Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo

8/10/2019 Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo

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E N G R . P R O F E S S O R I . N . I T O D O

D E A N , C O L L E G E O F E N G I N E E R I N G

U N I V E R S I T Y O F A G R I C U L T U R E

M A K U R D I , N I G E R I A

E - M A I L : D R I T O D O @ Y A H O O . C O M

Biogas Production in Rural

Communities

Sensitization and Awareness Forum (SAF) on Renewable EnergyInitiatives in Edo State, Barden-Barden Hotel,

Benin, 25thAugust, 2009
mailto:[email protected]:[email protected]


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Outline2

Introduction Feedstocks Production

Factors affecting production Methods of improving production

Economics Technologies

Types of plants Construction of plant

Preconstruction considerations Construction

Operation Output and pressure

Maintenance Safety issues

Prof. I. N. Itodo


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Introduction3

Biogas is produced when biomass is subjected tobiological gasification.

Nigerias animal waste resource base is estimated to

be 61 million tonnes/year Nigerias crop residue resource base is estimated to

be 83 million tonnes/year

Prof. I. N. Itodo


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Prof. I. N. Itodo 4

Energy source CapacityHydropower, large scale 10,000

Hydropower, small scale 734 MW

Fuelwood 13,071,464 ha (forest land1981)

Animal waste 61 million tonnes/year

Crop residue 83 million tonnes/year

Solar radiation 3.5-7.0 kWh/m2-day

Wind 2.4 m/s (annual average)

Nigerias Renewable Resources

ECN (2005). Renewable Energy Resources, Technology and Markets. Renewable EnergyMaster Plan. Energy Commission of Nigeria, Abuja. Pp.3-4


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Introduction

Prof. I. N. Itodo

5

Biogas is a methane-rich gas produced from theanaerobic digestion of organic materials.

It is a high-grade fuel of 22 MJ/m3 (15.6MJ/kg).

The density of biogas is 1.2 kg/l at atmosphericpressure, which makes it denser than air.

The biomass materials are held in a digester orreactor.


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Introduction6

The gas is produced from a three-phase process namely,hydrolysis, acid-forming and methane-forming phases.

It is a biological-engineering process in which a complex set ofenvironmentally sensitive micro-organisms are involved.

The gas is typically composed of 70% methane, 30% carbondioxide, 1-10% hydrogen, 1-3% nitrogen, 0.1% oxygen andcarbon monoxide and traces of hydrogen sulphide.

Factors affecting the production of this gas includetemperature, pH, total solids concentration of the slurry,

digester type and design, presence of toxic ingredients in thewaste stream and the carbon to nitrogen ratio of the slurry.

Prof. I. N. Itodo


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Introduction7

Biogas is used for cooking and heating and as such can beused in unit operations like frying and cold storage ofagricultural produces such as the refrigeration of fruitand vegetables.

Worldwide installed power capacity of biomass for grid-connected power generation and estimated annualenergy generation in 2008 is 4 GW and 227-357 TWh

Bubbling the gas through lime solution purifies it byremoving the carbon dioxide thereby improving itsheating value to about 56 MJ/m3.

The hydrogen sulphide is removed by bubbling the gasthrough sawdust impregnated with iron filling in amixture of 1:1.

Prof. I. N. Itodo


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Introduction8

The advantages of this technology are:

It is also a waste management technique because theanaerobic treatment process eliminates the harmfulmicro-organisms. About 85% of the pathogens contained

in the waste are killed by the anaerobic digestion process. The digested slurry is relatively odourless and attracts

much fewer flies than the fresh slurry.

Anaerobic digestion has also been used for sewage

treatment. It is a cheap source of energy because the feedstock is

usually waste materials.

Prof. I. N. Itodo


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Introduction9

The technology ensures energy independence as aunit can meet the needs of a family or community.

The digested slurry is a good fertilizer. It is claimed

that its value as fertilizer could double crop yield. The treated effluent from the anaerobic digestion

process is a good animal feed when treated andmixed with molasses and grains.

Prof. I. N. Itodo


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Introduction10

The disadvantages of the technology are:

Gas yield from the digester may not be steady whichtherefore makes it unreliable thereby necessitating

storage. It is a low-pressure gas production system and as

such cannot be bottled for use outside the site of production thereby restricting the technology only to

the site of production.

Prof. I. N. Itodo


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Introduction11

To date the main interest in the third world in biogastechnology has come from countries of Asia and thePacific region.

Despite the numerous advantages of using biogas

technology as a source of energy and a source of nitrogen-rich fertilizer, it has made only little impact in

Africa and Latin America.

Attitude to biogas technology varies from region toregion. While the west often sees new and renewableenergy sources as morally superior, green or soft orappropriate, the third world suspects that they aresecond-class technology.

Prof. I. N. Itodo


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Introduction12

The Sokoto Energy Research Centre has constructed andoperated more than twenty one (21) biogas plants of 10 20 m3 capacity across the country using differentfeedstocks such as cow dung, human excreta, piggery andpoultry wastes.

The Raw Materials Research and Development Councilfunded the construction of a float-drum type of biogasplant at the University of Agriculture, Makurdi in 1999.

The United Nations Development Programme (UNDP)has successfully introduced the floating drum, plastic

balloon and other types of biogas plants to Yobe, Kanoand Jigawa states under the African 2000 Low Technology Biogas System.

Prof. I. N. Itodo


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Introduction13

The success story of the use of biogas in Nigeria isillustrated by its use in Kwachiri community where afamily of forty (40) have been using it for their dailycooking needs since 2003.

The United Nations Development Programme hasalso introduced this technology to some abattoirs insome Northern states of Nigeria.

Prof. I. N. Itodo


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14

Fig. 1: Biogas plant at the University of Agriculture, Makurdiand the burning flame from the plant

Prof. I. N. Itodo


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Feedstocks15

Animal wastes and plant residues are excellentfeedstock for biogas production because they areorganic compounds that contain carbon andnitrogen in the required proportion.

Animal waste such as poultry waste, cattle waste,piggery waste and human excreta are used in biogasproduction.

Crop residues and crops such as water hyacinth havealso successfully been used as feedstock in biogasproduction.

Prof. I. N. Itodo


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Prof. I. N. Itodo 16

Livestock Manureproduced(milliontonnes)

Populationbased onFMA, 1997(million)

Manureproduced2001calculated(milliontonnes)

Cattle 170.4 21 197.6

Sheep 13 38.5 15.1

Goat 21.1 62.4 24.5

Pig 13.2 9.6 15.3

Poultry 28.1 42.9 32.6Total 245.9 285.1

Calculated manure production of Nigerias livestock

ECN (2005). Renewable Energy Resources, Technology and Markets. Renewable EnergyMaster Plan. Energy Commission of Nigeria, Abuja. Pp.3-4


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Production17

Biogas is produced from a three-phase processnamely the hydrolysis, acid-forming and methane-forming phases.

In the hydrolysis phase, extra cellular enzymessecreted by acidogens break down the complexorganic material into simple, soluble molecules.

Prof. I. N. Itodo


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Production

Prof. I. N. Itodo

18

These molecules are broken down into volatile fattyacids (e.g. propionic and butyric acids), carbondioxide, ammonia and hydrogen by acidogens in theacid-forming phase.

In the methane-forming phase, methanogens ormethane-formers convert the VFA into methane,carbon dioxide, carbon monoxide, nitrogen and

hydrogen sulphide. In this phase too, a synthesis ofcarbon dioxide and hydrogen takes place to alsoform methane and water.


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19

Hydrolysis phase

Acid-forming phase

Methane-formingphase

Simple soluble molecules

CH4,

CO2, N, H

2, H

2S

VFA,NH

3,CO

2,H

2,etc

CO2+4H

2= CH

4+2H

2O

Feedstock (e.g. poultry waste) + water

Fig.2: Flow diagram of biogas production process

Prof. I. N. Itodo

F ff i bi d i


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Factors affecting biogas production

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Temperature

Total solids concentration (TS)

Retention time

pH Loading rate

Carbon-to-nitrogen ratio of slurry

Toxicity

Prof. I. N. Itodo


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Temperature21

Temperature is an important parameter that affectsbiogas production.

This is because it affects the enzymatic activities of

the micro-organism responsible for thebioconversion of substrates into gas.

Biogas can be produced at the psychophilic (below20c), mesophilic (20c-40c) and thermophilic

(40c-65c) temperatures. Table 1 is the advantages and disadvantages of

producing gas at each of these temperatures.

Prof. I. N. Itodo


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22

Temperature

range

Advantage(s) Disadvantage(s)

Psychophilic None 1. Bioconversion is

slow and incomplete

2. Longer detention

time is required

3. Heating of the

digester is required

Mesophilic This temperature

corresponds to the

ambient temperature of

the Tropics and as such

no heating is required

thus reducing cost of

production

Longer detention time

may be required to

enable complete

conversion of the

available carbon

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Thermophilic 1. Higher rate of gas

production

2. Allows heavier organic

loading

3. Lower detention time4. Enables the use of

comparatively smaller

size digesters

5. Digestion is much

more sanitary than

digestion at the other

temperatures because

of the few pathogens

that can survive at this

temperature

6. Mechanical transport

and handling of the

digester is easier

because the slurry is

less viscous

Digestion is easily

upset at this

temperature

Prof. I. N. Itodo

T t l lid t ti f l (TS)


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Total solids concentration of slurry (TS)

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Slurry is diluted by the addition of liquid and concentrated by theaddition of slurry solids.

Slurries of feedstock used in the anaerobic digestion process toproduce biogas are usually classified as low (less than 10% TS) andhigh (TS greater than 20%).

Low TS Slurries of low TS are easier to handle by pumps and pipe works

compared to those of high TS. If the slurry is too thin, the solid matter separates and falls to the

bottom instead of remaining in suspension resulting in reduced gasyield.

High TS If the slurry is too thick, the biogas produced is trapped within the

slurry and rises to the surface with great difficulty resulting inreduced gas yield.

Prof. I. N. Itodo

R t ti ti


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Retention time

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Generally, 30 days is considered as a minimum timeframe for optimum bacterial decomposition to takeplace to produce biogas and destroy the toxicpathogens found in waste.

Prof. I. N. Itodo

H


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pH

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The pH value of the slurry in the digester is animportant indicator of methanogenic performance.In the absence of any other indicator, pH value alonehas been used to check the digester environment.

Gas will be produced if the pH is between 6.6 and7.6. Gas production is highest when the pH is

between 7.0 and 7.2.

Beyond this pH limits, digestion can proceed butwith less efficiency.

Prof. I. N. Itodo

Loading rate


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Loading rate

27

The quantity of waste that is fed into a digester dependson the capacity of the digester, the temperature at whichdigestion is taking place, the retention time and theefficiency of bioconversion of the waste into biogas.

Increasing the loading rate after the optimum valueincreases the TS concentration of the slurry, whichresults in an accumulation of some inhibitory compounds that reduce the rate of gas yield.

In a simple biogas plant, 1.5 kg/m3/day is already quite ahigh loading rate. Temperature controlled andmechanically stirred large scale plants can be loaded atabout 5 kg/m3/day.

Prof. I. N. Itodo

Carbon to Nitrogen ratio of slurry


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Carbon- to-Nitrogen ratio of slurry

28

The microbial population involved in anaerobic digestionrequires sufficient nutrient to grow and multiply. Each speciesrequire both a source of carbon and nitrogen.

If there is an insufficient quantity of nitrogen present, thebacteria will be unable to produce the enzymes which are

needed to utilize the carbon. If there is too much nitrogen, particularly in the form of

ammonia, it can inhibit the growth of bacteria. An optimum ratio of Carbon to Nitrogen (C: N) of

between 20:1 and 30:1 is recommended for optimummethanogenic performance.

A deficiency in the carbon content of animal manure used foranaerobic digestion can be corrected by the addition of plant

wastes, which are high in carbon content.

Prof. I. N. Itodo

Toxicity


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Toxicity

29

Many compounds can be toxic to methanogens if presentin sufficient concentration in digesters although some areneeded, they quickly become inhibitory. Sources of toxicity in biogas plants are:

The various salts, heavy metals such as Copper, Zinc and

Nikel present in the waste, antibiotics in the feed foranimals that produce the waste and ammoniaconcentrations of the slurry in excess of 3000 mg/l.

Formation of aromatics such as phenol, P-cresol, ethylphenol, indole and skatole during the microbial

degradation of proteins contained in the waste being fedinto the digester.

High concentrations of volatile fatty acids in the digester.

Prof. I. N. Itodo

M th d f i i bi d ti


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Methods of improving biogas production

30

The anaerobic digestion process can be improved bythe pre-treatment of organic wastes, the mixing ofdifferent waste types, the addition of chemicals anduse of media materials among others.

The addition of certain chemicals such as nickelaccelerates and increases gas yield.

The use of mixed substrate. E.g. 25% poultry manureand 75% brewery waste water.

Pre-treatment of the feedstock such as milling todiminish the particle size, swelling in an alkalinesolution and heating of the feedstock.

Prof. I. N. Itodo


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Methods of improving biogas production

31

Re-concentrating flushed waste (waste to whichfresh waste has been added to increase its TSconcentration).

Stirring or mixing of the digester content. Two-phase anaerobic digestion of waste. The two-

phase concept consists of first digesting the waste inan acid phase. The gaseous and liquid products of

this phase are separately conveyed into separatemethane fermenters to enable biogas production.

Prof. I. N. Itodo

Economics of Biogas Production


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Economics of Biogas Production

32

A biogas plant is economically viable if:

1 m3 of biogas is produced from 1m3 of digestervolume

18-20 m3

of biogas is produced from 1m3

of feedstock

Prof. I. N. Itodo


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Fig. 3: Floating-drum Plant

Prof. I. N. Itodo


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Fig. 4: Fixed dome plant

Prof. I. N. Itodo

Construction of Biogas Plants


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Construction of Biogas Plants

36

Preconstruction consideration

Availability of feedstock to meet the daily need ofmanure to be fed into the digester

Location Sizing of plant

Material of construction

Tools

Prof. I. N. Itodo


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Availability of feedstock37

The amount of manure fed daily into a digester isdetermined by the volume of the digester itself,divided over a period of 30-40 days.

Thirty days is chosen as a minimum time frame foroptimum bacterial decomposition to take place toproduce biogas and destroy many of the toxic

pathogens found in wastes.

Prof. I. N. Itodo


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Location38

The digester pit should not be dug within 13 meters of a drinkingwater well or spring.

If the water table is reached during digging, it will be necessary tocement the inside of the digester pit although this increases the cost.

The digester should be located near the source of the feedstock sothat excessive time is not spent transporting the manure.

Be sure that there is enough space to construct the digester. Be sure that water is readily available for mixing with the manure. Provision should be made for slurry storage. Select a site that is open and exposed to the sun. Locate the gas plant near the point of gas consumption this tends to

reduce cost and pressure losses in piping the gas.

Prof. I. N. Itodo

Sizing of Biogas Plant


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Sizing of Biogas Plant

39

How much gas can be expected per day from theavailable feedstock?o The available feedstock is from six (6) cattle

o Each cattle produces an average of 10 kg of waste per day

o 1 kg of fresh manure yields 0.05 m3 of biogas

o The animals will, therefore, produce about 3.0 m3 of gas

o Therefore, the size of the plant will be 3 m3.

How much gas is required to meet the needs of the user?o Six (6) persons are required to use the plant to meet their cooking

and lighting needso Each person requires an average of 0.6 m3 of gas for lighting and

cooking per day

o Therefore, six (6) persons will require 3.6 m3 of gas per day

Prof. I. N. Itodo


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Sizing of biogas plant40

What will be the volume of the fermentation tank orpit needed to handle the required mixture of manureand water?o The ratio of manure to water is 1: 1

o 6 cattle will give 60 kg/manure + 60 kg/water = 120 kg

o The total input per day will be 120 kg

o The input for six weeks (42 days) will be 120 kg x 42 days =5040 kg

o The rule of the thumb is 1000 kg = 1 m3

o Therefore, 5040 kg is 5.4 m3

o The minimum capacity of the fermentation well is 5.4 m3

Prof. I. N. Itodo


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What size and shape of fermentation tank or pit isrequired?o The shape of the tank is determined by the soil, subsoil and

water table. The example illustrated assumes that the earth is

not too hard to dig out and that the water table is low even inthe rainy season.

o An approximate size for the 6 m3 tank would be a diameter of1.5 m. Therefore, the depth required is 2.3 m.

Prof. I. N. Itodo


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What is the volume of the gas storage cap?o The drum is made to hold between 60% to 70% of the total

daily gas production

o Therefore, the volume of the gas holder will be 70% x 4 m3 =

2.8 m3

o If the gas holder is of diameter 1.5 m, the height of the gasholder will be 1.1 m

Prof. I. N. Itodo

Materials of Construction


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Materials of Construction

43

The materials required for construction of the 4 m3 plantare:

Baked bricks, approximately 4000

Cement, foundation and wall covering, 28 -40 bags of

(50 kg) cement Sand 12 m3

Copper wire screen (25 cm x 25 cm)

Rubber or plastic hose

Gas outlet pipe 3 cm in diameter Mild steel sheeting 0.32 mm (30 gauge) to 1.63 mm (16

gauge) -9 m

Prof. I. N. Itodo

Tools


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Tools

44

Some of the tools required for construction are:

Welding equipment for gas cap construction, pipefittings, etc

Shovels for concrete and masonry works Metal saw and blades for cutting steel

Prof. I. N. Itodo


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Construction45

Foundation and Walls Dig a pit 1.5 m in diameter to a depth of 2.5 m Line the floor and walls of the pit with baked brick bound

with lime mortar or clay.

Make a ledge or cornice at two-thirds the height of the pitfrom the bottom. The ledge should be some 15 cm widefor the gas cap to rest on when empty.

Extend the brickworks 30-40 cm above the ground, tobring the total depth of the pit to approximately 3 m.

Build the ledge up to the height of the brickwork extension above the ground. This forms the space to befilled with water in which the gas holder with sit in andfloat.

Prof. I. N. Itodo


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46

Fig. 5: Construction of biogas plant at the University of Agriculture, Makurdi

Prof. I. N. Itodo


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Foundation and walls47

Put in place the input and output piping for theslurry from 20 cm clay pipe. Place the input pipe 70cm above the bottom of the pit.

Place the output pipe 40 cm above the bottom of thepit opposite the input pipe and end at ground level.

Put copper screening of 0.5 cm holes at the mouth ofthe input and output pipes to exclude foreign matter

from the pit

Prof. I. N. Itodo

Gas Cap Drum


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Gas Cap Drum

48

Fabricate the gas cap from mild steel sheeting of 1.63 mm (16gauge)

Make the height of the drum 1/3 the depth of the pit

Make the diameter of the drum 10 cm less than that of the pit

Cut a 3 cm hole on the cap Fix a rubber hose on the 3 cm hole.

Paint the inside and outside of the drum with a coat of paintor tar

Ensure that the drum is air tight by filling with water to check

for leakage Attach handles to either side of the drum for lifting the drum

during maintenance.

Prof. I. N. Itodo

Mixing and Effluent Tanks


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g a d ue a s

49

Build a mixing pit to be placed near the outsideopening of the inlet pipe

Also, provide a pit at the outlet to catch the effluent.

Make provision for drying the effluent when theinfluent goes into full operation

Prof. I. N. Itodo


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50

Plant

size

(m3)

No.

of

animals

Water: waste

Per

day (1:1)

(Kg)

Vol. of

well

for

40 days

digestion

(m3)

No.

of

bricks

No. of

cement

Bags

(50 kg)

Qty.

of

Sand

(m3)

Gas

Prod.

Per day

(m3)

Qty. of

fertilizer

per

day

(kg)

No. of

persons

served

(cooking

+

lighting)

2 4 80 3.5 2800 22 9 2 4-8 4-6

3 6 120 5 3200 25 12 3 6-12 6-8

4 8 160 7 4000 28 12 4 8-16 9-11

5 10 200 8.5 4000 30 14 5 10-20 12-15

7.5 15 300 13 5200 32 16 7.5 15-30 15-20

10 20 400 17 6400 35 18 10 20-40 20-30

Table 2: Measurement for a number of biogas plants

Prof. I. N. Itodo


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Operation51

4 m3 (4000 liters) of manure are necessary for the start-up of the newdigester. In addition, approximately 20 kg of seeder is required to get the

bacteriological process started. The seeder can come from severalsources.

Put the manure and seeder and an equal amount of water into the mixingpit. Stir it into thick liquid called slurry. A good slurry is one in which themanure is broken up thoroughly to make a smooth, even mixture havingthe consistency of a thin cream. 50 kg of fresh manure is mixed with 50 kgof water and the mixture added to the digester every day.

It can take 4 to 6 weeks from the time the digester is fully loaded beforeenough gas is produced and the gas plant becomes fully operational.

The first drum full of the gas will probably contain so much carbon dioxide

that it will not burn. On the other hand, it may contain methane and air inthe right proportion to explode if ignited.

Prof. I. N. Itodo

Output and Pressure


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p

52

The pressure output from the floating drum plantcan be regulated by the addition and reduction of

weight on the gas holder to increase the pressure ofgas flow from the plant.

This also affects the volume delivered at theappliance.

Prof. I. N. Itodo


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Maintenance53

Common problems encountered when operatingbiogas plants and the attendant maintenancepractices are provided in table 3.

Prof. I. N. Itodo


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54

s/no. Problem Possible reason(s) Solution

1 Gas drum will not rise Scum formation No gas formed

Leakage in the system

Patience. Thesystem needs

about 4 to 6 weeks

to get properly

started

Stir the digester

Dilute the digester

by adding some

water

Ensure that there is

no leakage in the

system

2 No gas at the appliance No gas formed

Not enough pressure inthe system to force the gas

from the digester to the

appliance

Gas leakage

Consider solution

#1 Adjust the inlet jet

of the appliance

Prof. I. N. Itodo


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55

3 No gas formed Toxicity in digester

Inappropriate waste-

water mixture

Flush out the

content of the

digester with water

Add more waste to

the digester

4 Inadequate quantity of

gas being formed

Inappropriate waste-

water ratio

Slurry too thick or toothin

Few population of

required microorganisms

Add a seeder from

another plant or a

sewage to thedigester

Add more waste to

the digester

5 Flame dies off too quickly

at the appliance

Pressure from the

digester too high

Adjust the inlet jet

of the appliance

Reduce the weighton the gas holder

Prof. I. N. Itodo


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Safety56

Spontaneous ignition of methane occurs when 4 -15% of the gas mixes with air and it has an explosivepressure of between 90 and 104 psi.

Do not attempt to light the first drumful of gas.Empty the gas contained and let the drum fill again

because it may contain methane and air in the rightproportion to explode when ignited.

Prof. I. N. Itodo


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By-products57

Fertilizer The sludge that is produced from the anaerobic

digestion process is a better fertilizer and soil conditionerthan either composted or fresh manure. This is because:

a. The liquid effluent contains many elements essential toplant life. It contains nitrogen, phosphorous, potassiumand small amounts of metallic salts that areindispensable for plant growth.

b. When the sludge is applied on the soil as fertilizer, itsnitrogen is converted to ammonium ions (NH4

+), which

fix themselves to the negative charged clay particles ofthe soil, thereby making nitrogen available to theplants.

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Biomass Feedstock Efficiency and Biogas Production in Rural Communities. by Prof. i.n Itodo

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