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ABE 482Environmental

Engineering in Biosystems

September 26

Lecture 10

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Today

Wrap up anaerobic digestion

Experimental design

Lab 2

Question for next class

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Questions so far

Explain why anaerobic digestion is a neutral

GHG method of generating energy Why are anaerobic digesters not good for

disposing of wood waste?

Name a few factors that affect biogasproduction in anaerobic digesters (ratio orquantity)

What are the 3 anaerobic digester outputs

we must consider when doing a massbalance?

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Digester Heat Balance

Balance between energy producedfrom biogas and energy required tomaintain mesophilic temperatures

Other energy requirements of

anaerobic digester? Stirring, pumping, etc.

Energy produced depends on OMR, so

for feedstocks with lower ODM,energy produced will be lower

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Example 5Digester heat balance

If the 7,500 m3 per day of biogas is used to

produce hot water only, what percentage ofthis hot water energy is required fordigester heating?

What percentage of the hot water energyfrom a CHP unit is required for digesterheating?

What percentage of energy produced (hotwater only) is required for digester heatingduring a Saskatchewan winter?

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12 weeks3 weeks digestion, plus

5 weeks composting

Process time required to produce

mature compost

Nil100 150 m3

/MgBiogas production

Energy demandEnergy surplusEnergy balance

100%20%Odours

100%50%Space requirement (footprint)

CompostingAnaerobic Digestion

Comparison Table From: Introduction to Anaerobic Digestion,Wolfgang Muller and Axel Huttner, ORA -Organic Resource Agency Ltd., Malvern Hills Science Park, Geraldine Road, Malvern, Worcestershire WR143SZ, and IGW Ingenieurgemeinschaft Witzenhausen Fricke & Turk, and GmbH, Bischhuser Aue 12, D-37213 Witzenhausen, Germany. Presented at the Biowaste: Digesting the Alternatives Seminar, April 2005,UK.

A Comparison of Anaerobic Digestion and Composting

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References

Wikipedia, 2007. Anaerobic Digestion. Online:

http://en.wikipedia.org/wiki/Anaerobic_digestionAccessed: October 25, 2007.

Class notes for ChEng 882. 2006. University ofSaskatchewan.

Kiely, G. 1997. Environmental Engineering. McGrawHill:USA.

Chesshire, M. 2005. Process Calculations for Full-Scale Digesters. Biogas from Energy Crops andAgrowastes. 15th Jyvskyl Summer School:Cropgen.

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Experimental Design

You have been asked to determinethe biogas production potential ofseveral types of feedstock

How do you do it?

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Feedstock biogas production

0.952.11.5

Feedstock 3Feedstock 2Feedstock 1

L of biogas/L of feedstock per day

2.33.61.9

0.81.41.4

1.90.81.7

2.13.41.8

1.70.81.2

1.83.91.1

0.952.11.5

Feedstock3

Feedstock2

Feedstock1

L of biogas/L of feedstock per day

0.571.340.30stdev

1.652.291.51average

Replication allows the degree of

variability in the data to be

assessed

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Feedstock biogas production

Biogas production from various feedstocks

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Biogas production (L of biogas/L of feedstock per day)

Feedstock 1Feedstock 2

Feedstock 3

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Experimental Design

You have been asked to optimize theoperating parameters to improvebiogas production from a specificfeedstock

How do you do it?

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Biogas production by varyingparameters

4.4955

3.67401.1435Feedstock 3

2.41855

2.41245

2.4730Feedstock 2

0.71550

2.11040

1.8535Feedstock 1L of biogas/L of feedstock per dayDM ContentTemperature

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Factorial Experimental Design

When several factors are of interest in an experiment,

a factorial experiment should be used In each complete replicate of the experiment, all

possible combinations of the levels of the factors areinvestigated

Each feedstock should be digested at each

temperature and each DM content for validcomparisons 3 feedstocks x 3 DM contents x 3 temperatures equals

27 experiments

The effect of each factor can then be separatelyassessed

Can also investigate the interaction of effects (butonly with a factorial experimental design)

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1.7104012.35401

1.93401

0.7510301

2.153012.13301

1.510251

2.15251

1.83251L of biogas/L of feedstock per dayDM ContentTemperatureFeedstock

Biogas production by varyingparameters

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Factorial Experimental Design

Effect of new treatments or factorsshould always be compared to acontrol

Treatment = new coating for o-rings

Effect = increase tensile strength of o-rings at lower temperatures

Experimental design

Measure the tensile strength of untreatedand treated o-rings at 3 temperatures

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Factorial Experimental Design

Are the results significant?

Cannot make that assessment without a measure ofthe variability of data

1.810% DM

2.65% DM

2.33% DM

2.440 degrees

2.430 degrees

2.025 degrees

2.1Feedstock 3

2.9Feedstock 2

1.8Feedstock 1

Average

0.85

0.62

0.69

0.75

1.00

0.49

0.79

0.62

0.47

StdDev

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Factorial Experimental Design

How many replicates?

Depends on how powerful you want yourexperiment to be

Are the results significant?

Can crunch the numbers by hand, butstatistical software is very useful

SPSS in computer labs

Minitab more user friendly

Excel will work in a pinch (if you know whatyoure doing)

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Lab 2 Experimental Design

We have 12 reactors to play with

Lets go with 2 replicates so we have6 treatment combinations to work

with 3 feedstocks, 2 DM contents?

1 feedstock, 2 DM contents, 3 pHs?

? What will you measure?

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Question for next class

Calculate the $ value of the electricity produced if all theMSW waste and manure waste produced in Canada eachyear was anaerobically digested. 25 million wet tonnes of MSW/year 132 million wet tonnes of manure/year

30% dairy cow 30% beef cow

20% pig 20% other

Assume digester runs 365 days a year, 24 hours a day Assume you can sell electrical energy for 14 cents/kW-hr Assume you can convert methane to electricity with an

efficiency of 32%

How many Canadians will this serve?

Use: Table 1 from lecture, ASABE standards for manurecomposition, internet for electricity consumption of Canadians.

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Next Day

Waste to energy calculation anddiscussion