The Sequencing Batch Reactor (SBR) is an activated sludge process designed to operate under non-steady state conditions. An SBR operates in a true batch mode with aeration and sludge settlement both occurring in the same tank. The major differences between SBR and conventional continuous-flow, activated sludge system is that the SBR tank carries out the functions of equalization aeration and sedimentation in a time sequence rather than in the conventional space sequence of continuous-flow systems. In addition, the SBR system can be designed with the ability to treat a wide range of influent volumes whereas the continuous system is based upon a fixed influent flowrate. Thus, there is a degree of flexibility associated with working in a time rather than in a space sequence [1]. SBRs produce sludges with good settling properties providing the influent wastewater is admitted into the aeration in a controlled manner. Controls range from a simplified float and timer based system with a PLC to a PC based SCADA system with color graphics using either flow proportional aeration or dissolved oxygen controlled aeration to reduce aeration to reduce energy consumption and enhance the selective pressures for BOD, nutrient removal, and control of filaments [1]. An appropriately designed SBR process is a unique combination of equipment and software. Working with automated control reduces the number of operator skill and attention requirement. The majority of the aeration equipment of sequencing batch reactors consist of jet, fine bubble, and coarse bubble aeration systems. The main focus of this report is a jet aerated sequencing batch reactor activated sludge system. Sequencing Batch Reactor Process Cycles The operating principles of a batch activated sludge process, or SBR, are characterized in six discrete periods:
1. Anoxic Fill
2. Aerated Fill
3. React
4. Settle
5. Decant
6. Idle.
Anoxic Fill The influent wastewater is distributed throughout the settled sludge through the influent distribution manifold to provide good contact between the microorganisms and the substrate [1]. The influent can be either pumped in allowed to flow in by gravity. Most of this period occurs without aeration to create an environment that favors the procreation of microorganisms with good settling characteristics. Aeration begins at the beginning of this period. Aerated Fill Mixed liquor is drawn through the manifold, mixed with the influent flow in the motive liquid pump, and discharged, as motive liquid, to the jet aerator [1]. This initiates the feast period. Feast is when the microorganisms have been in contact with the substrate and a large amount of oxygen is provided to facilitate the substrate consumption. Nitrification and denitrification occurs at the beginning of this stage. This period ends when the tank is either full or when a maximum time for filling is reached. React During this period aeration continues until complete biodegradation of BOD and nitrogen is achieved. After the substrate is consumed famine stage starts. During this stage some microorganisms will die because of the lack of food and will help reduce the volume of the settling sludge. The length of the aeration period determines the degree of BOD consumption [1], [2]. Settle Aeration is discontinued at this stage and solids separation takes place leaving clear, treated effluent above the sludge blanket. During this clarifying period no liquids should enter or leave the tank to avoid turbulence in the supernatant. Decant This period is characterized by the withdrawal of treated effluent from approximately two feet below the surface of the mixed liquor by the floating solids excluding decanter [1]. This removal must be done without disturbing the settled sludge. Idle The time in this stage can be used to waste sludge or perform backwashing of the jet aerator. The wasted sludge is pumped to an anaerobic digester to reduce the volume of the sludge to be discarded. The frequency of sludge wasting ranges between once each cycle to once every two to three months depending upon system design. Aeration Equipment A. Jet Aeration Header Jet aeration offers significant advantages in the SBR process due to its flexibility, good contact between substrate and microorganisms, and efficient oxygen transfer. One of its main features is that it can mix without aerating.Therefore it can provide for aerated and anoxic mix periods. The header in conjunction with a computer controlling for flow proportional aeration makes more oxygen available at higher flows than at lower flows by measuring the rate of change in the flow level in reactor. B. Decanter Decanting is best achieved through solids excluding decanters. The floating decanter is one of the most efficient and contains a spring loaded plug valve operated by hydraulic differential [1]. This decanter is sustained about sixteen inches below the scum by a float therefore avoiding the decanting of floating matter. Features of Ionberg SBR
Constant water level
Continuous flow
Simple operation
Superior performance even in low-strength, low-temperature wastewaters common
Adept at processing high-peak hydraulic flows due to storm events
Quiescent settling prior to clarification phase
Optimized, enhanced biological nutrient removal
Advantages of Ionberg SBR
No need for separate structures
Unique flow through system
Basin configuration optimized
Existing aeration equipment can be used
Fully automated control system
Better sludge flocculation; no sludge collection mechanisms
Low TSS discharge; effective nitrification, denitrification and phosphorus removal
Application Of Ionberg SBR Any municipal or industrial wastewater system with effluent requirements ranging from carbonaceous oxidation to enhanced biological nutrient removal.