PICK CONGRESS HOTEL
CHICAGO, ILLINOIS
FEBRUARY 23-24, 1971
-------
ADVANCED WASTE TREATMENT AND
WATER .REUSE SYMPOSIUM
PICK-CONGRESS HOTEL
Florentine Room
Chicago, Illinois
February 23-24, 1971
Sponsored By-
Environmental Protection Agency
and
Co-Sponsored By
State Water Pollution Control Agencies of:
Illinois
Indiana
Michigan
Minnesota
Ohio
Wisconsin
-------
ADVANCED WASTE TREATMENT AND
WATER REUSE SYMPOSIUM
Session #3, Wednesday, February 24
Moderators: Indiana and Ohio Water Pollution
Control Agency Representatives
8:45 A.M. Ammonia Removal: Specific Ion Exchange
and Air Stripping
Dr. Joseph B, Farrell, Chemical Engineer
Ultimate Disposal Research
Advanced Waste Treatment
Research Laboratory, EPA, Cincinnati
9:30 A.M. Modification of a Trickling Filter
Plant to Allow Chemical Precipitation
Richard C. Brenner
EPA, Cincinnati
10:00 A.M. Chemical Precipitation of Phosphorous
Dr. S. A. Hannah, Chemist
Physical-Chemical Research
Advanced Waste Treatment Research
Laboratory, EPA, Cincinnati
10:30 A.M. Coffee Break
to
10:45 A.M.
10:45 A.M. Utilization of Sludge as a Resource for
Agricultural Purposes
Dr. William J. Bauer
Bauer Engineering, Inc., Chicago
11:30 A.M. Lunch
to
1:00 P.M.
-------
CONTENT
"Modification of a Trickling Filter Plant to Allow
Chemical Precipitation"
James E. Laughlin, P.E.
"Chemical Precipitation"
Sidney A. Hannah
-------
MODIFICATION OF A TRICKLING FILTER PLANT
TO ALLOW CHEMICAL PRECIPITATION
*James E. Laughlin, P. E.
This paper is intended to give the reader information on how a trickling
filter waste treatment plant was modified to permit chemical precipitation of
phosphorous and other substances. Also, some very preliminary performance
data are included from the operational phase of this Advanced Waste Treatment
Project.
One performance objective in this project is reduction of phosphorous
(as P) to a level of one mg/1 or less. Reduction of BOD and suspended solids
to 10 or 15 mg/1 are further goals of the project. If this plant can perform
that well, consistently and economically, a contribution may be made toward
enhancing performance of thousands of other trickling filter plants in use
today.
Both the modifications described and subsequent performance studies are
part of a 28-month Advanced Waste Treatment Project. Physical modifications
are complete. Operational investigations are underway and will continue
through 1971. By early 1972 it should be possible to assess whether the
modifications were well conceived, and whether the process can be optimized
and made part of the plant operating procedure. The appendices to this paper
*Partner, Shimek-Roming-Jacobs & Finklea, Consulting Engineers, Dallas, Texas
This paper describes part of an Advanced Waste Treatment Project now underway
at the City of Richardson, Texas. Mr. Robert E. Derrington, Water Superin-
tendent, is Project Director. Mr. Laughlin is Associate Director. The project
is 757» funded by the Environmental Protection Agency.
1
-------
include the project schedule, and background on generation and processing
of data.
EXISTING TREATMENT FACILITIES
In this project, chemical treatment is intended as an adjunct to the
typical physical and biological treatment already provided. Furthermore,
it vas intended that required modifications be as simple as possible and that
existing facilities be fully utilized. The plant's existing facilities can
be shown in a schematic sketch. Design capacity is 1.6 MGD.
CITY OF RICHARDSON, TEXAS
WASTEWATER TREATMENT PLANT
1969
4- FINAL SLUDGE a RECIRCULATION
INFLOW \\sjs
SCREI
TRICKLING
FILTERS
2
-------
A mechanical bar screen precedes a wet well serving four raw sewage
pumps which lift the water into a flow splitter box. Proportional weirs
there divide flow between three clarifier-digesters. Primary effluent is
combined in a splitter box, then divided and sent to two standard rate rock
filters. Filter effluent is combined and carried to the final clarifier.
Chlorination and settling are simultaneous in that clarifier. A mixture of
final sludge and recirculation are returned to the head of the plant; the
amount of recirculation is regulated by a level control system in the raw
sewage wet well.
Sludge is digested in the lower compartment of each primary clarifier-
digester. No heat is provided (gas is wasted through a burner) and mixing
consists of gentle stirring by a 3 rph mechanism revolving on the same shaft
as the clarifier rakes above.
Sludge is dried on sand beds. Filtrate collected in the underdrains
goes back to the head of the plant. Digester supernatant is drawn and
batch treated before return to the head of the plant. Three 500 gallon
fill-and-draw tanks receive raw supernatant; alum is added, 250 mg/1, then
20 minutes of air agitation yield a finished liquor which separates into
sludge (which goes onto drying beds) and treated supernatant with strength
comparable to raw sewage.
Detailed plant data can be condensed into the table which follows.
3
-------
DATA ON TREATMENT UNITS
Diam Depth Circum Area Volume
(Ft)
(Ft) (Ft)
(Sq Ft )
(Cu Ft)
(Gal)
Primary Clarifier No. 1
2
3
Primary Clarifiers Combined
40
40
40
8 126
10 126
10 126
378
1257
1257
1257
3771
10,054
12,570
12,570
35,194
75,200
94,000
94,000
263,200
Final Clarifier
70
6 220
3848
23,088
173,000
Filter No. 1
2
Filters Combined
84
120
6.5
6.5
55U2^\
11310(J->
16852^'
36,000
73,500
109,500
—
Digester No. 1
2
3
Digesters Combined
40
40
40
14 3(2) --
uV2> -
& -
1257
1257
1257
13,000
13,000
13,000
39,000
135,000
135,000
135,000
404,000
Sludge Drying Beds 12,000
(1) Area in acres: 0.127,
(2) 14.3 Effective, 18.0 Si
Square Feet
0.260 and 0.387, respectively
fD, 15.8 Clear @Center
4
-------
These physical dimensions allow estimation of clarifier detention
times at different flows, an important factor in predicting lag time through
the plant. Hyperbolic equations describing assumed plug flow are plotted on
the following graph.
DETENTION (HOURS)
Although the plot is only an approximation of actual conditions (and
this is further compounded when assuming plant detention time equals elf
detention time), it has proven most helpful in predicting passage of o
conditions through the system.
5
-------
The following table summarizes data on the load received at the existing
plant, and on the performance of the system.
CHARACTERISTICS OF WASTEWATER
(mg/1 unless noted)
Typical Influent Conventional Effluent
(Apr-Nov 1970) (Apr-Aug 1970)
Flow
Suspended Solids
BOD
Phosphorous (p)
Phosphorous (P)
Total Kjeldahl Nitrogen (N)
Iron (Fe)
Aluminum (Al)
Alkalinity (Ca C0.j)
Ratio BOD/COD
*1.6 MGD
145 *15
140 *20
8.8 8
122 lb/day
21 10
0.84
*0.23
175
0.45
*Geometric means, all other values are arithmetic means.
Richardson's treatment plant has been attended full time for some years.
Approximately 320 manhours per week are required to operate and maintain the
facility. In addition, an analyst devotes 40 man hours per week in the control
laboratory.
6
-------
MODIFICATION FOR CHEMICAL ADDITION
Early in the project two coagulants were selected for operational trials:
aluminum in the form of liquid alum, and iron in the form of liquid ferric
chloride. Both are available in bulk, from commercial firms, at haul distances
of about 250 miles. Both are similar enough in character to permit use of
common storage and feeding hardware. Use of polymers was also predicated at
this point, assuming they would be worthwhile in improving settling character-
istics of solids involved.
The flow diagram of the plant could now be modified to permit addition of
these chemicals at the head end and just ahead of the final clarifier.
CITY OF RICMAROSON, TEXAS
WASTEWATER TREATMENT PLANT
1970
4- FINAL SLUO0E A RECIRCULATION
| coagulant]
SCREEN
TRICKLING
FILTERS
7
-------
One 6000 gallon fiberglass stores liquid coagulant In a central location.
Two chemical feed pumps are Installed beside the tank, and piped to deliver
to either the head or effluent ends of the plant, or both ends simultaneously.
Both pumps have variable feed controls covering their 0-110 gph discharge range.
Pump controls have automatic-manual capability. Wetted parts are of materials
resistent to alum and ferric chloride.
Two 1200 gallon fiberglass polymer storage tanks are provided: one near
the plant influent sewer and the othei? near the final clarifier, Both have
feed pumps similar to the pair at the coagulant tank. In addition, polymer
tanks have eductor assemblies for dispersing polymer, and 3 hp mixers for
blending fresh batches of polyelectrolytes.
The junction box preceding the final clarifier was modified to provide
flash mixing of coagulant. The change involved baffling off a section and
installing a mixer there to promote rapid dispersal of the metal salts
injected. The arrangement is shown in the following isometric view.
8
-------
FLASH MIX MODIFICATION
FINAL CLARIFIER JUNCTION BOX
The mixer delivers 2.2 water hp. The approximate velocity gradient
for this system is 6 equals 650/sec. At the average flow of 1.6 mgd, detention
is some 50 sec, so Gt equals 32,000.
Further analysis of this dispersion-flocculation system gives information
on the reaction times available for flash mixing, intense flocculation, and
gentle flocculation. These detention periods are based on simple displacement
through: mixing chamber, pipeline, and that part of the centerwell area in the
clarifier where active flocculation is observed.
9
-------
Volumes involved, in-gallons:
Flash Mix 1,000
High Energy Flocculation 4,000
Low Energy Flocculation 20,000
TOTAL VOLUME 25,000 Gal
Flow Rates Coagulation Flocculation Time (Minutes)
MGD
GPM
(Minutes)
High Energy
Low Energy
Total
1
700
1.42
5.71
28.6
34.3
1.5
1,050
0.95
3.81
19.1
22.8
2
1,400
0.71
2.86
14.3
17.1
2.5
1,750
0.57
2.28
11.4
13.7
3
2,100
0.48
1.91
9.5
11.4
Flash mixing of coagulants added to raw sewage uses kinetic energy of
the turbulant flow entering the wet well. Chemicals are injected at a
manhole; mixing begins in a ten feet section of steeply descending sewer
which carries plant inflow to the wet well, and dispersal is completed in a
confined receiving zone in the wet well.
After a brief (and indeterminant) stay in the wet well, flow is picked
up by pumps and passes into the splitter box. Detention time is short and
energy levels are fairly high from pumps to clarifiers. All this is followed
by flocculation in the centerwell area of the clarifiers, but an estimate of
the size of the flocculation zones there has not been possible.
Summarizing, coagulant dispersal and flocculation in raw sewage takes
place at ill-defined energy levels and reaction periods. The arrangement
10
-------
is probably not as effective as that in the final effluent, but there has been
an attempt to make the best of the existing situation.
At both ends of the plant, polymer injection facilities deliver into the
high energy rlocculation zones. Polymers are mixed with 20 gpm carriage water
and jetted into a hydraulic regime where there is sufficient turbulence to
promote dispersal. A two minute lag time is intended between injection of
coagulant and addition of polymers.
IMPROVEMENTS IN FLOW CONTROL AND SAMPLING
One primary clarifier was found to suffer poor inlet hydraulics due to
its piping arrangement into the centerwell skirt. A combination splitter-
deflector was fabricated and installed to redirect inflow; a good approximation
of a velocity dissipating centerwell was obtained.
There were some inaccuracies in the control of flow division in the
splitter box preceding the trickling filters. This had been regulated by
manual adjustment of gate valves. Proportional weirs were fabricated and
installed in the box, insuring an accurate division at all rates of flow.
Recirculation (which includes final sludge) had not been sampled and
tested previously. It flows from the bottom of the clarifier, through a
gravity line, to the raw sewage wet well. There is a vault housing a flow
meter and an air-operated throttling valve at the midpoint of the line.
Facilities for automatic sampling were Installed In the vault, and function
per the following sketch.
11
-------
CONTINOUS
FLOW AT
CONSTANT
HEAD
K
SOLENOID
drain\ | | Sample
aAa/9
TIME-PULSE SIGNAL TO RECORDER
RECIRCULATION SAMPLER
12
-------
A continuous sample flow is withdrawn and split between a constant head
shunt and a sample shunt which normally is directed to drain. When the flow
meter generates a signal indicating flow in the recirculation line, that
signal energizes a solenoid which diverts sample flow to a receiving can.
The amount- of sample caught is proportional to the amount of recirculation flow.
Two magnetic flow meters were added to the supernatant treatment system:
one measures raw flow coming in, and the other measures treated supernatant
going to the head of the plant. The difference between their cumulative
readings gives the volume of precipitated sludge diverted to drying beds.
The throttling valve on the plant recirculation line had, for years,
been controlled by water level in the wet well. Recirculation occurred on
a demand basis. For reasons discussed later it became necessary to sharply
reduce this flow. An electric timer was wired into the control circuit in a
manner which allowed it to override other signals. This timer was eventually
set to trigger a 25 second flushing flow every 20 minutes; this pattern
established a 70,000 gpd recirculation rate.
Underdrain facilities at the sludge drying beds collect fiiltrate from
wet sludge. Underflow from seven beds comes to either of two filtrate
manholes. The manholes were partially dammed and a sump pump was placed in
each. A standard water meter was put into the discharge line of each pump,
and this permits a record of bed drainage.
A static head of nearly 15 feet of water is available to push digested
sludge from digesters to drying beds. This gravity arrangement appears
entirely suitable from an operational standpoint. For this project, however,
an accurate measure of sludge flow is needed. A piston type sludge pump, with
13
GPO 821-371-1
-------
attached stroke counter, was installed for that reason.
MISCELLANEOUS IMPROVEMENTS
A small manually adjusted chlorlnator had served the plant adequately
for some years. It was replaced by an automatic 2000 ppd unit with compound-
loop automatic controls. This changeout was made more to support the demonstra-
tion project than it was to'modify the plant for chemical addition. Also, after
trial operations the waste flow sensing leg was disconnected in the compound-
loop control; chlorine flow can be closely controlled by the automatic residual
analyzer.
A recording pH meter was installed to monitor plant influent, and a record-
ing dissolved oxygen meter was set up on the effluent. Both of these supply
information valuable to the demonstration project, but neither would be really
necessary in a normal plant modification.
Ten small pipelines, mostly PVC, were installed at various locations
around the plant. These deliver coagulant, polymer dilution water, diluted
polymer, rinse water, and sample flows.
Prior to the project, all three digesters were drained and cleaned. Steel
stirring mechanisms were strengthened or rebuilt as necessary. This Insured
that the digestion system was free of grit and was mechanically functional for
the study.
LABORATORY FACILITIES AND PERSONNEL
The existing plant had its control laboratory located in the main building.
The arrangement was somewhat cramped, so a separate lab building was built just
14
-------
prior to beginning the project. Additional space and personnel were added to
support the study.
There are thirteen sampling points in the treatment plant, and up to
twenty-three analyses may be run on the composite samples taken. Appendix B
shows the stations and analyses involved. Approximately 140 items of data
are reported on each sample day.
A staff of three analysts works five days per week, usually Monday through
Friday. The samples they run are those collected Sunday through Thursday.
Occasionally they work on weekends to gain data on samples collected Friday
and Saturday. A fourth analyst, who works about 30 hours a week, helps
handle the heavy lab load involved in the project.
Lab effort related solely to the project includes a statistical quality
control program to verify data, zeta and jar test studies on coagulants and
polymers, total and fecal coliform tests, turbidity, COD, and a broad range
of analyses to trace buildup or removal of particular substances.
From a strict standpoint of normal operational control of chemical
precipitation, the typical tests for a conventional plant (BOD, solids,
pH, temperature, dissolved oxygen) should be supplemented by phosphorous,
alkalinity, and perhaps element s involved in the coagulant (iron or aluminum,
and sulfate or chloride). Some phosphorous tests should be made on hourly
grab samples, as discussed later. The other tests would be run on dally
composites. Also, jar tests would be needed to guide determination of proper
chemical feed; these would be similar to those required in a water treatment
plant.
15
-------
A final category of tests has been run routinely for some time: various
nitrogen forms and sulfides. Whether these are required for operational
control at other plants would be a matter of individual judgement.
PRELIMINARY OPERATIONAL RESULTS
Liquid alum was added during waste treatment in the fall of 1970.
Considerable data were taken and are .still being analyzed. This information
has scant value until the study is finished and put into perspective. It
seemed proper to share some of the data, with the understanding that THESE
ARE PRELIMINARY OBSERVATIONS—NOT DEFINITIVE CONCLUSIONS. Readers should
appreciate this point and temper their views accordingly.
To begin, two illustrations show typical values of phosphorous coming
into the plant. The first plots phosphorous concentration based on hourly
samples.
16
-------
IOA NOON
MID-
NIGHT
17
-------
Composite phosphorous income (as F) was 8.1 mg/1, slightly less than
the statistical mean. The next plot shows typical phosphorous load (lb/day)
and shows the soluble fraction.
NIGHT
Total phosphorous in the composite was 113 lb/day. The soluble fraction
was 70%, a ratio which is believed consistent.
During September liquid alum was added to flow entering the final clarifier.
After a period of fixing leaks in chemical delivery pipes, recalibrating chemical
18
-------
pumps, and other startup activities, some proper results developed. Two key
Items were learned: hourly effluent grab samples are vital to regulation of
feed rates, and low recirculation rates (70,000 gpd) are necessary to preserve
the floe blanket which develops around the centerwell. When the blanket is
present, effluent is clear and low in phosphorous, BOD, and suspended solids.
When the blanket is absent, results suffer. The next plot shows performance
during a day when two chemical pump settings were used.
NIGHT
19
-------
Notice the mole ratio of aluminum to total phosphorous was 1.9 to 1.0.
Phosphorous levels in plant inflow were normal. Effluent phosphorous got out
of control near midnight, and the mean effluent concentration that day was
0.8 mg/1. This performance led to changing chemical feed rate five times
per day, and resulting improvements are shown in the next graph.
NIGHT
In this case the mole ratio*was 2.1 to 1.0. There were no sharp peaks in
effluent phosphorous levels, and the composite sample showed 0.5 mg/1 escaped.
20
-------
At this time it is felt that multiple settings of chemical pumps are vital to
good performance with minimum alum consumption.
In October alum was added to raw sewage. Performance seemed not as good
as before, arid signs of digester overloading led to termination after nine
days of trial. No data or further comments can be offered at this point.
In November split feeding (to raw and final) was tried. The following
figure shows results of one of the better days.
4.0
v
at
£
3.0
PLANT INFLUENT
9.2 COMPOSITE
EFFLUENT PHOSPHOROUS
SPLIT FEED Al/P - 2/1
WEDNESDAY, NOV 4, 1970
to
o
v>
§2.0
o
x
G.
V)
O
X
a.
< 1.0
o
4.1
16.4
{
20% OF ALUM TO RAW
3.9 6 PH
4.7 GPH
4.1
18.8 GPH
80% OF ALUM TO FINAL
(6.4
2.7 GPH
10.8 GPH
4.11
16.4
(OA NOON
MID-
NIGHT
21
-------
Feed was 20% to raw and 80% to final. The mole ratio was 2 to 1.
Composite samples showed phosphorous was 9.2 mg/1 in plant influent and 0.3
mg/1 in the effluent.
The preceding plots illustrate performance on some of the better days to
date; there are indications that good results can be gotten day after day,
but this point lacks proof. Further, it has not been proven that digesters
can accept increased loads (from any of the feed regimes) on a long term basis.
The changes in character of digested sludge have not been properly studied.
Much data already collected is not discussed here. More data is needed. The
only point made in this section is that the precipitation facilities which
have been used so far appear to perform mechanically, and the overall approach
holds some degree of hope for reliable performance.
COSTS OF FACILITIES AND OPERATIONS
Part of the Richardson treatment plant was built in 1953 at a total
cost of $75,000, exclusive of land. In 1961, treatment facilities were
enlarged to the present arrangement; the total cost of those improvements
was $0.25 million, excepting land.
A new laboratory building was added in 1969. This facility is considered
an integral part of the treatment system, but perhaps one-third of its cost
went to extra space for the demonstration project. The building was built
at a total cost of $33,000.
The laboratory was outfitted at a cost of $11,000. Furniture accounted
for $2,000 of the total, and the $9,000 balance went for equipment and supplies.
22
-------
Some of the equipment might not be required except far the demonstration
projects a $3,000 zeta meter, a S60G recording pH neter ta monitor plant
inflow, a $700 recording dissolved oxygen meter to monitor effluent, and
some $700 worth of special glassware and chemicals. The remaining $4,000 would
have been spent for laboratory facilities to support chemical coagulation
in the treatoent plant; major items include $800 for an advanced type of
jar test apparatus, an $600 analytical balance, and a $500 spectrophotometer,
IE the laboratory had been built solely to support chemical coagulation
in the treatment plant, it would have cost about $21,000 for the building
and $6,000 for furniture, equipment, and apparatus.
Modifications to the treatment plant came to a total cost of $53,000
distributed as follows:
Materials $35,QQQ
Labor 7,000
Supervision. 3,500
Design and Kiac, 7,500
TOTAL $53,000
Construction labor and supervision were by city personnel, and figures
cited include a factor for overhead. The high ratio of materials to labor
relates to such expensive equipment as a $6,800 automatic chlorinator, two
magnetic flow meters at a $4,200 cos-t, three fiberglass chemical tanks at
$5,000 total, tvo poJLyaer mlxere a* $2,200 trtfiJ, and four c^eaical feed pvacps
at $6,800 total, A31 these. icons total 325,000 vaich ±3 ;Er-s.idaratl» mots
than, it cost to install them.
23
-------
Combining all facility costs related to providing chemical coagulation,
a total outlay of $80,000 was required. This converts to $50,000 per MGD of
plant capacity, but that unit cost figure could not be extended to estimate
costs at other plants. For example, perhaps $60,000 would be required to
outfit a 0.5 MGD plant, and $100,000 might outfit a 5 MGD plant. In other
words, the basic equipment would cost about the same no matter what size
plant is involved.
Operating costs for chemical coagulation consist almost entirely of
chemical costs alone. Additional power might cost $200 or $300 per year.
The existing operating staff can run the equipment. Control testing might
require an additional analyst in the laboratory, but insufficient experience
is available to verify this. Liquid alum costs 33c per pound i r. luminum,
delivered in Richardson. Making some broad assumptions regarding demand,
alum costs might run 4c to 5c per 1000 gallons of water. This would total
some $25,000 per year at this plant. No information is available now regard-'
ing efficiency or cost of ferric iron as a coagulant, nor has the role of
polymers been studied.
In summary, construction costs for chemical coagulation are well defined
for the Richardson facilities, but they might be quite different at another
plant. It appears most of the operating costs would go to purchase coagulant,
and some highly generalized figures have been offered to give some sort of
perspective.
24
-------
1969
PHASE
I l
2
3 a
b
c
4
M I
t f
CITY OF RICHARDSON, TEXAS ADVANCED WASTE TREATMENT PROJECT
PROJECT SCHEDULE
1970 (871
MONTH
13.1
z
3
4
-J
10
II
12
qYABP ^
Q ^ E^PQ
O
o
o
13
14
U
15
16
+¦ Clo
o—b
qJAH TEST METALS^
+ CU+ SUPERNATANT TRT
O
CHEMICAL FEED EQUIP
A( (FINAL)
O AI(fWW|
O ^jlSPLIT}
O
17
16
M
20
M
21
BASE
O
O
Fe(FINAL)
Fa(RAW)
Fa(SPLIT)
o
JAR TEST 1 METAL S POLYt
o
-o
-o
BASE
o
22
23
24
25
26
27
28
o
M +¦ POLY
° 6C'2
Q_t- StJPERNAT. __q
Q W + POLY [ SPLIT FEED)
0—CK^u
o
Q—Q
ORIO: OCT 1969
REV: JULY 1970
V
O H
M D*
1 fl>
I'
: 13
3 O
t» I-*
It)
t) n
(D r>
09 A
a,
00 p>
H- O
h.
a <
H-
0 «¦
O K.
rj (B
ft a
a en
(1) n
rr (B
M* CO
i— cr
CO Q
o 3
0
o
to 3
cr
Or* rr
^ 3"
n i*
< CD
H-
lb n
rt sr
R» ft
£L ft
rt
ft -
9
rr
~t >
ft £
CD H
K
ft
v
-------
City of Richardson, Texas Advanced Waste Treatment Project
SUMMARY OF PROJECT SCHEDULE
Phase Task Month Activity
Yard Equipment (Meters, Manholes, Samplers, &2 Equip),
Provide & Install
Lab Equip, Provide & Install
Plant Baseline Operation
Plant Baseline Operation plus Chlorlnatlon of Effluent
Plant Baseline Operation plus Chlorlnatlon and Supernatant
Treatment
Jar Test Metal Salts on Raw
II 1 1-12 Chemical Feed Equip, Provide & Install
Baseline Operation plus Alum Salt In Final
Baseline Operation plus Alum Salt In Raw
Baseline Operation plus Alum Salt Split Feed
Baseline Operation (Purge & Check)
Baseline Operation plus Iron Salt In Final
Baseline Operation plus Iron Salt In Raw
Baseline Operation plus Iron Salt Split Feed
Jar Test (Metal Salt + Polymer) on Raw and Filter
Effluent
III la 20 Baseline Operation (Purge & Check)
Baseline Operation plus Salt-Poly Fed at Best Points
Baseline-Operation plus Salt-Poly plus Chlorlnatlon
of Effluent
Baseline Operation plus Salt-Poly plus Chlorlnatlon
plus Supernatant Treatment
Optimize for best performance and economy
IV 1 1-12 Monthly Letter-Reports
Preparation & Submission of Expense Statements
Progress Reports (Phase I and II)
Final Report
1
1-5
2
1-5
3a
6-9
b
10-11
c
12
4
6-11
1
1-12
2a
13
b
14
c
15
3a
16
b
17
c
18
d
19
4
12-20
la
20
b
21
c
22
d
23-26
2a
23-26
1
1-12
2
1-24
3
13&20
4
27-28
Orig: t Oct 1969
Rev: Jul 1970
26
-------
APPENDIX B DATA MATRIX
This sheet shows major items reported daily. All are calculated and recorded
directly on Lab Bench Sheets, then transferred directly onto computer cards.
A typical Bench Sheet (for ammonia nitrogen) is shown on the following page.
R
A
W
P
R
1
M
E
F
F
F
1
L
T
E
F
F
F
1
N
A
L
E
F
F
R
E
C
1
R
C
S
L
U
D
G
E
1
S
L
U
D
G
E
2
S
L
U
D
G
E
3
R
A
W
S
u
p
1
R
A
W
S
U
P
2
R
A
W
S
u
p
3
T
R
E
A
T
P
B
E
D
D
R
A
1
N
FLOW
•
•
•
•
•
•
•
•
•
•
SUS SOL
SUS VOL SOL
SET SOL
•
•
•
•
BOD
•
•
•
•
•
•
•
DO
•
•
COD
PHOS
TKN
NH 3
•
•
•
•
•
•
•
•
•
•
•
N02
•
NO 3
•
•
ALK
•
•
•
•
•
•
•
•
•
•
•
FE
AL
S
•
S04
CL
•
•
•
PH
TEMP
TURB
•
•
•
COLI
•
•
FECAL
•
•
27
-------
0AT£r
/
4
, /
/_
A/US
S7AT/OA/
ABSOX£AMC£
FACTO/?
M6/SAA/fL£
O/L L/T/OA/
ttSULTS
£OMPtfT£R
•
FPimrarrj
P#iMA*Y£&£
•
J
Z9 ao 3/
ail
/% 7W cm.
1 1
wriw-'ir-rim
/?/M4t
. I- 1
rrar-arrar^j
/?£
7S
aeo £}/%A/M
«
.irjf.jp/ii
5rAA/DA/?D
• III
42£" m jul
-------
APPENDIX C
DATA PROCESSING
Electronic data processing Is used to handle the 140 Items of data generated
each day. There are two major programs: a dally report, and a statistical
report. In the daily report the following Items are printed out on one page:
1. Up to 23 parameters at each of 13 sampling stations
2. Five computed loadings at up to 12 stations, expressed in lb/day
3. Two ratios at 10 stations: BOD/COD, and SVS/Susp Solids
4. Six clarifier loadings: hydraulic, and" solids
5. Four filter loadings: hydraulic, and organic
6. Two digester loadings: hydraulic, and volatile solids
7. Twelve percentages of removal: primary units, and overall
The statistical report comes from processing selected groups of daily reports,
and each onerpage printout considers one parameter (e.g. BOD) at all of the
sampling stations. Printouts include:
1. Tally of number of occurrences
2. Hax-Mln values
3. Arithmetic mean, and standard deviation
4. SD/Mean
5. Mean i" SD
6. Mean * 2SD
7. Five selected cumulative probability tables
a. Group, limits and plotting position
b. Population within groups
c. Exceedance within groups (957. gaussian normality)
d. Cumulative frequency
29
GPO 02 t —571—2
-------
CHEMICAL PRECIPITATION
Sidney A. Hannah
-------
CHEMICAL PRECIPITATION
Sidney A. Hannah
1. Historic
The recent interest in chemical precipitation for treatment of wastewater
was preceded by a similar interest some sixty years ago. The Royal
Commission of London (-24.) issued a report which endorsed the practice.
The process was intended to replace primary sedimentation. Alum or lime
was used to flocculate raw sewage to produce effluents with 10-40 mg/l
of suspended solids. The practice was not widely adopted, however,
because of the engineering difficulties and particularly because of the
problems of handling the sludge.
The Guggenheim process proposed in the thirties also involved chemica"
precipitation but this also failed to be widely adopted. Possibly, a
dominant reason for the failure of adopting chemical precipitation at
that time, aside from the extra cost, engineering and sludge problems,
was the lack of pressure to produce a better effluent.
2. Objectives of Chemical Precipitation
The impetus to use chemical precipitation is provided by the need to
remove phosphorus. But chemical precipitation, while removing phosphorus,
also removes in excess of 95 percent of the suspended solids yielding a
fully clarified effluent with 95 percent of phosphorus removed or in pre-
cipitated form.
Conventional treatment techniques of settling and biological oxidation
are capable of removing some phosphorus as shown in Fig. 1. In spite of
some encouragement that certain plants are capable of greater removals,
the most that can be expected in general are 5-15 percent by sedimentation,
20-30 percent through a tricking filter and up to 50 percent by activated
sludge. Moreover, actual phosphorus removal will ultimately depend on
the amount of sludge permanently removed from the process stream. This
means that phosphorus concentrated in the sludge must be removed from
digester contents.
-------
- 2 -
FIGURE 1 Phosphate Removal by Conventional Waste
Treatment Plants
Type of
%
Treatment Plant
Phosphorus Removal
Primary Sedimentation
5-15
Primary and Trickling Filter
20-30
Primary and Activated Sludge
30-50
The most economic and reliable method of removing phosphorus and suspended
solids is chemical precipitation. The choice of point of addition depends
on several factors which are shown in Fig. 2. Chemicals may be added to
raw sewage with separation of solids occurring in the primary, to the
aerators with separation obtained with the biological sludge, or chemicals
may be added to the final clarifier as a tertiary process. All of these
variations have been studied and are technically feasible.
A choice also has to. be made on the chemical to use. The factors to be
considered here are shown in Figure 3. The influent phosphorus level and
particularly the permissible residual phosphorus are important consider-
ations. Wastewater characteristics determine in part the chemical dosage
and finally, facilities for sludge handling and ultimate disposal of the
sludge must be considered.
A variety of chemicals can be used for chemical precipitation. These
are shown in Fig. Various salts of iron are equally effective. These
salts include ferrous chloride or ferrous sulfate, ferric chloride or
ferric sulfate, and waste pickle liquor which is a waste product from
steel processing and consists of largely ferrous chloride or sulfate
with some ferric salts. Lime or sodium hydroxide must be added with
the ferrous salts. The pH of optimum precipitation with the latter
appears to be around pH 8.0.
Aluminum salts may also be used. Commercial aim, aluminum sulfate, is
the more common although sodium aluminate has also been used. The latter,
while more expensive, has the advantages of containing some excess
caustic which helps to maintain pH and does not add sulfate ion, as alum
does.
Lime as a precipitant is very attractive because of its cheap initial
cost and because sludge can be calcined to recover reuseable lime while
at the same time incinerating the organic sludge.
All of the metal precipitants may require the addition of polymer to
obtain effective settling and separation of solid from liquid.
-------
- 3 -
COMBINED
CHEMICAL- BIOLOGICAL CHEMICAL
Sludge-
figure 2 PHOSPHORUS CONTROL BASIC SYSTEMS
-------
Figure 3
FACTORS AFFECTING CHOICE OF CHEMICALS
1.
INFLUENT PHOSPHORUS LEVEL
2.
EFFLUENT DISCHARGE STANDARD
3.
WASTEWATER CHARACTERISTICS
4.
PLANT SIZE
5.
CHEMICAL COSTS INCLUDING TRANSPORTATION
6.
SLUDGE HANDLING FACILITIES
7.
SLUDGE DISPOSAL FACILITIES
8.
OTHER PROCESSES UTILIZED
Figure U Alternative Chemical Systems for Phosphorus
Removal in the Primary
A. Iron
Ferrous Chloride - Base - W/0* Polymer
or Sulfate
Commercial or Lime or
Waste Pickle Sodium
Liquor Hydroxide
Ferric Chloride C - W/0 Polymer
or Sulfate
B. Aluminum
Alum or Aluminate - W/0 Polymer
C. Lime - W/0 Additives
1 or 2 Stage
* .
W/0 - With and Without
-------
- 5 -
3. Performance Results
(a) Precipitation with iron salts
All of the chemicals mentioned and all of the points of addition have
been tested at full scalQ. These tests provide the information for any
plant to determine the choice of chemical and point of addition using
the factors pointed out in Fig. 2 as the basis for decision.
The addition of metallic salts to primary clarifiers not only removes
phosphate but obtains clarification thus providing suspended solids,
BOD-COD and phosphate removal all at the same time. Thus, the organic
load to the secondary system is reduced with possible reduction in air
requirements and waste activated sludge production.
The results of full-scale chemical treatment at Grayling, Michigan, are
shown in Figure 5. Without chemicals, removal in the primary amounted
to 50% for SS and U1% for BOD. No removal is reported for phosphorus,
although I suspect that some removal was obtained. Adding 15-30 mg/l
of iron as ferrous chloride increased SS removal to 78 percent, BOD
removal to 58 percent and 72 percent of the phosphate was precipitated.
Note that with ferrous salts, sodium hydroxide at the rate of 30-50 mg/l
as CaCO., had to be added. Most chemical precipitation requires polymer
for effective clarification. In this case 0.3-0.5 mg/l was used.
A similar use of ferrous salt was tried at Mentor, Ohio, Fig. 6. In
this case waste pickle liquor was used as the source for ferrous
chloride. Waste pickle liquor was added at a dosage to yield 4-3 mg/l
as Fe. Lime, rather than caustic, was added at the rate of 66 mg/l.
Again polymer was required - 0.4 ing/l« Removals of SS and BOD were
similar to the Grayling test but phosphate removal was superior amounting
to 83.5 percent. The greater phosphate removal can be accounted for by
the greater iron dosage. Removals in excess of 90-95 percent can be
obtained with even greater iron dosages and careful separation of the
precipitated phosphate. The two forms of pickle liquor are apparently
interchangeable. Ferrous sulfate was successfully used at Texas City.
When available within reasonable hauling distances, waste pickle liquor
containing 6-9 percent of ferrous iron can be an inexpensive source for
iron. The hauling costs amounted to 1.5^/lb of Fe at Texas City and
2^/lb Fe at Mentor. The cost of lime or sodium hydroxide must be con-
sidered. Also, the ferrous iron must be oxidized to ferric form to
obtain removal of both phosphate and iron, hence sufficient oxygen must
be present. Theoretical work with ferrous iron in a contract with
Atomics International has shown that the optimum pH centers around pH 8.0.
The need to control pH and to ensure availability of oxygen to prevent
excessive soluble ferrous compounds in the effluent has tended to diminish
-------
- 6 -
Figure 5 RESULTS AT GRAYLING, MICHIGAN
CHEMICALS:
FeClj a 15-30 mg/l as Fe
NaOH » 30-50 uig/1 as CaC03
A-23 «= 0.3-0.5 mg/1
WITHOUT CHEMICALS
CIO weeks')
WITH CHEMICALS
(10 weeks)
Raw
mc/1
Pri.Eff.
mpVl
%
Rem.
Raw
ms/l
Pri.Ef£.
me/1
%
Rem.
SS
157
78
50
224
50
78
BOD
170
101
41
178
74
58
TOTAL P
No removal
15.5
4.4
72
Figure 6 RESULTS AT MENTOR. OHIO
CHEMICALS:
WASTE PICKLE LIQUOR (FeC^) *" 43 mg/1 as Fe
LIME » 66 mg/1
A-23 " 0.4 mg/1
PERCENT REMOVAL WITH CHEMICALS
SS = 747.
BOD « 59%
TOTAL P - 83.5%
-------
- 7 -
the advantages of the low coat ferrous iron. For these reasons ferric
chloride has been more widely accepted. Full-scale testing with ferric
chloride and polymer in the primary is being conducted at Grand Rapids,
Michigan, at Benton Harbor, Michigan, and elsewhere.
Addition of chemicals to the primary and increased capture of organic
solids clearly indicate that more sludge solids will have to be handled.
Good quantitative data on this aspect are lacking although the study at
Grand Rapids should be informative. Some data were obtained at Benton
Harbor, Michigan, Fig. 7. The study was conducted in three stages; a
baseline period with no chemical addition; a second period when ferric
chloride and polymer were added but with wasting of activated sludge to
the primary, and a third period when chemicals were added but waste
activated sludge was not cycled to the primary. The plant uses the
"Kraus Process" which involves returning a reaerated portion of the
waste activated solids to the primary.
Chemical addition actually reduced the volume of sludge pumped but the
solids content increased from 3.8 to U-82 percent with chemical addition
and no recycle. With increased organic removal, dissolved oxygen in the
aeration tank increased from 4.8 to 6.6 mg/l. This benefit is obscured
by the increased air supplied to the tank.
The presence of chemical sludge posed no problem in the digesters. Witty
increased organic solids pumped to the digester, total gas production
increased. Gas production per pound of solids also increased from 3.4-8 ft-ylb
to 3.67 ft^/lb. Operation was otherwise normal. A point worth mentioning
here is that soluble phosphate concentration in the digester supernatant
return flow was very low.
(b) Precipitation with aluminum salts
Either alum or sodium aluminate can be used for precipitation in the
primary but has been little used for this purpose. Aluminum salts have
been used as a chemical precipitant in the aerator. This aspect is
discussed by another speaker. One reason why wlmn has not been so widely
used in raw sewage clarification is its higher cost over iron salts.
Sludge from iron precipitations are easier to handle than alum sludges.
Alum, nevertheless, is widely used in Sweden in raw sewage flocculation
because of the much lower cost of commercial ai™ in Sweden.
If very high quality effluent is required for discharge or reuse, treat-
ment of the final effluent or tertiary treatment may be necessary. Both
iron or aluminum salts can produce an effluent low in phosphorus, BOD
and suspended solids. Alum, rather than iron salts, was chosen for the
-------
- 8 -
Figure 7 Plane Data at Benton Harbor Using Ferric Chloride
Primary Clarification
Volume Pumped, Gal/Day
Solids Concentration,
Percent Volatile
Mo Chemical
Addition
53,200
3.80
64
Chemical Addition
* . *
Recycle to Primary No Recycle
51,600
4.29
63
46,100
4.82
60
Mixed Liquor Data
Suspended Solids, mg/1 2500
Sludge Volume Index 85
Dissolved Oxygen 4.8
Air Applied, cfm 4480
Digester Operation
3
Gas Production - ft_ 37,800
Gas Production - ft /lb of 3.48
solids
2700
78
5.9
4940
44,400
3.82
2400
64
6.6
4710
40,800
3.67
With and without Recycling of Waste Activated Sludge
400 gpm plant at Nassau County, New York. The objective of this study
is to determine the feasibility of treating secondary effluent to a
quality suitable for ground water discharge. In this instance, iron
could not be' used. The processes include, alum clarification, dual
media filtration, and adsorption on granular activated carbon. Fig. 8
shows results of operation of the clarification and filtration portions
of the systems. With an average alum dose of 200 mg/l, phosphorus was
reduced to 1.4 mg/l in the clarifier effluent. It is significant that
filtration produced a highly clarified effluent containing 0.08 mg/l P
and 0.2 JTU turbidity. The filter served to capture the precipitated
phosphates that did not settle in the clarifier. An important obser-
vation is that when sufficient chemical is added to obtain good clari-
fication, good phosphorus removal is also obtained.
-------
9
Figure 8 NASSAU COUNTY OPERATING RESULTS
CLARIFIER FILTER
CONSTITUENT INFLUENT EFFLUENT EFFLUENT
POLYPHOSPHATE, mg/1 P 0.5
TOTAL PHOSPHATE, mg/1 P 7.2 1.4 0.08
TURBIDITY, JTU 50 6 0.2
The quality of secondary effluents can be considerably increased by
chemical precipitation and sand filtration. Some work done by the Water
Pollution Research Laboratory in England on two treatment plants is
summarized in Fig. 9. All parameters of product quality were substantially
reduced. Final effluent contained 2-5 SS, 2-2. BOD, 1.5-0.15 phosphate
and turbidity 0.8 to 3.5 units. Soluble aluminum ranged 0.1 to 0.45 mg/l.
FIGURE 9
TREATMENT OF EFFLUENTS OF POOR QUALITY
BY CHEMICAL COAGULATION AND SAND FILTRATION
mg/1 unless Effluent A Effluent B
'otherwise stated Initial Final Initial Final
SUSPENDED SOLIDS 84 2 26 5
BOD 35 2 25 3
COD 83 26
PHOSPHATE 11 1.5 2.5 0.15
ALUMINUM 0.1 0.45
COLOR (HAZEN UNITS) 90 33 42 27
TURBIDITY (ATU) 0.8 3.5
-------
- 10 -
(c) Lime precipitation
The chemistry of lime precipitation is entirely different from the
chemistry of iron or aluminum. With the latter the dose is related to
phosphate content and the requirement to provide sufficient hydrolysis
products of the metal. In practice these requirements have been met
vith dosages of alum or iron ranging from 150 to 300 mg/l. These dosages
will generally produce a clarified effluent low in phosphorus. Lime
dosage, on the other hand, is more dependent on the wastewater character-
istics, principally alkalinity and hardness. In practical terms the dosage
is determined by the pH required to obtain the desired clarification and
phosphorus removal. When slaked lime CaCOH^ is added to wastewater, it
reacts with alkalinity precipitating calcium carbonate; it reacts with
orthophosphate to precipitate hydroxyapatite, Ca«j(0H)(P0,) . Precipitation
of magnesium hydroxide begins around pH 10 and is complete-'at pH 12.
The amount of lime required to raise the pH to a given value is a function
of the initial alkalinity. This relationship is shown in Fig. 10. Waste-
waters with high alkalinity (buffer capacity) necessarily require high
doses to reach a pH range where phosphorus precipitation is effective.
The higher the alkalinity, the greater the lime requirement. The pH
range that must be obtained for high phosphorus removal is about pH 10
to 11. At these pH's residual total phosphorus will range around 0.1
to 0.3 mg/l. This relationship is shown in Fig. 11. Looking at Fig. 10
again, the lime dose to obtain pH 10 can range from as little as 50-75 mg/l
for a wastewater with an alkalinity of 22 mg/l to almost 4.00 if the
alkalinity is 600 mg/l.
The two extremes of lime clarification in high and low alkalinity waters
can be illustrated by the operation of the pilot plants at Lebanon, Ohio,
and Blue Plains at Washington, D.C. A pilot plant at Lebanon, Ohio,
treats secondary effluent with lime and media filtration. This wastewater
has a relatively high hardness and alkalinity. Operation at pH 10.7
resulted in a phosphorus concentration of 0.5 mg/l and 0.1 mg/l in the
clarifier and filter effluents respectively. The lime requirement has
ranged from 300-400 mg/l. Because, of the relatively high hardness at
Lebanon, a sufficient portion of the sludge consisted of dense calcium
carbonate which settles readily, thus the entire operation can be con-
ducted in a single stage.
Lime clarification at the Blue Plains pilot plant where the wastewater
is low in both hardness and alkalinity must be operated either as a
two-stage system or a single-stage with the addition of carbonate as
soda ash or There is insufficient alkalinity to permit the for-
mation of a dense, good settling calcium carbonate sludge with lime
addition alone. The most effective treatment sequence has been a two-
stage processj lime to pH 11.5 in the first-stage clarifier, reduction
of pH to 9*5-10.0 by addition of CO^ and clarification in the second
stage vith the aid of 6-12 mg/l Fe''I. Results obtained with single—stage
-------
- 11 -
FIGURE 10
ALKALINITY, LIME DOSE, AMD pH
800
TOTAL ALK.(initial)
A 22(mg/|)
_ A 120 (mg/I)
° 240(mg/l)
0 600(rog/l)
600
400
200
-------
- 12 -
FIGURE 11
LIME PRECIPITATION Af!D PHOSPHORUS REMOVAL
FROM RAW WASTEWATER.
-------
- 13 -
and two-stage lime clarification are shown in Fig. 12. In the two-
stage process 350-400 fflg/l fl-S CaO was added to obtain a pH of 11.8-12.0.
For the single-stage process 250 mg/l of lime was added to a pH of 9.5*
Both processes achieved a residual P content after media filtration of
0.4 and <1 mg/l P, respectively, or 96 and > 89 percent removal. Thus,
while high alkalinity waters require more lime to reach any desired pH,
phosphorus removal can be obtained with lower pH's.
Thus far, I have emphasized the phosphorus removal capabilities of
chemical precipitation and have only mentioned that clarification is
also obtained concurrently. The data in Fig. 12 illustrates that with
good phosphorus removal, equally good clarification is obtained. In
the two-stage process, lime clarification of primary effluent obtained
67.6 percent removal of COD and 75 percent removal following filtration.
Similarly, the single-stage process obtained 65 percent COD removal after
lime precipitation and filtration. These excellent removals of COD by
precipitation and filtration compare well with secondary treatment of
wastewater by trickling filters.
4-. Sludge Handling
One of the more important factors to be considered for choice of chemical
to use is the sludge handling characteristics. This subject will be
covered in more detail elsewhere. Iron sludges and particularly alum
sludges from a clarifier are likely to contain only about 0.5 percent
solids and will dewater slowly. Hence costs for concentrating and dis-
posal may be high. In contrast, lime sludge, particularly sludge con-
taining calcium carbonate from high alkalinity waters is granular and
dewaters easily. Lime sludge from the Lebanon operation, for example,
is removed as a 3 percent slurry from the clarifier, then thickened in
a gravity settler to a 15 percent slurry which is pumped to sand drying
beds. The sludge dewaters on the beds to 50 percent solids. Dewatering
can also be obtained on vacuum filters or by centrifuges. In contrast
to alum or iron for which no practical method for recovery of metal is
available, lime can be recalcined to recover useful calcium oxide. Work
at Lake Tahoe demonstrated that recalcined lime recovered from a tertiary
lime treatment is as effective as virgin lime in the treatment process.
5. Cost of Treatment
Cost of chemical precipitation is subject to so many variables as choice
of chemical, point of addition, and waste characteristics, etc., as
pointed out earlier, that this discussion can do no more than indicate
approximate costs. Fig. 13 illustrates the total cost of single-stage
lime clarification for plant sizes ranging from 1 to 250 mgd. The cost
is shown to range from 6.09^/1000 gal for the smallest plant to 3.78^/1000
for the largest. Savings are indicated when lime is recalcined.
-------
- H -
Figure 12 Results of Treatment by Lime Clarification, Filtration and
Carbon Adsorption of Primary Effluent at Washington, D. C. —"
(I) and Lebanon, Ohio (II)
Two-Stage Lime
Clarification - Low
Alkaline Wastewater(I)
Single-Stage
Clarification - High
Alkaline Wastewater(II)
mg/1 X Removal mg/1 X Removal
Primary Effluent
Phosphorus, P 10.A 8.8
TOC 78.A 76
BOD 139 76
COD 265 192
Lime Clarified Effluent
Phosphorus, P 0.5 9A.8
TOC 27.1 65.2
BOD A2.0 69.7
COD 86 67.6
Filtered Effluent
Phosphorus 0.39 96.2 <1 >89
TOC 22.6 69.9 26 52.3
BOD 28 80.0 25 67.2
COD 66 75.0 67 65.0
Carbon Effluent
Phosphorus - <1 >89
TOC 6.5 90.6 10 87
BOD A 97 10 87
COD 11 95.8 27 86
-------
- 15 -
Figure 13 Total Cost of Phosphate Removal for Single-Stage
Lime Clarification
(Cents per 1,000 gallons)
Size of
Plant
1 mgd
10 mgd
100 mgd
250 mgd
Capital amortization
1.25
1.12
.84
.77
Land amortization
.12
.12
.12
.12
Operating and maintenance
2.30
.79
.50
.47
Cost of chemicals
Lime
1.75
1.75
1.75
1.75
Cost of sludge disposal by
hauling to land fill
(25-mile one-way trip)
.67
.67
.67
.67
TOTAL
6.09
4.45
3.88
3.78
Savings if lime can be
reclaimed
-.67
-.67
-.67
-.67
TOTAL (with recalcining) 5.42 3.78 3.21 3.11
GPO 021 —37 I —3
-------
- 16 -
References
1. Convcry, J. J., "The Use of Physical-Chemical Treatment Techniques
for the Removal of Phosphorus from Municipal Wastewaters."
Presented at the Annual Meeting of the New York Water Pollution
Control Association, January 29, 1970.
2. Wukasch, R. F., "New Phosphate Removal Process,"
Water & Wastes Engineering, No. 9, 58 (1968).
3. Brenner, R. C., "Phosphorus Removal by Chemical Addition During
Primary Treatment," presented at the Nutrient Removal Seminar,
University of Pittsburgh, Feb. 17-18,' 1970.
4. Barth, E. F., and Ettinger, M. B., "Mineral Controlled Phosphbrus
Removal in the Activated Sludge Process," JWPCF, 39, 1361 (1967).
5. Ebcrhardt, W. A., and Nesbitt, J... B., "Chemical Precipitation of
Phosphorus in a High Rate Activated Sludge System," JWPCF, AO,
1239 (1968).
6. Barth, E. F., Brenner, R. C., and Lewis, R. F., "Chemical-
Biological Control of Nitrogen and Phosphorus in Wastewater
Effluent," JWPCF, AO, 2040 (1968).
7. Brenner, R. C., "Phosphorus Removal by Chemical Addition During
Secondary Treatment," presented at the Nutrient Removal Seminar,
University of Pittsburgh, Feb. 17-18, 1970.
8. Final Report, Contract No. 14-12-15, FWQA.
9. Peters, J. H., and Rose, J. L., "Water Conservation by Reclamation
and Recharge," Jour. ASCE, 94, SA4, 625 (1968).
10. Duff, J. H., Dvorin, R., and Salftra, E,, "Phosphate Removal by
Chemical Precipitation," presented at the Second Workshop on
Phosphorus Removal, FWPA, Chicago, 111., June 26-27, 1968.
11. Stamberg, J. B., Bishop, D. F., Warner, H. P., and Griggs, S.,
"Lime Precipitation in Municipal Wastewaters," presented at
the National Meeting of the A.I.Ch.E., Washington, D. C. Nov. 1969.
12. 0'Farrell, T. P., Bishop, D. F., and Bennett, S. M., "Advanced
Waste Treatment at Washington, D. C., presented at the 65th
Annual A.I.Ch.E. meeting, Cleveland, Ohio, May 1969.
-------
- 17 -
13. O'Farrell, T. P., and Frauson, F. P., "Ammonia Stripping at
Washington, D. C.presented at the Nutrient Removal Seminar,
University of Pittsburgh, Feb. 17-18, 1970.
14. Bishop, D. F., and Bennett, S. M., "Disposal and Reuse of Lime
Sludge," presented at the Nutrient Removal Seminar, University
of Pittsburgh, February 17-18, 1970.
15. Mulbarger, M. C., Grossman, E., Dean, R. B., and Grant, 0. L. ,
"Lime Clarification, Recovery, Reuse and Sludge Dewatering
Characteristics," JWPCF, 41, 2070 (1969).
16. Berg, E. L., Brunner, C. A., and Williams, R. T., "Single-Stage
Lime Clarification of Secondary Effluent," Water & Wastes
Engineering, _7> 3, 42 (1970).
17. Culp, R. L., "Wastewater Reclamation at South Tahoe Public
Utilities District," JAWWA, 6JD, 84 (1968).
18. Albertson, 0. E., and Sherwood, R. J., "Phosphate Extraction
Process," JWPCF, _41, 1467 (1969).
19. Schmid, L. A., and McKinney, R. E., "Phosphate Removal by a
Lime-Biological Treatment Scheme," JWPCF, 4_1, 1259 (July 1969).
20. Zuckerman, M. M. and Molof, A. H., "High Quality Reuse Water
by Chemical-Physical Wastewater Treatment," JWPCF, 42, 437 (1970).
21. Anon., "FWQA Steps up Tertiary Treatment Study," Environmental
Science & Technology, 4^ 550 (1970).
22. Bishop, D. F., Internal Report, Advanced Waste Treatment
Laboratory, FWQA, 19 70.
23. Mulbarger, M. C., Page, G. L.,Jr., Yates, 0. W., Jr;, and
Sharp, N. C., "Manassas, Va., Adds Nutrient Removal to Waste
Treatment," Water & Wastes Engineering, 6^ 4, 46 (1969).
24> Royal Commission on Sewage Disposal: 5th Report, HM Stationery
Office, England (1908).
-------
ADVANCED WASTE TREATMENT PLANTS
FOR TREATMENT OF SMALL WASTE FLOWS
I. J. Kugelman, W. A. Schwartz, and J. M. Cohen
Introduction
During the last two decades, the need for waste treatment in localities
where connection to a centralized system is not possible or economically
feasible has become more and more urgent. Typical examples include
suburban housing developments, institutions, rest areas along highways,
tourist areas in parks, isolated work camps, etc. In these situations
the flow is low because the population served is limited, and consequently
such plants are referred to as "small flow" treatment plants. As a rule
of thumb, plants in excess of 500,000 gal/day capacity (equivalent
population 5,000) are considered outside the "small flow" class. This
size limit is based on limitations of shop fabrication and typical sizes
of communities not connected to regional sewerage systems, but is some-
what arbitrary. Data on the number of plants of this type which will be
required in the near future are virtually non-existent. Table 1 presents
some estimates of the present "market" for such plants. An overall
estimate of the significance of this problem is given by the data of
Smith which show that 10% of the total weight of BOD in municipal sewage
discharges is generated in communities with a population below 5,000.
Performance Criteria
'fhe "small flow" treatment plant market has not been ignored by commercial
interests. During the last 20 years they have installed approximately
5,000 package sewage treatment plants. These have all been designed on
the basis of biological treatment technology and for the most part they
have done the job required. However, these plants are limited in
applicability. In many locations, which shall or already do require
"small flow" systems, one or more of the following conditions can be
expected which will exclude the use of a purely biological unit:
a. Toxic materials in the waste
b. Extreme diurnal flow and load variation
c. Requirement for nutrient removal
d. Requirement for start and stop operation
e. Reuse of the treated effluent
A pertinent example of the inability of biological package plants to meet
recent upgrading in treatment criteria is given by the recent action of
several localities halting subdivision home construction pending the
installation of adequate waste treatment. Biologi'cal package plants did
not meet the stringent effluent criteria established by these local
governments.
-------
- 2 -
TABLE 1
ESTIMATES - SMALL FLOW TREATMENT PLANT NEEDS
CATEGORY ESTIMATED NO. OF PLANTS
SMALL COMMUNITIES 3,000 - 6,000^
PARKS AND MARINAS 2,000 - 10,000^
ALASKAN WORK CAMPS & ESKIMO VILLAGES 500 - 2,000
(a) The Economics of Clean Water - Vol. I, USDI, March 1970.
(b) Personal Communication - U.S.Park Service
TABLE 2
TYPICAL "SMALL FLOW" WASTE CHARACTERISTICS
Typical^ ^
Municipal
Sewage
Household^
Wastewater
Houseboat^
Wastewater
Winter^ ^
Recreation
Area
SUSPENDED SOLIDS, mg/1
200
376
173
342
COD, mg/1
350
776
460
790
BOD, mg/1
210
435
222
390
TOTAL NITROGEN, mg/1—N
33
84
67
78
AMMONIA NITROGEN, mg/l-N
12
64
—
23
TOTAL PHOSPHATE, mg/1 P04
24
61
49
32
GREASE, mg/1
14
68
92
—
(a) Water Supply & Sewerage, Steel, E. W., McGraw Hill - 1960
(b) Watson, et al., JWPCF, 39, 2039 (Dec 1967)
(c) Clark, B. D., "Houseboat Waste Characteristic & Treatment," PR-6,FWQA (Sept.1967)
(d) Clark, B.D., "Basic Waste Characteristics at Water Recreational Areas,
PR-7, FWQA (Aug. 1968).
-------
- 3 -
Waste treatment technology which can meet the stringent performance
criteria for small flow plants has been under development in the Advanced
Waste Treatment program for the last decade. These new methods are
primarily physical and chemical in nature rather than biological. Demon-
stration of these concepts on a large scale (> 10 mgd) is soon to take
place. As these systems have worked well in pilot plants, it is reason-
able to assume they shall do so in "small flow" systems. These pilot
plant studies were conducted on typical domestic sewage. Although small
flow wastes are in general stronger than typical domestic sewage they are
not fundamentally different in character. Table 2 compares the character-
istics of typical small flow wastes and typical domestic sewage.
Small Flow Advanced Waste Treatment Plants
A. Basic design consideration
Treatment of small flow wastes may require one or more of the following
steps: suspended solids removal, dissolved organic carbon removal,
nitrogen and/or phosphorus removal, and disinfection. The Advanced
Waste Treatment program has developed one or more processes to meet each
of these treatment requirements. However, design of a treatment train
cannot be predicated only on achieving a desired effluent quality but must
be concerned with reliability and cost. On these latter points conditions
are somewhat different when comparing small velume and conventional flow
plants. Because of the highly variable nature of the wastes to be
treated a premium must be placed on processes which function well regard-
less of waste variability. A second factor to consider is the apportion-
ment of total cost between capital and operation. In most "small flow"
situations a full-time operator is not economically feasible, thus a
treatment system with a relatively high capital expenditure for automation
can be justified.
Based on the special requirements of small flow treatment plants discussed
above, three generalized treatment trains have been selected as worthy
of consideration for future development.
B. Physical-Chemical System
Figure 1 illustrates a wholly physical-chemical treatment system
employing chemical clarification followed by carbon adsorption. Either
powdered or granular activated carbon can be utilized. The system
performance is quite flexible in that the degree of treatment obtained
can be varied by the use of optional filtration steps and by altering
dosage of chemicals or powdered carbon or the frequency of replenishment
of granular carbon. In some cases activated carbon treatment may not
-------
COAGULANT
Fig.1. SCHEMATIC FLOW DIAGRAM OF A PHYSICAL-CHEMICAL TREATMENT SYSTEM
-------
5
be required as chemical clarification consequently yields 70% to 75% COD
removal from raw sewage. It is anticipated that only for the largest
scale small flow plants will carbon regeneration be provided. For most
of these plants the cost of discarding carbon after one use appears less
than the required capital expenditure for a regeneration system.
Chemical clarification with a sufficient dose of iron or aluminum salts
or lime can provide any degree of phosphorus removal required. In general,
the extra chemical cost associated with dosages to the level required for
phosphorus removal is relatively minor in the overall cost figures for
small volume treatment systems. In addition, dosage to this level will
always assure excellent clarification.
Ammonia nitrogen removal is not provided for specifically in this scheme.
The most feasible method for nitrogen removal would be breakpoint chlor-
ination, because it is the method which requires least attention from an
operator. Thus effluent disinfection and ammonia nitrogen removal can be
achieved in one step. Howevers a significant increase in chloride ion can
be expected in the effluent.
C. Ultrafiltration System
The second general treatment scheme is iLlustrated in Figure 2. This
provides for a variety of optional pretreatment steps leading to an
ultrafiltration membrane assembly. A membrane providing total suspended
solids capture with some degree of dissolved organic removal would be
utilized. In essence, the role of the membrane in these systems is to
function as a polishing or safety device which will produce a consistent
effluent quality regardless of fluctuations in the raw waste. The pre-
treatment steps serve to reduce the load on the membrane and reduce the
rate of membrane fouling.
D. Chemical - Biological System
Figure 3 illustrates a chemical-biological treatment system. This
treatment train is less generally applicable than the others in that
it is heavily oriented to biological treatment. It is only applicable
where neither toxicity nor flow interruption is anticipated. In this
system mineral addition to the aerator is included not only for phosphorus
removal but to prevent biological solids loss from the sedimentation tank
under varying hydraulic load. Provision of an automatic backwash deep bed
filter serves as an effluent polishing device. Nitrogen removal may be
obtained with this system by operation of the activated sludge system
such that nitrification will take place and injecting sufficient methanol
ahead of the filter so that denitrification will take place.
-------
Optional Pretreatments:
RAW
WASTE
I
I
FIGURE 2. SCHEMATIC DIAGRAM OF ULTRAFILTRATION SYSTEM
-------
FIGURE 3. SCHEMATIC DIAGRAM OF CHEMICAL-BIOLOGICAL SYSTEM
-------
- 8 -
Sludge Treatment
As is the case for large scale plants the greatest problem for small
flow plants is sludge disposal. Of the several sludge disposal methods
available some such as sludge drying beds, are more applicable to small
plants than large plants, while some such as mechanical sludge filtration
appear to be too expensive for small plants. Treatment and disposal
methods which are being seriously considered include:
a. dewatering on drying beds with or without lime treatment
b. gravity thickening and temporary storage with periodic pump-out
c. incineration
d. aerobic digestion
Incineration is the most costly of these but the most attractive as the
only residue for disposal is a sterile ash. A fluidized bed incineration
system which has been successfully applied to the incineration of plastic
wastes will soon be evaluated for incineration of sludge. This system
shows promise for small treatment plants because fluidized beds hold
their temperature well during shutdown of several days, and are relatively
easy to automate.
Our knowledge of fundamental characteristics of the chemical-biological
or chemical raw sewage solids sludges which will result from small flow
systems is not as extensive as our knowledge of conventional primary and
secondary sludges. These data will be required in order to design sludge
handling systems. In future research activities in the small flow treat-
ment plant field, gathering data on sludge handling will be of prime
importance.
Current Models of Small Advanced Waste Treatment Plants
There are very few examples of small Advanced Waste Treatment plants
which are commercially available at the present time. However, these
are worth discussing in some detail in order to demonstrate their
inherent advantages. In principle, physical- chemical plants differ
basically from biological plants in that they can be designed to be
much more compact than the latter, and so lend themselves better to
small or modular installations. Moreover, since all suchjAdvanced
Waste Treatment plants consist of 2-3 distinctly different physical-
chemical treatment processes in series, obviously these varied elements
can be assembled in a variety of ways to serve any specific desired
purpose and to minimize space requirements. An array of processes is
available to effect: solids removal, organic removal, nutrient removal,
and, where necessary, some degree of inorganic removal. Since even
biological processes require solids removal, it is possible (as we
shall see) to substitute an Advanced Waste Treatment process for the
traditional gravity settling to effect an improvement in a biological
package plant, both in terms of treatment efficiency and space
requirements.
-------
- 9 -
There are several small plants with which we have some experience. The
small Advanced Waste Treatment plants which we shall consider are of
interest for three basic reasons: 1) they represent several distinctly
different process sequences; 2) they represent some of the combinations
of the physical-chemical treatment processes which are most likely to be
applied in the future, both at large or small scale; and 3) they
demonstrate applications in situations where small Advanced Waste Treat-
ment plants hold great promise for the future. Four different plants
shall be considered, three of which have been tested at a commercially
applicable scale, and the other of which is still being tested in the
laboratory.
Clarification-Carbon Treatment
The most popular physical-chemical treatment design currently being
evaluated consists of chemical clarification followed by granular
activated carbon adsorption, with or without an intermediate filtration
step. (See Figure 1). The Met-Pro Water Treatment Company of Lansdale,
Pennsylvania*, has designed a unit of this type (Model 1100-10) for the
treatment of laundry wastes. However, the plant has wider applicability.
The Met-Pro unit (see Plate 1) consists of an upflow solids contact
clarifier followed by two-stage granular carbon treatment: the first
stage is a downflow column of carbon on an anthracite coal base and the
second stage is an upflow carbon column. The unit is rated at about
24,000 GPD. In our evaluation of this unit at Cincinnati, a comminuted
and degritted wastewater was dosed with any of several coagulants just
prior to entry into the sludge blanket, where the retention time was
about one hour. Supernatant overflowed a weir onto a 33" deep bed of
carbon (12 x AO mesh) at a rate of between 1.3 and 2.5 gpm/sf. The
second (upflow) stage had the same amount of carbon as the first, and
the empty bed contact time for both stages was 16-32 minutes for our
range of flows. Carbon effluent was used to backwash the upflow carbon
bed. The operation is countercurrent in that spent carbon from the
upflow bed is used to replace spent carbon from the preceding downflow
bed. Spent carbon from the first contactor is discarded.
Before proceeding to the results of the plant evaluation, we should
consider the application intended for the pLant so that the data can
be put in proper perspective. The situation is typical of many for
which this and similar small plants are envisioned, i.e., a remote
area where no other waste treatment facilities are within reach and
where some degree of water reuse is projected because water supply is
either in short supply or expensive.
^Mention of commercial products does not imply endorsement by the
Federal Water Quality Administration, U. S. Department, of the Interior.
-------
- 10 -
PLATE 1
MET-PRO PACKAGE PLANT
CLARIFIER IN INNERMOST
CHAMBER & ADSORPTION
COLUMNS IN THE ANNULUS;
CHEMICAL FEEDER AT LOWER LEFT
-------
11 -
The North Slope of Alaska is a developing area of oil production. Being
remote and highly susceptible to the effects of pollution, a treatment-
reuse scheme is a desirable goal. The Met-Fro plant was thought suitable
to serve the needs of work camps (see Plate 2) and two such plants have
been installed for waste treatment (see Plate 3). The total water use
of a 300-man camp might be 30,000 GPD. The principal opportunity for
reuse is for toilet-flushing, which would not require drinking water
quality. This use represents a very significant fraction of the total
water use, perhaps 6,000-8,000 GPD.
The Met-Pro plant was operated during 3-4 months on an 8-hour-per-day
basis. This permitted us to evaluate the effect of starting and stopping.
About 200,000 gallons were treated as part of 26 separate runs which tested
various coagulants, dosages, flow rates, and raw wastewaters. A summary
of the results is shown in Table 3. Results for all the runs were
averaged. The organic effluent level is obviously much superior to
biological secondary effluent. Microbiological quality is still somewhat
poor and disinfection might be in order. Some idea of the variability of
influent and effluent characteristics can be gained from the graphs showing
frequency distributions for COD, turbidity, and phosphate (Figures 4-6).
It should be noted that both COD and turbidity are always at least of
secondary effluent quality. The sharply inclined line for P0^ effluent
is obviously meaningless here because high P0^ values are due to
inadequate coagulant dosages.
The chemical costs are given in Table 4. The costs are FOB and do not
include freight.
Poliovirus I inactivation by disinfection was evaluated and the results
are given in Table 5. Two separate trials were made using both iodine
and chloramine. It is important to notice that even where water is being
used for non-potable purposes, the water must be thought of as potentially
for human contact. Therefore, aesthetic and microbiological criteria are
just as much of a concern as solids and organic removal standards.
Activated Sludge-Ultrafiltration Treatment
A quite different sort of small Advanced Waste Treatment plant is represented
by the biological "package" plant which has been upgraded by addition of an
Advanced Waste Treatment process. The I0P0R System is manufactured by
Dorr-Oliver, Inc., of Stamford, Connecticut*. It consists of a high solids
activated sludge process followed by an ultrafiltration membrane for com-
plete solids separation. The use of the membrane to replace settling or
conventional filtration is intended to conserve space and to achieve a
^Mention of commercial products does not imply endorsement by the Federal
Water Quality Administration, U. S. Department of the Interior.
-------
PLATE 2
WORK CAMP IN ALASKA
-------
-------
- 14 -
TABLE 3
SUMMARY OF PERFORMANCE
OF THE MET-PRO CLARIFICATION-CARBON PACKAGE PLANT
(FWQA, CINCINNATI, OHIO)
AVERAGE VALUES, mq/1
PARAMETER
INFLUENT
EFFLUENT
% RE MO!
COD
330
17
95
COLOR (UNITS)
48
8.3
83
TURBIDITY (JTU)
91
2.5
97
PH
7.6
—
--
TSS
151
--
--
TOTAL P
6.7
<1.1
--
AMMONIA-N
21.1
13.3
ORGANIC-N
7.8
1.6
TOTAL COUNT (PER ML)
6.45xl06
170,800
97.4
TOTAL COLIFORM (PER ML)
278,000
1,418
99.5
FECAL COLIFORM (PER ML)
59,000
175
99.7
FECAL STREPTOCOCCI (PER ML)
13,840
91
99.3
-------
- 15 -
FIGURE 4
DISTRIBUTION OF INFLUENT & EFFLUENT COD
(MET-PRO PACKAGE PLANT)
% OF VALUES LESS THAN A GIVEN COD
-------
- 16 -
FIGURE 5
DISTRIBUTION OF INFLUENT & EFFLUENT TURBIDITY
(MET-PRO PACKAGE PLANT)
T
T
8C-
7C-
INFLUENT
o o
o o
O / o
O /
/
/
/
/
/
/
o /
/
/
/
99.8% REMOVAL
/
/°
EFFLUENT °
°
o 9- -°
V
o'
/
_i.o;
_0.9
-0.8
-0.7
-0.6
-0.5
_3.4
_L
_L
JL
10 20 30 40 50 60 70 80 90
% OF VALUES LESS THAN A GIVEN TURBIDITY
-------
- 17 -
FIGURE 6
DISTRIBUTION OF INFLUENT & EFFLUENT PO.-P
(MET-PRO PACKAGE PLANT) 4
-------
- 18 -
TABLE 4
CHEMICAL COSTS
FOR THE MET-PRO PACKAGE PLANT
(FWQA, CINCINNATI, OHIO)
ALUMINUM SULFATE
FERRIC SULFATE
ACTIVATED CARBON
~capacity =0.05
capacity =0.75
capacity - 1.00
QUANTITY
(1000 gal)
2.51 lb
2.51 lb
1.67 lb
1.25 lb
0 84 lb
COST
(per lb)
2.91*
2.16*
32*
32
-------
- 19 -
TABLE 5
POLIOVIRUS I INACTIVATION AT 15°C
IN THE MET-PRO PACKAGE PLANT
(FWQA, CINCINNATI, OHIO)
RUN NO. DISINFECTANT CONCENTRATION pH KILL TIME
DOSE RESIDUAL (minutes)
mg/1 99% 99.9%
I
IODINE
5
3.0
7.3
16
25
IODINE
1
0.2
7.5
84
150
CHLORAMINE
15
14.9
7.3
25
60
II
IODINE
5
3.7
7.5
11
20
IODINE
2
1.6
7.4
27
44
CHLORAMINE
22
17.7
7.6
6
24
-------
20 -
higher solids removal, the latter being necessary in view of the high
solids mode of activated sludge operation which is used.
Ultrafiltration is the lesser known counterpart of hyperfiltration, or
reverse osmosis, a process of increasing interest for desalination
applications. Ultrafiltration by definition removes only solids and no
inorganic salts. Although it requires a sophisticated hydrodynamic
system similar to that of R0, it is operated under a much lower pressure,
usually about 50 psi versus the 400-1500 psi required for RO. Like R0,
it has a problem with membrane flux decline, but this is usually controlled
by routine hydrodynamic cleaning techniques. Since ultrafiltration is
presently more expensive than settling or filtration, its principal current
application is in situations such as small Advanced Waste Treatment plants
where space is important, and where the product quality and consistency
of supply is vital.
The I0P0R System to be discussed is currently located on the top of
Pikes Peak (14,110 ft) in Colorado, and is thus perhaps the world's
highest sewage treatment plant. As with the case of Alaska, Pikes Peak
is a remote site where pollution hazards in the water-shed are great and
where water supply is likewise a difficult matter. (See Plate 5). The
wastes are generated largely by the tourist facilities on the Peak.
(See Figure 7).
Formerly, large quantities of potable water had to be trucked up the
mountainside over tortuous roads from the 10,000 foot level. This was
used for both potable and non-potable purposes. However, ,since the vast
majority of this demand was actually for non-potable water, specifically
for toilet-flushing, reuse of treated wastewater for this purpose will
make the water supply task considerably less difficult. The recent loss
of a tank truck over the mountainside emphasizes the hazards of water
supply to the Peak. Toilet-flushing represents a high proportion of the
total use because other uses are minimal. Little food preparation is
done on the premises. The I0P0R unit is designed to treat 15,000 GPD,
leaving only roughly 5,000 GPD to be trucked up the mountain for drinking
and washing water.
Since the population and tourist trade of Pikes Peak is projected to
increase steadily, both the water supply and pollution control aspects
are obviously of high priority. Moreover, this demonstration at a
remote site is potentially applicable for many other similar sites such
as resorts and parks. Special plant design requirements here include:
high product quality, both analytically and aesthetically, and ability
to function for extended periods on recycled flow (from overnight to
several, days, up to 100% recycle).
-------
PIKES PEAK: CONCEPTUAL VIEW
SET ON AN AERIAL PHOTO
-------
^ DISCHARGE
¦POTABLE WATER SUPPLY
-DISINFECTION
POTABLE
NON-POTABLE
TOURIST
USE
USE
FACILITY
MEMBRANE
HOLDING
TANK
GRINDER
HIGH-SOLIDS
ACTIVATED SLUDGE
PRESSURIZED
REACTOR
o
cr>
Fig. 7. SCHEMATIC FLOW DIAGRAM OF THE PIKES PEAK TREATMENT & REUSE SYSTEM
-------
- 23 -
The IOPOR unit was tested for several months at .Colorado Springs, during
which time mechanical difficulties were corrected. (See Plate 5). A
summary of results for the preliminary testing are given in Table 6. Raw
sewage from the city was used as a feed. The unit performed extremely
and consistently well under a very heavy loading in every respect except
perhaps color. Effluent organics were generally of tertiary quality and
even the odor was minimal. Frequency distributions for influent and
effluent COD are shown in Figure 8; effluent COD was always better than
secondary quality.
The IOPOR unit was moved to Pikes Peak in August 1970 as soon as
necessary site construction was completed. Membrane modules and plastic
parts were removed with the onset of winter in late September, when the
Peak facilities and roads were closed. In the meantime, about 3 weeks
of operation was completed which included some recycling experience but
no direct reuse. Operation with full reuse will commence next summer.
A summary of results for operation on the Peak is given in Table 7.
Operation was generally good as in the preliminary trial, even though
the waste was somewhat different. The Peak waste has a higher proportion
of human wastes than normal municipal waste. Color was again on the high
side, but not necessarily a problem. It may be that a small amount of
powdered carbon will improve the color. Phosphorus removal was typi'cal
of biological treatment. Physical-chemical treatment plants would be
superior in this respect if phosphorus were of concern here. However,
it is possible that phosphorus removal, if desired, could be improved by
adding a precipitant to the aerator. COD and turbidity frequency
distributions are shown in Figures 9 and 10. Not much variation is
evident for either of them, illustrating that both consistent waste
strength and consistent plant performance can probably be expected.
The membrane flux decline is shown in Figure 11. The initial flux of
30 gfd was the result of washing the membrane after the preliminary trial.
Although flux declined to 7-8 gfd in 20 days, no washing was done so the
flux decline shown is misleading. If, however, it continued at the rate
shown, it would be illustrated by the extrapolated dashed line. The flux
would be about 2.5 gfd at 6 months and 1.5 gfd at 1 year. Six months
coincidently represents both the membrane guarantee period and the
approximate upper limit for the length of any one tourist season. Washing
the membrane daily or several times weekly would keep the flux above the
design flow (15,000 GPD =7.8 gfd) for six months.
-------
-------
- 24 -
TABLE 6
SUMMARY OF PERFORMANCE
OF THE DORR-OLIVER ACTIVATED SLUDGE-ULTRAFILTRATION PLANT
PRELIMINARY RESULTS FROM COLORADO SPRINGS
PRIOR TO OPERATION AT PIKES PEAK,
MARCH-JUNE, 1970
PARAMETER
INFLUENT
mg/1
EFFLUENT
mg/1
%
REMOVAL
BOD
382
<1
>99
COD
678
20
97
TOC
192
7.5
96
TURBIDITY (JTU)
-
<0.1
-
COLOR (UNITS)
-
28
-
TSS
323
0
100
MLSS
5510
-
-
COLIFORM (PER 100 ML)
-
0
100
PO.-P
12.2
7.7
37
pH
7.02
6.62
-
THRESHOLD ODOR NUMBER
5.6
FLUX
10.1 GFD = 19,400
GPD
-------
1000
900-
800
700U
10C -
9C -
- 8C-
^ 7C-
- 6( -
Q
O
O
° 50
4C -
30-
20-
- 25 -
FIGURE 8
DISTRIBUTION OF INFLUENT & EFFLUENT COD
FROM THE DORR-OLIVER AS-UF PLANT
(PRELIMINARY TRIAL)
96.9% REMOVAL
EFFLUENJ
o o
o o.
-O 3
10
_L
_L
20 30 40 50 60 70
80
90
% OF VALUES LESS THAN A GIVEN COD
-------
- 26 -
TABLE 7
SUMMARY OF PERFORMANCE
OF THE DORR-OLIVER ACTIVATED SLUDGE-ULTRAFILTRATION PLANT
OPERATIONS AT PIKES PEAK
AUGUST-SEPTEMBER, 1970
PARAMETER
INFLUENT
EFFLUENT
%
mg/1
mg/1
REMOVAL
BOD
285
<1
>99
COD
547
32
94
TOC
136
6.6
95
TURBIDITY (JTU)
47
0.33
-
COLOR (UNITS)
320
40
-
TSS
129
0
100
MLSS
3954
-
-
COLIFORM (PER 100 ML)
-
0
100
PO.-P
9.1
11.1
-
PH4
7.9
5.9
-
THRESHOLD ODOR NUMBER
6
AVERAGE FLUX
11.0 GFD = 21,000 GPD
-------
- 27 -
FIGURE 9
DISTRIBUTION OF INFLUENT & EFFLUENT COD
FROM THE DORR-OLIVER AS-UF PLANT
(PIKES PEAK)
% OF VALUES LESS THAN A GIVEN COD
-------
- 28 -
FIGURE 10
DISTRIBUTION OF INFLUENT & EFFLUENT TURBIDITY
FROM THE DORR-OLIVER AS-UF PLANT
tPIKES PEAK)
0.1 ' 1 1 l ! I I I I
10 20 30 40 50 60 70 80 90
% OF VALUES LESS THAN A GIVEN TURBIDITY
-------
MEMBRANE FLUX DECLINE
IN THE DORR-OLIVER AS-UF PLANT
(PIKES PEAK)
FIGURE 11
-------
30 -
Clarification by Moving Bed Filtration
An interesting concept which has applicability to treatment of small
flows is the moving bed filter developed by Johns-Manvilie Corporation
Manville, New Jersey*. This device operates at hydraulic loading rates
normally associated with deep bed rapid filters but at solids loadings
usually applied only to clarifiers. It provides clarification superior
to that achieved by a clarifier but in a space similar to that required
by a rapid filter. Figure 12 illustrates the operation of this device.
Raw waste is dosed with appropriate chemicals and flows into a tank
which provides head for the filter operation. The sewage filters down-
ward through the inclined packed bed of sand to a screened pipe and
thence flows to a collector. Sewage solids and floe collect primarily
on the filter face although some depth filtration is obtained. When the
head loss exerted by the accumulated solids becomes excessive the sand
bed is pushed upward and a cutter slices off the top layers of sand and
suspended solids. The sand-sludge mixture is collected in the bottom of
the head tank and is then pumped to a sand washer. Clean sand is returned
to a hopper and eventually to the bottom of the sand bed.
This system has been tested with raw sewage, primary effluent, and
trickling filter effluent at the Bernards Township Sewage Treatment
Plant. The pilot plant had a capacity of 10 gpm at the average hydraulic
loading 2 gpm/sf. Alum and an anionic polyelectrolyte were used as the
treatment chemicals. The results obtained in two weeks operation on raw
sewage are given in Table 8. Excellent phosphorus, suspended solids, and
BOD removals were obtained. In fact, the MBF produced treatment superior
to that achieved by the Bernards plant during this period (which consists
of secondary treatment by trickling filter).
This work shall be expanded to other coagulants, and to evaluate the
performance when powdered activated carbon is added to the feed to obtain
additional organic removal. It is expected that the cost of once-used
carbon required to insure organic carbon removal to the level of
secondary treatment will be economically feasible for small flow application.
Johns-Manville estimates that the total cost of a 1 MGD plant is 12.0C per
1000 gallons. This estimate includes all operation, maintenance, chemicals
(alum and polymer) and amortization of the capital expenditure of
$264,000.
Clarification-Carbon-Ultrafiltration Treatment
A potential small Advanced Waste Treatment plant is presently being
evaluated in the laboratory and with a small prototype model by Oak
Ridge National Laboratory. No significant amount of data has been
^Mention of commercial products does not imply endorsement by the Federal
Water Quality Administration, U. S. Department of the Interior.
-------
INFLUENT
(AFTER JOHNS-MANVILLE)
FIGURE 12
-------
- 32 -
PARAMETER
PHOSPHORUS
TOTAL
FILTERABLE
ORTHO-
TABLE 8
SUMMARY OF PERFORMANCE
OF THE MOVING BED FILTER
IN THE TREATMENT OF RAW SEWAGE
(AFTER JOHNS-MANVILLE)
MBF
RAW SEWAGE EFFLUENT
(Average Values, mg/1)
21.5
18.6
13.2
2.16
0.79
0.57
% REMOVAL
90
96
96
pH
TSS
TURBIDITY (JTU)
BOD
7.2
156
119
115
7.0
27
16
19
83
87
84
NOTE: COAGULATED WITH 200 mg/1 ALUM AND =0.5 mg/1 MAGNIFLOC 860A
-------
33
collected yet, but the device is nonetheless worth mentioning.
This plant scheme consists of chemical clarification, powdered carbon
contacting, and ultrafiltration separation of solids, as shown in Figure 13.
The wastewater is contacted with coagulant as usual (so far, iron salts
have been used, but lime is probably equally applicable) and flocculated,
but no separation of floe is effected yet. A small dose of powdered
activated carbon is added. The floc-carbon suspension is then pumped
into the ultrafiltration cell where solids are separated. So far in lab
tests, considerable fractions of organics as well as all of the solids
are removed from the water with a membrane flux of about LOO gfd, or almost
10 times the I0P0R flux.
The I0P0R membrane used in the Dorr-Oliver plant is typical of conventional
membranes. It is cast from a synthetic polymer on a rigid support in the
form of parallel plates. Casting conditions as well as casting solution
ingredients are closely controlled to assure the desired flux and rejection
for the membrane.
The membrane in this plant is more unique. It is cast on a very coarse
membrane support in the form of a firehose jacket on a stainless steel
porous plate. The membrane itself is formed dynamically of a film of
sewage constituents and filter-aid (here the coagulant). The dynamic
forming process must also be closely watched since too heavy a membrane
film will produce too tight a membrane. This in turn would reject a high
fraction of the salts and produce a correspondingly lower flux (and
greater flux decline). Given proper hydrodynamics, the membrane flux
decline may be reasonable. Such a membrane has the advantage of
negligible cost and ease of replacement, since it can be formed and
destroyed in place. This unusual small Advanced Waste Treatment plant
is very experimental to date, but holds promise of great versatility for
a wide variety of pollutants.
Summary
1. An urgent need exists for "small flow" treatment plants for a variety
of situations.
2. Treatment systems based on Advanced Waste Treatment processes are far
superior to biological package plants for small flow situations because of
their stability of operation in the face of biologically toxic materials,
and significant load variations. In addition, reuseable water if required
can result from Advanced Waste Treatment processing.
3. Three general Advanced Waste Treatment based schemes of utility for
"small flows" have been discussed. The three schemes involve
a) clarification-carbon, b) ultrafiltration, c) chemical-biological
processing.
-------
CONCENTRATE RECYCLE WASTE SLUDGE
SCHEMATIC FLOW DIAGRAM OF A CLARIFICATION-POWDERED CARBON-ULTRAFILTRATION SYSTEM
(AFTER OAK RIDGE NATIONAL LABORATORY)
FIGURE 13
-------
35
4. Four specific systems which may have utility as "small flow"
treatment plants have been described in some detail. Preliminary
treatment performance from three is discussed.
5. Only one of these was specifically designed as a "small flow"
plant and probably none are ideal for such a purpose.
6. Extensive development and testing will be conducted in the future
to meet the needs for small flow plants.
-------
- 36 -
References
Bell, G. R., Llbby, D. V., and Lordi, D. T.,
"Phosphate Removal Using Chemical Coagulation and a
Continuous Countercurrent Filtration Process."
Final Report - FWQA Contract 14-12-154 (June 1970).
Kreissl, J. F., Clark, S. E., Cohen, J. M. and Alter, A. J.
"Advanced Waste Treatment and Alaska's North Slope."
Paper presented at the Cold Regions Engineering Symposium,
21st Alaska Science Conference, College, Alaska (August 1970).
Smith, R., "A Rational System for Assigning Research and
Development Priorities at the Advanced Waste Treatment
Research Laboratory, Cincinnati, Ohio."
Internal FWQA Report (September 1970).
-------
PHYSICAL - CHEMICAL TREATMENT
Jesse M. Cohen
I. INTRODUCTION
In recent years it has become apparent that conventional biological treat-
ment may not be the optimum solution to all waste treatment problems. There
have been numerous instances wherein the wastewater under consideration con-
tained non-degradable substances or materials which were deleterious to the
performance of biological systems. Operating difficulties, sludge handling
problems and large land area requirements are intrinsic to biological pro-c-
esses and have led to consideration of alternatives to the activated sludge
and trickling filter processes for so-called secondary treatment.
II. DESIRED EFFLUENT QUALITY
First of all, let us define what effluent quality we consider equivalent to
secondary effluent. It is fair to say that an effluent BOD of less than
10 mg/1, COD of less than 60 mg/1, and suspended solids of less than 10 sg/1,
could be considered good quality secondary effluent. It is clear then that
efficient removal of organic material and suspended solids are the major
functions of alternative processes for secondary treatment. With the current
interest in phosphorus removal for the control of eutrophication we should
also consider that function in the development of alternative processes.
III. THE CLARIFICATION-ADSORPTION PROCESS
The most promising combination of unit processes which will produce the
desired effluent quality at a reasonable cost appears to be chemical clari-
fication followed by adsorption on activated carbon. A simplified schematic
flow diagram of a typical coagulation-adsorption process is shown in Fig. 1.
A. Clarification
Here raw waste water, after screening and grit removal, is treated
with a coagulating chemical - lime, iron or aluminum compounds,
polyelectrolytes, or a combination thereof. Iron, alum and lime
are all excellent phosphorus precipitants. The dosed wastewater
is flocculated and clarified and the sludge from the clarification
system can be dewatered and disposed of, or in the case of lime,
can be recalcined for lime recovery if found to be economical.
Experience at Lake Tahoe^ on tertiary treatment with lime has
shown that no significant saving in chemical cost is achieved by
recalcining the lime sludge. However, sludge disposal costs are
reduced because only a fraction of the lime sludge must be bled
off to disposal to limit the buildup of inerts. Recalcined and
-------
- 2 -
reused lime has proven to be as effective as commercial lime in clari-
fication and phosphorus removal. Recovery schemes for iron and aluminum
sludges have not yet been developed and so the use of these coagulants
will probably be limited to smaller installations where coagulant recovery
would not be economical. Polyelectrolytes have been used on plant scale
to enhance primary clarification but they have no phosphorus removal
capability and thus their use as primary coagulants in new physical-
chemical processes will probably be limited. They do have the advantage
of minimizing increased sludge production.
Clarified waste can then be filtered - preferably by dual-media filtration -
or applied directly to carbon adsorption systems.
B. Carbon Adsorption
There are two general types of carbon adsorption systems, granular carbon
systems and powdered carbon systems. Of these granular carbon holds the
most promise but powdered carbon systems are also being investigated and
may find some application. In the common granular carbon systems being
considered, the clarified wastewater is passed through a bed of granular
activated carbon particles, usually 8x30 or 12x40 mesh, where organic
molecules are adsorbed on the carbon surfaces. At such time as the
capacity of the carbon to adsorb additional organic materials is decreased
to such an extent that the effluent COD increases to a predetermined limit
the carbon bed is removed from service. The spent carbon is transferred
to a thermal regeneration system where the adsorbed organics are volatil-
ized and driven off the carbon surface, and the adsorption capacity of
the carbon is thus restored.
In powdered carbon systems clarified wastewater is contacted with a
slurry of powdered activated carbon. The carbon is separated by floccu-
lation with polymers, followed by clarification and filtration. Powdered
carbon regeneration systems are in the development stage but several
appear promising. Until the regeneration of powdered carbon has been
successfully demonstrated granular carbon will be the adsorbant of choice.
C. Filtration
A dual-media filtration system could be utilized either before or after
the adsorption system for nearly complete removal of suspended solids.
The filtration system must follow powdered carbon adsorption systems
for complete removal of carbon particles.
-------
- 3 -
IV. PERFORMANCE OF PHYSICAL-CHEMICAL SYSTEMS
(2)
A. Pilot Plant Study
Only limited data have been generated in studying the combination
of processes discussed here. Under an FWPCA contract the FMC
Corporation performed a pilot-scale investigation of the coagulation-
adsorption process for treatment of primary effluent. One objective
of this study was a parallel comparison of adsorption in downflow
packed beds and upflow fluidized beds. Figure 2 shows a schematic
of the clarification system used. Primary effluent was fed to the
system at a rate of 5.5 gpm.
An average dose of 170 mg/1 FeCl^ was added, followed by two minutes
of mixing at 1500 rpm and 15 minutes of flocculation at 18 rpm.
Clarification was accomplished in a one-hour detention time upflow
clarifier. The clarifier effluent was filtered by an anthracite-
sand dual-media filter.
Clarified waste was applied to parallel sets of carbon columns,
one upflow fluidized bed and the other downflow packed bed as
shown in Figure 3. The rate was 5 gpm/sf in each column and the
empty bed contact time was 64 minutes. Figures A, 5, 6 and 7
show the results of the study. Considerable organic removal took
place in the clarification system. Final effluent TOC was around
5 mg/1, BOD around 5 mg/1, turbidity around 1 JTU and phosphate
2-3 rag/1 as P0^ (around 1 mg/1 as P).
(3)
B. Comparison of Carbon Adsorption and Activated Sludge
A comparison of carbon adsorption and activated sludge for the
removal of organic material from primary effluent was made over
a six-week period at Lebanon, Ohio. Settled and filtered primary
effluent was applied to granular carbon columns with a contact
time of 37 minutes. The carbon column effluents were compared
with sand-filtered secondary effluent from the 1 MGD activated
sludge plant at Lebanon. Table 2 shows that carbon adsorption
was more efficient in the removal of organics than activated sludge.
C. Development of a Full-Scale Installation
Several studies have been made utilizing polymer addition to exist-
ing primary plants followed by small-scale pilot carbon adsorption.
One such study was done at the 10 MGD primary facility at Rocky
River, 0hio(4). An anionic polymer was added to the existing
primary clarifier at a dosage of 0.3 mg/1, and a side stream of
-------
- 4 -
clarified effluent was applied to small carbon columns for a period
of about one month. The summary of the data is shown in Table 3.
It can be seen that, even with less than optimum clarification,
effluent comparable to good secondary effluent was produced with
33 minutes carbon contact time. On the basis of this preliminary
work the City of Rocky River applied for and was awarded a Research
and Development Grant from FWPCA to help support a full-scale investi-
gation of the clarification-adsorption process for secondary treatment.
One of the principal motivations for the city to use physical-
chemical treatment is shown in Figure 8. The installation of con-
ventional activated sludge facilities would necessitate the condem-
nation of a considerable area of very expensive property, whereas
a carbon adsorption system could easily fit into the existing site.
Testing has been undertaken to determine what coagulant or combination
of chemicals will be used in the clarification system. If phosphorus
removal is required an inorganic coagulant will necessarily be the
choice. Figure 9 shows the schematic flow diagram of the carbon
adsorption system to be constructed at Rocky River. In Table 4 the
last column shows the estimated treatment costs at Rocky River. The
total cost including amortization is estimated at 10c/1000 gal. The
makeup carbon cost is based on a carbon exhaustion rate of 500 lb/MG,
and 5% carbon loss per regeneration cycle. The chemical cost item is
for 0.3 mg/1 of anionic polymer which may or may not be used. The
capital cost of the proposed installation is estimated at $1.6 million.
There is other work going on in the investigation of such systems and before
too many years we will have the answers to some of the as yet unresolved
questions. The major question is, of course, how much does it cost? When
some full-scale systems have been in operation for a period of several years
this big question can be resolved.
References
1. Smith, C. £., "Recovery of Coagulant, Nitrogen Removal, and Carbon Regener-
ation in Waste Water Reclamation," Final Report, FWPCA Grant WPD-85(June 1967).
2. Weber, W. J. Jr., Hopkins, C. B., & Bloom, R. Jr., "Physiochemical Treat-
ment of Wastewater," Presented at the 42nd Ann. Conf. of the Water Pollution
Control Federation, Dallas, Texas, Oct. 1969.
3. Schwartz, W. A., Internal Report, AWTRL, FWPCA (1969).
4. Rizzo, J. L., and Schade, R. E., "Secondary Treatment with Granular
Activated Carbon," Water & Sew. Wks., 116, No. 8, pp.307 (1967).
-------
TABLE 1
DESIRED EFFLUENT QUALITY
BOD 10 MG/L
COD 60 MG/L
SS 10 MG/L
P 1 MG/L
-------
TABLE 2
COMPARISON OF PHYSICAL-CHEMICAL TREATMENT
TO BIOLOGICAL TREATMENT
AT LEBANON (8/21-10/3/69)
(Effluent quality, mg/L)
TOC
Total
Soluble
COD
Color
Turbi di ty
PRIMARY EFFLUENT
87.0
32.5
309
—
—
Settled
68.5
30.2
251
53
57
Dual-Media Filtered
49.0
26.7
186
45
23
CARBON EFFLUENT-S
11.7
7.3
57
28
13
CARBON EFFLUENT-F
8.3
5.5
48
26
6.6
SAND-FILTERED SECONDARY EFFLUENT
25.6
16,1
64
14
8.4
S - feed of settled primary effluent
F - feed of dual-media filtered primary effluent
-------
TABLE 3
Pocky River Waste Treatment Plant
Clarification/Carbon Process
Raw
Clarified
Carbon
Contact Time,
Minutes
Percent
Water
Water
h.l
1U
23.^
32.6
Suspended Solids, mg/l
107
65
31
13
15
7
93-3
BOD, mg/l
118
57
27
21
11
8
93-3
COD, mg/l
235
177
117
67
50
kk
81.3
TOC, mg/l
52
53
33
18
15
13
75
-------
TABLE 4
Capital And Operating Costs
Granular Carbon Adsorption
Pittsburgh Activated Lake Stocky
Carbon Co. Tahoe Poaona ftlver
Capacity, ngd 10 7.5 10 10
Investment ($1,000) 1,489 1,306 1,670 1,600
Operating Cost, (tf/1000 gal.)
Carbon 1.20 1.18 1.10 0.69
Fuel 0.11 0.25 0.12
Chemicals C.99 -=°- 3.80
Power 0.85 0. 75 0.85 0.55
Labor 0.74 0.40 1.50 1.10
Overhead 0.27 -••• •••• ••••
Amortization 3.07 3.53 4. 10 3.23
(20 yrs) (20 yrs) (15 yrs) (20 yr«)
Maintenance 0.63 0.33 0.50 0.55
Total Operating Cost 6.87 7.18 8.30 10.04
-------
FIGURE 1
FLOW DIAGRAM OF A PHYSICAL-CHEMICAL TREATMENT SYSTEM
COAGULANT
sj
I
-------
RAPID MIX
CHAMBER
FLOW DIAGRAM OF CLARIFICATION SYSTEM
FIGURE 2
-------
EXPERIMENTAL SET-UP FOR 24 FT CARBON BEDS
EXPANDED-BED ADSORBERS PACKED BED ADSORBERS
FIGURE 3
-------
150 200 250 300
VOLUME TREATED 1000 GALLONS
450
TREATMENT OF PRIMARY EFFLUENT BY CLAR.FICATION AND ACTIVATED
CARBON IN EXPANDED BEDS figure 4
-------
figure 5. REMOVAL OF BOO FROM PRIMARY
EFFLUENT BY CHEMICAL CLARIFICA-
TION AND 24 FT. ACTIVATED CARSON
-------
40
z>
»-
->
#•
>
h-
30
o
GD
% 20
h
CLARIFIED PRIMARY
EFFLUENT
V
EXPANDED BEDS
PACKED BEDS
MAY I JUNE I JULY I AUG
FIGURE 6. REMOVAL OF TURBIDITY FROM PRIMARY EFFLUENT BY
CHEMICAL CLARIFICATION AND ACTIVATED CARBON BEDS
-------
REMOVAL OF PHOSPHATE FROM PRIMARY EFFLUENT
BY CHEMICAL CLARIFICATION AND 24 FT ACTIVATED
CARBON FIGURE 7.
-------
Area
companion for
darification/ea r-
bon procon vj
activated iludgo
plant at Rocty
Rirer.
EXlSTNC SEv.AGE
TREATMENT PLANT
PROPERTY
r^\rr~^
aerated
LANO AREA REQU1 RE'/E NT FOR
PROPOSED CAROON COLUMN PLANT
PROPOSED PROPERTY
ACQUISITION' FOn ACTIVATED
SLUDGE PROCESS
APPROX 26 ACRES
Carson X\".,.
''A
I iCHLCPi'.E ,0
' I CONTACT 'A
j A
UCRlG PLANW
ir . 'A
£ ^ ^
X'.J \ /
v—X
I / r '/ \ ' \ A
! vl
-------
Granular carbon adsorption for waste treatment
FIGURE 9
-------
SOLIDS REMOVAL PROCESSES
Sidney A. Hannah
If one were to rank wastewater treatment operations in order of overall
importance, separation of solids from liquids would probably assume major
importance. This operation may be required to remove objectionable
components from a waste, to render the waste more amenable to subsequent
treatment or disposal, or to support another treatment operation.
SEDIMENTATION
Sedimentation tanks are employed for various applications which have one
common objective - the removal of solid matter from a flowing liquid.
The solid matter may have been present in direct suspension, such as in
municipal sewage, or may alternatively be a precipitate resulting from
prior chemical treatment, such as lime precipitation or alum or iron
coagulation.
Horizontal Plow Design
The principal basis of the earliest designs of horizontal-flow sedimen-
tation tank was the "retention time". The objective was to move water
so slowly through the tank that there would be ample time for settlement.
The nominal detention period allowed was usually more than four hours.
However, each drop of water did not take the same time to travel from
inlet to outlet, since some degree of "short-circuiting" was bound to
occur. In fact, a typical pattern of flow under ideal conditions in an
elementary design of a horizontal-flow tank is represented by Fig. 1.
Diagram (a), solid line, represents the most favored flow-path, while
the dotted lines indicate typical eddies which are induced in the remain-
der of the tank volume. Diagrams (b) and (c) represent the flows which
result, respectively, to entering water being warmer or colder than the
water in the tank.
The basic design which has been most widely used for sewage treatment is
a tank circular in plan. The inflow is introduced at the center of the
tank and the outflow is collected at a peripheral launder. As the general
direction of flow is mainly a radial spread from the center, it is reason-
able to regard this design as in the horizontal-flow category.
-------
- 2 -
(«)
y \Ss/ v2f
(»)
y$7 \Xj V: 7 \^>/ \
A*' \l / \v # ^
(O
fifwrc I—iedimentation tank of horizontal-flow typt undof difftrtnt condition* of rtlotito tm^nlWl.
-------
- 3 -
Vertical-Upflow Design
The improved performance obtained in upflow tanks has led to a variety
of new designs, incorporating variants of the upflow principle. These
new designs are designated by various proprietary names - Accelator,
Clarifow, FLocsettler, Reactor-Clarifier, etc. One of the earliest of
the upflow tanks was the Spaulding Precipitator, shown in Fig. 2. In
this design, the flow is introduced into the center of the tank and
flows upward through a blanket of previously formed solids.
The principal advantages of the upflow versus the horizontal tanks are
(1) improved flow control, and (2) sludge blanket effect. Salt-injection
tests performed on a variety of tank designs clearly show the superior
efficiency of the upflow principle in the matter of flow control. The
radial-flow still largely used in sewage treatment is distinctly inferior,
being subject to short-circuiting.
Tube and Lamella Settlers
In an ideal settling basin, as defined by Camp, the paths of all discrete
particles will be straight lines, and all particles with the same settling
velocity will move in parallel paths. The settling pattern shown in Fig. 3
would be the same for all longitudinal sections. It is apparent from this
that as the interval (h) is reduced, the size of the basin required to
remove a given percentage of the incoming settleable material decreases.
Many devices have been proposed since this principle was first proposed
by Hazen in 1904- and further developed by Camp in 194-6. None of the
proposed devices were accepted commercially until the recent introduction
of the device called the tube settler. These consist essentially of
closely packed rnnaH diameter tubes, 1-4- inches in diameter and 2-4 feet
in length, inclined at some angle to provide for removal of sludge as the
water flows upward through the tubes. Detention times are in the order of
6 minutes and less. The tubes provide as much as 24 hours of sludge stor-
age, depending of course, on the amount of suspended solids, and sludge
is readily removed by gravity drainage. A schematic diagram of the tube
settler integrated into a complete clarification device which consists
of coagulation-flocculation, a tube settler unit and a mixed media filter
is shown in Fig. 4. More recently, a device consisting of parallel plates
rather than tubes has become available. The device is called a "1*^11^.
*low is co-current in contrast to the countercurrent flow of the tube
settlers. The plate arrangement in a tank is shown in Fig. 5.
-------
- 4 -
Drain
"LJ"
FIG. 2 —SpaMing frtc^Mattr
-------
-- 5 -
Surface Area A
Direction of Fiow Q
L-
¦H
Lo
V
Vo
^4
J
fig. 3 Idealized Settling Paths of Dis-
crete Particles in a Horizontal Flow Tank
-------
^tiyttectroiyte
Alum
Raw Water
Finished Water
Fig. 4. Schematic Diagram of Apparatus Used la Pleld Tests of Tnbe Settler
-------
-------
- 8 -
DISSOLVED AIR FLOTATION
The use of dissolved air to float suspended solids was first used in
industrial operations. In recent years, the process has been adapted
to domestic wastewater and particularly to sludge thickening. The
process achieves the separation of suspended particles by attachment
of gas bubbles to the suspended particles, thereby reducing the effective
specific gravity of the particles to less than that of the water.
A. A flotation system using the pressurization and de-pressurization
sequence consists of the following elements (Fig. 6).
1. Pressurizing pump
2. Air injection facilities
3. Retention tank or contact vessel
U' Back-pressure regulating device
5. Flotation device
6. Facility for addition of chemicals if needed
B. Advantages and Disadvantages
1. Much reduced retention time - 10-20 minutes
2. Greater solids concentration in float than in settled sludge
3. Greater efficiency of solids recovery
4-. Offers mechanical control over the process
5. Increased cost of operation for pumping, etc.
6. Need to remove top and bottom solids
SCREENING DEVICES
Microscreening is a fonn of simple filtration by straining (Fig. 7).
These mechanical filters consist of a rotary drum which revolves on a
horizontal axis. The peripheral surface of the drum is covered with
a stainless steel fabric. The effectiveness of the woven mesh screen
for retaining fine particles is dependent on the size of the openings
in the screen and on the pattern of the weave. Influent enters the
open end of the drum and is filtered through the fabric with the inter-
cepted solids being retained on the inside surface of the fabric. As
the drum rotates, the solids are transported and continuously removed
at the top of the drum by pumping strained effluent, under pressure,
through a series of spray nozzles which extend the length of the drum.
The solids and wash water are collected in a central trough within the
drum and discharged through a hollow axle. The microstraining device
is available in several unit sizes ranging from 51 in diameter and l1
width with a capacity of 0.05 to 0.5 mgd to 101 diameter and 10* wide
with a capacity of 3-10 mgd.
GPO 621-371-7
-------
- 9 -
Bopreoaurlzed Portion of Peed
-Flow by Gravity
Portloo of
Peed vblch has
b«eo pressurized
Back Pr«siur<}
~*lv«
'Uapresaurlzod Peed
-Effluent
Partial Pressurizatioo of Feed
Preseurl-
sat loo
Sequeoco
Partial Prensurlzatloo of Effluent
Methods employed for partial and total pressurizations.
Figure 6
-------
Fig. 1 Typical Microstrainer Unit
Not Shown
Wastewater Hopper
Ultra-violet Lamp
Wash-water Pump
1. Drive Unit
2. Rotating Drum
3. Wash-water Jets
4. Micro-fabric
5. Influent Chamber
6. Effluent Chamber
7. Effluent Weir
-------
- 11 -
Microscreening devices have found their greatest application to treat-
ment of river waters, information on their performance on wastewaters
is quite scarce. The effect of aperture size on removal efficiencies and
flow rate is shown below.
Fabric
Mark 0 (23 microns)
Mark 1 (35 microns)
Removal Efficiency
Solids BOD
70-80$
50-60$
60-70$
4.0-50$
Flow
gals/hr/ft2
400
600
The advantages of microstraining are the low initial capital cost and
ease of operation. The disadvantages are the incomplete solids removal
and the inability to handle solids fluctuations.
Capital and Operating Costs
The capital and operating costs associated with-microstraining have been
prepared by Smith and are shown in Fig. 8. For a 10 mgd plant, total cost
for microstraining is calculated to cost about 1.5^/1000 gallon.
In-Depth Filtration
In-depth filtration is the passage of a fluid through a bed of granular
media designed to permit the captured particles to be retained within
the filter. The degree of penetration and solids removal efficiency can
be altered by changing the size and character of the particulates to be
removed as well as the size and composition of the filter media itself.
A basic prerequisite for the operation of rapid sand filters is that good
coagulation and flocculation must be obtained. Barring adequate pretreat-
ment of the wastewater, filtration efficiency is decreased as evidenced
by "breakthrough" of floe. With good pretreatment by coagulation, higher
filtration rates are attainable while still maintaining clarity of the
effluent.
It is beyond the scope of this talk to discuss the subject of coagulation
and flocculation. A variety of coagulants and flocculants are available
including various salts of aluminum' and iron, lime and organic polymeric
flocculants. The former inorganic salts, in the proper dosages can also
provide for precipitation of phosphate in addition to clarification.
-------
- 12 -
mc*osiPAmw or oookmpt oruaorr
capital Coat. Operating % (fcintaaane* ?oat. Dvbt Sr*le#
fiNlfn O^tclty
1-0 10.0 100.
D»al«a (Opacity, allltona of «*Uon« ytr toy
0.10
0.101
1
*
I
«¦*
*
i
C • Capital Coat, alllton* of dollars
A • Drfet Hrvlca. canta per 1000 5 jrr.)
Old' Operating and Itelatananca foot, canta par 1000 ^alloaa
T • Total fraaiiat Coat, carta par 1000 *allona
FIG. 8
-------
- 13 -
In the past 70 or 80 years there has been a gradual improvement in the
basic process of media filtration. Some of the earlier work centered
on increasing the filtration rates of slow sand filters to the modern
rapid sand filter rates. Various cleaning methods were also developed
including backwashing and surface scouring. More recently, the engineer-
ing advances have been concerned with modifications of filter media that
would allow greater production of high quality water from a given filter
area.
The evolution of filter design is illustrated in Fig. 9. The cross-
section shown at the top represents the rapid-sand filter which is in
common use in many filter plants today. Typical effective size of the
media used is 0.5 mm although effective sizes from 0.35 to 1.0 mm have
been used. During filter backwashing, the sand grades hydraulically
with the finest particles rising to the top of the bed. As a result,
most of the material removed by the filter is removed at very near the
surface of the bed. Only a small part of the total voids in the bed
are used to store particulates and headloss increases very rapidly.
When secondary effluent is being processed, the high solids concentration
will blind the surface in a very short time. As much as 75-95% of the
headloss, under these conditions, will occur at the upper 1-inch layer
of the filter. Filter runs will be so short as to be prohibitive. Further,
floe breaking through the topmost layers, have increased opportunity to
pass through the entire filter since voids become increasingly larger with
increase in depth.
One approach to increasing the effective filter depth is the use of a
dual media bed using a discrete layer of coarse coal above a layer of
fine sand. The filter provides basically a two-layer effect to achieve
increased penetration of particles. The amount of sand is reduced to
afford lower headlosses at the higher throughput rates used. Normally,
such a bed is designed so that 24- inches of anthracite coal, with a
nominal size of about 1 mm, overlays a 6 inch sand layer with a size of
about 0.45 mm- Hydraulic stratification still occurs following back-
washing but the difference of specific gravity is such that the larger
coal remains on top of the sand. The bulk of filtration is accomplished
in the*upper layers of the coal and at the top inch or two of the sand
bed.
With low applied turbidities and constant rate operation, the coal-sand
media bed has demonstrated an ability to operate in the range of
4.-5 gal/min/sq/ft of filter surface area. A defect in this design is
that if a flow change occurs, the particles held in the relatively large
void volume of a coal bed, can become dislodged and will be captured by
the fine layer of sand and the filtration run would have to be terminated
either because of high head loss at the coal-sand interface or because of
breakthrough of particles through the relatively shallow sand bed. This
design, then, presents a serious inconsistency in design.
Ideally, the effluent should pass through as fine a filter material as
is feasible. This ideal design is illustrated in the bottom cross-
section of a filter uniformly graded from coarse to fine from top to bottom.
-------
- u -
Ptgur* 1
C r oao- S«c 11 on Through
Slngla-Madl* ltd
Such m Conventional.
Rapid Send Plltar
drain also
Flgur* 2
Croa»-Section Through
Dual thdl« ted
CottM Coal Abova
Fin* Sand
I
drain else
Vigor* 3
CroM-Sscclofl Through
Id««l Filttr
Unlforaly Cr«4*d Froo
CoarM to F1m
Fron Top to BoCtea
drain »1m
FIG. 9
-------
- 15 -
One solution is the use of three materials of differing specific gravity
of such size gradation that some intermixing of the materials occur at
the interfaces of the bed layers. The third media material is garnet
which has a specific gravity of about 4.2. An ideal filter bed, then,
would consist of about 60$ of anthracite with a size of 1.0 to 1.5 mm at
the top, 30$ sand with a size of 0-4. to 0.5 mm at the middle and 10% of
garnet with a size of about 0.15 mm. The materials are so sized that
intermixing occurs at the interfaces. In this ideal filter, the effluent
is passed through increasingly finer media. The uniform decrease in media
particle size with filter depth allows the entire filter depth to be used
for floe removal and storage.
Cost of the filtration step is shown in Fig. 10. For a 10 mgd plant this
cost amounts to about 3.5^/1000 gallon, when operating the filter at
4 gpm/sq ft. Further economy, of course, can be obtained at higher rates.
Rates as high as 6-8 gpm/sq ft have been shown to be feasible when proper
pretreatment of coagulation-flocculation followed by sedimentation is
practiced.
Moving Bed Filter Technique
A new filtering technique has been evaluated by Johns-Manville under
contract with FWQA. The technique is designed to overcome the problem
of surface clogging and to achieve what is obtainable by multi-media
filtration. A schematic diagram of the moving bed filter is shown in
Fig. 11.
The unit is basically a sand filter. Particulate matter is removed as
the water passes through the sand (0.6 to 0.8 mm). As the filter surface
becomes, clogged, the filter media is moved forward by means of a mechan-
cal diaphragm. The clogged filter surface is removed either hydraulically
or, as shown, mechanically thereby exposing a clean filter surface. The
sand and accumulated sludge is collected and washed. The sand is returned
via a hopper to the base of the bed. The unit is thus a form of counter-
current extraction device feeding sand countercurrent to the water being
filtered. The moving bed filter has a renewable filter surface analogous
to the microstrainer and the advantage of depth filtration comparable'to
the coarse media filter. The unit does not have to be taken off-stream
for backwashing. In theory, 1% of the filter is being backwashed 100$
of the time compared to the conventional practice of backwashing 100$ of
the filter 1$ of the time.
Several pilot MBF units have been built to date and used to treat settled
and non-settled trickling filter effluents and primary effluent. The
system lends itself well to the use of chemical aids ahead of filtration
because of designed flexibility to handle high solids loadings.
-------
10.
£ l.o
o.i
Figure 10
FILTRATION THROUGH SAND OR GRADED MEDIA - 4GFM/SQ F71
Capital Cost, Operating & Maintenance Cost, Debt Service
vs.
Design Capacity
10.0
Design Capacity, millions of gallons per day
.01
100.
1.0
(0
fi
a
0.1
o
•o
w
c
o
•p
w
o
o
-------
BASIC CONCEPT OF MOVING BED FILTER
INFLUENT
CHEMICALS
(OPTIONAL)
FEED
HOPPER
DIAPHRAGM
HYDRAULIC
SYSTEM
SAND
P~rEcycle
WASH
WATER
EDUCTOR
SLUDGE
WASTE
SLUDGE
5
O
<—\
6
ra
H
H
I
-------
- 18 -
Fig. 12 shows some data with the MBF treating non-settled trickling
filter effluent with various dosages of alum and coagulant aid., Product
quality was maintained at about 10 BOD while being fed an influent with
a widely varying BOD content of =¦ 4-0 to as high as 180 BOD.
It is too premature to talk about cost of this method of filtration.
Design and performance information developed from these pilot units
will be used to obtain these costs.
ULTRAFILTRATION
One of the newest unit processes to separate solids from liquids is the
operation known as ultrafiltration. While this method has been under
development over the past 10 years, it is only within the past two-
three years that has seen the commercial development of this process.
Ultrafiltration is closely related to reverse osmosis with the distinction
generally made on the basis of size of particle separated. Reverse osmosis
removes all molecular sizes including inorganic salts. Ultrafiltration
generally will not separate molecules smaller than ^500-1000 MW, thus
inorganic salts are not separated from solution. Ultrafiltration uses
pressures of about 50 psi in contrast to reverse osmosis where pressures
in excess of 500 psi are generally used.
Membrane ultrafiltration is a pressure activated process using semi-
permeable membranes which act as molecular screens to separate molecular
and colloidal materials dissolved or suspended in a liquid phase.
Thus far, the principal commercial applications of the process have been
in (l) industrial operations where valuable products can be recovered by
separation from a bulk solution, (2) analytical application which provides
a new method to separate molecules according to size and molecular weight,
and (3) in a package waste treatment plant which separates mixed-liquor
solids from a biological reactor. Solids are returned to the aerator and
clarified product water is discharged.
A plant employing ultrafiltration has been installed on Pikes Peak to
provide waste treatment and water reuse. The essentials of the process
are shown in Fig. 13. The 15,000 gpd plant treats wastewater by high-
solids activated sludge. The solids are separated in an ultrafiltration
unit. Solids are returned to the aerator. Product water is excellent.
Some typical removals are shown below.
-------
EFFLUENT
SAMPLI NG
-------
ENZYME REACTOR
CONCENTRATE
PUMP
FIG. 13 REACTION SYSTEM
-------
- 21 -
Removals by Activated Sludge and Ultrafiltration
Influent
Effluent
% Removal
BOD
382
<1
>99
COD
678
20
97
Turbidity
-
<0.1
-
SS
323
0
100
P0.-P
12.2
7.7
37
These results emphasize that only molecules or particles greater than
500-1000 MW are separated. Inorganic ions such as phosphate are nttt
retained. The 31% reduction of phosphate was due to biological uptake
in cells which were removed.
-------
- 22 -
REFERENCES
Evans, G. R., "Microstraining Tests on Trickling Filter Effluents
in the Clear Creek Watershed Area, Texas," Public Works, October 1965).
Bodien, D. G., and Stenburg, R. L., "Microscreening of Effluent from
a Municipal Activated Sludge Treatment Plant," Water and Wastes Eng.,
(September 1966).
Truesdale, G. A., Birkbeck, A. E., and Shaw, D., "A Critical Examina-
tion of Some Methods of Further Treatment of Effluents from Percolat-
ing Filters," Conference Paper No. 4, Water Pollution Research
Laboratory, Stevenage, England (July 1963).
Diaper, E. W., "Microstraining and Ozonation of Sewage Effluents,"
Presented at the 41st Annual Conference of the WPCF, Chicago,
Illinois ( September 1968).
Truesdale, G. A., and Birkbeck, A. E., "Tertiary Treatment of Activated
Sludge Effluent," Reprint No. 520, Water Pollution Research Laboratory,
Stevenage, Herts, England (1967).
Smith, R., "Cost of Conventional and Advanced Treatment of Wastewaters,"
Jour. Water Pollution Control Federation, 40, 1546-;574 (September 1968).
Rich, Linvil G., Unit Operations of Sanitary Engineering, John Wiley
and Sons, Inc., New York, 1961.
Camp, T. R., and Stein, P. C., "Velocity Gradients and Internal Works
in Fluid Motion," Jour. Boston Soc. Civ. Engrs., 30, 219 (1943).
Robeck, G. G., "High Rate Filtration Study at Gaffney, South Carolina,
Water Plant," USPHS, R. A. Taft Sanitary Engineering Center,
Cincinnati, Ohio (1963).
Craft, T. F., "Review of Rapid Sand Filtration Theory," JAWWA, p.428-439,
April 1966.
O'Melia, Charles R., and Crapps, David K. , "Some Chemical Aspects of
Rapid Sand Filtration, JAWWA, 56, 1326 (1964).
Hudson, H. E., Jr., "Physical Aspects of Flocculation," JAWWA,July 1965.
Gurnham, C. F., Industrial Wastewater Control, Academic Press,Inc.,
New York 1965
-------
- 23 -
Katz, W. J., and Wullschleger, R., "Studies of Some Variables Which
Affect Chemical Flocculation When Used with Dissolved-Air Flotation,"
Proc. 12th Purdue Industrial Waste Conference (1957).
van Vuuren, L. R. J., et al., "Dispersed Air Flocculation/Flotation
for Stripping of Organic Pollutants from Effluents," Water Research,
P^rgamon Press, _2, 177-183 (1968).
Vrablik. E» R., "Fundamental Principles of Dissolved-Air Flotation of
Industrial Wastes," Proc. 14th Purdue Industrial Waste Conference (1959).
MLchaels, A. S., "New Separation Technique for the CPI," Chemical
Engineering Progress, 64, December 1968.
Weissman, B. J., Smith, C. V. Jr., and Okey, R. W./'Performance of
Membrane Systems in Treating Water and Sewage," Water - 1968, 64,
Chemical Engineering Progress Symposium Series.
Hohanka, S. S., "Multilayer Filtration," JAWWA, 61, 504-511 (Oct. 1969).
Ives, K. J., and Gregory, J., "Basic Concepts of Filtration,"
Proc. Society for Water Treatment & Examination, 16, Part 3 (1967).
Boby, W. M. T., and Alpe, G.', "Practical Experiences Using Upward
Flow Filtration," Proc. Society for Water Treatment & Examination,
16, Part 3 (1967).
Rimer, A. E., "Filtration Through a Trimedia Filter," Jour. San Eng.Div.,
ASCE, SA 3, June 1968.
-------
DEMINERALIZATION OF WASTEWATERS
Jesse M. Cohen
I. Introduction
A. Today's best conventional waste treatment processes were not
designed to remove non-biologically degradable organics or inorganic
salts. It appears certain that improved wastewater treatment will
be based on the addition of physical-chemical separation processes
to the current biological processes.
B. Degree of treatment required of a renovation process will be
determined by the specific purpose for which the water is intended.
C. For certain industrial use and tor deliberate municipal recycle,
it will be essential to reduce the salt content of wastewater.
D. Need for demineralization is based on the fact that each water-
use cycle results in an incremental addition of dissolved inorganic
salts.
1. Average values for mineral increments through one municipal
use are shown in Figure 1.
2. Increase of total dissolved solids ranges 100-500 mg/1.
3. Most important increments, in terms of magnitude, are
sodium, sulfate, bicarbonate, and chloride.
E. Three principal methods are in varying stages of development
designed to restore the mineral quality of sewage effluent to at
least the quality of river water or better.
1. Electrodialysis
2. Reverse Osmosis
3. Ion Exchange
II. Electrodialysis
Electrodialysis is useful for partial demineralization of low mineralized
waters, preferably not exceeding 2000 mg/1 of TDS. Since municipal waste-
waters generally do not exceed 1000 mg/1, this process is applicable.
GPO 021-371-8
-------
- 2 -
A. Principles
1. Principle of operation of an electrodialysis unit is shown
in Figure 2. When a direct electric voltage is impressed across
a cell containing mineralized water, the positively charged ions
(cations) migrate to the negative electrode and the negatively
charged ions (anions) migrate to the positive electrode. If
cation and anion-permeable membranes are placed alternately
between the electrodes, alternate compartments become more con-
centrated in salts while the intervening compartments become
more dilute.
2. Multiple compartments can be interconnected by manifolds
which produce two products, one low in dissolved solids, one
concentrated. Figure 3.
3. Membranes are composed of ion-exchange materials. The
driving force for the migration of ions from solution to the
membranes is electrical energy.
B. Operating problems
1. Stagnant films at the membrane surfaces lead to concentration
gradients producing scaling from precipitation of compounds with
low solubility.
2. Electrolysis of water, which produces hydrogen and hydroxyl
ions, leading to increases in power consumption.
3. Deposition of colloidal negatively charged particles on the
anion membrane causing fouling and decrease in demineralization.
C. Pilot plant operation
1. Experimental electrodialysis equipment was investigated,
Figure 4, with the following conclusions:
a. To maintain operation, the secondary effluent had to be
pretreated for removal of organics by activated carbon and
clarified by alum coagulation,
b. pH of the concentrate stream was held at 5 or less to
prevent calcium carbonate scale formation,
c. Operation was very sensitive to fouling by colloids.
Figure 5.
-------
- 3 -
(1) Extended operation could be maintained only by
reducing turbidity to 0.03 JTU. Higher turbidities
produced short runs.
(2) Biological growth on the membranes contributed
to fouling.
(3) Recovery from fouling could be obtained by shutting
down for a day or so.
d. Blow-down amounted to about 10% of the product to
prevent scaling.
2. Electrodialysis removes ions to varying degrees. Figure 6.
a. Selectivity for ions varies with time and with degree
of fouling. Both phosphate and sulfate removal rates were
affected.
3. Volume of waste concentrate will amount to = 10% of product
and methods for disposal of this concentrated waste must be found.
4. Firm costs for electrodialysis are not available» For a
10 mgd plant, capital cost to produce partially demineralized
water from wastewater has been estimated at 0.34 dollars per
gallon per day and operating costs at 16.1 cents per 1000 gallons.
No provision is made in these costs for pretreatment and disposal
of brine.
III. Reverse Osmosis
The theoretical capability of reverse osmosis to remove in excess of 90%
of the inorganic ions, organic matter and colloids (bacteria and virus)
makes this process an important discovery.
A. Principles
1. Figure 7. In normal osmosis when two liquids of differing
salt concentrations are separated by a semi-permeable membrane,
water will flow from the dilute solution to the more concentrated.
Driving force is the concentration gradient.
2. In reverse osmosis pressure, in excess of the osmotic pressure,
is applied to the concentrated side causing the normal flow of
water to be reversed; i.e., from the concentrated to the dilute
side of the membrane.
-------
- 4 -
3. Keys to the successful application of reverse osmosis to
wastewater reclamation are:
a. Development of a membrane capable oY reasonable service
under operating conditions,
b. Proper incorporation of the membranes into a system to
maximize product flow at minimum cost.
B. Membranes
1. Practical reverse osmosis was achieved when Loeb and
Sourirajan in 1960 developed a modified cellulose acetate
membrane capable of water permeabilities some 500 times greater
than earlier films.
2. Membranes consist of two distinct layers. One a spongy
porous material which accounts for 99.8% of the thickness and
an active layer which accounts for all of the separation of
contaminants. Figure 8. Surface layer is typically 0.25y
thick, porous layer 100y thick.
3. Original theory of operation considered a "straining"
mechanism. Current theory is that water molecules dissolve in
the membrane material and then diffuse through it. Inorganic
ions have lesser solubility in the membrane and have restricted
mobility.
C. Water throughput-flux
1. Flux is defined as the flow of water through a membrane,
measured in gallons per square foot per day.
2. Flux is directly proportional to applied pressure - minus
the osmotic pressure - and inversely proportional to thickness of
membrane.
3. Relationship of pressure and salt rejection (solute retention)
are shown in Figure 9.
a. At low pressures, low flows and little salt removals
are obtained,
b. As pressure exceeds osmotic pressure, flow and salt rejection
increase and 100% salt rejection is approached asymptotically.
-------
- 5 -
4. Fluxes in the range of 20-40 gfd are required to make R0
economically attractive. Current fluxes of «= 10 gfd at 750 psi
are common.
5. A major current problem is the inability to maintain flux
because of fouling and chemical and physical changes that occur
in the membrane.
D. Materials rejected
1. Inorganic salts are rejected in amounts exceeding 90%.
2. Organic molecules, with the exception of certain low molecular
weight materials like amines, alcohols and acids, are removed.
3. Suspended and colloidal materials including bacteria, virus
and sewage colloids are completely removed.
E. Membrane separator design
A key factor in practical operation of R0 is the mechanical design
of the unit.
1. Plate and frame, using flat membrane sheets in a device similar
to a filter press was one of the earliest designs. Figure 10.
a. Units capable of producing 100,000 gal/day have been
developed by Aerojet-General. Largely used for brackish
water treatment.
2. A simple tubular design consists of porous tubes which are
lined with cellulose acetate membranes. Design is similar to
heat exchangers. Flow is from inside the tubes at pressure and
discharged from the outside surfaces of the tubes at ambient
"pressure. Figure 11.
3. To obtain a maximum of membrane area in a small volume,
a "spiral-wound" design was developed by General Atomics. Several
hundred feet of membrane can be accommodated in a cubic foot of
pressure vessel volume. Figure 12.
4. The ultimate in greatest area per unit volume is approached
by "hoilow-fiber" design,
a. About 20 million hollow fibers can be packed into a
shell 1 foot in diameter and 7 feet long.
-------
- 6 -
b. A 12-inch permeater 7 feet long contained in a unit
only 5.5 cu.ft. in volume provides about 50,000 square feet
of membrane surface and will produce 7500 gal/day.
c. Flux with these fibers is small - currently about 0.15
gal/ft /day. Fluxes of 1.5 gfd may be attainable but this
will still be 1/10 that obtainable with other designs.
d. This configuration can be characterized as "very high
surface area, low flux permeater."
F. Cost
Application of RO to wastewater is still in early stage of development.
1. Based on experience in treating brackish water, cost estimates
have ranged from 30-60 cents/1000 gallons.
2. These problems remain to be solved before R0 can be success-
fully applied to wastewater.
a. Increased fluxes.
b. Maintenance of flux in the face of fouling and physical
and chemical changes occurring at the membrane.
c. Increased product to waste ratios. Up to 90% has been
obtained.
d. Disposal of concentrate.
IV. Ion Exchange
Ion exchange has been used for many years in water treatment for softening
and boiler water conditioning. Development of newer types of resins which
are not fouled by organics and newer techniques of using these resins
demonstrate that ion exchange is a practical method for demineralization
of wastewater.
A. Principle
1. Ion exchange materials, both natural and synthetic, are
absorbents which carry charged ionic groups. To maintain
electroneutrality, each ionic site must have associated with it
an ion of opposite charge (counter-ion). The success of ion
exchange depends on the ability of the counter-ion to be replaced
or exchanged for another ion of the same charge.
2. When all counter-ions have been replaced, the ion exchange
material is exhausted. Regeneration is obtained by contacting
the exchanger with a concentrated solution of the original
counter-ion.
-------
- 7 -
B. Classification
1. Ion exchangers are classified by the charge of the exchangeable
ion. Tfous acid or cationic resins will exchange cations like Ca
and Mg and base or anionic resins will exchange OH or CI anions.
2. Classification also considers the degree of dissociability
of the active group. Thus:
a. Strong acid resins (cationic) contain sulfonic acid groups.
b. Weak acid resins (cationic) contain carboxyl or phenolic
groups.
c. Strong base resins (anionic) carry quaternary ammonium
groups .
d. Weak base resins (anionic) usually have amine groups which
are only slightly ionized in the OH form.
3. A common matrix material of synthetic resins is styrene or
vinyl benzene which has been polymerized and which have ranging
functional groups attached. Figure 13.
a. A very wide variety of resins can be prepared to meet
specific needs by varying functional groups, degree of
ionization, and physical characteristics.
C. Selectivity
1. A general purpose resin will exchange any of the common ions
but, in a mixture of ions, selectivity will occur.
a. For strong cation exchangers the order of selectivity is
Ca"^ < K+ < NHj < Na+
b. For weak anion exchangers the order of selectivity is
S0£ < HFO^
-------
- 8 -
a. Capability of regeneration at theoretical efficiencies
using low cost acids and bases.
b. High operating exchange capacities.
c. Ease of removal of regeneration chemicals with a
minimum of rinse water.
d. Long life of resin to physical and chemical attrition.
e. Waste regenerants should pose a minimum disposal problem.
E. Desal process developed by Rohm and Haas has promise for economic
demineralization of wastewater.
1. One modification consists of a 3-bed design consisting of a
weak anion, a weak cation and a weak anion exchanger in series.
Figure 14.
a. First column converts all anions to the bicarbonate form.
Removes all other anions.
b. Second column converts bicarbonates to CO^ and removes
cations.
c. Third column in OH form absorbs to become the
bicarbonate form. This column then becomes the first in
the series after columns 1 and 2 have been regenerated with
ammonium hydroxide and sulfuric acid respectively.
2. A modification more applicable to wastewater treatment is
shown in Figure 15.
a. Weak anion exchanger, in the bicarbonate form, removes
all anions: SO?, POT, NO- and CI".
b 4 3
b. Column effluent is polymer flocculated, C02 removed and
lime softened which removes: suspended solids, Ca**, Mg4-1",
and Fe111.
c. Final column, a weak cation exchanger, removes remaining
cations: NH^, Na+ and K+.
d. Exchangers regenerated with ammonium hydroxide and
sulfuric acid. Calcining of lime would provide C0£ for
conversion of anion exchanger to bicarbonate form.
-------
- 9 -
e. About one-half of the COD is removed by the anion
exchanger and quantitatively removed by the regenerant.
f. Final product, containing residual amounts of inorganic
solids - = 50 ppm - and 1/2 of the original COD, could be
blended with undemineralized water to reduce cost.
F. Cost
Process has not been applied on a sufficiently large scale to obtain
reliable cost data.
1. Estimate for 1 and 10 mgd plants, including capitalization,
equipment and chemical costs for the modified Desal process is
17-18 cents/1000 gallon.
a. CO2 is assumed to be available.
b. Resin life estimated to 3 years.
c. No costs included for ammonium recovery and brine disposal.
-------
10 -
REFERENCES
Electrodialysis
Wilson, J. R., "Demineralization by Electrodialysis," Butterworths
Scientific Publications, London, 1960.
Smith, J. D., Eisenmann, J. L., "Electrodialysis in Advanced Waste
Treatment," Water Pollution Control Research Series Publication
No. WP-20-AWTR-18.
Brunner, C. A., "Pilot Plant Experiences in Demineralization of
Secondary Effluent Using Electrodialysis," presented at the 39th
Annual Conference of the Water Pollution Control Federation, Kansas
City, Missouri, September 1966.
Calvit, B. W., Sloan, J. J., "Operation Experience of the Webster,
South Dakota, Electrodialysis Plant," presented at the First Inter-
national Symposium on Water Desalination, Washington, D. C.,
October 1965.
Gillilard, E. R., "The Current Economics of Electrodialysis," pre-
sented at the First International Symposium on Water Desalination,
Washington, D. C., October 1965.
Farrell, J. B., Smith, R. N., Ind. Eng. Chem., 54, No. 6, 29-35 (1962)
Dubey, G. A., et al. TAPPI, 48, 95 (1965).
Mason, E. A. Kirkham, T. A., Chem. Eng. Prog. Symposium Series, 55, No
173 (1959).
Mintz, M. S., Ind. Eng. Chem., J55, No. 6, 19 (1963).
Solt, G. S., Wegelin, E., and Chapman, C. V. G., "Electrodialysis as a
Unit Operation," British Chemical Engineering, July 1963.
Dasare, B. D., Harkare, W. P., Indusekhar, V. K., and Krishnaswamy, N.
'• Demineralization with Ion-Exchange Materials," Desalination, _3, 183-
194 (1967).
-------
11-
Reverse Osmosis
Michaels, A. S., "New Separation Technique for the CPI," Chemical
Engineering Progress, _64, December 1968.
"Desalination by Reverse Osmosis," Ulrich Merten, editor. The M.I.T.
Press, Cambridge, Massachusetts, 1966.
Wilford, J., and Perkins, F. R., "Test of G.A.Reverse Osmosis Unit in
New Jersey, 1965." New Jersey State Department of Health and New Jersey
Department of Conservation and Economic Development. January 1966.
Loeb, S. and Johnson, J. S., "Fouling Problems Encountered in a Reverse
Osmosis Desalination Pilot Plant," Preprint 21A - Presented at the
Symposium on Desalination: Part II. Sixtieth National Meeting,
American Institute of Chemical Engineers, September 1966.
Marcinkowsky, A. E., et al., "Hyperfiltration Studies - IV. Salt
Rejection by Dynamically-Formed Hydrous Oxide Membranes," Journal
American Chemical Society, j!8, 5744-46, 1966.
Kraus, K. A. et al, "Hyperfiltration Studies - VI. "Salt Rejection by
Dynamically-Formed Polyelectrolyte Membranes," Desalination, _1, 225-230, 1966.
Bray, D. T., et al., "Reverse Osmosis for Water Reclamation," Report No.
GA-6337. General Atomic Division, General Dynamics Corporation, San
Diego, California.
Okey, R. W., and Stavenger, P. L., "Industrial Waste Treatment with Ultra-
filtration Processes," Dorr-Oliver, Incorporated, Stamford. Connecticut.
Wiley, A. J. et al. "Application of Reverse Osmosis to Processing of
Spent Liquors from the Pulp and Paper Industry," Tappi, _50, 9, 455-60
September 1967.
Weissman, B. J., Smith, C. V., and Okey, R. W., "Performance of Membrane
Systems in Treating Water and Sewage," Chemical Engineering Progress
Symposium Series, _64, No. 90, 1968.
Friedlander, H. Z., and Rickles, R. N., "Membrane Technology: Part II.
Theory and Development," Analytical Chemistry, 3T_> 27A-62A, July 1965,
Merten, Ulrich and Bray, Donalt T., "Reverse Osmosis for Water Reclam-
ation," Third International Conf. on Water Pollution Research, Paper 15,
Section III, Munich, Germany, 1966.
"Reverse Osmosis - An Old Concept in New Hardware," Industrial Water
Engineering, 20-23, July 1967.
Mattson, R. J., and Tomsic, V. J., "Improved Water Quality," Chemical
Engineering Progress, ^5,62, January 1969.
Okey, R. W., and Stavenger, P. L., "Membrane Technology: A Progress Report,"
Industrial Water Engineering, March 1967.
-------
12 -
Ion Exchange
Helfferich, F., "Ion Exchange," McGraw-Hill, New York, 1962.
Higgins, I. R., Ind. Eng. Chem. _53, 635 (1961).
"Amber-Hi-Lites," published bi-monthly by Rohm and Haas Company,
Philadelphia, Pennsylvania.
Eliassen, R., Bennett, G. E., "Anion Exchange and Filtration Techniques
for Wastewater Renovation," presented at the 39th Annual Conference of
the Water Pollution Control Federation, Kansas City, Missouri, September
1966.
Kunin, Robert, "Further Studies on the Weak Electrolyte Ion Exchange
Resin Desalination Process (Desal Process)," Desalination, k, 3.8-44
(1968) .
Eliassen, R., Wyckoff, B. M., and Tonkin, C. D., "Ion Exchange for
Reclamation of Reusable Supplies," Jour. AWWA, ^7, 113 (September 1965).
Pollio, Frank, and Kunin, Robert, "Ion Exchange Processes for the Reclam-
ation of Acid Mine Drainage Waters," Environ. Sci. & Tech., _1, March 1967.
Pollio, Frank, and Kunin, Robert, "Tertiary Treatment of Municipal Sewage
Effluents," Environ. Sci. & Tech., 2,January 1968.
Downing, D. G., Kunin, R., and Pollio, F. X., "Desal Process - Economic
Ion Exchange System for Treating Brackish and Acid Mine Drainage Waters
and Sewage Waste Effluents," Chemical Engineering Progress Symposium
Series, _64, No. 90 (1968).
-------
FIG. 1
AVERAGE COMPONENTS IN DOMESTIC
SEWAGE EFFLUENTS
APPROX HJ ID-UP NORMAL RANGE REPRESENTATIVE
CONSTITUENT THROUGH ONE MUN USE OF BUID-UP SECONDARY EFFLUENT
Ca (CaCOj)
BO ppm
15- 40
95
Mg (CaCOa)
13
20-40
39
Na
55
40-700
84
S04
25
10-40
51
CL
35
20-125
50
P04
30
15-40
30
NO3
8
0- 18
8
S i02
15
80-20
35
ABS
3
1- 4
3
COD
70
4k
0
1
O
70
BOD
5
9- 40
15
TDS
250
100-500
550
HCO3
dH
65
---
170
75
-------
DILUTING %
COMPARTMENT y.
CONCENTRAT-
ING COMPART
MBMT
! DILUTING
COMPARTMEN
ANION A CATION A-ANION PERMEABLE MEMBRANE
C—CATION PERMEABLE MEMBRANE
FIGURE 2 &
FIGURE 3. ELECTRODIALYSIS PRINCIPLE
-------
FIGURE 4
-------
RUN TIME (hr )
fig. 5 Effect of turbidity on demineralization.
-------
FIG. 6
Ion Removal Selectivity
Fraction of Ion Removed
Fraction of All Ions Removed
Ion
Average
Range
Bicarbonate
0.77
0.63-0.95
Chloride
1.25
1.07-1.51
Nitrate
1.22
1.02-1.48
Phosphate
0.72
0.25-1.03
Sulfate
1.11
0.21-2.00
Ammonium
1.15
1.05-1.3
Calcium
1.25
1.01-1.48
Magnesium
0.98
0.71-1.35
Potassium
1.14
0.77-1.35
Sodium
0.79
0.52-0.99
Calcium and
1.13
1.05-1.28
magnesium
GPO 621—S7I-9
-------
FIG. 7
Normal osmotic system
wm0.
IfSSi
Fresh A Saline
water water
Semipermeable membrane
Pressure on osmotic system leads to reverse osmosis
Osmotic equilibrium
Fresh
water
il#BI
Saline
water
.............
Semipermeable membrane
water
Semipermeable membrane
-*•: -ivV-v.
•v:V;V;V::V;;-^.va;-:
water T water
Semipermeable membrane
-------
DENSE
SURFACE
kAYEfi •
IG" 8 COMPOSITE OF TWO ELECTRON PHOTO-MICROGRAPHS OF CROSS
SECTIONS OF MODIFIED CELLULOSE ACETATE MEMBRANE
-------
UJ
K
UJ
(E
UJ
o
(A
SOLUTE RETENTION »100%
SOLUTE
RETENTION
x
D
-------
WHS'ite ijM? li
FRESH
WATER
OUT
O-RING-SEALS
SEA WATER
t
O-RINO SEAL.
POROUS
PLATES
O-RING-
SEAL.
MEMBRANES
CONCENTRATED
BRINE
FIGURE 10
-------
OUT
(1) FIBERGLASS TUBE
(2) OSMOTIC MEMBRANE
(3) END FITTING
(4) PVC SHROUD
to collect product water
(5) PRODUCT WATER
(6) FEED SOLUTION
(7) EFFLUENT
Figure il. A Tubular Reverse Osmosis Unit
-------
BRINE-SIDE
SEPARATOR ^ ^
SCREEN ^ '
BRINE FLOW
\
PRODUCT WATER s v
PRODUCT-WATER FLOW
(AFTER PASSAGE
THROUGH MEMBRANE)
PRODUCT-WATER-SIDE BACKINGN
MATERIAL WITH MEMBRANE ON ^ \
EACH SIDE, GLUED AROUND EDGES
AND TO CENTER TUBE
\
MEMBRANE
PRODUCT-WATER-
SIDE BACKING
MATERIAL
MEMBRANE
BRINE-SIDE SPACER
2S
38^
Figure 12. A Spiral-Wound Reverse Osmosis Module
Reprinted with permission from Gener al Dynamics,General Atomic Division
-------
ch3
—CH^—N — CH3
ch3
STRONG BASE RESIN
-CH-CH2-CH-CH3
H+SO3
SOjH*
—CH—CH}—
STRONG ACID RESIN
FIG. 13
-------
NeCl
WEAK
BASE
REStN
OK"
FORM
No HCO3
HjO ~ CO3
Figure 14. DESAL Process
-------
C02 a AIR
POLYELECTROLYTE
CaO
COLD LIME
SOFTENING'
SLUDGE
SECONDARY SEWAGE
EFFLUENT FEED H20
RENOVATED CLARIFIED
SECONDARY
SEWAGE EFFLUENT H20
Figure 15. Flow diagram of ion exchange process for renovation of
secondary sewage effluent
-------
FIG. 16
Cost Estimate for Renovation of Haddonfield, N. J.,
Secondary Sewage Effluent
$ Cost/1000 Gal.
1,000,000 10,000,000
gal. /day gal./day
Alkalization 0.0655 0.0631
Dealkalization 0.0500 0.0478
Carbonation 0.0030 0.0030
Degasification 0.0042 0.0029
Flocculation
(chemicals only) 0 .0436 0.0436
Lime softening 0.0158 0.0158
Grand total $0.1821 $0.1762
-------
Moderator:
1:00 P.M.
1:45 P.M.
2:00 P.M.
3:15 P.M.
to
3:30 P.M.
3:30 P.M.
4:15 P.M.
5:00 P.M.
ADVANCED WASTE TREATMENT AND
WATER REUSE SYMPOSIUM
Session #4, Wednesday, February 24
Wisconsin
Chemical-Physical Treatment for
Small Flows
Jesse M. Cohen, Chief
Physical-Chemical Research
Advanced Waste Treatment Research
Laboratory, EPA, Cincinnati
Ultimate Disposal
Dr. J. B. Farrell
EPA, Cincinnati
Chemical-Physical Processes
Jesse M. Cohen
EPA
Coffee Break
Solids Removal Processes
Dr. S. A. Hannah
EPA
Demineralization
Jesse M. Cohen
EPA
Closing
-------
CONTENT
"Advanced Waste Treatment Plants for Treatment of
Smal1 Waste Flows"
Kugelman, Schwartz, and Cohen, EPA
"Physical-Chemical Treatment"
Jesse M. Cohen, EPA
"Solids Removal Processes"
Sidney A. Hannah, EPA
"Demineralization of Wastewaters"
Jesse M. Cohen, EPA
Additional Papers for Future Reference
"Current Status of Advanced Waste-Treatment Processes,
July 1, 1970," EPA
"Sludge Handling," Robert B. Dean, EPA
"The Porteous Process," J. D. Phillips
"The Concept of Wastewater Reclamation," L. G. Suhr
-------
CURRENT STATUS
OF ADVANCED WASTE-TREATMENT
PROCESSES
JULY 1, 1970
ADVANCED WASTE-TREATMENT RESEARCH LABORATORY
-------
PPB
1101
1105
1603'
1706
1701
1702
1703
1704
1705
1706
1707
1708
1709
1700
PAGE
1
11
15
21
35
45
53
61
69
73
81
87
101
CURRENT STATUS OF ADVANCED
WASTE TREATMENT PROCESSES
TABLE OF OONTENTS
Municipal Pollution Control Technology-Sewered Wastes
Non-Sewered Municipal Wastes
Virology
Dissolved Nutrient Removal
Dissolved Refractory Organlcs
Suspended and Colloidal Solids Removal
Dissolved Inorganic Removal
Dissolved Biodegradable Organics Removal
Microorganisms Removal
Ultimate Disposal
Wastewater Renovation and Reuse
Waste Treatment Optimization
Scientific Bases of Waste Treatment Processes
-------
FOREWORD
Waste treatment technology is moving rapidly nowadays,
A huge impetus has been given to this field by the substantial
sums of money made available for research by the Congress and
administered by the Research and Development Office of the
Federal Water Quality Administration. The Advanced Waste
Treatment Research Laboratory (AWTRL) in Cincinnati, Ohio is
a key element in conducting treatment research for FWQA.
This status report is current as of July 1, 1970, It
reports the programs of the Advanced Waste Treatment Research
Laboratory but mentions other pertinent work as well. It is
not, however, a comprehensive review of the field. The pur-
pose of the report is to inform Federal Water Quality Adminis-
tration operating and managing officials of the state of the
art of treatment. It is expected others will find it useful.
If the details of the scientific investigations are desired,
they are available in various reports named in the text.
F. M. Middleton
Director of Research
Advanced Waste Treatment
Research Laboratory
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
Cincinnati, Ohio
CURRENT STATUS OF ADVANCED
WASTE TREATMENT PROCESSES
July 1, 1970
PPB 1101 61 1105 Municipal Pollution Control
PPB 1700 Waste Treatment and Ultimate
Disposal Technology
PPB 1603 (Biological Identification of
Pollutants) Virus Studies
DIVISION OF PROCESS RESEARCH & DEVELOPMENT
FEDERAL WATER QUALITY ADMINISTRATION
U. S. DEPARTMENT OF THE INTERIOR
GPO 821-371-10
-------
AEVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, I9TO
MUNICIPAL POLLUTION CONTROL TECHNOLOGY
SEWERED WASTES
PPB 1101
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
1.
-------
MUNICIPAL POLLUTION CONTROL TECHNOLOGY
PPB - 1101 - SEWERED WASTES
APPLICATION OF ADVANCED WASTE TREATMENT PROCESSES
TO THE TREATMENT OF MUNICIPAL WASTEWATER
Transfer of advanced waste treatment technology from laboratory
scale or experimental pilot plant scale is taking place through the
continuing evaluation and development of specific processes and treat-
ment systems in large-scale pilot plants and full-scale demonstration
plants. The following discussion covers specialized treatment processes
that have achieved full-scale application. Comments are made as to the
general effectiveness and limitations or disadvantages of such processes
under actual use. conditions.
PURE OXYGEN IN ACTIVATED SLUDGE PROCESS
Promising results were obtained from a study recently completed
at Batavia, New York in which the use of pure oxygen was compared with
air in the activated sludge process. The test plant has two identical
and separate 1.25 mgd trains. Each treatment train has separ?t-e aeration
tanks, final sedimentation tanks, and return sludge facilities. Primary
sedimentation is not provided. One train was covered and converted to
use of pure oxygen and operated in parallel with the air system. With
recent developments in oxygen production and dissolution technology, under
the conditions of the Batavia test, pure oxygen was shown to be competi-
tive with air. The oxygen can be produced economically on site.
Under test conditions the pure oxygen train achieved 90 percent or
more BOD removal at detention times of 1 to 1.5 hours. With 3 hours
detention time BOD removal averaged 85 percent for the air train and 93
percent for the oxygen train. Another significant difference in per-
formance was quantity of waste activated sludge. Although confirming
data are needed, preliminary results indicate a reduction of 30-40
percent. Further information will be obtained during a continuation
of the study.
Based on the Batavia data, cost estimates projected for new plants
indicate the possibility of lower capital investment and operating costs
for the pure oxygen treatment. The major factor contributing to the cost
reduction is the ability to carry higher MLSS and thereby reduce aeration
tank capacity to 40 or 50 percent of that required for the conventional
systems. Additional savings are indicated for sludge handling and dis-
posal.
Results of the study are being published as an FWQA research report
titled "An Investigation of the Use of High Purity Oxygen Aeration in the
Conventional Activated Sludge Process." Copies of the report, expected
to be ready by September 15, 1970, may be obtained by writing Planning
2
-------
and Resources Office, Office of Research and Development, FWQA,
Department of Interior, Washington, D. C. 20242.
Further evaluation and development of the pure oxygen process
will be accomplished under terms of an FWQA R&D Grant recently awarded
to New York City. A 20 mgd train at the Newtown Creek treatment plant
will be converted to the use of pure oxygen and operated for at least
12 months.
The use of pure oxygen for the treatment of municipal waste
waters is being aggressively promoted by Linde Division of Union
Carbide Corporation who was contractor for FWQA oti the Batavia study,
GRANULAR ACTIVATED CARBON
The use of granular activated carbon for removal of nonbiode-
gradable organics, color and residual BOD has been demonstrated in
full-scale plants and is felt to be sufficiently developed to be used
on full-scale applications wherever conditions warrant such treatment.
Because suspended solids are partially removed on the carbon, the
solids load and need for pretreatment must be considered when designing
a carbon adsorption system. In order for the carbon treatment system
to be economical, the used carbon must be regenerated and reused.
Large-scale plants currently using and regenerating granular activated
carbon include the 7.5 mgd plant at Lake Tahoe and the 0.5 mgd plant
at Nassau County, New York. A number of articles have been published
covering the Tahoe plant. One appeared in the June, 1969 issue of
Civil Engineering entitled "Wastewater Reclamation and Export at South
Tahoe." A few copies are available from the Cincinnati Laboratory.
At the 300,000 gpd Pomona, California Pilot Plant secondary
effluent is applied directly to the carbon columns without requiring
excessive backwashing. This is only possible, however, because of
exceptionally high quality secondary effluent at this location.
Results of this study will appear in a 1970 issue of the Chemical
Engineering Progress Symposium Series.
Full-scale evaluation of granular carbon adsorption as a replace-
ment for biological treatment will be obtained on a 10 mgd plant at
Rocky River, Ohio. This is an R&D Grant project which involves chemical
pretreatment of raw sewage in an improved primary treatment ahead of the
carbon columns. Construction of this plant is scheduled for completion
by fall of 1971. Further details regarding design and operating condi-
tions scheduled for this plant may be obtained from Mr. A. N. Masse,
Cincinnati, Ohio.
3
-------
PHOSPHORUS REMOVAL
Phosphorus removal from wastewater on plant scale has been
carried out for a number of years at certain locations where the
water was needed for industrial reuse purposes. It has been rela-
tively recent, however, that phosphorus removal has been considered
necessary as a pollution control measure.
Although purely biological methods of phosphorus removal have
been proposed, it appears that addition of chemicals to the water to
precipitate the phosphorus is the only dependable method. Chemicals
that can be used are iron salts, aluminum salts, and lime. The simplest
method for carrying out chemical precipitation is to add the chemicals
at some point in a conventional activated sludge plant. The point of
addition can range from before primary treatment to near the exit of
the aerators. Iron salts and aluminum salts are preferable to lime.
A number of R&D Grant projects have been sponsored by FWQA including
Grand Rapids, Michigan at 45 mgd. Contact Mr. E. F. Barth, Cincinnati,
Ohio for additional information.
An alternative method for carrying out precipitation of phosphorus
is by using a clarifier-settler combination either for treating screened
raw sewage or as a tertiary treatment. Lime presently appears most
appropriate for this method of removal. Excellent phosphorus removal
can be obtained along with a high degree of solids removal, especially
if the settler is followed by a filter. Probably the best known example
of tertiary chemical clarification is the 7.5 mgd plant at Lake Tahoe.
Reference has been made to this plant in connection with carbon treat-
ment. Other FWQA supported projects include plants at Colorado Springs
and Nassau County. When chemical clarification is used for treatment of
raw sewage, it can serve as the first stage of a purely physical-chemical
treatment system. Under an R&D Grant, a 5 mgd plant will be constructed
and operated at Painesville, Ohio that utilizes chemical clarification
followed by carbon treatment. There is increasing interest in this type
of treatment system. Additional plants are likely to be constructed in
the near future.
AMMONIA STRIPPING
Up to 95 percent of the ammonia in wastewater can be air-stripped
from solution using about 400 ft^ of air per gallon of water treated.
Effective ammonia removal requires a pH of 11. A nitrified secondary
effluent cannot be treated by this method.
4
-------
A 3^ mgd ammonia stripping tower has been operated at South Lake
Tahoe to treat one-half of the total flow at that location. This is
part of a two-stage lime precipitation process. Lime is added in the
first stage to raise the pH to 11. This step removes most of the
suspended solids, phosphates, and carbonate compounds. Effluent from
the first-stage clarifier is then subjected to countercurrent air
contacting to remove ammonia; effluent from the stripping tower is
recarbonated with CO-2 to precipitate excess calcium as CaCO^ in the
second-stage clarifier; at this point the pH is dropped to 9.5.
Although the process has been quite effective in reducing the
ammonia content of the wastewater, operational problems raise questions
as to the desirability of promoting the widespread use of ammonia
stripping towers. The process is subject to freezing problems in cold
climates and reduction of the ammonia removal efficiency at low tempera
tures. Lime deposits on the slats and superstructure of the tower
create serious maintenance problems. At this time, use of stripping
towers will most likely be restricted to more temperate locations where
freezing is not a problem or areas where high percentage removal is not
required during winter months.
POLYMER ADDITION TO PRIMARY SEDIMENTATION
The addition of polymers to raw sewage to improve sedimentation
of suspended solids was studied at the District of Columbia Water
Pollution Control Plant. The study was carried out at full scale on
this 240 mgd plant. The test involved three separate phases in which
each of three polymer suppliers carried out extended studies with his
own most effective polymer. Best results were obtained with anionic
polymers used in doses of less than 1 mg/1. The amount of solids
removed by sedimentation increased by as much as 25 percent. Because
of hydraulic overload at the plant, which affected operation of the
final settlers, the improved primary treatment did not improve overall
treatment significantly. For plants having only primary treatment,
however, use of polymers could increase effectiveness of treatment
significantly. Use of polymers to improve primary treatment may also
improve secondary treatment where organic load to the aerators is very
high. Additional results of the study will be reported in an FWQA
research report entitled "Raw Wastewater Flocculation with Polymers
at the District of Columbia Water Pollution Control Plant." Copies
are expected to be available from FWQA's Research Division by October
1, 1970.
5
-------
combination conventional-awt treatment
The treatment plant at South Tahoe, California is probably the
best known advanced treatment plant in the country. Reference has
already been made to the plant several times. It is of 7.5 mgd capacity
and includes conventional primary treatment and activated sludge treat-
ment followed by tertiary processes including two-stage lime clarifica-
tion with ammonia stripping between stages, pressure multimedia filtra-
tion and granular carbon treatment. The effluent from the plant is of
high clarity and contains only traces of phosphorus and organic materials.
The water is presently exported to Nevada for eventual use in irrigation
of crops after prior holding in a recreational lake, Indian Creek
Reservoijj. The l-ake can be used for all types of water recreation
including contact -sports. Use has been restricted, however, by a lack
of facilities. Because of the high quality of the water, algae are not
a significant problem.
Since biological treatment is included in the Tahoe system, the
system is a hybrid between conventional and purely physical-chemical
advanced treatment. There is increasing interest in pure physical-
chemical systems. These have the advantage of not being affected by
toxic materials that can upset the operation of b-iological processes
for long periods. They also require less land area. Where only organic
and phosphorus removal is required, chemical clarification followed by
carbon treatment are the processes considered most reliable at this time.
R&D Grants at Rocky River and Painesville, Ohio utilize variations of
these processes. The effluents from these plants will not be of as high
a quality as that from the Tahoe plant. The effluents are expected to
be the equivalent of secondary effluent. Where nitrogen removal is
required, ammonia stripping or selective ion exchange are most likely
candidates. Stripping is less expensive but is subject to several
operating problems. More work is needed to develop a completely satis-
factory physical-chemical nitrogen removal system.
DESIGN MANUALS FOR ADVANCED WASTE TREATMENT PROCESSES
We have recognized the need for improved methods of disseminating
results from research and development programs and we are currently
making arrangements for a series of treatment process design manuals.
These manuals will supplement technical seminars and publications
covering results of the Advanced Waste Treatment Laboratory inhouse
and extramural projects.
The information needed by consulting engineers for design of
advanced waste treatment plants is now available for some processes.
6
-------
However, the data are contained In numerous segmented publications,
reports and manufacturers' literature. The purpose of the manuals
will be to compile available information in a form which can be readily
utilized, and provide detailed information on hardware selection and
system design.
Contracts are being negotiated for preparation of the following
design manuals:
1. Activated carbon adsorption, primarily for the treatment of
secondary effluent or an equivalent waste stream.
2. Phosphorus removal by chemical treatment and solids separation.
3. Suspended solids removal including such techniques as micro-
screening, filtration, tube settlers, etc.
A. Upgrading of existing plants through the application of such
techniques as pure oxygen treatment, flow equalization, etc.
Target date for completing the first manuals is March, 1971. At
that time the manuals should be ready for general distribution to con-
sulting engineers and other treatment plant design interests.
7
-------
PPB - 1101 - SEWERED WASTES
Flow Reduction From Individual Homes and
Alternative Waste Collection Systems
FLOW REDUCTION
A study on state-of-the-art of methods for flow reduction has
been completed by Electric Boat Division of General Dynamics Corporation.
This study concluded that use of modified plumbing fixtures for flow,
reduction is economically feasible and would result in cost savings in
many cases. There are many household functions in which water is used
wastefully. Water usage could be reduced up to 35 percent by use of
presently available devices and technology. Feasible devices are
shallow trap toilets, toilets with separate flush cycles for urine and
feces, flow control showers, and faucet aerators. Treatment and reuse
of wastewater in individual homes is not economically feasible, except
for filtration and reuse of wash waters or aerobic unit effluent for
toilet flushing in water-short areas.
A study is planned for demonstration of flow reduction devices
and technology for 8 homes. Present water usage will be monitored prior
to installation of modified plumbing fixtures. The program will include:
4 homes with flow control showers and shallow trap-dual cycle
toilets
2 homes with flow control showers and with recycled (filtered)
wash water reused in normal trap-dual cycle toilets
2 homes with shallow trap-dual cycle toilets and flow control
showers, and with recycled (filtered) wash water used for
lawn watering
PRESSURE SEWER SYSTEMS
Collection and treatment of wastewater at a central point should
be utilized where feasible in lieu of individual home systems. However,
it is not always practical to install conventional gravity sewer systems
because of rough terrain and necessity for rock excavation. One possible
solution is use of a pressure system, which is being studied under an
R&D Grant at Grandview Lake, Indiana.
The Grandview Lake system will serve about 60 homes initially.
Individual grinders and pumps will be installed at some homes. Septic
tank effluent will be pumped directly without grinding at others.
Three and one-fourth inch PVC pipe will be used for the pressure sewer
8
-------
with 1-inch connections from homes. Wastes will be treated by a combined
anaerobic and aerobic lagoon. Lagoon effluent will be utilized for
irrigation of a hay field.
The individual home pump and grinder unit was designed using
commercially available home garbage grinders, pumps, and check valves.
Unit cost without installation is $450 to $500.
VACUUM SEWER SYSTEMS
One of the most interesting developments in water closets and
waste collection is the Liljendahl vacuum system. This system uses air
rather than water as the major transport system for a vacuum toilet.
A vacuum toilet requires only one-half gallon per flush compared to 4
to 6 gallons for conventional toilets. The vacuum system can also be
utilized for waste collection from groups of homes in lieu of conven-
tional gravity sewers.
The Sanivac Division of National Homes Corporation is marketing
the Liljendahl vacuum system. This system has been used in Europe, the
Bahamas, and in Latin America. A grant project is being developed for
demonstration of the vacuum system in an area now served by septic tanks.
Connections with house sewers will be made at lot lines. Another grant
is planned for demonstration of the vacuum toilet system.
9
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July l, 1970
MUNICIPAL POLLUTION CONTROL TECHNOLOGY
NON - SEWERED WASTES
PPB 1105
Division of ProcesB Research & Development
Federal Water Quality Administration
U, S, Department of the Interior
11
-------
PPB - 1105 - NON-SEWERED MUNICIPAL WASTES
INTRODUCTION
A study on state-of-the-art of Individual home waste treatment
systems has been completed by Electric Boat Division of General Dynamics
Corporation (Report 11050 FKE, "Flow Reduction and Treatment of Waste
Water from Households," available September, 1970), In addition, an
inhouse survey of proprietary equipment developed by industry but not
now commercially available has been conducted.
SEPTIC TANK SYSTEMS
At the present time, there are approximately 15 to 17 million
septic tanks in use. 1.4 million new systems have been installed since
1960. In many cases, operation of septic tank systems has not been
satisfactory and has resulted in health hazards. This is due to poor
soils which do not readily accept effluent. Lack of maintenance by
homeowners is also a contributing problem. Regulatory agencies now
require large lots in areas with low soil permeability. This has
prohibited housing developments in many areas. However, in areas with
high soil permeability and low population density, septic tanks usually
perform satisfactorily and will continue to be an acceptable disposal
method.
Septic tank costs are upwards from $120 and installation from
$250. Tile field costs vary from $200 to $2400 depending on type of
soil and regulatory requirements.
ACTIVATED SLUDGE PACKAGE PLANTS
Individual home aerobic package plants have been marketed since
about 1955. It is estimated that there are 20,000 to 30,000 units now
in operation. Initially, State health departments allowed discharge to
natural waterways. Because of periodic discharge of suspended solids,
subsurface disposal is now required by most regulatory agencies. Unit
costs vary from about $800 to $1600 installed. If filtration and dis-
infection are required, costs are increased by $300 to $800.
DEVELOPMENT OF IMPROVED SYSTEMS
If an acceptable individual home treatment unit to replace septic
tanks could be developed, a multimillion dollar market would exist.
This potential market has induced industries to expend funds for R&D.
From results of the inhouse survey, there are 5 companies that have
conducted studies on unit development. In several cases, system
components and total systems are now ready for field evaluation.
12
-------
The basic problem in unit development is acceptable capital and
operating costs. The Electric Boat study has concluded that use of
advanced treatment processes, including distillation, reverse osmosis,
electrodialysis, chemical treatment, and activated carbon adsorption,
is not economically feasible at this time.
The basic problem area is solids disposal, as is the case for
large-scale conventional treatment. Capital and maintenance costs for
incineration are expected to be high. Another problem area is air
pollution potential of incineration. Solids could be stored in the
unit and disposed of similarly to sediment from septic tanks. However,
this may not be aesthetically acceptable to all homeowners.
Fail-safe design is necessary. Homeowners tend to ignore operating
and maintenance requirements for presently available package plants. There
have been cases where power to units has been shut off. Policing of a
large number of units by regulatory agencies is difficult. A possible
solution to maintenance requirements is a permanent service contract with
the manufacturer.
FUTURE STUDIES
In view of effort expended by industry on development of new
equipment and approaches to individual home treatment, support of basic
research on new systems or hardware development is not planned at this
time. Planned studies include demonstration of commercially available
hardware and modifications to improve treatment, and new proprietary
equipment developed by industry. Studies on the relative absorption
rates of effluent from package plants as compared to septic tanks will
be conducted.
13
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
VIROLOGY
PPB 1603 - 1706
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
15
-------
Virology Section
Robert A. Taft Water Research Center
Cincinnati, Ohio
I603-ITO0
Introduction
Large quantities of viruses of human origin are present in sewage,
sewage effluents, and in rivers and streams. Viruses of animal, plant
and bacterial origin must also abound in these waters, but their presence
is not as well documented, and their importance to the human animal is
largely unknown.
The viruses cf human origin are small in numbers compared with the
numbers of bacteria that are excreted. Moreover, viruses do not multiply
outside of living susceptible cells, and these numbers decrease even in
that most nutritional environment constituted by domestic waste. The
great importance of viruses in water, however, lies not Just in their
numbers, but in their great capacity to infect their hosts. The smallest
amount of virus capable of infecting the most highly susceptible cells
in cultures, our most sensitive indicators of infection, 1b usually
capable of producing infection in man.
The clear capability of minimal quantities of viruses for producing
infection in man is sufficient Justification for seeking the total
removal of viruses from any waters which man might consume. The
permissible level for viruses in such waters should be none.
Epidemiology
Small amounts of viruses ejected into rivers and streams with
partially treated wastewater became a potential hazard to downstream
recreationalists and to those in downstream communities /who must consume
these waters, liven 19 PFU per 50 gallons of river water, an amount we
have recovered with an inefficient technic even in cold months, constitutes
a considerable hazard, for what this means in terms of the amounts of
viruses that may enter the intakes of any community every day is readily
calculable.
Unfortunately, small amounts of waterborne viruses may infect swimmers
and consumers and not be readily detected by the effect they produce.
This is so because small amounts of ingested viruses are likely to produce
infection, but not disease. Infection is the state whereby the virus
enters and multiplies within susceptible cells. It is a disease state
with no overt signs. Overt disease exists when sufficient damage has
been done to bring about systemic malfunctions. Thus, individuals
infected with small amounts of virus may show no signs; yet, they may
excrete large amounts of virus, their contacts may be infected with
16
-------
large amounts and recognizable illness may result. The spread of infection
and disease in this fashion vill appear to be by the personal contact
route with no indication that the original source was water. The frustration
of epidemiological studies intended to demonstrate a water source of trans-
mission may be the result of using clinical illness and not index infection
rates as criteria. In bathing water and similar studies, the disease rates
in secondary contacts might well be a much better indicator of source than
the disease rates in bathers themselves. Hi is same principle may hold for
bacterial infection and disease, for the main thrust of efforts in this
area has always been in the direction of disease and not infection.
Recovery of Small Quantities of Viruses from Large Volumes of Water
Several years ago, we set a tentative standard for ourselves of less
than 1 PFU of virus per 100 gallons of water. This standard was based on
our assessment that detection of one PFU of virus in 100 gal Ions of water
would be feasible within five years of that time, and not on any conviction
that water with less than that amount of virus would be safe. It was our
intent to raise our sights if developing technology allowed, and to lower
them should a more modest limit need to be imposed upon us.
Clearly, the recovery of 1 PFU of virus from one-hundred galIons of
water or more requires exquisite concentration procedures, and many are
under study. It is not yet clear which of the several systems presently
under investigation will prove the most efficient and utilitarian if, in
fact, any one does become universal in all of the several applications
for which such methodology is needed. Viruses must be recovered from
waters of qualities ranging from raw sewage to completely renovated.
Except in the unusual situation where raw sewage or primary effluents
need to be pasteurized or sterilized, only small volumes of such waters
need to be tested for viruses because relatively large amounts of viruses
are usually present. This is generally true of secondary effluents as
well, and in these situations, effective technics, not adaptable to large
volume efforts, are already available. The AlCOH)^ adsorption procedure
is reportedly capable of recovering 100$ of several enteroviruses
experimentally added to sewage effluents, but the method leaves most
of the large reoviruses and adenoviruses behind. England (l6030 DWW)
recently reported efficient recovery of experimentally added reoviruses
and adenoviruses from effluents by precipitation with protamine sulfate
which leaves most of the smaller picornaviruses behind. England uses
both methods for maximum recovery of all of these viruses. Protamine
precipitation of the larger viruses from Al(0H)o-adsorbed effluents is
an important approach today to the effective recovery of viruses from
heavily contaminated waters.
The phase separation technic suffers some disadvantage from an
overnight time requirement for completion. It has also been reported
recently that the method is not efficient with all viruses.
17
-------
Both the Al( OH ^-protamine sulfate and the phase separation procedures
are limited by the volumes they can accommodate, this the result of the
large quantities of chemicals required for each unit volume of water
tested. When only a few liters or gallons need to be tested, these
technics may be considered. When a hundred gallons or more must be
tested, other methods must be looked to.
To accommodate large volumes of water, a filtration system seems
the best approach. This technic consists of filtering water through
0A5 H cellulose nitrate membrane filters to which viruses adsorb and
from which they can be eluted. For some time now, we have consistently
obtained quantitative recovery of enteroviruses and about 80$ recovery
of reovirus 1. Most of our studies were done with 1-liter samples, but
we achieved complete recovery of viruses from 25 gallon quantities as
well. With larger quantities of water, recovery has so far been less
efficient. In most of these experiments, less than 100 FFU of virus
were added to the total volume studied. Most of these experiments were
done in distilled water, but several were done in tap water from which
we could not always recover viruses quantitatively. As others have
reported, certain substances, presumedly organics, apparently can react
with the adsorptive sites on the membranes and make them unavailable
to the virus. Thus, our immediate goal is to apply the technic to
renovated and other clean waters, but it may be necessary to pretreat
even such relatively clean waters to remove interfering substances
before the membrane filter method can be effectively used for quantitative
recovery of viruses. Whether waters of poorer quality can be sufficiently
purified without removing or destroying viruses so that such waters can
be tested with this technic is still conjecture. However, there is
another filtration approach currently in a state of reincarnation that
offers promise for quantitative recovery of viruses from water--the ion
exchange resin, more voguishly, the insoluble polyelectrolyte. This
method consists of filtering water through two Millipore AP 20 fiberglass
prefilters between which a Monsanto insoluble polyelectrolyte designated
PE 60 is sandwiched. The virus is eluted with 10$ fetal calf serum in
borate saline at pH In our hands, when small amounts of viruses in
1-liter volumes of distilled water were passed through such filters,
relatively poor recoveries resulted. Poliovirus 1 recovery in experiments
sometimes ranged over 80$, but echovirus 7 recoveries were sometimes
somewhat lower than 30$ and reovirus 1 recoveries were sometimes lower
than 20$. The extent to which the ion exchange resin is affected by
water quality is not clear, but apparently, it is less affected than the
cellulose nitrate filter.
Nonetheless, we have repeatedly used the technic for virus recovery
studies from 50-gallon samples of river water, and repeatedly obtained
recoveries. As much as 19 FFU of virus have been recovered from samples
taken long distances from outfalls along a large fast-flowing river
during the winter months. Thus, despite its low and erratic efficiency
18
GPO 021 —37 1 — 1 I
-------
at present, the technic appears to be the most sensitive presently
available. Since the numbers of different ion exchange resins that
can be produced is vast, these substances clearly warrant the rein-
carnation they now experience.
Other technics including osmotic ultrafiltration and electro-
osmosis are also under study, but it is not yet clear what their final
contribution to the developing technology will be. Nor is it clear
at present whether we will eventually achieve a universal recovery
system that can be utilized efficiently with waters of all qualities,
or whether we will have to tailor the recovery system to the water
under study.
Gerald Berg, Ri.D.
July 7, 1970
19
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
DISSOLVED NUTRIENT REMOVAL FROM WASTEWATER
PPB 1701
Division of Process Research & Development
Federal Water Quality Administration
U.S. Department of the Interior
21
-------
NITROGEN REMOVAL - GENERAL
Municipal wastewaters have nitrogen contents in the 15-25 mg/1 range in
untreated and primary settled wastes; the nitrogen is divided between
organic compounds, which are mostly insoluble, and ammonia. In general,
we can depend on conventional biological processes to transform almost
all nitrogenous components in wastewater into ammonia and biological
sludge. Once this has been accomplished, we can design systems to
remove ammonia by.air-stripping. Ammonia stripping at high pH in cooling
towers following lime treatment is effective but cannot be used during
freezing weather and may suffer from serious scale problems.
Under favorable conditions, biological processes may also oxidize ammonia
to nitrates by a two-step sequence called nitrification. It would be
beneficial if waste treatment plants were required to produce nitrified
effluent. Ammonia nitrogen in effluents has several undesirable features:
(1) Ammonia consumes dissolved oxygen in the receiving water;
(2) Ammonia reacts with chlorine to form chloramines which are
less effective disinfectants than free chlorine;
(3) Ammonia is toxic to fish life;
(4) Ammonia is corrosive to copper fittings;
(5) Ammonia increases the chlorine demand at waterworks downstream.
A nitrified effluent, free of substantial concentrations of ammonia, offers
several advantages:
(1) Nitrates will provide oxygen to sludge beds and prevent the
formation of septic odors;
(2) Nitrified effluents are more effectively and efficiently
disinfected by chlorine treatment;
(3) A nitrified effluent contains less soluble organic matter
than the same effluent before nitrification.
A nitrified effluent is far preferable to one containing substantial
ammonia. However, ammonia and nitrate are interchangeable nitrogenous
nutrients for green plants and algae, as well as bacteria. If the
nitrate level is too high and is helping to stimulate undesirable aquatic
growths, the effluent can be further treated by biological action to
convert the nitrates to nitrogen gas. This process is called denitrifi-
cation. The best developed method at this time for control of nitrogen
compounds is biological oxidation to nitrates followed by denitrification
with the aid of methanol.
22
-------
Selective ion exchange of ammonia with lime regeneration may be practical
but the process is still in the pilot stage. Several other processes
are being studied including selective ion exchange of nitrate and chlori-
nation of ammonia to liberate nitrogen gas.
NITROGEN REMOVAL BY BIOLOGICAL SUSPENDED GROWTH REACTORS
Success in providing a high efficiency for nitrogen removal by biological
denitrification requires that the biological transformation of ammonia
nitrogen to nitrate nitrogen be under good process control. Any reduced
nitrogen compounds introduced into the denitrification stage will pass
through the process unaltered and impair overall nitrogen removal efficiency.
Complex factors are involved in maintaining nitrification with a conven-
tional activated sludge system. If nitrification occurs at all, it may
be due only to an unintentional accident of design. A three sludge
variation of the activated sludge process, developed at the Robert A.
Taft Water Research Center, greatly simplifies the process control
problems associated with maintaining nitrification.
The three sludge system allows management of the separate biological
transformations which are necessary for successful denitrification. The
three sludge systems are staged in sequence, with flow passing from one
stage to the next. The first stage is a high-rate sludge system, the
second stage a nitrification sludge system, and the third a denitrification
sludge system. The high-rate system handles the bulk of the carbonaceous
removal and at this station the waste activated sludge is removed. Thus,
the nitrification stage receives a predominantly ammonia nitrogen feed
and an enriched culture develops because each sludge system has its own
sludge recycle. This process design also has other desirable features.
The high rate system protects subsequent nitrification stages from toxic
chemicals. Since this is a staged system there can be no direct short
circuiting of materials from the influent to the effluent. Temperature
effects on the enriched culture of the nitrification stage are not as
extreme as with a single sludge system which contains only a marginal
population of nitrifying organisms.
Once controlled nitrification has been established, the biological
denitrification process can be optimized. The nitrified effluent flows
to a slowly stirred anaerobic reactor where methyl alcohol is added in
proportion to the nitrate nitrogen concentration. The organisms in this
stage use the oxygen component of the nitrate radical to oxidize the
organic carbon of methyl alcohol. The end products of this metabolism
are elemental inert nitrogen gas and carbon dioxide, which are liberated
to the atmosphere.
The stage approach to nitrification has been investigated in work at the
Robert A. Taft Water Research Center (1) and in large pilot plant operations
at the University of'Notre Dame (2) and Manassas, Virginia (3). The
23
-------
process has also been evaluated on a 1 mgd scale at Hazel Crest,
Illinois. A summation of these studies show that biological denitri-
fication is a controllable process if the reaction is forced with an
organic supplement, such as methyl alcohol. Total nitrogen in an
effluent can be reliably reduced to about 2 mg/1. The cost of the
methyl alcohol for 20 mg/1 of nitrate nitrogen is estimated to be about
2c/1000 gallons treated. For more information contact:
Mr. E. F. Barth
U. S. Dept. of the Interior, FWQA
4676 Columbia Parkway
Cincinnati, Ohio 45226
Phone: 513-871-1820
References:
(1) Barth, E. F., et al.„ "Chemical-Biological Control of Nitrogen and
Phosphorus in Wastewater Effluent," Jour. Water Pollution Control
Federation, December 1968.
(2) Echelberger, W. F. and Tenny, M« W., "Control of Organic and
Eutrophying Pollutants by Combined Chemical and Biological Wastewater
Treatment," Division of Water, Air and Waste Chemistry, American
Chemical Society, Minneapolis, Minnesota, 1969.
(3) Mulbarger, M. C., et al., "Manassas, Virginia, Adds Nutrient Removal
to Waste Treatment," Water and Wastes Engineering, April 1969.
24
-------
NITROGEN REMOVAL FROM WASTEWATERS BY COLUMN REACTORS
Columnar nitrate reduction represents a second alternative to the suspended
growth systems as a means of biochemically reducing the nitrate ion to
elemental nitrogen. In e packed column, the cell residence time of the
surface bound slime is much greater than the hydraulic detention time.
This, combined with a large contact surface and short diffusion dis-
tances afforded by small media such as sand, provides an efficient system
for rapid denitrification of an applied feed.
Work at the FWQA Lebanon, Ohio Pilot Plant (J. M. Smith, 1970, Unpublished)
has shown that the smaller media systems (sand to 3/4 inch diameter
stone) are effective when operated downflow at surface loading rates of
7.0 gpm/ft and at actual contact times of 50 to 30 minutes. Daily back-
washing is required to relieve pressure drop due to the accumulation of
suspended solids in the upper portion of the column. The denitrifying
slime is firmly attached to the media surface, and is not removed during
the backwash operation. Greater than 90 percent nitrate reduction can
be achieved within these columns at contact times of 10 minutes for sand
and 30 minutes for the 3/4 inch stone. The effluent normally contains
less than 2.0 mg/1 of nitrate nitrogen with effluent turbidities less
than 3 JTU, indicating little solids contribution from the attached
organisms.
Larger media varying in size from 1 inch to 2 inch aggregate have been
successfully employed to denitrify agriculture subsurface drainage at
Firebaugh, California (Tamblyn, T.A., and Sword, B.R., "The Anaerobic
Filter for the Denitrification of Agricultural Subsurface Drainage,"
24th Purdue Industrial Waste Conference, 1969.) The larger media permits
upflow operation without backwashing at the expense of longer contact
times and increased effluent suspended solids. Nitrate reduction of
greater than 90 percent were achieved in contact times of 1 hour for
the 1 inch aggregate and 2 hours for the 2 inch aggregate at temperatures
above 12°C. The 2 inch columns have been operated continuously for
over six months on agriculture subsurface drainage without the loss of
efficiency or solids accumulation.
As with suspended growth denitrification, methyl alcohol is used as the
supplemental organic carbon source of choice for columnar denitrification
because of its low cost, biodegradability and ease of handling. Approxi-
mately 3 mg of methyl alcohol are required per mg of nitrate nitrogen
removed including the requirement for deoxygenating the nitrified feed.
The chemical cost for removing 20 mg/1 of nitrate nitrogen in the presence
of 5 mg/1 of dissolved oxygen is estimates to be about 2c/1000 gallons
treated. For additional informatiort, contact:
Mr. John M. Smith
U. S. Department of Interior, FWQA
4676 Columbia Parkway
Cincinnati, Ohio 45226
Phone: 513-871-1820
25
-------
AMMONIA NITROGEN REMOVAL BY STRIPPING WITH AIR
Ammonia can be removed from a wastewater effluent by raising the pH to
convert ammonium ion to dissolved ammonia and then contacting the effluent
with a sufficient quantity of ammonia-free air. This physical process
is called desorption or, more commonly, "stripping."
If the contacting is done in a packed tower, the pressure drop across the
tower is about 1.0 psi or 28 inches of water. Since the volume of air
required per unit volume of wastewater effluent is very high, about 400
cubic feet per gallon in a countercurrent operation, the cost for power
to overcome even this relatively low pressure drop is prohibitive.
The problem of high power cost was solved by investigators at the South
Lake Tahoe Public Utility District (Slechta, A. F. and Culp, G. L.,
"Water Reclamation Studies at the South Tahoe Public Utility District,"
Jour. Water Pollution Control Federation, May 1967).who used a slat-
filled tower such as is used for cooling water to contact water and air.
The pressure drop across such a device is very low, about 1/2 inch of
water, so power costs are reduced to reasonable levels. Removal effi-
ciencies as high as 90 percent were obtained in a 24-foot high tower
in which wastewater effluent and gas were contacted in a nearly counter-
current fashion. On the basis of this experience, a full-seal® stripping
tower was constructed at South Lake Tahoe. The tower was designed to
remove 90 percent of the ammonia from 3-1/2 MGD of Tahoe's removated
wastewater. The air flow is not countercurrent to the liquid but flows
across the tower (cross-flow), while the wastewater drips downward
through the packing.
Initial operation of Tahoe's stripping tower was in the winter and
immediately revealed a limitation of ammonia stripping. When air temp-
erature fell below 0 C,freezing of water occurred at the air inlets,
making the tower inoperable. Also, since ammonia solubility is higher
in cold water than in warmer water, more air is required to remove It
(800 cubic feet per gallon at 0 C). The Tahoe tower was designed for
400 cubic feet per gallon; therefore, removal was much lower than 90%.
Another problem which developed at Tahoe is the formation of scale in
the tower. The scale is chiefly calcium carbonate. It forms because the
previously lime-treated effluent is supersaturated with respect to
calcium carbonate. In the case of the tower at Tahoe, the sludge can be
flushed from the tower except from inaccessible areas which cannot be
reached with a water jet. A pilot scale ammonia stripping tower at
FWQA's Blue Plains, Washington, D. C. Pilot Plant, has had similar
scaling problems, except the scale is hard and adheres to the tower
fill. The causes of the differences in the nature and amount of scale
in various locations has not been resolved. Studies are in progress to
see if the scale can be prevented from forming, or if it can be made
nonadherent.
26
-------
The cost of ammonia stripping has been estimated for the South Lake
Tahoe facility to be about 2.9c per 1000 gallons of wastewater treated.
This does not include the cost of the lime and facilities to raise the
pH to about 11. These costs have been charged to phosphorus removal
because this is the direct objective of the lime addition. If 90%
removal of ammonia nitrogen is required even in cold weather, these costs
should be increased by about 50% to provide for a higher air-to-water
ratio.
Ammonia stripping is feasible when the temperature is above freezing
but there is danger of serious fouling by scale. The best approach for
minimizing scale and its effects appears to be to use a pH of about
10.5, countercurrent operation rather than cross-flow, and an open fill
to allow for easy flushing of accumulated solids. For more information
contact:
Dr. J. B. Farrell
U. S. Dept. of the Interior, FWQA
4676 Columbia Parkway
Cincinnati, Ohio 45226
Phone: 513-871-1820
NITROGEN REMOVAL BY CHEMICAL METHODS
A. Removal of Ammonia by Selective Ion Exchange
Conventional water softening ion exchange resins which are selective
for calcium and magnesium do a relatively poor job of removing ammonium
from dLlute solutions. Total deionization by mixed bed ion exchange
resins will, of course, remove ammonium ions along with other cations
but this process is too costly for wastewater treatment.
Certain zeolites show unusual selectivity for the ammonium ion. A
number of these hava been investigated by the Atonic Energy Commission
because they also show selectivity for cesium and potassium ions. A
demonstration project at the Battelle Memorial Institute - Pacific
Northwest (Hanford) Laboratories, 1969 (Mercer, B. W., et al., "Ammonia
Removal from Secondary Effluents by Selective Ion Exchange," Jour. Water
Pollution Control Federation, Research Supplement, February, 1970) showed
that certain zeolites, including the naturally occurring mineral clinop-
tilolite, had a high selectivity for ammonium in natural and wastewaters.
A trailer mounted demonstration plant with a capacity of 100,000 gallons
per day was built as a cooperative demonstration project between the FWQA
and Battelle-Northwest. This trailer is now operated under contract to
the FWQA to demonstrate selective ion exchange removal of ammonium ions
from solution.
Clarified secondary effluent is passed downward through columns
containing clinoptilolite. When a column becomes loaded with ammonia, it
is regenerated with limewater containing sodium chloride to speed up
the rate of regeneration. The high pH of the limewater converts the
27
-------
ammonium ion to unionized ammonia gas in solution. The ammonia laden
limewater is then pumped through a packed column through which heated
air is blown to remove the ammonia.
Pilot studies at Battelle-Northwest indicated a cost approaching
10
-------
PHOSPHORUS REMOVAL - GENERAL
Phosphorus is considered by many investigators to be the key nutrient
in breaking the eutrophication cycle, However, conventional secondary
plants are not efficient in phosphorus removal. Phosphorus enters a
plant in the highest oxidized form. But, no common biological systems
reduce phosphorus; therefore, it cannot be liberated in a gaseous form
as nitrogen, carbon, and sulfur are. Removal by biological means, then,
is limited to cell metabolic needs and whatever excess phosphorus can be
encouraged to be taken by and stored by the cells. The quantity stored
above the 1% required for maximum growth is usually classified as "luxury
uptake."
A few plants have reported efficient phosphorus uptake on a sustained
basis, including the San Antonio Rilling Plant and the Baltimore,
Maryland Plant. These results cannot be readily duplicated at other
plants by manipulation of operating conditions. We have not learned
enough about thephenomenon to take advantage of it. The removal of
phosphorus by biological synthesis and "luxury uptake" is not a
controllable process at this time.
If we are to reliably remove phosphorus from wastewaters on a sustained
basis, we must choose the chemical or the chemical-biological methods.
Strict chemical methods precipitate phosphorus either in the primary
settler or in a tertiary clarifier. The chemical-biological method
employs direct chemical dosing to the aerator of an activated sludge
plant. The chemically-bound precipitated phosphorus is removed with
the sludge and is not resolubilized during sludge disposal unless the
pH is substantially lowered. Effluent phosphorus concentrations of
1-2 mg/1 as P can be regularly achieved if the precipitation is accom-
plished in the primary or secondary portions of the plant. Tertiary
lime clarification followed by filtration will lower the concentration
to less than 0.5 mg/1.
BIOLOGICAL PHOSPHORUS REMOVAL
The literature indicates that several factors exert an inrluence on
biological phosphorus removal. The rate of aeration and the aeration
time have been indicated by most investigators as the most important
criteria, the rate of air supply probably being the more critical of
the two. Aeration rates in the order of 3 to 7 cfm/gal and detention
times of 4 to 6 hours appear to be desirable.
There is some disagreement in the literature with respect to optimum
concentration of mixed liquor suspended solids (MLSS). Apparently,
increased uptake has been attained at both low and high MLSS from 500 mg/1
up to 4300 mg/1. At the San Antonio, Texas treatment plants, the optimum
appeared to be 1000 mg/1 or slightly higher (1). It was also found that
the maximum overall phosphorus removal occurred at organic loadings of
45 to 55 pounds of BOD/day/100 pounds of MLSS under aeration.
29
-------
It also appears essential from the literature that a ^dissolved oxygen
(DO) level of at least 2 mg/1 should be maintained in the last half o£
the aeration tank to insure that phosphorus will not be released in the
secondary clarifier. It is possible that a still higher DO level of
3 to 5 mg/1 may be advancageous to maintain a minimum DO concentration
of 1.5 mg/1 in the sludge until it is through the secondary clarifier.
Phosphorus leakage or resolubilization will occur in the secondary clar-
ifier when the sludge consumes available dissolved oxygen. It has been
suggested that solids detention time in final clarifiers should be less
than 30 minutes.
These key design criteria and operational parameters have not been suffi-
ciently isolated and identified to effectively predict and implement con-
trolled phosphorus removal by the solely metabolic mechanism. As more
data have been collected, an alternative chemical explanation has been
advanced (2). Simply stated this theory indicates, especially in hard
water areas, that phosphorus can be precipitated within the biological
floe as calcium phosphate at the end of the aeration period, where carbon
dioxide is scrubbed from the water by aeration and a substantial increase
in pH occurs. This amount of precipitated calcium phosphate and the pre-
cipitation of additional phosphorus by traces of iron, aluminum,and mag-
nesium normally present in wastewater would produce an efficient overall
removal.
The calcium phosphate theory has been tested at several treatment plants
with erratic results. Operating a segment of the Hyperion, California
Plant according to the guidelines outlined by the theory has greatly in-
creased the efficiency of phosphorus removal. At Baltimore, Maryland
where efficient phosphorus removal occurs routinely, observations show
no major increase in pH during operation. Studies at Texas City, Texas
where attempts were made to deliberately force calcium phosphate pre-
cipitation by the addition of 200 mg/1 of lime to the aerator have not
shown efficient removal.
The preliminary data reported from these full-scale treatment plants
are still not complete or detailed enough at this date to confirm either
the metabolic or calcium phosphate precipitation theory. For further
information contact:
Dr. C. H. Connell
The University of Texas Medical Branch
Department of Preventive Medicine and
Community Health
Galveston, Texas 77550
or
Dr. R. L. Bunch or Mr. E. F. Barth
U. S. Dept. of the Interior, FWQA
4676 Columbia Parkway
Cincinnati, Ohio 45226
Phone: 513-871-1820
30
-------
References
(1) Vacker, D., et al., "Phosphate Removal Through Municipal Wastewater
Treatment at San Antonio, Texas," Jour. Water Pollution Control
Federation, May 1967.
(2) Jenkins, D. and Menar, A. B., "The Fate of Phosphorus on Waste
Treatment processes: the Enhanced Removal of Phosphate by
Activated Sludge," Proceedings of the 24th Purdue Industrial
Waste Conferer.ee, 1969.
PHOSPHORUS REMOVAL BY MINERAL ADDITION TO THE PRIMARY OR SECONDARY
Mineral addition is out of the research stage and into the application
stage. Field experience on full-scale and large demonstration pilot
plants shows that ferrous, ferric, and aluminum salts can be equally
effective as phosphorus precipitants in wastewater. Plants can accomplish
80 to 90 percent phosphorus removal with a minor investment in capital
equipment for chemical storage tanks, chemical pumps, and control equip-
ment (Barth, E. F. and Ettinger, M, B., "Mineral Controlled Phosphorus
Removal in the Activated Sludge Process," Jour. Water Pollution Control
Federation, August, 1967).
For trickling filter plants, the chemical precipitation should be
accomplished in the primary tank. Direct dosing of chemicals to the
trickling filter has not proven highly effective. A small dose of
polymer is needed to flocculate and settle the phosphorus which is
insolubilized by the mineral addition. Subsequent passage through the
trickling filter to satisfy metabolic needs serves as a polishing step.
Dow Chemical has conducted several studies of iron-polymer precipitation
in the primary at Midland, Lake Odessa, Grayling, and Benton Harbor,
Michigan. FWQA sponsored projects include Grand Rapids, Michigan (45 mgd)
and Richardson, Texas (1.5 mgd). For further information contact:
Mr. Ronald F. Wukasch
The Dow Chemical Company
2020 Abbott Road Center
Midland, Michigan 48640
Phone: 517-636-2634
With an activated sludge plant, it makes very little difference where
the point of addition of themetal ion is. Efficient removals have been
obtained when dosing raw wastewater before primary settling, after primary
settling, in the aeration tank, or near the mixed liquor exit point. Phy-
sical constraints of a particular plant may favor one point of addition
over another. However, the key factor in this approach is that no matter
where the metal ion insolubilizes the phosphorus, the overall plant effi-
ciency is dependent upon the ability of the biological floe to collect
31
-------
these dispersed precipitates and remove them from the final plant effluent.
Polymer addition in the primary is not necessary for an activated sludge
plant as the naturally occurring polymeric materials in the mixed liquor
will serve the same purpose. FWQA sponsored projects of phosphorus pre-
cipitation in an activated sludge plant include Penn State University (2 mgd) ,
Texas City, Texas (0.75 mgd), University of Notre Dame (50,000 gpd), Man-
assas, Virginia (1 mgd), Xenia, Ohio (1 mgd), and Detroit, Michigan (7,000 gpd).
For more Information contact:
Mr. E. F. Barth
U. S. Dept. of the Interior, FWQA
4676 Columbia Parkway
Cincinnati, Ohio 45226
Phone: 513-871-1820
Dosages of 1.5 to 2.0, on a molar basis, of metal ion to phosphorus can
produce effluents with a residual total phosphorus of 1 milligram per
liter or less consistently on full-scale application. As is true with
other parameters such as BOD, COD, and suspended solids, if very low re-
siduals are desired, filtration of the effluent would be required. If
commercial aluminum and iron minerals are used, the chemical cost will
vary from 2-5c/1000 gallons, depending on the phosphorus concentration
and the chemical employed. If waste pickle liquor is available for the
cost of' trucking only, the chemical cost may be as low as 0.5
-------
Currently, lime precipitation is also being considered as the first
step itv a chemical-physical treatment sequence for raw wastewater that
does not include a biological unit. Subsequent units in the sequence
include lime recovery, filtration, carbon adsorption and possibly ammonia
stripping.
The above sequence is similar to the tertiary sequence demonstrated for
several years at Lake Tahoe's 7.5 mgd Water Reclamation Plant. The Lake
Tahoe Plant utilizes secondary effluent as feed water. Phosphorus removal
costs at Tahoe vary monthly from 6-8c/1000 gal. including amortization,
operating costs, and recalclnation.
For additional information on chemical-physical treatment of raw waste-
water, contact:
Mr. J. M. Cohen
U. S. Dept. of the Interior, FWQA
4676 Columbia Parkway
Cincinnati, Ohio 45226
Phone: 513-871-1820
For additional information relative to Lake Tahoe's operations, contact
Dr. R. B Dean at the same address.
33
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT" STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
DISSOLVED REFRACTORY ORGANICS
PPB 1702
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
35
-------
DISSOLVED REFRACTORY ORGANICS
PPB 1702
PROCESSES FOR ORGANICS REMOVAL
I. Introduction
Most liquid wastes, both domestic and industrial, contain a complement
of organics which must be removed or altered before discharge. The
classical approach and the method now most widely used has been biologi-
cal oxidation. Decades of research have produced a great variety of
processes, all dependent on biological activity, to consume organics for
energy and for cell protoplasm. Biological oxidation has limitations:
some organics are not degradeable, toxic materials must be avoided and
low temperatures slow biological activity. Recognition of these limita-
tions plus the need to produce increasingly higher quality effluents for
discharge or for reuse, led AWT to search for alternatives to biological
treatment.
Several processes for removal of organics from both domestic and indus-
trial waste streams are in varying stages of development. These are:
1. Granular activated carbon
2. Powdered activated carbon
3. Adsorbent resins
4. Oxidation processes
II. Granular Activated Carbon
Activated carbon is an adsorbent medium characterized by an extensive
system of internal pores which provide it with a very large surface area
per unit of weight. This large area plus the variety of functional groups
(acidic, basic, oxygenated, etc.) attached to the surface give activated
carbon a significant adsorptive capacity for most dissolved organics in
wastewater. The carbon, when exhausted^ can be reused after regeneration
by heating to high temperature (ca 1700 F).
The method of application is primarily determined by the particle size
of the carbon to be used. Granular carbon, in the mesh size range from
8 x 30 to 40 x 60, is generally contacted with the wastewater in a fixed
36
GPO 621—571—12
-------
or fluidized bed of carbon. Originally, carbon adsorption was con-
sidered as a tertiary treatment to supplement biological processes to
produce a high quality product of reuseable quality. More recently,
the main thrust of research has shifted from the treatment of biologi-
cal secondary effluent to treatment of clarified raw sewage. Success
in the latter effort will provide the sanitary engineer an alternative
to biological treatment.
One of the first large-scale applications of granular carbon to waste-
water treatment was the South Tahoe Wastewater Reclamation Plant.
This 7.5 mgd granular activated carbon plant treats secondary effluent
after clarification by lime and mixed media filters. The carbon
effectively reduces an influent BOD from 5-20 mg/l to 2-5 mg/l; COD
from 20-30 mg/l to 2-10 mg/l; and color from 20-50 to less than 5 units.
The average dosage of carbon to accomplish this treatment has been
300 lb/million gallons of treated wastewater.
Large-scale studies at Pomona have substantially confirmed the results
obtained at Tahoe. Carbon dosage, however, was found to average about
350 lbs/million gallons. Here, too, effluent quality has been good.
Total COD was reduced from 47 mg/l to 9.5 mg/l; color from 30 units to
3 units and turbidity from 10 JTU to 1.6. Significantly the CCE, which
has been used as a measure of water quality for drinking water supplies,
was 0.014. mg/l, substantially below the recommended 0.2 mg/l.
These two large-scale studies plus bench investigations firmly estab-
lished that activated carbon can produce effluents with low organic
contents and at a cost that is reasonable. To make the process economic
it was recognized very early that multiple use of the carbon, in contrast
to the single use practiced in water treatment, was necessary. Current
regeneration techniques using temperatures of 1600-1700°F plus steam have
been able to recover 92-35% of the carbon. Some losses, both physical and
chemical, do occur during regeneration. Attempts to regenerate carbon in
situ with chemical oxidants or caustic washes have not been successful.
The manner in which the carbon is contacted with the wastewater has been the
subject of considerable investigation. The wastewater can be upflow or
downflow; the carbon can be static or moved continuously or in slugs; or
a fluidized bed can be used. In most of these applications pressure has
been used to maintain flows. Simple gravity flow contactors (using lower
flow rates) have been suggested as economic. Recent estimates by Swindell-
Dressier show that the gravity flow system is less expensive by about
2^/1000 gallons in spite of the smaller flow rate. Flow rates in pressure
systems have ranged 6-10 gpm/ft^ while gravity flow will range 2-4. gpm/ft^.
37
-------
The most thorough estimate of the cost of treating secondary effluent by
carbon adsorption was prepared by Swindell-Dressier. Various systems were
subjected to side-by-side economic analyses, using data then available in
the literature. Total costs have ranged from as little as 8.5^/1000 gallons
for the gravity system to as much as 12.5^/1000 gallons for a 10 mgd plant.
These studies and others have clearly established that activated carbon
can produce good quality effluents from secondary effluent at some reason-
able and predictable cost.
A more recent concept in the use of activated carbon is replacement of the
biological secondary treatment process in conventional treatment. The
process sequence consists of chemical clarification of raw sewage by either
organic flocculants or by metal coagulants, when phosphate removal is desired,
followed by carbon adsorption. To date, technical feasibility has been
demonstrated only at small scale, but full-scale application will be demon-
strated within the next two years.
Some impressive information has already been developed on this process
which could replace biological treatment by a purely physical-chemical
process. Calgon's studies of the treatment sequence (clarification-carbon)
has shown the following removals are obtainable when content time with the
carbon is 24 minutes; suspended solids 93%; BOD 93%; COD 81% and T0C 75%.
When metal coagulants are used in the clarification step, phosphate removals
in excess of 90% can be obtained.
Pilot scale investigations at the Lebanon Pilot Plant of AWTRL have shown
that lime clarification followed by carbon adsorption of primary effluent
can consistently produce an effluent equal or better in quality than
secondary biological treatment. Over five million gallons of primary
effluent were processed to produce an average effluent product containing
10 mg/l T0C and BOD with a range of 2-23 mg/l. Effluent turbidity averaged
less than 2 JTU and phosphate removals were consistently 90% or better.
Some advantages that can be cited for a physical-chemical process are:
1. Substantially less land would be required. Calgon claims as
little as 1/10.
2. Capital costs for conventional plants may be 30-40% greater than
that for the P-C plant.
3. P-C process should be less influenced by shock loads, low
temperature and by substances which would be toxic to a
biological system.
38
-------
4. The plant should be easy to operate and could be readily
adjusted to produce a ranging quality of effluent as desired.
5. Odor problems should be minimal.
6. Significantly, much less sludge will need to be handled. For
example, a conventional 10 mgd activated sludge plant will
produce about 150,000 gpd of sludge, about 10% of which, or
105,000 gpd, is secondary sludge. The P-C plant could very
well reduce the volume to about one-half of the total, depending
on the flocculant used, and this sludge should be readily
filterable.
A major disadvantage of the P-C process is that ammonia nitrogen
will be unaffected. Substantial reductions of organic nitrogen can be
expected through solids removal both by the clarification step as well
as by the filtering function of the carbon beds.
The plant which will probably be the first to demonstrate the P-C
process sequence is located at Rocky River, Ohio. While the original
process envisions polymer flocculation, phosphate removal and clarification
is being studied for possible use. The carbon adsorption plant will consist
of eight pressure contactors, 25 feet high (15 feet of carbon bed) and 16
feet in diameter, and will process a peak flow of 20 mgd (nominal flow of
10 mgd). Flow rate will be 4-«3 gpm/ft2 with a peak rate of 8.6 gpm/ft^.
Carbon will be thermally regenerated at an anticipated rate of 300-500
lbs/day/million gallons. Loss on regeneration is expected to be no more
than 5%• Effluent quality objectives are 15 mg/l BOD and 10 mg/l suspended
solids, but actual quality may exceed these.
Another plant at Painesville, Ohio, will be designed for a flow 'pf 5.0 mgd,
part of which (up to one-half) consists of oil and chemical wastes.
Fluctuations of pH from 2-11 and the presence of high concentrations
of phenol and chlorine would make biological treatment difficult if not
impossible.
Preliminary studies have shown that the wastewater can be effectively
clarified (and phosphate precipitated) by ferric chloride. Initial plans
call for clarification, roughing sand filters and gravity-flow carbon
contactors. The latter will be 15 feet deep, containing 8 x 30 mesh carbon
in columns operated in parallel at 2 gpm/ft*. Effluent quality objectives
are, BOD, 20 mg/l; COD, 30 mg/l; phosphates 80$ removal and suspended solids
10 mg/l.
39
-------
Status Summary
The technical feasibility of adsorption of organics by activated carbon
has been well established. Regeneration of exhausted granular carbon can
be considered to be operational. It remains for the two P-C demonstration
plants discussed above to provide operational and cost information. If
cost of P-C treatment is comparable to conventional biological secondary
and for comparable effluent quality, then increasing numbers of these plants
will be used. Reliability of the effluent quality, the smaller land
requirements, the freedom from toxic influences, the lack of odor nuisance
in areas of population, are some of the reasons why P-C plants will find
increasing use.
III. Powdered Activated Carbon
Powdered carbon has developed into a rival of granular carbon. Its finer
grain size increases the kinetics of adsorption such that 90%. of its
adsorption equilibrium is attained in less than 10 minutes. Powdered
carbon is dosed in slurry form, after which it is separated by sedimenta-
tion following polymer flocculation. Other methods of separation are
being investigated. Powdered carbon has the advantage over granular in
that its cost is about 1/3 as great. Unit cost and the possibility to
control the dosage applied are two of the advantages over granular.
Powdered carbon can be applied to either primary or secondary effluent
and is being tested on both feeds. Determination of the technical and
economic feasibility must await the results of contracts with Eimco Corp.
and Infilco. In contrast to granular carbon regeneration, recovery of
spent powdered carbon has been accomplished only in small prototype
furnaces. Larger scale regeneration will have to be done before the
powdered carbon process is a practical alternative to granular carbon.
IV. Other Methods for Organic Removal
At the present time, powdered and granular carbon provide the reagents
of choice for removal of organics. Other methods, however, are being
investigated as alternatives to carbon or for specialized applications.
Adsorbent synthetic resins are available and newer ones are being
developed which have the ability to sorb organics without any substantial
inorganic exchange capacity. At this point of development, sorbent resins
are not likely to replace carbon but the search for better ones is
continuing.
A variety of chemical oxidation methods have been investigated such as
chlorine catalyzed by U-V light, metal catalyzed photo-oxidation and
ozone. Of these, only ozone appears to be promising. Technical
40
-------
feasibility was established in the laboratory by Airco, Inc., which is
currently constructing a 50,000 gpd plant to establish economic
feasibility. Because of the cost of ozone itself and the rather large
doses, up to 100 mg/l, required for oxidation, application is likely
to be limited to treatment of low organic content feeds, such as carbon
effluents which need further organic reduction. A valuable benefit of
ozonation is its disinfection of the waste stream.
41
-------
Recent Publications and Reports
Oxidation and Adsorption in Water Treatment Theory and Application. The
University of Michigan Dept. of Civil Engineering, Division of
Sanitary and Water Resources Engineering, February 196.5•
Bishop, D. F., et al., "Studies on Activated Carbon Treatment". Jour. WPCF,
February 1967.
Removal of Organic Contaminants. Sorption of Organics by Synthetic Resins
and Activated Carbon. Sanitary Engineering Research Laboratory,
College of Engineering and School of Public Health, University of
California, Berkeley, SERL Report No. 67-9, December 1967.
Masse, Arthur N., "Removal of Organics by Activated Carbon". Robert A.
Taft Water Research Laboratory, August 1968. (mimeo)
A Comparison of Expanded-Bed and Pack-Bed Adsorption Systems. Robert A.
Taft Water Research Center Report No. TWRC-2. December 1968.
Ozone Treatment of Secondary Effluents from Wastewater Treatment Plants.
Robert A. Taft Water Research Center Report No. TWRC-4-. April 9, 1969.
Nutrient Removal and Advanced Waste Treatment. Robert A. Taft Water
Research Laboratory. Symposium on April 29-30, 1969, at Stouffer's
Inn, Cincinnati, Ohio.
42
-------
Appraisal of Granular Carbon Contacting. Phase I Evaluation of the Literature
on the Use of Granular Carbon for Tertiary Waste Water Treatment.
Phase II Economic Effect of Design Variables. Robert A. Taft Water
Research Center Report No. TWRC-11. May 1969*
Appraisal of Granular Carbon Contacting. Phase III Engineering Design and
Cost Estimate of Granular Carbon Tertiary Waste Water Treatment Plant.
Robert A. Taft Water Research Center Report No. TWRC-12. May 1969-
Rizzo, J. L., and R. E. Schade, "Secondary Treatment with Granular Activated
Carbon". Water & Sewage Works, August 1969-
Hager, D. G., and P. B. Reilly, "Clarification-Adsorption in the Treatment
of Municipal and Industrial Wastewater". Presented at the 4-2nd Annual
Conference of the Water Pollution Control Federation Meeting in Dallas,
Texas, October 5-10, 1969.
Weber, W. J., Jr., C. B. Hopkins, R. Bloom, Jr., "Physicochemical Treatment
of Primary Effluents". Prepared for the 42nd Annual Conference of the
Water Pollution Control Federation Research Symposiun Session, October 7,
1969, Dallas, Texas.
Knopp, P. V., and W. B. Gitchel, "Wastewater Treatment with Powdered
Activated Carbon Regenerated by Wet Air Oxidation". Presented at the
25th Purdue Industrial Waste Conference, May 5-7, 1970.
A3
-------
Sources of Information
Much of the research on processes for removal of organics from
wastewaters is conducted at or out of the Advanced Waste Treatment Research
Laboratory. The address of the laboratory and the principal investigators
are given below:
1. Francis M. Middleton Director Research
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513)871-1820, X-225
2. Arthur N. Masse Chief, Municipal Treatment Research Program
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513)871-1820, X-416
3. Jesse M. Cohen Chief, Physical & Chemical Treatment Research
Program
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513)871-1820, X-230
44
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
JULY 1, 1970
SUSPENDED AND COLLOIDAL SOLIDS REMOVAL
PPB 1703
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior.
45
-------
SUSPENDED AND COLLOIDAL SOLIDS REMOVAL
PPB 1703
PROCESSES FOR SOLIDS REMOVAL
I. Introduction
Removal of suspended or colloidal solids from domestic and industrial
wastewater is of major importance in any treatment system,. Evidence of
its importance is the great variety of methods and devices which have
been developed for this tas.k„ This brief review can only discuss the
more widely used processes and describe the newer, more promising tech-
niques now being developed. The subject material can be considered in
two parts; the physical aspects which relate to the equipment and the
physical methods of solids-liquid separation, and the chemical aspects
which involve chemical modifications to facilitate or improve the
separation of solids. The principal unit processes employed for solids
removal include:
1. Sedimentation
2. Flotation
3. Filtration
4. Microscreening
5. Coagulation-flocculation
6. Miscellaneous processes which include: moving bed filter,
ultrafiltration, magnetic separation, ultrasonic flocculation,
etc.
II. Physical Processes
A. Sedimentation
The time-honored method for separation of solids involves sedimentation
by gravity. In the conventional horizontal flow sedimentation tank, de-
tention periods of 2 to 4 hours are used to enable suspended particles
to settle by gravity. It is the simplest of the processes to remove
solids, and it is also the least efficient. Colloidal particles settle
at such a slow rate that they are not effectively removed. Some degree
of short circuiting always occurs leading to lesser detention times for
portions of the flow. Because of the inefficiencies of this process
many attempts have been made to improve on the separation, still using
gravity as the driving force.
One such improvement is the tube settler developed in this country and the
Lamella separator developed in Sweden. Both processes achieve separation
46
-------
by causing the particles to settle only inches rather than the several
feet as in the conventional settler. This is accomplished by conducting the
wastewater upward thru inclined tubes or plates, the solids move toward the
lower end of the tubes while the water passes out of the tops. The tube
settler has been rather widely used for separation of floe in chemically
treated river water. It is also finding application for removal of solids
from chemically treated wastewater. There is sufficient information to
indicate that this device does separate particles, but insufficient
evidence is at hand to conclude that the increased capital investment over
conventional sedimentation alone is warranted.
B. Flotation
Another process which separates particles by gravity is flotation.
Separation is achieved by attachment of air bubbles, which effectively
reduces the specific gravity of the particles to less than that of water.
Flotation has found application for clarification of a number of industrial
wastes, however, the process is little used at the present time for clarifi-
cation of domestic wastewater. Its widest application in wastewater treat-
ment is for sludge thickening operations. With additional development, air
flotation may find wider application to raw sewage clarification following
flocculation by chemical additives.
Air flotation has some attractive potential advantages over sedimentation:
1) a more positive control over the separation rate by controlling process
variables such as air/solids ratio or chemical addition; 2) a lower initial
capital cost owing to higher separation rates and shorter detention times;
3) reduction of septicity and associated odors owing to aeration of feed
and shorter detention times; 4) greater sludge density allowing use cf
smaller equipment for devatering;and 5) multiple use of a single treatment
unit for removal of heavy grit, suspended solids and oil or grease. These
advantages are gained with the following disadvantages: 1) higher operation
costs, and 2) greater operational skill is required. The process clearly
needs additional research to define in more detail the above advantages and
disadvantages.
C. Filtration
Whenever a high degree of clarification is required, then in-depth filtration
after chemical treatment is the process of choice. Rapid sand filtration has
been practiced for decades by water treatment plants but only recently for
wastewater application. In this process, the wastewater passes through a
bed of granular media which captures the particles within the filter. When
the capacity to store particles is reached, the filter is restored by back-
washing. In an ideal filter for downflow operation, the media is uniformly
graded from coarse to fine from top to bottom. The usual sand filter does
47
-------
not meet this ideal requirement, hence mixtures of media have been
employed to approach the ideal filter. The most common is a two
component filter of coal on top of sand. A tri-media filter contains
coal, sand and garnet.
One of the difficulties with filters is that the upper layers of the bed
become clogged with solids well before storage capacity is reached in the
remainder of the filter. Several approaches have been taken to overcome
this problem. The filter can be operated upflow in which case the flow
proceeds from coarse to fine media approaching the ideal. Some filters
have been designed to introduce the feed into the middle of the filter
with flow in two directions.
One of the more promising techniques developed by Johns Manville is
described as a moving bed filter. The object here is to renew the sand
bed surface either continuously or intermittently to avoid surface plugging.
This process has been tested at pilot scale and a full scale installation
is being made in Manville, New Jersey. Yet another approach has been pro-
posed by the Research Triangle Institute in which a lightweight media floats
to form a packed bed. Wastewater is filtered upflow. As the media becomes
clogged, it is removed from the bed, washed, and then reintroduced with the
wastewater. The concept is sound but feasibility remains to be tested.
D. Microscreening
Microscreening involves straining of wastewater through a woven metal fabric
having openings ranging upwards from 23 microns. The screen is continuously
cleaned by pressure sprays. Only larger suspended particles are removed
since straining is limited to particle sizes greater than the mesh size.
These devices have thus far found their greatest application in treatment
of river waters. More recently, application to removal of suspended solids
from secondary effluents has been tested. Chicago's Hanover Treatment Plant
has successfully operated a microstrainer to reduce suspended solids in
secondary effluent to less than 5 mg/l. Since about one-half of the
residual BOD of secondary effluent is attributable to the suspended solids
content, removal of the solids effects a reduction of the BOD as well as
suspended solids.
III. Chemical Processes
A. Meial Coagulants
The colloidal components of wastewater cannot be removed by any of the
physical processes described above. To remove these solids, the particles
must be coagulated and flocculated to iirger size before physical methods
can be effective. In conventional secondary treatment the colloids are
48
-------
flocculated by organic polymers produced during the biological oxidation.
Coagulation and flocculation can also be achieved by chemical additives.
Chemical coagulation and flocculation were first proposed some thirty years
ago but was never widely employed. Today, chemical flocculation is the
essential first step in physical-chemical treatment. The use of chemical
additives has gained impetus from the need to remove phosphates from
wastewater, All metal coagulants now being used for phosphate removal
also accomplish clarification.
A wide variety of metal coagulants are suitable for clarification (also
phosphate removal). These include: aluminum salts, such as aluminum
sulfate, and sodium aluminate; iron salts, such as ferric or ferrous
chloride or sulfate, pickling liquor which is an iron-containing waste
stream from the steel industry; and lime. Which one of the several
coagulants to use in any specific instance cannot be predicted beforehand.
All metal coagulants are effective and the choice of one from the many has
to be made for any application. The choice for any particular application
is generally based on relative dosage, the cost of the coagulant and the
chemical composition of the wastewater. It is well to remember that to
obtain clarification and phosphate removal in wastewater will require
substantial dosages of coagulant which in turn will produce chemical
sludges which must find disposal. The range of dosages for iron or
aluminum salts range 100 to 300 mg/l while for lime the range is 300 to
600 mg/l or more.
In addition to being the first step in physical-chemical treatment, chemical
clarification may have some other benefits in solids removal in the primary
prior to biological treatment. This concept is being tested at Grand Rapids,
Michigan, at full scale. Some of the advantages that may emerge from this
are: decreased air requirement in activated sludge resulting from the
increased solids capture in the primary; less difficult-to-filter sludge
from the secondary while producing more but filterable solids in the primary.
And, of course, phosphates will be removed. One of the advantages of lime
is that the sludge can be calcined to recover reuseable lime. This has
been demonstrated at Tahoe for lime used in secondary effluent and will be
applied to lime sludge from raw sewage precipitation at Rocky River, Ohio.
One of the interesting developments of recent years has been the synthesis
of a wide variety of organic polymers. Use of organic polymers or poly-
electrolytes as sole coagulants or as aids to the inorganic coagulants has
added a new dimension to clarification. Very low dosages of polymer may
improve efficiency of solids removal, permit reduction of inorganic coagulant
dosages and increase settling rates, thus allowing operation of existing
equipment at higher flow rates. Dosages range from fractions of a mg/l to
several mg/l. Thus, in contrast to inorganic coagulants, sludge volume is
49
-------
not increased. But organic polymers are not a total panacea. They do
not remove phosphates, they are all expensive ranging$l-$2/lb for the
100$ product, and their behavior for any particular application is
unpredictable. The plant operator is faced with selecting a single
polymer from the literally hundreds available and even then he cannot
be sure that his choice will be effective all of the time. Polymer
clarification of raw sewage has been tried at Cleveland's Easterly
Plant and at Grand Rapids.
Whether primarily for clarification or for phosphate removal, chemical
addition to wastewater is a growing practice. The resulting chemical
sludges will pose problems for their disposal.
IV. Miscellaneous Processes
A number of other processes for solids separation are in varying stages
of development. One of these is ultrafiltration which is a process akin
to reverse osmosis except that inorganic minerals are not removed. The
process involves application of wastewater under pressure to a porous
membrane. The process cannot compete economically with other solids
removal processes for treatment of large volumes of wastewater. But
there are special applications for small volume filtration where ultrafiltration
may have application. For example thickening of organic sludges or powdered
carbon sludge has been investigated.
Another membrane process, called "cross-flow" filtration by the inventor
at Oak Ridge, may be useful for solids separation. In this process a
membrane is formed on a support and solids separation is obtained under
pressures of 30-50 psi.
V. Assessment for the Future
Research of the last decade has provided the consulting engineer with an
arsenal of processes for removal of solids. This development comes at a
time when, more than ever, better and cheaper ways of solids removal are
required. Phosphate precipitation, improved clarification of raw or
secondary effluent, and higher quality effluents for tertiary processes
have increased the need for separation processes which are more effective
and sophisticated than the simple gravity sedimentation now so widely used.
Of the processes discussed here, media filtration, microstraining and
chemical coagulation and flocculation are the processes which are now
bein'g used. The other processes will be applied as this technology is
improved.
50
-------
Recent Publications and Reports
Rimer, Alan E.
"Filtration Through a Trimedia Filter"
Jour. San.Engng. Div. , ASCE, SA 3 (June 1968).
Miller, D. G.
"Rapid Filtration Following Coagulation, Including
the Use of Multi-Layer Beds"
Proc. of The Society for Water Treatment & Examination,
Vol. 16, Part 3, 196/.
Culp, Gordon
"Secondary Plant Effluent Polishing, Part 1"
Water & Sewage Works, 145 (April 1968).
Ives, K. J., and Gregory, J.
"Basic Concepts of Filtration"
Proc. of The Society for Water Treatment & Examination,
Vol. 16, Part 3, 1967.
Diaper, E. W. J.
"Tertiary Treatment by Microstraining"
Water & Sewage Works, 202 (June 1969).
Packham, R. F.
"Polyelectrolytes in Water Clarification"
Proc. The Society for Water Treatment & Examination,
Vol. 16, Part 2, 1967.
Smith, R. M.
"The Use of Synthetic Organic Flocculants in the Treatment
of Industrial Water and Wastewater"
Proc. International Water Conf., Pittsburgh, Pa., Oct. 1965.
Culp, Gordon
"Chemical Treatment of Raw Sewage, Part 1 and 2"
Water & Wastes Engineering, July 1967 and October 1967.
O'Melia, Charles R.
"A Review of the Coagulation Process"
Public Works, 87 (May 1969).
"Nutrient Removal and Advanced Waste Treatment"
Technical Symposium, Cincinnati, Ohio, April 29-30, 1969
Published by U.S.D I., Federal Water Quality Adm.
51
-------
Sources of Information
Much of the research on processes for removal of suspended and colloidal
solids from wastewater is conducted at or out of the Advanced Waste Treat-
ment Research Laboratory. The address of the laboratory and the principal
investigators are given below:
1. Francis M. Middleton Director of Research
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513) 871-1820, Ext. 225
2. Jesse M. Cohen Chief, Physical & Chemical Treatment
Research Program
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513) 871-1820, Ext. 230
3. Sidney A. Hannah Supervisory Research Chemist
Physical & Chemical Treatment Research Prog.
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513) 871-1820, Ext. 309
52
GPO 82 I—371 — 13
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
DISSOLVED INORGANIC REMOVAL
PPB 1704
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
53
-------
DISSOLVED INORGANIC REMOVAL
PPB 1704
PROCESSES FOR REMOVAL OF MINERALS
I. Introduction
During domestic and most industrial uses of water there is added an
increment of dissolved inorganic minerals which must be removed if
water quality is to be maintained,, If recycle of wastewater will be
practiced in the future, then almost surely methods will be required
to remove inorganic salts. Soluble inorganics are even now a signi-
ficant problem for many municipalities. For example, a recent survey
has shown that of the 20,215 municipal water supplies in the 50 states
and 5 provinces in the United States and Canada, 1066 had raw water
supplies with a total dissolved solids (TDS) of 1000-3000 mg/1; there
were an additional 31 supplies that had a TDS of 300-10,000 mg/1.
The rising salinity of many water supplies and the increasing cost of
developing alternate sources of better quality make it difficult or
uneconomic in many locations to meet the USPHS recommended limit of
500 mg/1 TDS for potable water. These factors justify the support for
research to develop inorganic removal processes.
Several processes are currently being investigated for reducing the
mineral content of municipal wastewater to an acceptable level. These
include: (a) ion exchange, (b) reverse osmosis, (c) distillation,
(d) electrodialysis, (e) freezing and (f) electrochemical treatment.
These processes are in varying stages of development and only the first
four mentioned are currently being given serious consideration as
practical processes for demineralization.
All demineralization processes produce a brine solution. The disposal
of this brine represents a major technical problem in the development
of demineralization technology. In coastal areas it may be feasible
to discharge brines to the ocean. Solar evaporation in lined lagoons
can be employed where climatic conditions are favorable. However,
inland areas with limited potential for solar evaporation will require
the development of more sophisticated techniques for brine disposal.
54
-------
II. Ion Exchange
Ion exchangers are materials containing ions that can be replaced by
other ions from solution. The replaceable ion carried by the exchanger
is known as the counter ion. Carriers of exchangeable cations are
called cation exchangers, and carriers of exchangeable anions, anion
exchangers. Once all the counter ions are replaced the exchanger is
exhausted and must be restored by regeneration with a solution con-
taining the original counter ion.
Ion exchange will almost certainly be an economic process for deminerali-
zation of wastewater, if the mineral solids do not exceed 1000-1500 mg/1.
This development derives from the commercial availability of new anion
resins which have 1) high selectivity for chloride ion, 2) require less
regenerant and rinse water, yielding a more favorable ratio of product to
feed. But most important has been the discovery that these anion resins
do not become "fouled" by organics - the single most important deterrent
to ion exchange with the older resins. Up to 50-60% of the COD is re-
moved from secondary effluent with no detectable loss of exchange capacity.
The COD is eluted with the regenerant.
Research at AWTRL has confirmed that COD is removed and that fouling does
not occur. Studies at the Pomona Pilot Plant facility demonstrated that
an effluent containing about 50 mg/1 of TDS can be produced from a feed
of about 800 mg/1 TDS. The bulk of the residual TDS was silica which is
not removed by a weak anion resin. Total cosfc-e for the process were
estimated to be 24c/1000 gal, excluding the cost for disposal fo the brines.
In practice, the product of ion exchange will be blended with good quality,
but not demineralized, effluent to provide a product with, say 300-400 mg./l
TDS thus yielding a final cost of about one-half of the 24C/1000 gal cited.
Other cost estimates cited for the DeSal Process (weak anion exchange process
developed by Rohm & Haas) have been 18c/1000 gal for a 1 MGD plant as
determined by Rohm and Haas and24c/1000 gal for a 10 MGD plant estimated
by Infilco. Culligan, Inc., is currently investigating several ion exchange
processes on a pilot plant scale of 50,000 gpd. Work is also continuing at
Pomona and at AWTRL.
The most encouraging work was that done by some Italian workers who came to
the following conclusions:
1. The DeSal Process is far superior to conventional ion exchange and makes
earlier estimates of cost out of date.
2. Up to 65% of the organic matter is removed and is quantitatively eluted
from the resin.
3. After one year's operation no change could be observed on the physical
or chemical properties of the resin.
55
-------
The authors also concluded chat ion exchange was applicable to feeds up
to 3000 mg/1 TDS - a level that we had not generally considered competi-
tive for ion exchange. Of the four methods being considered for de-
mineralization of wastewater, ion exchange will most likely be applied
earliest to full scale. The technology is well-developed and the costs
appear to be reasonable.
III. Reverse Osmosis
Reverse osmosis is a membrane process in which water is forced to flow
from a solution of high salts concentration to one of lower concentration.
In natural osmosis, water flows in the opposite direction. Pressures of
600-800 psi are required to obtain this reversal of flow. The earliest
applications of reverse osmosis were in the fields of chemical purifi-
cation and brackish water desalination. The discovery of the cellulose
acetate membrane was, perhaps, the single biggest advance in the appli-
cation of reverse osmosis to desalination.
Membranes are defined as imperfect barriers which "retain" or "reject"
molecules of a certain minimum size and will "pass" smaller molecules.
The membranes car. be tailored to almost any degree of porosity. Several
types of materials have been identified as having membrane forming prop-
erties suitable for reverse osmosis. Research is continuing on develop-
ment of more useful membranes.
Cellulose acetate membranes developed for brackish water desalination are
relatively tight (i.e. low water permeability) and can reject over 99%
of most mineral species. The water flux through these membranes is very
low ( ~ 10 gal/day/ft2 ) and are not economic for wastewater deminerali-
zation. Moreover, in treating wastewater, the membranes become "fouled"
by dissolved and colloidal organic material leading to drastic reduction
in flux. These problems have led FWQA to a membrane development program
pointed specifically toward wastewater treatment. Most of the effort to
date has been in new membrane development and in methods to control flux
decline. The most attractive membranes appear to be modified cellulose
acetate types. Current judgment is that the optimum membrane will reject
50-75% of the inorganics and 90% of the organics with fluxes of 50-100 gfd.
At the same time substantial effort is being directed toward alleviating
the fouling problem. Essentially two approaches are being taken:
(a) prevention of fouling by pretreatment procedures or by changes in the
hydraulics of the system and (b) cleaning methods once the membrane has
become fouled. A promising method for the latter is periodic rinsing
of the membrane surface with an enzyme solution. Interestingly, the
most effective enzyme solutions have been the common commercial detergent
pre-soak mixtures such as Biz.
56
-------
In addi.tl.on to membranes an extremely important aspect of reverse osmosis
is the hardware. Current modules are of several types and configurations:
(a) tubular, (b) spiral wound and (c) hollow fiber. Each of these con-
figurations has its advantages as well as disadvantages, and at this point
in development no single choice can be made. All are being investigated
concurrently. A recent projection of the economics of RO by Kaiser
Engineers compared the configuration as follows:
sq ft membrane flux
cu ft equipment gpa/sf
productivity
gpd/cf
Tubular
20
32
640
Spiral wound 250
Hollow fiber (nylon) 5400
Hollow fiber (CA) 2500
32
1
10
8000
5400
25000
From this comparison, it would seem that the follow fiber configurations
are superior but in practice hydraulic inadequacies may be a serious
drawback.
Another approach to reverse osmosis has been entitled "dynamically formed"
membranes. In this development, the membrane is formed either from the
constituents of the wastewater or from small additions of a variety of
additives. The advantage of these homemade membranes is that they can
be destroyed and re-formed whenever the membrane becomes fouled. This
work is still in the early stages of development.
Reverse osmosis has enormous potential for wastewater treatment.
Theoretically, it is conceivable that most components of wastewater can
be removed to a high degree in a single unit process. Typical removals
that have been obtained are shown in the following table:
Typical Removals from Secondary Effluent
(CA membrane, 450 psi, - 8 gfd)
% rejection
TOC
99
Phosphate
94
TDS
93
Nitrate
65
Turbidity
99+
Ammonia
85
Alkalinity
90
Organic Nitrogen
86
Chloride
80-85
57
-------
•The practical achievement of the above theoretical capability must await
the solution of some serious problems, among which are: membrane foul-
ing}membrane cost, greater (and therefore economic) fluxes, and reduction
of operating costs. On the latter, the best estimate is on the order
of 40c/1000 gal projected for brackish water desalination. Because of
the potential of this process, research on all of the problems is being
pursued vigorously-
IV. Distillation
Distillation is now the most commonly practiced method for obtaining
fresh water from sea water. Today there are 90 million gallons per day
of plants in operation or under construction in various parts of the
world, and this capacity is being expanded rapidly. As everyone knows,
distilled water is a common synonym for pure water, hence it is not
surprising that distillation is being considered for wastewater treat-
ment and renovation. But distillation of wastewater is substantially
different than distillation of sea water. Preliminary studies have
revealed that some treatment of the distillate (product) will have to be
practiced to remove volatile substances. It is also likely that the
solids and organics in wastewater will pose additional problems. All of
these aspects are being pursued.
V. Electrodialysis
Another membrane process for demineralization is electrodialysis, but,
in contrast to reverse osmosis which uses pressure as the driving force
to separate water from minerals, the energy in this case is electrical.
A direct electric voltage applied across a cell containing mineralized
water will cause the cations to migrate to the negative electrode and
the anions to the positive electrode. If cation and anion permeable
membranes are inserted between the electrodes, then mineral ions can
.be separated from the water. Characteristically, 40-50% of the dis-
solved salts can be removed in a single pass through an electrodialysis
stack.
The technical feasibility of electrodialysis has been demonstrated both
for brackish water desalination and wastewater demineralization.
But, as with reverse osmosis, membrane fouling by wastewater solids and
organics has deterred practical application. The process is being
investigated at both the Lebanon and Pomona pilot plants of AWTRL.
Emphasis of the research is on controlling the membrane fouling by
intensive treatment of the feed and by enzyme flushing of the membrane
surfaces. The process could be economically attractive once the foul-
ing problems can be solved since cost, exclusive of brine disposal,
has been estimated to be 15-20c/1000 gallons.
58
-------
Assessment for the Future
Almost surely, increasing parts of this country and the world, will look
to their wastewater as an additional source of water resources. And
just as surely, some form of demineralization will have to be applied to
reduce mineral salts. At this time, no single process, of the several
being studied, is ready for full-scale application and no single process
has a clear and obvious advantage over the others. However, ion-exchange,
because of its highly developed technology in other fields, appears to
be the process which will find earliest application. A modest breakthrough
in reverse osmosis could find this process applied, particularly to certain
industrial waste streams. It bears repetition that a suitable method has
to be found for disposal of the brine concentrates from any demineralization
process.
Recent Publications and Reports
Eliassen, R., Wyckoff, B. M., and Tonkin, C. D.
"Ion Exchange for Reclamation of Reusable Supplies"
JAWWA, 57, 1113 (Sept. 1965)
Sturla, Piero (Rome, Italy)
"Pilot Plant Studies of the Kunin Process"
Paper presented at International Water Conf., of The Engineer's Society of
Western Pennsylvania, September 30, 1964, Pittsburgh, Pa.
Pollio, F. X., and Kunin, R.
"Tertiary Treatment of Municipal Sewage Effluents"
Environmental Science & Technology, 2, 54 (Jan. 1968)
Parkhurst, J. D., Chen, C., Carry, C. W., and Masse, A. N.
"Demineralization of Wastewater by Ion Exchange"
Paper to be presented at 5th International Conf. on Water Pollution Research,
August 1970, San Francisco, California.
Kraus, K. A., Shor, A. J., and Johnson, J. S. Jr.
"Hyperfiltration Studies X. Hyperfiltration with Dynamically-Formed Membranes"
Desalination, 2, 243 (1967)
Hindin, E., and Bennett, P. J„
"Water Reclamation by Reverse Osmosis", Water and Sewage Works, 66 (February 1969)
"Study and Experiments in Waste Water Reclamation by Reverse Osmosis"
Final Report - Gulf General Atomic - Contract 14-12-181 prepared by
I. Nusbaum, J. H. Sleigh, Jr., and S. S. Kremen
"Engineering & Economic Evaluation Study of Reverse Osmosis", F. L. Harris,
Kaiser Engineers, Presented at Office of Saline Water 2nd Symposium on
Reverse Osmosis, (April 1969)
Merten, U., and Bray, D. T„, "Reverse Osmosis for Water Reclamation"
Presented at 3rd International Conf. on Water Poll. Research, Paper
No. 15 (1966).
59
-------
Cooke, W. P.
"Hollow Fiber Permeators in Indus-trial Waste Stream Separations"
Desalination, (1969/70)
Brunner, C. A.
"Pilot-Plant Experiences in Demineralization of Secondary Effluent
using Electrodialysis"
JWPCF, 39, R1 (October 196 7)
O'Connor, B., Dobbs, R. A., Villiers, R. V., and Dean, R. B.
"Laboratory Distillation of Municipal Waste Effluents"
JWPCF, 39, R25 (October 1967)
Sources of Information
Much of the research on processes for removal of minerals from wastewater
is conducted at or out of the Advanced Waste Treatment Research Laboratory.
The address of the laboratory and the principal investigators are given
felow:
1. Francis M. Middleton Director of Research
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research pe.nter
Cincinnati, Ohio 45226
(513) 871-1820, Ext. 225
Chief, Physical & Chemical Treatment
Research Program
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513) 871-1820, Ext. 230
Research Chemist, Physical & Chemical
Treatment Research Program
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513) 871-1820, Ext. 362
Sanitary Engineer,
Municipal Treatment Research Program
Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
Cincinnati, Ohio 45226
(513) 871-1820, Ext.' 262
2. Jesse M. Cohen
3. Richard A. Dobbs
4. John M. Smith
60
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
DISSOLVED BIODEGRADABLE ORGANICS REMOVAL
FROM WASTEWATER
PPB 1705
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
61
-------
PURE OXYGEN AERATION OF ACTIVATED SLUDGE
Linde Division of Union Carbide, under contract to FWQA, has completed a
comparison of pure oxygen aeration and air aeration in the conventional
activated sludge process. The study was carried out in identical parallel
trains at the 2.5 mgd Batavia, New York plant. Inefficient utilization of
costly pure oxygen has discouraged similar full-scale operation in the past.
The .covered-staged oxygen injection and dissolution concepts developed by
Linde overcome this obstacle and 90-95% utilization of the input oxygen
was achievedo
The oxygenation system used employed sealed covers on the aeration tanks
and intertank baffles to form a series of staged compartments„ Each com-
partment or stage is equipped with a submerged turbine-rotating sparger
unit and a recirculating gas compressor located on the top of the tank
cover.
The three points demonstrated by this study with the greatest potential
for reducing the cost of waste treatment are:
1. The substantial reduction in aeration volume possible with oxygen
aeration while maintaining efficient carbon and solids removal.
The oxygen train achieved better treatment in 1-1/2 hours aeration
detention time than the air train at 3 hours.
2. The high solid content of the waste activated sludge achieved by
the oxygen system; thereby, possibly eliminating the need for a
separate thickener operation. Oxygenated sludge had a Sludge
Volume Index of 40 and concentrated to about 370 in the final
clarifier underflow.
3. The reduced quantity of waste sludge produced with oxygen.
Significant reduction in the quantity of waste activated sludge
produced by the oxygen system was noted. The best estimates at
this time are that the reduction, by weight was 30-407.. Better
data on the exact amount will be obtained this summer.
The economic substitution of pure oxygen for air may eventually prove to
be one of the most significant breakthroughs in the history of the activated
sludge process. The pure oxygen process, in addition to offering potential
reduction in new plant construction, is also applicable to many existing
high-rate or overload plants which are performing poorly.
62
-------
For more Information, see report "Investigation of the Use of High Purity
Oxygen Aeration in the Conventional Activated Sludge Process" by Llnde
Division of Union Carbide Corporation, Contract No. 14-12-1+6 5, or contact:
Mr. Richard C. Brenner
Advanced Waste Treatment Research laboratory
Ohio Basin Region
Cincinnati, Ohio 45226
TRICKLING FILTERS
There has been no major breakthrough in the past two years. This process
is capable of producing a good quality effluent having a BOD^ of less than
20 mg/l if lightly loaded. In the United States, the tendency is to load
the filter at a much higher rate than is done in England. Thus, we find
today many installations that will have difficulty in meeting the more
stringent water quality standards.
It is not enough to Just look for completely new processes, but attention
and action must be given immediately to applying known technology to up-
grading present treatment plants. All the needed new plants and plant
expansion cannot be built in a short time. Substantial amounts of pollu-
tion can be prevented from reaching our surface waters by upgrading present
plants. There are several ways of achieving higher removals. There is
probably no one solution that will work at all installations, for each
plant is different. If a plant is not getting good removal and the impair-
ment is not due to toxic or grossly atypical waste, then it is usually due
to either hydraulic overload, organic overload, or poor final liquid-solids
separation. The following are suggested ways of alleviating these conditions.
Easing hydraulic overload
1. Find and reduce needless sources. Infiltration, downspouts, and
cross connection can contribute greatly to the flow.
2. Use large interceptors as holding tanks. Many towns use their
main interceptor to the plant to back-up the flow during the day
and treat it at night when the flow is low.
3. Construct an equalizing or surge tank to smooth out the high peak
flows. An equalization tank will mix and dilute toxic wastes,
giving better downstream settling and lessen load fluctuations.
Aiding organic overloaded plants
Most organically overloaded plants can be aided by the same methods
suggested for hydraulic overloads since they commonly occur con-
currently. Additional methods are:
63
-------
1. Have industry program the load for slow release. In smaller towns,
most industries are willing to program extremely high organic waste
flows.
2. Have industry treat at source using a roughing filter or other
appropriate means to relieve part of the load.
3- Treat digester supernatant return by alternate methods or program
return load to time of low load.
4. Remove more material in the primary tank by using iron or aluminum
salts and polymers in the incoming waste. This will also remove
phosphorus.
Lessen final solids discharge
One of the greatest improvements that can be made in secondary treat-
ment is reliable solid removal from effluents. For efficient overall
removal, the final settler must remove better than 98$ of the solids.
If overflow weirs are submerged several inches with the present flow,
then there is no recourse except to increase settler capacity. For
less hopeless cases, the following can be tried.
1. Chemical flocculation or precipitation in process or final effluent
treatment.
2. Improve inlet and/or overflow design.
3. Install a mlcroscreener.
Install mixed media filters.
5. Install tube settlers.
If a town has a trickling filter that is water tight or can be made so, the
filter unit can be simply converted to an aeration tank. This can be done
by removing the filter media and installing a surface aerator. The existing
primary and final clarifiers can be utilized with minimal structural and
piping changes. This type of conversion will usually increase the capacity
of the plant twofold for a fraction of the cost of a completely new plant.
All the methods discussed are not new, but are well-proven processes. Thus,
there are answers to the question on how a town can meet the new water quality
standards. All that is needed is an awareness of the fundamentals Involved
and a willingness to pay for and use all the technology that is kncwn.
64
-------
ROTATING BIOLOGICAL DISCS
The rotating biological disc method of treating waste has been used In
Europe for at least the last five years. The system basically consists
of closely spaced rotating discs alternately submerged In wastewater and
exposed to air. Wastewater continuously flows parallel to the discs. The
waste level Is slightly less than half the disc diameter. The units are
usually arranged In series or stages.
The discs are molded of low-density expanded polystyrene. The entire
downward load is offset by the buoyancy of the discs. Thus, the only power
required to rotate the discs is that needed to overcome bearing friction.
Microorganisms attach themselves to the discs and perform the same function
as in a trickling filter. The blomass sloughed off the discs is removed in
a final clarifier. In short, the rotating biological disc method is a modem
version of the "Immersion Filter" developed by Buswell in the middle twenties.
IWQA has funded a grant (1701 EBM) with Rutgers University to assess the
degree of treatment and to obtain operating data on this method of treatment.
The pilot plant used In this study is a ten-staged unit with a design flow
of 8 gun. This gives a detention period of 5 minutes per stage or a 50-
minute overall detention time for the disc unit. The plant has been in oper-
ation for about one year at the Jamaica Treatment Plant In New York City near
the Kennedy International Airport. Data obtained thus far show that the unit
is oxidizing about 93^ of the biodegradable carbonaceous matter and 8o£ of
the anmoniacal nitrogen In the primary effluent being treated. A report on
the work Is not available at this time.
A demonstration grant (11010 EBX) has been awarded to the Village of Pewaukee,
Wisconsin to evaluate the effectiveness and efficiency of the rotating bio-
logical disc method for treating municipal wastes on a full-scale community
level. The performance of the unit will be compared directly with sua existing
trickling filter under identical conditions. The design flow of the disc unit
is 0.46 mgd. The unit is scheduled to be on-Btream the latter part of thl6
year.
The rotating disc system has an advantage over a trickling filter unit In
that recycle is not necessary at night to keep the biological mass wet be-
cause the trough always contains liquid. It seems quite possible that the
method can produce an effluent in quality some place between that of a trick-
ling filter and an activated sludge unit. It is conceivable that the system
would find application at seme of our Federal installations, such as small
parks or rest stations where there is a wide variation in the flews. There
is a small two-stage unit available that handles population equivalents of
12 to 200 persons.
The main disadvantages of the method are that it must be housed to protect
It from storms, hail, etc. and the large disc surface area required. For
90ia removal, the unit load is 2.7 gal/day/ft of disc surface area. Normally
the discs are ten feet in diameter and the disc spacing is 0.81*6 Inches.
65
-------
DT3THIMESTATION OF WASTE TREATMENT PLAIfTS
Instrumentation and control have not yet caught up with the basic require-
ments of wastewater plants. There are several reasons for the limited use
of continuous automatic analysis and control. Some of these are the absence
of sensors to measure seme of the most important factors directly, the fairly
high cost of instruments available, and the willingness of those in the waste
treatment field to decide that automatic operation is necessary and to take
all the steps required to bring it to fruition. In the past, the cost of
Instrumentation has eliminated them from consideration by managers of 1
and medium-sized plants.
Recent emphasis on water quality standards is bringing about a natural in-
crease in the extent of automatic control. This is especially evident in
never facilities where instrumentation is no longer an "afterthoughtM, but
an integrated part of plant design. Unfortunately, sane engineers engaged
in designing new plants have not kept up with the Improved processing tech-
niques . The design of a modern plant for treatment of wastewater requires
a considerably broader knowledge of treatment and control techniques than
in the past.
Many sensors cannot be used in treating wastewater because they became fouled
by the gross solids, greases, oil, and aquatic growths. Despite the encum-
brances inherent in the physical makeup of raw wastewater and sludge drawoff,
measuring devices and instrumentation are now available that can monitor and
control most of the secondary plant flow systems. The real problem in auto-
mating the various flow regimes is not a lack of flow controlling equipment,
but the inability to rapidly measure biological activity or "state-of-health"
of the system. For instance, wasting of activated sludge could logically
be based on the active mass of microorganisms in the system. However, the
closest we cam ccme now to determining active mass is mixed liquor volatile
suspended solids and this has been estimated to represent 50 to 100 percent
more active solids than are actually present. Thus, the difficulty in con-
trolling the treatment plant is directly attributable to the inability to
model constantly changing life processes.
It would appear that the best index for understanding and controlling the
activated sludge process would be the amount of living cells in the aeration
tank. No method now exists which permits determination of the microbial
activity in a manner useful to process control. Adenosinetriphosphate (ATP)
is present in and essential to all living cells. Measurement of ATP would
be a rapid and unequivocal method for active microbial mass. Blospherlcs
Incorporated is under contract (14-12-1^9) to design and fabricate an in-
strument for use in the ATP assay. In addition, they vlll adapt the fire-
fly blolumlnescent method to determine the ATP of activated sludge which is
directly proportional to the biomass. E.I. DuPont is now producing commer-
cially the reagents needed for the test; therefore, there will not be any
difficulty in obtaining the reagents if the method becomes a reality. This
method probably can be automated. The time to perform the tests should be
about 15 minutes if done manually.
66
-------
Biological process efficiency Is nov measured by various laboratory analytical
techniques. The time required to collect, transfer samples, and perform the
analyses may take anywhere from three hours to five days. The time involved
In obtaining data seriously hinders rapid and effective process control. On-
line Instrumentation designed to yield reliable, useful information in terms
of minutes instead of hours would contribute significantly to Improving plant
operation. Contracts are nov being let to develop an on-line Instrument to
measure the organic strength of influent and effluent streams at a waste treat
ment plant. The instrument will be capable of analyzing both filtered and un-
flltered samples. This will entail developing an on-line macerating device
as well as an on-line filter. Within the next year, it Is hopeful that a
full automatic on-line COD and TOC analyzer will be available to treatment
plants.
A wastewater treatment plant can have too much instrumentation and auto-
mation or it cannot have enough. Most wastewater treatment plants now have
too little instrumentation to give adequate control. The new pilot plant
at AWTRL In Cincinnati will test new process control equipment and Instru-
ments in the coming year. The aim here is to operate them under controlled
conditions to determine durability, performance, and limitation. ThlB In-
formation will then be made available to construction grants people and con-
sultants so that new plants can be operated more efficiently.
67
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
MICROORGANISMS REMOVAL FROM WASTEWATER
PPB 1706
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
69
GPO 821-571—14
-------
Introduction
In this first annual report covering the status of disinfection of wastewater
and AWT treatment plant effluents, it is believed that a look at where we
stand now and what is planned for the future should provide a better under-
standing of what may be expected from this subprogram.
Present Status of Chlorination
The most desirable objective is to be able to say that application of a
specified dose of chlorine would provide safe disinfection of all effluents.
The coliform test should be considered the primary standard; the chlorine
residual can only be considered as a secondary standard and it is only valid
to the extent confirmed by the results obtained in the coliform test. The
conclusions of Browning and McLaren (jour. Water Poll. Control Pted., August
1967) indicate the problems of operating on a basis of a specified combination
of chlorine residual and contact time. They state *\3enerally speaking, a
correlation exists between chlorine residual and coliform density (coliform
densities decrease with increased chlorine residuals) but the individualities
of waste treatment plants and their effluents make it difficult to apply a
correlation detemined from one plant to other plants." Each plant must
develop its own data for correlating chlorine dosage, residual, and contact
time to yield predictably the desired reduction in colifora count.
The most highly clarified and oxidized effluents are the easiest to disinfect.
If good control of microorganism content is to be attained by chlorination,
good secondary waste treatment should be the minimum. Chlorination of pri-
mary effluents should not be considered an acceptable practice In mo6t sit-
uations except as an Interim process until secondary treatment facilities
can be constructed.
Same concern has been expressed regarding the fact that numerous viruses
are more resistant to chlorine than the coliform bacteria. Methods of using
viruses as an indicator of chlorination efficiency have not reached the stage
where practical tests for routine use are available. The coliform test still
remains an effective criterion for disinfection of drinking water. Except
for hepatitis, clearly defined outbreaks of virus diseases traceable to
drinking water have not been reported (Clarke, Berg, et al., Adv. Water Pol.
Control Research, Fergaunon Press, McMillan Company, New York, Vol. 1, I96U).
Epidemics of hepatitis originating in chlorinated water supplies Judged satis-
factory by the coliform test have not been reported except In instances where
obvious deficiencies In chlorination were shown or suspected. It Is not,
therefore, considered likely that effluents disinfected to satisfactojy colifonn
70
-------
destruction levels are much of a health hazard. FWQA has funded a grant
(69-G385) to investigate the possibility of locating a nev bacterial indi
cator that is sufficiently more resistant than collform organisms to pro-
vide a safety factor for virus destruction. The emphasis is on the dis-
covery of an organism that can be enumerated by simple plate count or MF
procedures.
Status of Research
Because of personnel limitations and other problems, research in the dis-
infection program haa been limited in scope thus far. The outlook for the
future is improving and a marked increase in the number and variety of
grant and contract projects is anticipated in FY 1971.
In-House:
There have been numerous reports in the literature of a major synergistic
effect of gamma radiation on the disinfecting action of chlorine, but the
work reported has not been adequately controlled. An investigation to de-
termine whether gamma radiation exerts a synergistic effect on the dis-
infecting action of chlorine is now in progress. This work is being done
under very carefully controlled conditions. Present progress indicates
that this project will be completed in FT 1971, and it is anticipated that
definitive data will be produced to either support or negate the existence
of a synergistic effect.
Grants :
Grantee
Illinois State Water
Survey, University of
Illinois, Urbana,
Illinois.
Subject
Disinfection of
Sewage Effluents
with Chlorine and
Bromine.
Project Director
Expected Ccmp. Date
Dr. F. W. Sollo
9/30/70
City of St. Michaels
St. Michaels, Maryland.
(Clow Waste Treatment
Division Aer-o-Flo
Yeomans, Melrose
Park, Illinois En-
gineering Operator for
Grantee)
Controlled Treatment
System-Ultraviolet
Disinfection.
John A. Roeber
7/9/70
University of Illinois
Urbana, Illinois
New Microbial Indi-
cators of Wastewater
Disinfection.
Dr. R. S. Engelbrecht
9/30/71
Much of our research in disinfection of wastewater deals vith problems re-
lated to the use of chlorine. Chlorine, however, is not necessarily the
answer to all of our disinfection problems, and little information is avail-
able regarding the use of other disinfectants for the destruction of micro-
71
-------
organisms in wastewater. Other disinfectants are, therefore, beir^? in-
vestigated. The program is planned to develop, as rapidly as possible,
methods for the use of a variety of disinfectants and provide guidelines
for their practical application. The rationale for this approach is to
make available to the sanitary engineer a spectrum of proven disinfection
processes from vhich he can select the one most applicable to a specific
waste treatment disinfection problem.
Research Statements of Weed
The extent to which the Disinfection Subprogram can satisfy the needs of
the respective Regional Programs depends upon how well we can identify
those needs and formulate work programs to satisfy them. Satisfaction
of those needs can best be expedited by, good liaison with the Region.
It would be most helpful if the Regions would submit statements of re-
search needs to cover specific problems in need of solution. The devel-
opment of an adequate research work plan to satisfy a particular need,
however, depends upon the content of the need submitted. This can best be
accomplished through a preliminary discussion of the proposed need by the
Program Chief and the proponent.
The Comnercial Telephone Number: (513)-871-lB20, ext. 202
The ITS Telephone Number: (513)-871-lB20, ext. 202
For further information contact:
Cecil W. Chambers
Robert A. Taft Research Center
Advanced Waste Treatment Research Laboratory
Ohio Basin Region
Cincinnati, Ohio 45226
72
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
ULTIMATE DISPOSAL
PPB 1707
Division of Process Research & Development
Federal Water Quality Administration
U0 S. Department of the Interior
73
-------
IE ULTIMATE DISPOSAL RESEARCH PROGRAM
at the
Robert A. Taft Water Research Center
Cincinnati, Ohio
The Ultimate Disposal Research Program is responsible for finding places
to put the pollutants "which have been extracted from waters "by conventional
and Advanced Waste Treatments. Disposal of residues must of course be done
In -ways that vill not cause pollution and ideally the residues should be
reused to the maximum extent possible. Our responsibilities cover disposal to
the air, waters, and to the land, as well as reuse and recycling of constituents.
Control of pollution of underground waters is a specific assignment of the
Robert S. Kerr Water Research Center, but general considerations of deep-
well disposal are also reviewed here. Deep-well disposal Is not a generally
applicable method and should be used only where the local geological forma-
tions are particularly favorable and there are no acceptable alternative
methods for disposal.
Disposal of wastes Is the most frequently neglected part of our modern
industrial civilization, and is directly responsible for our polluted planet.
Attention to unit operations, with little regard for the fate of by-products
which are no longer interesting and are frequently embarassing, has produced
the present situation. In an attest to focus attention on disposal problems,
and to reduce some forms of pollution at their sources, a number of papers
have been published calling attention to valid and invalid disposal methods
(see Bibliography).
Disposal of organic sludge from conventional wastewater treatment
plants accounts for up to 50$ of the total costs Df treatment. Disposal of
sludge requires removal of the water content which accounts for 95 to 99,5^6
of the weight, followed by storage of oxidation of the organic matter.
Since activated sludge has a much lower solid content than primary sludge,
the addition of secondary treatment greatly increases the sludge disposal
problems of the plant. Equipment which was effective for primary sludge
frequently proves to be inadequate when waste activated sludge is added. The
current JWQA policy, requiring secondary treatment for most large plants
discharging to inland waters, will greatly magnify the sludge disposal pro-
blems in this country.
Incineration can be accomplished in modern equipment without producing
pollution of the air or water. An outstanding example of pollution-free
incineration maybe seen at the South Lake Tahoe Advanced Waste Treatment
Plant (see "Product Recovery" in attached list of contracts). At Lake Tahoe,
organic sludge and lime sludge are separately incinerated in two incinerators
which produce absolutely no plume or odor. It is impossible to tell from
outside the plant whether the incinerators are working or not.
The cost of incinerating sludge is directly dependent on the water
content; therefore, efficient dewatering is the key to efficient incineration.
Present dewatering techniques include sedii&entatlon, vacuum filtration,
pressure filtration, and centrifuging. All of these techniques are being
74
-------
examined in full-scale equipment under demonstration grants. There are a
number of chemicals vhich aid devatering, including lime and salts of iron
and aluminum, as veil as synthetic polymeric flocculants. A limited amount
of laboratory vork is devoted to evaluation of available products, but it
is recognized that field experience provides the most usefuly information.
Radiation, freezing, pressure cooking, treatment vith enzymes and the
addition of sludge ash have all been proposed as useful aids to devatering.
Both radiation and freezing have turned out to be too expensive for the
benefits achieved. Pressure cooking vith or vithout the addition of oxygen
is being evaluated at Colorado Springs, Painesvllle, Ohio and Santee Cali-
fornia. Pressure filtration vith ash is being evaluated at Cedar Rapids,
Iova, and vacuum filtration has been studied in the laboratory. A contract
for the development of enzymes to thicken sludge has been undervay at
Aerojet-General.
Land disposal of sludge vithout previous devatering is particularly
attractive, since it uses a lov cost filter, the earth, and lov temperature
oxidation by microorganisms. Although larger quantities have to be trans-
ported vhen the sludge is not first devatered, the transportation can be
done economically by pipeline. A recent contract vith Bechtel, Inc.
appraises the cost of pipeline transport of sludges for the case of Cleveland,
Ohio, but can be applied to many other situations. Land disposal of sludge
if properly operated is true conservation of resources and recycles essen-
tial elements to the biosphere. On lov grade land, sludge improves
fertility and enhances the value of the environment. Political objection
to other people's "sludge" and a natural aversion to old fashioned smelly
sevage farms has held back rational utilization of the land for sludge
disposal even though its cost may be as lov as one fourth of that for drying
and incineration. Papers have been published and talks given to point out
the advantages of land disposal. Greenhouse and field plot studies are
undervay, both in-house and under grants, to improve our knowledge of land
disposal, A recent vorkshop at Chicago revieved the state of the art of
land disposal and an excellent summary has appeared in the May 16, 1970
issue of the Prairie Fanner.
There are valid objections to land disposal of sludges, particularly
if they are improperly applied. Excessive loadings of sludge can contaminate
ground vater and in some situations it may be necessary to collect and treat
vater from underdrains as it is done in major irrigation projects. Nitrates
are apt to be the principal pollutant, Just as they are vith irrigation.
There is little evidence that the soil vill be poisoned by excessive
quantities of organic matter or by heavy metals in the sludge, if proper
care is taken. Pathogens can be controlled by pasteurization if necessary,
or by long holding periods in lagoons. Even vithout these protective
measures there have been no reports of sludge bom disease since 1919,
despite videspread application of sludge to farm lands in this country and
in Europe. Studies of pathogen survival in soil are undervay.
Sludge can not be stored vithout 6ome form of stabilization to prevent
putrefaction and the development of objectionable odors. Anaerobic digestion
is a reasonably veil understood process that causes a great deal of difficulty,
particularly vhen practiced on a small scale. Aerobic stabilization is poten-
tially capable of destroying nitrogen compounds and appears to be an ideal
pretreatment for land disposal. The process is poorly understood, and the
75
-------
costs of aeration are high. Some in-house work on aerobic stabilization
has been carried out and we are looking for a suitable contractor to investi-
gate this process further. Treatment with lime is an attractive alternative
to digestion preceding land disposal.
Petroleum wastes represent an interesting application of land
disposal. Despite common knowledge that oil "kills the soil", well-oxidized
soil will destroy up to 12 inches of petroleum by-products in a year under
favorable conditions of temperature and humidity, provided that the soil
is kept well-aerated (Dotson, et al., 1970).
Industrial sludges frequently consist of soil minerals such as calcium,
carbonate and sulfate and oxides of iron and aluminum. There minerals can
be incorporated into the soil in substantial quantities without destroying
the agricultural value of the land. In all applications of wastes to the
land it is necessary to have good farm management, and not to treat the
land as a dump.
The land treatment of sewage is of interest for small communities.
This process is frequently referred to as the "living filter". Extensive
work on this application has been done at Pennsylvania State University and
by several food processes. We have recently received a number of proposals
for grants to use the "living filter" treatment for phosphate removal in
the Great Lakes area.
Disposal to the atmosphere should be limited to gases which are naturally
present. In addition to nitrogen, oxygen, water vapor, and carbon dioxide
these include ammonia, nitrous oxide (NgO;, and products of combustion such
as higher oxides of nitrogen and sulfur. The last two groups are well-
re cognized air pollutants, but are contributed in insignificant quantities
by well-operated incinerators. Nitrous oxide is remarkably inert and is
probably not an air pollutant. Ammonia is rapidly absorbed by moisture and
vegetation and reacts with the oxides of sulfur, preventing formation of
sulfuric acid. It could be an objectionable nutrient if released upwind
of a large body of water, but it could reduce air pollution in some
industrial areas. We are studying the removal and destruction of amoonia
under a contract with Battelle-Northwest.
Conversion of nitrates to nitrogen gas by dilute solution reduction has
been the subject of another contract which is being brought to a close. Die
process does not appear to be practical for municipal effluents but may be
useful for certain industrial wastes.
Brine disposal can contribute a significant part of the cost of water
renovation in inland areas. The problem of brine disposal at three major
western cities is being evaluated under a contract with Burns and Roe. If
salt water lakes or playas are not available, it may be necessary to evapo-
rate the bulk of the water and transport the remaining slurry to a salt-
water area. Evaporation ponds appear to be the best solution in arid areas
where desalting is most necessary. A small evaporation pond study is being
carried out as a part of our cooperative research program with IACSD at
Pomona. We are currently regotiating a contract to evaluate the potential
of cooling towers for evaporating bring solutions, particularly in high
rainfall areas.
76
-------
Recovery and reuse of the chemical values in sludge Is eethetically
attractive, but only in rare cases are sludges attractive sources of rav
materials for other operations. Utilization of sludge to increase the agri-
cultural value of land is, of course, one form of reuse which ie economically
attractive. At the other end of the Bcale, although sludge 1b a good source
of Vitamin B-12, extraction of this substance does not significantly reduce
the problem of sludge disposal. The sale of dried sludge for agricultural
purposes at Chicago defrays only a quarter of the cost of drying sludge.
Recovery of chemicals used to treat sewage or sludge is seldom able to pay
the cost of recovery. Lime recovery at Lake Tahoe is probably no better
than a break-even proposition; however, it reduces the sludge disposal pro-
blem significantly. We are investigating under contract possible markets for
the phosphate-rich fraction of the recovered lime which "would otherwise be
disposed of in a land-fill. In-house studies of aluminum recovery from
Bludges containing aluminum that was used to remove phosphates indicate
that in most situations the recovered aluminum salt would cost more than
new chemical; however, the recovery process greatly improves the dewatering
qualities of the sludge and may be economical from that point of view. We
have also found that recovered lime is superior to fresh lime on a calcium
hydroxide basis when used for phosphate removal. The recovered lime pro-
duces sludges which are easier to filter and centrifuge because of the
presence of inert filter aids formed by the ash.
A small contract has studied the recovery of amino add values from
sludge and their utilization as aninal feed. Activated eludge ia essentially
a form af eicgle-cell protein tenGaining, unfortunately, substantial quanti-
ties of undigestible matter, If the nutritive amino acids and sugars can
be economically separated from the undigestible fraction, it should be
possible to make a valuable feed supplement (Bean and Bouthilet, 1970).
Attached is a list of references to pertinent publications from the
Ultimate Disposal Program and a list of contracts dealing with significant
aspects of our work.
For further information contact:
Robert B. Lean
Robert A. Taft Water Research Center
Advanced Waste Treatment Research Lab.
Ohio Basin Region
Cincinnati, Ohio 45226
77
-------
PUBLICATIONS
Ames, L. L., Jr., and Dean, R. B., May 1970. "The Use of Alumina Columns
for Phosphorus Removal from Secondary Sevage Effluents," J. Water
Pollution Control Federation h2(5), l6l-lT2
Dean, R. B., December 1968. "Ultimate Disposal of Waste Water Concentrates
to the Environment," Environmental Science & Technology 2(12), 1079-1086.
Dean, R. B., March 1969. "Ultimate Disposal of Advanced Waste Treatment
Residues," TAPPI 52(3), 1*57-^61
Dean, R. B., June 1970. "Wastes from Membrane Processes," Environmental
Science & Technology U(6), U53.
Dean, R. B., 1969. "Ultimate Disposal of Waste Water: A Philosophical Viev,"
Water - 1969", Chemical Engineering Progress Symposium Series 6^,(97), 1-^.
Dean, R. B., September 1969. "Colloids Complicate Treatment Processes,"
Environmental Science & Technology. %(9), 820-82U.
Dean, R. B. and Bouthilet, R., July 1970. "Hydrolysis of Activated Sludge,"
to be presented at the Fifth International Conference on Water Pollution
Research, San Francisco, California.
Dotson, G. K., Dean, R. B., Kenner, B. A., and Cooke, W. B., July 1970.
"Land Spreading, A Conserving and Non-Polluting Method of Disposing of
Oily Wastes," for presentation at the Fifth International Conference
on Water Pollution Research, San Francisco, California.
Evans, J. 0., February 1968. "They Spread 'Black Gold* on Their Fields,"
Pennsylvania Farmer 178(3). 36.
Evans, J. 0., June 1969. "Ultimate Sludge Disposal and Soil Improvement,"
Water & Wastes Engineering 6(6). 14-5-US.
Farrell, J. E., Salotto, B. V., Dean, R. B., and Tolliver, W. E., 1968.
"Removal of Phosphate from Wastewater by Aluminum Salts and Subsequent
Aluminum Recovery," "Water - 1968", Chemical Engineering Progress
Symposium Series bU(90), 232-239.
Mercer, B. W., Ames, L. L., Touhill, C. J., Van Slyke, W. J., and Dean, R. B.,
February 19T0. 'Ammonia Removal from Secondary Effluents by Selective
Ion Exchange," J. Water Pollution Control Federation ^2(2), R95-RIO7.
Mulbarger, M. C., Grossman, E,, III, Dean, R. B., and Grant, 0. L., December
1969. "Lime Clarification, Recovery, Reuse, and Sludge Devatering
Characteristics," J. Water Pollution Control Federation l»-l(l2),
2070-2085.
78
-------
CONTRACTORS' REPORTS
TVRC-1 (lU-12-52), October 1968. "Dilute Solution Reactions of the Nitrate
Ion as Applied to Water Reclamation", Rocketdyne Division of North
American Rockwell Corporation.
TWRC-5 (WPRD 26-01), March 1969. "Ammonia Removal from Agricultural Runoff
and Secondary Effluents by Selected Ion Exchange", Battelle-Northvest.
TVRC-8 (l^-12-Ul3), March 1969. "Evaluation of Operating Parameters of
Alumina Columns for the Selective Removal of Phosphorus from Wastewaters
and the Ultimate Disposal of Phosphorus as Calcium Phosphate", Battelle-
Northvest.
TWRC-10 (1U-12-U15), September, 1969. "Mathematical Model of Sewage Sludge
Fluidized Bed Incinerator Capacities and Costs", General American Trans-
portation Corporation.
WPRC 1T0T0 DJW (lU-12-U95)» November 1969. "State of the Art Review on
Product Recovery", Resource Engineering Associates.
WP-20-4 (PH 86-66-32), May 1968. "A Study of Sludge Handling and Disposal",
R. S. Burd, Dow Chemical Company.
1^-12-171, January 1970• "Ultimate Disposal of Phosphate from Waste Water
By Recovery as Fertilizer", W. R. Grace & Company, Dearborn Chemical
Division.
79
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
WASTEWATER RENOVATION AND REUSE
PPB 1708
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
81
-------
1970 STATUS OF WASTEWATER RENOVATION AND REUSE
PPB - 1708
Reuse applications of wastewater include irrigation, formation of
recreational lakes, industrial uses, groundwater recharge for a
variety of reuses, and direct domestic reuse. Some of the applications
can no»? be considered well established. Others are only beginning to
be considered. There is, however, some activity in each area at this
time.
IRRIGATION
Use of biologically treated wastewater for irrigation of non-edible
crops and for parks and golf courses has become fairly widespread.
With the technical feasibility of this application no longer in doubt,
it should become more common in the future. Use of wastewater has the
benefit of supplying significant amounts of plant nutrients, thus
reducing fertilizer requirements. R&D Grant projects at Colorado Springs,
Antelope Valley near Los Angeles, Irvine Ranch, California, and South
Lake Tahoe, California include production of water for irrigation. An
area in which wastewater is not used is for irrigation of food crops.
Studies are needed to define better the water quality for this application.
RECREATIONAL LAKES
Filling of recreational lakes with renovated wastewater was begun at
Santee, California in 1961. The success of that project has resulted
in the establishment of several other lakes and many more are now being
planned. To use wastewater for this application requires at least
biological treatment and phosphorus removal. At Santee, phosphorus removal
was first accomplished by passing biologically treated water through
natural gravel beds. This method will probably be replaced by chemical
precipitation using lime. Work at the site is being supported by an R&D
Grant.
At Antelope Valley, California filling of a recreational lake with
renovated wastewater was begun early this year. Treatment of the water
at this location includes oxidation ponds and chemical clarification with
alum. Development of the treatment system was partly supported by FWQA.
The full scale project is being supported by an R&D Grant.
Another recreational lake project is that at South Tahoe. Indian Creek
reservoir receives very high quality water from the Tahoe advanced waste
treatment plant. The water is secondary effluent that has been clarified
using lime and carbon treated.
The use of wastewater for recreational lakes can often be combined with
irrigation. The lake merely serves as a reservoir for the irrigation
water. The Tahoe site is an example of this dual purpose reuse.
82
-------
INDUSTRIAL REUSE
Industrial reuse of wastewater represents a very large potential application.
The largest single industrial use of water is for cooling water with an
estimated annual volume of 57,000 billion gal. Two other important uses
are for process water and boiler water feed.
The only major industrial reuse of wastewater up to this time has been
for cooling water. For a number of years the Bethlehem Steel Company
plant near Baltimore has been using secondary effluent for this purpose.
Generally, it has been found that phosphorus removal is required for the
water to be acceptable. At Baltimore the peculiar composition of the
water allows phosohorus removal to occur during biological treatment.
At other locations, such as at Las Vegas where the Nevada Power Company
uses wastewater in their condensers, tertiary phosphorus removal is
required. Lime treatment is used at the latter site.
FWQA did not support the early work on reusing wastewater for cooling
purposes. Presently, however, Colorado Springs is receiving R&D Grant
support for work in this area. A recently funded R&D Grant to Contra
Costa County, California also includes reclamation of wastewater for
cooling.
There is a need to investigate the use of wastewater for other industrial
applications. The recent R&D Grant to Contra Cos^a County includes study
of wastewater for boiler water feed. Work at that location may be
extended to other industrial uses. More projects of this nature appear
justified.
GROUNDWATER RECHARGE
An increasingly serious problem in water short areas is the lowering of
the groundwater level. This occurs because water is pumped out but is
not replaced. In coastal areas the result can be intrusion of seawater
into aquifers making them unusable. In other locations brackish water
may eventually replace the water removed.
It has been recognized that renovation of wastewater and recharge of
this water may be a practical method for overcoming the problem.
Recharge may be carried out by surface spreading of the water or injection
into a well. In the Los Angeles area, surface spreading is being practiced.
Recharge was begun in 1962 of the effluent from the Whittier Narrows Plant.
This plant, operated by the Los Angeles County Sanitation Districts, pro-
duces a very high quality secondary effluent. Because of the porous
nature of the spreading surface, no further treatment has been found
necessary. Additional biological oxidation and nitrification of the
effluent do take place during percolation through the soil. The quality
of the renovated water is further improved by dilution with the natural
groundwater.
83
-------
In locations where the percolation rate is low or where spreading
areas are not available, well injection would be necessary. Care
must be taken in these cases to assure that the water is of proper
quality to be compatible with the strata of the aquifer, i.e., will
not form precipitates which clog the area around the well. Further-
more, the water must not contain suspended matter that will cause
clogging. Orange County, California has experimented with injection
of wastewater to decrease seawater intrusion. Treatment of the
wastewater consisted of oxidation in a trickling filter followed by
alum clarification. Nassau County, Long Island is studying injection
for prevention of seawater intrusion and for other uses. This work is
being supported by an R&D Grant. Treatment of the wastewater at this
location consists of activated sludge, alum clarification, and granu-
lar carbon treatment. Nitrogen removal is also being considered.
DOMESTIC REUSE
Reuse of wastewater for domestic purposes involves both non-potable and
potable applications. Non-potable use is not new and is no longer rare.
Since 1925 treated wastewater has been used for flushing and other pur-
poses at the Grand Canyon. Treatment consists of activated sludge, coal
filtration, and chlorination. Similar systems are being used in other
water-short resort areas. A biological treatment unit followed by
membrane filtration is being tested at Pikes Peak. This work is being
supported by an R&D Grant. It produces water of high clarity.
Instances of indirect potable use of renovated wastewater, such as occurs
when a municipality practices water recharge, are increasing. In these
cases there is usually a large amount of dilution water. The situation
is similar to that occurring in many cities where river water containing
effluents from cities upstream is used for the water supply.
The concept of direct reuse of wastewater for potable water has been
discussed at length by many authorities in the water field-for a decade
or more. Essentially no direct reuse was actually carried out, however,
until 1969 when a renovation plant at Windhoek, Southwest Africa began
operation. For more than a year this plant has been supplying about
one-third of the total water supply. The treatment system includes
biological oxidation by trickling filter, further oxidation in
maturation ponds,algae separation by alum flotation, foam fractionation
for removal of foaming contaminants, filtration, carbon treatment for
removal of remaining organic materials, and breakpoint chlorination for
removal of any residual ammonia and for disinfection. This pioneering
operation will have an important bearing on the growth of direct waste-
water reuse. Other African communities are very much interested in
similar projects. Continued success at this location should contribute
significantly to the acceptance of this reuse concept.
84
-------
OTHER SOURCES OF INFORMATION
Many articles have been written recently about reuse of wastewater. While
these have dealt at length with the philosophy of reuse and possible
treatment systems, they have not often reported actual reuse results.
Much practical information on reuse has, undoubtedly, never been published.
This information is of great importance to municipalities and to potential
reuse customers in making decisions. There is a strong need to collect
and analyze existing reuse results and to make them available in unified
form.
A number of reuse articles have been collected in "Water Reuse", Chemical
Engineering Progress Symposium Series No. 78, Vol. 63, 1967. Reading of
this publication is recommended.
For additional information contact Robert A. Taft Water Research Center,
4676 Columbia Parkway, Cincinnati, Ohio 45226.» Attention: Francis M.
Middleton or Carl A. Brunner.
85
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
WASTE TREATMENT OPTIMIZATION
PPB 1709
Division of Process Research & Development
Federal Water Quality Administration
U. S. Department of the Interior
87
GPO 821—571—15
-------
Waste Treatment Optimization
PPBS Category 1709
The four principal areas of activity for PPBS Ca.tegory 1709, Waste
Treatment Optimization are shown in Figure 1. A list of in-house
reports completed is shown in Table I.
Design and performance technology is principally concerned with
finding quantitative expressions for performance and cost of waste-
water treatment processes as a function of the nature of the waste-
water to be treated and the decision variables associated with the
individual processes. These quantitative relationships take the
form of mass bcl^nce relationships for all of the elementary chemical
and physical constituents of contamii nt present in the water, rate
of reaction equations, an-i equations expressing the separation
efficiency between liquid, particulate, and gaseous phases. Normally,
a group of equations is required to express the performance of the
process operating over the full gamut of operating modes and design
decisions. This group of equations is often referred to as a
mathematical model for the process. Mathematical models can be
steady-state, quasi-steady-state, or time-dependent. Time-dependent
models are of interest when the quality of the effluent stream from
the process as a function of time is important or when the effective-
ness of various kinds of control schemes is being considered. The
computational procedure for solving all of the quantitative equations
simultaneously is usually too laborious to be accomplished by hand
calculation. The digital computer is, therefore, used in most cases.
Expressing the models as computer programs has the additional advantage
of packaging the information in succinct form readily usable by design
engineers and planners.
A list of reports produced as a result of in-house activity is shown
in Table I. A list of reports which have been completed as a result
of contracting activity is shown in Table II. Only three of these
contractor reports are now available for distribution. Other
contracts in force will produce models for multiple hearth incinera-
tion of sewage sludges and microscreening. Contracts in force will
also produce capital and operating and maintenance cost data for all
of the conventional processes as well as a cost estimating guidelines
manual and a staffing guidelines manual.
88
-------
TREATMENT OPTIMIZATION RESEARCH PROGRAM
I. DESIGN AND PERFORMANCE PREDICTION TECHNOLOGY
1. Develop quasi-steady-state and time-dependent models
for preliminary design and simulation
2. Validate design and simulation models by comparison
with detailed measurements on operating plants
3. Develop quasi-steady-state models into a recognized
standard of performance for use by governmental
agencies for regulation and administration of grant-
in-aid programs
II. OPERATION, MAINTENANCE, AND PLANT MANAGEMENT TECHNOLOGY
1. Plant performance standards and effluent quality
control methods
2. Plant management, training, and staffing criteria
and methods
3. State, County, or Regional systems for management
and regulation
III. AUTOMATIC CONTROL FOR PLANTS
1. Study feasibility of proposed control loops with
time-dependent models to solve transient problems
2. Study cost-effectiveness trade-off between automation
and additional or better trained staff or better
managerial surveillance
3. Demonstrate and evaluate control schemes on a loop-
by-loop basis
4. Demonstrate interprocess control of complete plants
IV. COST-EFFECTIVENESS STUDIES
1. Selection of processes and design policies for least
cos t
2. Collection and organization of basic cost information
3. Develop recommended cost guidelines for cost estimation
89
FIGURE 1
-------
TABLE I
PRINCIPAL REPORTS PRODUCED BY
TREATMENT OPTIMIZATION RESEARCH PROGRAM
1* Smith, Robert, "Preliminary Design and Simulation of Conventional
Wastewater Renovation Systems Using the Digital Computer",
FWPCA Publication No, WP-20-9 (March, 1968).
2. Smith, Robert, "Cost of Conventional and Advanced Treatment of
Wastewater", FWPCA Publication (July, 1968)*
30 Smith, Robert, Eilers, Richard G, and Hall, Ella D., "Executive
Digital Computer Program for Preliminary Design of Wastewater
Treatment Systems", FWPCA Publication No. WP-20-14 (August, 1968).
4. Roesler, Joseph F. and Smith, Robert, "A Mathematical Model for
a Trickling Filter", FWPCA Publication No. W69-2 (February, 1969).
5. Smith, Robert and McMichael, Walter F., "Cost and Performance
Estimates for Tertiary Wastewater Treating Processes", FWPCA
Publication (June, 1969), TWRC-9 Released January 15, 1970.
6. Roesler, Joseph F., "Preliminary Design of Surface Filtration
Units (Microscreening)", FWPCA Publication (June, 1969).
7. Smith, Robert and Eilers, Richard G., "A Generalized Computer
Model for Steady-State Performance of the Activated Sludge
Process", FWPCA Publication (October, 1969).
8. Smith, Robert, "Factors to be Considered in Developing a Data
Gathering and Analysis Plan Leading to Improvement of the
Operational Effectiveness of Conventional Wastewater Treatment
Plants", FWPCA Publication (December, 1969)„
9. Roesler, J. F., Smith, R. and Eilers, R. Go, "Mathematical
Simulation of Ammonia Stripping Towers for Wastewater Treatment",
In-House Report.
10. Smith, Robert and Eilers, Richard G., "Simulation of the Time-
Dependent Performance of the Activated Sludge Process Using the
Digital Computer", In-House Report 90% Complete.
11. Smith, Robert and Eilers, Richard G., "Cost to the Consumer of
Collecting and Treating Wastewater in the United States", In-
House Report (July, 1970).
90
-------
TABLE II
1. "Cost of Wastewater Treatment Processes", IWRC-6, Dorr-Oliver,
Inc.
2. "Mathematical Model of Tertiary Treatment by Lime Addition",
TWRC-14, General American Research Division/General American
Transportation Corp.
3. "Mathematical Model of Sewage Sludge Fluidized Bed Incinerator
Capacities and Costs", TWRC-10, General American Research
Division/General American Transportation Corp.
4. "Mathematical Model of the Electrodialysis Process", Process
Research, Inc.
5. "A Mathematical Model of a Final Clarifier for the Activated
Sludge Process", Rex Chainbelt Inc.
6. "Ammonia Stripping Mathematical Model for Wastewater Treatment",
IIT Research Institute.
7. "Mathematical Model of Recalcination of Lime Sludge with Fluidized
Bed Reactors", General American Research Division/General American
Transportation Corp.
8. "Mathematical Model for Wastewater Treatment by Ion Exchange",
IIT Research Institute.
9. "Methodology for Economic Evaluation of Municipal Water Supply/
Wastewater Disposal Including Considerations of Seaw&ter
Distillation and Wastewater Renovation", Bechtel Corp.
10. "Mathematical Model for the Reverse Osmosis Process", Aerojet-
General Corp.
91
-------
As a resalt of the work repotted in the first report in Table J,
it was realized that a tool was. needed which would allow the process
designer to select the group of processes and the piping arrangement
to be used and then calculate the performance and cost of the
system as a whole. To meet this need an Executive Program was
develo?e4 as described in the thicd repoct of Table X.
By itpraiive techhigues the Executive Program calls each process
subroutine in turn Sttjd recomputes ail recycle stzescs& until the
correct solution tot tt»e -systew. is found. Performance and cost
for eacb process and for the System as a. whole is printed. This
pcagr^ is simple in concept and requires a digital coiaputei with
a ccie newory cf about 16K viords.
Evecy quasi-steady-state nwdel developed will. ultimately be included
in the Executive Program. A list of the i-ndivi'dM.a.l processes to
be included in the Executive Prograie are shown in Table HI witfc
t'ne ol %a.ct\ wa wastewater treatment systems ate
&hown in tbe fifth report of Table I (TWRC-^K Estimated removal
efficiency for all significant contaminants, ace ^iven "ocetliec
with capital and operating arKj ®aisit.en.ance cost.
A geiseralized model for the activated sludge process has been
developed and has been shown to fit data from a wide range of
process modifications from the shoyt detention tiate, low missed
liqyor suspended solids, "modified process'- to the "extended
aeraficxc process''. Xftis nodel is described in the seventh report
listed in Table I, The moat significant discovery associated with
this work was that the Maximum tata constant for synthesis is riot a
true constant i>«t varies significantly with the loading on the process
A time-dependent model for the activated sludge process has also b«en
cc*(ilet«d and! tte report on this iaodel is about 90% con^lete. Three
classes of active solids are considered; betsrottopas whicli wnveit
biodegradable carbon to new cells, Nitrps grappas vhicli cotiverts
amonia nitrogen to new cells- and nitrite, and Nitrobact&r which
converts nitrite to new cells and nitrate. This model has been used
to investigate a rtaatoer of s^hec.e-s. for automatic control of the acti-
vated sludge process» The most practical of the sc^ewes involve
sludge storage in the stabilization tank.
-------
Another model for which a report has recently been completed is
the model for ammonia stripping and cooling towers. The ammonia
stripping portion of the program is embedded in the cooling tower
calculation in order that the variation of Henry's Law constant
with water temperature can be taken into account. The program can
be used to calculate either ammonia stripping tower performance or
cooling tower performance. Both crosscurrent and countercurrent
towers are simulated. A numerical integration technique is used
in which the tower is divided into cubical elements. Performance
from various sources is being used to find the height of a transfer
unit as a function of the type of packing and design decisions.
Experimental data received from the Marley Co. for a particular
packing have been analyzed to find the relationship between height
of a transfer unit and the liquid and gas loading, (lb/hr/sq ft).
The height of a transfer unit was found to depend on the ratio of
gas to liquid loading as follows :
1.257
Height of Transfer Unit, ft = 4.1272 (Gas loading/liquid loading)
Various in-house and contract activities are underway to develop
operation, maintenance, and plant management policies and methods
which can be used to assure that a level of performance commensurate
with the capability of the installed treatment works will be con-
sistently achieved. The eighth report listed in Table I deals with
these problems. Various contracts are either funded or being
considered for funding.
The State of Minnesota has shown an interest in developing and
demonstrating a computerized system for surveillance and regulation
of treatment works within the State. The system would make use of
all design and simulation relationships known to be valid for treat-
ment processes. The physical characteristics of each particular
treatment plant would be stored in the computer program. Design and
simulation relationships would be used to compute the expected
performance of each plant as a function of the measured influent
stream. The transient nature of the feed stream and the stochastic
aspects of performance relationships would be used to compute a range
of expected performance. Monthly performance reports submitted by
individual plants would be analyzed and evaluated in a matter of
minutes. If deficiencies are detected some sort of remedial action
could then be initiated.
Our approach to automatic control of plants is to study the cost and
effectiveness of each individual control loop. Performance must be
measured and documented with and without the control loop installed.
Time-dependent mathematical models will be used to study the
93
-------
feasibility of untried control loops and to study the significance
of time-dependent measurements made on individual processes. The
tenth report in Table I deals with a time-dependent model for the
activated sludge process.
Various cost-effectiveness studies are undertaken to show the cost
contribution of various process system components and to study the
cost-effectiveness trade-offs for competing process systems. The
influence of size of community and the contribution of ancillary
elements such as Customer Services and Accounting or General and
Administrative Expense are studied to show the general cost
perspective. A recent report shown as number eleven in Table I
deals with these ancillary costs. Three selected figures from this
seventy page report are shown in Figures 2, 3, and 4.
94
-------
TABLE III
PROCESS SUBROUTINES TO BE INCLUDED IN THE EXECUTIVE PROGRAM
CONVENTIONAL PROCESSES
I. Physical Processes
1. Conveyance for Ultimate Disposal
a* Pipelines
b. Truck and Rail Transportation RFP (1/15/70)
c. Ocean Outfalls
2. Sewage Pumping Facilities (In-house Task)
3. Pretreatment
a. Bar Screens
b. Comminution (In-house Task)
c. Grit Removal
4. Primary Sedimentation (Completed)
5. Sludge Drying Beds (In-house Task)
6. Post and Pre Aeration (In-house Task)
II. Biological Processes
1. Activated Sludge Process (Completed)
2. Trickling Filter Process (Completed)
3. Waste Stabilization Ponds
a. Aerated Lagoons
b. Facultative Ponds RFP (1/15/70) + (In-house Task)
c. Oxidation Ditches
4. Anaerobic Digestion (Completed)
5. Aerobic Digestion RFP (1/15/70)
III. Physical-Chemical Processes
Gravity
1» Thickening of Organic Sludges RFP (1/15/70)
2m Centrifugation of Organic Sludges -(Contract 515 Underway)
3, Flotation Thickening of Organic Sludges (Proposal Recommended)
4. Vacuum Filtration of Organic Sludges RFP (1/15/70)
95
-------
5* Use of Chemicals to Promote Sedimentation (No PlariS)
6. Elutriation of Organic Sludge (No Plains)
7. Multiple Hearth Incineration of Sludges (Contract 547 Underway)
8. Fluidized Bed Incineration of Organic Sludge (Completed)
9. Wet Oxidation of Organic Sludge (No Plans)
ADVANCED PROCESSES
I. Physical Processes
1. Cooling Towers (Completed)
2» Microscreening (Contract 819 Underway)
3. Rough Filtration of Secondary Effluent RFP (1/15/70)
4. Dual Media Filtration RFP (1/15/70)
II* Biological
1. Disinfection
a« Chlorine
b. Iodine (No Plans)
c. Ozone
2» Denitrification in Columns RFP (1/15/70)
111* Physical-Chemical Processes
1* Lime Clarification (Completed)
a* Recalcination of Lime Sludge (Fluidized Bed Complete)
b. Recarbonation using (X>2 (In-house Task)
2. Ammonia Stripping Towers
a* Countercurrent (Completed)
b. Crosscurrent (Completed)
c. Aeration (In-house Task)
d. Biological Activity (In-house Task)
e. Scaling (In-house Task)
96
-------
3. Granular Carbon Adsorption RFP (l/15/70)
4. Powdered Carbon Adsorption (No Plans)
5. Electrodialysis (Completed)
6. Reverse Osmosis (Completed)
7. Ion Exchange (Model Complete - In-house Task Req'd)
97
-------
280
260
240
220
200
180
160
140
120
lOp
80
60
40
20
0
Sewered Population
Total Treated Population
Secondary Treated
Population
150 1960 1970 1980 1990
Year
rATUS OF MUNICIPAL WASTEWATER TREATMENT FACILITIES
IN THE UNITED STATES
FIGURE 2
98
-------
Type of Treatment
Activated
Sludge
Interceptor
and Outfall
Trickling
Filter
Primary
Sedimentatii
Upgrading F:
Primary to
Activated
Sludge
Stabilizatic
Ponds
I
Total Sewered
Population
28.95
29.88
29.46
-17,71
17.49
5.23
Activated Sludge
and Extended
Aeration
25.53
29.49
Trickling
Filter
45.14
Primary
Sedimentation
16.04
15.10
Stabilization
Ponds
21.42
NATIONWIDE AVERAGE CONSTRUCTION COST, DOLLARS PER CAPITA (1968 DOLLARS)
Source: cost data - R. L. Michel, Construction Grants and Engineering Branch, FWQA
population distributions - 1968 Inventory of Municipal Waste Facilities in the U.
FIGURE 3
-------
FIGURE 4
TOTAL COST OF SEWAGE COLLECTION AND TREATMENT IN 1968
ON A CONTINUOUS CASH FLOW BASIS
1968 dollars/capita/year
Amortization_Cost
House Connection $ 1.38
Municipal Sewers $ 8*64
Interceptors and Outfalls $ 2«46
Treatment Plants $ 2<,83
Total Amortization Cost $15.31
Current Expenses
Municipal Sewer Maintenance $0.86
Treatment Operation and
Maintenance $1.55
Customer Service and Accounting $0.71
General and Administrative $1,37
Total Current &cpenses $4.4?
Total Cost of Municipal Collection $19*80
and Treatment
Imputed Cost of Industrial $ 5.05
Wastewater Treatment
Total $24.85
For additional information contact:
Robert Smith
Robert A. Taft Research Center
Advanced Wa9te Treatment Research Laboratory
Ohio Basin Region
Cincinnati, Ohio 45226-
100
-------
ADVANCED WASTE TREATMENT RESEARCH LABORATORY
CINCINNATI, OHIO
CURRENT STATUS OF ADVANCED WASTE TREATMENT PROCESSES
July 1, 1970
SCIENTIFIC BASES OF WASTE TREATMENT PROCESSES
PPB 1700
Division of Process Research & Development
Federal Water Quality Administration
U.S. Department of the Interior
101
-------
Status of Research on
Scientific Bases of Waste Treatment Processes
Waste treatment is a chemical process industry. Its function is to
treat a starting material (sewage) of some chemical composition by
optimum processes to convert it to another material of higher economic
value/lower nuisance effect (treated effluent). Optimum processing
requires adequate knowledge of the chemistry, physics, and biology of
the raw material, treatment agents, and final product.
The major research effort has been on composition of wastes and its
changes. Though sewage has been analy2ed for nearly a century, our
background knowledge is slight and expressed in quite general terms.
An intensive analytical program has begun only now, both in-house and
by contracts and grants. A first effort has been to determine how to
sample effluents and transport samples to the laboratory. Freeze-
concentration, though highly praised, is unsuitable. Vacuum concentra-
tion is the only practical means available so far. Though a systematic
analytical program is evolving, we have leapfrogged to seme more
specific approaches. One of these, just begun by contract, consists of
liquid chromatography of primary and secondary sewages, yielding finger-
print chromatograms. First trials show some 50 - 75 separated organic
components, with conspicuous differences developing during biological
treatment. Another of these leaps involves developing specific analyses
for contaminants of special significance in sewage* Methods were
developed for residual polymeric coagulant in treated sewage and for
nitrilotriacetic acid in sewage receiving proposed new detergent formu-
lations.
The molecular weight of sewage components is an important property for
two reasons: (1) It controls the fractionation of organic components
necessary to achieve ultimate isolation and identification of each,
and (2) it has been claimed to be the controlling parameter in physical
waste treatment processes. Molecular weight studies, both contract and
in-house, are employing three techniques; membrane ultrafiltration, gel
permeation chromatography, and osmometry. Comparison of the methods
shows unexpected discrepancies in the apparent molecular weight values,
also evidence of these fractions being complexed with metals. Early
results indicate that the major part of secondary effluent organics
average below 500 in molecular weight.
Of the treatment agents susceptible of elucidation by fundamental
scientific research, activated carbon is the most important economi-
cally and also is most productive of useful information to guide processes,
which have been largely empirical until now. The efficiency of activated
carbon was found to depend on its basic characteristics, surface area,
pore volume and dimensions, and surface functional groups, as predicted
by theory. Other fundamental properties, not yet isolated, appear to be
related to these. Apparently for the first time, meaningful information
is being obtained about used and exhausted carbons, relating basic parame-
ters to the performance of these carbcms and their behavior on reactiva-
tion, In a different but related approach, thermal analysis has begun to
102
-------
be explored as a means of characterizing both the activated carbon
and the adsorbed sewage components, as well as being used to predict
reactivation behavior. These theoretical studies are aimed at
establishing a sound scientific basis for carbon treatment processes
now conducted-with inadequate understanding*
One of the favorable characteristics of sewage, namely, that it supports
well the bacterial population effecting biological treatment, is also a
disadvantage, in that it makes sewage a hospitable medium for disease-
producing bacteria. An intensive research program has been started to
pass far beyond today's fixation on indicator organisms* Methods for
assaying important pathogens in sewage -- Salmonella, Pseudomonas,
Shigellae, among others -- are being developed and applied as criteria
to measure the effectiveness of treatment processes in removing or
destroying these organisms* Information about pathogens and indicator
organisms has been assembled systematically to demonstrate the pollutional
effect of primary effluent, even where BOD is not an issue*
If bacteria produce biological treatment, they can also interfere with
other forms of treatment, especially physical methods, and with ultimate
disposal of waste concentrates. Adverse bacterial effects have been
characterized in carbon treatment (growth of pathogens) membrane processes
(fouling organisms), and sludge disposal (persistence of bacteria).
The above research areas are fundamental and relatively long-term con-
tributions to the efficiency of waste treatment processes. Since the
bulk of treatment research, by other components, is immediate and neces-
sarily empirical, this research must be guided by extensive analytical
surveillance. To take advantage of the intrinsic efficiencies of
specialization and centralization of advanced instruments, most of the
required analyses are provided by a central analytical service labora-
tory, supplying about 3,000 analyses per month, distributed among some
35 methods. This support is also supplied to research contractors and
grantees, including assistance in setting up and standardizing their
laboratories.
To supply these services requires a constant program to select appro-
priate analytical methods, adapt them to labor-saving systems and
instruments, develop new methods and systems for this purpose, and to
shake down and calibrate these instrumental adaptations*
If the initial premise of this review is reprised — that effective
processes require adequate knowledge of the composition of starting and
final materials and the way specific processes affect these compositions --
then it is apparent that the concept applies as well to full-scale treat-
ment plants. The objective of automated control of treatment plants is
accepted; such control can be accomplished only if equally automated
methods of sensing composition changes can be developed* The automated
instrumentation developed for volume work in the analytical laboratory
is also the most promising approach to plant control instrumentation. A
103
GPO 821-571-16
-------
research effort in this direction, necessarily limited by meagre
resources, has attained initial success in controlling a denitrifica-
tion pilot plant by on-line analysis of nitrogen compounds and of
denitrifying reagent feed. The extension of automated chemical
instrumentation to full-scale treatment plant automation is a major
program objective.
For additional information contact:
Dr. A. A. Rosen
Robert A. Taft Water Research Center
Advanced Waste Treatment Research Laboratory
Ohio Basin Region
Cincinnati, Ohio 45226
104
-------
SLUDGE HANDLING
Robert B. Dean
FWQA. Cincinnati, Ohio
Presented by Dr. J. B. Farrell at the Dallas Symposium
Sludge has always represented the major source of problems in sewage
plants and accounts for up to half of the cost of treatment (Burd, 1968,
Dean, 1968). Primary sludge thickens to about % solids and can be
digested when all goes well to remove about half of the organic matter and
all danger of putrefaction# However, primary treatment is not enough for
most cities and secondary treatment will be required. Waste activated
sludge from secondary treatment is much more dilute and much harder to dewater
than primary sludge even after digestion,.
Ocean disposal of sludges is becoming less and less acceptable (Miller,
1970)• A sludge, unfortunately, carries large quantities of grease and
may contain pesticides and heavy metals which are objectionable in the ocean.
Incineration is a popular method of sludge disposal. It returns organic
matter to the atmosphere as COg and nitrogen and produces an ash that is
sterile and small in volume. A good incinerator with adequate scrubbers need
not produce odors or discharge anything visible to the air (Culp & Moyer
1969)« High temperature incinerators operating above 1600^ such as fluid
bed and slagging incinerators should be carefully checked for oxides of
nitrogen which are difficult to remove in fume scrubbers. Sludge will burn
without supplemental fuel if it is above 25-30$ solids (Burgess, 1969)0
This means that about 3 tons of water can be evaporated by each ton of dry
-------
-2-
solids burned. Fuel costs are about one dollar to evaporate each additional
ton of water in the sludge.
Since sludge normally contains from 20 to 100 tons of water per ton
of dry solids it is necessary to dewater it as far as practical "before in-
cineration. Conventional vacuum filtration can reduce the water to 3-6
tons per ton of solids if the sludge is conditioned with iron salts and lime.
Thickening of sludge is the most economical way to remove a part of
the water. Our ability to thicken sludge by sedimentation frequently
exceeds the capabilities of the plumbing to remove the thickened product
(Voshel, 1966). All too often ve see rakes or other devices to mix the
sludge with water so that it can be drawn off as a liquid in small pipes.
There are also reports of sludge being diluted with water from a hose to
get it out of the tank. The use of small diameter pipe with multiple right
angle bends between a thickener and a sludge pump is Just asking for trouble.
There are real opportunities for equipment manufacturers to design improved
methods for moving thickened sludge. Chemical sludges, especially lime
sludges do not behave like sewage sluiges and must be studied on a realistic
scale before equipment to handle them can be designed (Mulbarger, et. al., 1969).
In small plants one can show that direct incineration of thickened
sludge with evaporation of all of its water content would be less costly
than operation of an intermediate filter or centrifuge (Culp, 1969). Some
interesting work is being done on flotation (Mulbarger and Huffman, 1970).
It has been veil established that vacuum filter yields are proportional to
sluige concentration so efficient thickening can substantially reduce
filtration costs. On the other hand centrifuges may operate more efficiently
-------
-3-
with. a low solids feed since sedimentation is easier in a low viscosity-
system (Schultz, 1968)0
Polymers increase the yield or rate of filtration and improve solids
capture but do not help the moisture content. Solid bowl centrifuges can
also produce dry cake but solids capture may be as low as ^Qffo unless polymers
are used.
Sludge ash is an efficient low cost filter aid that is already available
at the plant incinerator. Ash from multiple hearth incinerators is said to
make a better filter aid than fluidized bed incinerator ash. We have found
that fly ash from coal makes a less effective filter aid than sludge ash.
Net yields from vacuum filters are doubled by additions of up to 200$ of
ash based on sludge solids. Moisture of the cake does increase slowly
relative to the sludge solids so fuel costs for incineration would also
rise. In Stuttgart, Germany, a vacuum filter uses sludge ash collected
directly from the flue gases by a spray of wet sludge (Vater, 1969)* The
flue gases also heat the sludge,reducing its viscosity.
In the same Stuttgart plant there is a newly installed pressure filter
using a precoat of sludge ash as a parting agent together with body feed
of more ash. The press is completely automatic and produces a much drier
cake than the vacuum filter so that almost no fuel is needed for incineration.
In contrast to older manually operated filter presses the new presses are
completely automatic even to the washing of the filter cloths. The operation
is batchwise but can be fully automated. Dry sludge can be removed at the
convenience of the operator once the press is full. Filter presses of this
type are now available in this country.
-------
Many other types of devatering devices are "being offered including
top filtersj roll presses, and tower presses, Each of these devices -produces
a final cake that needs supplemental fuel for burning and each requires poly-
mer additions for efficient solids capture (Coackley, P., 196?).
Some form of stabilization of sludge "before dewatering is usually re-
quired. to prevent peptic decomposition and odors. However, stabilization may
not be necessary if the dewatered sludge is fed directly to an incinerator.
The chemicals used as filter aide, especially Iron salts and. lime, irfiiitit de-
composition and reduce odors ¦while the sludge is in the plant.
Anaerobic cEigestion is the classical method for stabilising sludge. Vhen
operating properly, anaerobic digesters remove heat in the fonn of methane,
carry putrefaction to completion, and reduce the volume of solids to "be filtered
or dried. Unfortunately, digesters are herd to operate properly and even very
large Installations can be upset by trivial quantities of heavy metals or
chlorinated solvents. Becent vorh in England has shewn that as little as
one drum of methyl chloroform or lj,l3l trichloroethane, a solvent which is
used for safe degreasing and cleaning, can upset JtO million gallons of di-
gesters (Swaiwick end Foulkes, 1970). Another problem with anaerobic digesters
is that they solubiliie a substantial part of trie BOD and nutrient3 an4 return
them to the plant in the supernatant soup (Barth, et alj, 1966),
Anaerobic digesters vcrk well vith sludge to -which iron or aluminum
salts have been added, tc rename phosphates (Cornell, 1970-Tl). Of course^
the percent of noil-volatile solids ia increased. lime in sufficient quantities
to remove phosphates either in primary or tertiary treatment may produce an
undigestible sludge If the pH is too hign. Fort"iHia.telnj, lissed. &lu&ge Is very
-------
resistant to putrefaction at a pH above 10«
Lime sludge may be incinerated at l800° F to recover the fraction of
the lime that has combined -with carbonates.
CaCO^ heat CaO + COg
Rebumed lime pay be better than fresh lime on a CaO basis because sludge
ash in the used lime acts as a filtration aid (Mulbarger et al., 1969).
Aerobic stabilization is often used in small plants because it requires
less capital than anaerobic digestion and is less likely to be upset by
poisons. Power costs are definitely higher, especially if useful gas can be
produced by anaerobic digestion (Ritter, 1970). Aerobic stabilization
usually leads to nitrification of the ammonia. It is possible to denitrify
a fully nitrified sludge by holding it for about 5 days with mild agitation
without the addition of methanol or other source of BOD. Aerobic stabilization
tends to hold phosphates in the sludge particles "but denitrification releases
some of the phosphates again to the supernatant (Randall and Koch, 19^9)•
Aerobic stabilization reduces volatile solids by oxidation with the
liberation of heat (Kambhu and Andrews, 19&9)• Anaerobic digestion in
contrast liberates potential heat in the form of methane which can be burned
separately. The heat liberated in aerobic stabilization must be carried off
as the heat of vaporization of water in the exhaust air. If insufficient air
is supplied, the sludge will heat up and consume oxygen faster while at the
same time the solubility of oxygen is reduced. The result is that part of
the sludge will go anaerobic producing foul odors. To avoid this problem
one must either supply more air or dilute the sludge. Foul odors are rarely
experienced when stabilizing waste activated sludge but mixtures of activated
and primary sludge will need a lot of air to carry off the heat and prevent
-------
-6-
odors. Aerobic stabilization works well with biological sludges containing
iron salts or alum and has been used with Fe + CaO.
Lime has already been mentioned as a chemical stabilizing a^ent.
Boyle (I96T) has sho't/n that raising the pH to 12 with lime will destroy
pathogens in raw primary sludge although it does not completely sterilize
it. Lime also inhibits odors, except ammonia, and produces a sludge that
can be filtered and incinerated or can be applied to the land. If piled
deeply in a land-fill this sludge would eventually putrefy but it would
not contribute pathogens or nutrients to ground water. The cost will be
less than digestion in most cases.
Pathogens cam also be killed by very heavy chlorination or by pasteuri-
zation. toeithefi* treatment destroys volatile organic matter and decomposition
will eventually set in. Heavy chlorination could chlorinate aromatic
compounds in the sludge producing to::ic substances that inhibit bacterial
attack and whose effect on aquatic life is unknown. Proof of safety o^ the
effluent should be demanded before heavy chlorination is approved for sludge
treatment. Pasteurization sufficient to destroy Ascaris ova does not improve
sludge settling or filterability (Keller, 1951).
Heat treatment by pressure cooking is offered by several manufacturers.
Typically, sludge is heated to about 200°C for half an hour (Brooks, 156ci).
If dissolved oxygen is added there will be about 15$ wet oxidation of COD
(Teletzke et al., 1967). The net result is a solids fraction thai settles and
filters very well and a supernatant soup that is rich in nutrients, BOD,
and odors and is similar to digester supernatant. Wet oxidation produces a
different odor from pressure cooking. The soup is a serious load on a
-------
-7-
biological treatment plant especially if dumped as a shock load;
pretreatment "by extended aeration or trickling filter may be necessary
(Berridge and Brendish, 1967# Erickson and Knopp, 1970).
Heat treatment hydrolyzcs organic matter in sludge "but sludge is normally
at the ]^ast efficient pll for hydrolysis. We have done experiments using
S02 as a mild catalyst which is known to give efficient hydrolysis of proteins
(Bouthilet and Dean, 1970)• As expected, we get good filtration after heat
treatment at temperatures below 150 'C and we get even more soluble matter
in the soup. Analysis of the soup showed a high amino acid content with
good representation of the nutritionally useful species. Feeding tests on
rats showed that the organic molasses obtained by evaporating this soup was a
good feed supplement that increased food utilization. Preliminary calculations
indicate that the sale of animal feed supplement might be profitable for a
large sewage treatment plant but much more work needs to be done before this
becomes an acceptable process. Previous.attempts to feed whole activated
sludge were unsuccessful at levels above of the diet (Hurwitz, 1957)•
Land disposal of sludge is the oldest and least glamorous method of
sludge disposal. It is also the cheapest of all methods except dumping in
the ocean See Fig. 1 (Dalton, et al, 1968). Soil bacteria oxidize organic
matter to CO2 by a form of low temperature incineration which can be free
from nuisances. Nutrients are recycled to crops or forests and the more
refractory organic matter remains for a while in the soil as humus (Evans, 1970).
The neutralizing and water holding properties of sludge can' restore barren
mining spoil (Knabe, 1965)• Two inches of sludge has permitted grass to grow
on land which was so acidic that seed carbonized as it dried out.
-------
-8-
Sludge can be economically conveyed up to 100 miles by pipe lines from
larger plants. A study at Chicago showed that pipe line and distribution
costs would go down as the distance increased because land values fell off
more rapidly than piping costs increased. See Fig. 2 (Bacon, 1968). Smaller
plants will employ tank truck or tank car transport. Chicago currently is
running sludge trains to Areola, Illinois to empty "permanent" lagoons on
prime industrial acreage. The sludge is to be distributed on mine spoil.
In addition to nutrient and fertilizer values many farms are willing
to pay for sludge for its water content alone. However, the low cost of
land disposal makes this process attractive even if it is necessary to lease
or buy land for disposal purposes. If properly applied and if the sludge is
not heavily contaminated with toxic metals, land disposal only increases tne
value of the soil. This is in marked contrast with dumps and permanent
lagoons which remain as permanent liabilities..
The quantity of sludge which can be applied per year depends on several
factors. Soil bacteria in a warm climate can oxidize up to one-inch of dry
solids a month. This corresponds to 20 feet of 5$ sludge each year. These
oxidation rates have been obtained on a continuous basis on oily sludges
in Houston, Texas for the past 8 years (Dotson, G. K. et al.,1970).
Obviously, most soils could not tolerate such a heavy application of water.
Actually in trials in Illinois the limiting factor in the application of
digested sludge appears to be the nitrogen content (Hinesly and Sosewitz,
19T0). Ammonia in fresh digested sludge is toxic to germinating seeds.
Free ammonia evaporates after a few days on the field but enough nitrogen
may be left to exceed the nitrogen demands of crops. Any excess is
-------
oxidized, by soil bacteria and enters the ground water as nitrates.
If sludge is applied properly in thin layers and septic puddles are
avoided there is little justification for pretreatment by anaerobic di-
gestion since soil bacteria will rapidly oxidize and stabilize the organic
matter (Thomas and Bendixen, 1969). However, since it may be necessary to
hold sludge until it can be applied, some treatment is usually necessary to
prevent putrefaction. Lime treatment and aerobic stabilization both appear
to be better than anaerobic digestion for this purpose. Both control nutrients;
lime holds phosphates and hastens evaporation of ammonia while aerobic stabiliza-
tion with nitrification and denitrification converts organic nitrogen to nitrogen
gas. Ihe choice of a stabilization method will depend on soil and crop require-
ments as well as on the costs of the treatment.
Pasteurization is required in Germany and Switzerland before sludge is
to be spread on pastures during the grazing season. Other countries do not
require this precaution and there is no evidence that sludge properly spread
on land causes disease of humans or livestock. Pasteurization costs about $6 per
ton of sludge solids at the Niersverband plant near Cologne.
Salts including nitrates formed from excess ammonia may leach through
the soil from heavy applications of sludge and contaminate the ground water.
It is frequently possible to collect ground water in suitably located drain
tiles so that it may be treated in the same way that irrigation under-drain
water is treated (Tamblyn and Sword, 1969). If discharge to saline water is
available, all that is necessary may be to remove nitrates. The soil is a very
efficient adsorbent for all cations except sodium and lithium as well as for
phosphates and organic compounds such as pesticides so the only contaminants
remaining after soil filtration will be soluble salts.
-------
- 10 -
Disposal of salt "brines is a general problen -whenever pure water is
extracted from wastewater "by evaporation or by any of the desalination
processes such as reverse osmosis. If the ocean is nearby, it is possible
to discharge salt brines -without causing pollution. However, in inland areas
the disposal of waste salts nay contribute a major part of the cost of
treatment '(Rapier, 197*0). Artificial or natural evaporation ponds can be
used to reduce the volume of brine and the dry salts can eventually be
hauled away to the ocean. Deep veil injection nay be acceptable in some
areas but it not a general solution because of the risk of ground water
contamination and even earthquakes if excessive volumes are injected
(Cleary and Warner, 1970)•
SUIfliARY
Sludge handling will remain a costly and troublesome part of sewage
treatment in spite of all the new developments. We can only hope that
engineers developing new treatment processes will integrate sludge handling
and brine disposal into the overall systems and not leave their residues.for
soneone else to worry about.
-------
REFERENCES
Bacon, V., 1968. Personal communication.
Barth, E. F,, Mulbarger, M. C., Salotto, 3. V., and Ettinger, M. B., 1966.
"Removal of Nitrogen by Municipal Wastewater Treatment Plants," J. Water
Poll. Control Fed. ^8(7), 1208-19.
Berridge, H. B., and Brendish, K. R., 196T« "Heat Treatment Supernatant,"
Activated Sludge, Ltd., Water Poll. Control 66, 597-600, 602.
Bouthilet, R. J., and Dean, R. B., 1970« "Hydrolysis of Activated Sludge,"
Presented at Fifth Intl. Water Pollution Research Conference, San Francisco.
To be published by Pergamon Press, 1971, in Advances in Water Pollution
Research. Paper 111-31.
Brooks, R. B., 1968. "Heat Treatment of Activated Sludge," Water Poll. Control
67, 592-601.
Burd, R. S., 1968. "A Study of Sludge Handling and Disposal," FWQA Publ.
WP-20-4.
Burgess, J. V., 1968. "Comparison of Sludge Incineration Processes," Process
Biochem. 27-30.
Cleary, E. J., and Warner, D. L., 1970. "Some Considerations in Underground
Wastewater Disposal," J. Amer. Waterworks Assn. 62(8), U89-98.
Connell, C., 1970. "Phosphate Removal at Texas City, Texas." Report of
FWQA Grant WPRD 126-91-67* In preparation.
Culp, R0 L., 1969® Personal communication.
Culp, R. L., and Moyer, H. E., 1969. "Wastewater Reclamation and Export at
South Lake Tahoe," Civil Eng. ASCE, 38-te.
Dalton, F.E., Stein, J. E., and Lynam, B. T., 1968. "Land Recleunation—A
Complete Solution of the Sludge and Solid Waste Disposal Problem," J. Water
Poll. Control Fed. k0(5), 739-804
Dean, R. B., 1963. "Ultimate Disposal of Wastewater Concentrates to the
Environment," Env. Science and Tech. 2(12), 1079-86.
Dotson, G. K., Dean, R. B., Cooke, V/. B., arul Kenner, B. A., 1970. "Land
Spreading—A Conserving and Non-Polluting Method of Disposing of Oily
Wastes," Presented at Fifth Intl. Water Pollution Research Conference,
San Francisco. To be published by Pergamon Press, 1971, in Advances in
Water Pollution Research. Paper II-36.
Doyle, C. P., 1967. "Effectiveness of High pH for Destruction of Pathogens
in Raw Sludge Filter Cake," J. Water Poll. Control Fed. J9(8), 1403-9.
-------
Erickson, A. H., and Knopp, P. V., 1970. "Biological Treatment of Thermally
Conditioned Sludge Liquors," Presented"at Fifth Intl. Water Pollution
Research Conference, San Francisco. To be published by Pergamon Press,
19T1 j in Advances in Water Pollution Research.
Evans, J. 0.. 1970. ,,Tlie Soil as a Resource Renovator," Env. Science and
Tech. 4(9), 732-5.
Evans, D. R., and Wilson, J. C., 1970. "Actual Capital and Operating Costs
for Advanced Waste Treatment (at South Lake Tahoe)," Presented to the
43rd Annual Meeting, Water Pollution Control Federation, Boston.
Hinesly, T. Do, and Sosewitz, B., 1969° "Digested Sludge Disposal on Crop
Land," J. Water Poll. Control Fed. Ul(5), 822-30.
Hurwitz, E., 1957* "Feeding Dried Activated Sludge to Pigs, Poultry, Steers
and Sheep," Wastes Eng. 28, 388-93*
Kambhuj K., and Andrews, J. F., 19^9» "An Aerobic Thermophilic Process for
the Biological Treatment of Wastes—Simulation Studies," J. Water Poll.
Control Fed. 4l(5), R127-R141.
Keller, P., 1951* "Sterilization of Sewage Sludges," J. and Proc. Inst, of
Sewage Purif.
Knabe, W., 19&5* In "Ecology and the Industrial Society,11 John Wiley.
Edited "by G. T. Goodman et al.
Miller, S. S., 1970. "Ocean Dumping Poses Growing Threat," Env. Science
and Tech. 4(10), 805-6.
Muliarger, M. C., Grossman, E. Ill, Dean, R. B., and Grant, 0. L., 1969.
"Lime Clarification, Recovery, Reuse, and Sludge Dewatering for Wastewater
^treatment," J. Water Poll* Control Fed. 4l(l2), 2070-85.
Mulbarger, M. C., and Huffman, D. D., 1970o. "Mixed Liquor Solids Separation by
Flotation," J. San. Eng. Div., ASCEi <£, No. SAh, Proc. Paper fkkj, 861-871.
Randall, C. W., and Koch, C. T., 1969# "Dewatering Characteristics of
Aerobically Digested Sludge," J. Water Poll. Control Fed. 4l(5), R215-R238.
Rapier, P. M., 1970. "Ultimate Disposal of Brines from Municipal Waste Water
Renovation." To be published in "Water-1970"j Chem. Eng. Progress Symposium
Series.
-------
Ritter, L. E., 1970. "Design and Operating Experiences Using Diffused
Aeration for Sludge Digestion," J. Water Poll. Control Fed. h2, 1782-91*
Schultz, S. E., 1967. "Dewatering of Domestic Waste Sludges "by Centrifugation,"
Thesis, Univ» of Florida, 23^ pp; Diss,, Abstr., 1968, 2£, B, 10^5.
Swanvick, J. D., and Foulkes, M., 1970. "Inhibition of Anaerobic Digestion
of Sevage Sludge "by Chlorinated Hydrocarbons," Presented N.W. Branch of
Inst, of Water Polio Control.
Tariblyn, T. A., and Svord, B. R., 1969- "The Anaerobic Filter for the
Denitrification of Agricultural Subsurface Drainage," Proc« 24th
Annual Purdue Industrial Waste Conference, Part 2, 1135-1150•
Teletzkc, G. II., Gitchel, V/. B., Diddams, D. G., and Hoffman, C. A., 1967*
"Components of Sludge and Its Wet Air Oxidation Products,11 J. Water Poll.
Control Fed. 39(6), 99^1005*
Thanac, R. E«, and Bendixen, T. W., 1969. "Degradation of Wastewater
Organics in Soil," J. Water Poll. Control Fed. ^-(5), 808-13.
Vater, W., 1969® "European Practices in Sludge Devatering and Disposal,"
in 'Advances in Water Quality" by Gloyna and Eckenfelder« U, of Texas Press,Austin.
Voshel, D., 1966. "Sludge Handling at Grand Rapids, Michigan Wastewater
Treatment Plant," J. Water Poll. Control Fed. 38, 1506-17.
-------
COSTS OF DISPOSAL METHODS
FOR ACTIVATED SLUDGE
DRYING AND SALE AS FERTILIZER
WET AIR OXIDATION
(ZIMPROj*
DEWATERIN6 AND INCINERATION*
DIGESTION AND PERMANENT LAGOONS
DIGESTION AND RECLAMATION
OF FARM LANDS
DIGESTION AND RECLAMATION
OF STRIP MINES
*Preceded by High Rate Digestion
COST PER EQUIVAENT DRY TON
-------
LAND UTILIZATION OF SOLIDS
OIPOSAL COST vs. LAND PURCHASED PRICE
40 TON /ACRE/YEAR APPLICATION + A 50 YEAR WRITE OFF
COST FOR DISPOSAL
(DOLLAR/DRY TON]
COST/ACRE
$16.51 COST/TON
W
MM
w
•jYlWivivlvivivivi'i'i'i'
mmmwmm
$20.85 COST/TON
rip®
$250 $1000
$2000
$3000
$4000
ISA
TRANS DISTANCE
45
39
31
23
15 mi.
-------
THE PORTEOUS PROCESS
BY
JAMES D. PHILLIPS
SUPERINTENDENT, SEWER DIVISION
CITY OF COLORADO SPRINGS
DEPARTMENT OF PUBLIC UTILITIES
November 1970
-------
THE PORTEOUS PROCESS
In January of 1969 the City of Colorado Springs started a
program of sludge conditioning with the Porteous Process. This
process is based on the work done by W. K. Porteous during the
early 1900's with batch process, in England.
Process operation is based on the Heat Syneresis principle.
An organic sludge gel is a colloidal system incorporating within its
structure large amounts of water. The structure is made up of
cell walls containing cell water, and both soluble and particulate
matter. Outside the cell is a gelatinous sheet composed of protein
and carbonaceous material along the surface water. By heating the
sludge, the cells rupture and release the entrained liquor. This
phenomena is based on time and temperature, and the expulsion of the
liquid from the gel is "termed SYNERESIS.
After the collapse of the colloidal structure, the aqueous
solution can be separated from the solids by decanting, and the solids
processed by vacuum filtration, centrifuges, or presses.
The sludges now being processed in Colorado Springs are composed
of 70% raw material, 10% secondary sludges, and 20% digested material.
The primary raw and secondary are blended in the primary clarifiers
and pumped directly to the Porteous unit; the digested sludges flow only
-------
when the pumps are not in operation from the primary clarifiers.
The material now flowing from the digesters cannot truly be classed
as digested since pH range, volatile acids, and alkalinity are out of
the normal range of good digester operation. Instead, the material
could be classed as thickened septic sludge which is only being held
for heat processing. This, however, does not pose a problem, and
the ultimate goal of operation is to empty the digester completely.
One of the major questions asked about the Porteous unit is,
"Do sludges in the septic range, or any other configuration, cause
treatment problems?" The answer so far has been, "No. " It has
been quite apparent in the Springs' operation that heat syneresis
can be applied to any type of sludge and many other organic waste
slurries. The process, being physical, is not affected by sludge type,
chemical waste, or other toxic matter which so drastically affects
conventional digestion systems.
Another question is, "How does the process affect filterability ? 1
It has been determined that ptocessed sludges where the specific
resistances have been lowered to 40 x 107 sec/gm (1) will produce
acceptable filterability. The. Porteous produces material easily below
10 x 107 sec^/gm, and in the Colorado Springs operation, specific
resistance of 1.0 x 10 are normally found. This allows operation on
vacuum filtration of 15 lbs. D. S. /hr/sq. ft. of area at a moisture 1
content of 62%. This high yield has produced two beneficial operation
results. The first is the fact that two vacuum filters installed in 1965
-------
to handle a sludge load from 20 mgd flow have been increased to 55 mgd.
The second is land area for drying; under normal digester operation
24 acres had been used for beds -- with chemical treatment, this area
had been reduced to 12 acres, but handling the sludges with heavy-
equipment was almost impossible since the material refused to dry.
With the Porteous system, this area has been reduced to less than 4
acres, and piles of sludge up to 25 feet in height have been accomplished.
Another question asked is, "Does the sludge tend to reverse?"
The answer to this is, "No. " Since the material is heated to a point
where all known pathogenic bacteria and seeds are sterilized, the
material therefore, unless seeded from an outside source, remains
essentially the same.
The Colorado Springs operation was built under the European
flow-pattern, utilizing sludge-to-sludge heat exchange in a double-tube
system. Upon startup the raw material was run through the interior tube,
with the cooked material in the outside tube. After 194 hours of operation,
plugging occurred, and the flow was reversed, with the raw on the
outside and cooked on the inside, and again plugging occurred. Upon
investigation of the sludges, it was decided that the rag content was
much higher then the normal European sludges, and a water/sludge system
was set up. (Figure 1.) Under this system the raw material is carried
in the inside smooth tube, and water heated oy the cooked sludges is
recirculated in the outer tube for heat exchange.
-3-
-------
Total process per day in this unit is approximately 108, 000 gpd
with an average solids range of 5%. This handles the full amount of
raw material received and allows continuous removal of stored sludges
in the digesters.
Probably the most maligned area of heat treatment is the
production of so-called HEAT TREATMENT LIQUOR (HTL).
The biological-load imposed by this liquor can be treated the same as
the load imposed by supernatant liquor from a digester. It is truly
not an additional load but part of the function of treating wastes.
However, in most installations that have been made, the design engineer
would rather treat it as an imposed load, which can be summarized
as follows:
Hs - Is = ds
or
Hs = Kds + Is
Where:
Hs = Strength of heat treatment liquor in BOD Mg/1
ds = Dissolved solids on ash-free basis in mgl
Is = Initial strength of supernatant in BOD5 mgl*
K = Imposed BOD5 per mgl of dissolved solids
*BOD5 In the breakdown of the sludge structure a proportion of the
organic matter is hydrolyzed, leading to an increase in the biological
load of the sludge liquor over and above the initial supernatant strength.
From a series of tests using sludges from different sources and
-4-
-------
varying solids content, it would appear that a direct relationship
can be established for the BOD5 load imposed in relation to the
milligrams-per-liter of solids taken into solution. (2)
At the Colorado Springs plant, a computer-run on eight months
of operation set up a loading factor of from 8% to 10% of the influent BOD
as an additional loading on the plant, not taking supernatant into
consideration. (3)
In the operation of a plant, probably the worst problem with the
HTL is the immediate odor while it remains hot from the heat exchanger
and reactor process. This, however, drops quite rapidly as cooling
takes place.
It has also been experienced that the BOD5 is readily
biodegradable and can be reduced over high-rate filters with no
problems apparent. Future plan for this material is to add it to flow to
the proposed activated-sludge plant, which also seems to have an
excellent removal system for this type of material.
COST FACTORS
In the Colorado Springs plant, cost per ton of dry solids runs
approximately $2. 10 without labor and amortization; with these factors,
cost is approximately $10.60 per ton. Trying to set a figure that
would cover all installations is impossible since cost factors at each
-5-
-------
installation would be different. We do know, however, that our costs
have dropped sharply from chemical sludges, which ranged from $18 to
$25 per ton of dry solids, for lime and ferric alone. The other plus factor
which have not been figured in dollars, are land saving and time saving.
IN CONCLUSION, heat treatment in Colorado Springs has been
an excellent asset to the operation. The mechanical difficulties that
have been encountered have been far outweighed by the Process operation
in producing dried sludges of a stable nature without the problems found
in standard biological digesters.
JDP:rb
Att: Acknowledgements
Figure 1.
-------
ACKNOWLEDGEMENTS
(1) J. Swannick
F. Lussignea
R. Bakersville
International Conference
Water Pollution Research
London, September 1962
(2) K. G. Mulhall - Associate
B. D. Nicks
Discussion by the East Anglian
Branch of the Institute of Water
Pollution Control on Heat Treatment
(3) Gene Suhr
ch2m
Corvallis, Oregon
Predesign Report
Sewerage System Improvements
Colorado Springs, Colorado
June 1970
Figure 1
BSP Corporation
-7-
-------
F" I & O rl C- t
COf?PO{?Ar/OA/
A/v ewmrecH company
CAKE
Schematic diagram of porteous process
Sat ftmtisto' Box 8/58 • Ct/if. • 94128 ¦ 100 Va/fty Drive * Brtshsne • (4 15] 4673806 • fe/ex 340 33f
-------
THE CONCEPT OF
WASTEWATER RECLAMATION
L. G. Suhr
Technical Consultant
Cornell, Howland, Hayes & Merryfield
Engineers - Planners - Economists
Corvallis, Oregon USA
For presentation at the 44th Annual Meeting of the Rocky
Mountain Sections of AWWA - WPCA - September 1970.
-------
INTRODUCTION
The concept of wastewater reclamation is neither new nor unique. Even in Biblical
times it was known. Ecclesiastics, Chapter 1, Verse 7, states: "All the rivers run to the
sea, yet the sea is not full. Unto the place from whence the rivers came, thither they
return again."
Like any "new" concept, water reclamation has its friends and its foes. Both sides
have many arguments supporting their positions. By way of a comparison, detractors of
the Wright brothers said of man's early attempts to fly, "If God intended that man
should fly, He'd have given us wings"! In answer to similar hysteria over the reuse of
wastewater, we could as easily retort, "If God had meant us to use only new water, He'd
either have given us more of it or created far fewer of us".
The purposes of this paper are twofold: to advance some of the many logical
arguments in favor of wastewater reuse; and to cite some actual case histories of
wastewater reuse operations as a means of showing what has already been accomplished.
ALTERNATIVE CONCEPTS
There is at least one alternative approach to most concepts. If we consider the
reclamation concept as one possibility, its antithesis might be termed the wastewater
concept. These two concepts are briefly defined below.
1. THE RECLAMATION CONCEPT
Water, once used for domestic and industrial purposes, still constitutes a natural
resource that can be renovated and reused. To be justified, the reuse must be shown to
be beneficial, economically feasible, and above all safe public health practice. Benefits
accruable to reclamation and reuse include the identifiable economic, ecological and
social impact on receiving waterways because of greatly reduced pollutional loads. These
benefits are to some extent intangible since a dollar value or "price tag" for elimination
of pollution is difficult to calculate. In addition, other benefits, including reduced costs
for development of alternate sources of potable water supply, maximum development and
use of the existing water resource, the ability to serve more people and industries and the
increase of the tax base, must be considered. Failure to recognize both tangible and
intangible benefits of water pollution abatement will generally result in making economic
justification of water reclamation and reuse impossible
- 1 -
-------
2 THE 'VASTEVATEft CONCEPT
This approach iiJip&'es continued aeesjJtancft of Che premise thzt sewsge is merely
wastewater, something fit orly to be discarded This concept itniiiid togfc&lly lead to tise
MmVastfor. Uttt tS'ce pollution wroblem csm be solvetf by muCTi tfe ss.-nc .-netftods
presently used; y. t., »esw-"a], of as ir,u:h :i (fcs pstlntapfe ¦coiliifl-iji in wastewater is is
necessary to fliest disposal rfcqv.Etjy.e:W: CaAavr. TTro&fscatlens sa treatnrerit ana dispoiU
tse&a&jues wmlc have to be developed and raplKDsnted as psiJutfan afcateirent
stajitigrfte became roorc st(!;t, tut tf,e tnain idea wot-id fc-s to dispose of las ¦«\ss a» a
wasfe. prsjarts a* rinssiy as tsossfaJs. sorjsisteni ^;th its r»esds cf Jas ecology of the
liters. BsTpf-t5 jxr;=fc|s '¦>-> accept riJ-jiie the juianeible aspens of
afratemeirf, si in th? ivater reclamation dotic^ja \iuTnQ\>&Ji c'rtw, to a le.wtrr
exletit, Gtp^ridsng eaay pfct>tc ascsptancs. Hd#s*vers the ".ir-te-'atar concept also has «Kat might be termed
"rwgatriS benefit?," srrtf tftes? busk &? jr- ,°s.y lewfel ovtraj cs>j*vpan»ati- T:
replace effioent wastes dovr.swenKt. £fi<3 lie p&ssix.tI * if ^-'acing liri'J :-c sjsa powth
by rlrtiii of a finite limit co available nsw future to reOTgaUe these and possibly
other "rtejjariw benefits" rjiay in (act coasitwit 5i>r justification (and a fcJ;e ore)
foe continusd \raite of tre^tec sewage effluents, at (east in areas wtifere "flaisa ia *0 wfeat
factor.
BENEFITS OF WASTEWATER RCCtftWArKJA'
1. ?OLLUTTON ABATE&GLnT
Or,s -af the rriajof 5erects oi £-¦>> ws^.feVoVa rsitksiattoa pMgr&v is the riiriovai zf
ft-ftclints iVcri vHclCr^atft I: -1 ^ncalsr tbar. :ral ofctairatv^ norm ccive n oiij
seconiary waste Uaalar.ent jrocssses GeceraMy. The quality ;lar.c.9t of COD removai. Items which can.tribute so &0D ci COD in wastewteis cacse a
depletion of di&solved oxygen conrenr w.thix rscgiving waters. Corise-yu>\rr<.Vy. virtiess tfi-e-
receiving has 2 sufficietit capacity to assimilate the oxygen demand of the incoming
wastes, dissolved oxygen levels fall below desirable lev^is, MfiU* atteraiant loss of deairacrvf:
aquaiic fsms.
-------
Nitrogen and phosphorus are the primary algal nutrients. Wastewaters rich in
phosphorus and nitrogen stimulate the growth of algae. In clean reservoirs and streams, a
delicate balance is maintained between the growth of algae and the growth of other
aquatic flora and fauna. In water which receives an over-abundance of nitrogen and
phosphorus, the usual result is the stimulation of greatly increased algal activity with
attendant "blooms" of these minute plants. A stream or reservoir which suffers from a
continuing over-abundance of nitrogen and phosphorus inevitably is on the road to
degradation and eventual death as a usable body of water. This process of enrichment,
because of nutrients, is termed eutrophication. Eutrophication is a naturally occurring
process; eventually, the fate of most streams and lakes would be conversion first to
swamps, and eventually, meadows, even without the enrichment provided by the activities
of man. The rate at which eutrophication occurs is unfortunately tremendously
stimulated by the activities of man, primarily because of wastewater discharges, but also
to a significant degree because of the use of agricultural fertilizers on crop lands, lawns
and gardens.
Suspended solids carried in wastewater effluents tend to settle in quiescent pools, in
reservoirs, or receiving streams, forming sludge deposits on the bottom. These deposits are
commonly known as benthol deposits and have at least two major detrimental effects. If
the benthol deposits remain on the bottom, they are subject to decomposition. If this
decomposition takes place in the presence of oxygen, it represents an oxygen demand. If
the decomposition takes place in the absence of oxygen, malodorous conditions result.
Even if suspended solids did not settle to the bottom, they represent an undesirable
condition by causing increased turbidity, which decreases the aesthetic appeal of a
receiving water. In addition, if present in large quantities, suspended solids have an
adverse effect upon aquatic life, especially the more desirable fish species such as salmon
and trout.
The presence of materials which cause color, taste or odor in receiving water
probably needs little discussion since these materials are readily ascertainable to anyone
who takes the trouble to use his senses.
Refractory substances, in general, may be defined as those substances which
contribute to the total organic carbon content of water, but do not generally represent
either a BOD or COD demand. In particular, these include synthetic detergents and many
of the organic pesticides which may find their way into waters. These substances can
definitely be linked to such diseases as cancer in humans and, even if not carcinogenic,
may cause undesirable side effects such as foaming or frothing of receiving waterways.
- 3 -
-------
2. SUPPLEMENTING THE AVAILABLE WATER RESOURCE
Another major benefit of water reclamation and reuse is the supplementing or
enlargement of what may otherwise be a fixed quantity of water available for use to a
given area. In many areas of the U. S., the quantity of water available from either surface
or subsurface sources is limited; such a limit in turn imposes a limit on the total number
of people and/or the total amount of industry which can be supported in a given area.
Water reclamation and reuse can multiply the apparent supply by recycling reclaimed
water without the necessity of developing new sources of water. Figure 1 illustrates this
concept graphically.
In conjunction with water reclamation and reuse, the quality of water required for
various uses often dictates the most desirable form of reclamation and reuse. For
example, water for most agricultural uses and many industrial uses need not be of as high
a quality as that used for human consumption. In such cases, water reclamation may take
the form of irrigation of crops and use of treated effluents for industrial purposes. The
net result is that the potable water supply source and system can be relieved of the
burden of supplying these needs. In areas which depend largely on groundwater sources,
artificial recharge of the groundwater resource either by injection or spreading of
reclaimed water is often possible. This also results in augmenting the available source by
essentially "banking" reclaimed water in the subsurface against the time when withdrawal
of groundwater exceeds the natural recharge.
Finally, in areas where sufficient potable water is not available, highly purified
reclaimed water can be recycled into the potable water system, thus increasing the overall
quantity of potable water available. Such action certainly should not be implemented
without considerable study and research covering all possible effects. It is not, however,
an action without precedent; direct domestic recycling is now being practiced in some
areas of the world and will undoubtedly become more widespread in the future. A case
history involving such a direct potable water recycle is dicussed later in this paper.
3. ECONOMIC ADVANTAGES
The final major benefits of water reclamation and reuse may very well prove to be
economic in nature. For example, the State of Nevada recently adopted water quality
standards for the Las Vegas area which are so stringent that, if met, treated wastewater
would be purer in nearly all respects than the waters of Lake Mead. However, Lake
Mead, after the completion of the Southern Nevada water project, will constitute the
major source of potable water for the Las Vegas area. Under the present Nevada water
quality standards, desalinization of wastewater before discharge into Lake Mead would be
- 4 -
-------
FLOW-G
ILOW f (Q)
CONSUMTIVE
USE Of
POTABLE WATER
SEWER
^SrSTEH
MAXIMUM
EQUIVALENT POPULATION
SERVED AT "X"gal./copita/doy
X
EFUUEHT
TO STREAM
A NON RECYCLING SYSTEM
"THE WASTEWATER CONCEPT"
CONSUMPTIVE
USE OF 4
FLOWQr
DIST.
POTABLE WATER
./'SYSTEM
£ FL0W=(l-f)(0+Qr) 1
MAXIMUM
EQUIVALENT POPULATION
SERVED AT X"s#)./copito/doy
= O+Qr
SEWER
SYSTEM
RECLAMATION
PLAMT
A RECYCLING SYSTEM
"THE RECLAMATION CONCEPT"
FIGURE 1
GRAPHIC COMPARISON OF THE WASTEWATER
AND RECLAMATION CONCEPTS
(OHMWMKVmt
-------
required. It would therefore be far superior in many characteristics to natural Lake Mead
water. Hence, unless the wastewater were to be reused it would, at least in some respects,
be polluted by admixture with Lake Mead water. Thus, the very high cost of treatment
would be lost for the most part, since the relative volumes are such that Lake Mead itself
would be but little improved. On the other hand, reclamation and reuse plans currently
under study include the use of some of the wastewater for cooling thermal power
generation facilities and, in conjunction with such generation facilities, recovery and
desalinization of. some of the wastewater by multiple effect distillation. The desalinized
reclaimed water would then be fed directly into the potable water system, actually
improving the quality of the supply from the standpoint of dissolved solids content. At
this point in time, the estimated net costs involved appear to be less than the cost of
merely treating wastewater for disposal.
In other areas where treatment requirements may not be as restrictive, savings may
still b ¦ realized by planned water reclamation. Certainly a portion of water use in nearly
any sizable community may be satisfied with less than drinking water quality. The City
of Colorado Springs provides such an example. For a number of years the City has
maintained a nonpotable water system to supply irrigation water. This system has utilized
both untreated surface water and sewage effluent that has passed through secondary
treatment. Recently, the City began construction of a tertiary treatment system to
augment their nonpotable water supply system. Their tertiary treatment plant will
provide additional treatment for about 12 mgd of secondary effluent and produce two
qualities of nonpotable water: a high grade water for cooling thermal power generation
and a water of lower quality for irrigation. The system will, in addition, significantly
reduce the amount of pollution entering Fountain Creek, which is the receiving stream
for the effluent. Even without considering any costs for possible development of other
sources of water to meet increasing demands, Colorado Springs found water reclamation
to be economically justifiable. Certainly if the costs of new source development and the
intangible benefits of pollution abatement were to be added, water reclamation at
Colorado Springs would be even more economically favorable.
A BRIEF HISTORY OF WASTEWATER RECLAMATION
1. THE CHANUTE STORY
The City of Chanute is a relatively small community in southeastern Kansas. Its sole
source of water supply is the Neosho River. Chanute maintains and operates a
conventional rapid sand filtration plant to provide treatment for Neosho River water
prior to introduction into the City's potable water distribution system. During the years
1953 through 1957, a record drought struck the tributary area of the Neosho; and as a
- 6 -
GPO 821 —97 1 — 10
-------
result, flow in the river became progressively smaller until in early 195.6 it practically
ceased. Although all possible water conservation measures and limited flow augmentation
procedures were pressed into use at Chanute, the water supply continued to dwindle. The
situation became progressively worse until on October 14, 1956, without fanfare of any
sort, City officials opened a valve which permitted mixing of sewage effluent which had
received conventional secondary treatment, with water stored iiP the Neosho River
channel behind the water treatment plant impoundment dam. During the period of water
reuse, the waste treatment removed, on the average, 86 percent of the BOD and 76
percent of the COD content of the wastewater. It substantially reduced both total and
ammonia nitrogen concentrations; detergent concentrations decreased an average of 25
percent. The recycling process was employed for a total of five months during the fall
and winter of 1956 and 1957. It was estimated that one complete cycle through the
waste treatment and back through the water treatment required about 20 days. Thus,
during the total period of time during which water recycling was practiced, the same
water passed through the treatment plant approximately seven times.
The treated water discharged from the water treatment plant had a pale yellow
color and an unpleasant musty taste and odor. It foamed when agitated and contained
undesirable quantities of minerals and inorganic substances. However, there were no
known cases of water-borne disease or other adverse effects upon health resulting from
the use of the recirculated water supply.
As a young sanitary engineer with the Kansas State Board of Health at the time, I
vididly remember, in particular, one of the humorous anecdotes that arose from this
episode. The comment was made that the water at Chanute "finally got so damn strong
that we shut off the high service pumps and it pushed itself through the mains."
2. THE WINDHOEK STORY
Since the Chanute episode in 1956, the technology of wastewater treatment has
indeed come a long way as represented by the latest example of reclaiming waste for
domestic water supply at Windhoek in Africa.
Near the end of 1968, Windhoek, the capital of South-West Africa, became the first
city in the world to practice large-scale and continuous reclamation of wastewater
effluent for drinking purposes. Its wastewater reclamation plant has a design capacity of
1.2 million imperial gallons per day. Treated wastewaters constitute approximately
one-third of the City's total water supply.
- 7 -
-------
Prior to installation of the reclamation plant, Windhoek's main sources of water
supply were a number of wells and a surface water supply from a nearby impoundment.
In order to maintain the City's rate of development, augmentation of these sources of
supply became necessary. The City of Windhoek is situated in a very arid region and
surface water resources are scarce and expensive to develop because they involve the
.pumping of water over long distances. Under these circumstances, reclamation offered the
cheapest solution to the problem.
The reclamation process involves the following unit process use:
flocculation-flotation, detergent removal by foam fractionation, lime treatment,
sterilization by chlorination, settlement of calcium carbonate sludge, sand filtration,
filtration through activated carbon, and final rechlorination.
The quality of the reclaimed water easily complies with World Health Organization
standards for drinking water. Excessive build-up of total dissolved solids is limited by the
high natural consumptive water use in the area so that desalting is unnecessary.
No public opposition to the final scheme has become apparent.
The Windhoek plant was officially opened on January 21, 1969, by the South
African Prime Minister, Mr. Vorster. The prime minister stated in his formal address that,
". . . in the future it might prove more advantageous to subsidize local authorities to
reclaim their effluents than to build new reservoirs which would involve the piping of
water over long distances."
3. THE TAHOE STORY
There are only about five full-scale advanced wastewater treatment plants in the
U. S. that are capable of producing the high degree of treatment required for domestic
recycling of reclaimed wastewater. Perhaps the most notable of these, and certainly the
first to go , into full-scale operation, is the South Tahoe Public Utility District water
reclamation plant at South Lake Tahoe, California.
Since March 31, 1968, the South Tahoe plant has operated without shutdown, 24
hours a day, and has continuously produced an effluent quality exceeding all the
stringent requirements of regulatory agencies exercising jurisdiction in the area. At the
present time, it is probably the only such facility in the U. S. which has for nearly three
years produced an effluent capable of meeting drinking water standards.
Figure 2 is a simplified, schematic flow diagram of the process employed at STPUD
to provide the high degree of purification and nutrient removals required. The process
consists of 10 major component systems as follows:
- 8 -
-------
-------
1. Conventional Primary Treatment
2. Completely Mixed Activated Sludge Secondary Treatment
3. Chemical Coagulation and Sorption with Lime
4. Nitrogen Removal by Air Stripping of Ammonia
5. Filtration Through Mixed Media Separation Beds
6. Granular Activated Carbon Adsorption
7. Disinfection by Chlorination
8. Coagulant Recovery by Recalcination
9. Thermal Activated Carbon Regeneration
10. Sludge Incineration
The continuously high degree of pollutant removal from the reclaimed water
achieved by the Tahoe Process is shown by the data in Table 1, which gives the average
overall efficiency since commencement of operations in March 1968.
TABLE 1
REMOVAL EFFICIENCY FOR THE SOUTH TAHOE
PUD WATER RECLAMATION PLANT
Parameter
Percent Removal
BOD
99.4
COD
96.4
MBAS
97.9
Phosphorus
99.1
Suspended Solids
100
Color
100
Odor
100
Turbidity
99.9
Coliform Bacteria
100
Virus
100
While the efficiency of removal of pollutants shown in Table 1 is indeed impressive,
it is perhaps of greater significance to compare the average quality of reclaimed water
from the Tahoe Process tr various recommended drinking water standards. -This
comparison is made in Table 2.
- 10 -
-------
TABLE 2
COMPARISON OF RECLAIMED WATER FROM THE
TAHOE PROCESS AND THE RECOMMENDED AWWA GOALS
FOR POTABLE WATER
Recommended
AWWA Goals Reclaimed "Water
for from
Parameter
Potable Water
STPUD Plant
Remarks
MBAS
mg/1
0.2
0.2
Meets Standard
a*
mg/tft
250
28
Meets Standard
S04"
mg/1^
250
36
Meets Standard
Color
units
3
0
Meets Standard
Odor
ton
None
None
Meets Standard
TDSt+
mg/1
500
300
Meets Standard
Exceeds Standard
COD*
mg/1
10
11
by 1 mg/1
BOD+
mg/1
6
1.5
Meets Standard
no3
mg/1 as N
10
0.2
Meets Standard
s. s.
mg/1
1.0
0
Meets Standard
Turb.
mg/1
0.1
0.3
Better than most
U.S. water
supplies
Coliform
MNP
None
Nont
Meets Standard
Hardness
mg/1 as CaCO-j
80
150
P04~
mg/1 as P
No Standard
0.1
tt USPHS Drinking Water Standard - Not AWWA Goal,
t World Health Organization Standard — Not AWWA Goal.
Reclaimed water from the Tahoe system is not reused for domestic-supply purposes.
Rather, in conformance with state 'aw, it is exported out of the Tahoe basin. However,
beneficial use is made of the reclaimed water. All effluent is impounded in a new*
man-made reservoir located some 30 miles from the treatment plant in Alpine County,
California. The reservoir has a capacity of about 3,000 acre-feet, and since its initial
filling has consistently maintained a very pleasing appearance. It has been approved by
local and state regulatory agencies for all water contact sports. The reservoir supports a
thriving population of rainbow trout and a state grant has been awarded for construction
- 11 -
-------
of additional recreation facilities. Its water is sparkling clean and Secchi disc observations
have been recorded as high as 20 feet. The low level of phosphorus in the water, coupled
with the very low organic carbon content, appears to control algal growth adequately.
During the irrigation season, a portion of the water in the reservoir is released for
irrigation of forage crops by downstream ranchers in the area.
4. THE DENVER SUCCESSIVE REUSE PROGRAM
The Denver Board of Water Commissioners has long been recognized as one of the
most progressive bodies in the water utility field. Their past engineering achievements in
supplying high quality water to the City and County of Denver include some of the most
difficult projects ever constructed. For example, the H. D. Roberts tunnel, completed in
1962, is the world's largest major underground tunnel (23.2 miles). The tunnel bore is as
deep as 4,465 feet below the earth's surface and provides transmountain diversion of Blue
River water to the Denver system.
With what must be termed typical foresight, the Denver Water Board has recognized
that the time is approaching when even such enormous projects as transmountain
diversion of west slope water will not assure totally adequate reserves of fresh water for
Denver. They have therefore embarked on a research and development program to
investigate and design reclamation systems to reuse wastewater. Initial plans call for a 10
mgd industrial reuse system. The Board proposes to expand the reclamation system to, an
ultimate capacity of 100 mgd of wastewater, with a large portion being recycled into
domestic use. This project represents the largest reuse plan yet undertaken anywhere in
the world and certainly is in keeping with the past achievements of the Denver Water
Board.
5. OTHER RECLAMATION EXAMPLES
The foregoing examples are but a few of the many operational or projected
reclamation systems. Another example of direct domestic reuse will soon be operational
in South Africa with a one mgd potable water reuse plant now in experimental operation
at Daspoort, Pretoria, South Africa. The Daspoort plant is very similar to the Tahoe
system, using lime coagulation, ammonia stripping, and activated carbon filtration. In our
own country, no listing of reclamation projects would be complete without mention of
the Santee, California, project which provides reclaimed water for recreational uses. Other
examples include Hyperion, California; and Long Island, New York, where reclaimed
water is injected into subsurface formations to provide a salt water barrier. Finally,
numerous examples of advanced wastewater treatment for pollution abatement are now
under construction in the U. S. These include plants at Blue Plains (Washington, D. C),
Rocky River, Pennsylvania, and Chicago, Illinois.
- 12
-------
PROBLEMS ASSOCIATED WITH WASTEWATER REUSE
There are still problems to overcome before wastewaicr reclamation, at least foi
domestic reuse, can become an everyday occurrence. First, the reliability of treatment
processes must be improved, and along ^with this, the rapidity with which analysis of
various pollutants can be made must be increased. Until these improvements are possible,
it will probably be necessary to impound reclaimed water in reservoirs prior to release to
raw water intakes at potable water treatment plants.
Bacteriological and virological testing techniques also need improvement. Today, our
techniques are extremely limited. Even though extensive virological testing at both Tahoe
and Windhoek have indicated no passage of viable virus through the treatment system, we
are not certain that no such passage occurs, because of the difficulty of culturing any but
a very few of the known viral organisims.
The progressive build-up of dissolved solids is another potential problem in water
reclamation. Fortunately, this is a problem which can be solved by current technology,
albeit at considerable cost, by such techniques as distillation, ion exchange, reverse
osmosis and dialysis. Also, fortunately, the build-up of dissolved solids in most cases is
not great due to the natural "blow-down" of dissolved solids from conventional U. S.
water systems because of our prevailing rather high consumptive water use practices. The
equilibrium concentration of dissolved solids that can be anticipated in any given
recycling water system can be rather easily computed for any given moment if proper
records are available. Figure 3 shows the general formulations necessary to solve such a
problem. The technique shown was developed for computer solution with an IBM 1130
system, but it is adaptable to any computer system, or even hard calculations for that
matter.
An interesting example may be obtained by using average figures for Denver (1968
data).
DATA
1968 average monthly potable water produced - 150 mgd
1968 average monthly TDS content of potable water - 135 mg/1
1968 average, monthly TDS content of wastewater - 480 mg/1
ASSUMPTIONS
1. Assume 90 mgd reclaimed water recycled to domestic raw water supply.
2. Assume 50% of total flow consumptively used.
3. Assume 10% of reclaimed water consumptively used by irrigation and/or
industry.
- 13 -
-------
Q1
TDS1
Q2
TDS2
DISTRB.
SYSTEM
CONSUMPTIVE
USE LOSS
03
W
TDS3
Q4
TDS4
SEWER
SYSTEM
BIOLOGICAL
TREATMENT
EFFL. NOT
RECLAIMED
INDUSTRIAL
CONSUMPTIVE
RECL.EFFL. USE
FIGURE 3
SCHEMATIC DIAGRAM OF A RECYCLING
WATER SYSTEM
-------
NOMENCLATURE (For Figure 3)
Ql
=
Flow into system from potable water supply
mgd
Q2
=
Flow recycled into system from water reclamation
mgd
Q3
=
Total flow to distribution system
mgd
Q4
=
Consumptive water use in distribution system
mgd
Q5
=
Flow to sewer system from distribution system
mgd
Q6
=
Q5 = flow to biological treatment plant
mgd
Q7
=
Flow from biological treatment plant not reclaimed
mgd
Q8
=
Flow from biological treatment plant to reclamation
mgd
Q9
=
Flow from reclamation plant to consumptive industrial use
mgd
TDS1
=
Dissolved solids concentration of Ql
mg/1
TDS2
=
Dissolved solids concentration of Q2
mg/1
TDS3
=
Dissolved solids concentration of Q3 ¦
mg/1
TDS4
=
TDS3 = Dissolved solids concentration of Q4 or Q3
mg/1
TDS5
=
TDS3 = TDS4 = Dissolved solids concentration of Q3 or Q4 or Q5
mg/1
TDS6
=
Dissolved solids concentration of Q6
mg/1
TDS7
=
JDS6 = Dissolved solids concentration of Q6 or Q7
mg/1
TDS8
=
TDS6 = TDS7 = Dissolved solids concentration of Q6 or Q7 or Q8
mg/1
TDS9
=
TDS6 = TDS7 = TDS8 = Dissolved solids concentration of Q6 or Q7
mg/1
or Q8 or Q9
W
=
Increase in TDS due to passage through sewer system
mg/1
X
=
Decimal fraction of Q3 consumptively used
Y
=
Decimal fraction of Q6 not reclaimed
Z
=
Decimal fraction of Q8 not recycled
EQUATIONS
Ql
=
Given
Q5
=
(1 - X)(Q1 + Q2)
TDS1
=
Given
Q6
=
Q5
Q2
=
Given
TDS6
=
TDS2
Q3
=
Ql + Q2
W
=
Given
TDS2
=
(Ql x TDS1 + Q2 x TDS2)
W + (Ql + Q2)
Q7
Y
=
Y(1 - X)(Q1 + Q2)
Q'
TDS3
(Ql. x TDS1 + Q2 x TDS2)
(1 - XXQl + Q2)
(Ql + Q2)
TDS7
=
TDS 2
X
=
Given
Q8
=
(1 - XXI - YXQ1 •
04
=
X(Q1 + Q2)
TDS8
=
TDS2
TDS4
=
TDS 3
Z
=
Given
TDS 5
TDS 3
Q9
TDS9
:
Z(1 - XXI - YXQ1
TDS2
15 -
-------
By using the formulations shown on Figure 3, and solving the problem for the
equilibrium concentration of TDS in the blended domestic water supply, we find that
such a practice would result in an increase in TDS to the consumer of 207 mg/1. Stated
in other terms, drinking water at the homeowners tap would have increased from a TDS
content of 135 mg/1 to 342 mg/1. It would not rise above the value of 342 mg/1 unless
the relative volumes of 90 mgd reclaimed water to 150 mgd of "virgin" water were
changed. It is doubtful if the consumer could detect such a change in TDS content, and
furthermore the final TDS concentration would still be well below the USPHS allowance
of 500 mg/1 TDS.
Finally, we must be cognizant of public reaction to water reuse. The general public
will not welcome the idea of drinking their own wastes. Experience has shown that the
only way to overcome this rather natural reaction is by means of public education. The
establishment of recreational reservoirs such as Indian Creek at the Tahoe project and the
Santee Lakes at the Santee project have help the cause immeasurably. Such reservoirs
may well be a vital key to public acceptance of wastewater reclamation; they may also be
required unless or until better testing techniques are available to insure an absolute
guarantee of safety for domestic reuse.
SUMMARY
In this discussion, I have attempted to show the merits of water reclamation as a
concept. It may be that in some areas of the world, wastewater reuse, aside from its
merits, will soon become an absolute necessity, as it already is in Africa.
We have seen what our nation's scientific and technological forces have been able to
accomplish in both the nuclear and outer space areas when given unlimited financial
support. If our national government supports their verbal pledges with actual
appropriation of funds, we can expect that a large part of the nation's technical resources
will move into the environmental control fields. Probably, in our usual manner, we will
waste a lot of money and effort in our rush to develop solutions. However, there can be
no doubt that the end result will be the development of many valuable new processes not
known today.
The decade of the 1970's may well mark the era when America realizes that only
"wastewater" fit to drink is fit to throw away. If that criterion should indeed be adopted
by our society, I am certain that the technology will exist to accomplish that goal at a
cost which we will be able to bear.
16 -
-------
Finally, I would leave you with this thought: If the only water fit to throw away
is fit to drink, then there is obviously no such thing as "wastewater." I believe we should
discard this word from our vocabulary and along with it such terms as sewage and refuse
liquids. We should come to realize that there is no such thing as new water; nearly all
water or the earth's surface has been used and reused in one way or another. Perhaps we
should refer to the water which carries our wastes as "transport water." Then in our
treatment plants we can remove the pollutants from the water used to transport the
pollutants to the plant and end up with plain water. The result might be far more
acceptable to the public than trying to get them to drink "reclaimed sewage."
GPO 821-971-1
- 17 -
------- |