+ Effluent Cone, pt.5
o
o
as
g
*H
8
Average
Influent
Average
Effluent
4567 8 9 10 11 12
MONTH
Figure 64
TOTAL COLIFORM REMOVAL HISTORY WITH ALUM
119
-------
10
o Influent Conc.pt2
Effluent Con. pt5
Average
Influent
_
-------
Influent Cone. pt. 2
Effluent Cone. pt. 5
o
o
fcl
01
p.
B
o
o
w
H
CO
-------
TABLE VIII
Alum Dose vs Percent Reduction
of Total Coliforms
% Reduction of
Total Coliforms
Date Alum Dose, mg/1 (pt. 2 - pt. 6)
4-8-71 0 80.0
7-15-71 14 99.7
7-6-71 35 100.0
8-3-71 74 97.8
4-27-71 80 97.6
9-28-71 94 98.0
5-20-71 100 98.8
5-25-71 115 98.8
6-1-71 154 99.8
4-20-71 168 98.9
6-10-71 203 99.6
Filter Flow Rates
In-depth filtration is a key element in the efficacy of
this system. This type of filtration was achieved in thjs
study with the dual-media filter. One of the primary factors
influencing the performance of an in-depth filter is the filter
flow rate. This is particularly true for a filter that must
process chemically-treated, nonsettled wastewater, such as
that produced in this investigation.
In order to compare various filter flow rates, filter
headloss curves have been plotted as a function of total solids
capture in the filter. These curves are shown in Figures 67
through 72. Each figure shows several headloss curves which were
produced at a constant filter flow rate. The five figures, 67
through 71, show headloss curves at filter flow9rates of 2.3,
3.0, 3.8, 5.0, and 5.7, all expressed as gpm/ft .
The^data are presented as headloss vs solids captured in
grams/ft rather than headloss vs time because of the great varia
tion in influent suspended solids coming onto the filter. These
solids are the primary cause of headloss development in a filter
122
-------
CO
CO
w
X
5
Median Curve
Filter Flow Rate = 2.3 gpm/ft2
J I I L
20
40
60 80 100
SOLIDS CAPTURED (grams/ft3)
Figure 67
FILTER HEAD LOSS AS A FUNCTION OF SUSPENDED SOLIDS CAPTURED
123
-------
14
12 -
C 10 -
o
-------
W
i/>
o
W
W
s
>-(
fn
14
12
10 -
4
0
Median Curve
Filter Flow Rate = 3.8 gpm/ft2
JL
_L
J_
0 20 40 60 80 100
3>
SOLIDS CAPTURED (grams/ftj)
Figure 69
FILTER HEAD LOSS AS A FUNCTION OF SUSPENDED SOLIDS CAPTURED
125
-------
Breakthrough
Median Curve
Filter Flow Rate = 5.0 gpm/ft'
J | L
20 40 60 §0 itnr
SOLIDS CAPTURED (grams/ft3)
Figure 70
FILTER HEAD LOSS AS A FUNCTION OF SUSPENDED SOLIDS CAPTURED
126
-------
Q>
0
-------
0)
•H
w
s
o
X
a.
14 -
12 -
5.0 gpm/ft2
100
SOLIDS CAPTURED (grams/ft )
Figure 72
FILTER HEAD LOSS AS A FUNCTION OF SUSPENDED SOLIDS CAPTURED AND
FLOW RATE
128
-------
at most flow rates due to their plugging effect and restric-
tion of fluid flow through the filter. Therefore, a plot of
filter headless vs solids captured can incorporate both wide
ranges in filter flow rates and large variations in filter
influent suspended solids. This plot also helps to give a
clearer picture of the comparative efficiencies of a filter
operated at a constant flow rate and receiving wide-ranging
concentrations of influent suspended solids during each of
several days of filter operation. The alum dose during these
runs was approximately 100 mg/1 with an accompanying polymer
dose of about 0.2 mg/1.
In each of Figures 67 through 71 a median curve has been
plotted to represent the typical headloss curve for that par-
ticular flow rate. Each of these median curves is reproduced
in Figure 72 to show the effect of filter flow rate on filter
headloss. As expected, the higher flow rates produced higher
headlosses than the lower flow rates. This difference in
headloss is quite significant when comparing flow rates of
3.8, 5.0, and 5.7 gpm/ft2 in this study. At flow rates rang-
ing from 2.3 to 3.8 gpm/ft2 the headloss development rate did
not vary significantly. This illustrates the effect the higher
filter flow rates have in breaking up the floe particles in
the upper, coarse layers of the dual-media filter and carrying
them further down into the smaller pore areas of the filter bed
where they cause increased filter hea,dloss because they then
block off many of the smaller pore openings. Combined with
this increased headloss at higher filter flow rates is the in-
creasing head required to produce increasing flow-through veloc-
ities in any granular filter, whether clean or clogged.
At the higher filter flow rates there will also be the
tendency for the hydraulic gradients to wash the solid particles
caught in the filter pores completely out of the filter. This
tendency must be compensated for by adding a polyelectrolyte
filter aid to the filter influent. This helps to strengthen the
chemical floe and keep it in the filter. In this research the
slightly anionic acrylamide polymer "Separan" a product of Dow
Chemical Company, has been found to be effective in the dose of
range 0.1 to 0.3 mg/1.
Figure 73 is a plot of filter headloss vs flow rate in gpm/ft2
for clear water flowing through the dual-media filter. The curve
indicates the hydraulic head that is produced at each of the
various filter flow rates, and this head is shown in Figures 67
through 72 as the point when solids capture began (filter run
was initiated).
129
-------
CO
a)
w
K
W
5
6 -
5 -
4 -
3 -
2 -
1 -
10
FILTER FLOW RATE (gpm/ft )
Figure 73
HE4DLOSS AS A FUNCTION OF FLOW RATE FOR CLEAR WATER FLOWING
THROUGH THE DUAL-MEDIA FILTER
130
-------
The dual-media filter generally produced runs of acceptable
effluent quality of 5 to 6 hours duration at a filter flow rate
of 3 gpm/ft2 and a polymer dose of about 0.2 mg/1. When the
flow rate was increased to 5 gpm/ft^ the duration of run was
reduced to about 2 to 3 hours because of rapid headless develop-
ment. All filter runs were terminated either when effluent
turbidity measurements showed that solids breakthrough was
occurring, or when the headless reached 14.5 feet, which was
the limit for the unit.
131
-------
IX. ACKNOWLEDGEMENTS
Numerous organizations and individuals made highly signifi-
cant contributions to the conduct of this investigation. Of
particular note was the input provided by the staff of the Denver
Water Department to the design, operation, and analyses of the
pilot plant system. Individuals responsible for much of this
cooperation were: J. L. Ogilvie, K. J. Miller, R. C. McWhinnie,
S. W. Work, R. L. Heaton, W. R. Van Nattan, J. C. Dice, C. G.
Farnsworth, Marsha Heinig, and John Akin.
Valuable assistance was also provided by the staff of the
Denver Metropolitan Sewage Disposal District No. 1. Bill Korbitz,
Joe Woodley, John Puntenney, William Martin and Harry Harada were
instrumental in coordinating this assistance.
Several students at the University of Colorado were actively
involved throughout the program in the sampling and analysis of
the pilot plant system. These included: Doug Merrill, Bob Fox,
Kamlesh Shah, Anthony Koltuniuk, and Ben Harding.
Helpful review and discussion of the project progress was
provided throughout the duration of the investigation by E. F.
Earth, the Project Officer for EPA.
133
-------
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139
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1
Accession Number
2
Silbjefl /-'ivld &. Croup
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organisation
Department of Civil and Environmental Engineering
University of Colorado, Boulder, Colorado
Title
EVALUATION OF TREATMENT FOR URBAN WASTEWATER REUSE
1Q Authorfs)
LT pfitprf t
Bennett ,
, K.
E.
D.
R.
16
21
Project Designation
Project No.
17080 - DOI
Note
22
Citation
Environmental Protection Agency report number,
EPA-R2-73-122, July 1973.
23
Descriptors (Starred First)
Water Reuse, Tertiary Treatment, Reclaimed Water, Coagulation,
Flocculation, Chemical Precipitation, Filtration, Biological Treatment
Nitrification, Nutrients, Phosphate
25
Identifiers (Starred First)
Denver, Colorado, Water Renovation, Nutrient Removal
27 Abstract This study was undertaken to evaluate the efficacy of combining bio-
logical nitrification with each of two modes of chemical clarification for pro-
duction of a water suitable for specific industrial reuse applications.
For this purpose, a 7200 gpd pilot plant was constructed, operated, and
analyzed. The nitrifying activated sludge system was operated to identify the
effect of variations in detention time, loading, and temperature on the per-
formance of the system. In the temperature range of 5-30 C, a maximum nitrifi-
cation rate was observed to occur at about 25 C. Variations in BOD, COD, and
ammonia loadings were investigated over a wide range, with complete nitrifica-
tion observed for loadings at or below the following levels: 0.4 #BODCV#MLSS/DAY
1.4 #COD/#MLSS/DAY; and Q»16 £NH3-N/#MLSS/DAY. The oxygen demand for ammonia
oxidation by nitrification was determined to be 4.6 #0?/NH_-N.
In the conventional clarification system, low doses of lime or alum were showt
to be effective in removing greater than 95% of the BOD, turbidity, and suspendec
solids from the nitrified secondary effluent. Efficient phosphorus removals
necessitated higher lime and alum additions. With either coagulant chemical,
practical rapid sand^filter runs of 16 hours were observed to be possible.
Similar removal results were obtained with alum in a high-rate clarification
flow system with direct dual-media filtration of alum flocculated wastewater.
rnns "f 5~6 hours cpuld he realized.
Abstractor
K. D. Linstedt
Institution
University of Colorado
WR:I02
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