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- DOI 10.18231/j.ijmr.2023.024
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STP design calculation for 100 KLD SBR (Sequential batch reactor)
- Author Details:
-
Gayathri Parivallal
-
Ranadive Ananth Govindaraju *
-
Sumitha Devarajan
Ranadive Ananth Govindaraju *
Introduction
Sewage treatment systems aid in the removal of impurities or pollutants coming from various sources. Physical, chemical, and biological processes are three crucial techniques or approaches used to remove or degrade pollutants. The primary, secondary, and tertiary treatment units are the three stages in the sewage treatment process.[1], [2], [3] In response to diverse circumstances brought on by waste water discharge into water bodies that raised concerns for public health,[4] methods of waste water treatment were developed. Waste water treatment uses a variety of physical and chemical qualities, such as turbidity, total dissolved solids, biochemical oxygen demand (BOD), chemical oxygen demand (COD), dissolved oxygen, nitrates, and total phosphates. Utilising percentages of specific indicators, the effectiveness of the sewage treatment plant is assessed.[5] The parameters BOD, COD, and TSS are frequently utilised. The primary goals of traditional waste water treatment planning processes are to minimise capital and operating expenditures.[6]
Discussion
STP Design Basis
Design Capacity: 100 KLD
Operating Hours: 20 Hrs
Sewage Source: Residential Apartments
Design Technology: SBR (Sequential Batch Reactor)
Designed by: M/s. Green Enviro Polestar, Pondicherry
|
Description |
Influent Parameter |
Effluent Parameter |
|
pH |
6.0 – 8.5 |
6.5 – 7.5 |
|
BOD5 (Biochemical Oxygen Demand) |
250 mg/L |
< 10 mg/L |
|
COD (Chemical Oxygen Demand) |
450 mg/L |
< 50.0 mg/L |
|
TSS (Total Suspended Solids) |
320 mg/L |
< 10.0 mg/L |
|
TKN (Total Kjeldal’s Nitrogen) |
22 mg/L |
< 5.0 mg/L |
|
Temperature |
250C |
- |
|
Units available in SBR Scheme |
Equipment available in SBR Scheme |
|
Bar Screen Chamber |
Raw Sewage Transfer Pumps |
|
Oil & Grease Chamber |
Air Blowers |
|
Equalization Tank |
Air Diffusers |
|
Anoxic Tank |
Decanter System |
|
SBR Tank |
Filter Feed Pumps |
|
Decant Tank |
Sludge Transfer Pumps |
|
Disinfection & Filtration |
Chlorine Dosing system |
|
Treated Water Tank |
Pressure Sand Filter |
|
Sludge Holding Tank |
Activated Carbon Filter |
Designing Each Units
Design a bar screen chamber
The raw sewage must first be screened via a manual bar screen to remove any particles larger than 5 mm in diameter as well as floating suspended debris like rags and other materials. These devices are intended to guard against damage and blockage by rags and other big debris in downstream equipment such as pumps, pipes, valves, etc. Gravity transports the clean effluent after screening to the equalization tank.
Rectangular or Square horizontal – flow Bar Screen Chamber is provided
This is designed with a design velocity of 0.3048 m/sec.[7], [8]
Average flow rate
(215000 /24)
8958 Litres / hour
Peak Factor: Peak flow rate shall be thrice the average flow rate
So peak flow rate anticipated
26875 Litres/hour
7.4 Litres/sec
Detention time assumed shall be: 60 sec (Advisable is 45 to 90 Sec)
Chamber Volume
1.7 Litres*60 Sec
448 Litres
0.448 m3 (Hence provide a volume of 0.5 m3)
Provide a chamber of size
Length: 1.00 m
Breadth: 1.00 m
Depth: 0.5 M below the Invert Level
Volume Provided
1.00 m * 1.00 m * 0.50 m
0.50 m3
Equalization tank
The raw wastewater collected in the equalization tank, where it is equalized with respect to its characteristics, homogeneity, flow and uniform pollution load as well as to make bacteria acclimatized. The equalization tank is designed for hydraulic retention time of around 6 hours.[9] Proper equalization process minimizes the shock loadings and stabilizes the pH to improve the biological oxidation reaction in the next downstream units.[7]
Plant flow rate: 100 m3/d
HRT (Hydraulic Retention Time): 6 hours to 12 hours (Metcalf Eddy 2004)
HRT Considered: 8 hours
Provided Tank Volume
Flow Rate * HRT Considered/24 hours
100 m3/d * 8/24
33.33 m3
Designed Tank Volume : 34 m3
SBR tank (Secondary-treatment)
The process of Oxidation, synthesis and endogenous respiration happens in the SBR tank or aeration tank. Eco-friendly available in the sewage facilitates the above process; hence the complex organic compound gets converted to simpler organic substance. Bacteria or bio augmenter staying in the SBR zone and does the job utilizing the supplied oxygen through Air blowers.[10], [11]
Plant flow rate: 100 m3/d
BOD Load: 200 mg/l to 350 mg/l (Metcalf Eddy, 2004)
BOD Load Considered: 250 mg/l
Total BOD Load enters the system
Flow Rate * BOD/1000
(100 m3/d * 250 mg/l) /1000
25 Kg/d (BOD considered to be the food for microorganisms)
MLSS: 2500 mg/l to 4000 mg/l (Metcalf Eddy, 2004)
MLSS Considered: 3500 mg/l
MLVSS: 60% to 65% value of the MLSS (6)
MLSS * 65%
3500 mg/l * 65%
MLVSS Calculated: 2275 mg/l
F/M Ratio Standard: 0.07 to 0.2 (Metcalf Eddy 2004)
F/M Ratio: BOD/MLVSS
F/M Ratio Calculated: 0.11
Decant tank
The flow from the SBR tank i.e., the supernatant liquid is let into the decant water tank, which has a minimum 4 hours detention capacity. The decanted water would meet the pressure sand and activated carbon filter units' prerequisites.
Flow Capacity : 100 m3/d
HRT Provided : 10 hours
Decant Tank Volume
Flow capacity * HRT Provided/24 hours
100 m3/d * 10 hours/24 hours
41.66 m3
Designed Decant Tank Volume : 42 m3
Treated water tank
The treated water tank capacity must be provided for no more than 24 hours, as longer treated water retention times make it impossible to maintain the FRC (Free Residual Chlorine) level of 0.5 ppm (parts per million). Foul odour would result from organic growth in the treated water if the FRC level could not be maintained, which is more likely to happen. The standard retention time provided would be 12 hours to 24 hours.[12]
Flow Capacity: 100 m3/d
HRT Provided: 12 hours
Decant Tank Volume
Flow capacity * HRT Provided/24 hours
100 m3/d * 12 hours/24 hours
Designed Tank Volume: 50 m3
Sludge holding tank
The sludge holding tank volume can be provided depending upon the WAS (Waste Activated Sludge) rate.[13] The waste activated sludge can be calculated considering the value of MLSS (Mixed Liquor Suspended Solid) available in the treatment system.
Waste Activated Sludge (WAS)
(Flow * MLSS) / (1% Consistency of MLSS - MLSS)
(100 m3/d * 3500 mg/l) / (10000 mg/l – 3500 mg/l)
53.84 m3/d
Slurry to be Wasted
WAS Rate * 10% (10% of slurry volume should be wasted/day)
53.84 m3/d * 10%
5.38 m3/d
Designing Electromechanical Equipment
Raw sewage transfer pumps[8]
The raw sewage transfer pumps could be used to transfer the incoming waste water from the equalisation tank to the SBR zone. These pumps are designed in accordance with the sewage inflow capacity and the size of the solids present in the sewage water.
Flow Capacity: 100 m3/d
SBR Number of Batch: 3 Batch (8 hours / batch)
Flow per batch
(100 m3/d) / 3 batch
33.33 m3/ batch
Filling hours
1.5 hours (1.15 hours to 2 hours)
Raw water Feed Pump Capacity
Flow per batch / Filling hours
33.33 m3/ 1.5 hours
22.22 m3/hr
Designed Pump Capacity
24 m3/hr
Air blower capacity
The procedure of aerating wastewater is done in order to promote the bio-degradation of the polluting components. Bacteria used in wastewater treatment and stabilisation are given oxygen through aeration. The bacteria require oxygen for biodegradation to take place. In a sewage treatment facility, an air blower's job is to provide high pressure and effective airflow to supply air for the aeration process. Airflow is also known as flow rate. The naturally occurring aerobic bacteria or microorganisms must have access to air in order to treat sewage and wastewater. The BOD (Biochemical Oxygen Demand) load entering the system and the amount of oxygen needed to meet the oxidation needs could be used to design the air blower capacity. The amount of oxygen needed could be twice as much as the system's BOD load. In designing the air blower capacity, additional variables such as the atmosphere's percentage of oxygen, OTE (Oxygen Transfer Efficiency) in waste water, air density, alpha and beta factors, etc., are crucial.[10]
Flow Capacity: 100 m3/d
BOD: 250 mg/l
Total BOD load
Flow Capacity * BOD Load
100 m3/d * 250 mg/l
25 Kg/d
Twice the amount of Oxygen would be required to remove the BOD Load.
Hence, the Oxygen required
Total BOD Load *2
25 Kg/d * 2
50 Kg/d
% of Oxygen in Atmosphere: 21%
Oxygen Transfer Efficiency (OTE): 25% (Considered)
Density of air: 1.2 Kg/m3
Air required for SBR zone
(50 Kg/ day) / {(1.2 Kg/m3) * 0.21 * 0.25 * 0.65 * 0.75 * 24}
67.83 m3/hr.
68 m3/hr.
(Whereas, 1.2 Kg/m3 is the density of air, 21% will be percentage of oxygen in atmosphere, 25% will be considered as OTE (Oxygen transfer efficiency), 65% is the Alfa factor and 75% was considered as Beta factor).
Air required for Equalization:
Volume * 85%
35 m3 * 85%
28.9 m3/hr
30 m3/hr.
Air required for Treated water tank
Volume * 85%
50 m3 * 85%
42.5 m3/hr.
44 m3/hr.
Total Air requirement
SBR Zone + Equalization Tank + Treated Water Tank
68 m3/hr + 30 m3/hr + 44 m3/hr
142 m3/hr
Designed Air Blower Capacity: 150 m3/hr
Filter feed pumps
The waste water that has been cleared or decanted is pumped into the pressure sand and activated carbon filter using feed pumps. Based on the sewage flow rate and the filtration pressure, this might be designed. Between 2 Kg/Cm2 and 3.5 Kg/Cm2 may be the filtration pressure.[10]
Flow Capacity: 100 m3/d
Hours of Operation: 16 hours (12 hours to 24 hours)
Feed flow/hour
100 m3/d / 16 hours
6.25 m3/hr
Designed Pump Capacity: 7 m3/hr
Sludge transfer pumps
For sludge recirculation and wasting, sludge transfer pumps are used to pump sewage sludge from the decant tank to the equalisation tank and sludge holding tank. Sludge pumps are designed based on the rate of recirculation activated sludge, the rate of waste activated sludge, and the consistency of the sludge. The majority of sludge pumping in treatment plants comprises sludge of varying consistency.
Slurry production rate considered
Flow Capacity * 10%
100 m3/d* 10%
10 m3/d
Designed Pump Capacity
Slurry Production Rate/Operating hours
10 m3/d / 2 hours (Considered)r
5 m3/hr
Disinfection System
Chlorine disinfection system installed to oxidize the pathogenic bacteria from the treated sewage water and then allowed to pass through the filtration units like PSF and ACF. The oxidation process could be carried out with the dosage ranging from 2 mg/l to 3 mg/l online downstream to the decanted water. After the process oxidation the suspended solids or the dead sludge would be filtered through the PSF (Pressure Sand Filter) and excess chlorine will be removed through the ACF (Activated Carbon Filter) to maintain the FRC (Free Residual Chlorine) level at 0.5 mg/l.
Pressure sand filter (PSF)
From the filter feed tank, the clear water is pumped to the pressure sand filter. The filtration takes place in the downward mode. The filter is filled with a layer of graded sand media supported by a layer of graded gravel. The suspended matters from the effluent get filtered. The process of filtration can also be improved through dosing chemical coagulants[14] and natural coagulants. Some the natural coagulants such as seed extracts of Moringa olefeira Lam which can help in turbidity and hardness reduction in waste water[15], [16] and Strychnos Potatorum Linn which can help in turbidity reduction.[17]
Feed Pump Flow Rate: 7 m3/hr
Filtration Velocity: 12 m/hr
Filtration Area
Feed Flow Rate/ Filtration Velocity
7 m3/hr / 12 m//h
0.583 m2
Diameter: 0.676 m
Filter Diameter provided: 0.8 m (800 mm)
Activated Carbon Filter (ACF)
In this unit the feed flow is downward through a layer of granular activated carbon filter in which dissolved organics of the effluent are absorbed. It is necessary to backwash the carbon filter every eight hours.
Feed Pump Flow Rate: 7 m3/hr
Filtration Velocity: 14 m/hr
Filtration Area:
Feed Flow Rate/ Filtration Velocity
7 m3/hr / 14 m//h2
0.50 m2
Diameter: 0.626 m
Filter Diameter provided: 0.8 m (800 mm)
Conclusion
The suggested SBR calculations can be used to construct the ideal sewage treatment facility with a 100 KLD capacity. The four-stage SBR system is a batch-operated treatment process. The four steps filling, aeration, settling, and decanting are carried out in three batches of eight hours each. Sequential batch reactor is the finest technology for our communities and corporations in our burgeoning population, since it is a batch process with a suspended growth treatment. SBR systems have minimal operating and maintenance costs, can withstand shock loads, and reduce odour using aerobic microorganisms. The best possible aeration and digestion of organic matter also makes it possible to significantly reduce BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), TSS (Total Suspended Solids), Oil and Grease. The treated water would adhere to the discharge regulations and be suitable for use in gardening or for safe disposal.
Source of Funding
None
Conflict of Interest
The authors declare no conflict of interest
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- Introduction
- Discussion
- Designing Each Units
- Design a bar screen chamber
- Rectangular or Square horizontal – flow Bar Screen Chamber is provided
- SBR tank (Secondary-treatment)
- Decant tank
- Treated water tank
- Sludge holding tank
- Designing Electromechanical Equipment
- Raw sewage transfer pumps[8]
- Air blower capacity
- Filter feed pumps
- Sludge transfer pumps
- Disinfection System
- Pressure sand filter (PSF)
- Activated Carbon Filter (ACF)
- Conclusion
- Source of Funding
- Conflict of Interest