OPERATION AND MAINTENANCE MANUAL FOR

JO-NA’s WASTEWATER TREATMENT PLANT

Prepared by: Voltaire L. Acosta

1. WASTEWATER TREATMENT FACILITY

JO-NA’s International Philippines, Inc. is a

manufacturing firm that is engaged primarily on the

production of noodles, snack foods, and preserved

products such as nata de coco (coco gel) and kaong, with

markets in the U.S., Japan, and Europe.

Located in Novaliches, Quezon City, the site is under

the jurisdiction of the Laguna Lake Development

Authority (LLDA) and it was in 1998 when the company has

put up a 150-m2 wastewater treatment plant (WWTP) in a

500-m2 lot to accommodate the wastewater generated from

all its production lines through two major influent

streams: one from the production of preserves and the

other from corn washing and noodle production.

Figure 1: Vicinity map of JO-NA’s administrative, production

and wastewater treatment facilities.

WASTEWATER

TREATMENTFACILITY

SNACKS AND NOODLES

SECTION

PRESERVES SECTION

ADMINISTRATIVE

BUILDING

25 m

17 m

20 m

22 m

He

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le

s

S

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e

et

Clemente Street

H

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rc

u

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e

s

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2. INTRODUCTION

This manual includes two parts:

• Operation

• Routine Maintenance

Operation includes the control of the treatment process,

minor checking and adjustment of equipment, operational

maintenance and preparation of operation and maintenance

records.

Routine maintenance consists of all tasks of a periodic

nature, including non-critical ones, which are necessary,

such as upkeep of surrounding areas.

The routine critical maintenance includes the performance

of all works necessary to ensure the effective

functioning and long life of facility structures and

equipment. Examples include checking of pH controller,

pumping rate, lubrication of bearing and the repacking of

stuffing boxes.

3 DESCRIPTION OF THE TREATMENT PLANT

3.1 General

The treatment plant consists of the following treatment

processes:

• Stationary Screens

• Oil/water Separator

• Equalization/Neutralization Tank

• Primary Settling Tank

• Aeration Tank

• Secondary Clarifier

• Holding Tank

• Rapid Sand Filter

• Slow Sand Filter with Activated Carbon

• Sludge Drying Beds

and systems:

• Air Compressor and Diffusers

• Lime slurry Dosing System

• Control Box

• pH Controller System

• Diffuser Control System

• Pump Control System

• Return Activated Sludge System

• Waste Sludge Transfer System

A process flow diagram of the treatment plant is shown

in Figure 2.

Screening

Oil-Water Gravity Separation

Equalization

& Neutralization

Primary Settling

Aeration

Secondary Clarification

Rapid Sand Filtration

Slow Sand Filtration with

Activated Carbon Adsorption

Wastewater

Suspended Solids

Oil and Grease

Air

Lime

pH 6.8-7.0

1O

Sludge

pH 6.8-7.3

Air

Lime

Urea & DAP

2O

Sludge

Suspended Solids

Suspended Solids

Sludge Drying Beds

Compost Pit

RAS

WAS

Treated Wastewater

Figure 2: The wastewater treatment facility.

3.2 Design Criteria

The basic design criteria for the treatment plant is

shown below:

Wastewater flow 50-70 kL/d

COD of wastewater 4 g/L

pH of wastewater 4.5 to 6.0

MLSS in aeration tank 4-5 g/L

Effluent COD <100 mg/L

Effluent BOD5 <50 mg/L

pH of final effluent 6.0 to 9.0

TSS of final effluent <70 mg/L

Oil and Grease <5 mg/L

For the Treatment Plant:

Oil/Water Separator 1.5 m x 1.2 m x 1.0 m

Equalization Tank 6.0 m x 2.2 m x 4.0 m

Diffuser power rating 5 Hp

Flowrate to 1o settling 60 L/min

Primary Settling Tank 3.8 m x 3.0 m x 8.3 m

RAPIDFILTER

OIL-WATERSeparator

Boiler

Boiler

NEUTRALIZATION

TANK

PRIMARYSETTLING TANK

EQUALIZATIONTANK

SECONDARYCLARIFIER

HOLDING TANK

CHLORI-NATION

TANK

AERATION TANK

SLUDGEDRYING

BEDS

2(3mx3mx2m)= 36cu.m.

1.5mx1.2mx1m =1.8cu.m.

7mx6mx4m = 168cu.m. 6mx2.2mx4m =52.8cu.m.

2.5mx2.5mx3m =18.75cu.m.

2.5mx1mx2.2m =

5.5cu.m.

1mx1mx2m =2cu.m.

3.8mx3mx4m =45.6cu.m.

3.8mx3mx4m =45.6cu.m.

Proposed

Aeration

Tank No.2

for future use

Lime Slurry

Dosing System

for Neutralization

Slow Sand

Filter / ActivatedCarbon

Aeration Tank 7.0 m x 6.0 m x 4.0 m

Diffuser power rating 4 x 5 Hp

Flowrate to 2o clarifier 32 L/min

Mono pump power rating 1 Hp

Secondary Clarifier 2.5 m x 2.5 m x 3.6 m

Holding Tank 2.5 m x 1.0 m x 2.2 m

Chlorination Tank 1.0 m x 1.0 m x 2.0 m

3.3 Process Description

The wastewater produced from the production operation

primarily consists of acids, food coloring,

carbohydrates, sugars, oil and grease, and coarse and

fine solids. This is drained to the wastewater treatment

facility via series of channels but the solids are

trapped onsite the production area where screens are

placed.

Then, it will pass through a baffle-type oil/water

gravity separator, and enters the equalization tank for

normalized flow and concentration. The equalization tank

also serves as the neutralization tank where a lime

slurry dosing system is placed to initially neutralize

the incoming wastewater at a pH range of 6.8-7.0. Lime

is added to the Equalisation Tank using an automatic lime

slurry dosage system to raise the pH of the wastewater in

the tank to above 6 at all times. Furthermore, this tank

also acts as the primary aeration tank because diffusers

are placed at the bottom of the tank to aerate the

wastewater at the same time provide a good mix for the

raw wastewater.

Likewise, the level controller is synchronized to the

transfer pump where the normalized wastewater is pumped

to the adjacent primary settling tank at a rate of 60

L/min where primary sludge could be settled. Quiescent

conditions should be maintained in this tank to allow

good settling rates, but the residence time should be

kept below 2 hours to prevent the formation of anaerobic

conditions that will produce bad odour and form bubbles.

The clarified wastewater is then transferred to the

aeration tank at a rate of 32 L/min through overflow v-

notch weirs.

The aeration tank serves as the main mechanism to

stabilize organic matter and hence, reduce BOD5 value.

The aeration tank is equipped with four (4) units of

submersible aerators or diffusers to inject oxygen and

maintain the wastewater and the activated sludge in

suspension. Thorough mixing and aeration should be done

and lag spaces should be avoided to enhance biological

activity.

The value of pH in the aeration tank should be maintained

at 6.8-7.3 as an ideal range for microbial growth. To

achieve this, a lime slurry dosing system with automatic

controller should be operational. 2 kilograms of urea

and 1.5 kilograms of diammonium phosphate are also added

to the aeration tank three times a day to supplement the

nutrient requirement for the biological treatment.

From the aeration tank, the mixed liquor is continuously

pumped at a rate of 32 L/minute to the secondary

clarifier. This is where the sludge is allowed to settle

at the bottom of the tank hopper while the decanted

effluent flows at the top, towards the clarified water

holding tank. The effluent passes through the rapid sand

filter and is chlorinated before being discharged to the

nearby sewer system.

The settled solid (biomass) flows by gravity through the

sludge hopper at the bottom of the secondary clarifier.

The valve is opened every two (2) hours for 3 minutes to

allow the return of the activated sludge to the aeration

tank. Wasted sludge, at a rate 10% of the return sludge,

is drawn out to the sludge drying beds.

4. OPERATION

The operation of the wastewater treatment plant should be

done continuously, particularly the aeration of the

activated sludge.

The first thing to do before running a plant is to make a

visual inspection of all the motors, accessories, pipes,

fittings, and valves for possible damage or defects. If

everything is in good condition, run all chemical feeders

in AUTO position in the control box for automatic dosage

control. Before feeding chemicals, make sure that

chemicals are thoroughly mixed, especially those in

slurry form, before feeding.

4.1 Screens

Screens are installed inside the production area to

remove the solids, especially bits of nata de coco, on-

site. The size of the screen is currently 3/16-in.

aperture but smaller screen apertures should be placed

when new product specifications are set. The size should

always be set such that most solid particles are removed

prior to the wastewater’s entry into the treatment plant.

Screens should be regularly cleaned to avoid clogging.

Production-based personnel should be assigned for this

task.

4.2 Oil/Water Separator

The oil-water separator is used to allow an oil-water

interface to form by gravity to remove the lighter

fraction, i.e. the oil, before it enters the wastewater

treatment plant.

Oil is not as amenable to biodegradation unlike the

starchy and carbohydrate materials, and therefore should

be skimmed off the upper layer whether or not floating

raw solid waste sludge absorbs it. Floating solids

should be collected regularly and disposed off as solid

waste to the compost pit.

4.3 Equalization Tank

This tank serves three main purposes: (1) the

equalization tank serves as a collection tank that

normalizes the hydraulic flow and the concentration of

the pollutants, (2) neutralization is done in the

equalization tank to ensure that the wastewater coming

through the aeration tank already has a pH of 6.8-7.0,

(Normally, the pH is set to 6.8-7.3 but operating on the

lower range is safe in this case because it is expected

that pH will slightly increase in the aeration tank upon

the addition of urea), and (3) it serves as a primary

aeration tank because diffusers keep the wastewater in

suspension.

Notes:

� Ensure that the screens are able to trap all suspended

solids, particularly nata de coco bits.

o If not, use screens with finer mesh.

� Assign production-based personnel to regularly collect the

screenings and dispose them of as solid waste.

o Otherwise, there will be a build-up of solids that

can clog the screens.

Notes:

� WWTP operator should skim off the collected oily solids

from the top layer of the separator.

o Otherwise, it will produce bad odor and attract

insects and rodents.

� WWTP operator should ensure that the baffles (metal traps)

are exactly fit to the walls of the separator.

o Otherwise, the flow will divert to these openings

and oil and other solids will not be collected.

Uncollected solids may damage pumps.

4.3.1 Operation of Diffusers

A 5-Hp blower provides compressed air to submerged air

ducts so that wastewater in the equalization tank is

agitated and aerated.

Safety

(1) BEFORE WORKING IN THE VICINITY OF ANY EQUIPMENT

THE APPROPRIATE ISOLATOR ON THE MAIN SWITCHBOARD

SHOULD BE TURNED OFF, THE LOCAL PLUG SOCKET ISOLATOR

SHOULD BE TURNED OFF AND A SAFETY LOCK APPLIED.

(2) WEAR PROPER PROTECTIVE EQUIPMENT TO AVOID ANY

INJURY DURING OPERATION OR MAINTENANCE PROCEDURES.

THE LOCATION AND WAY TO THE VALVE MAY BE SLIPPERY AND

BE SURE TO WEAR SAFETY SHOES AND HOLD ON TO HANDRAILS

BEFORE ADJUSTING THE VALVES.

The air ducts are made of holes that are evenly spaced

along three major tube branches: two at the sides and one

in the middle. A valve can be adjusted so that more

volume of air is released on either side or at the

middle.

4.3.2 Neutralization with Lime

Lime is used for two major purposes: (1) to adjust the pH

of the incoming wastewater above 6 at all times and

maintain the pH at a 6.8-7.0 range, and (2) to protect

the cement walls of the tank from corroding.

Safety

(1) WEAR PROPER PROTECTIVE EQUIPMENT TO AVOID ANY

INJURY DURING CHEMICAL PREPARATION.

Notes:

� Observe proper safety procedures.

� Always set the valve to a position where most of the air

is released in the middle. The force of air is strong

enough to ensure that wastewater in the equalization tank

is in uniform suspension.

o However, the WWTP operator can divert the air flow

to either side twice a day (one in the morning and

another in the afternoon) to prevent solids from

settling at the corners or near the walls of the

tank.

� Once a week, check whether the holes of the diffusers are

clogged. Likewise, the blower should be inspected for

good operating condition. It should always provide the

necessary volume of compressed air for effective

equalization.

(2) OBSERVE PROPER PRECAUTIONARY MEASURES IN HANDLING

CHEMICALS. ALWAYS POUR IN CHEMICALS IN WATER AND NOT

THE OTHER WAY AROUND!

For the automatic dosage, prepare 20 kgs. of lime and mix

with 100 liters of tap water (If an 8-liter pail is used,

add 1.5 kgs of lime and then fill the container with

water). Mix them slowly while adding to completely

dissolve the chemicals in water before feeding. Then

pour the slurry into the lime slurry-dosing tank.

Switch the slurry dosing control system connected to the

pH control system to automatically dose the required lime

to achieve the pH range of 6.8-7.0. Pour in another

batch of lime slurry when the slurry level is almost ¼ of

the container.

Lime is not completely soluble in water and settles under

quiescent conditions inside the slurry tank. Instead of

a paddle mixer, a small air tube, which is connected to

the diffuser line, is used to agitate the chemical

mixture.

4.3.3 Pumping into Primary Settling Tank

Wastewater coming from the equalization tank should be

transferred to the primary settling tank to remove the

raw sludge from the wastewater. Presently, the pump used

delivers wastewater at a rate of 60 L/min. This is a

relatively high flowrate and may prevent the wastewater

to settle properly under undisturbed conditions.

A pipe branch was used to decrease the pump flow by

diverting some of the wastewater back to the equalization

tank. However, Jo-Na’s may replace the pump with another

one that delivers flow at 25-35 L/min at a low rpm. In

this case, a single pipe (without elbows) can be used.

The pump should operate continuously.

Notes:

� Observe proper safety procedures.

� Prepare a lime slurry solution by adding 1.5 kgs. of lime

powder to an 8-L pail of water and then pour the mixture

into the lime slurry dosing tank. Repeat procedure until

the slurry tank is almost full.

� Add succeeding batches of lime slurry to make sure that

the content of the tank is no less than ¼ full.

� In case that the lime slurry is not sufficiently agitated,

check for leaks in the aeration tube line.

Safety

(1) BEFORE WORKING IN THE VICINITY OF ANY EQUIPMENT

THE APPROPRIATE ISOLATOR ON THE MAIN SWITCHBOARD

SHOULD BE TURNED OFF, THE LOCAL PLUG SOCKET ISOLATOR

SHOULD BE TURNED OFF AND A SAFETY LOCK APPLIED.

(2) WEAR PROPER PROTECTIVE EQUIPMENT TO AVOID ANY

INJURY DURING OPERATION OR MAINTENANCE PROCEDURES.

THE LOCATION AND WAY TO THE PUMP MAY BE SLIPPERY AND

BE SURE TO WEAR SAFETY SHOES AND HOLD ON TO HANDRAILS

BEFORE OPERATING THE PUMP.

Faults

The following fault conditions may occur:

� No-flow

� Thermal overload

� Thermistor-Motor overheat

� Low level alarm

� High level alarm

No-flow

This can be due to blockage in pump or pipelines or no

liquid in the equalization tank.

Thermal Overload

A common cause of a thermal overload is pump blockage.

4.4 Primary Settling Tank

Ideally, the function of the primary settling tank is to

settle out raw undigested sludge at the bottom of the tank

and at the same time to collect the scum that floats on the

top of the tank. Hydraulic retention time should only be

between 1-2 hrs, velocity be kept below 0.3 m/s.

Notes:

� Observe proper safety procedures.

� Operate the pump continuously.

� Check for faults, as described above.

o If not operating properly, repair the pump OR

o Replace the pump with a low-rpm mono pump.

0.6m

3.0m

3.8m

2.2m

2.8m

0.3m

1.15m 1.25m

1.55m

1.65m

60

0.3m

0.5m

As shown in figure 3, the primary

settling tank consists of a

center well with a perforated

plate to provide a laminar regime

for sedimentation, a sloped

bottom to enhance settling, a

sludge hopper to collect the

sludge, a sludge collection line

to remove the settled sludge

using a submersible pump, and a

weirs to provide an overflow

leading to the aeration tank.

The wastewater should only stay

in the primary settling tank for

less than two hours, just enough

time for the raw sludge to settle

but not keeping it too long to

create anaerobic conditions. If

the operator notices bubble

formation, it is an indication

that the water stays there too

long. The settled solids should

be removed and the effluent needs

to be transferred to the aeration

tank.

Note that these gas bubbles may

be poisonous or flammable and

proper precautionary measures

should be observed.

Figure 3: 1O Settling Tank Design

Figure 4: Settling Operation

4.4.1 Transfer of wastewater to aeration tank

Wastewater is transferred to the aeration tank through v-

notch weirs located at all sides of the primary tank.

This will lead to a common duct located at one side of

the tank to be transferred by gravity to the aeration

tank.

4.4.2 Pumping out of primary sludge

Primary sludge should be pumped out regularly to prevent

decomposition and formation of bubbles and bad smell.

The presence of scum shows that the primary tank is not

in good condition.

Safety

(1) SEE SAFETY PROCEDURES IN SECTION 4.3.3 FOR PUMP

INSPECTIONS.

(2) USE APPROVED LIFTING TRIPOD SYSTEM AND HOIST TO

REMOVE PUMPS FROM WET WELL FOR INSPECTION.

4.5 Aeration Tank

The aeration tank is where the heart of the activated

sludge process takes place. This is where raw wastewater

mixes with the activated sludge and consequently,

synthesized by the latter.

It is also where proper conditions for growth should be

strictly observed to ensure a more efficient BOD/COD

removal. Proper aeration, sunlight, pH conditions, and

nutrients are amended for more effective reduction of

BOD/COD.

Notes:

� Ensure that the duct is not clogged.

� Check for any scum that rises at the surface of the tank.

o If present, skim the floating solids off the surface

and handle them as solid wastes.

Notes:

� To prevent the rising of solids, o Operate the transfer pump from the equalization tank

continuously.

o Use the submersible pump to pump out the primary

sludge once every two hours during peak production

rates. Otherwise, the submersible pump need not be

operated if all the sludge has been removed.

4.5.1 Operation of Diffusers

To start the treatment, turn on the switch of all four

diffusers at the Control Box and allow it to operate

continuously. At night-time, when there is no production

going on, one of the diffusers may be turned off. The

following day, turn on the switch of all diffusers to

allow it to operate continuously for the day. Each

diffuser should have its turn of rest once every four

days during the night.

This practice is only done to maintain the diffusers in

good condition because of frequent breakdowns. But

technically, Jo-Na’s should add another diffuser or a

compressed air system to ensure a sufficient volume of

air into the activated sludge.

Safety

(1) SEE SAFETY PROCEDURES IN SECTION 4.3.1 FOR

DIFFUSER INSPECTIONS.

(2) USE APPROVED LIFTING TRIPOD SYSTEM AND HOIST TO

REMOVE PUMPS FROM WET WELL FOR INSPECTION.

Notes:

� Operate all four diffusers during the day.

� One of the diffusers may be turned off at night when there

is no production schedule.

� If any of the diffusers give insufficient airflow or

produce no air at all,

o Inspect the switch of that particular diffuser in

the Control Box and correct if necessary.

o Inspect for blockage at the diffuser and remove them

if there is any.

o Repair or replace the diffuser if necessary.

� If the sludge volume is decreasing,

o Operate all diffusers continuously even at night.

o Check all the other parameters as discussed below

and do corrective actions.

� If the problem persists, add another diffuser

system. The airflow may not be sufficient

anymore.

Figure 5: Diffuser configuration Figure 6: Handrails

4.5.2 pH correction with Lime

The microorganisms are grow and are only active at a pH

range of 6.8-7.3. If the aeration tank has its own

automatic lime slurry dosing: (1) If the pH of the

aeration tank is below 6.8, follow the instructions at

Section 4.3.2, otherwise, gradually add lime slurry until

pH is 6.8-7.3. (2) If the pH goes above 7.3, inspect

again after 4 hours to check if the pH is already within

the range, otherwise, gradually add phosphoric acid until

pH is 6.8-7.3.

4.5.3 Nutrients Dosing

Urea and diammonium phosphate (DAP) of a total of 6 kg/d

and 4.5 kg/d respectively are added to the aeration tank

to satisfy the growth requirements of the biomass. In

this case, 2 kg of urea and 1.5 kg of diammonium

phosphate are added three times a day.

4.5.4 Maintaining MLSS/SV at the aeration tank

The MLSS in the Aeration Tank should be maintained at

approximately 5000-mg/L level to effect the desired

treatment efficiency.

When the MLSS is still lower than this level, it is

required that ALL settled sludge from the Secondary

Notes:

� Observe proper safety procedures in Section 4.3.2.

� If pH is below 6.8, prepare a lime slurry solution by

adding 1.5 kgs. of lime powder to an 8-L pail of water.

Gradually add half a pail of the slurry to the activated

sludge and wait for 5 minutes to check the pH. Repeat

this until the pH reaches 6.8-7.3.

� If pH goes beyond 7.3, wait for 4 hours if the pH becomes

acceptable. Otherwise, correct using phosphoric acid.

Notes:

� Observe proper safety procedures in Section 4.3.2.

� Add 2 kgs. of urea to an 8-L pail of water and then pour

the mixture evenly into the four corners of the aeration

tank. Rinse the pail with tap water and also pour the

rinsings into the aeration tank.

� Add 1.5 kgs. of diammonium phosphate (DAP) to an 8-L pail

of water and then pour the mixture evenly into the four

corners of the aeration tank. Rinse the pail with tap

water and also pour the rinsings into the aeration tank.

� Do the first three steps above three times a day (9AM,

12NN, and 3PM).

Clarifier be returned to the aeration tank to ensure

sufficient population of microorganisms to eat up the

organic matter. This is called return activated sludge

(RAS).

When the MLSS is higher than this level, it is required

to draw out appropriate volume of settled sludge from the

Secondary Clarifier leading to the sludge drying bed to

reduce the mass of sludge returned to the Aeration Tank.

This is called waste activated sludge (WAS).

In order to determine the amount of sludge to be drawn

out, the operator will require to carry out settling test

on the Aeration Tank activated sludge sample using a 1-

liter Imhoff cone every morning when the production line

was in operation the day before. The test results will

then be used to estimate the volume of settled sludge to

be drawn out from the Secondary Clarifier.

A simple operational procedure has been developed and is

summarised below to assist the operator to carry out the

test and estimate the volume of sludge to be drawn out

for disposal.

1. Collect 1 litre sample of activated sludge from the Aeration Tank.

2. Pour the sample into a 1-liter Imhoff cone. 3. After 30 minutes of settling measure the volume of settled sludge.

The reading, which is the sludge volume, should be at a

range of 700-800 mL/L. Above 850, open the waste

activated sludge line for 3 minutes, instead of going to

the return activated sludge line. Continue wasting until

the sludge volume reaches a little less than 800 mL/L.

Notes:

� Monitor and record the sludge volume using the Imhoff

cone.

o Collect two 1-L sample from the aeration tank.

o Pour into the Imhoff cones.

o Get the reading after 30 minutes.

� In case the SV is within the 700-800 range, continue with

the operation.

o If SV is below 700, return all settled sludge from

the secondary clarifier to the aeration tank and

check other parameters such as pH, diffusers, and

records of nutrient amendments (urea and DAP).

� It is also important to check whether CIP

(cleaning-in-place) is done only at one

schedule within the day. Antibacterial

solutions and chlorine can kill all the

activated sludge at one abrupt discharge.

o If SV goes beyond 850, gradually waste the sludge

through the WAS line going to the drying beds.

4.5.5 Additional pointers

Ensure that the diffusers are running all the time 24

hours a day and 7 days a week, except for provisions

discussed in Section 4.5.1.

Do not throw away the contents of the aeration tank! It

takes 6 months to a year to grow and acclimate the

biomass.

Remove any floating material at the surface of the

aeration tank as it may block the sunlight. Removing the

floating scum will also promote surface aeration of the

activated sludge using wind forces.

Regularly inspect the water level at the aeration tank,

as the present diffusers may not be able to accommodate a

high water level.

4.5.6 Pumping into Secondary Clarifier

Wastewater coming from the aeration tank should be

transferred to the secondary clarifier to separate the

activated sludge from the clean or treated water. A 1-Hp

pump is used to deliver wastewater at a rate of 32 L/min,

a flowrate good enough to promote undisturbed and better

settling of the sludge.

The pump should operate continuously.

Safety

(1) SEE SAFETY PROCEDURES IN SECTION 4.3.3 FOR PUMP

OPERATIONS.

Faults

(1) SEE POSSIBLE CAUSES OF PUMP FAILURE IN SECTION

4.3.3 FOR PUMP OPERATIONS.

Notes:

� Free the aeration tank from scum and other floating

materials.

� Regularly inspect the water level.

� Do not throw away the contents of the aeration tank at any

time! It takes 6 months to a year to grow and acclimate

the biomass.Exceptional cases would be for irreparable

system error inside the tank, as declared by the Pollution

Control Officer (PCO).

Notes:

� Observe proper safety procedures.

� Operate the pump continuously.

� Check for faults, as described above, and repair if

necessary.

4.6 Secondary Clarifier

The secondary clarifier operates in the same manner as the

primary settling. Both tanks separate the wastewater from

the settleable materials called the sludge.

0.6m

2.5m

2.5m

1.4m

0.3m

0.95m 0.95m

0.95m

0.95m

1.6m

60

0.3m

0.5m

The only major difference

is that the secondary

clarifier settles out the

activated sludge, the

sludge that contains the

useful microorganisms, from

the treated water.

Since most, if not all, of

the microorganisms need to

be returned to the aeration

tank, and some need to be

wasted when overpopulation

occurs, RAS and WAS lines

are operational.

The settled sludge is

accumulated at the bottom

of the hopper and is

transferred by gravity to a

valve that connects the RAS

and WAS lines.

To maintain the active

microbial population inside

the aeration tank, the

valve is opened every two

hours for 3 minutes to

drain the sludge back to

the aeration tank, or to

the sludge drying beds for

wastage.

If this is not done

regularly, there will be

rising sludge, bubble

formation, and foul odor

generation at the surface

of the clarifier. Worse,

the sludge may go along

with the clean water and

contribute to high total

suspended solids (TSS) and

high BOD at the effluent.

If this happens, the water

analysis will fail the prescribed standards.

Figure 7: 2O Clarifier Design

The WWTP operator may follow the instructions and safety

procedures as discussed in Section 4.4.1. In case of

removing the settled sludge from the clarifier, the operator

should merely inspect for blockage along the gravity

transfer line to RAS and WAS.

4.7 Rapid Sand Filter

The rapid sand filter is used to further remove any

suspended solids from the clear water. However, the sand

filter needs to be backwashed whenever the pressure

differential reaches 10 psi. The initial pressure going to

the filter tank and the pressure loss inside the tank. Sand

filter will be backwashed at the flow rate of 27.5 gallons

per minute for 15 minutes. The backwash water will be

deviated back to the neutralization tank.

4.8 Slow Sand Filter with Activated Carbon

The slow sand filter has the same purpose as the rapid sand

filter with the objective of removing the residual or finer

solids that the rapid sand filter has missed. The activated

carbon inside the filter tank is used to further remove the

odor and color from the wastewater.

Notes:

� Ensure that RAS and WAS lines are not clogged.

o If clogged, repair the pipes.

o Use a submersible pump to clear out the sludge

completely.

� Check for any scum that rises at the surface of the tank.

o If present, skim the floating solids off the surface

and transfer them to sludge drying beds.

o Otherwise, there will be high TSS and BOD values in

the effluent analysis.

� To prevent the rising of solids,

o regularly open the valve leading to the RAS line to

return the activated sludge once every 2 hours for a

3-minute period or as soon as the RAS becomes clear.

o The WWTP operator should ensure that all the sludge

is removed from the secondary clarifier after each

production day before he goes home.

Notes:

� Ensure that the sand filter line is not clogged.

o If clogged, repair the line.

o Backwash, if necessary.

Notes:

� Ensure that the flow is not held back.

o Backwash if necessary.

o Regenerate the activated carbon.

5. ROUTINE MAINTENANCE

5.1 Screens

Inspect the screens every hour if the solids become

too much for the screens to handle. Replace or add a

successive screen with finer mesh when solids still

manage to pass through the slots.

5.2 Oil-Water Separator

Inspect the baffles inside the tank once on a daily

basis and cover any opening near the walls of the

tank. Replace the baffles when they become weak with

rust. Remove any coarse solids retained at the bottom

to avoid clogging of pipes and pumps as soon as

wastewater enters the equalization tank.

5.3 Equalization Tank

Inspect the tank once daily and remove any floating

coarse solids from the tank.

5.4 Primary Settling Tank

Inspect the tank once daily and remove any floating

solids from the tank. Ensure that the raw sludge is

removed once every 2 hours. If there is uneven flow

through all four sides of the v-notch weirs, adjust

the weirs.

5.5 Aeration Tank

Free the aeration tank from any material that had been

accidentally gone into the tank as they may cause

damage to diffusers. Remove all floating material

from the tank every hour.

5.6 Secondary Clarifier

Inspect the tank once daily and remove any floating

solids from the tank. Ensure no blockage along the

line.

5.7 Pumps and Diffusers

Inspect all motorised equipment, which include

submersible pumps, mono pumps, chemical dosing pump,

compressor, air flow lines, and diffusers once daily.

During the operation, the following checks should be

made:

� Excessive or abnormal noise and vibration

� Temperature (by hand touch or any metering device)

of motor, casing, bearings, gearboxes and other

accessories

� Leakage from joints, pipes, valves and fittings

� Lubricant spillage or leakage

Once every month, the following checks should be made:

� Accumulated dust / dirt on the equipment

� Abnormal vibration of moving parts

� Voltage supply of the motor

� Running condition of the motor

� Tighten all electrical connections

Quarterly, the following checks should be made:

� Winding resistance of the motors

� Valve seats of chemical pumps

Once every year, the following checks should be made:

� Lubricant levels in gear boxes

� belt drives

� Machine guards and safety equipment

� Repaint all rusted portion if necessary

� Clean motor winding with motor cleaner and revarnish

if necessary.

Refer to the Maintenance Manual supplied by the

Manufacturer for maintenance procedures.

5.8 pH Controller

Check the pH reading of the pH controller once every

day. Collect a 500 mL sample from the equalization

and/or aeration tanks and measure its pH with the

calibrated pH meter in the laboratory. Compare the

reading obtained with that of the pH controller.

If the two readings are the same, no calibration of

the pH controller is required. If the two readings

are different, calibrate the pH controller in the

Control Box. Refer to the calibration procedure in

the Maintenance Manual provided by the manufacturer.