4.3.2.2 Sequencing Batch Reacto

Categories: 4.3.2 Suspended growth Process
Time of issue: 2022-04-28 18:30:00
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Description:

Information

Sequencing Batch Reactor (SBR)

It is a fill-and-draw activated sludge system with a single reactor to treat wastewater in batches, where aerobic decomposition, settling, and sludge return occur in the same tank.

Figure 4.9 Schematic diagram of a SBR

(Source: HJ 577-2010)

Treatment Process:

The treatment process in a SBR includes five steps:

Step 1 – Fill: wastewater flows into the reactor with aeration system cycled on and off during filling to maintain proper oxygen level.
Step 2 – React: the aeration system keeps on creating aerobic conditions for microorganisms to oxidize and/or absorb organic matters and nutrients in the wastewater.
Step 3 – Settle: after aerobic degradation, the aeration system is off to allow solid-liquid separation and sludge settles at the bottom of the reactor.
Step 4 – Draw: the treated effluent (supernatant from Step 3) is discharged to disposal system.
Step 5 – Idle: this stage is not a required SBR operating stage and may not happen, especially during high flows. At this stage, waste sludge is removed from the bottom of the reactor, while the remaining sludge keeps production in the reactor to a desired concentration to initiate the next treatment cycle.

When the required operating liquid level in the reactor is reached, influent flow stops and a specified, timed treatment sequence begins. Each stage has a specified time duration, and the stage timing is controlled by a programmable logic controller. Mixed liquor remains in the reactor and no sludge return is required.

Treatment Efficiency:

Pollutant/Parameter	Removal efficiency
BOD	80% - 95%
COD	80%-90%
NH₃-N	85%-95%
TN	60%-85%
TP	50%-85%
TSS	70%-90%
Pathogen	NA
Note: The treatment efficiency varies depending on temperature, wastewater characteristics, hydraulic retention time, time for aeration, as well as hydraulic and organic loading.

Design Criteria:

Key parameters. Determination of key parameters shall be based on the requirements on carbon, nitrogen and phosphorous removal.

Mixed liquor suspended solids (MLSS): typically 2,000 to 6,500 mg/L.
Hydraulic retention time (HRT): typically 9 to 30 hours.
Solid retention time (SRT): typically 20 to 40 days.
Food to mass ratio (F/M): typically 0.04 to 0.20.
Total cycle time: typically 4 to 12 hours. It should be tuned to effluent quality requirements, wastewater flow, and other site constraints.
Typically, from two to six complete treatment cycles will be completed in each reactor each day.

According to HJ577-2010 technical specifications, recommended values for some parameters are listed below:

Parameter	Unit	C removal	N removal	P removal
BOD₅/MLSS	kg/(kg day)	0.10-0.25	0.04-0.13	0.4-0.7
MLSS	kg/m³	3-5	3-5	2-4
HRT	h	8-20	15-30	3-8
HRT for aeration phase	%	/	80	67-75
HRT for anoxic phase	%	/	20	/
HRT for anaerobic phase	%	/	/	25-33
Dissolved oxygen	kg/kg	1.1-1.8	0.7-1.1	0.7-1.1

Source: Technical Specifications for Sequencing Batch Reactor Process (HJ577-2010))

Low temperature can decrease the activity of bacteria and therefore impact the treatment efficiency. Measures such as decreasing organic loading, reducing waste sludge, adjusting hydraulic retention time for anaerobic or anoxia phases, and insulation shall be taken as needed.
At least two SBR tanks should be configurated to accommodate continuous inflow of wastewater, redundancy, and maintenance.
Several small blowers are preferable to one single large blower in the SBR. If a single blower is applied, a variable frequency drive should be considered.
Baffles or weirs are typically used to prevent scum and other floating solids from entering the effluent discharge.
A battery backup should be installed to provide power to the reactor controller in case of power failure.

Operation and Maintenance:

Require a highly skilled and technical operator to manage the system.
Regular monitoring on the quantity or “age” of sludge within the reactor.
Close monitoring on the dissolved oxygen concentration and F/M ratio within the reactor.
Regular monitoring on the quality of influent and effluent.
Adjust cycle time sequences, decanter operation and waste pumping as needed.
Continuous maintenance and control of the mechanical equipment, including pumps and aerators.
Perform manufacturer’s required maintenance activities.

Capital Cost and O&M Cost:

High capital costs as the reactor is highly mechanized.
High operating costs due to high energy consumption, sludge disposal, costly mechanical parts maintenance, and requirement of professional operation.

Applicability

Suitable for rural areas where land is limited.
Appropriate if removal of nitrogen and phosphorus is required, as the treatment cycle can be adjusted to aerobic, anoxic and anaerobic conditions.