ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
EPA-330/2-78-021
EVALUATION OF
OPERATING AND MAINTENANCE PROCEDURES
AT THE
BLUE PLAINS WASTEWATER TREATMENT PLANT
WASHINGTON, D.C.
DECEMBER
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Environmental Protection Agency
Office of Enforcement
EPA-330/2-78-021
EVALUATION OF
OPERATING AND MAINTENANCE PROCEDURES
AT THE
BLUE PLAINS WASTEWATER TREATMENT PLANT
Washington, D.C.
David L. Brooman
December 1978
National Enforcement Investigations Center
Denver, Colorado
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CONTENTS
I. INTRODUCTION 1
II. SUMMARY AND CONCLUSIONS 4
III. HISTORY AND CURRENT OPERATING STATUS OF THE BLUE PLAINS
PLANT 8
HISTORICAL BACKGROUND 8
CURRENT OPERATING STATUS 10
IV. EVALUATION OF TREATMENT PLANT OPERATING AND MAINTENANCE
PROCEDURES 14
LIMITATIONS OF THE MODIFIED AERATION A.S. SYSTEMS . 14
CHEMICAL ADDITION 24
SOLIDS REMOVAL AND DEWATERING 28
GENERAL PLANT MAINTENANCE 34
V. EVALUATION OF DISTRICT'S NEEDS FOR ADDITIONAL LIME
HANDLING FACILITIES 36
GRANT REQUEST 36
DESIGN STUDIES 36
NEIC EVALUATION 39
REFERENCES 41
APPENDIX
TABLES
1. Summary of Treatment Unit Design Parameters 13
2. Comparison of Treatment Unit Operating Parameters . . 16
3. East Plant Pollutant Removal Efficiencies 17
4. West Plant Pollutant Removal Efficiencies 18
5. West Plant Pollutant Removal Efficiencies
with Sludge Processing Recycle Loads 20
6. East Plant Operating Data 21
7. West Plant Operating Data 22
8. Effect of Chemical Addition on Removal Efficiency -
East Plant 25
9. Effect of Chemical Addition on Removal Efficiency -
West Plant 26
10. Wastewater Sludge Solids Handling Summary 31
FIGURES
1. District of Columbia Blue Plains Wastewater Treatment
Plant Flow Diagram 12
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I. INTRODUCTION
During the first three months of 1978, the District of Columbia's
Blue Plains Wastewater Treatment Plant effluent did not not comply
with the District's NPDES* permit limitations for BOD and TSS.** The
permit requires that the effluent concentrations for both BOD and
TSS not exceed 30 mg/1 based on a 30-day average. The permit also
limits the total loadings of both BOD and TSS which can be discharged
from the plant to 34,800 kg (77,400 lb)/day on a 30-day average. The
plant's BOD and TSS concentrations for January, February and March
1978 were 31 and 31 mg/1, 32 and 32 mg/1, and 32 and 34 mg/1, respec-
tively. In January and March, the loading limitations for BOD and
TSS were also both exceeded by about 10%.
The District notified USEPA-Region III of these permit viola-
tions each month. District personnel stated that the main cause of
these violations was that the existing sludge solids processing
equipment at the plant was inadequate to handle the solids load gen-
erated by the treatment processes. The solids inventory in the waste-
water treatment units had thus built up to the point that the plant
effluent deteriorated and permit violations had occurred. The District
stated that the permit violations would probably continue until late
summer 1978 at which time additional sludge solids processing equip-
ment was anticipated to be operational at the plant.
The District adds chemicals (ferric chloride and polymer) to the
wastewater in the plant's secondary treatment units to remove phosphor-
ous and to improve the suspended solids removal efficiency. In April
1978 the District informed Region III that the chemical addition rates
* NPDES = National Pollutant Discharge Elimination System.
** BOD = Biochemical Oxygen Demand; TSS = Total Suspended Solids.
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were being cut back in an attempt to reduce the solids inventory of
the plant. The District reasoned that, by reducing the chemical
addition rates, less chemical sludge volume would be generated, al-
beit at some reduced suspended solids capture efficiency.
'* In early 1978, the District requested additional construction
grant monies from Region III for the design and construction of lime
handling facilities to be used in conjunction with the new solids
dewatering units at the plant. The District contended that the lime
facilities were required to improve the dewatering characteristics of
the sludge and had not been included in the original design for the
new dewatering units.
In May 1978, the Director of the Enforcement Division, USEPA
Region III requested that the National Enforcement Investigations
Center (NEIC) conduct an inspection at the Blue Plains plant. The
purposes of this inspection were threefold: (a) to determine if the
District's failure to comply with its NPDES permit limitations was
due to improper maintenance and operation of the plant treatment
units, (b) to evaluate whether the District's decision to reduce chem-
ical feed rates at the plant constituted a violation of the NPDES
permit general condition that the plant be operated as efficiently as
possible at all times, and (c) to determine if the new lime handling
facilities requested by the District were required for efficient sludge
dewatering.
On July 18 to 20, NEIC engineers, accompanied by Region III person-
nel, conducted an on-site inspection at the Blue Plains plant. The in-
spection team ,met with key District operating personnel, observed the
*„
various treatment processes, and collected pertinent data on the plant
operations. This report summarizes the findings of that inspection.
It was not within the scope of this project to have NEIC develop
an independent data base by sampling and analyzing the plant wastewater
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streams. The NEIC evaluation of the plant operating practices there-
fore used the monthly operating data summaries generated by the
District, since these data were all that were available. However,
the reader should be aware that the validity of the District's data
is questionable and conclusions derived from these data may subse-
quently be biased accordingly. The Appendix summarizes analytical
problems previously identified at the District's laboratory by Region
III and District personnel. Potential sampling and flow monitoring
discrepancies, identified by NEIC engineers during their inspection
at the plant, are also discussed in the Appendix.
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II. SUMMARY AND CONCLUSIONS
Findings of the July 18 to 20, 1978 NEIC inspection of the
operating and maintenance procedures employed at the District of
Columbia's Blue Plains Wastewater Treatment Plant and the conclusions
drawn from these findings are discussed below.
1. The Blue Plains wastewater treatment systems were designed
around the modified aeration mode of the activated sludge
(A.S.) process. Inherent in this process mode are interme-
diate levels of BOD and TSS removal, ranging from 60 to
80%. Based on the plant's average BOD and TSS influent
concentrations of about 145 mg/1 and 160 mg/1, respectively,
and the above removal efficiencies, the plant effluent con-
centrations should range between 29 and 58 mg/1 BOD and 32
and 64 mg/1 TSS. At these concentrations the permit 30-day
average effluent limitations of 30 mg/1 BOD and 30 mg/1 TSS
would be exceeded.
2. The District adds ferric chloride and polymer to the acti-
vated sludge mixed liquor just ahead of the secondary set-
tling tanks to increase the activated sludge process BOD
and TSS removal efficiencies above those inherent in the
modified mode and, also for phosphorous removal. District1
data indicate that the quality of the plant effluent is
quite dependent on the constant addition of these chemicals.
During most of 1977 and early 1978 several mechanical prob-
lems were encountered with the chemical feed systems for
both ferric chloride and polymer. Several of the permit
effluent violations, or near violations, experienced at the
plant were related to the loss of chemical feed. Apparently
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these problems were related to the temporary nature of the
chemical feed equipment and should be eliminated when con-
struction of new permanent chemical facilities is completed.
3. The major operating problem at the Blue Plains plant during
1977 and 1978 has been the lack of adequate sludge solids
handling equipment. At the time of this inspection, the
sludge solids could not be removed from the wastewater treat-
ment processes as fast as these processes generated them.
The sludge solids in excess of the capacity of the removal/
dewatering equipment were recycled to the plant influent.
Consequently, this recycle load increased to the point where
the treatment processes could no longer remove the solids
efficiently enough to meet the permit limitations, and vio-
lations occurred.
The bottlenecks in the sludge handling system were the
gravity sludge thickening units and the sludge dewatering
vacuum filters, the latter units playing the major role.
Since the existing vacuum filters had insufficient dewat-
ering capacity, they could not keep pace with the solids
load being sent to the gravity thickening tanks. As a re-
sult, the thickener became overloaded and the thickener
supernatant quality deteriorated, increasing the solids
load in the recycle stream.
District personnel reported that new solids handling/
dewatering equipment, incorporating dissolved air flotation
thickening units for waste-activated sludge and twenty-four
new vacuum filters for dewatering sludge solids, was on-line
by late August 1978. This new equipment should eliminate
the solids handling problems which have plagued the plant,
resulting in a marked improvement in the plant effluent
quality.
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4. General equipment maintenance at the plant is a potential
problem which could ultimately affect performance. The
general appearance of the plant grounds and structures is
poor. NEIC engineers noted maintenance problems with the
final clarifer scum collection systems and effluent weirs.
District personnel acknowledged that the lack of full-time
maintenance personnel at the plant has caused reduced plant
performance when emergency repairs were needed during off-hours.
5. The data available to the NEIC are insufficient to substan-
tiate or refute the District's claims that it requires ex-
tensive lime handling/feed equipment to condition the sludge
solids to be dewatered at the new vacuum filter units. Par-
ameters such as solids capture by the filters and optimum
filter cake solids content do not appear to have been ade-
quately addressed. Some lime handling/feed facilities are
probably needed at the plant for those periods of time dur-
ing the year when changes in sludge characteristics dictate
lime conditioning.
6. Previous inspections of the District's laboratory facili-
ties, conducted since May 1976 by personnel from Region
Ill's Surveillance and Analysis Division, have documented
numerous problems with the physical condition of the lab-
oratory and the analytical procedures employed. Intra-
Regional memoranda and correspondence between the Region
and the District have highlighted these problems. The
problems are serious and, though the District has made some
progress toward correcting them, recent Region III inspec-
tions at this laboratory have revealed that many problems
still remain.
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The problems existing with the laboratory plus those
noted by NEIC with the sampling procedures, flow monitoring
equipment and techniques, and the methods used to calculate
the final effluent loads could affect the accuracy of the
data the District generates. However, this data base is
the only one available for the plant and was therefore used
by NEIC for evaluation of the treatment systems.
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III. HISTORY AND CURRENT OPERATING STATUS OF THE BLUE PLAINS PLANT
HISTORICAL BACKGROUND
To appreciate some of the operating problems currently encoun-
tered at the Blue Plains plant, an understanding of the historical
development of the treatment processes at the site is necessary.
This development is briefly summarized below.
1938 The original treatment facility, consisting of a pumping
station, plus process units for grit removal, grease separa-
tion, primary sedimentation and anaerobic digestion, elutria-
tion, and vacuum dewatering of sludges, was placed in opera-
tion. These units, which today are incorporated in the
West plant, were designed to treat an average flow of 5.7
m3/sec (130 mgd).
1949 Four primary sedimentation tanks and four anaerobic diges-
tion tanks were added to increase the plant capacity to 7.7
mVsec (175 mgd).
1953 to 1955 Pre- and post-chlorination were added and sludge
incineration facilities were installed. The incinerator
equipment proved unsatisfactory and was abandoned.
1959 Biological secondary treatment units were added and
the primary capacity was increased to 10.6 m3/sec (240 mgd).
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1968 Design was initiated to increase the plant capacity to
13.6 nrVsec (309 mgd) as well as to provide extensive new
treatment units for nutrient removal and tertiary filtra-
tion of the total wastewater flow (this design is further
discussed later in this section).
1971 to 1974 Six vacuum filters were added to increase the
sludge dewatering capacity of the plant.
1974 Twenty new primary sedimentation tanks and a new pump sta-
tion were added. These facilities plus the addition of
increased secondary treatment units, discussed below, con-
stitute the East plant which parallels the older West plant
operation.
1976 Two new aeration tanks and attendent settling tanks for the
East plant were added to provide a total secondary treatment
capacity for 13.6 m3/sec (309 mgd). Also, the plant began
adding ferric chloride and polymer to the wastewater to
remove phosphorous.
The District has been confronted with space problems at the Blue
Plains site. Because of this and because effluent limitations for
BOD and TSS were significantly less stringent during the 1950's and
early 1960's when the first Blue Plains activated sludge batteries
were designed and constructed, the District opted to install the mod-
ified aeration mode of activated sludge (A.S.) treatment. The modi-
fied A.S. mode employs a significantly shorter aeration period than
does the conventional A.S. mode, about 2 hours versus 4 to 8 hours,
respectively.'' The modified A.S. systems sacrifice treatment effi-
ciency due to the reduced contact period, generally achieving 60 to
80% reduction of BOD and TSS. The more conventional A.S. modes can
consistently achieve in excess of 90% reduction of these parameters.
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10
During the late 1960's, as the flow rate to the plant increased
and the hydraulic detention time in the aeration basins decreased,
the Blue Plains effluent quality deteriorated. Simultaneously, the
new pollution control awareness which developed throughout the nation
resulted in stricter effluent limitations for wastewater treatment
plants. In 1968, the District contracted with Metcalf and Eddy (M&E)
consulting engineers, to evaluate the needs of the District to meet
future effluent limitations. In their summary report1, M&E concluded
that the modified A.S. mode alone could not attain the greater than
90% BOD and TSS reductions anticipated to be required by future ef-
fluent limitations, and they recommended that the District convert to
the step aeration A.S. mode for their existing and future A.S. sys-
tems. However, in this same report, M&E implied that if certain
treatment options were adopted in the future for removal of nutrients
(for example, heavy metal addition for phosphorous removal, ammonia
stripping or biological processes for nitrogen removal), then it might
be economically practical to use the modified A.S. process for BOD
and TSS removal. With chemical addition (ferric chloride and polymer)
it had been shown in pilot plant studies that the modified A.S. system
was capable of 90% reduction of BOD and TSS.
CURRENT OPERATING STATUS
Subsequent to the 1968 M&E evaluations, several pilot plant studies
convinced the District that metal ion addition for phosphorous removal
and biological nitrification and denitrification reactors for nitrogen
removal were the most reliable and economical nutrient removal processes.
Once the District committed itself to these processes, modified A.S.
became the most practical A.S. process for the plant expansion. As a
result, the current secondary treatment portions of both the East and
West plants 'are operated in the modified mode. Ferric chloride and
polymer are added to the mixed liquor just before it enters the secon-
dary settling tanks, both for phosphorous removal and to increase the
BOD and TSS removal efficiency of the systems.
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11
At the t,» of the NEIC inspection, the Blue Plains treatment
Plant cons,sted of two parallel, Codified A.S. treatment plants with
a total average design capacity of 13.6 .Vsec (309
Th West plant, the older of the two, has an average treatment cap -
city of about 5.5 mVsec (124 mgd); the newer East p,ant has an aver-
age treatment capacity of about 8.1 mVsec (185 mgd) [Table 1]. The
treat d ffluents fr0ffl ^ ^ ^ ^ ^ ^
fected w,th chlorine and discharged at Outfal, 002 to the Potonac
Kiver estuary.
There is a considerable amount of construction underway at the
P ant S1te. The new nitrification reactors and related sedimentation
tank, are est,mated to be in operation in early ,979. The new Solids
Process,ng Bu,lding, housing dissolved air flotation units for waste-
actmted sludge thickening and twenty-four new sludge dewatering
vacuum filters, was essentially completed at the time of the NEIC
inspection. The tertiary effluent filtration units are under con-
structs but are not expected to be operating until 1980 or later
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Influent
Influent
EAST PLANT
i
GKIT
REMOVAL *V
WEST PLANT
__._ ^™
REMOVAL ' 1^
Ove
>
QJ '
i-
U.
HIGH RATE -*i
DIGESTION
Digested
Sludge
0)
~l 1SI,
[ON
IS
PRIMARY 1 1 •• •• ATRAT
f l\irinl<> '11 HLt\n 1
BASINS^r-1 BAS
ION
INS
T ^ ^
rkpnpr ^polymer
rflow ,
1 1 1 1 1 Lr l\l_M L- 1 » 1
jT'Raw" Sludqe
L
r~i r
O)
\ 4->
.«._..-. ...... Tl
Wash Water i;
1 =
1
J |J
ELUTRIATION P
J
~l
m
'a
— ^
S-
1
l_
«£ Ef fluent
' '
CLARIFIERS
i i
Combined Effluy
to Outfall 00^
S-.
QJ
. ^ Fl MAI » u
CLARIFIERS Z
C_J
{
m
-, r— 0>
0 E .*— «^_
QI r- y"'^ ^V
' i 'i -. A/An HIM I
SLUDGE I FILTER K
COND. ~*Vs/_I^ "?aw S1udoe
| Polymer
; 10 uisnosai
._ f van HIM i
UDGE VFILTER/\^
OND. ~^\»^_^'7 ^ Dioested Sludne
to Disnosal
Figure 1. District of Columbia, Blue Plains Wastewater
Treatment Plant Flow Diagram, as of July, 1978
ro
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13
Table 1
SUMMARY OF TREATMENT UNIT DESIGN PARAMETERS2l3
BLUE PLAINS WASTEWATER TREATMENT PLANT
Process and Parameter
Grit Chambers
Type
Number of Chambers
Volume in Service, m3(ft3)x!03
Primary Sedimentation Tanks (all
Number of Tanks
Diameter, m(ft)
Total Volume, m3(ft3) x 106
Total Surface Area, m2(ftz)xl03
Secondary Aeration Tanks
Number of Units
Total Volume, m3(ft3)x!06
MLSS,a mg/1
Average
Peak
MLVSS,b mg/1
Average
Peak
Maximum Return Sludge Flow,
m3/sec(mgd)
West Plant
4
2.0 (71.0)
circular)
16
32.3 (106)
0 05 (1.93)
13.1 (141.2)
2
0.044 (1.54)
1300
2000
800
1000
1.6 (36)
East Plant
12
5.9 (210.0)
20
36 5 (120)
0 09 (3 23)
21 0 (226.2)
4
0.060 (2.11)
1300
2000
800
1000
2.1 (48)
Total
Aerated
16
7.9 (281.0)
36
0.14 (5.16)
34.1 (367.4)
6
0.104 (3 6b)
3.7 (84)
Secondary Sedimentation Tanks (all rectangular)
12
24
Number of Units 12
Total Volume, m3(ft3)x!06 0.078 (2.77) 0.084 (2.98) 0.162 (5.75)
Total Surface Area, m2(ft2)x!03 22 (237) 23 (248) 45 (485)
Gravity Thickeners
Number of Units
Diameter, m(ft)
Sidewall depth, m(ft)
Anaerobic Sludge Digestion
Number of Tanks
Type
Total Volume, m3(ft3)xl06
Operating Temperature, °C (°F)
19.8 (65)
3 (10)
12
Fixed Cover, High Rate
0 05 (1 71)
35 (95)
Elutriation Tanks
Number of Units
Total Volume, m3(ft3)x!03
Vacuum Filters. Digested Sludge
Number of Units
Diameter of Units, m(ft)
Total filtration area, m2(ft2)
Vacuum Filters. "Raw" Sludge
Number of Units
Diameter of Units, m(ft)
Total Filtration Area, m2(ft2)
2.83 (100)
4.3 (14)
186 (2000)
4 9 (16)
334 (3600)
a MLSS = Mixed Liquor Suspended Solids
b MLVSS = Mixed Liquor Volatile Suspended Solids
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IV. EVALUATION OF TREATMENT PLANT OPERATING
AND MAINTENANCE PROCEDURES
The main objectives of this project involved evaluation of the
District's operating and maintenance (0 & M) procedures at the Blue
Plains plant to determine if they were the cause of the NPDES permit
violations experienced in early 1978. To accomplish these objectives,
the NEIC engineers relied heavily on discussions with District operating
personnel and review of the District's historical operating data for
the plant. As mentioned in the Introduction and discussed in detail
in the Appendix, the validity of the District's historical operating
data is questionable. NEIC engineers, however, used these data ex-
tensively in evaluating the plant operations because no other data
were available.
Three areas of operating problems at the Blue Plains plant were
identified during the NEIC evaluation: the inherent limitations of
the modified aeration A.S. system, the unreliability of the chemical
feed systems used to improve the performance of the A.S. systems, and
the limitations of the sludge processing systems. Deficiencies in
the general plant maintenance program were also detected during the
NEIC inspection. The 0 & M problems evaluated during this project
are discussed below.
LIMITATIONS OF THE MODIFIED AERATION A.S. SYSTEMS
The modified aeration A.S. mode is characterized by a relatively short
aeration period of from 1.5 to 3 hours, a high food-to-micro-organism ratio
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15
(F/M) of 1.5 to 5.0 kg(lb) BOD/kg(lb) MLVSSVday, a low biomass concen-
tration (MLSS* = 200 to 500 mg/1), a low return sludge ratio (0.05
to 0.15) and a very low sludge age of 0.2 to 0.5 days. The process
can achieve BOD removals of 60 to 80%. Some operational difficulties
have historically been experienced with the process resulting in poor
biomass characteristics and high suspended solids concentrations in
the effluent4.
The District's operating parameters for the East and West plants
at Blue Plains approximate the general guidelines for the modified
aeration systems discussed above. Table 2 summarizes the ranges for
these parameters at the two plants from June 1977 to May 1978. The
District runs slightly higher sludge ages, higher return sludge ratios,
and substantially higher MLSS concentrations than normally employed
in the modified aeration mode. The MLSS concentrations approach those
encountered in the more conventional activated sludge systems.
Tables 3 and 4 summarize the BOD and TSS removal efficiencies
for the East and West plants, respectively, from June 1977 to May
1978. These data reflect the plant's operations with chemical addi-
tion and are not indicative of true modified aeration A.S. systems.
During this period, the BOD and TSS removal efficiencies for the East
plant ranged from 78 to 86% and from 79 to 88%, respectively. Removal
efficiencies for these pollutants at the West plant ranged from 67 to
79% and from 63 to 82%, respectively. Obviously, neither plant can
consistently achieve 90% removal of these pollutants even with chemical
addition. Also, the East plant apparently is more efficient in removing
these pollutants than the West plant.
The plant removal efficiencies [Tables 3 and 4] were calculated
solely on total plant influent and effluent pollutant mass loadings,
* MLVSS = Mixed Liquor Volatile Suspended Solids; MLSS = Mixed
Liquor Suspended Solids.
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16
Table 2
COMPARISON OF TREATMENT UNIT OPERATING PARAMETERS
WITH GENERAL GUIDELINES FOR MODIFIED AERATION SYSTEMS
BLUE PLAINS WASTEWATER TREATMENT PLANT
Parameter
Aeration Period, hr
F/M Ratio3, kg(lb) BOD/kg(lb)
MLVSS/day
MLSS, mg/1
Return Sludge Ratio, QR/Q
Sludge Age, Day
Normal Design4
1.5 to 3.0
1.5 to 5.0
200 to 500
0.05 to 0.15
0.2 to 0.5
East Plant
1.3 to 1.9
0.17 to 2.10
1040 to 1940
0.13 to 0.19
0.62 to 1.38
West Plant
1.7 to 2.5
0.87 to 1.64
1400 to 3800
0.14 to 0.31
0.5 to 0.95
a F/M Ratio = Food to Microrganism Ratio
QR = Return
m3/sec(mgd)
b QD = Return Sludge Rate, m3/sec(mgd); Q = Wastewater Influent Rate,
K
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Table 3
EAST PLANT POLLUTANT REMOVAL EFFICIENCIES
BLUE PLAINS WASTEWATER TREATMENT PLANT
Month
1977
June
July
August
September
October
November
December
1978
January
February
March
April
May
Primary
Influent
kg(lb) x 103/day
TSS BOD
79 174 75 165
94 208 83 183
125 276 103 227
116 255 139 307
87 192 83 183
102 225 83 182
113 250 132 291
113 250 103 228
88 194 97 214
125 275 90 199
153 337 97 214
116 255 93 206
Secondary
Influent
kg(lb) x 103/day
TSS BOD
35
49
55
52
67
67
53
72
62
59
67
59
77
108
121
115
148
148
116
159
137
131
b!47b
b!30b
48
61
78
93
86
71
91
85
78
68
69b
64b
106
135
171
206
189
157
200
188
173
149
153b
140b
Secondary
Effluent
kg(lb) x lOVday
TSS BOD
13
16
15
20
16
18
18
24
18
17
20
21
28
36
34
44
36
40
40
52
40
37
44
46
13
14
15
20
16
18
19
22
18
18
19
21
29
31
32
44
36
40
41
48
39
40
41
46
Removal Efficiency, %
Primary Secondary Total
TSS BOD TSS BOD TSS BOD
56
48
56
55
63
48
54
36
29
52
56
49
36
26
25
33
34
27
31
18
19
25
29
32
64
67
72
62
76
73
66
67
71
72
70
65
73
77
81
79
81
75
80
74
77
73
73
67
84
83
88
83
a
a
84
79
79
87
87
82
82
83
86
86
a
a
86
79
82
80
81
78
a A portion of West plant primary effluent sent to East plant secondary influent.
b Recycle from flotation thickening included.
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Table 4
WESJ PLANT POLLUTANT REMOVAL EFFICIENCIES
BLUE PLAINS WASTEWATER TREATMENT PLANT
Month
1977
June
July
August
September
October
November
December
1978
January
February
March
April
May
Primary
Influent
kg(lb) x 103/day
' TSS BOD
48 106
48 105
48 106
40 88
94 207
80 176
60 133
91 201
79 174
71 157
64 142
56 123
48 105
49 108
42 92
46 101
83 183
68 150
67 147
84 185
83 183
68 149
50 110
51 113
Secondary
Influent
kg(lb) x 103/day
TSS BOD
78 171 86 189
63 139 88 193
114 251 80 177
67 147 62 136
100 221 96 212
118 260 92 203
161 356 133 293
186 411 139 306
117b259b 91b200b
200 440 147 324
186 409 143 316
101 223 94 208
Secondary
Effluent
kg(lb) x lOVday
TSS BOD
17
18
14
14
14
15
15
16
17
23
17
16
37
39
31
30
30
32
34
36
37
50
38
35
16 35
13 29
11 25
12 26
13 29
13 29
16 35
18 40
17 38
20 43
15 32
14 31
Removal Efficiency, %
Primary Secondary Total
TSS BOD TSS BOD TSS BOD
-61
-32
-137
-67
-45a
-66a
-168
-104
-48
-180
-188
-81
-80
-79
-92
-35
-53a
-51a
-99
-65
-9
-117
-187
-84
78
72
88
80
86
88
90
91
86
89
91
84
81
85
86
81
87
86
88
87
81
87
90
85
65
63
71
66
a
a
74
82
79
68
73
72
67
73
73
75
a
a
76
78
79
71
71
73
a A portion of West plant primary effluent sent to East plant secondary influent.
b Sludge processing recycle stream returned directly to secondary influent part of month.
00
-------
19
ignoring the effect of any process recycle streams. As will be dis-
cussed later, the West plant receives all the recycle loads from the
sludge processing and dewatering units at the facility. The pollutant
loads from these recycle streams are not reflected in the West plant
influent sample data; hence the removal efficiencies shown in Table 4
do "hot take into account these additional loads.
Table 5 shows the removal efficiencies achieved by the West plant
when the recycle loads are included in the calculations. The TSS
removal efficiency ranged from 84 to 96% from June 1977 to May 1978.
The BOD removal efficiency was consistent, ranging from 85 to 89%
during this same period.
The sludge processing recycle stream has a dramatic impact on
the operation of the West plant. This stream contributes from 1 to
5.5 times as much TSS and about the same amount of BOD to the West
plant influent as does the raw wastewater [Table 5]. It is remark-
able that the West plant operates as well as it does under these con-
ditions. Reduction of this recycle load is the key to improving the
operating performance of the Blue Plains plant.
The District personnel have made several physical changes at the
East and West secondary plants in an attempt to compensate for the
additional TSS and BOD loads contributed to the West plant by the
sludge processing recycle stream. By using various valving arrange-
ments, installing stop logs, etc. they have increased the aeration
basin contact time and decreased the secondary settling tank overflow
rates for the West plant. However, this has been accomplished at the
expense of the East plant. Tables 6 and 7 summarize the impact of
these parameters on the plants' operating performance. The West plant
consistently achieves higher percentage removal rates for both TSS
and BOD than does the East plant, often more than 10% higher.
-------
Table 5
WEST PLANT POLLUTANT REMOVAL EFFICIENCIES
WITH SLUDGE PROCESSING RECYCLE LOAD
BLUE PLAINS WASTEWATER TREATMENT PLANT
Primary
Month Influent
kg(lb) x 103/day
TSS BOD
1977
June
July
August
September
October
November
December
1978
January
February
March
April
May
48 106
48 105
48 106
40 88
94 207
80 176
60 133
91 201
79 174
71 157
64 142
56 123
48 105
49 108
42 92
46 101
83 183
68 150
67 147
84 185
83 183
68 149
50 110
51 113
Sludge Recycle
to Primary
kg(lb) x 103/day
TSS BOD
79 175 55 122
61 135 38 83
108 237 52 114
108 237 65 143
146 322 49 109
212 469 60 132
320 705 68 150
332 731 43 94
133b294b37b 82b
330 727 66 145
342 755 62 137
280 617 62 136
Secondary
Influent
kg(lb) x lOVday
TSS BOD
78 171 86 189
63 139 88 193
114 251 80 177
67 147 62 136
100 221 96 212
118 260 92 203
161 356 133 293
186 411 139 306
117b259b 91b200b
200 440 147 324
186 409 143 316
101 223 94 208
Secondary
Effluent
kg(lb) x 103/day
TSS BOD
17 37
18 39
14 31
14 30
14 30
15 32
15 34
16 36
17 37
23 50
17 38
16 35
16
13
11
12
13
13
16
18
17
20
15
14
35
29
25
26
29
29
35
40
38
43
32
31
Removal
Primary
TSS BOD
39
42
27
55
43a
55a
58
56
64b
50
54
70
17
-1
14
44
4a
20a
1
-10
39b
-10
-28
16
Efficiency, %
Secondary Total
TSS BOD TSS BOD
78
72
88
80
86
88
90
91
86
89
91
84
81
85
86
81
87
86
88
87
81
87
90
85
87
84
91
91
a
a
96
96
92
94
96
95
85
85
88
89
a
a
88
86
86
85
87
88
a A portion of West plant primary effluent sent to East plant secondary influent
b Sludge processing recycle stream returned directly to secondary influent part of month.
ro
o
-------
Table 6
EAST PLANT OPERATING DATA
BLUE PLAINS WASTEWATER TREATMENT PLANT
Aeration
Month Basin
Contact Time
hours
1977
June
July
August
September
October
November
December
1978
January
February
March
April
May
1.90
1.65
1.34
1.52
1.56
1.74
1.69
1.64
1.90
1.69
1.61
1.51
Secondary Secondary
Settling Tank Effluent
, Overflow Rate, Quality, mg/1
m3/m2(gal/ft2)/day TSS BOD
28.2 689
28.2 689
31.3 766
35.1 858
27.4 669
28.2 690
34.0 832
36.0 881
28.9 706
34.0 831
33.6 822
34.6 847
19
25
22
25
26
28
25
31a
28
23
26
26
20
21
20
25
26
28
25
29
27
25
25
26
Secondary MLSS
Removal Concentration,
Efficiency,% mg/1
TSS BOD
64
67
72
62
76
73
66
67
71
72
70
65
73
77
81
79
81
75
80
74
77
73
73
67
1040
1276
1438
1134
1357
1642
1689
1941
1618
1558
1678
1517
a Indicates effluent exceeded permit limitations.
l\5
-------
Table 7
WEST PLANT OPERATING DATA
BLUE PLAINS WASTEWATER TREATMENT PLANT
Aeration
Month " Basin
Contact Time
hours
1977
June
July
August
September
October
November
December
1978
January
February
March
April
May
2.03
1.95
2.28
2.51
2.08
1.97
1.84
1.75
1.90
1.92
2.27
2.18
Secondary Secondary
Settling Tank Effluent
, Overflow Rate, Quality, mg/1
m3/m2(gal/ft2)/day TSS BOD
22.6 553
20.5 502
18.0 441
15.7 385
21.3 521
19.5 477
20.5 502
22.6 552
23.6 576
23.4 572
15.2 371
16.6 405
37a
42a
38a
45a
33a
33a
34a
33a
40a
52a
50a
44a
36a
31a
31a
39a
32a
31a
36a
37a
40a
45a
44a
39a
Secondary
Removal
Efficiency ,%
TSS BOD
78
72
88
80
86
88
90
91
86
89
91
84
81
85
86
81
87
86
88
87
81
87
90
85
MLSS
Concentration,
mg/1
1512
2183
2839
1413
1868
2302
2536
2969
2429
2617
3775
2006
a Indicates effluent exceeded permit limitations.
ro
ISJ
-------
23
At least two factors probably account for the differences in the
BOD removal efficiencies between the two plants. First, in biological
systems, the removal rate of dissolved organics is proportional to
the organics concentration in the substrate. Since the West plant
has a higher organic loading, it logically would have a higher BOD
removal efficiency. Secondly, the West plant contact period is about
0.4 hours longer than the East plant, a difference of 25% [Tables 6
and 7]. This additional contact period allows the West biomass to
remove additional BOD.
Several factors can also affect the TSS removal efficiency of a
secondary system, such as the age of the biofloc, the mass flux load-
ing to the clarifiers, the physical constraints of the clarifiers,
and the temperature of the wastewater. However, at Blue Plains, two
items appear most critical, the chemical feed systems and the hydraulic
loading rate of the clarifiers. The chemical feed systems are discussed
below under Chemical Addition. The East plant clarifiers have overflow
rates which are about 60% higher than those of the West plant [Tables
6 and 7], a factor which affects its TSS removal efficiency.
It should not be construed from the above discussions that the
District has improperly operated the two plants by modifying the aera-
tion period and clarifier overflow rates at the East plant. On the
contrary, considering the constraints they are working under, they
appear to have optimized the plants' available treatment capability.
The East plant effluent exceeded the NPDES permit TSS concentration
limitation only one month during the evaluation period and, as will
be seen later, this resulted from a chemical feed system failure.
The West plant, however, exceeded the permit limitations for both BOD
and TSS every month. If District personnel had not effected the treat-
ment modifications discussed, the West plant effluent would have been
even worse, possibly resulting in more significant permit violations,
at an earlier date.
-------
24
CHEMICAL ADDITION
As previously mentioned, ferric chloride (FeCl3) and polymer are
added to the mixed liquor channels from the aeration basins just ahead
of the point where the mixed liquor enters the final clarifiers. No
sophisticated chemical addition systems or mixing tanks are used.
The chemicals are pumped from storage through pipes which discharge
directly to the mixed liquor channels. Mixing of the chemicals and
mixed liquor is achieved solely by the flow turbulence in the channels.
Tables 8 and 9 summarize the chemical addition data at the plant
from June 1977 to May 1978. The sensitivity of the treatment systems'
TSS removal efficiencies to the range of chemical feed rates is not
apparent from these tables. These data, however, only reflect average
monthly chemical addition rates and removal efficiencies; hence, the
daily fluctuations in effluent quality typical of chemical precipita-
tion systems are masked in this data. It is also possible that, above
certain minimum chemical feed rates, the variations in the secondary
settling tank overflow rates have a more substantial effect on the
effluent TSS concentrations than do the chemical addition rates.
Tables 8 and 9 substantiate this to some degree.
Four significant chemical system malfunctions occurred during
the evaluation period affecting the plant operations for the months
of June, July and September 1977, and January and February 1978. In
June and July 1977, a malfunction of the polymer preparation and feed
systems resulted in loss of polymer feed to both plants for about 23
days. TSS removal efficiencies dropped to 64 - 67% in the East plant,
and to 72 - 78% in the West plant. In September 1977, rupture of an
FeCl3 transfer line resulted in the loss of FeCl3 feed to both plants
for four days. Effluent TSS levels climbed to 79 mg/1 during this
outage and the monthly TSS removal efficiencies dropped to 62 and 80%
for the East and West plants, respectively. High clarifier overflow
rates for the East plant compounded the TSS removal problems. In
-------
25
Table 8
EFFECT OF CHEMICAL ADDITION ON REMOVAL EFFICIENCY-EAST PLANT
BLUE PLAINS WASTEWATER TREATMENT PLANT
Chemical
Month Addition Rate,
mg/1
Polymer FeCl3
1977
June
July
August
September
October
November
December
1978
January
February
March
April
May
0.16
0.04
0.31
0.23
0.22
0.25
0.24
0.28
0.004
0.20
0.46
0.31
28.6
27.0
27.9
26.9
34.2
31.1
30.2
24.0
27.4
28.8
23.0
17.8
Secondary Secondary
Settling Tank, Effluent
Overflow Rate, Quality, mg/1
m3/mz(gal/ft2)/day TSS BOD
28.2
28.2
31.3
35.1
27.4
28.2
34.0
36.0
28.9
34.0
33.6
34.6
689
689
766
858
669
690
832
881
706
831
822
847
19
25
22
25
26
28
25
31
28
23
26
26
20
21
20
25
26
28
25
29
27
25
25
26
Secondary
Removal
Efficiency,%
TSS BOD
64
67
72
62
76
73
66
67
71
72
70
65
73
77
81
79
81
75
80
74
77
73
73
67
-------
26
Table 9
EFFECT OF CHEMICAL ADDITION ON REMOVAL EFFICIENCY-WEST PLANT
BLUE PLAINS WASTEWATER TREATMENT PLANT
<, Chemical
Month Addition Rate,
mg/1
Polymer FeCl3
Secondary
Settling Tank,
Overflow Rate,
m3/m2(gal/ft2)/day
Secondary
Effluent
Quality, mg/1
TSS BOD
Secondary
Removal
Efficiency,%
TSS BOD
1977
June
July
August
September
October
November
December
1978
January
February
March
April
May
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
12
04
34
28
25
31
29
31
08
29
44
38
37.
35.
41.
30.
33.
33.
32.
24.
27.
29.
20.
18.
6
5
8
7
0
2
0
2
7
0
7
6
22.
20.
18.
15.
21.
19.
20.
22.
23.
23.
15.
16.
6
5
0
7
3
5
5
6
6
4
2
6
553
502
441
385
521
477
502
552
576
572
371
405
37
42
38
45
33
33
34
33
40
52
50
44
36
31
31
39
32
31
36
37
40
45
44
39
78
72
88
80
86
88
90
91
86
89
91
84
81
85
86
81
87
86
88
87
81
87
90
85
-------
27
January 1978, another rupture of the FeCl3 transfer lines resulted in
a loss of FeCl3 feed to both plants for seven days and excessive TSS
discharges. The East plant TSS removal efficiency dropped to 67%;
the West plant did not appear to be substantially affected. In
February 1978, failure of a polymer transfer pump resulted in loss of
polymer feed to both plants for essentially the whole month. TSS re-
moval efficiencies declined to 71 and 86% for the East and West plants,
respectively.
The secondary treatment systems obviously depend on the chemical
feed systems to obtain good TSS removal efficiencies. District per-
sonnel are aware that the reliability of the existing systems leaves
a lot to be desired. They feel that the addition of the new Chemical
Building at the facility (being built as part of the plant expansion)
will eliminate many of the chemical handling problems which have
plagued the interim chemical handling equipment.
In March 1978, District personnel, being faced with an ever-
increasing solids inventory in the treatment units, made the decision
to reduce the FeCl3 feed rate to both the East and West plants. It
was their opinion that, by reducing the FeCl3 feed, there would be
less chemical sludge and wastewater solids to handle, albeit forfeit-
ing some treatment efficiency. The TSS removal efficiencies for both
plants have decreased since March 1978 as expected [Tables 8 and 9].
Region Ill's question as to whether the District's reduction in chemi-
cal feed rates constitutes a violation of its NPDES permit's general
condition, which requires that the plant be operated as efficiently
as possible at all times, is difficult to answer with the available
data. Granted, the reduced chemical feed rates did apparently result
in increased effluent TSS quantities. However, it is possible that
even greater effluent deterioration would have occurred had the District
not attempted to reduce the volume of sludge produced by the treatment
systems and subsequently the sludge processing recycle loads to the
-------
28
West plant. In view of the fact that the District's operating per-
sonnel were faced with a lesser-of-two-evils choice, NEIC concurs in
their decision.
SOLIDS REMOVAL AND DEWATERING
The most persistent operational problem at Blue Plains is that
of dewatering and ultimate disposal of the solids (sludges) removed
from the wastewater stream. In simple terms, the plant is solids
bound; the solids handling equipment has insufficient capacity to
consistently dewater the amount of solids generated by the treatment
processes. As a result, the solids that cannot be dewatered are re-
cycled to the treatment process. Over a period of months, the solids
storage capacity of the treatment processes is exceeded and the excess
solids escape to the plant effluent.
The existing sludge processing systems at Blue Plains are shown
schematically in Figure 1. Primary sludges and waste-activated sludges
are pumped to six circular gravity sludge thickening tanks, the primary
and secondary sludges being combined in the pipelines ahead of the
thickener units. Polymer is added to the combined sludges where they
enter the thickeners. The thickened sludge withdrawn from the bottom
of the thickeners can be handled in two ways. A portion of the thick-
ened sludge is sent to the anaerobic digesters for biological decompo-
sition; the remainder is dewatered on rotary vacuum filters as "raw"
sludge. The digested sludge is washed free of inorganic chemicals
and fine solids in elutriation tanks and dewatered on separate vacuum
filters. The "raw" and digested sludge filter cakes are ultimately
hauled to land disposal sites. Wastewaters comprised of the sludge
thickener supernatants, vacuum filter filtrates, and digested sludge
elutriates are recycled to the influent of the West plant for treatment.
-------
29
The gravity thickening tanks are severly overloaded, being oper-
ated at several times their design loadings. In normal practice, a
gravity thickener used for combined primary and modified aeration
waste-activated sludges can be loaded at 59 to 98 kg/m2 (12 to 20
Ib/ft2)/day to effect a thickening of 3 to 4% incoming sludge to 8 to
11% underflow sludge. At Blue Plains, the gravity thickeners have
been operated at loading rates of up to 370 kg/m2 (76 Ib/ft2)/day
during the past year. As a result, the thickener solids capture effi-
ciencies have suffered, dropping into the 40 to 50% range and the
supernatant recycle loads to the West plant have increased in pollutant
strength. In April 1978, the recycle stream had TSS and BOD concentra-
tions of 6,844 mg/1 and 1,242 mg/1, respectively. The recycle load
has increased significantly from June 1977 to May 1978, to the point
where it contributes significantly more TSS loading to the West plant
than does the raw wastewater [Table 5].
A second problem with the gravity thickeners is that they are
being used to thicken combined primary and waste-activated sludges.
Gravity thickening operates best with primary sludges. Waste-activated
sludges are best dewatered using flotation thickening processes.
Gravity thickening of combined primary and waste-activated sludges
often results in decreased solids capture efficiency and heavy recycle
loads.
The most serious problem affecting the solids handling systems
appears to be the limited capacity of the sludge vacuum filtering
systems. The existing units simply do not have sufficient filtering
capacity to handle the Blue Plains solids production. Consequently,
the sludge levels in the thickening tanks build up to the point where
the supernantant quality deteriorates and recycle loads to the West
plant increase. The recycle solids are removed in the West plant and
sent back to the thickeners. The recycled solids plus the "virgin"
solids removed in the East and West plants impose a still greater
-------
30
load on the thickeners and vacuum filters resulting in increased re-
cycle loads and so on.
A summary of the solids handling data for the Blue Plains plant
is presented in Table 10. The far right column tabulates the quan-
tity of sludge solids which was consistently removed from the solids
handling systems, as measured by the amount of thickened sludge solids
sent to anaerobic digestion or directly to "raw" sludge vacuum filtra-
tion dewatering. Two separate data summaries are given for the total
sludge solids produced by the East and West plants. The first column
summarizes the actual sludge quantities reported by the District.
These data include the recycle stream to the West plant. The second
data column shows the calculated sludge solids load from both plants
if the recycle solids load was not imposed on the West plant.
Table 10 emphasizes the fact that the plant cannot remove solids
from the systems at the rate they are being generated, much less make
any headway toward reducing the TSS inventory involved in the recycle
stream. During only two months, July 1977 and-February 1978, did the
solids removal systems' production equal or exceed the solids genera-
tion systems' production. It was inevitable therefore that solids
would build up in the recycle system and deteriorate the West plant
effluent quality.
It can be deduced from the above discussions that the District
must increase the solids removal systems' capacity in order to con-
sistently meet the NPDES permit limitations. There are only a few
areas that the District can address to accomplish this: a) the filter
yield of the existing vacuum filters can be increased, b) the anaerobic
digestion capacity can be increased, and c) the number of vacuum filters
can be increased. These options are briefly discussed in the following
paragraphs.
-------
31
Table 10
WASTEWATER SLUDGE SOLIDS HANDLING SUMMARY
BLUE PLAINS WASTEWATER TREATMENT PLANT
Total Sludge Solids
Month
1977
June
July
August
September
October
November
December
1978
January
February
March
Apri 1
May
'East
Plant
112 246
97 213
146 323
132 290
117 258
114 252
124 273
107 235
89 196
144 317
158 349
134 295
Produced, kg(lb)x!03/day Total Soli
West West Plant
Plant w/o recycle3
172
154
159
163
206
280
403
346
240
350
446
364
380
340
350
360
455
617
888
763
529
771
984
803
78
65
77
52
79
77
77
72
60
90
74
63
171
143
170
114
175
170
170
158
133
198
163
139
Both Plants
w/ recycle w/o recycle
284
251
305
295
323
394
527
453
329
494
604
498
626
553
673
650
713
869
1161
998
725
1088
1333
1098
190
162
223
184
196
191
201
179
149
234
232
197
417
356
493
404
433
422
443
393
329
515
512
434
ds Removed
from both Plants
kg(lb)x!03/day
142
163
141
117
142
161
144.
143
158
165
175
178
313
360
311
259
313
356
317
315
349
364
385
392
a Computed based on East plant sludge production and ratio of waste-
water flows between East and West plants
b Data includes solids sent to anaerobic digestion plus solids de-
watered in "raw" form
-------
32
The existing vacuum filters are operating at near-design capacity.
Both the "raw" sludge and digested sludge filters are yielding nearly
15 kg/m2 (3 Ib/ft2)/hour, which is comparable to other installations
of this type. The existing filters have experienced some maintenance
problems which have reduced their on-line time. However, the main-
tenance frequency has not been excessive considering the age of the
equipment.
The anaerobic sludge digestion facilities at Blue Plains appear
to be operating at near-design capacity. Within the last few years,
the District has implemented a program to clean and renovate the diges-
ters routinely. One problem noted with the digesters is that when
FeCl3 is added to the secondary treatment systems, the percent volatile
solids in the sludge from the secondary systems decreases. As a result,
the percent volatile solids reduction and the gas production of the
digesters has decreased proportionately. In general, however, the
anaerobic digesters at the Blue Plains facility appear to be well
operated and performing at their capacity.
The last alternative, that of increasing the total number of
vacuum filters available for dewatering the wastewater solids, ap-
pears to be the most logical remedial action.
As previously mentioned, the new Solids Processing Building is
nearly completed. When this facility becomes available, the solids
thickening and sludge dewatering bottlenecks should be eliminated.
Eighteen new flotation sludge thickening tanks and 24 new rotary
vacuum filters will be included in this facility. Waste sludges from
the secondary activated sludge units and the new nitrification re-
actors will be thickened in flotation thickener units. The existing
gravity sludge thickeners will be used only to thicken the primary
sludges from the East and West plants. Having separate gravity and
-------
33
flotation thickeners should dramatically improve the sludge
thickening process and minimize solids carryover in the recycle
stream.
Present plans call for the continued use of the anaerobic diges-
ters, at least until the new sludge handling facilities are on-line
and de-bugged. A portion of the thickened primary sludge from the
gravity thickeners will be anaerobically digested, elutriated and
dewatered on the existing four digested-sludge vacuum filters. The
remainder of the thickened primary sludge will be pumped to the new
sludge handling building, blended with the thickened waste-activated
sludge, and dewatered on the twenty-four new vacuum filter units.
Piping provisions have also been made so that the elutriated digested
sludge can be pumped to the new facility, blended with the other sludges
and dewatered on the new vacuum filters. If this alternative proves
feasible, the four old digested sludge vacuum filters will be abandoned.
There should be more than adequate sludge thickening and vacuum
filtration capacity available with the addition of the new solids
handling equipment. These facilities were designed with adequate
capacity to handle not only the existing primary and secondary sludges
and the sludges from nitrification reactors, but also full denitrifica-
tion sludge loads, increased solids loads from the furture tertiary
filtration backwash streams and blowdown of solids from a potable
water treatment plant contributory to the District's sewerage system.
Since the solids handling facilities were designed, decisions have
been made to delay the Blue Plains denitrification system for several
years and to not accept the potable water plant sludges into the sew-
erage system. . Therefore, the new facilities should have reserve ca-
pacity already built in. Lastly, the six vacuum filters currently
used to dewater the "raw" sludge from the gravity thickeners can be
reconditioned and moved to the new Solids Processing Building. Space
has been allotted for them. With their addition, thirty vacuum filters
would be available for dewatering the sludges.
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34
GENERAL PLANT MAINTENANCE
It was not within the scope of this project to do an in-depth
evaluation of the maintenance program at the Blue Plains plant. To
effectively audit the manpower ledgers, spare parts inventory, lubri-
cation schedules, and other items involved with the maintenance program
for a plant this size would take an experienced team of 2 to 3 indivi-
duals a week or more. The NEIC evaluation of the plant's maintenance
program was therefore based on observations made during the plant
inspection and limited discussions with the District personnel.
It was the general opinion of the NEIC engineers that the plant
was not well maintained. The condition of the plant grounds undoubt-
edly influenced this decision. Even allowing for the disruption to
the plant site necessitated by the on-going construction, the condition
of the plant grounds must be rated less than acceptable for a municipal
wastewater treatment plant. Grass is almost non-existent, the ground
being either bare or infested with tall weeds. Guardrails, above
ground piping, exposed structural members and other readily visible
items need paint. Large open areas are used for random storage of
old mechanical parts, pipes and pipe fittings. In general, the
plant's appearance did not instill confidence in the District's main-
tenance program.
Specific maintenance deficiencies noted during this inspection
involved the condition of the scum removal systems at the West plant
secondary clarifiers and the effluent weir adjustments for these clar-
ifiers. The scum troughs on the majority of the units were observed
to be choked with scum and floating items such as plastic bottles.
The troughs require periodic operator attention to function properly.
They did not appear to have received such attention for several days
prior to the inspection. Scum build-up in a final clarifier can re-
sult in deterioration of the final effluent quality.
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The effluent weirs in several of the clan'fiers were not level
and the weir elevations varied from clarifier to clarifier. Unlevel
weirs within a given clarifier result in short circuiting of flow
patterns within the clarifier. Differences in weir elevations be-
tween various clarifiers with a common inlet feed system result in
uneven flow distribution to the clarifiers. Both conditions can
result in decreased TSS removal efficiencies.
It is probable that the effluent quality problems created by the
sludge processing recycle load overshadow those which could be attri-
buted to the scum and weir situations discussed above. However, once
the recycle load is significantly reduced, lesser problems such as
these will have to be eliminated if the plant's effluent quality is
to be maximized.
Plant operating personnel indicated to the NEIC engineers that
general maintenance at the plant has deteriorated since the mainte-
nance function was transferred from the control of the plant superin-
tendent to a separate District bureau which supplies maintenance ser-
vices for all of the District's functions. As an example of the
maintenance restrictions at the treatment plant, the operating person-
nel cited the fact that electricians and mechanics are only on-site
from 7:00 am to 3:00 pm, five days per week. If problems occur during
other hours, off-duty personnel must be called in to perform the neces-
sary repairs. On several occassions, this situation has resulted in
increased downtime of critical process equipment.
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V. EVALUATION OF DISTRICT'S NEEDS FOR ADDITIONAL
LIME HANDLING FACILITIES
GRANT REQUEST
In April 1978, the District requested that EPA Region III approve
additional construction grant funds to finance design and construction
of lime handling facilities at the new Solids Processing Building.
The District stated that the lime from these facilities was needed to
condition the sludges prior to vacuum filtration, and thus improve
their dewatering characteristics. Also, liming to elevate the final
pH of the sludge is apparently required if the sludge cake is to be
disposed of by landfilling. The District noted that the solids de-
watering equipment had originally been designed (and in fact construc-
ted) without lime facilities because original pilot studies had indi-
cated that the sludges would dewater well with only ferric chloride
and polymer addition. They stated that full-scale experience had
proven these conclusions to be inaccurate. One factor contributing
to this problem was that the addition of chemical treatment (FeCl3
plus polymer) at the secondary treatment facilities had dramatically
increased the secondary solids capture, thus increasing the secondary-
to-primary sludge ratio and making sludge dewatering more difficult.
DESIGN STUDIES
Background information regarding the design of the new solids
processing equipment (specifically the new vacuum filter units) is
sparse. NEIC requested that Region III and District personnel supply
copies of any design information regarding these units. Only two
documents were provided: a brief report authored in 1973 by Whitman,
Requart and Associates5, the consulting firm which did the majority
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of the design work on the solids handling facilities, and a July 1977
memo report by Komline-Sanderson6, the suppliers of the vacuum filtra-
tion equipment.
The Whitman, Requart and Associates report appeared to be only a
preliminary conceptual design document. It addressed such items as
the anticipated quantity of sludge solids to be handled at the new
facilities, the use of flotation units for thickening of waste-acti-
vated sludge, and the recycle of thickening waste loads. No mention
was made in this report of the specific types of sludge conditioning
chemicals to be used with the dewatering vacuum filters.
Subsequent to 1973, the District and its consulting engineers
must have made some pilot studies to determine the optimum sludge
dewatering configurations for the new Solids Processing Building.
However, no documentation of this work was provided to NEIC. Based
on the information available, the new facilities were designed and
constructed without lime addition equipment. It should be noted that
the District did have the six "raw" sludge vacuum filters in opera-
tion during this period and were gaining operating experience with
these units on various mixtures of primary and secondary sludges.
Until recently (concurrent with the advent of increased secondary
solids loads from the new East plant secondary systems) the "raw"
sludge filters were operated without lime conditioning of the sludge
solids. Only FeCl3 and polymers were employed. New lime addition
equipment has recently been installed at the existing sludge fil-
tration site and is currently used for all "raw" sludge dewatering
operations. District personnel report that at the current primary-
to-secondary sludge ratios, the mixed sludges will not dewater
effectively without lime.
In January and again in July 1977, Komline-Sanderson (K-S) con-
ducted a series of dewatering studies at the Blue Plains plant to
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"demonstrate the vacuum dewatering step on full-scale equipment"6. A
pilot plant 3x2 Flexibelt Filter was used for these studies. The
sludge tested was a mixture of 67% secondary sludge and 33% primary
sludge (note: it is unknown whether these sludges were obtained from
the East, West or both plants and whether or not they contained the
heavy solids recycle loads). The secondary and primary sludges were
blended together within 14 hours of the filtration runs to approxi-
mate actual plant conditions. Nylon fabric (K-S 519) was used as the
filtering medium. DuPont ferric chloride solution (12% solution
strength) and one of two polymers, Nalco 610 or Allied Chemicals
Percol 776 (both prepared at 0.1% solution strength) were used as
sludge conditioning chemicals. The sludge mixtures were conditioned
in a K-S Model 0 rotating conditioning tank prior to being introduced
into the vacuum filter vat. The polymer was introduced into the
sludge at the inlet to the conditioning tank; the FeCl3 was added at
the inlet to the conditioning tank's second chamber.
The test results obtained indicated that the filter could operate
at specification standards with this sludge mixture and using only
ferric chloride and the Percol 776 polymer. At FeCl3 and polymer
addition rates of 7.1 and 0.22%, respectively (weight-to-weight per-
cent based on total solids), the filter yield ranged from 10.7 to 29.7
kg/m2 (2.2 to 6.1 Ib/ft2)/hr with filter cake solids of 16.5 to 19.2%.
No problems with cake release, cloth blinding, or solids capture were
detected during these runs.
A.M. Fischer of Komline-Sanderson concludes in his letter to the
District6,
"I believe that this testing totally met the objectives of
providing a more realistic look at this vacuum dewatering
step using polymer and ferric chloride for conditioning.
We may proceed with the start up of the new Flexibelt Fil-
ters with additional confidence that lime conditioning is
not required."
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He continues however,
"Confirming our conversation, however, Komline-Sanderson
does not believe there is sufficient evidence that continued
operation can be maintained without using lime as a sludge condi-
tioning agent. Knowing the changing conditions of your biological
solids, we feel that a lime supply should be provided at the
solids handling building."
NEIC EVALUATION
The above conclusions by K-S seem to imply that the sludges can
be dewatered under some conditions without lime, even at a secondary-
to-primary sludge ratio of 2:1. The District's operating data for
the East plant (the plant without recycle loads) for the period June
1977 to May 1978 indicate that the secondary-to-primary sludge ratio
is about 1.2:1, significantly less than the 2:1 ratio tested. Since
the ratio is lower, the blended sludges should dewater easier than
those in the K-S tests of 1977, and the required frequency of lime
usage could be even less critical.
The variability of the District's sludges is an important factor
to consider. It is conceivable that the K-S tests were run under
optimum sludge conditions, atypical of the normal sludge variability
conditions experienced at the plant. It probably would be unwise to
initiate operation of the new vacuum filters without some lime feed
capacity being available.
One item not adequately covered by the K-S letter report is that
of the solids capture efficiency of the filters during the 1977 tests.
The types and amounts of chemicals used to condition the sludges will
have a significant effect on this parameter. If the capture efficiency
is not adequate, a significant solids recycle load could be applied
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to the wastewater/sludge treatment processes resulting in problems
similar to those that currently exist at the West plant.
One vaccuum filter operating parameter at Blue Plains may need
re-evaluation, that of filter cake solids content. High filter cake
solids content (in excess of 20% solids) is important if the ultimate
sludge disposal method is incineration or involves long truck haul
distances. If incineration is used, it is important to.maximize the
solids content of the cake to minimize fuel costs involved with eva-
porating the cake water. High solids content is also important if
long trucking distances are involved because it is desirable to mini-
mize the weight and volume of sludge to be hauled. Wet sludges also
result in more difficult handling and disposal problems in some land-
fill situations.
Current plans call for the District to use on-site composting
techniques for ultimate disposal of a large portion of the Blue Plains
sludge. Solids content of the filter cake may be less critical with
composting. In fact, a wetter sludge may well be benefical to the
composting process. If a wetter sludge cake can be tolerated, the
frequency of lime conditioning needs may be decreased substantially.
In anticipation of the startup of the new solids processing equip-
ment, the District has initiated purchase of equipment and construction
of a temporary lime feed system at the Solids Processing Building.
The District will purchase powdered lime which will be pneumatically
transferred from the supplier's vehicle to a jet mixer located atop
one of the four sludge blending tanks at the building. This jet mixer
will mix the l.ime with water forming a lime slurry solution. This
solution will be stored in the sludge blending tank until required
for sludge conditioning. The lime solution will be added to the sludges
ahead of the sludge storage/blending tanks. District personnel anti-
cipated that these lime facilities would be available by August 15,
1978. In subsequent telephone conversations with them, it was deter-
mined that the equipment was operational the last week of August.
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REFERENCES
1. "Development Plan for the Water Pollution Control Plant with
Implementation Program for 1969-1972," Metcalf and Eddy Engineers,
February, 1969.
2. "Wastewater Treatment Plant of the District of Columbia," Brochure
ES-6, Government of the District of Columbia, Department of Environ-
mental Services, March 1974.
3. "Report on Capacity Evaluation of the Wastewater Treatment Plant,"
Metcalf and Eddy Engineers, October 1976.
4. Wastewater Engineering, Metcalf and Eddy, Inc., McGraw-Hill, Inc.,
1972, pp. 497, 498 and 501.
5. "Engineering Design Summary for the Solids Processing Building-Unit
33." Whitman, Requardt and Associates, December 4, 1973.
6. Letter of July 18, 1977 from A.M. Fischer, Komline-Sanderson to
Alan F. Cassel, Chief, Research Division, Bureau of Wastewater
Treatment, District of Columbia, Subject: "Pilot Plant Vacuum
Dewatering Tests Run 6-17-77 thru 6-18-77 at Blue Plains."
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APPENDIX A
EVALUATION OF PLANT OPERATING DATA
As a result of the NEIC's discussions with Region III and District
personnel, and on-site observations made at the Blue Plains plant,
three areas of concern related to the accuracy of the District's plant
operating and Discharge Monitoring Report (DMR) data have been identi-
fied. These are laboratory analytical techniques, sampling procedures,
and flow monitoring; each is discussed below.
LABORATORY ANALYTICAL PROCEDURES
Correct analytical procedures are essential to the production of
reliable plant operating and DMR data. It has been known for at least
two years that the analytical procedures and practices employed by
the District's laboratory personnel were suspect and could lead to
inaccurate data generation. Several memoranda and letters in the
Region III files document the problems at the District's laboratory.
In May 1976, personnel from the Region III Surveillance and Analysis
(S&A) Division inspected the District's laboratory and noted the follow-
ing serious deficiencies:
1. Staff - Serious employee-supervisor-management difficulties
with routine employee insubordination were noted. The analytical
staff does not receive outside training. Poor laboratory
t
practices are employed by many of the analysts.
2. Facilities - The existing laboratory facilities are not
suitable, being hampered by dust, ventilation and temperature
control problems.
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3. Safety - Several safety deficiencies were noted including
inaccessible eyewash stations, improper employee use of
lab coats, safety glasses, etc.
4. Sampling - Sample identification and logging procedures
were so poor that some District personnel implied that they were
unable to relate the data results to the plant operating
conditions.
5. Quality Assurance - Only minimal quality assurance programs
are practiced; employees resist use of quality assurance
techniques.
6. Data Handling - Some analysts refuse to do final calculations,
leaving these for the supervisors to complete.
7. Chemical Laboratory Methodology - Recommended analytical
procedures are not followed, glassware is often dirty, water
seals are not maintained on BOD bottles, etc.
These deficiencies were so serious that Region Ill's Regional
Administrator, acting upon the advice of the Region's District of
Columbia Team leader, withheld the District's FY 1978 grant funding
for laboratory operations, pending marked improvement in the noted
problems. Follow-up inspections by Regional personnel at the labora-
tory in early 1978 indicated that some improvements were being made,
so grant funding was resumed. Region III personnel continue to conduct
quarterly inspections at the laboratory. In a telephone conversation
with these personnel in mid-November, NEIC engineers were informed
*_
that numerous'deficiencies still exist, and that additional curtail-
ment of grant funding is being considered.
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The District's operating personnel are aware of their labora-
tory's deficiencies and have taken some steps to offset the problems.
Where data are crucial to plant operations, redundant samples of
process streams are obtained as cross-checks on data accuracy. Split
samples are also periodically analyzed by contract laboratories to
verify the District results. It was the opinion of the plant opera-
ting personnel that the data tabulations, material balances, and other
statistics presented in the monthly summaries were reliable, particu-
larly those for 1978.
SAMPLING PROCEDURES
The District uses manual sampling procedures exclusively at the
Blue Plains plant. Grab samples are obtained hourly by the operating
personnel using dip samplers. The hourly samples are refrigerated at
the sampling site and then flow-composited daily. The District has
evaluated numerous types of continuous, automatic sampling equipment
configurations but, not being satisfied with their accuracy and relia-
bility, has resorted to manual sampling throughout the plant.
It should be noted that the District does not actually sample
the combined East and West plants' effluents discharged through
Outfall 002. District personnel reported that it is not physically
possible to obtain grab samples from this buried conduit. The data
reported on the DMR forms for the Outfall 002 effluent are calculated
values derived from East and West plant sample data and their respec-
tive flow data.
The District's use of manual grab sampling techniques and its
methods of calculating and reporting DMR data are acceptable under the
terms of the NPDES permit if all steps in the procedures are performed
accurately. However, the sampling, analyzing, and flow monitoring dupli-
cation involved in the District's procedures does significantly increase
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the chance for error in the reported DMR data. It is the NEIC
opinion that accurate and reliable continuous sampling equipment is
available which could be installed at the Outfall 002 conduit. This
equipment, if actuated by properly installed and maintained flow
metering devices, would provide realistic composite samples of the
true total plant effluent and minimize the chances for human error.
FLOW MONITORING
The accuracy of the flow monitoring equipment at a wastewater
treatment plant has a significant effect on the reliability of the
operating and DMR data generated by the facility. As previously
noted, all of the composite samples at the Blue Plains plant are
manually flow-composited. The accuracy of calculations based on
these samples obviously depends, in part, on the accuracy of the flow
monitoring equipment. The monthly plant operating summaries incor-
porate extensive mass balance computations and, hence, also depend on
the accuracy of numerous in-plant flow monitoring systems.
It was not within the scope of this project for the NEIC engi-
neers to evaluate the accuracy of the flow monitoring systems at the
Blue Plains plant. However, in discussions with District personnel,
one item of concern regarding these systems was noted. Plant opera-
ting personnel remarked that the influent flow meters for the East
plant were not consistently reliable. The meters operate on a sonic,
Doppler-effect principle and have been adversely affected by the flow
patterns through them and downstream flow restrictions. Since these
flow meters are the only devices available for determining the waste-
water flow rate through the East plant, the accuracy of the DMR flow
and pollutant mass data is suspect. Also, since the data from these
meters are used to calculate the Outfall 002 effluent parameter con-
centrations, these values are also suspect.
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