United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S2-84-081 May 1984
&EPA Project Summary
Characterization of Operating and
Maintenance Practices for
Wastewater Treatment Systems
in the Iron and Steel Industry
Richard T. Price, William F. Kemner, William E. Gallagher, and
Gopal Annamraju
The purpose of this study was to
document effective operations and
maintenance (O&M) practices for
wastewater treatment systems in the
iron and steel industry and to ascertain
how their application might affect per-
mit parameters and operational upsets.
The wastewater generating processes
selected for study were byproduct
cokemaking, ironmaking (blast fur-
naces), steelmaking (basic oxygen fur-
naces), hot forming, and acid pickling.
Selections were based on pollutant
loadings, system complexity, control
costs, and commonality among most in-
tegrated steel mills.
Information was gathered from sev-
eral sources: a literature search for
wastewater-related O&M practices in
the iron and steel industry, discussions
with state and regional agency person-
nel to identify major areas of concern
and effective O&M practices, review of
agency files, discussions with waste-
water treatment equipment vendors and
chemical additive manufacturers, and
discussions with industry represen-
tatives.
Various steel mills were visited, and
treatment plant operators and en-
vironmental staff members were inter-
viewed. The information produced by
these visits includes typically en-
countered problems and their solutions,
troubleshooting efforts, extent of op-
erator training, efforts to minimize the
effect of operational upsets, and preven-
tive maintenance practices.
The study produced a report that: pro-
vides a better understanding of waste-
water problems in the iron and steel
industry, helps agency inspectors to be
more effective in evaluating the effect
of O&M practices on wastewater treat-
ment performance, and provides infor-
mation that will assist plant personnel
in practical and cost-effective fine-
tuning of their systems.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Effective O&M practices at a wastewater
treatment system are those that can keep the
system operating at its optimum perfor-
mance with minimal downtime.
It is management's responsibility to initiate
and maintain an O&M plan. Although such
O&M practices as communication, operator
training, staffing, recordkeeping, preventive
maintenance, and treatment system audit-
ing/evaluation are probably implemented in
some degree at all plants, their effectiveness
depends on the degree to which they are
practiced, how carefully they are practiced,
and whether they are fine-tuned periodically
(if necessary) to achieve optimum results.
The plant visits made during this study
showed that the management organization
for water pollution control has much to do
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with successful communications and with
obtaining the cooperation necessary to solve
problems expeditiously. Generally, the
management structure at the plants visited
was:
• The utilities (power and fuels) depart-
ment is responsible for operating the
wastewater treatment systems.
• The process department, responsible for
the steel mill process operations, as-
sumes at least part of the responsibility
for proper handling of the wastewater.
• The environmental department keeps all
pertinent personnel informed of current
and expected water regulations that will
have an impact on the plant. This de-
partment is a go-between for the plant's
pollution control section of the utilities
department and the regulatory agencies
and is responsible for all correspondence
with the agencies.
The wastewater generating processes
studied were byproduct cokemaking, iron-
making (blast furnaces), steelmaking (basic
oxygen furnaces), hot forming, and acid
pickling. The report discusses the O&M
problems and practices of each process
separately and also presents general obser-
vations regarding the components of effec-
tive industry-wide O&M practices.
Management-Based O&M
Practices
These management-based practices in-
clude communications, operator training,
logs/recordkeeping, staffing, and treatment
system auditing.
Communications
Good communication is essential to effec-
tive O&M. Figure 1 illustrates effective and
ineffective communication structures, both
of which are found in the industry. Usually,
the utilities supervisor is the key person in
making a communications system work.
Only through effective communication ties
between operators, supervisors, and main-
tenance personnel can problems be brought
to the attention of the necessary parties, and
alternate solutions discussed and imple-
mented.
Operator Training
Proper and adequate training of operators
is critical to the effective operation of a
wastewater treatment system. Operators
need to know:
• How their systems operate and how to
handle routine problems.
• What pollutants are being removed and
where they are destined to go (sinter
plant, landfill, recycle, etc.).
• Where the treated water goes.
Agency
Environmental
Supervisor
Utilities
Supervisor.
Polymer
Representative
Process^
Supervisor
Maintenance
Operator
Process Department Treatment Plant
Ineffective
Agency FN
Environmental
Supervisor ,'
Utilities
Process p-fl/ i
ProTees7Departmentg)''/"\^^w'SOA
| Lab
Results
Representative /
Maintenance Operator
Treatment Plant
Effective
Figure 1. O&M communication structure.
• How the steel mill depends on their per-
formance (directly for return of needed
water, or indirectly to avoid potential
regulatory action).
• What daily routines must be followed.
• What to do in emergencies.
It is important to keep subsequent genera-
tions of operators as well trained as those
who were there during system start-up and
had the benefit of receiving thorough train-
ing from the equipment manufacturers.
One useful aid that some operators have
developed involves the use of simplified
schematics of their equipment and/or overall
treatment scheme. These schematics are
usually much less complex than those in the
O&M manuals provided by the design
engineers.
Logs/Recordkeeping
Good recordkeeping is an effective O&M
tool. The plant visits made during this study
indicated that current practice varies from
maintaining essentially no records to record-
ing numerous operating parameters every 2
hours. Although the extent and frequency
of recordkeeping vary greatly from plant to
plant, it was obvious that the operators of
the well-operated systems made a practice
of logging key operating parameters on a
periodic basis. In addition, the operating
supervisors at these plants reviewed the logs
for abnormal conditions and initiated re-
quired followup action. In other words, the
logs were used, not just filed away. (See
Figure 2.)
Wrong
Treatment Plant
Bulletin Board
Right
Figure 2. Effective use of records.
Staffing
Proper operation of a treatment system re-
quires enough operators (and assistants and
helpers) with clearly defined job functions.
The plants visited were generally well
staffed. At one plant, however, one operator
had to devote all of his time to manually con-
trolling the treatment system (filtration
plant). Had this operator been responsible
for areas other than the filtration plant or
were he less efficient, the filters would have
plugged and the system might have been
damaged or the amount of filter effluent
might have increased greatly.
Treatment System Auditing
Results of this study indicate that most
plants have proceeded from permit negotia-
tions, to system design, to routine operation
without ever having stepped back to over-
view their situation. Some type of periodic
formal O&M audit would be beneficial to
provide such an overview.
It is suggested that audits or self-evalu-
ation programs by a plant team or an out-
side consultant be implemented periodically
(e.g., annually). When such evaluations
reveal less-than-optimum conditions, correc-
tive action should be taken, with followup
to ensure that approved suggestions have
been carried out.
Cokemaking—O&M Practices
Treatment systems and component ar-
rangements for treating coke plant waste-
waters vary throughout the industry, but
most plants have equipment specifically
designed to remove two pollutants — am-
monia and phenol.
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About two-thirds of the plants with coke-
making facilities have ammonia stills and
treatment systems for removing phenol. All
of this group have free ammonia stills, and
about 85 percent also have fixed ammonia
stills. About half of the plants that remove
phenol have dephenolizers; the rest are
equipped with oxidation systems (primarily
bio-oxidation). Figure 3 shows the compo-
nent arrangement at one plant.
Major Anas of O&M Concern
Improper handling of or lack of attention
to any of the following items can cause an
upset in the bio-oxidation system ranging
from minor to major proportions.
• Monitoring the performance of am-
monia stills
• Controlling biological basin pH
• Controlling basin temperature
• Adding nutrient
• Aeration
• Maintaining adequate dilution water
(where practiced)
• Introducing intermittent, experimental,
or toxic material
• Monitoring key parameters
• Communicating
• Operator attention and know-how, and
good supervisors
Some Effective O&M Practices
Ammonia Still
1) Maintaining adequate storage of crude
liquor to allow the coke batteries to
continue operating without interrup-
tion during still shutdowns.
2) Monitoring the return liquor flows
from the lime legs to the stills. One
plant monitors and records the flow
rate every 2 hours.
3) Properly adjusting the steam flow to
the lime leg discharge to ensure an
adequate supply of steam to strip the
ammonia from the liquor. Operators at
one plant use an easily read chart
showing proper steam/return liquor
flow ratios.
4) Regular monitoring and recording of
still pressure, noting changes and call-
ing them to the attention of the main-
tenance department.
Lime Slaker
1) Periodic checking of the level of the
lime storage bin or tank and reporting
low levels to the foreman.
2) Controlling slaker feed water. Feed to
the slaker should be steady and rela-
tively uniform in size. Lime mixing
spray should be inspected for block-
ages. Also, lime quality should be
f Waste
Liquor
''Holding
Tank
Splitter
Box
Overflow to
Settling
Lagoon
(330.000 gpd*)
Sludge
Recirculation
Pump
Figure 3. Biological plant flow diagram.
Liquor
— Tar Sludge and
Lime Waste
———~ Activated Sludge
(*) 1 gpd (gallon per day)
= 3.79m'
closely controlled; e.g., lime size as
received (about 80 percent less than
!/4-in. or 0.635 cm) and lime slurry
temperature (90 to 95°C). Carefully
controlling these parameters improves
dissolution of lime into the slaker
water and reduces lime consumption
considerably.
3) Controlling pH of the still effluent to
control the amount of lime water
being fed to the lime legs for reaction
with the crude liquor. Because of in-
herent plugging problems, a pH con-
troller with pH probes is not
dependable in a lime-based system;
therefore, effective O&M practices are
required to back up (or substitute for)
pH control. At one plant the operators
check the pH of the effluent and of the
liquor from the lime leg every 2 hours.
4) Preventive maintenance; e.g., fre-
quent inspections, scheduled
cleaning.
Biological Treatment Systems
1) Controlling pH in aeration basin. The
most effective practice observed is
monitoring the basin pH and its
sources. At one plant, operators take
samples every 4 hours from the
equalization tank effluent, secondary
storage tanks' influent and effluent,
basin inlet sump, and basin outlet
sump. The pH's are analyzed and
recorded on a daily log sheet. At
another plant, wastewater treatment
plant operators take bihourly waste-
water samples from the ammonia stills
and daily samples from the basin
wastewater feed and clarifier over-
flow. These samples are analyzed for
pH and recorded. These practices per-
mit early detection of pH deviations
and allow the immediate implementa-
tion of corrective action to protect the
system and effluent quality (e.g.,
diversion to an emergency storage
tank, if necessary).
2) Controlling basin temperature. Micro-
organism activity diminishes if the
wastewater becomes too cold, and
microorganisms can be killed if
wastewater temperatures get too
high. Plants are equipped with moni-
tors, control valves, and recorders on
control panels, but operators still
should manually record temperatures
at the source and log this information
to ensure good temperature control.
3) Checking nutrient addition. All of the
systems visited use phosphoric acid as
a nutrient. Some plants check the
phosphate residual daily. One effective
practice is to observe the addition of
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phosphoric acid to the primary clarifier
every 2 hours. This was not difficult
at one plant, as the addition point is
about 1 ft (30 cm) above the water
level. At one plant the phosphoric acid
tank is on stilts, above the primary
clarifier (which returns sludge to the
basins); this allows the acid to flow by
gravity into the clarifier's sludge recy-
cle pump. Gravity always works, and
the operators can visually check the
flow of acid.
4) Ensuring adequate aeration. The prac-
tice at one plant is to make an occa-
sional check of the dissolved oxygen
content of the basin water and to
make a physical check of the aerators
twice per shift to see if they appear to
be operating properly. Instead of
regularly monitoring the dissolved oxy-
gen content, one plant has installed
ammeters in a pump house, which are
connected to the aerator motors. Nor-
mal readings are 25 to 30 amps. The
operators observe these readings bi-
hourly, and enter a check on the log-
sheet if the readings are in this range;
if not, the actual reading is recorded,
and if the deviation is more than a cou-
ple of amps outside the normal range,
the operating supervisor is notified.
The amp readings correlate well with
cell wastewater dissolved oxygen
levels of 1 to 2 ppm. One plant that
recently had a problem with strat-
ification of the dissolved oxygen in-
stalled air lances for use at these times
to promote better localized mixing.
The lances also serve as a backup
when an aerator fails or is taken out
of service for a maintenance check.
Blast Furnace—O&M Practices
Blast furnace treatment systems do not
vary much from plant to plant. They gener-
ally consist of recycle systems with a
thickener/clarifier for solids removal, a cool-
ing tower, and a chemical treatment system
for deposit or scaling control. Several plants
use alkaline chlorination for removal of am-
monia and cyanide for blowdown water.
Major Areas of O&M Concern
• Controlling pH
• Removing phenol
• Removing cyanide
• Removing ammonia
• Controlling scaling by dissolved solids
• Handling sludge
• Maintaining a tight recycle for hydraulic
balance
• Temperature of recycle water
• Adding chemicals
Some Effective O&M Practices
O&M concerns at the operating level
focus primarily on the condition of the equip-
ment and the parameters used for daily
monitoring of the system. Effluent water
quality, on the other hand, is the concern of
the environmental department. The follow-
ing O&M practices were observed:
Controlling pH
1) Daily inspection of oxidation reduction
potential (ORP) and pH probes for
scaling problems and cleaning as nec-
essary. Maintaining spare probes and
experimenting with new types of
probes as they become available.
2) Manually checking pH readings. One
plant checks the pH of the blowdown
twice a shift and the pH at several
other locations in the system once a
shift.
3) Using standard solutions of 6 and 9 pH
to calibrate pH probes rather than the
usual standards, which are outside of
this control range.
Controlling Scaling by
Dissolved Solids
1) Maintaining chemical feed in a tight
recycle system. Some experiments
with softening have been reported.
2) Monitoring hardness, alkalinity, and
conductivity on each shift.
3) Adding a deposit control agent at the
hot well of the cooling tower.
4) Adding an antifoulant and dispersant
at the main recirculation sump.
5) Long-term analysis of hardness,
alkalinity, and conductivity, and using
graphical plots versus time to detect
and correct scaling trends.
Handling Sludge
1) Scheduled preventive maintenance,
which includes:
a) Changing gear box oil every 6
months.
b) Checking and lubricating all pumps
and other moving equipment every
week.
2) When a pump fails to work:
a) Operator checks to see if suction
line is plugged; if so, cleans line
and replaces it.
b) If problem is more major (e.g., a
badly worn impeller), maintenance
department repairs the pump.
Basic Oxygen Furnace—
O&M Practices
A basic oxygen furnace (BOF) shop
typically has two furnaces. Each has a
separate scrubber, but both share a common
water treatment system. The primary pollu-
tant of concern is suspended solids. Since
the water is recirculated, the concerns of
dissolved solids and scaling are similar to
those in blast furnace systems.
Major Areas of O&M Concern
Focus is primarily on BOF systems that
have recycle loops because many plants
have recirculation systems and because this
technology is emphasized in the guidelines
for steel mill effluent limitations.
• Controlling dissolved solids
• Controlling pH
• Controlling suspended solids
• Maintaining a proper rate of sludge
removal from thickeners/clarifiers to
avoid thickener upsets and/or rake
change.
Some Effective O&M Practices
Controlling Dissolved Solids
1) Using pH control, balanced schedule
of blowdown and makeup, and chem-
ical treatment. Two or sometimes all
three controls are combined.
2) Periodically inspecting the acid system
and pH sampling/analysis (to back up
automatic systems).
3) Regularly cleaning pH probes.
4) Manually adjusting acid metering
pump and periodically inspecting to
see if it is regulated properly.
5) Checking the discharge of blowdown
against the individual plant's criteria
and adjusting it if iron and zinc con-
centrations are too high.
Chemical Treatment
1) Quick maintenance action if the
polymer system breaks down and
becomes plugged.
Controlling Solids/Sludge
1) Inspecting cyclones and classifiers
each shift and periodically replacing
the rubber lining in cyclones.
2) Monthly inspection of classifiers by
maintenance department and work
performed as needed. A spare is main-
tained.
3) Draining thickeners yearly for
thorough inspection.
4) Visually inspecting sludge pumps (by
operators) each shift.
5) Periodic testing polymer additions by
the manufacturer to ensure optimum
dosage rate. Polymer representatives
work closely with operators and peri-
odically perform bench tests with new
polymers against which operators can
compare their bench tests to see if
they are in agreement.
6) Providing automatic rake-lifting
devices on thickeners if torque be-
comes too great.
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7) Periodically monitoring and recording
torque by operators and notifying
supervisors if readings are above
normal.
8) Maintaining on-line spares for all
sludge pumps.
Hot Forming—O&M Practices
Treatment technologies used in hot form-
ing include: primary sedimentation, surface
oil removal, secondary settling or filtration,
and recycle.
Major Areas of O&M Concern
The major areas of O&M concern for hot
forming (primarily on hot strip mills) waste-
water treatment systems are:
• Operating scale pits
• Communicating
• Handling sludge
• Treating with chemicals
• Backwashing filters
• Operator and maintenance attention/in-
spection/monitoring of key parameters
Some Effective O&M Practices
Operating Scale Pits
1) Systematically removing material that
has settled out in the scale pits once
a week. This permits maintenance of
good working volume and reasonably
constant retention time.
2) Clam-shelling of finishing scale pit on
Sunday (when the hot strip mill is
down) to allow the solids adequate
time to settle before start-up of the mill
the following day. This was observed
at one plant.
3) Frequently inspecting the scale pit by
the operator to allow him to detect
and remove debris (e.g., twigs) on the
rope skimmers. This is very important;
several hundred gallons of oil could ac-
cumulate if a "short-circuited" skim-
mer went undetected for several
hours.
4) Maintaining a good supply of spare
rope skimmers on site.
5) Attaching heat lamps near the skim-
mer's driving gear mechanism to re-
duce skimmer stiffness during cold
weather.
6) Monitoring key parameters; e.g., fre-
quency of backwashing and the filter
media level at a plant with deep-bed
gravity filters.
7) Monitoring the following parameters
at plants with settling ponds:
a) Pond levels and flows (once per
shift)
b) Oil skimming equipment (once per
shift)
c) Periodic checks (every several
months) of solids depth in the
ponds. (Sometimes determined by
taking soundings from a boat.)
Backwashing Filters
1) Extended backwashing of sand filters
to remove accumulated solids that or-
dinary backwashes do not remove
(performed every weekend).
2) Periodically steam cleaning filters to
remove accumulated oil and grease.
Other Observed Practices
1) Periodically inspecting pipes that are
subject to abrasion to see if thick-
nesses are safe (by sonic testing).
2) Stringing floating booms diagonally
across settling basins to direct floating
oil and grease to belt skimmers. These
booms are replaced about every 3 or
4 months. Catwalks at the end of the
basins allow access to the final settling
area to pump off floating oil.
3) Periodically sampling filter media by a
contractor who performs an ash test
to see how much scale is accumu-
lating. This information is used to
determine when the media should be
changed.
4) Notifying the utilities operator by
phone (by mill rolling foreman) of
shutdown and start-up times and oil
spills.
5) Routinely maintaining wastewater-
related equipment: lubricating; vibra-
tion monitoring/testing of major
pumps, motors, and air blowers; cali-
brating meters; checking software
weekly; maintaining computer soft-
ware; and inspecting electrical
equipment.
Acid Pickling—O&M Practices
Wastewater is generated from three
sources in the pickling operation: rinse
water, fume scrubber water, and spent acid.
Major Areas of O&M Concern
Major areas of O&M concern in the acid
pickling wastewater treatment systems are:
• Sludge accumulation
• pH monitors
• Lime addition
• Sludge buildup in aeration tank
• Exhaust fan
• Reactor cyclone
• Waste pickle liquor feed point
• System pressure drop
• Preventive maintenance
• Fines formation
Some Effective O&M Practices
pH Monitors
1) Frequent checking of the readout of
pH monitors in the system, using a
portable pH meter.
2) Checking pH hourly, and plotting on
a daily chart to illustrate pH control
and variation in the aerators.
Lime Addition
1) Maintaining the proper ratio of
hydrated lime to limestone.
2) Checking lime shipments to ensure
that the lime meets plant quality
standards.
3) Using a single supplier (when possi-
ble), for a more consistent quality of
lime.
Clarifiers
1) Checking the height of the water
above sludge blanket (i.e., sludge
depth) every shift.
2) Inspecting the chemical additive
system and dosage rate, and visually
observing the formed floe to note
anything unusual about its ap-
pearance.
General O&M Practices -
Treatment Components
This discussion covers problems con-
cerned with the common treatment com-
ponents in use at steel mills and current or
suggested O&M practices. Many of the
components (e.g., clarifiers, filters) are used
to treat different process wastewaters (e.g.,
blast furnace, basic oxygen furnace).
Clarifier/Thickener
One of the most common clarifier
maintenance problems is a plugged sludge
line. Items such as hardhats, tools, and
general debris find their way into the clarifier.
At some facilities, a wire mesh or some other
barrier across the top or on the sides of the
clarifier prevents large objects from falling in.
When the clarifier is emptied for mainte-
nance, the sludge pump should be inspected
thoroughly before the unit is put back on
stream to ensure that nuts, bolts, etc. have
not been left there by maintenance per-
sonnel.
The condition of the clarifier feed can be
checked with a simple settling test, con-
sisting of putting a sample of clarifier feed
in a graduated cylinder or Imhoff cone and
noting the sludge level after a specific time.
Although such a test does not give an ab-
solute measure of the settling rate, it will
detect an upset in the system. If tested every
few hours, a problem in the clarifier feed can
sometimes be detected before it leads to a
major upset.
Turbidity in the clarifier overflow should
be checked frequently, either manually or
with an instrument. If an instrument is used,
turbidity should still occasionally be checked
-------
manually, to ensure that the instrument is
operating properly.
A visual inspection of the clarifier will show
the operator if the sludge level is getting near
the overflow weir. The operator should also
check the uniformity of the effluent flow over
the clarifier perimeter weir.
To be sure the clarifier is not operating at
too high a feed rate, the operator should
check the actual feed rate against the design
feed rate.
The flocculation and settling performance
of the clarifier feed can be checked, using
a standard jar test apparatus. After the set-
tling rate has been determined, some of the
liquid can be siphoned from the jar for a
suspended solids analysis. The suspended
solids level should approximate the clarifier
overflow, but this test is most useful for
comparison against a benchmark test.
Sometimes, settling can be improved by
switching polymers.
Water Recycling
Recirculating water in a process treatment
system or as part of an overall plant recir-
culation strategy involves many different
considerations; e.g., maintaining system
tightness, hydraulic balance, and water
chemistry, and providing adequate monitor-
ing and sampling. The report discusses each
in detail.
Scale Pits/Sedimentation Basins
Although scale pits are among the least
sophisticated and most low-profile treatment
technologies, they play a key role in the per-
formance of water treatment plants at hot
strip mills. If properly operated, systemati-
cally cleaned, and equipped with oil-skim-
ming equipment, they provide an effective
pretreatment step prior to secondary
treatment.
The solids removal efficiency of any scale
pit is a function of the effective detention
time. It is not uncommon for plants to ex-
perience increased solids loadings out of the
pit during scale removal activities; therefore,
it is advisable to dredge the pits during mill
operation downtimes or to have additional
cells or spare pits. Good housekeeping and
well-maintained oil skimmers are the most
effective controls for scale pits. If used, these
controls can intercept much of the free oil
resulting from oil spills and line breaks.
Filtration
In the iron and steel industry, filtration is
used to remove suspended solids from
wastewater (polishing filters) and to dewater
sludge (dewatering filters).
Polishing Filters
One of the mills visited was trying to im-
prove the operation of its multimedia filters:
6
it was experimenting with declining rate
filtration. This operation begins the filtration
cycle at a high flow rate and then reduces
the rate for the rest of the run, which reduces
the suspended solids in the filter effluent.
Another plant reported oil buildup in the
filter media. One way to wash out this ex-
cess oil is to use steam (in addition to air and
water) when backwashing the filter.
At one plant, with a horizontal multimedia
filter, the media was being washed out on
the backwash cycle. This filter had slotted
distributor plates, and the bottom distributor
plates were covered with gravel. To solve the
problem, the plant put screens on the slot-
ted plates at the top of the filter and bubble-
cap strainers on the bottom distributor
plates.
This plant also had rectangular sand filters,
and (during backwash) the air scour created
so much turbulence that the media washed
into the troughs and out with the backwash
water. This problem was solved by screens
on the rims of the discharge troughs.
Dewatering Filters
Most plants consider dewatering filters to
be a high-maintenance item because the
filter cloths are easily torn and the belt on
a drum filter can stretch and get out of align-
ment, ft is necessary to keep an adequate
inventory of spare cloths for each filter.
pH Control Systems
The pH electrode assemblies are a fre-
quent cause of malfunction of pH control
systems. The proper maintenance of these
electrodes is important to the precision and
the accuracy of pH control and monitoring.
The three types of maintenance required are
calibration, cleaning, and replacement. Many
plants calibrate daily, and daily cleaning is
not unusual. One plant piped service water
to the line containing the pH electrodes; the
process flow is turned off periodically, and
the service water valve is opened to flush the
electrodes with clean water.
Because of its low cost, lime is frequently
used for pH control. The amount of calcium
oxide in the lime must be controlled for con-
sistent operation. Sometimes a temperature
test is used to quickly evaluate the quality
of lime shipments. Measured amounts of
water and lime are mixed, and the tempera-
ture is recorded to determine the calcium
oxide content. Plants should be especially
cautious of lime quality with changing
vendors.
A common problem that occurs when lime
slurry is used to adjust pH is plugged equip-
ment. A control valve in lime slurry service
should be checked regularly for signs of
pluggage or erosion. Maintaining a historical
record of electrode failures, control valve
failures, line pluggage, etc., will allow a plant
to set up a preventive maintenance schedule
to avoid these problems. Good preventive
maintenance is the key to successful pH
control.
Chemical Addition Systems
Because the flow rate of chemical ad-
ditives (e.g., polymers) is low, it is some-
times difficult to determine if they are
flowing. Ideally, these chemicals should be
introduced above the level of the liquid to
which they are being added so the operator
can see them falling from the end of the pipe
into the tank and thereby verify the flow.
Care should be taken that the vendor's in-
structions regarding the use and mixing of
a specific polymer are followed closely. Ex-
cessive mixing can shear the polymer and
damage its effectiveness. Also, to achieve
maximum efficiency, many polymers must
be aged for 12 to 24 hours after they are
mixed.
Care should be taken not to use a polymer
that is so old it has lost its effectiveness.
Also, polymers should be stored where they
are protected from freezing, which is damag-
ing to them.
Some vendors provide jar test apparatus
to evaluate their polymers for application in
a particular plant. An evaluation by plant per-
sonnel may be more objective, however, and
certainly would provide results for com-
parison against those of the vendors.
Oil Skimming System
The simplicity of oil skimmer systems
makes them very reliable, and maintenance
relatively easy. Nevertheless, they should be
checked daily. The skimming mechanism re-
quires periodic lubrication, adjustment, and
replacement of worn parts. Heating is sug-
gested during winter months to keep the
skimmer from freezing. If this is not possi-
ble, a backup removal system (e.g., a
vacuum truck) should be provided.
The paddle skimmer should be checked to
ensure that each blade touches the water for
the full length of the blade. Rope skimmers
should be checked to ensure that the rope
is not rubbing against an object that could
scrape off collected oil or abrade the rope.
The inspector should observe the rope for
one full revolution to be sure it is not abrad-
ed at some point. The operator at one plant
said rope skimmers could be more effective
if the tubes penetrated the water surface bet-
ter. The plant was going to experiment by
injecting some lightweight antifreeze fluid
into the plastic tubes to provide additional
weight for better immersion. (This might also
make the skimmer operate better in subfreez-
ing weather.) Belt skimmers also should be
observed for one full revolution to check for
rips, holes, or other problems with the belt.
The operator also should check the scraper
-------
blade on the belt to be sure it is removing
he oil from the belt.
The skimmed oil usually falls into a trough
that drains into a collection tank. These
troughs must be kept clean so that the oil
does not build up and overflow. The level of
oil in the tank itself also should be checked
periodically.
Cooling Towers
Cooling towers remove heat from water
by evaporating the water. The ones dis-
cussed here involve contact water systems
(such as those used in blast furnace recycle
systems and, to a lesser extent, in coke plant
and rolling mill treatment operations).
It is important that the makeup and blow-
down rates be checked and that the cycles
be calculated (to minimize corrosion, de-
posits, and slime). Factors that affect cor-
rosion, deposits, and slime are controlled by
a bleed stream or blowdown, by coagulation
and filtering, or by adding inhibitors and
chemicals that attack the specific problems.
The latter include dispersants, fungicides,
and slimicides. Adding chemicals properly is
important, not only for performance, but also
because fungicides and slimicides are toxic.
Ammonia Stills
Ammonia stills reduce the ammonia con-
centration in the weak ammonia solution that
"> produced in the collecting mains of coke
jvens when water is sprayed on the hot
gases leaving the ovens.
Most problems with ammonia-stripping
systems involve the handling of lime. It is im-
portant for incoming shipments to be
checked to ensure the calcium oxide content
and particle size. Because lime tends to foul
and plug lines, control valves, instrumenta-
tion, and the stripping column itself, a
preventive maintenance schedule should be
set up to break apart and clean the equip-
ment before it becomes inoperable. Such a
schedule was developed by an operation's
supervisor at one plant. He plotted the am-
monia still effluent concentrations over a
period of time (Figure 4) and reviewed
maintenance logs to see if the times of equip-
ment pluggage and/or breakdown correlated
with the excursion dates. When a definite
correlation was evident, he developed a
schedule incorporating the finding.
Pressure drop across the column is a good
indicator of tray fouling, and the operator
should keep frequent watch to note when
the trays need to be cleaned. Operators
should also monitor the pressure in the bot-
tom of the ammonia still. When the pressure
reaches an established upper limit, the col-
umn should be taken off line and cleaned.
Since pH control is important, cleaning the
1 probe should be included as preventive
.500
1*00
S 300
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R. T. Price. W. F. Kemner, W. E. Gallagher, and Gopal Annamraju are with
PEDCo Environmental, Inc., Cincinnati. OH 45246.
Jeff Chappell is the EPA Project Officer (see below).
The complete report, entitled "Characterization of Operating and Maintenance
Practices for Wastewater Treatment Systems in the Iron and Steel Industry,"
(Order No. PB 84-182 666; Cost: $29.50. subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/967'
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