SBR
Designed to Operate in Non steady Condition
1. Op Opera erates tes In In Batch Batch Mode Mode 2. Equalization Aeration & settlement of solid both occur in a single tank using a timed controlled sequence thus no need of clarifier and thus reduce the area.
3. Capable of bearing peak/shock peak/shock loads as it also served served as equalization equalization tank 4. The operating cycle of SBR is characterized by five periods: (1) fill (3) react, (4) settle, (5) decant and (6) idle. 5. SBRs operate operate in time time rather rather than in in space and the the number number of cycles cycles per day can can be varied to control desired effluent limits, offering additional flexibility with an SBR 6. An SBR can be set up to sim simula ulate te any conventi conventiona onall act activa ivated ted sludge sludge process process,, includin including g BNR systems.
7. With SBRs there is no need for return activated sludge (RAS) pumps and primary sludge (PS) pumps like those associated with conventional activated sludge systems.
Can be designed to handle a wide range of volume unlike the conventional ASP (continuous type) designed to work under fixed flow. In an SBR, there are no influent or effluent currents to interfere with the settling process as in a conventional activated sludge system
Uses fine bubble, coarse bubble or jet aeration system Floating decanter is one of the most efficient, contains spring loaded plug valve.
Jet aeration system can mix the content without aerating therefore it is used in both aeration and anoxic periods.
SBR is uniquely uniquely
efficientt for low or intermittent flow. SBRs are typically used at efficien flow rates of 5 MGD or less (approx. 18.79 MLD) The more sophisticated operation required at larger SBR plants tends to discourage the use of these plants for large flow rates.
Source: Parsons Engineering Science, 1999.
A modified version of the SBR is the Intermittent Cycle Extended Aeration System (ICEAS) . In the ICEAS system, influent wastewater flows into the reactor on a continuous basis. As such, this is not a true batch reactor, as is the conventional SBR. A baffle wall may be used in the ICEAS to buffer this continuous inflow. The design configurations of the ICEAS and the SBR are otherwise very similar
After the SBR, the "batch" of wastewater may flow to an equalization basin where the wastewater flowrate to additional unit processed can be controlled at a determined rate An SBR serves as an equalization basin when the vessel is filling with wastewater, enabling the system to tolerate peak flows or peak loads in the influent and to equalize them in the batch reactor. Equalization may be required after the SBR, depending on the downstream process. If equa lization is not used prior to filtration, the filters need to be sized in order to receive the batch of wastewater from the SBR, resulting in a large surface area required for filtration. Sizing filters to accept these "batch" flows is usually not feasible, which is why equalization is used between an SBR and downstream filtration. Separate equalization following the biological system is generally not required for most conventional activated sludge systems, because the flow is on a continuous and more constant basis. In most conventional activated sludge wastewater treatment plants, primary clarifiers are used prior to the biological system. However, primary clarifiers may be recommended by the SBR manufacturer if the total suspended solids (TSS) or biochemical oxygen demand (BOD) are greater than 400 to 500 mg/L.SBR never require secondary clarifier.
Can be designed to handle a wide range of volume unlike the conventional ASP (continuous type) designed to work under fixed flow. In an SBR, there are no influent or effluent currents to interfere with the settling process as in a conventional activated sludge system Uses fine bubble, coarse bubble or jet aeration system Floating decanter is one of the most efficient, contains spring loaded plug valve. Jet aeration system can mix the content without aerating therefore it is used in both aeration and anoxic periods..
Disadvantages... (1) A higher level of sophistication is required (compared to conventional systems), especially for larger systems, of timing units and controls. (2) Higher level of maintenance (compared to conventional systems) associated with more sophisticated controls, automated switches, and automated valves. (3) Potential of discharging floating or settled sludge during the DRAW or decant phase with some SBR configurations. (4) Potential plugging of aeration devices during selected operating cycles, depending on the aeration system used by the manufacturer. (5) Potential requirement for equalization after the SBR, depending on the downstream processes.
Influent parameters typically include design flow, maximum daily flow BOD5 , TSS,TDS, pH, alkalinity, wastewater temperature, total Kjeldahl nitrogen (TKN), ammonia-nitrogen (NH3 - N), and total phosphorus (TP) and total coliform. For industrial wastewater applications, treatability studies are typically required to determine the optimum operating sequence. For most municipal wastewater treatment plants, treatability studies are not required to determine the operating sequence because municipal wastewater flowrates and characteristic variations are usually predictable and most municipal designers will follow conservative design approaches. Design Parameter
Municipal
Industrial
0.15 - 0.40
0.15 - 0.60
4
24
Typically low water level MLSS ( mg / L )
2,000 - 2,500
2,000 - 4,000
Hydraulic retention time ( hr )
14
Varies
F / M ( kg BOD / kg MLSS . day ) Treatment cycle duration ( hr )
Source: AquaSBR Design Manual, 1995.
Table 1. Design parameters for IF-type SBR treatment systems Parameter
SBR systems
Pretreatment
Septic tank or equivalent
Mixed liquor suspended solids (mg/L)
2,000 - 6,500
F/M load (lb BOD/d/ML VSS)
0.04 - 0.20
Hydraulic retention time (h)
9 - 30
Total cycle times (h)a
4 - 12
Solids retention time (days)
20 - 40
Decanter overflow ratea (gpm/ft2) Sludge wasting
<100 As needed to maintain performance
Cycle times should be tuned to effluent quality requirements, wastewater flow, and other site constraints.
Once the key design parameters are determined, the number of cycles per day, number of basins, decant volume, reactor size, and detention times can be calculated. Additionally, the aeration equipment, decanter, and associated piping can then be sized. Other site specific information is needed to size the aeration equipment, such as site elevation above mean sea level, wastewater temperature, and total dissolved solids (TDS) concentration
The fill step is of three types: 1. S tatic, 2.mixed and 3. Aerated Static: influent wastewater is added to the SBR partially filled with biomass. In this condition F/m ratio is high thus sludge with high settling characteristic is produced. Mixed: influent is added to the SBR mixing the wastewater with biomass already present in the SBR. Thus creating anoxic condition (denitrification)
Anoxic condition: absence of atmospheric oxygen and microorganism utilize the sulphates as e lectron acceptor to decompose the organic matter producing H2S Anaerobic condition: absence of atmospheric oxygen and microorganism utilize the nitrates/nitrites as electron acceptor to decompose the organic matter producing N2 gas (denitrification) Order: microorganisms first utilize the nitrates and then sulfates.
Construction...
Reactors Flow ( MGD )
Flow ( MLD )
No
Size ( ft )
Blowers Volume ( MG )
No
Size ( HP )
0.01
0.045
1
18 x 12
0.021
1
15
0.10
0.379
2
24 x 24
0.069
3
7.5
1.20
4.542
2
80 x 80
0.908
3
125
1.00
3.785
2
58 x 58
0.479
3
40
1.40
5.299
2
69 x 69
0.678
3
60
1.46
5.526
2
78 x 78
0.91
4
40
2.00
7.570
2
0.958
3
75
4.25
16.086
4
82 x 82 104 x 80
1.556
5
200
5.20
19.682
4
87 x 87
1.359
5
125
Note: These case studies and sizing estimates were provided by Aqua-Aerobic Systems, Inc. and are site specific to individual treatment systems.
For Biological Nutrient Removal (BNR) plants, an SBR eliminates the need for return activated sludge (RAS) pumps and pipes. It may also eliminate the need for internal Mixed Liquor Suspended Solid (MLSS) recirculation, if this is being used in a conventional BNR system to return nitrate-nitrogen. The control system of an SBR operation is more complex than a conventional activated sludge system and includes automatic switches, automatic valves, and instrumentation. These controls are very sophisticated in larger systems.
The SBR manufacturers indicate that most SBR installations in the United States are used for smaller wastewater systems of less than two million gallons per day (MGD) and some references recommend SBRs only for small communities where land is limited. This is not always the case, however, as the largest SBR in the world is currently a 10 MGD system in the United Arab Emirates. Tank and Equipment Description... lightheaded An appropriately designed SBR process is a unique combination of equipment and software The SBR system consists of a tank, aeration and mixing equipment, a decanter, and a control system. The central features of the SBR system include the control unit and the automatic switches and valves that sequence and time the different operations. SBR manufacturers should be consulted for recommendations on tanks and equipment. It is typical to use a complete SBR system recommended and supplied by a single SBR manufacturer.
Control system in SBR may be of two types 1. Floating & timer based system with PLC A PLC is an industrial grade microcomputer primarily designed to substitute relay logic. PLCs have an input/output (I/O) subsystem that easily adapts to most of the water treatment plant process requirements. Instruments and sensors are easily connected in order to gather information for inputs to the PLC, these inputs are processed within the PLC and outputs are
generated. (I.e. an upper level sensor sends an input signal to the PLC, the information is processed according to the program and the PLC turns the system off). For a small water treatment plant, one medium size PLC is enough, however, for a large water treatment plant, it may be necessary to use several interconnected PLCs. The PLC program automatically adjusts the number of cycles based on the flow rate through the plant. The number of cycles is variable (typically ranging from 4 to 8 cycles per day per SBR Tank), and as the number of cycles increases, the duration of the react stage decreases. The program is written in standard ladder logic and controls the plant equipment (actuated valves, blowers and pumps) based on input signals from field instruments such as float switches, tank levels, current draws, alarms, hour meters readings, pump and blower running status, and actuated valve status. Key process controls are adjustable by the plant operator through the PLC interface to allow changes to process and alarm set point values.
2.
PC based SCADA system A supervisionary control and data acquisition system (SCADA) often represents the human machine interface in a water treatment controly system. While a PLC effectively provides an effective control of a process they are oftenly scattered around the water treatment plant. The SCADA is installed in order to collect and analyze input from all these PLCs and to provide an interface for the plant operator to interact with the control system. A SCADA system gather the information as hard points (raw data from the PLC or other device) and soft points (processed data from hard points) and store them in a data base, therefore reports and other supervisionary information is easily created and accesed by the operators. Access to the control system is typically through a graphical computer interface Supervisory Control And Data Acquisition (SCADA) interface, such as Visual Tag System (VTS TM) operator interface, running on a dedicated PC computer. This enables process adjustments and logging data/trends of levels and alarms. Operator adjustable process variables are accessible through the computer interface. The interface also enables access to logged information on float switch positions, tank levels, alarms, hour meters readings, pump and blower running status, etc. The levels in the reactors are monitored by pressure transducers mounted in each reactor tank. The VTS provides accurate metering of the flow through the plant eliminating the need for a plant flow meter. The control system can be accessed from virtually anywhere in the world using a computer, software, modem link and telephone access. By this method the operator and support personnel can remotely check plant status and operational trends. This is particularly useful for alarm "call outs" so the operator can check the priority of the call and determine before leaving home (or a remote office) the type of response required. Also if the operator is away for a period of time, the operator can check the plant status by a modem link from anywhere in the world. The data acquisition is particularly useful for trouble shooting the plant. The system will incorporate a dialer for alarms.
Tank: 1. for municipal wastewater – concrete tank 2. For industrial wastewater: steel with inside rubber liner Mixing & Aeration System: 1.Jet aeration system; allow mixing either with or without aeration, 1.fine 3. & coarse bubble aeration system
Blowers: positive displacement type Decanter: 1. floating type/floating type, offer the operating flexibility to vary fill-and-draw volumes. 2. Fixed type
Performance... The performance of SBRs is typically comparable to conventional activated sludge systems and depends on system design and site specific criteria. Depending on their mode of operation, SBRs can achieve good BOD and nutrient removal. For SBRs, the BOD removal efficiency is generally 85 to 95 percent . SBR manufacturers will typically provide a process guarantee to produce an effluent of less than; (1) 10 mg / L BOD, (2) 10 mg / L TSS, (3) 5 - 8 mg / L TN and (4) 1 - 2 mg / L TP
Operation and Maintenance... Since the heart of the SBR system is the controls, automatic valves, and automatic switches, these systems may require more maintenance than a conventional activated sludge system. An increased level of sophistication usually equates to more items that can fail or require maintenance. The level of sophistication may be very advanced in larger SBR wastewater treatment plants requiring a higher level of maintenance on the automatic valves and switches. Significant operating flexibility is associated with SBR systems. An SBR can be set up to simulate any conventional activated sludge process, including BNR systems. For example, holding times in the Aerated React mode of an SBR can be varied to achieve simulation of a contact stabilization system with a typical hydraulic retention time (HRT) of 3.5 to 7 hours or, on the other end of the spectrum, an extended aeration treatment system with a typical HRT of 18 to 36 hours. For a BNR plant, the aerated react mode (oxic conditions) and the mixed react modes (anoxic conditions) can be alternated to achieve nitrification and denitrification. The mixed fill mode and mixed react mode can be used to achieve denitrification using anoxic conditions. In addition, these modes can ultimately be used to achieve an anaerobic condition where phosphorus removal can occur . Conventional activated sludge systems typically require additional tank volume to achieve such flexibility. SBRs operate in time rather than in space and the number of cycles per day can be varied to control desired effluent limits, offering additional flexibility with an SBR.
For BNR: first aerobic then anoxic condition alternately For BPR: only anaerobic condition Table 2. Suggested maintenance for sequencing batch reactor package plants Systems component
Suggested maintenance tasks
Reaction tank
Check for foaming and uneven air distribution; check for floating scum; check decanter operation and adjust as required; adjust cycle time sequences as required to achieve effluent target concentrations; check settled sludge volume and adjust waste pumping to maintain target MLVSS levels.
Aeration systemdiffused air
Check air filters, seals, oil level, and backpressure; perform manufacturer's required maintenance.
Aeration systemmechanical
Check for vibrations and overheating; check oil level, and seals; perform manufacturer's required maintenance.
Septic tank (primary clarifier)
Check for accumulated solids and order pumping if required.
Controls
Check functions of all controls and alarms; check electrical control box.
Sludge wasting
Pump waste solids as required to maintain target MLVSS range (typically 500 to 4,000 mg/L).
Analytical
Measure aeration tank grab sample for MLVSS, pH, and settleability; collect final effluent decant composite sample and analyze for water quality parameters as required (BOD, TSS, pH, N, P, etc.).
Costs...
Design flowrate ( MGD )
Equipment costs ( US $ / gallon)
0.5 - 1.0
1.96 - 5.00
1.1 - 1.5
1.83 - 2.69
1.5 - 2.0
1.65 - 3.29
Note: Installed cost estimates obtained from Aqua-Aerobics Systems, Inc., August 1998.
