4237-control in action, design a fermanter

8/13/2019 4237-Control in Action, Design a Fermanter

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ien e with e h oogy

A 66 6 ASE


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The Science with Technology Project

The Science with Technology Project is a joint initiative of the Association for

Science Education (ASE) and the Design and Technology Association (DATA).

It was set up to develop curriculum links between science and technology for

students in the 14 to 19 age range.

The project provides resource materials for students and support for teachers

of both science and technology.

The mater ials can be used with courses leading to GCSE, GNVQ and NAS level

qual ifications.

A programme of in-service t raining is available.

For details contact: ASE INSET Services, Barclays Venture Centre,

University of Warwick Science Park, Sir William Lyons Road, Coventry CV4 7EZ.

Telephone 01203 690053 Fax 01203 690726

The resource materials

The Science with Technology Project has produced two types of unit.

Extended uni t s provide in-depth coverage of a topic or an area of the curriculum.

Focused uni t s concentrate on a particular aspect of a topic.

Extended units

Managi ng Energy

Understanding Control

Investigating and designing

control systems

Developing Food Products

Developing Textiles Products

Making use of Renewable Energy

Further units will cover areas such as

materials science and technology.

Focused units

Control in Action: Designing a fermenter

Understanding Sensors

Understanding the Science of Food

Human Factors in Design

Evaluating Environmental Impact

Cars and the Environment

Energy Transfers: from source to load

The Science with Technology Toolkit

(3 separate units)

Project Management

Product Development

Teamwork

l i i ~ ~ l l i l m ~ 1 1 1N19824


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Acknowledgements

Steering Committee

John Holman (Chair 1991 to 1994)

Andrew Hunt (Chair from 1994)

Andrew Hutchinson

Ed Gillett

Dawn Grantham

Boyd Gunnell

David Moore

Ronald Somervi lie

Peter StevensonChristine Tacon

James Williams

The work of the Science with Technology Project has been funded by:

The Gatsby Charitable Foundation

British Gas picBrown and Root Ltd.

Cadbury Schweppes pic

Courtaulds pic

General Electric Company pic

The Institution of Electrical Engineers

National Grid Company pic

Nuclear Electric pic

Pilkington pic

The Royal Commission for the Exhibition of 1851

Vickers pic

The Science with Technology team owes a great deal of thanks to a wide range

of people and organisations who have helped to produce the project materials.

Many people in education, industry and the professions have given freely of their

time and expertise to write or comment on trial materials. A large number of teachers

and students were involved in the trials of the units; we would like to thank them all.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


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Science with Technology

~Ii

I

1.1


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..............................................................................................................................................................................

Contributors Jim SageRobert Sharp

Acknowledgements

Project team

Project Director

Project Officer

Project Assistant

Graphic Design

Jim Sage

Alan Goodier

Helen Mohan

Erika Pye

Printed and published by:

The Association for Science Education, College Lane, Hatfield, Herts AL 10 9AA.

The Association for Science Education 1995

ISBN 0 86357 235 9

Al l ri gh ts reserv ed. Thi s book is co py ri gh t materi al bu t permi ss io n is gr anted to

make photocopies for classroom use provided that the copies so made are used

solely within the purchasing institution. No other reproduction, storage in a retrieval

system or transmission in any other form or by any means may be made without

prior written permission from the publisher.

..............................................................................................................................................................................


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Contents Teachers' Notes

Plan of the unit II

By using the unit students will ... III

Links to other SwT units III

Usefu I resou rces III

Syllabus links IV

Using the unit V

Students' Material

Introduction - Biotechnology

Part 1 Research

INTRO. 1-6

1.1-7

ASE 1995

Part 2 Designing and making a fermenter 2.1-15

TEACHERS' NOTES. i


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................................................................................................................................................................................

Plan of the unit

Biotechnology

1 hour + independent study

This part:

introduces the importance of biotechnology and the range of biotechnological products;

- provides information about commercial fermenters and about batch and

continuous fermentation processes.

It also includes an overview of the unit for students.

It is recommended that the video A Taste of Things to Come (see page iii for details)

is used as part of this introduction.

Research

The time taken for this part of the unit will depend on how the investigations are used.

Each investigation will take about 1 hour to set up.

Data will need to be collected over several hours or days.

In this part students use a simple model fermenter and yeast to investigate the

optimum conditions to achieve the highest yield. The investigations cover:

temperature;

oxygen supplies;

pH;

glucose levels;

agitation and mixing.

They are provided with guidance on setting up the fermenter and methods for

measuring the yield.

Designing and making a fermenter

The time taken for this part of the unit will depend on the sophistication of the design.

It could take between about 5 and 10 hours.

Lesstime will be needed if the control systems are modelled using a systems electronics kit.

More time will need to be allowed if these are then turned into printed circuit boards.

Students are provided with a process to analyse the possible control systems to use with a

fermenter. They use this process to:

determine the physical conditions that could be controlled and use the results

of their research to set parameters for these conditions;

work out the type of control system required;

identify input and output transducers that could be used.

They are provided with practical information on:

ideas for maki ng a fermenter;

temperature control; controlling pumps;

making and controlling valves;

methods of agitation;

pH control;

monitoring and measuring output.

TEACHERS INOTES. i i ASE1995


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B y us ing the uni t s tudents wi l l ... carry out scientific investigations and research

in order to obtain data to be used to establish

design parameters and a specification for the

design of a fermenter;

learn about control systems within a context

related to industrial applications;

design and make a fermenter that can be used for

further research or for making a product using

batch production techniques;

learn about the importance of the biotechnology

industry and its products.

Useful resources

A cheap bioreactor (fermenter) suitable for

school use is available from the Science

Department at :

Woodway Park School and Community College,

Wigston Road, Coventry CV2 2RH,

telephone 01203 616155, fax 01203 602398.

Contact the school for details. .

Resources from the Nat ional Centre for

Biotechnology Educat ion (NCBE),

Department of Microbiology,

The University of Reading, Whiteknights,

PO Box 228, Reading RG6 6AJ.

A booklet containing a collection of fermentation

activities is particularly useful as it includes a

wide range of activities for making use of the

fermenter the students make.

NCBE also produce a bioreactor (fermenter)

for school use.

NCBE also provide advice about health and

safety and about safe organisms.

Links to other SwT uni ts

Understanding control

Investigating and designing control systemsThese units provide more detailed information about

control systems.

Understanding sensors provides more information

about the sensors that students could use in their

control systems.

Control in Action: A chocolate factory is a

complimentary unit.

Innovation: Wealth from Science and

Engineering Video 8: A Taste of Things to Come

is about biotechnology.

A set of these DTI sponsored videos has been

sent to most schools. In case of difficulty

contact: SPE,The Mansion House,

57 South Lambeth Road, -London SW8 1RJ.

This is recommended for use as part of the

introduction to this unit.

Topics in Safety

(revised second edition 1988) ASE

ISBN: 086357 104 2

This booklet includes sections on biotechnologyincluding fermenters and on microbiological

safety. It is strongly recommended.

TI=ArUI=I1f;' IVnTI=f; _ iii


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Syllabus links

Science

Experimental and investigative science

planning experimental procedures

obtaining evidence

analysing evidence and drawing conclusions

evaluating evidence

Design and Technology

A design and make assignment involving systems and control and

relating to industrial practice

Information TechnologyUsing IT to control and measure

Science

Foundation

Unit 1 Working on scientific tasks

Intermediate

Unit 1 Working on scientific tasks

Unit 3 Making useful products

Element 3.3 Make and test devices - electrical, electronicUnit 4 Monitor and control systems

Element 4.2 Monitor and control chemical reactions

A dv an ce d

Unit 4 Obtain products from organisms

Element 4.1 Evaluate organisms as a source of useful products

Unit 6 Control reactions

Element 6.3 Evaluate industrial processes

Unit 8 Communicate information

Element 8.1 Gather data for scientific purposes

Manufacturing

The unit can be used to cover both electrical/electronic and chemical/biologicalmaterials and products and scales of production - small batch and continuous.

Foundation

Unit 1 Manufacturing products

Unit 2 Exploring manufacturing operations

Intermediate

Unit 1 Working with a design brief

Unit 4 Manufacturing products

A dv an ce d

Unit 1 Design specifications

Unit 2 Communicating product design

Unit 5 Process operations

Design and Technology

The complete unit could be used asthe basis of a design and make activity .

...............................................................................................................................................................................

T E A C HE R S ' N O T E S. iv


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Using the unit

KS4/GCSE

The most effective use of this unit requires

co-operation between science and design and

technology. Aspects of information technology

are also involved.

Part 1 of the unit involves a series of scientific

investigations. These could be used within science

to meet some of the requirements of 'Experimental

and investigative science'. However, they are

designed to help students establish the design

parameters and specification for the fermenter

they design and make in Part 2.

This activity should be carried out within 0& T

but may require access to science, for example, to

sterilise the components used.

The Introduction should be used to provide the

common context for the activities.

GNVQ

The Introduction can be used to provide an

industrially related context.

Parts 1 and 2 can be considered as assignments

with structured activities built in. Each part can be

considered as a resource for the other. They could

be carried out in any order.

For example: Science (Intermediate)

Part 1 used to cover aspects of Unit 1 Working

on scientific tasks, followed by Part 2 to coverElement 3.3 Make and test a device

OR

Element 3.3 covered first using Part 2 with Part 1

used as a supporting resource but meeting some

of the requirements of Unit 1.

This second approach could also be used to deliver

aspects of Manufacturing.

Notes on the recipe to use in the fermenter

See page 1.2 in the students' material.

A medium with this amount of glucose may caramelise on autoclaving.

This can be avoided by adjusting the pH of the medium to pH 4 before

autoclaving and readjusting once the autoclaving is complete.

2 It is best to autoclave half the volume at a time at 121C for 20-25 minutes.

3 An alternative medium is:2% glucose

1% pure yeast extract

1% mycological peptone - this can be omitted for short durations.

ASE 1995 TFArHFllft' NrlTFft _V


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Biotechnology involves the use of

biological agents to make a product.

This could be a material, chemical,

drug, a new plant or many other

possible products.

It is a very good example of a

science-based industry.

Advantages of biotechnology

* Organisms can easily be grownin large quantity

* Organisms can be grown on verycheap foods, someti mes waste food

* Organisms can be grown at lowtemperature so the costs of heating

is small

*The product is often safe to handle sinceit does not involve poisonous chemicals

CONTROL IN ACTION: DESIGNING AND MAKING A FER MENTER

The basic piece of equipment used in biotechnology is

the fermenter. This is a chamber where the conditions are

controlled to encourage the fast growth, or a special kind

of growth, of one or more organisms.

PART1 Research

Science investigation

What are the optimum conditions inside a

fermenter to achieve maximum yields?

. . . . . . . ! :

All of these conditions need monitoring and controlling.

This is an example of process control.

The output of the fermenter also needs to be monitored.

These are known as the process variables or parameters.

You now have the data and information needed to establish the

design parameters for the fermenter. This will help you to produce

the detailed specifications for the control systems you need.

PART 2 Designing and making a fermenter

Using your fermenter

ASE 1995 INTRO.l


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P R O D U C T S O F

BIOTECHNOLOGY

FOOD

Make a list.

Use the informationbelow and on the next page to help you.

Fungi can be used to turn cheap carbohydrates into a high

protein food called mycoprotein. Mycoprotein is also high

in dietary fibre and low in fat content. Mycoprotein has an

excellent texture similar to that of meat. It can also absorb

flavours readily; this means that it can be used in a wide

range of products.

Cheaper food for

consumption by humans

and farm animals

Beer, wine, bread, cheese,

vinegar, yoghurt, sauerkraut

MATERIALS

New materials that could

have less environmental

impact such as biodegradable

plastics

CHEMICALS

New chemicals

Fertilizer, pesticides

Washing powders

Chemical tests

Metal salts taken from

their ores

MEDICINES

A wide range of new

medicines

New vaccines or known

vaccines produced in

greater quantity

Growth hormones

FUELS

Methane, Ethanol

Fuels from waste products

cereals or

potatoes

enzymes -----~

starch

enzymes ------~\

glucose syrup

air

What are the advantages of

mycoprotein over meat protein?

What are the disadvantages?

You wi!! find it useful to visit a

supermarket and find out about the

range of food products made from

mycoprotein. Mycoprotein is sold

under the trade name QUORN.

MYCOPROTEIN

COLLECTION

for proceeeing

and packaging

INTRO.2

....................................................................................................................

AS E 1 99 5


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ASE 1995

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INTRO.3


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Methods of fermentation

There are two main methods of fermentation:

solid substrate fermentation - growing microorganisms on a solid or

semi-solid layer.

aqueous fermentation using a liquid with a high water content.

This can be batch or continuous fermentation.

Batch fermentation

Batch fermentation takes place in a closed

fermenter. The microorganism is put into

the fermenter with a nutrient medium.The product is separated at the end

of the fermentation.

temperature

pro be

In a fed-batch process nutrients are

added at intervals during the process.

In this unit we will concentrate on

batch fermentation.

Precise control of pH, oxygen levels

and nutrient levels is vital.

cooling

water in

The advantages of the batch process

It is easy to set up and control

It is versatile - it can be used for

a range of products.

If contamination or a problem

occurs only one batch is lost.

pH pro be

water

jacket

stirrer

air sparge

microorganisms

and product

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Continuous fermentation

In continuous fermentation nutrients are addedand products are removed continuously.

Precise control of pH, oxygen levels and

nutrient levels is vital.

INTRO.4

Theoretically this process is more cost-effectiveand greater productivity is possible. However,

the process is difficult to control and there are

practical problems such as foaming and the

clumping together of cells.

ASE 1995


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ASE 1995 INTRO.5


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Setting up an

industrial fermenter

There are three stages in setting up

an efficient industrial fermenter to

produce an economic product.

Stage 1 Screening and research

The microorganism to be used is

cultured in small laboratory vessels.

This is to check the characteristics of

the microorganism and to find the

optimum conditions for its growth.

Stage 2 A pilot plant

A small-scale fermenter between

about 5 and 200 Iitres capacity is

used to find the optimum operating

conditions. These may be different

from the laboratory conditions.

Why do you think the optimum

operating conditions may be

different from the optimum

laboratory conditions?

Stage 3 Full scale plant

A full size fermenter is used forcommercial production.

This could have a capacity of

thousands of Iitres.

INTRO.6 AS E 1 99 5


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Context

Imagine you are a biochemical engineer in charge of the

manufacture of yeast which is used to make bread rise.

About a million tonnes of yeast is sold every year to bakers

in the UK. It is your job to make the manufacture of yeast as

cheap as possible and to make sure that the process runs

efficiently and reliably. This will involve looking closely at

growi ng yeast ina fermenter.

ASE 1995

Fermenters are fi lied with a

liquid broth. This broth has

food dissolved in it.

A small sample of a specific

microorganism is added to

the fermenter. In you r case

this is yeast. This small sample

is known as the inoculum.If this inoculum is provided

with the right conditions

it will reproduce quickly.

Your task is to grow as much

yeast as you can as quickly

as you can using the

minimum amount of food!

The investigations in this

section will help you find out

the optimum conditions in the

fermenter to obtai n the

maximum yield.

This will help you design the

control systems you wi II need

in Part 2 of this unit.

1 1


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Here isa design for a simple fermenter that

you could use for your investigations.

For a 2 litre fermenter:

Make up 1. 4 dm3 (litre) of fermentation broth

using 30g/dm3 glucose and 15g/dm3 yeast extract

in distilled water.

2 Sterilize the broth by placing it ina conical flask

with a cotton wool bung and heating in an

autoclave for 20 minutes

You will need to autoclave half the volume at a time.

3 Dissolve 14 g of dried yeast in the broth.

4 Put the broth into a thoroughly cleaned fermenter.

What are the variables?

Make a list of the conditions that you could change.

How will you measure the effect of the change?

What conditions will affect the growth

of cells inside the fermenter?

Cells require food, oxygen and a

suitable temperature and pH.

Carbon and nitrogen are essential

elements found in large quantities in all

living tissue. Cells must be provided

with a suitable source of both.

Carbon is usually provided as some

form of carbohydrate such as glucose.

Nitrogen is needed in lower quantities

and is present in a suitable form in

yeast extract. Growing cells can have

too much food as well as too little.

Oxygen is obtained from that

dissolved in the broth.

Aeration and mechanical stirrers

are used to provide good mixing

and to increase the rate at which the

oxygen dissolves.

The pH is controlled by adding acids

and bases as required.

1 2

screw clip to

control air supply

from air filter and

aquarium pump

t gasoutlet

growth

medium

2 litre

pop bottle

pH?

temperature?

ASE 1995


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You are interested in the growth of the organism.

Here are some ideas for measuring this growth.

Measuring the growth in the fermenter

When oxygen is not present (ANAEROBIC

conditions) little growth occurs and most of the

glucose will be converted into carbon dioxide

and alcohol.

yeast

Measuring carbon dioxide

As the cells multiply they produce carbon dioxide

gas. The more cells there are, the more CO2is

produced. Measuring the amount of CO2produced will give an indication of growth.

YEAST CAN GROW IN A GLUCOSE SOLUTION

WITH OR WITHOUT OXYGEN.

When oxygen is present (AEROBIC conditions)

the yeast cells divide rapidly producing largequantities of new cells.

yeast

C6H1206 + 02 -7 CO2+ H20 + Energy

glucose growth of new cellsSee Part 2 [Resource Activity 5

for details.

Measuring "cloudiness"

As the cell population grows the mixture will

become cloudy. By measuring this cloudiness

you can get a measure of the growth.

One problem with this method is that the

cells may stick together in clumps.

This is called flocculation.

The clumps will tend to

sink to die bottom in large

fermenters and can beovercome by stirring.

This method has the advantage that you could

use a computer to collect the data.

--7 2C02 + 2C2H30H + Energy

alcohol

These reactions are 'temperature dependent I

Counting cells

Another way of measuring the amount of growth

is with a haemocytometer.

Samples are taken at regular intervals throughout

the fermentation. The number of cells on an

etched grid can be counted.

You need to take account of flocculation.Stir the suspension before the sample is taken.

EXAMPLE OF RESULTS

Total number of cells in 10 squares = 270

Average number per square= 27

Each square =0.004mm3 of liquid.

NOTE: You need to check the size of

the grid squares on your slide.

In time there could be too many cells to count so

dilute the suspension and take this into account.

1cm3 of

suspension

9cm3

of water

9cm3

of water9cm3

of water

0.004mm3 x 250,000

= 1 cm3

therefore multiply 27

by 250,000 to get

number of cells

in 1cm3

= 6,750,000 cells

If dilution was 1000x

then number of cells

in 1cm3 of culture

= 6,750,000,000

ASE 1995 1.3


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IN V ES TIG A T IO N P L A N N IN G C H EC K L IS T

What are you trying to find out?

What do you know already?

What do you expect to happen?

What is your strategy?

What willyou measure and how?

How willyou record your data?

What equipment do you need?

How accurate do you need to be?/5 there anything else that you need?

Make a clear statement(s).

List the information that might help you.

Try to make some predictions.

Usea flow chart ora series ofclear

statements.

Note down the variables you will:

change;

measure and record;

keep the same.

Make a list ofall the things you

need to measure and record and

the equipment that you will need.

When the investigation is complete, write down what you found out.

How good were your predictions?

Write a report.

How willyou report and display your findings?

Your report should include:

the aim of the investigation;

your prediction of the results;

the practical plan including the equipment and resources to be used,

the measurements required and how you made them, and how you ensured

it was a fair test;

your results;

your conclusion - the pattern ofyour results, what the results tell you,

relationships, effects of the variables, reliability and accuracy.

1 .4ASE1995


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suitable liquid to

transfer the

thermal energy

12Vaquarium/

immersion heater

optimum growth

temperature

10 20 30 40 50

temperature of growth (0G)

4

o

Some practical hints

The temperature can be changed by:

placing the fermenter in a water bath;

using a 12 volt aquarium or

immersion heater.

The heater will need to be sterilized

or placed in a sterilized tube.

l rJi lestigation

W H A T IS THE

OPTIMUM

TEMPERATURE?

Use the simple fermenter

(page 1.2) to find out the

temperature range to give

the best yield.

It is important to find out

the range rather than a

specific temperature.

A range is much easier

to control.

air should be passed

through a cotton wool

air filter - Whyis this?

clamp to adjust

./ air supply

You can also calibrate the air flow by

collecting the air overa period of time

using the displacement of water.

1 $ - - J i ! = i ~ : ; . .-. . . . .: ;. . .~. . . ;. .. . . . . . r. . . i= -r 1 F . . . . . . . . . ..J

loose rollofpaper

long glass tube

(You may need to

try several.)

glass bead

whichjust fits

air from

aquarium-type

air pump

Invest igat ion

A IR (O XYG EN)

SUPPLY

To measure the amount of

oxygen dissolved in the

solution accurately you can

use a dissolved oxygen

meter and sensor.

Measuring the airflow

A simple airflow meter

could be used. This should

be placed in the top of the

fermenter in the gas outlet.

You can usea simple

screw clip tocontrol the

air supply from the pump

or control the pump.

ASE 1995 1 . 5


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syringe

(eg.20cm3)

1cm silicone rubber

tubing (3mm diameter)

optimum

. . - - . . . 3 growth pH~~

's ::J'--' 2. . s : :~~\:S)

4-

C)

~~~

04 5 6 7 8 9

acid -1--alkalineutral

pH of growth medium

pipette B

bent pipette for sampling

fermenter vessel

The fermenter vessel and pipettes are autoclaved.

pipette A

(5 or 10cm3)

cotton wool

air filter

citric acid (0.1 M)

to decrease the pH

(more acidic)

Suitable solutions

sodium acetate (O.lM)

to increase the pH

(more alkaline)

You can try using different concentrations of glucose

when you charge your fermenter.

Glucose detecting strips can be used to indicate

glucose levels in samples.

....................................................................................................................

Invest igat ion

G L U C O S E

L E V E L S

Inoculation

This can be carried out through either

pipette with a sterile syringe and needle.

Sampling

The piston in the syringe is set

in a middle position.

Pipette B and the syringe are

connected with tubing.

A sample is withdrawn but as the

liquid breaks in the expanded part

of the pipette, it can be emptied

with no backflow by pushing and

pulling the piston gently.

Afterwards the syringe, the tubing

and the outer part of the pipette B

are washed with 70% ethanol and

the parts are connected.

This will prevent overflow of the

contents of the fermenter caused by

bubbles which might collect in the

vertical tube.

Aseptic sampling

You will need to check the

pH regularly by sampling

and using pH paper.

You could use a pH meter

if one is available.

The pH of the mixture canbe altered by adding

acids oralkalis.

1.6 AS E 1 99 5


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invest igation

A G ITA TION

A ND M IX IN G

Testing your ideas

Set up some different ways ofproducing agitation using

plastic bottles. Some ideas are shown below.

Mixing the broth helps to:

1 bring fresh nutrients to

the growing microbe;

2 dissolve more oxygen;

3 disperse the heat

throughout the liquid.

Efficient agitation is

therefore important.

In large fermenters it is

often the controlling

process which costs

the most.

12Vmotor

and gearbox

end contains

an air-store

paddle

(model boat

propel/or)

airlift or

bubble lift

of liquid

inside the

central tube

air from

pump

ASE 1995

With accurate measurement it should be possible to see

which system is best for agitating and therefore dispersingnutrients and heat, as wellas dissolving oxygen.

Filleach bottle with the same volume ofdistilled ~ater

at a temperature of40C.

AS SOON AS THE AGITATION STARTS add to each

bottle a 1 % mass to volume ofglucose powder.

(This means 19ofglucose for every 100cm3 of liquid.)

Run the agitation for 5

minutes and then testsamples drawn from the top and bottom ofeach

bottle for concentration ofglucose.

This can be done using a CLINISTIXor a DIABAR 5000

(Boehringer Mannheim) strip.

You could also check for the concentration of a

dissolved dye, such aspotassium permanganate.

Another method is to use carbon powder and take

photographs.

Heat the contents and check the temperature

difference using either a thermometer or an

electric thermocouple.

1.7


25/41


26/41

Analysing the control situationThis section is designed to help you fully analyse the control aspects

of your fermenter. This will help you design and make a suitable fermenter .

.Follow the process below.

Identify the physical conditions that need to be controlled.

(Use your results ofyour research in Part 1.)

Each of these can be treated as a separate sub-system.

FOR EACH SUB-SYSTEM

Work out what type of control system is needed.

Drawa block diagram to show the components.

Identify which input/feedback and output transducer( s) could be used.

Use the Resource Activities to help you design suitable sub-systems.

(pages 2.5 to 2.15)

Look for ways to link sub-systems together.

For example, use the same power supply.

COMPLETE SYSTEM

Design your complete solution using block diagrams.

ASE 1995 2 1


27/41

Ae;sig nm enl~

DESIGNING

A ND M A K IN G

YOUR

FERMENTER

The research activities in

Part 1 should provide you

with enough information

to design a laboratory

batch fermenter.

Design requirements

Your fermenter needs to:

be easy to set up;

be safe to use;

be capable of

incorporating

monitoring and

control systems;

include systems for

heating, aeration and

agitation;

have a method for

monitoring the growth

of cells.

2. 2

B asic c om pon en ts yo u n ee d S ug ge stion s;

A suitable fermentation vessel 1-2 litre Kilner jar

and top or a 2-3 litre plastic

soft drink bottle;

.A heater and control circuit 12V aquarium or

immersion heater

or home brew kit heater;

Pump for air supply and 12V aquarium pump

control circuit

Tubing

A way of monitoring the output Infra red turbidity meter

Electrical supply

Air filters

Electrical meters multimeter

or 0-lSV voltmeter

and O-SA ammeter;

Al l co mp on ent s sh ou ld be easy to ster il i ze o r easy to replace.

ASE1995


28/41

The fermenter: monitoring and control

1 NUTRIENTSGrowth medium, made

out of waste chemicalsfrom other industries,mixed with water.

. . . . . . . . . . . . . . . . . . ~

. w g : ~ ~ t ~ : . : m ~ q J i J i! ! ~ . : :

6 The watery liquid left afterfermentation is over contains

new chemicals made bythe microorganism.

7 Chemicals separated andcollected after further processing.

ASE 1995

2 Microorganisms

grown in a largeflask ready to addto fermenter.

fermenter

~te~~c~ou~~ganism

---------

Watery l iquid passesthrough filter.

8 The microorganismcollected from the filtering

stage is dried before further

processing.

9 Further processing ofdried microorganisms

2.3


29/41

Matching the stages in your control system

There are four things to consider.

-'... .

.. . I

.. .

. . . .

~com pare~

. . . . . . . . . . . . . . .'.\ .: +6V

:. supply }

. . . . . . . . . . . . . . ( . . . . . . . . iiii

. ' , . . . . ' ' i \OV-f-E)ii ....,.

Does your power supply

provide the voltage

and current required

by the load?

2 Do al l of the s tag es in

your system operate at

the same voltage?

1

12Vsupply

+6V-HI

3 Does each stage in the systemprovide the current needed

by the next stage?

. r"'\.. .

. . . , . . . . .. . C ! J ( .

I .

. .ov -L..c +-1- -1:.)

~ . . . . . . . I '.... 1

..

..

'.1

.... . . . 1

. . ~ftt.

- 'I

. .

. .

.

.....

. . . ..

.. G I~

.. L.

. r. I,..... G-o-

. .

. .. .., i

. . . . . - ... ..i . ' ._ " " .. ~ , . . . . . , . . . .

.J .. '.J ....., ~-

You wi II often need a power or

transducer driver for the output

transducer.

The output may require a

separate power supply

controlled by a relay

or a high power driver.

~

I~

A ,/22'C12V / , - - 1 1 : 1 1 ]~ : 1 ! { -40W

heater

4 Does the output transducer match the load?

For example:

does the electrical heater

have sufficient power?

does the electric motor

have enough torque?

can a gearbox be used to

slow the motor output?

half hour later

You need tocarry out some research.

This may involve practical investigations and/or calculations.

2. 4 AS E 1 99 5


30/41

silicone

sealant

tightening

nut for probe

pipe

connector

fastening

nut

Fitting devices to the bottle

Holes can be made using a piece

of heated copper pipe of the

correct diameter.

Ports can be attached as shown

in the diagram.A large hole will be needed to

attach the inside nut. This will

need to be sealed later.

insertion point

for sensor probe

bottle

wall

rubber sealing

grommet

Resource

A c tivity 1

S OM E IDE A SFOR MAKING A

FERMENTER

VESSEL

The vessel must be:

possible to sterilize;

easy to attach sensors

and other devices to; easy to obtain.

Using a plastic bottle

A 2 or 3 litre plastic fizzy

drink bottle can be used

as a fermenter vessel.

Because they are easy to

obtain they can bereplaced regularly.

This solves some of the

problems of sterilization.

sampling

tube

Using a glass Jar

(Kilner type)

The advantages of using

a glass vessel is that they

can be autoclaved for

sterilization.

Sensors, heaters and other

attachments can be fitted

through the lid.

heaterair tube with

spinneret

ASE 1995 2. 5


31/41

1 < 8Bo u r c e

A c tiv i~ t~ y2

TEMPERATURECONTROL

Response time - how quickly

the system responds to

changes in the conditions

being controlled.

See SwT unit Investigating

and designing control systems.

The temperature control system requires feedback to

maintain a constant temperature.

Feedback control can be:

ON/OFF control; or proportional control.

You need to try out both methods tofind out which

provides the control you need. You should consider their

response time and lag in the system.

Doyou need tomaintain a precise temperature or willa

range of, say, 2D C be OK?

O N/O FF t em p e rat u r e c o n t ro l

T E M P E R A T U R E

T R A N S D U C E R

set

- . 0 - - - 1 S W IT CH ~

temperature ~ ,,"-, I ~COMPARISONELEMENT

A system using an electronics kit

P O W E R

DRIVER HEATER actual

temperature

temperature probe

e g o UNILAB

540-350

2. 6

12 volt supply

AS E 1 9 95


32/41

Proportional temperature control

TEMPERATURE

T R A N S D U C E R

@-.[:>--.set~+temperature

C O M PA R IS O N A M PL IF IE R

ELEMENT

A system using an electronics kit

P O W E R

DRIVER HEATER actual

temperature

temperature probe

eg o UNI LA B

540-350

12volt supply

heater

eg o UNI LA B

089-021

+6Tthermistor

ASE 1995

Notes

Any waterproofed 12 volt heater could be used.

The temperature probe could be made by

waterproofing a 4.7 kQ general purpose disc

thermistor (for example, RS 256-089) arranged in

a potential divider.

See the SwT unit Understanding Sensors for more details.

2. 7


33/41

R esou rceA c tiv ity :3

CON TROL L I N GPUMPS

Investigating a water pump

One problem with car windscreen washer pumps is that

they pump the water too quickly. Can the pump be

controlled using voltage or current control?

l iquids - a car windscreen

washer pump works well;

it operates on 1 2 volt.

A ir - a 12 volt aquarium

pump is suitable.

The pump requires a 12Vsupply and takes a high

current. You will need a high

power driver for the pump.

Use this circuit to

investigate how the rate

the pump works depends

on the applied voltage

and the current

supplied to the pump.

You will need the results

of this investigation to

design the control system

for your pump.

0-12V DC supply

0-15V

water out

You will need:

a variable 12V DC

supply;

0-5A ammeter;

0-15V voltmeter;

leads;

a car windscreen

washer pump with

pipes - you may need

to mount the pump;

a means of measuringthe volumeof water

pumped and a stop-

clock or stop- watch;

a water supply

and sink.

2. 8

Things to consider in this investigation

What are the variables?

Which will you control?

Which will you measure and record?

How will you measure the rate the pump works?

How will you record and present your data?

C O N T R OL LIN G T H E PU M P

You needto consider the following questions.

Do you need to turn the pump on and off?

What determines when the pump is turned on

and when it is turned off?

Do you want the pump to be on or off for a set time?

Do you want "the pump to turn on at set intervals

oftime?

Doyou need proportional control?

....................................................................................................................

ASE1995


34/41

l


35/41

CON TROL L I N G SOL EN OIDS

Veing Seneore

Setting a level

12 V DC power supply


1

1

1

1

1- _

1

1

I

I

1

1

1

1

or - - - - - - - - - - - -JI1

1

I

I

I

I

I

J

I

1

1

1

1

1

I

I

I

I

1 1

COMPARATOR

INPUTVOLTAGE

UNIT

set the level

using this

potentiom ete r

Veing Logic

.

....i..........

. ..

.

.

-' .. .

.

. . . .

lit'

..............................................................................................................................................................................

2.10 ASE 1995


36/41

UsinB a latch

Once the latch is activated it keeps the output on.



or .- - - - - - - - - - - ~I

I

I

I

I

I

I

1

I

I

1

1

I

I

I

1

1

1, - 1

I

I

I

I1- _

1

I

1

I

I

I

I

Imark

output

voltage

Proportional control -

usinB a Pulse Generator

When a solenoid is used to control a valve it is

usually done by opening and closing the valve

continuously. This can be done using an electrical

pulse like this:

--. . . . -t

1 t

2

The mark to epace or ON/OFF ratio

can be changed using an astable circuit.

The pulse can be obtained using a BBB ae;table circuit

+9V

BBB

1 8

2 7

:3 6

4 5

OUTPUT

O V

Approximate values of the HIGH time ( t, )

and the LOW time ( t2

) can be calculated using

these formulae:

Typical values

R,= 100kn R 2= 50kn C= 10JlF

t1 = (l 00 + 50) x 103

X lOx 10-6

= 1 .5 seconds

t2 = 50 x 103 X lOx 10-6 = 0.5 seconds

ASE 1995 2 11


37/41

Servo motors Servo motors provide slow speeds but high turning forces.They can be positioned very accurately and are often

used for position control where continuous feedback of

position is required.

If the motor is forced out of position, internal feedback

detects this and the motor wiI I try to return to the set

position. This makes them useful for operating valves.

Servo motors require a 'pulsed signal'. The duration of

the signal controls the amount of movement. This signal

is provided by a 'servo motor driver'.

You can investigate the action of a servo motor

using a suitable electronic systems kit.

BATTERY ANY NON-C ON NE CT OR S EN SIN G IN VE RT IN G

UNIT AM PLIFIER

servo motor

Connect the following boards together:

INPUT

Any sensor - the light sensor works well

PROCESS

The servo motor driver requires an

analogue input voltage. Use an op-amp

non-inverting amplifier to do this.

OUTPUTServo motor driver and motor

Change the levelof the input - in this

case the light level. What happens?

What is the effect of changing the

potentiometer on the sensor or

the op-amp?

A range ofattachments is available with

the servo motor. How could these beused with the motor to operate a valve?

.................................................................................................................................................................................

2 . 12 AS E 1 99 5


38/41

Resource

A c tiv ity 5

A G IT A TIO N

R esou rceA c tiv ity 6

p H C O N T R O L

The block diagram of the pH

control system looks like this.

The contents of your fermenter will need continuous

agitation and mixing. Two practical ways of achieving

this are:

using a mechanical stirrer driven

by an electric motor;

using the air supply to your

fermenter to spin an agitator.

Use the results ofyour earlier investigations to determine

which method is most suitable for your fermenter.

You should consider whether:

you need to control the agitator;

for example, its speed, switch it on and off?

the system needs to be sterilized.

You may consider controlling the pH level in your

fermenter. This can be done by regular sampling and the

addition of a suitable solution but could be done using

feedback control.

You will need the results of the investigations you did

earlier to determine the optimum pH. In most cases the

medium will tend to become more acidic requiring the

addition of an alkaline solution.

p HTRANSDUCER

ASE 1995

set

- - - . 0 - - - - 1 S WITCH I " " ' " -V A t J E ~ : ~ M P

pH leve l ~ ~

This is an example of ON/OFF feedback control.

actual

p H

2 13


39/41

MONITORINGA N D

MEASURING

THE OUTPUT

One way of automatically monitoring growth in the

fermenter is to use a turbidimeter which can be easily

made. This removes the need to keep taking samples.

It uses a light or infra red (lR) beam. This is passed

through the contents of the fermenter. As more product

is produced the contents become cloudier.

Your system will need to provide a display.

The display needs tobe calibrated.

Do you need or want touse a computer for data logging?

Your sub-system for monitoring the output should have

the following components.

LIGHTorlR

SOURCE

TRANSDUCER SIGNAL

PROCESSING

DISPLAY and/orRECORDING

(DATA LOGGING)

2 14

changes in light level

indicate density of

medium - hence, growth

L i g h t or IR ?

In both cases you need:

a source of light or IR;

a detector;

a circuit to process the signal and give an output.

This needs to be calibrated.

Use the information on the next page to set up an

investigation to compare the use of visible light and IRin a turbidity meter.

......................................................................................................................

ASE 1995


40/41

+3V

O V

OUTPUT

(meter)

O v

This can be

changed to

give the output

range required.

This circuit

provides a

linear output.

ORP 12

R - typically 1 M Q

200kQ

-ve

+ve

-ve

DETECTOR - Photodiode

DETECTOR - LDR

V is i b le L i g h t

SOURCE

6-12V lamp

with shield

The detector unit will

need to be shielded from

sunlight or other external

light sources.

You need to try them on

your fermenter or a

mockup.

The source and detector

need to be correctly

aligned.

In f r a Red

SOURCEIR emitter

ego RS635-296

RAPID 58-0110

DETECTOR - IR sensorego RS635-303, RAPID 58-0115

Range about 1m

+6V

58-0110

(RAPID)

O V

ASE1995 2 15


41/41

The Science with Technology ProjectScience withTechnology

The Science with Technology project provides:

Curriculum materials

for the 14 to 19 age range

Science, D&T and IT

GCSE and A/AS level courses

GNVQ

Support for teachers

using the curriculum materials

strategies for linking work in science and technology

in-service support .

. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . .

I.~:""Design and Technology AssociationDATA is the recognised professional association representing all those involved in Design &

Technology Education. It promotes design and technology and disseminates good practice,

through a wide range of activities including seminars, workshops, INSET and exhibitions. DATA

has a growing organisation with regional groups which aim to share expertise and consider

curriculum and policy issues.

DATA members receive two free journals, Primary DATA and Design & Technology Teaching, a

newsletter and other occasional publications.

Full details of DATA membership are available from the address below:

DATA16 Wellesbourne House, Walton Road,

Warwickshire, CV35 9JB.

Tel: 01789470007 Fax: 01789841955

. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . ..

The Association for Science Education

Association for Science Education membership is open to:

teachers, advisers, technicians, industrialists

and others contributing to science education .

promote, support, and develop science education

from pre-school through to tertiary levels and beyond.

ASE encourages, initiates, promotes and publishes curriculum developm ent projects in science.

ASE publishes avariety of journals, newsletters and occasional publications.

4237-control in action, design a fermanter

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