Training

Sequential Batch Reactor - Training Notes
1. Activated Sludge
2. Principles of Biological Treatment
3. Basic Terminology
a. Mixed Liquid Suspended Solids
b. Food/Mass Ratio
c. Sludge Age or Mean Cell Residence Time
4. Influent Characterization
5. Nitrogen Removal
6. Phosphorus Removal
7. Alkalinity and pH
Doha South SBR Phase II

Activated Sludge
Culture of microorganisms mixed with wastewater in an aerobic, anoxic, and/or anaerobic
environment for the removal of organic matter and nutrients.

Principles of Biological Treatment
Raw sewage represents an
excellent medium in which
to grow bacteria and
microbes. It has a high
biodegradable organic
content and is also rich in
nutrients. If oxygen is added
to the system, all of the
conditions needed to grow
bacteria are present.
New Organisms
+
Carbon Dioxide
+
Water
+
Inert Matter
Organic Matter (BOD5)
+
Nutrients
+
Microorganisms
+
Inert Matter
+
Oxygen

Terminology
MLSS: Mixed Liquor Suspended Solids, biomass or microorganism mass including other
particulates.
F/M Ratio: “F” is the food or biodegradable organic matter (BOD5). “M” are the
microorganisms or MLSS.
Sludge Age: Sludge Age or mean cell residence time is the average duration of time an
organism spends in the system. Often the first step in plant design, dictated by need to
nitrify and wastewater temperature.
SludgeVolume Index (SVI): is an extremely useful parameter to measure in a wastewater
treatment process. In simple terms, SVI is the result of a mathematical calculation. It takes into
account the 30-minute settleability test result and the activated sludge mixed liquor suspended
solids (MLSS) test result to come up with a number (or index) that describes the ability of the
sludge to settle and compact. SVI gives a more accurate picture of the sludge settling characteristics
than settleability or MLSS alone.

Key Parameters
SBRs are analogous to activated sludge process and the biological process parameters are the same as conventional
activated sludge process. The process parameters that are necessary to control SBRs are as follows:
F/M ratio (Food to micro-organisms ratio)
Sludge age
MLSS (mixed liquor suspended solids) at bottom water level
Hydraulic retention time
SSVI (stirred specific volume index) corrected to 3500mg/l.
The parameter which differs from one process to another is the sludge loading or F/M ratio and can be calculated as
follows:
F/M = Q x BOD / V x MLSS
where Q is the flow rate of wastewater to SBRs in m³ / day.
BOD is the biochemical oxygen demand of the wastewater to SBRs in mg/l.
V is the volume of the SBRs in m³.
MLSS is the mixed liquor suspended solids in mg/l.

Mixed liquor suspended solids (MLSS)
MLSS is the concentration of suspended solids, in an aeration tank during the activated
sludge process.
Mixed liquor is a combination of raw or unsettled wastewater and activated sludge within
an aeration tank.
MLSS consists mostly of microorganisms and non-biodegradable suspended matter.
MLSS is an important part of the activated sludge process to ensure that there is a sufficient
quantity of active biomass available to consume the applied quantity of organic pollutant at
any time.

It has different types of Microorganisms:
Ciliates
Flagellates
Protozoa
Rotifers
Bacteria
The organic matter is removed by the
bacteria.
Protozoa and Rotifers consume the bacteria
not flocculated and small flocs.
Filamentous Bacteria must be prevented .

Ciliates:
Free swimming or Stalked ciliates
Important because they work with the
bacteria.They feed on the bacteria and thus
help to clarify the effluent
Stalked ciliates are usually an indication of a
stable activated sludge operation
Usually occur at higher Medium Cell
Retention Time and DO, Stable Wastewater
environment and mature flocs structures has
developed.

Protozoa - Flagellates:
usually present when there are large
amounts of soluble food available (high
F:M or high BOD)
Found during start up when the sludge
is young
If flagellates are present as the
dominant protozoan group, this could
indicate an unstable wastewater

Suctorians
These are the microorganisms to shoot for in
most activated sludge plants.
They almost always indicate an extremely
healthy system and usually the BOD in the
final effluent is very low, the TSS is low and
things are running smoothly.
Rotifers
Multiple celled organisms that feed on
good, stabilized floc.They are highly
sensitive to high BOD loadings and toxic
shocks.Typically found in conditions with
low F/M ratios, high MCRT or high MLSS
rates.They can reduce turbidity and BOD
and control slime growth that can lead to
anaerobic conditions.They graze on the
floc structure and increase oxygen
penetration

Food/Mass Ratio (F/M)
One of the most fundamental control parameters for the activated sludge process is the
relationship between the load (i.e. kg/day as opposed to mg/l) of BOD (or bacterial 'food')
entering the aeration plant, and the 'mass' of bacteria in the aeration tank available to treat
the incoming BOD.This is therefore known as the Food to Mass ratio (F:M ratio), also often
referred to as the Sludge Loading Rate (SLR).
It determines the degree of BOD removal likely to be achieved.The lower the F/M loading
the greater the BOD removal efficiency. However, if the F/M ratio becomes too low, certain
operating problems can occur (Sludge Bulking, Pin-floc/deflocculation, etc)
Typically, F/M ratios in the range 0.05 to 0.1 result in BOD removal efficiencies of about 95
to 99%. Between 0.1 and 0.2 the removal efficiency may be about 90 to 95%. Pilot trials may
be used to determine the most likely BOD removal efficiency for a proposed new plant.

High F/M and Low F/M
A high F/M ratio of say 0.5 day -1 means that micro-organisms have a rapid growth rate
because the food is not limited and they can consume the food, grow and multiply. Here
the food is in excess when compared to micro-organisms and as a result the micro-
organisms will not remove all the organic matter in the wastewater and the remainder
will pass out in the treated effluent.
On the contrary a low F/M ratio of say 0.08day -1 will have limited food supply and
micro-organisms will remove virtually all the organic matter and the treated effluent will
be of good quality.
SBRs operating at low F/M ratio will produce a good quality effluent but there is a limit :
it is not possible to operate the SBRs with very low F/M ratio less than 0.04 day-1
because the sludge age will be too high and pin floc will be seen in the effluent.

Sludge Age
May be defined as the mass of solids (MLSS) in the
plant at any time divided by the mass of new solids
made each day.
The higher the F/M loading the shorter the sludge
age and vice versa.This is because new biomass is
produced at a fast rate when food supply is high and
at a slower rate as food supply is reduced.
Sludge age is typically about 10 - 30 days in activated
sludge plants operating at high (>95%) BOD removal
efficiencies.A long sludge is required for certain
specific objectives, nitrification being the most usual.
However, solids-liquid separation problems can
result if the sludge age is excessively long (Foaming)
Sludge Age Impacts:
1. Oxygen Demand (endogenous
respiration)
2. Sludge Quantity & Composition
3. Nitrification
4. Phosphorus Removal
5. Alkalinity

Influent Characterization
Flow
Hydraulic and organic loading
BOD5
Organic loading
Basin size
Aeration system
TSS
Sludge age
Nitrogen
Aeration system
Aerobic/anoxic environment
Phosphorus
Anaerobic environment
Temperature
Basin size

Nitrogen Components
P a r tic u la t e S o lu b le A m m o n ia N it r ite N itr a te
O rg a n ic
N itr o g e n
In o r g a n ic
N itr o g e n
T o t a l S o lu b le
N itr o g e n
S o lu b le
K je ld a h l
N itr o g e n
T o t a l
NO
T o t a l
K je ld a h l
N itr o g e n
x
Macronutrient for biomass (100C:10N)
Domestic sewage TKN
40 - 60 mg/L
Ammonia nitrogen (NH3-N)
60%TKN
25 - 40 mg/L
Organic nitrogen (Org-N)
40%TKN
Biological removal process

Nitrification
Temperature 4 - 45° C
For every 10°C drop, nitrifier growth rate will drop by ≈ 50%
Alkalinity 50 mg/L as CaCO3 min effluent
DO 1.0 - 3.0 mg/L (>2.0)
pH 6.5 - 8.8
SRT 10 - 25 days (temp dependent)
Nitrifiers (autotrophic) are more susceptible to
toxicity than BOD removers (heterotrophic)
and slowest growing.
NH4
+ + 1.5 O2 → NO2
- + H2O + 2H+
NO2
- + 0.5 O2 → NO3
-
NH4
+ + 2.0 O2 → NO3
- + H2O + 2H+

Denitrification
Nitrate and organic carbon in presence of
denitrifiers + anoxic conditions results in
External carbon source (requirements based on
influent)
Alkalinity recovered
3.54 g as CaCO3 / g of NO3-N denitrified
Oxidation reduction potential (ORP)
-50 to +50 mV
2 NO3
- + 2H+ → N2+ H2O + 2.5 O2

Phosphorus
Macronutrient for biomass (100C:2P)
Domestic sewage total-P
6 - 10 mg/L
Typical municipal = 8 mg/L
Organic-P (organically bound-tissue) 2 - 5 mg/L
Inorganic-P (ortho- and poly-P) 4 - 8 mg/L
P content in sludge 2% - 7%
Biological, chemical, and physical removal
processes

Biological Phosphorus Removal
Step 1: Anaerobic Phase
Phosphorus release
Step 2: Aerobic Phase
Phosphorus uptake and creation of new
PAOs
Phosphorus removal by sludge wasting
Successful bio-P removal depends on:
• Anaerobic conditions (zero dissolved
oxygen and zero nitrate)
• Volatile fatty acids (VFA, rbCOD)
• Solids management (SRT,WAS, and side
streams)

Alkalinity and pH
pH range for optimal biological treatment is 6 – 9
Alkalinity is the buffering capacity; resistant to pH changes
Alkalinity is very important in balancing acid generated by nitrification
Alkalinity varies based upon raw water source and geographical area

ICEAS Basin Layout
Intermittent Cycle Extended Aeration System

SBR Fill and Draw Theory
3. Settle
4. Draw Effluent
2. React
TWL
1. Fill
(Aerated or Un-aerated)
Screened and
De-gritted
Influent
5. Idle
Waste
Sludge
Influent valves
required to control
flows (open and
close every cycle)

ICEAS
• Intermittent Cycle Extended Aeration System
• Developed in Australia by Xylem to meet the needs of
sparsely populated areas
Single
Basin

• Domestic & industrial wastewater treatment
• BOD5 & TSS removal
• Nitrification & denitrification
• Biological phosphorus removal
ICEAS Process Applications

1. React 2. Settle
3. Decant Treated
Effluent
Continuous Flow
of Screened and
De-gritted
Influent
Waste Sludge
ICEAS Operating Cycle
Continuous
Flow

ICEAS Equipment

ICEAS Basin Layout
Pre-React Zone
• Typical 12-15% of basin volume
• Acts as selector
• Discourages filamentous growth
• Allows for continuous flow
• Continuous supply of carbon
Main React Zone
• Length to width ratio
» Typical 3:1
» Minimum 2:1
• Top Water Level (4 – 6 m)

Rectangular Tanks
Salida WWTP, California USA
Doha South WWTP, Qatar

Nitrification (NIT)
• BOD & TSS removal
• Nitrification
• Partial denitrification
Nitrification, Denitrification, and
Phosphorus Removal (NDNP)
• Complete nutrient removal
• Nitrogen
• Phosphorus
ICEAS NIT & NDN(P) Operating Modes

SBR compared to Conventional Activated Sludge
 Aeration and clarification occurs in single tank
 Elimination of RAS pumping and capital cost
 Future nutrient removal requirements easily addressed
 Biological nutrient removal
 Anaerobic
 Anoxic
 Aerobic
 Flexible process operation to suit changing needs.
 Consistent, high quality effluent achieved at variable flow and
loading

ICEAS Advantages Over SBR
Highly Effective Sanitaire Aeration
• Fine bubble full floor
coverage
Easy-to-Access Equipment
• Decanter is accessible from
walkway
• Pumps and mixers are on
guide rails
Single Basin Operation
• No need for flow storage
space when servicing a basin

ICEAS Process Advantages:
• Continuous flow
• Equal flow and load to all basins at all times
• Diurnal variations received by all basins
• Biomass characterized the same in all basins
• Biological nutrient removal
• Allows for single basin operation during times of
maintenance or periods of low flow

ICEAS Basin in Doha South
Intermittent Cycle Extended Aeration System

ICEAS NDN Cycle Charts – Normal Flows
Basin 9
Basin 11
Basin 10
Basin 12
Basin 13
Basin 15
Basin 14
Basin 16
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
SETTLE
(12 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-12
min)
SETTLE
(36 min)
DECANT
(72 min)
AIR OFF
(24 min Mix)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
SETTLE
(48 min)
DECANT
(72 min)
AIR OFF
(24 min Mix)
AIR ON
(0-12
min)
AIR ON
(13-24
min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
SETTLE
(48 min)
DECANT
(36 min)
AIR ON
(13-24
min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
SETTLE
(48 min)
DECANT
(72 min)
AIR OFF
(24 min Mix)
DECANT
(36 min)
AIR OFF
(24 min Mix)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
SETTLE
(48 min)
DECANT
(72 min)
AIR OFF
(24 min Mix)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
DECANT
(72 min)
AIR OFF
(24 min Mix)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
SETTLE
(48 min)
DECANT
(72 min)
AIR ON
(0-24 min)
SETTLE
(48 min)
DECANT
(72 min)
AIR OFF
(24 min Mix)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
144 168 216 288
AIR OFF
(24 min Mix)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
AIR ON
(0-24 min)
0 24 48 72 96 120
AIR ON
(0-24 min)
SETTLE
(48 min)

Basin 9
Basin 11
Basin 10
Basin 12
Basin 13
Basin 15
Basin 14
Basin 16
AIR ON
(0-9
min)
SETTLE
(9 min)
AIR ON
(10-18
min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
SETTLE
(36 min)
DECANT
(54 min)
AIR OFF
(18 min Mix)
AIR ON
(0-9
min)
SETTLE
(27 min)
DECANT
(54 min)
AIR OFF
(18 min Mix)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(10-18
min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
SETTLE
(36 min)
DECANT
(54 min)
AIR OFF
(18 min Mix)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
DECANT
(54 min)
AIR OFF
(18 min Mix)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
DECANT
(27 min)
AIR OFF
(18 min Mix)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
SETTLE
(36 min)
DECANT
(27 min)
AIR ON
(0-18 min)
SETTLE
(36 min)
DECANT
(54 min)
AIR OFF
(18 min Mix)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
DECANT
(54 min)
AIR OFF
(18 min Mix)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
SETTLE
(36 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
SETTLE
(36 min)
AIR OFF
(18 min Mix)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
AIR ON
(0-18 min)
SETTLE
(36 min)
DECANT
(54 min)
0 18 36 54 72 90 108 126 171 216
ICEAS NDN Cycle Charts – High Flow Mode

ICEAS Process – REACT PHASE

ICEAS Process – SETTLE PHASE

ICEAS Process – DECANT PHASE

High Flow Mode Initiation
Automatic Detection of High Flow Based on Ultrasonic Level Signal :
 The rate of rise of water level, in the SBR basin, is measured during the last
25% of the react phase and throughout the settle phase. If the basin level is
rising faster than would be the case for Peak Dry Weather Flow (see Next
slide) the PLC initiates high flow cycle.
Automatic Detection of High Flow based on High Level electrode :
 If the high level electrode is made (this is set to operate just above TWL),
the PLC initiates the High flow cycle.
Manual Selection of High Flow Mode :
 The High flow mode can also be selected manually at the SCADA.

High Flow Mode Initiation
4,55
4,65
4,75
4,85
4,95
5,05
5,15
5,25
5,35
5,45
5,55
5,65
5,75
5,85
5,95
6,050
4
8
12
16
20
24
28
32
36
40
44
48
52
56
60
64
68
72
76
80
84
88
92
96
100
104
108
112
116
120
124
128
132
136
140
144
148
152
156
160
164
168
172
176
180
184
188
192
196
200
204
208
212
216
BasinLevel(m)
Real Water Level
75% of react phase
(162 min)
Predicted Water
Level
if RWL – PWL
> 20 mm

Out of Service Basin
A maximum of one basin in each group of four SBRs can be taken out of service.
When a basin is taken out of service, the PLC closes that basin's inlet penstock at the SBR
distribution chamber.
When a basin is selected out of service at the SCADA the following automatic actions
occur :
• The air isolation valve is closed
• The decanter is returned to the parked position and stopped.
• The SAS pump is inhibited.
• The high flow detection for that SBR is inhibited.
• The blower is stopped unless emergency manual aeration is selected (see below).

Out of Service Basin
When a basin has been selected out of service at the SCADA, the operator has the option
of selecting the basin for emergency aeration.
When this selection is made at the SCADA the basin will switch to manual aeration control
and will be aerated during its aeration phase.
The basin is selected to return to service manually by selection at the SCADA but will only
do so at the appropriate point in its operating cycle as determined by the PLC.

Decanter Limit Switches
Four magnetic reed limit switches per decanter. Raised
and Ultimate Raised limits stop the decanter at the
parked position while rising. Lowered and Ultimate
Lowered limits stop the decanter at bottom water level
while lowering.
The limit switches are wired to the MCC via
the local control panel, which also provides
stop/start control when MCC starter
selected to Remote.

Decanter Travel
(4 Basin Normal Mode)

Decanter Operation
While the decanter is lowering, the PLC gradually reduces the speed command to the decanter in
order that the basin decants at a constant rate.
Control of the decanter is independent of the actual water level in the basin. If flows are low then
there will simply be a longer gap between decanter effluent discharges from the system.
While the decanter is raising, the PLC runs the decanter at 100% speed.
The decanter operation is inhibited due to any of these conditions :
 If the basin is out of service.
 During settle or react phase (except while rising to the parked position after decant phase).
 If the decanter is unavailable or faulty.
 If the basin air inlet valve is not fully closed (the decanter is inhibited from lowering only).
Alarm conditions associated with decanter :
 Decanter fails to start when commanded by PLC, or fails to move off limit switch in 2 mins.
 Decanter fails to return to the parked position within 25 minutes of the end of decant.
 The basin level exceeds bottom water level at the end of decant phase.

Arrangement of Blowers

Blowers Duty Operation
Duty / Standby operation of aeration blowers :
As only one basin out of two is ever in the react phase at any one time, the blowers are controlled by each basin during its react
phase.
Fixed duty configuration:-
• Blower 09 = Duty - supplies aeration to SBR basins 10 and 12
• Blower 11 = Standby for any Duty blower.
The standby Blower can supply aeration to any of the 8 SBR basins through automatic valve arrangements at the standby blower. If
any of the above blowers fail, the standby will take its place. Should a blower be taken out of service the standby will become the
duty blower.
Dissolved Oxygen (DO) Setpoints :
• DO setpoint for the first 90% of the aeration phase (typically 2.0 to 3.0 mg/l)
• DO setpoint for the last 10% of the aeration phase (typically 3.0 to 4.0 mg/l)

Aeration Control
The blowers are normally controlled automatically via a DO control loop.
There is a preset minimum diffuser position at the blower. This is because (a) there is a minimum air flow through each diffuser and (b)
the blower itself needs to run with the inlet guide vane at minimum positioning or the blower would surge and trip
Auto Control of Blowers
From SCADA and HMI it is possible to select each basin to either automatic or manual blower control. When manual blower control is
selected, the operator can, from SCADA and HMI, directly control the output of o running blower. When automatic blower control is
selected the blower output is automatically adjusted to control the dissolved oxygen in that basin, via a PID control loop. PID obtains a
DO set point from SCADA . The process variable is measured by DO transmitters in the basin.
During aeration for a particular basin, the PLC adjusts the blower output using the “more air” and “less air” commands in order to
maintain the dissolved oxygen (DO) close to the set point.
In the event that the DO exceeds the set point by 0.5 mg/l for a continuous period of 15 minutes and the duty blower is already running
at minimum air flow, the duty blower is stopped. This happens if the “Enable High DO” option is selected
There is a lockout facility within the PLC ( 20 MINUTES ). This is to prevent blowers exceeding the maximum number of starts per
hour.

Aeration Inhibit Conditions
Aeration is inhibited if any of these conditions arise:
 When the basin is out of service.
 During the settle or decant phase.
 If the basin air inlet valve is unhealthy.
 If the decanter is in ‘lowered’ or ‘ultimate lowered’ position as detected by limit switches.
 If the decanter has failed to return to the parked position (as detected by the ‘raised’ or
‘ultimate raised’ limit switches) within 25 minutes of the start of the react phase.
 During the decant period of the partner basin if the other basin’s air valve is not fully
closed.
 If the basin level reaches the high level electrodes.

DepressurizationValves
 When the depressurization valve closes at the end of the react period the aeration grid remains pressurized : it is
necessary to relieve this air so it doesn’t escape through the diffusers when the level in the SBRs falls during the
decant phase, and possibly disturbing the settled sludge.
 Each basin is equipped with an depressurization valve immediately downstream of the air inlet valve. If air bubbling is
noticed by the operator, he can manually adjust the length of time the valve is opened.The depressurization valve is
opened automatically for this duration following the air valve closing at the end of the react period.
 The default value is 0 seconds and can be set to remain open for as long as 120 minutes.
 Note that the membranes are self sealing to prevent mixed liquor intake through the diffusers, however it is
preferable not to relieve all of the pressure in the grid to inhibit mixed liquor entering the grid through any gaps in
the distribution system pipe work system.

Surplus Activated Sludge Removal
 Each basin has two submersible SAS pumps, control of which is based on a ‘SAS duration’ value which is
set at the SCADA.This is varied by the operator in response to manually-taken samples of the solids
level in the basin.
 SAS is wasted at the end of the decant period.The PLC calculates the SAS start time in order that SAS
removal ends at the end of decant.
 The PLC records the total sludge wasted by monitoring the signal from the flowmeter in the common
sludge line.The SCADA is presented with the total sludge wasted from each basin on a daily basis as
totalized flows.

Controlling your SBR
Once the system is fully commissioned, two tests should regularly be performed : mixed liquor suspended
solids and sludge settleability test. It is recommended that these tests are initially carried out on a daily
basis.
It is necessary to maintain a minimum sludge age of 10 days . The MLSS in each SBR basin is controlled by
wasting sludge from the SBRs during the decant phase.
There is a correlation between wasting sludge (SAS time) and sludge age as shown below:
Sludge age (days) = Mass of MLSS in SBR basin /( Mass of sludge (SAS) removed from the basin per day +
Mass of SS in the effluent per day)
It is advisable to control the SBRs on the sludge age rather than on F / M ratio because in order to
calculate the F / M ratio it is necessary to know the current BOD5 of the wastewater.

Sludge settleability is measured by Sludge Volume Index (SVI). The objective of this test is to simulate what happens during settling phase of
the SBR. SVI is defined as the volume in millilitres occupied by 1 gram of activated sludge after settling for 30 minutes. SVI is expressed as
ml/g.
SVI = Volume of settled activated sludge after 30 minutes (ml)/ Concentration of MLSS (mg/l)
SVI can indicate changes occurring in the activated sludge treatment process. By trending SVI data over a period of time, operators are
able to prevent problems. Many textbooks give guideline SVI numbers, but since every plant operates differently, the best SVI for each
plant will be different. The SVI should be determined when the facility is running at optimum, and should be used as a benchmark.
SVI = 80 mL/g or less. This usually indicates a sludge that is dense and has rapid settling characteristics. This is most often attributed to
an old, over-oxidized sludge typically seen in an extended aeration facility. The floc particles would be dense and granular in appearance
SVI = 100 to 200 mL/g. Most activated sludge plants seem to produce a clear, good-quality effluent with an SVI in this range. The sludge
typically settles more slowly and traps more particulate matter as it forms a uniform blanket before settling. Microscopic examination of
this MLSS would show an irregularly shaped floc particle with some filaments forming a backbone for floc-forming bacteria to attach and
colonize.

SVI = 250 mL/g or higher. At this elevated SVI, the sludge settles very slowly and compacts poorly in the settleability test. The MLSS
looks light and fluffy, not very dense. There are several reasons the SVI may be high.
If the treatment plant is new and undergoing startup, the sludge age is considered young and the floc particles are just forming. The MLSS
result is usually low (less than 1,000 mg/L), and the supernatant above the sludge blanket will be cloudy, sometimes grayish/ green. This
type of sludge usually leaves behind straggler floc particles that either settle slowly or not at all. Effluent BOD and TSS may still be above
regulatory requirements. The term Classic Sludge Bulking has been used to describe this young sludge condition.
A high SVI may also indicate filamentous sludge bulking. In this case, a microscopic exam is recommended and might show light floc
particles that contain long filaments extending out of the particle and touching filaments from other particles. Or, the filaments may be
contained within the floc, causing a dispersed, open floc structure. In these cases, the liquid above the sludge blanket is usually very clear.
The sludge can sit in the settleability test container for long periods and settle very little, or not at all.

In case of maintenance and/or operation problems (last option), the basins can be emptied. To restart them in a
short period of time, the following procedure can be followed:
1. Divert the wasted sludge (healthy) from the other basins to the one which is been commissioned, by closing
the valve to the SAS balancing tank, and open the NRV’s
2. Feed raw sewage (reduced flows) to build up MLSS in the basin (mostly from SAS flows from the other
basins)
3. When feeding and seeding, the normal cycle for the basin can be active, but don’t allow the water level to
reach BWL, in the first 2 days.
4. Check the MLSS in the basin in a regular basis
5. When MLSS reach the desired value start normal operation

Treated Effluent Quality
SBR Phase II are designed to produce a good quality effluent to meet the following discharge
consents:
TSS 10 mg/l
BOD 10 mg/l
AMMONIA 1.0 mg/l
TSS means suspended solids that float on the surface or in suspension in the effluent. Normally
volatile, non volatile and inert materials are present in the suspended solids.
BOD means biochemical oxygen demand. It is a standard test used in assessing wastewater strength.
It is the quantity of oxygen used in the biochemical oxidation of organic matter in a specific time at
a specified temperature.
AMMONIA Bacteria are used to convert ammonia and nitrate to gaseous nitrogen, so that it can be
released into the air. Nitrification and Denitrification processes are carried out in the wastewater
treatment system to remove nitrogen from wastewater.

Activated Sludge Process
In an activated sludge process, the wastewater and the activated sludge are mixed and aerated in a tank.Then the activated sludge is
allowed to settle and separated from the treated water (mixed liquor) to produce a treated effluent.
Some of the settled sludge is wasted as SAS (surplus activated sludge) and some is recycled to the front end of the tank as RAS
(returned activated sludge).
The three major parameters that control the activated sludge process are :
• Sludge age which is controlled by altering the sludge wasting rates.
• F/M ratio ( Food to Micro-organism ratio).To control the F/M ratio, it is necessary to know the BOD & the flow rate of the
SBRs and also the MLSS in each basin.
• Control of aeration rates ( oxygen rates )
The factors that affect oxygen requirements are :
• The influent BOD concentration and the basin dissolved oxygen(DO).As the concentration of BOD entering the basin
increases, the amount of oxygen required to maintain the DO level will rise also.
• There is another relationship concerning DO and the amount of bacteria (MLSS) in the aeration basin.As the concentration of
bacteria (MLSS) in the basin goes up, the aeration rates must be increased to maintain the desired level of DO.

SBR Process Training
The factors that affect the sludge wasting (SAS) rates are:
• Sludge age : It will be low if the SAS rate is high and vice versa.
• Oxygen consumption :It will be high if the SAS rate is low or organic loading (BOD) to the basins is high.
• Mixed liquor suspended solids (MLSS) concentration in the basin : MLSS will be high if the SAS rate is
low and vice versa.
• F/M ratio : a high SAS rate for a fixed BOD load will have a high F/M ratio and vice versa.The quality of
the effluent will be poor if the F/M ratio is higher than 0.20
• The possibility of nitrifying : Increasing the SAS rate will reduce the nitrification rate.
• The quality of the final effluent : a moderate SAS rate to achieve the target sludge age should produce
good quality effluent.

Regular Checks on SBRs
These checks are to be carried out on a regular basis, preferably daily :
• MLSS in each operating basin.
• SVI of mixed liquor taken from each basin during aeration (the mixed liquor in the basin should be at least aerated for
10 minutes.)
• Microscopic examination of settled mixed liquor sludge.
• DO in each basin during aeration.The DO in the basin during aeration should be more than 2 mg/l.
• Average daily flow rate, pH, ammonia Nitrogen and suspended solids of wastewater to SBRs.
• SAS pump run time in each basin.
• The concentration of the wasted sludge (SAS).
• F/M ratio.
• Sludge age.
• Sludge blanket level in each basin during decanting cycle.
• General observation of SBRs. Check whether scum or sludge is floating on the surface or whether solids carrying
over through the decanters.
• The quality of the treated effluent and analyse for Ammonia, BOD5, TSS .

Do’s and Don’ts
• DO keep the blowers available to run at all times.
• DO increase SAS pump time between 10 & 30 minutes to control the mixed liquor in the basin and to maintain it to
the target MLSS.
• DO take readings of the sludge blanket level during the decanting period.The blanket level should at least 1.5 metres
below the bottom water level.
• DO check whether the dissolved oxygen instruments are working properly in each basin on a regular basis.
• DO calibrate dissolved oxygen probes in air on a weekly basis.
• DO NOT overload the basins hydraulically and organically because the quality of the treated effluent that is produced
from the basins will be poor.
• DO NOT ever switch the blowers off overnight or at weekends.The bacteria will die and the SBRs will not treat the
influent if oxygen is not provided.

Do’s and Don’ts
• DO NOT return septic supernatant from the sludge treatment plant to the distribution chamber of SBRs because it will affect the
settleability of the sludge, SSVI readings will be high and solids carryover through the decanter is more likely and the quality of the
treated effluent will be poor.
• DO NOT operate the SBRs with either low pH (less than 6.0) or very high pH (greater than 9) wastewater because it will affect the
performance of SBRs : the sludge will bulk.
• DO NOT return activated sludge (RAS ) to the pre-react zone periods all the time without removing some of the sludge (SAS)
from the basin because the level of the sludge blanket will rise and solids carryover with the effluent is more likely.
• DO NOT operate the basin with the DO less than 1.5 mg/l during the react period because the quality of the treated effluent may
not meet the discharge consents.The DO should be between 1.5 and 3.0 mg/l during react period.
• DO NOT operate the basin if the SAS pump is faulty because the level of the sludge blanket and MLSS will rise.
• DO NOT set SAS pump run time in each basin to more than 30 minutes because too much sludge will be removed from the basin
in a day, the concentration of mixed liquor in the basin will go down and the nitrifying bacteria will be removed (washed out).

Process Calculations
F/M Ratio
Sludge Production
Sludge Age
SAS Times

Calculation of F/M Ratio
Following process data are required to calculate the F/M ratio:
Average daily flow rate of wastewater to SBRs
BOD of wastewater to SBRs.
MLSS at bottom water level (BWL)
Volume of SBRs at BWL.
Working level in each basin
Example Calculation of F/M ratio of SBR
The BWL is 4.55 m
The cross sectional area of each basin is 1,799 m²
The volume of SBR basin at BWL = 1,799 m² x 4.55 m = 8,185 m³
The total volume of SBR basins (8 no.) = 8 x 8,185 m³ = 65,484 m³
If the daily average flow rate to SBRs is 93,575 m³/day and the average BOD is 263.3 mg/l then the organic loading (F) to
SBRs = 263.3 x 93,575 / 1000 kg/day = 24,638 kg/day

Calculation of F/M Ratio
Say the mixed liquor suspended solids (MLSS) in the basin is 5,100 mg/l at BottomWater Level (BWL)
The cross sectional area of each basin is 1,799 m²
The volume of SBR basin at BWL = 1,799 m² x 4.55 m = 8,185 m³
Mass of mixed liquor in one basin = 5,100 x 8,185 / 1000 = 41,746 kg
The mass of micro-organism (M) in one basin = 41,746 kg
BOD of the influent = 263.3 mg/l
F, the food to one basin = 24,638 (kg/day) / 8 basins = 3,080 kg/d
F/M ratio in that basin = 3,080 kg/d / 41,746 kg = 0.074 per day

Calculation of Sludge Production
In order to estimate sludge production the following information is required:
•The average BOD load of wastewater to SBRs
•The average daily flow of wastewater to SBRs
•Sludge yield
Example Calculation of Sludge Production
Say the average daily flow of wastewater to SBRs = 93,575 m3 / day and the average strength of BOD is 263.3
mg/l.
The BOD loading to SBRs = 263.3 x 93,575 / 1000 kg/day = 24,638 kg/day
The sludge yield varies from 0.75 to 1.2 kg of dry solids/kg of BOD destroyed and it depends on F/M ratio,
sludge age, wastewater characteristics including inert suspended solids.The sludge yield will be higher than 1.0
if the ratio ofTSS/BOD is more than approximately 1.3.

Calculation of Sludge Production
Based on the sludge yield of 0.8 kg dry solids / kg of BOD, the sludge production is = 0.8 x 24,638 kg dry
solids / day = 19,710 kg/day of SAS dry solids.
Note:The sludge yield will be higher than 1.0 if the ratio of SS / BOD is higher than1.3.
The sludge (SAS concentration) produced from SBRs varies from 0.75% to 0.9% dry solids (7.5 kg/m3 to 9.0
kg/m3) depending on the concentration of mixed liquor in the basin .
Assumption : all 8 basins are operating
Based on 8.5 kg/m3 dry solids concentration, SAS production = 19,710 / 8.5 m3/day
= 2,319 m3/day
= 290 m3/day per basin

Calculation of Sludge Age and SAS Removal Time
In order to estimate SAS Pump RemovalTime, the following is required :
• Desired Sludge age.Typical sludge age required will between 10 & 14 days.
• The concentration of the SAS.
• The capacity of SAS pumps.
• The solids in the treated effluent.
• The influent flow rate per basin.
Example Calculation of Sludge Age & SAS Pump RunTime
The required sludge age is around 14 days.
The concentration of MLSS in the basin at BWL = 5,100mg/l.
The volume of the basin at BWL = 8,185 m3.
The concentration of SAS = 8.5 kg/m3
Sludge age = Solids in the basin / (Solids removed by SAS pumps + Solids in the effluent)

Calculation of Sludge Age and SAS Removal Time
The mixed liquor solids in basin = 8,185 x 5,100/1000 kg = 41,746 kg
The solids in the treated effluent = 10 mg/l
The influent average flow rate per basin = 11,697 m3 /d
The solids carried away with the effluent = 10 x 11,697 / 1,000 kg/d/basin = 117 kg/d/basin
The SAS / basin to maintain a sludge age of 14 d = (41,746/14) – 117 kg/d = 2,865 kg/d of dry solids
The concentration of SAS = 8.5 kg/m3
Therefore SAS removal rate /basin = 2,865 / 8.5 m3 / d
= 337 m3 /d
Therefore the SAS pump run time per basin per cycle can be estimated as follows:
The SAS pump capacity (average) is 72 l/s and it operates 5 times per day on a normal mode.
SAS pumps run time = (337 / 5) / (72 x 3,6 ) x 60 = 15.6 minutes approx.

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