SBR Design Report

Sequencing Batch Reactor Design Report

AIT Waste Water Treatment System

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AIT Waste Water Treatment Facility: Sequencing Batch Reactor Design Report

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Document History

Version

Number

Description Date Author Checked

1 Original 27/03/13 TS LM


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Table of Contents Document History ............................................................................................................................... i

1.0 Introduction .......................................................................................................................... 1

2.0 Characteristics of the treatment process .............................................................................. 1

2.1 Treatment Process ................................................................................................................. 1

2.1.1 Fill ............................................................................................................................... 2

2.1.2 React ........................................................................................................................... 2

2.1.3 Settle .......................................................................................................................... 3

2.1.4 Decant ........................................................................................................................ 3

2.1.5 Idle .............................................................................................................................. 3

3.0 Treatment system design ...................................................................................................... 3

3.1 Preliminary Treatment .......................................................................................................... 4

3.1.1 Screening Influent Wastewater .................................................................................. 4

3.1.2 Influent-Flow Equalisation ......................................................................................... 4

3.2 SBR Design ............................................................................................................................. 5

3.2.1 Reactor basin .............................................................................................................. 5

3.2.2 Flow-Paced Batch Operation ...................................................................................... 5

3.2.3 Aeration ...................................................................................................................... 5

3.2.4 Decanting ................................................................................................................... 6

3.2.5 Bottom Slope .............................................................................................................. 6

3.3 Post-Basin Effluent Equalisation ........................................................................................... 6

3.4 Parameters to Be Monitored by the SCADA System ............................................................. 6

3.5 Sludge wasting and storage .................................................................................................. 7

4.0 Structural design of the treatment tank ............................................................................... 7

4.1 Equilibrium ............................................................................................................................ 7

4.2 Walls ...................................................................................................................................... 8

4.3 Base design ............................................................................................................................ 8


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List of Figures

Figure 1 – SBR treatment cycle ........................................................................................................... 2

Figure 2 - Treatment system P&ID…………………………………………………………………………………………………4


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1.0 Introduction

SBR’s are used all over the world and have been around since the 1920s. With their growing

popularity in Europe and China as well as the United States, they are being used successfully to treat

both municipal and industrial wastewaters, particularly in areas characterised by low or varying flow

patterns.

This type of plant is particularly suited for use on the AIT campus for a number of reasons, including:

As there is limited space to locate the system, treatment can take place in a single basin,

allowing for a smaller footprint. Low total-suspended-solid values of less than 10 milligrams

per litre (mg/L) can be achieved consistently through the use of effective decanting that

eliminates the need for a separate clarifier.

The treatment cycle can be adjusted to undergo aerobic, anaerobic, and anoxic conditions in

order to achieve biological nutrient removal, including nitrification, denitrification, and some

phosphorus removal. Biochemical oxygen demand (BOD) levels of less than 5 mg/L can be

achieved consistently. Total nitrogen limits of less than 5 mg/L can also be achieved by

aerobic conversion of ammonia to nitrates (nitrification) and anoxic conversion of nitrates to

nitrogen gas (denitrification) within the same tank. Low phosphorus limits of less than 2

mg/L can be attained by using a combination of biological treatment (anaerobic phosphorus

absorbing organisms) and chemical agents (aluminium or iron salts) within the vessel and

treatment cycle.

As wastewater discharge permits to the municipal sewer are becoming more stringent, an

SBR offers a cost-effective way to achieve lower effluent limits.

2.0 Characteristics of the treatment process

SBRs are a variation of the activated-sludge process. They differ from activated-sludge plants

because they combine all of the treatment steps and processes into a single tank, whereas

conventional facilities rely on multiple basins. According to a 1999 U.S. EPA report, an SBR is no

more than an activated-sludge plant that operates in time rather than space.

2.1 Treatment Process

The operation of the SBR has been based on a fill-and-draw principle, which consists of five steps;

fill, react, settle, decant, and idle, as shown in figure 1. These characteristics of each step can be


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altered for differing operational applications which may occur due to AIT’s academic cycle;

particularly the significant reduction in discharge during the summer period.

Figure 1 – SBR treatment cycle

2.1.1 Fill

During the fill phase, the basin will receive influent wastewater from the equalisation tank which is

discussed in more detail in section 3.1.2. The influent provides food for the microbes in the activated

sludge, creating an environment for biochemical reactions to take place. Aeration can be varied

during the fill phase to different scenarios, for the AIT SBR an aerated fill system has been selected.

Under an aerated-fill scenario, the aeration unit is activated. The contents of the basin will be

aerated to convert the anoxic or anaerobic zone over to an aerobic zone. No adjustments to the

aerated-fill cycle are needed to reduce organics and achieve nitrification. However, to achieve

denitrification, it is necessary to switch the oxygen off to promote anoxic conditions for

denitrification. By switching the oxygen on and off during this phase with the diffusers, oxic and

anoxic conditions are created, allowing for nitrification and denitrification. Dissolved oxygen (DO)

should be monitored during this phase so it does not go over 0.2 mg/L. This ensures that an anoxic

condition will occur during the idle phase.

2.1.2 React

This phase will allow for further reduction or "polishing" of wastewater parameters. During this

phase, no wastewater shall enter the basin and the aeration unit is on. Because there are no


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additional volume and organic loadings, the rate of organic removal will increase dramatically. Most

of the carbonaceous BOD removal will occur in the react phase. Further nitrification will also occur

by allowing the aeration to continue. The majority of denitrification will take place in the mixed-fill

phase. The phosphorus released during mixed fill, plus some additional phosphorus, will be taken up

during the react phase.

2.1.3 Settle

During this phase, activated sludge will be allowed to settle under quiescent conditions; no flow

enters the basin and no aeration takes place. The activated sludge tends to settle as a flocculent

mass, forming a distinctive interface with the clear supernatant. The sludge mass is known as the

sludge blanket. This phase is a critical part of the cycle, as if the solids do not settle rapidly, some

sludge may be drawn off during the subsequent decant phase and thereby degrade effluent quality.

2.1.4 Decant

During this phase, a submersible pump will be used to remove the clear supernatant effluent. Once

the settle phase is complete, a signal will be sent to initiate the opening of an effluent-discharge

valve. The submersible pump will offer the operator flexibility to vary fill and draw volumes. This

operation will be optimised by ensuring that the decanted volume is the same as the volume that

enters the basin during the fill phase. It is also important that no surface foam or scum is decanted.

The vertical distance from the decanter to the bottom of the tank has been maximised to avoid

disturbing the settled biomass.

2.1.5 Idle

This step occurs between the decant phase and the fill phase. The time will vary, based on the

influent flow rate and the operating strategy. During this phase, a small amount of activated sludge

(75 l/cycle), at the bottom of the SBR basin will be pumped out, a process called sludge wasting.

3.0 SBR system design

The SBR treatment system consists of several individual components. The design of the SBR

treatment system was completed by TNLS in conjunction with EPS Water, as outlined in the

following sections. All pumps, valves, pipe work etc. are to be provided by EPS. A P&ID for the

treatment system is shown in figure 2.


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Figure 2 - Treatment system P&ID

3.1 Preliminary Treatment

Preliminary treatment includes screening, equalisation and flow monitoring.

3.1.1 Screening Influent Wastewater

Mechanical screens have been incorporated into the design of the SBR to effectively remove debris

prior to entering the treatment process. Removing debris from the wastewater stream before it

reaches the basins is beneficial to both the treatment process and the settling phase; excess debris is

not present to interfere with the solids that need to settle, resulting in a high-quality sludge blanket.

Screens also provide protection for the pumps. A mechanical screening system for the plant will be

provided by EPS.

3.1.2 Influent-Flow Equalisation

Flow equalisation is critical as there will be significant variations in flow rates and organic mass

loadings. As the flow from the AIT’s Engineering Building will be inherently variable, both on a daily

and seasonal basis, an equalisation tank were incorporated in the design. The equalisation tank was

sized to provide 60m3 of storage, which represents twice the maximum daily flow rate. This will allow

sufficient storage of influent in the case of the majority of breakdowns or maintenance issues. The

tank was designed with an inclined “V” shaped base and sump containing a submersible pump for

ease of cleaning and the removal of settled solids. Submersible pumps for sludge wasting and for the

pumping of influent for further treatment will be provided by EPS.

Influent-flow equalisation benefits the SBR process in the following ways:

Allows for a smaller SBR-basin size because it allows for storage until the process cycle is

complete.

Allows for storage if the reactor basin must be taken off line for maintenance, or as a result

of a breakdown.


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Allows for an equal flow volume into the reactor basin, keeping the food to microorganism

ratio (F/M) reasonably stable.

3.2 SBR Design

3.2.1 Reactor basin

SBR designs should have a minimum of two basins to allow for redundancy, maintenance, high flows,

and seasonal variations. Two basins also allow for redundancy throughout the plant. Due to the

relatively low flow rate entering the plant it was found to be unsuitable to provide two dedicated

reactors. In order to provide a backup treatment unit, the post basin equalisation tank has been

designed similarly to the reactor basin. If the primary reactor is off line, the plant is still able to treat

influent wastewater, by bypassing the primary reactor and utilising the post basin equalisation tank

as a backup reactor.

The biomass from the primary basin will be used to stock the secondary basin. For this to happen, a

means of transferring sludge between the two basins must be provided, this will be achieved by

means of the wasting pump which can be redirected to the post basin equalisation tank.

The reactor was designed to take account of flow rates, influent characteristics, hydraulic retention

time, effluent requirements etc.. The design process was completed in accordance with the design

process outlined by (Tchobanoglous, et al., 2003). From this process the reactor was sized to be

3.0m x 1.5m x 3.0m with a 0.4m free board. The completed design is provided in appendix A.

3.2.2 Flow-Paced Batch Operation

Flow-paced batch operation has been chosen for the system, this is generally preferable to time-

paced batch or continuous flow systems. Under a flow-paced batch system, the reactor receives the

same volumetric loading and approximately the same organic loading during every cycle. The SBR

basin already has stabilised supernatant in it, which dilutes the batch of incoming influent.

3.2.3 Aeration

Generally the finer the air bubbles used to aerate the waste water the more effective and

economical the treatment process. As such fine bubble membrane diffusers have been chosen over

coarse-air bubble aeration. Fine-bubble diffusers transfer more oxygen to the water due to

increased surface area in contact with water. The same amount of air introduced in a big bubble has

less surface area in contact with water than an equal amount of air divided into smaller bubbles. The

amount of surface area in contact with water is proportional to the amount of oxygen transferred

into water. Depth of aerators also plays a part in oxygen transfer, due to contact time. The deeper

the aerator, the longer it takes for the bubble to come to the surface. The fine bubble membrane


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diffusers will be supplied by EPS, they will also supply blowers to supply air to the diffusers. As

previously mentioned the post basin equalisation tank will act as a standby reactor, as such it will

also be supplied with an aeration unit.

3.2.4 Decanting

During the decant phase, operating under a flow-paced batch operation, 60% of the volume

contained in the basin (i.e., the tank contents) will be decanted each time in order to prevent

disturbance of the sludge blanket. The decant phase should not interfere with the settled sludge,

and submersible pumps should avoid vortexing and taking in floatables. For the plant to run

optimally, it is important that the decant volume is the same as the volume added during the fill

phase.

3.2.5 Bottom Slope

As with the equalisation tank a sloped bottom with a sump has been provided for the purpose of

sludge wasting and for routine tank maintenance and ease of cleaning.

3.3 Post-Basin Effluent Equalisation

Post-basin effluent equalisation soothes out flow variations prior to downstream processes. By

providing storage and a controllable flow, a more economical downstream sewer system could be

deigned. This was possible as the flow from the basin is metered out and does not hydraulically

surge the downstream processes. The equalisation tank was provided which will receive effluent

from the reactor. Effluent equalisation also ensures that there are not large variations in operating

ranges. The tank was sized to hold one decantable volume of the reactor. The tank was also

designed similar to the primary reactor with an aeration system, sloped bottom with a sump and

submersible pump for sludge removal.

3.4 Parameters to Be Monitored by the SCADA System

SCADA is a computer-monitored alarm, response, control, and data acquisition system used by

operators to monitor and adjust treatment processes and facilities.

Oxidation reduction potential (ORP), dissolved oxygen (DO), pH, and alkalinity are parameters that

should be monitored by the Supervisory Control and Data Acquisition (SCADA) system.

Manufacturers determine what parameters can be monitored and controlled by the SCADA system.

Alkalinity monitoring and addition ensures that a pH of less than 7.0 does not occur. Nitrification

consumes alkalinity, and with a drop in alkalinity, pH also drops. If the plant has adequate alkalinity,

pH does not change, so it does not need to be raised. Monitoring of certain parameters is important,

and the ability to adjust these parameters from a remote location is ideal. The operator needs to be


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able to add chemicals to raise the alkalinity and subsequently the pH. The set point should be an

alkalinity value rather than pH based. The operator should have the ability to fully control (i.e.,

modify) the plant-operating parameters, such as (but not limited to) cycle times, volumes, and set

points. The SCADA system will be installed and commissioned by EPS.

3.5 Sludge wasting and storage

Sludge wasting will occur during the idle cycle to provide the highest concentration of mixed liquor

suspended solids (MLSS). The plant will operate on kg of MLSS and not concentration. Sludge from

the SBR basin will be wasted to a pre-cast storage tank, with storage for over 28 days (9m3). The

sludge-holding-tank capacity was based on approximate sludge characteristics, see appendix A. A

high-level alarm and interlock will be provided to prevent sludge-waste pumps from operating

during high-level conditions in the holding tanks. Controls will also be provided to prevent overflow

of sludge from the holding tank. The sludge holding tank will consist of a steel fibre reinforced pre-

cast concrete unit with an approximate footprint of 2.6m x 2.6m, supplied by Shay Murtagh Precast.

4.0 Structural design of the treatment tank

The SBR was designed to be housed within a single reinforced concrete tank with interior dividing

walls to create individual tanks. The SBR system was also designed to be located entirely below

ground level. This layout was select for several reasons, firstly due to restrictions regarding available

space. By incorporating all treatment processes within a single unit the area requirements of the

system were greatly reduced. Also due to the nature of the institute minimal aesthetical impacts

were desirable as such by locating the system below ground level the visual impact was also greatly

reduced.

4.1 Equilibrium

In order to ensure the stability of the completed works the tank design was checked to ensure that

uplift would not occur. Due to the paucity of geotechnical information for the SBR location it was

assumed that the water table can rise to the surface. Uplift checks were completed in accordance

with EC-7 and the base of the tank was sized accordingly to ensure uplift was not possible. In order

to eliminate the possibility of uplift for the worst case scenario a base thickness 0.6m was found to

be necessary. See Appendix B for complete uplift calculations.


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4.2 Walls

The exterior walls of the tank were analysed as retaining walls, as maximum stress will occur when

the tank empty and acting as an earth retaining structure. The design was completed in accordance

with EC-2. As stresses placed upon interior walls, including the worst case scenario, will be of a

lesser magnitude than that of the exterior wall similar reinforcing will be applied in those elements.

The completed structural design is supplied in Appendix C, and the associated bar schedule is

supplied in appendix D.

4.3 Base design

Similarly to the design of the walls of the tank the base was designed in accordance with EC-2

assuming the worst case scenario. The base was analysed as a one way spanning slab supported by

the side walls of the tank and loading was in the form of upward earth pressure. Upon completion of

the analysis it was found that minimum reinforcement governed. The base section was also analysed

for shear and was found not to require shear reinforcement. The section was also checked for crack

control, given the exposure class of the concrete and resulting minimum reinforcement the design

was found to be adequate. The section was also found to be adequate in relation deflection. The

completed structural design is supplied in Appendix C, and the associated bar schedule is supplied in

appendix D.


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Sponsor Acceptance

Approved by the Project Sponsor:

____________________________________________ Date: _____________________

Project Sponsor: AIT


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Appendix A: SBR Design


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AIT Wastewater Treatment System

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Reference Calculations Output

Primary data

Occupant No. 500

Flow (liters/day/person) 60

BOD5 (grams/person/day) 20

BOD5 (mg/l) 333

HYDRAULICS

Influent flow rate:

Q = No. occupants x Flow

= 500 x 60

= 30000 l/day

= 30 m3/day

Peak flow:

Daily flow Q through system assumed to occur between 9am and 6pm.

Time (T) = 9 hours

Peak flow factor =3.

Ts = 9 x 3600

= 32400 seconds

q = 𝑄 𝑥 1000

𝑇𝑠× 3

= 30 𝑥 1000

32400 𝑥 3

= 2.78 l/s

Q = 30m3/day

Q = 2.78 l/s


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Dimensions:

7.0 x 3.0 x 3.0

SYSTEM SIZING

Hydraulic Retention Time (HRT) = 6 hours

Reactor Decant Rate (R) = 60%

Inner tank dimensions: Width (W) = 3.0 m

Depth (D)= 3.0 m

Free board (FB) = 0.4 m

Equalisation tank to provide minimum 24 hours storage.

Equalisation tank Ve = Q x 2

= 30 x 2

= 60 m3

Equalisation tank length = 𝑉𝑒

𝑊 𝑥 𝐷

= 60

3.0 𝑥 3.0

= 6.667 m

1 No. Primary aeration basin to be provided. Post basin equalisation tank to

be designed to act as a standby reaction basin.

Batch Volume = 𝑄

24/𝑇

=30

24/6

=7.5 m3

Aeriation Basin Vr = 𝑄

24÷𝐻𝑅𝑇÷

𝑅

100

= 30

24÷6÷

60

100

= 12.5 m3

Ve = 60m3

Vr = 12.5m3


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Dimensions:

1.5 x 3.0 x 3.0

Dimensions:

1.5 x 3.0 x 3.0

Aeration Basin length = 𝑉𝑟

3.2 𝑥 3

= 12.5

3.0 𝑥 3.0

= 1.389 m

Post basin equalisation tank Vp = 12.5 m3

Post basin equalisation tank length = 𝑉𝑏

3.2 𝑥 3

= 12.5

3.0 𝑥 3.0

= 1.389 m

Vp = 12.5m3


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Reactor

MLVSS = 𝑆𝑆𝑖𝑛 𝑥 𝑉𝑟

𝑉 𝑥 𝐹𝑀

= 250 𝑥 7500

7500 𝑥 0.1

= 2500 mg/l

MLSS = (SS –VSS) 𝑀𝐿𝑉𝑆𝑆

0.8

= (250 –200) 2500

0.8

= 3175 mg/l

VSStotal = 𝑀𝐿𝑉𝑆𝑆 𝑥 𝑉𝑟

10𝐸6

2500 𝑥 7500

10𝐸6

= 18.75 kg

Parameter Value Unit

Effluent BOD5 25 mg/l

Reactor Volume 7500 l/d

Influent suspended solids, SS 250 mg/l

Influent volatile suspended solids, VSS 200 mg/l

Wastewater temperature 10 oc

Influent BOD5 for each day 250 mg/l

Hydraulic detention time, θ 6 h

Food-to-microorganism ratio, FM 0.1 MLVSS/MLSS

Kinetic coefficients: Biomass yield, Y 0.65 kg/kg

Endogenous decay coefficient, kd 0.05 d-1

Average concentration of settled sludge, C 8000 mg/l

Settled sludge specific gravity, G 1.02

Percent of the reactor volume which will be decanted, Dr 60 %

Liquid depth of SBR 2.6 m

Sludge wasting per day As required

Percent of biodegradable in effluent 80 %

Treatment Parameters


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SStotal = 𝑀𝐿𝑆𝑆 𝑥 𝑉𝑟

10𝐸6

= 3175 𝑥 7500

10𝐸6

= 23.813 kg

Reactor Sludge Storage S = (SStotal x 10E6)/(C x G x 1000)

= (23.813 x 10E6)/(8000 x 1.02 x 1000)

= 2.918 m3

Sludge Depth = 𝑆

𝐴𝑟𝑒𝑎

= 2.918

3.0 𝑥 1.5

= 0.648 m

Liquid Depth, d = D – FB

= 3.0 – 0.4

= 2.6 m

Liquid Depth Following Decant = 2.4 – (d x Dr)

= 2.4 – (2.6 x 0.6)

= 0.84 m

Sludge Depth < Liquid Depth Following Decant

Reactor sludge

storage = 2.918m3

Reactor

adequately sized


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SLUDGE PRODUCTION

Following calculations per 7.5m3 batch

Volitile Solids Px = (Y x (SS – VSS) x Vr) – (𝐾𝑑 𝑥 𝑀𝐿𝑉𝑆𝑆)

10𝐸6

= (0.65 x (250 – 200) x 7500) – (0.5 𝑥 2500

10𝐸6

= 0.244 kg

Inert Solids SSi = (SS – VSS) x Vr

= (250 – 200) x 7500

= 0.350 kg

Total solids produced SSt = SSi + Px

= 0.350 + 0.244

= 0.594 kg

Sludge Produced S = 𝑆𝑆𝑡 𝑥 10𝐸6

𝐶 𝑥 𝐺

= 0.594 𝑥 10𝐸6

8000 𝑥 1.02

= 73 l

Sludge produced

per batch = 73l


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Monthly Sludge

Storage = 9000m3

Monthly Sludge Storage = 𝑆 𝑥 4 𝑥 7 𝑥 4.33

1000

= 73 𝑥 4 𝑥 7 𝑥 4.33

1000

= 8.832 m3

Provide 9000m3 sludge holding tank


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Appendix B: Uplift Check


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Tank Data

Tank length, B = 11.2 m

Tank depth, H = 3.0 m

Tank width, W = 3.6 m

Wall thickness, t = 0.3m

2 No. internal walls

Concrete Lid to cover tank 0.2 m thick

Assume base depth, D = 0.6m

Soil Parameters

C,k = 0

∅’k = 30

γ = 22 Kn/m3

ULS DESIGN

𝑉𝑑𝑠𝑡,𝑑 ≤ 𝐺𝑠𝑡𝑏,𝑑 + 𝑅𝑑

DESTABILISING VERTICLE ACTION

𝑉𝑑𝑠𝑡,𝑑 ≤ 𝐺𝑑𝑠𝑡,𝑑

= 𝛾𝐺,𝑑𝑠𝑡 𝛾𝑤 (𝐻 + 𝐷) 𝐵

= 1.0 x 9.81 x (3.0 + 0.6) 11.2

= 384.6 Kn/m

EC – 7 Eq. 2.8

EC – 7 Table A.15


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STABILISING VERTICAL ACTION

𝐺𝑠𝑡𝑏,𝑑 = 𝛾𝐺,𝑠𝑡𝑏 (𝛾𝑐,𝑘 (4 𝑡 𝐻 + 𝐵 𝐷 + 𝐵 𝑡𝑙 + 2 𝑥 (𝐵(𝐻 + 𝐷)𝑥𝑡)

𝑊) )

= 0.9 (24(4 x 0.3 x 3.0 + 11.2 x 0.5 + 11.2 x 0.2 + 2(11.2(3.0+0.5)0.3

3.2))

= 405.9 Kn/m

Additional resistance between soil and tank side walls must be calculated

𝑅𝑘 = 2 (𝐻 + 𝐷)𝐾 𝜎𝑣′ tan 𝛿

𝜎𝑣′ = 0.5 (𝐻 + 𝐷)(𝛾 − 𝛾𝑤)

= 0.5 (3.0 + 0.5)(22 − 9.81)

= 21.3 Kn/m2

𝛿′ =2

3(∅𝐾

′ )

= 2

3(30)

= 20o

K = 0.29

𝑅𝑘 = 2 (3.0 + 0.5)0.29 𝑥 21.3 𝑥 tan 20

= 15.7 Kn/m

EC – 7 Table C.1.1

EC – 7 Table A.15


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𝑅𝑑 = 2 (𝐻 + 𝐷)𝐾𝑑 𝜎𝑣′ tan 𝛿𝑑

′

∅𝑑′ = 𝑡𝑎𝑛−1 (

tan ∅𝑘′

𝛾𝑚)

= 𝑡𝑎𝑛−1 (tan 30

1.25)

= 24.8o

𝛿𝑑′ =

2

3(∅𝑑

′ )

= 2

3(24.8)

= 16.5o

Kd = 0.5

𝑅𝑑 = 2 (3.0 + 0.5)0.5 𝑥21.3 𝑥 tan 16.5

= 22.1 Kn/m

𝑅𝑑 =𝑅𝑘

𝛾𝑚

= 15.7

1.25

= 12.6 Kn/m

𝑉𝑑𝑠𝑡,𝑑 ≤ 𝐺𝑠𝑡𝑏,𝑑 + 𝑅𝑑

384.6 ≤ 405.9 + 12.6

384.6 ≤ 418.5

EC – 7 Table C.1.1

Adequate to resist

uplift


22

Appendix C: Structural Design


23

Project


Revision

Part of Structure

Concrete Tank


1 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

21/03/13


BS-8005

Tank Data Tank length, B = 11.2 m Tank depth, H = 3.0 m Tank width, W = 3.6 m Base depth, D = 0.6m Wall thickness, t = 0.3m 2 No. internal walls Concrete Lid to cover tank 0.2 m thick Soil Parameters C,k = 0 ∅’k = 30 γ = 22 Kn/m3

Ka = 0.5 ABP = 300 kN/m2

Materrial Properties fck = 50 N/mm2 fct,eff = -4 N/mm2

fyk = 500 N/mm2 Ep = 200 kN/mm2 Ecm = 37.3 kN/mm2

National Annex Based Factors

G,sup SW = 1.35, Partial factor for unfavourable self-weight – ULS

G,inf SW = 1.0 Partial factor for favourable self-weight – ULS

Q,sup live = 1.5 Partial factor for unfavourable live loads – ULS

cc = 0.85 Compressive strength factor

c = 1.5 Partial factor for concrete (for ULS)

s = 1.15 Partial factor for rebar (for ULS)

EXPOSURE CLASS AND DURABILITY REQUIREMENTS

Exposure class = XD3

Minimum concrete cover to rebar = 45 mm

Allowable crack width = 0.30 mm


24

Project


Revision

Part of Structure

Concrete Tank Stability Check


2 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

23/03/13


HORIZONTAL FORCE

pa = Kaρgh

= 0.26 x 2200 x 10-3 x 9.81 x 3.6

= 20.2 Kn/m2

Allowing for the minimum required surcharge of 10 kN/m2, and additional

horizontal pressure of:

ps = 0.26 x 10

= 2.6 kN/m2

Hk(earth) = 0.5 pah

= 0.5 x 20.2 x 3.6

= 36.40 kN

Hk(sur) = psh

= 3.3 x 3.6

= 11.88 kN

VERTICAL LOADS

Permanent Loads:

Wall = 0.3 x 3.0 x 24 = 21.6 kN/m

Base = 0.6 x 1.8 x 24 = 25.9 kN/m

Lid = 0.2 x 1.8 x 24 = 8.6 kN/m

Total = 56.1 kN/m

Variable Loads

Effluent = 1.5 x 2.6 x 9.81 = 45.9 kN/m

Hk(earth) = 36.40

kN

Hk(Sur) = 11.88 kN


25

Project


Revision

Part of Structure

Concrete Tank Wall Design


3 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

23/03/13


BEARING PRESSURES AT THE ULTIMATE LIMIT STATE

Consider load combination 1 as the critical combination

p = N/D +/- 6M/D2

M = γf (Hk(earth) x arm) + γf (Hk(surcharge) x arm) + γf (wall x arm)

+ γf (Effluent x arm)

= 1.35 (36.4 x 3.6/3) + 1.5 (16.2 x 3.6/2) + 1.35 (21.6 x 0.75)

+ 1.5 (45.9 x 0.15)

= 59.0 + 43.7 + 21.9 + 10.3

= 134.9 kN m

Therefore bearing pressure at centre of tank:

P = (1.35 x (21.6 + 25.9 + 8.6) )/1.8 +/- (6 x 134.9)/1.82

= 42.1 +/- 249.8

= 291.9, -207.7 kN/m2

291.9 < 300 kN/m2 therefore passes bearing check

P = 291.9,

-207.7 kN/m2


26

Project


Revision

Part of Structure

Concrete Tank Wall Design


4 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

23/03/13


BENDING REINFORCEMENT

Wall:

Horizontal force = γf 0.5 Kaρgh2 + γf psh

= 1.35 x 0.5 x 0.26 x 2200 x 10-3 x 9.81 x 3.02 + 1.50 x 2.6 x 3.0

= 34.1 + 11.7

= 45.8 Kn

Considering the effective span, the maximum moment is:

MEd = 34.1 x (0.3 + 3.0/3) + 11.7 x (0.3 + 3.0/2)

= 65.4 kNm

MEd/bd2fck = 65.4 𝑥106

1000 𝑥 2452 𝑥 50

= .022

Therefore la = 0.95

As = 65.4 𝑥106

0.95 𝑥 245 𝑥 .87 𝑥 500

= 646 mm2/m

Provide H16 bars at 225 mm centres (As(Prov) = 894 mm2/m)

The minimum area for inner and transverse wall reinforcement is given by:

As = 0.15btd/100

= 0.0015 x 1000 x 245

= 368 mm2

Provide H12 bars at 225 mm centres (As = 393 mm2/m),

bottom and distribution steel

As(Prov) = 894 mm2/m



27

Project


Revision

Part of Structure

Concrete Tank Base Design


5 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

23/03/13


BASE Vertical Loads:

Permanent Loads:

Base = 0.6 x 3.6 x 24 = 51.8 kN

Variable Loads

Effluent = 3.0 x 2.6 x 9.81 = 76.5 kN

Ground Water = 9.81 x 3.6 x 3.6 = -127.1 kN MEd = (1.0(51.8) + 1.0 (76.5)) 3.6 / 4 = 115.5 kN m MEd = (1.0(51.8) - 1.5 (127.1)) 3.6 / 4 = -125.0 kN m

MEd/bd2fck = 125.0 𝑥106

1000 𝑥 5452 𝑥 50

= 0.008 Therefore la = 0.95

As,req = 125.0𝑥106

0.95 𝑥 545 𝑥 .87 𝑥 500

= 555 mm2/m The minimum area for steel and longitudinal distribution steel which is required in base is given by:

As = 0.15btd/100 = 0.0015 x 1000 x 545 = 818 mm2

Provide H16 bars at 225 mm centres (As = 894 mm2/m), all

directions



28

Project


Revision

Part of Structure



6 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

23/03/13


Base Shear

VEd = 37.7 kN

VRd,c = [CRd,ck(100ρlfck)1/3+k1σcp]bwd

K = 1 + √200

𝑑≤ 2.0

= 1 + √200

600

= 1 + 0.58

= 1.58

ρl = 𝐴𝑠𝑖

𝑏𝑤𝑑 ≤ 0.02

= 818

1000 𝑥 600

= .0014

σcp = 𝑁𝐸𝑑

𝐴𝑐 ≤ 0.2 fcd

= 138.9𝐸3

1000 𝑥 600 ≤ 0.2 x 50

= .232 ≤ 10

CRd,c = 0.18

𝛾𝑐

= 0.18

1.5

= 0.12

Kl = 0.15

VRd,c = [0.12 x 1.58(100 x 0.0014 x 50)1/3+ 0.15 x 0.232]1000 x 600

= 238’495 N

= 238 kN

VEd < VRd,c

No shear reinforcement required VEd < VRd,c


29

Project


Revision

Part of Structure



7 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

23/03/13


BS EN

1992-1-1

7.3.2 (2)

BS EN

1992-1-1

T 7.1N

BS EN

1992-1-1

7.4.2 (2)

Base Cracking

For exposure class XD3 wmax = 0.3 mm

As,minσs = kc k fct,eff Act

For pure bending kc = 0.4

K = 0.79

fct,eff = fctm

= 0.3fck2/3

= 0.3 x 502/3

= 4.1 N/mm2

Act =

𝑏ℎ

2

= 1000 𝑥 600

2

= 300’000 mm2

σs= fyk = 500 N/mm2

As,min,c = 0.4 x 0.79 x 4.1 x 300’000/500

= 777 mm2/m

As,prov > As,min,c

Therefore no additional steel required for crack control

Deflection

𝜌0

𝜌 =

𝑏𝑑√𝑓𝑐𝑘

𝐴𝑠,𝑟𝑒𝑞 x 10-3

= 1000 𝑥 600√50

738 x 10-3

= 5.7


30

Project


Revision

Part of Structure



8 of 8

Drawing Ref:

010

Calculations By:

TS

Checked By:

NMH

Date

23/03/13


The 'uncorrected' value of the limiting span/effective depth ratio, for

values of ρ0/ρ > 1.0 is given by

(l/d)0 = 𝐾[11 + 1.5√𝑓𝑐𝑘𝜌0

𝜌+ 3.2 √𝑓𝑐𝑘(

𝜌0

𝜌− 1)3/2]

= 1.3 x [11 + 1.5 √50 x 5.7 + 3.2 √50 x (5.7 - 1)3/2 ]

= 393

This value should be multiplied by 310/σs where the reinforcement stress under the characteristic load is given approximately by:

310/σs =500

𝑓𝑦𝑘 𝐴𝑠,𝑟𝑒𝑞

𝐴𝑠,𝑝𝑟𝑜𝑣

= 500

500 𝑥 738

818

= 1.11

(l/d)lim = 393 x 1.1

= 432

(l/d)act = 3600

600

= 6

Therefore section is adequate to meet deflection requirements


31

Appendix D: Bar Schedule


32

TNLS Consulting Engineers Drawing ref : 010 Rev: B

Site ref : AIT

Date prepared : 24-Mar-13

Job : Waste Water Treatment System

Prepared by : TS

Checked by : NMH

Member Bar

Mark

Type and size

No. of

mbrs

No. of bars

in each

Total no.

Length of each bar † mm

Shape code

A * B * C * D * E/R * Rev letter

mm mm mm mm mm

Wall 01 H 16 1 50 50 10825 41 210 3510 3510 3510 210 A

02 H 12 1 132 132 3750 23 210 3010 560 A

03 H 16 1 32 32 9050 12 3510 5555 A

04 H 16 1 14 14 10425 23 420 7045 3015 210 A

05 H 16 1 14 14 7950 41 210 3015 1625 3015 210 A

06 H 16 1 14 14 4725 23 210 3015 1545 A

07 H 16 1 50 50 4300 21 420 3510 420 A

08 H 10 1 32 32 12000 21 475 11080 475 A

09 H 10 1 32 32 4300 21 420 3480 420 A

10 H 10 1 28 28 10625 21 1770 7115 1770 A

11 H 10 1 56 56 5125 21 1770 1615 1770 A

12 H 16 1 14 14 850 00 840 B

This schedule conforms to BS 8666:2005

* Specified in multiples of 5mm. † Specified in multiples of 25mm.

type size


33

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