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WASTEWATERTREATMENTPLANTINECOTEX

INNOVATIONWITHSEQUENCINGBATCHREACTOR(SBR)

MD. SAIDUR RAHMAN SAJIB

T.T.H Pre-Registation No. 1651

Supervised By : Dr. Zulhas Ahmed signature : .

Head Of The Department of Wet Processing

College Of Textile Engineering & Technology(CTET)

Abstract: There are a lot of technology involve with waste water treatment. Ecotex is a

composite textile mill which is using the latest technology to treat their waste water. This paper

work considers the study of sequencing Batch Reactor (SBR) in waste water treatment plant. For

this purpose , Ecotex is taken for study. This report also contain a short description of the various

Hi-Tec process module involved with Ecotex wastewater treatment plant such as equalization

tank, coagulation, flocculation, Ozonation, , extended aeration, sequencing batch reactor e.t.c .

Thefeasibility of bench scale sequencing batch reactors (SBRs) in treating

in Ecotex effluent is

demonstrated at various influent chemical

oxygen demands (CODs) ranging from 300 to over

4,000 mg/L.The SBRs removed over 75% of the biodegradable fraction of

the influent COD at a

fixed react time of 5.5h. An easy to use process model is presented to

predict the temporal

variations of substrate, biomass, and dissolved oxygenconcentrations during the fill and react

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periods in SBRs. The

model satisfactorily predicted effluent COD and final biomass

concentrations, as

well as temporal variations of COD, biomass, and dissolved oxygen

throughout the fill and react cycles. The study provides a user-friendly approach to access

essential knowledge about SBR and the procedures to design SBR, including design

requirements, facilities selection and its advantage or disadvantage . it also describe the latest

Ozonator technology which is Used By Ecotex . The paper concludes that the result of SBR

technology involved with Ecotex by some spreadsheet calculation.

Keywords : Sequencing batch reactor(SBR) , Activated sludge , COD, BOD .

Introduction

The textile industry occupies an important

place in the economy of Bangladesh and

other developing countries. Textile

processing consumes enormous quantity of

water and chemicals for various operations

like washing, dyeing, etc. The low

efficiency of chemical operations and

spillage of chemical cause, a significant

pollution hazard and make the treatment of

discharged wastewater a complex problem.

Most of the wastewater treatment plants

recently adopt methods of chemical

precipitation and subsequent clarification.

Ecotex is a fully automated company

situated in the Chandra,Pollibydut,Gazipur.

It is a Uk-Bangladesh joint venture

company. It is a composite mill which have

a fully automated control wet processing

floor where a hue amount of water is used

per day . the waste water is discharged

through the waste water treatment plant pipe

Into their plant . every day they discharge

average 850 m3/day water . The water

parameter just before entering the treatment

plant are very high but after treatment this

parameter comes down near to the drinking

quality !! Actually they are using the

repetition of chemical precipitation and

subsequent clarification. On the other hand,

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for using the SBR technology with latest

ozonator technology they treat the water like

this . The initial COD value is over 300

mg/L but after treatment it comes down

average of 5 mg/L . This is a waste water

treatment plant which are using the physico-

chemical method. This treatment plant is

designed for treatment of 15 ton water per

day . the cost of treating water is 15 BDT /

m3

.The BOD and COD value of the water

is reduced because of the double chemical

action . For this reason the water parameter

after treatment is so good for the Ecotex .

The water characteristics , Design criteria

and constraints used in ecotex is given

below

Table 1 : water characteristics , constrains used in

Ecotex ( provided by Ecotex )

Parameters Unit

Effluent BOD5

mg/l

Influent flow rate, Q Mgal/d

Influent suspended solids, SSin

mg/l

Influent volatile suspended solids, VSSin

mg/l

Wastewater temperature oC

Influent BOD5for each day mg/l

Hydraulic detention time, h

Food-to-microorganism ratio, F/M

MLVSS/MLSS

Kinetic coefficients: Biomass yield, YEndogenous decay coefficient, k

d

lb/lb

d-1

Average concentration of settled sludge mg/l

Settled sludge specific gravityPercent of the reactor volume which willbe

%

decanted each day

Liquid depth of SBR ft

Sludge wasting per week

Biological solids in effluent mg/l

Percent of biodegradable in effluent %

Methodology

Plant layout

Ecotex having the great design to treat water

fully and eco-friendly . the total plant is

divided into two part. One part for chemical

treatment and another part is for biological

treatment . these two combination makes

Ecotex wastewater treatment plant more cost

effective .

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A typical flow diagram of this plant is given

below -

Raw water.

Ozone coagulant & polymer

supernant

Figure 1 : Process flow sheet of waste water treatment plant in Ecotex .

Process Description

The various section of waste water treatment

plant in Ecotex is given below shortly

Screening & Equalization

Screens are very simple materials having

iron bars in the form of square grids.

Effluent is allowed to pass through the grid

when large and coarse solid materials are

arrested by it allowing smaller particles and

effluent to pass through. In some several

grids are use with diminishing grid sizes. In

Ecotex they are using two screen ,one

manual Bar screen and another Mechanical

bar screen which is the product of Herman

company .

Figure : Mechanical Bar Screen

Equalization tank is a large chamber which

is designed for retention time . The

Manual +

Mechanical Screen

Flocculation

tank 2

Ozone

contactIntermediate

tank

Sequence

batch reactor

Clarifier 1

Equalisation

tank

Ozone

contact tank 1

Flocculation

tank 1

Aerobic

digestertank

Water

discharge

Clarifier 2

Sludge

disposal

Filter press

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equalization tank is specially built where air

is blown by two blowers alternately round

the clock on continuous basis. The purposes

of equalization are to supply oxygen so that

DO level increases and To mix various types

effluents and To reduce the temperature of

the Water .In Ecotex they are using blower

provided by SSR blower

.

Figure : Equalization tank in Ecotex

Ozonation for ozone contact tank

Ozone technology is the latest technology for

wastewater treatment plant . In this system the

Air is purified into the Oxygen . the machine

which is used for ozone technology is known as

ozonator . This ozonator machine is worked as

they took the air as their input and they mixed it

with the water separate the ozone , which is

being converted into the oxygen by spark

method . this oxygen then goes into the ozone

contact tank where the oxygen is mixed with the

waste water

.

Figure: Ozone machine in ecotex

In Ecotex there are 16 ozonator machine . this

machines are patented under the Mark 5 , Nuvo .

The 8 m/c is used for ozone contact tank 1 , and

another 8 m/c is used for ozone contact tank 2 .

The reaction for ozonator is given below -

Ozone (spark method) oxygen

The oxygen is carried out from the ozonator to

the tank by the pump and diffused through the

diffuser .

The ozone technology is one of the greatest

technology nowadays . it makes the water moresoften.

Flocculation And Coagulation

From the ozone contact tank the effluent is

taken to a small tank which is also called

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flash mixing tank of small retention time. In

the flash-mixing tank coagulants like lime

(Ca(OH)2) and flocculants like ferrous

sulfate (FeSO4) are dosed. This is done for

coagulation and removal of the total dye

particles. The basic idea of adding coagulant

is to bring together all the suspended and

dye particles so that they can be precipitated

out in the flash mixing tank and flocculation

tank by coagulation and flocculation

mechanism. The chemical re-action that

occurs in the coagulation and flocculation

process is shown be-low;

CaO + H2O = Ca(OH)2

The above reaction take place in flash

mixing tank when lime reacts with water

and we get calcium hy-droxide solution.

This solution reacts with the ferrous sulfate

solution, which as follows-

Ca(OH)2 + FeSO4 = CaSO4 + Fe(OH)3 +FeSO4(Un-reacted) + Fe(OH)2

Adequate quantity of poly-electrolyte

polymer solution is dosed in the flocculation

tank followed by flash mixing tank to

enhance the process of color removal by the

flocculation process. A substantial amount

BOD and COD etc. are re-moved in the

coagulation and flocculation process.

Figure : Flocculator tank

In Ecotex there are two flocculator tank .

One being use after ozone tank 1 and

another one is used after ozone tank 2 .

Clarifier

Clarifier is the big tank where the sludge is

settled for its gravitation . there are two

inclined sludge settler(clarifier) in the

Ecotex . One being used after the

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flocculation and onether one is used in the

last stage . these two clarifier is linked with

the aerobic digester where the sludge is

stored

.

Figure : Clarifier

Intermediate tank

Intermediate tank is the where the water rest

some time .

Figure : intermediate tank

Aerobic Digester

Aerobic digester is the small tank where the

sludge is stored for some times foe settling

.In here sludge is settled down for its own

mass and then it is taken out by the sludge

conditioning tank .

Filter Press

Filter Press is the pressing machine where

the sludge removes its water under pressure

.The water is then backed to the equalization

tank .In here the sludge are shaped into cake

form . This sludge then taken out for

dumping .

SEQUENCING BATCH REACTOR (SBR)

The sequencing batch reactor (SBR) is a fill-

and draw activated sludge system for

wastewater treatment. In this system,

wastewater is added to a single or lagoon

batch reactor, treated to remove

undesirable components, and then

discharged. Equalization, aeration, and

clarification can all be achieved using a

single batch reactor. To optimize the

performance of the system, two or more

batch reactors are used in a predetermined

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sequence of operations . SBR are uniquely

suited for wastewater treatment applications

characterized by low or intermittent flow

conditions. Currently, sequencing batch

reactor (SBR) technology is a well-

promoted and tested alternative, which has a

relatively low cost and small footprint. The

SBR process offers flexibility of operation,

where the sequence of successive phases can

be adjusted to create the required

combination of the growth conditions for

different groups of microorganisms to

remove different contaminants from

wastewater, i.e.:

aerobic for COD removal only,

aerobic/anoxic for COD/nitrogen removal

aerobic/ anoxic/ anaerobic for

COD/nitrogen/phosphorus removal.

Figure: SBR layout

In Ecotex they are using Lagoon SBR

system , which contain three chamber .they

are currently using two chamber ,Another

one is used for testing water parameter by

fish cultivation . The SBR system gives

them a unique miracle to treat the waste

water. After treatment the water parameter

comes down near to the drinking water .The

working procedure of SBR is given below-

Influent wastewater generally passes

through screens and grit removal prior to the

SBR. The wastewater then enters a partially

filled reactor, containing biomass, which is

acclimated to the wastewater constituents

during preceding cycles. Once the reactor is

full, it behaves like a conventional activated

sludge system, but without a continuous

influent or effluent flow. The aeration and

mixing is discontinued after the biological

reactions are complete, the biomass settles,

and the treated supernatant is removed.

Excess biomass is wasted at any time during

the cycle. Frequent wasting results in

holding the mass ratio of influent substrate

to biomass nearly constant from cycle to

cycle. Continuous flow systems hold the

mass ratio of influent substrate to biomass

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constant by adjusting return activated sludge

flow rates continually as influent flow rates,

characteristics, and settling tank underflow

concentrations vary. After the SBR, the

batch of wastewater may flow to an

equalization basin where the wastewater

flow rate to additional unit processed can be

is controlled at a determined rate. In some

cases the wastewater is filtered to remove

additional solids and then disinfected. The

solids handling system may consist of a

thickener and an aerobic digester. 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. With

the SBR, there is typically only one sludge

to handle. The need for gravity thickeners

prior to digestion is determined on a case by

case basis depending on the characteristics

of the sludge. 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. In many conventional activated

sludge systems, separate equalization is

needed to protect the biological system from

peak flows, which may wash out the

biomass, or peak loads, which may upset the

treatment process. It should also be noted

that primary clarifiers are typically not

required for municipal wastewater

applications prior to an SBR. 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.

Historic data should be evaluated and the

SBR manufacturer consulted to determine

whether primary clarifiers or equalization

are recommended prior to an SBR for

municipal and industrial applications.

Equalization may be required after the SBR,

Depending on the downstream process. If

equalization 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

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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. The SBR plant

treats a wastewater stream from a

commercial textile operation.

Figure: SBR in Ecotex

The influent characteristics for the SBR

plant are shown in Table 2 and Table 3

summarizes the physical design parameters

of the Ecotex Waste water treatment plant.

Table 2: SBR Influent CharacteristicsInfluent Parameter Value of Ecotex

BOD5 147 mg/L

TSS 98 mg/L

TKN 34 mgN/L

NO3 0 mgN/L

Total Average Influent

Flow

30,000 m3/d (7.9 MGD)

Total Average Peak Flow 49,000 m3/d (12.9

MGD)

Table 3: SBR Physical Design ParametersDesign Parameter Value of Ecotex

The original cycle settings are shown in the

center of Table 4. The design objectives for

effluent and maximum MLSS in the reactor

for the SBR plant are shown in Table 5.

Trains 4

Volume of Each Reactor 5,700 m3 (1.5 MGal)

Reactor Volume Total 22,800 m3 (6.0MGal)

Water Level 5.13m 6.5m (low/highwater levels)

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Table 4: Cycle Settings for the Designed

and Optimal SBR ProcessSBR Phases Phase length (minutes)

Filling and mixing 45

filling and aeration 45

Aeration only 135

Mix only (anoxic) 60

Settling 60

Decant 55

Desludge 20

Total cycle length 360

Table 5: Desired Effluent Quality andMLSSParameter Design Objectives (mg/L)

Effluent CBOD5 15

Effluent TSS 20

ffluent NH4 3

Effluent NO3 15,10,5

Maximum MLSS 3000

Advantages of SBR

Equalization, primary clarification (in

most cases), biological treatment, and

secondary

Clarification can be achieved in a single

reactor vessel.

Operating flexibility and control.

Minimal footprint.

Potential capital cost savings by

eliminating

Clarifiers and other equipment.

Disadvantages of SBR

A higher level of sophistication is

required (compared to conventional

systems), especially for larger systems,

of timing units and controls.

Higher level of maintenance (compared

to conventional systems) associated with

more sophisticated controls, automated

switches, and automated valves.

Potential of discharging floating or

settled sludge during the DRAW or

decant phase with some SBR

configurations.

Potential plugging of aeration devices

during selected operating cycles

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Result & Discussion

Water quality monitor

Ecotex have their own lab where they test

their own treated water. In here some

research has done. Some treated water was

taken from the plant. And after testing it into

the Ecotex laboratory found these

characteristics of the water-

Table 6: Water quality parameter

Costing

Ecotex is a very cost effective textile mill.

Their wastewater treatment plant is also a

cost effective plant. They spend only 15

BDT/m3 to treat their water. Here is a graph

of cost in month November, 2009 to treat

their water

Subject Inleteffluent

Outleteffluent

Flow rate 40M /hr 40M /hr

P 8-14 7-8BOD 400-600

PPM

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Figure: Total cost analysis in the month of November, 2009. (Provided by Ecotex)

Conclusion

This case study illustrates the benefits of

simulation for evaluation and optimization

of the operation of an SBR treating in

Ecotex a high strength industrial wastewater.

The waste water treatment plant in Ecotex

using SBR save a lot of money. The

operational

Improvements indicated by the simulations

were as follows:

1. High effluent TSS concentrations in the

baseline operation were due to inadequate

settling time in the secondary clarifiers,

2. The aeration stage in the baseline

operation was far longer than necessary,

consuming

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Excess energy with no additional benefit,

3. A reduction in the time for the aeration

stage could be used to provide an anoxic

stage to

Promote denitrification, and

4. The SBR treatment cycle could be

optimized to meet the stringent effluent

criteria for

Average and peak flow conditions, as well

as winter, spring and summer wastewater

Temperatures, with the exception of the

effluent NO3 at peak loading and 20C/68

F.

Acknowledgement

The author would like to acknowledge all

the stuff of Ecotex, Ecotex testing lab

assistant, Ecotex document database lab,

Asif Mohammad Sami (consultant and

designer of Ecotex), Subrata Paul (Assistant

Engineer) and all those people who help

author to write this document.

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asiatic limited

Subrata Paul, Engineer ,Ecotex .

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Activated Sludge Model No.1. IAWQ

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