THE POTENTIAL OF BIOGAS FOR MEETING ENERGY REQUIREMENTS AT MEETING ENERGY REQUIREMENTS AT

HOUSEHOLDS AND INSTITUTIONS

Dr. Charles B. NIWAGABA, PhDDepartment of Civil & Environmental Engineering

C ll f E i i D i A t d T h lCollege of Engineering, Design, Art and Technology(CEDAT)

Makerere Universitykwww.mak.ac.ug

UGANDA INSTITUTION OF PROFESSIONAL ENGINEERS (UIPE)

17TH NATIONAL TECHNOLOGY CONFERENCE (NTC 2012)17TH NATIONAL TECHNOLOGY CONFERENCE (NTC 2012)

STRATEGIC POSITIONING FOR POSITIVE TRANSFORMATION OF SOCIETY

GOLF COURSE HOTEL, KAMPALA 14-15 JUNE 2012

ORDER OF THE PRESENTATIONWhy biogas?What is biogas Origin of biogas, as well as present interestg g g , p

in AD process and the future of AD process?How is biogas formed?How does the energy content of biogas compare with

common fuels for cooking?What are health social and environmental benefits ofWhat are health, social and environmental benefits of

biogas?The biogas process spying on nature!Some examples of applications of biogas

WHY BIOGAS?Globally, indoor air pollution from the burning of biomass in

poorly functioning stoves is a major contributor to indoor airpollution.p

It causes 1.6 million deaths due to pneumonia, chronicrespiratory diseases and lung cancer, with the overall diseaseburden (in DALYS) exceeding the burden from outdoor airpollution five-fold.p

In high-mortality developing countries, indoor smokecontributes 3.7% of the overall disease burden.

WHY BIOGAS?Imagine, if this cooking

was done indoors???was done indoors???Poor indoor air quality

has been linked to: low-birth weight, increased infant and

perinatal mortality, pulmonary tuberculosis, nasopharyngeal and

laryngeal cancer andy ge c ce dcataract.

Open cooking in Katwe, Base Slum. Photo by Niwagaba, 10th June 2012

WHY BIOGAS? Approximately half of the worlds population and 90% of rural households in Approximately half of the worlds population and 90% of rural households in

developing countries rely on unprocessed biomass fuels in the form of wood, dung orcrop residues, which are burnt indoors in open fires or poorly functioning stoves.

Consequently, there are high levels of pollution, to which those responsible forcooking (especially the women and the girl children) and the young children, are themost heavily exposed.

The ferrying of trees for fire wood causes deforestation. Also, women are largely responsible for fire wood collection, often over long

distances in search for firewood, where they are can be raped!

Hence biogas, which can be produced in a home could offer a solution to thegrowing problem of firewood!

WHAT IS A BIOGAS?It is a gas that consists of several gases

mainly methane (~ 55 70%) and carbonmainly methane (~ 55 70%) and carbon dioxide (~ 25-40%).It b ith bl i h flIt burns with a bluish flame.Its flame temperature is about 850 900C.Due to hydrogen sulphide, it sometimes has a

light smell of rotten eggs. g gg

Burning with a bluish flamebluish flame

ORIGIN OF BIOGASo First seen as flickering lights from decaying matter

of swamps by Plinius in 17th centuryof swamps by Plinius in 17th century.o In 1776 Volts confirmed the biogas production

from the decaying organic matterfrom the decaying organic matter. o Gas produced was a mixture of gases and in

certain proportions was able to burncertain proportions was able to burn.o In 1804 Dalton, Henry and Davy identified the

different gases that form biogas .different gases that form biogas .

ORIGIN OF BIOGASMethane gas was identified as the most

important component of biogas that burns.important component of biogas that burns. In 1884 Gayon in France, fermented manure at

35C35 C.He established that biogas can be used for heating

and lightingand lighting. In1896 the biogas from sewage was used for

lighting streets in Englandlighting streets in England.

Present interest in anaerobic Present interest in anaerobic digestiona) f i d i b da) treatment of organic wastes and wastewaters in a broad

range of organic loads and substrate concentrations;b) d ti d tili tib) energy production and utilization;c) improvement of sanitation; reduction of odors;d) d i f hi h li f ilid) production of high quality fertilizer.

Future of anaerobic digestion R & D has shifted from basic studies on anaerobic

fermentation of quasi-homogeneous substrates, with contents of organic solids in the range of about 5 -10%, to the digestion of more complex materials that

d difi d di t d ineed modified digester designs. The main fields of R & D activities are: f t ti t hi h i l di fermentation at high organic loadings; high rate digestion of diluted wastewater of agro-industries

including substrate separation during fermentation; g p g ;immobilization of the microorganisms

Future of anaerobic digestion The main fields of R & D activities are (contd) : fermentation and re-use of specific materials in integrative

farming systems;farming systems; biogas purification; simple but effective digester design/construction of simple but effective digester design/construction of

standardized fermenters; domestic wastewater treatment.

PRODUCTION OF BIOGASMaterials for making biogas:Materials for making biogas: Biogas can be produced from any organic matter

Commerciall iable materials are: Commercially viable materials are:Animal dung (cow dung and pig dung)H t ( )Human excreta (sewage)

Examples of other materials are:Straws and leavesKitchen remains and poultry litter , as well as pig

manure Clean water .

Common Terms used in Biogas ProductionCommon Terms used in Biogas Production

Digester Is an airtight pit where biogas is produced. Feedstock (substrate) Is the organic material mixed with

water and fed into the digester from which biogas is produced. Slurry Is the liquid substance left in the digester after biogas is Slurry Is the liquid substance left in the digester after biogas is

produced. Biogas plant Is the entire system from which biogas is

produced and utilized. The main components are digester, gas holder, gas delivery line

and appliancesand appliances.

How is biogas produced?Biogas is produced by decomposition and

fermentation of any organic material mixed y gwith water in a pit (digester) under airtight conditionsTechnically the process is called Anaerobic

ReactionReactionThe decomposition and fermentation process

in simple terms is referred to as digestionin simple terms is referred to as digestion

How is biogas produced?ow s b og s p oduced?The digestion process is brought about by bacterial

activityactivity. The bacterial activity in the digester depends on

several factors:several factors:Amount of water used to dilute the feed stock. For

animal dung (cows, pigs and humans) ratio is 1:1-1:4 (material:water).

Temperature in the digester. Ideal is 25 35C.Type of feedstock used. The best feedstock is cow

dung, pig dung and human excreta.

How is biogas produced?How is biogas produced?oCarbon-Nitrogen ratio (C/N). For very good

d i h f d k C/N igas production, the feedstock C/N ratio should be 20-30 : 1.

oDigester pressure. The pressure inside the digester should not exceed 40m H2O.

oAlkalinity of the digester. The ideal alkalinity in the digester is pH of 6.5 7.5 (some g p (literature say pH of 6.8 7.6).

Benefits of Biogas Technology Biogas technology is very beneficial. It: Solves energy problemsSolves energy problems,Increase productivity of crops, fish farms

d iand piggery,Contributes to improving health and

environmental conditions of farmers and local communities,Contributes to reducing global warming.

Benefits of Biogas TechnologyBenefits of Biogas TechnologyUse of biogas as energy source:At household level biogas is used for:cooking, g,lighting, and operating refrigerators.operating refrigerators.

Lets us look at heating efficiencies in the nextLets us look at heating efficiencies in the next table.

Cooking and Lightingg g gFuel Application Efficiency

%Net Heating

Value (Kwh/m3)% ( )Wood Cooking 12 0.6

Charcoal Cooking 25 2.0

Cow dung Cooking 12 0.3g g

Biogas Cooking 55 3.28

Lighting 3 0.18

Biogas as a good cooking fuelBiogas as a good cooking fuelIt is clearly seen that biogasIt is clearly seen that biogas

has:9best heating efficiency, and 9the highest net heating value per unit.g g pthan all the commonly used

fuel sources in Uganda.

F ilFamily cooking using biogas

Ordinary pressure lamp been adapted tobeen adapted to use biogas for security lightingsecurity lighting

Bi l b i d t li htBiogas lamp being used to light rooms

U f bi l f tiliUse of biogas slurry as fertilizerThe slurry from digester is very good fertilizerThe slurry from digester is very good fertilizer. The digestion process frees the mineral elements in

the feedstock and makes them readily available.the feedstock and makes them readily available.The freed mineral elements are immediately

utilized by crops thus increasing their productivity.utilized by crops thus increasing their productivity.The farmer gains in time and utilizing all the

important minerals elements in the cow dung. p g

Matoke fertilized using slurry in Mukono district UgandaMatoke fertilized using slurry in Mukono district, Uganda

A happy farmer proudly showing high yield of matoke due to slurry in Mukono district, Uganda

Matoke being grown on hard soils due to slurry in Kitezi, Wakiso districtKitezi, Wakiso district

Sticks used to support the huge bunches

Health benefits of biogas technology

Use of biogas for cooking reduces incidences of respiratory and other diseases associated with smoke.

This therefore results into better health of women and children who are particularly involved in cooking p y g

The digestion process kills pathogens in feedstock and makes them harmless to human beings

Social benefits of biogas technologyg gy

The use of biogas for cooking relieves women and children from looking for fire wood and charcoal.

The time saved can enable women and The time saved can enable women and children engage in other economic activities of the households and use it foractivities of the households and use it for leisure.

Environmental benefits of biogas technologyg gy

The use of biogas for cooking reduces destruction of forests which significantly contribute to reducing global warming.

The use of biogas for cooking alsoThe use of biogas for cooking also improves cleanness in kitchen which results into better working environmentresults into better working environment for women and children

Spying on Nature What can we learn from cows?

Inlet OutletBiogas digester

Cows convert biodegradable plants and water to milk, cow dung and urine and gases

A new look at the cow and bull

The Biogas Plant

O tl t

The Biogas Plant

Inlet

Outlet

Biogas digester

A biogas plant operates though anaerobic A biogas plant operates though anaerobic digestion of organic material

The Biogas Plant

InletBiogas

Inlet Outlet

Integrating biogas in agriculture

Some examples of biogas plantsg p

C i h h ld fi d dConstructing a household fixed dome digester in Bwaise II, Kampala, March 2007

Constructing a biolatrine at Mengo Primary School, Kampala, May 2012

Some examples of biogas plants

Front part Behind part

The Biolatrine at Mengo Primary School, Kampala, May 2012

Where is biogas technology applied?Approximate numbers of biogas units in selected countries:Approximatenumbersofbiogasunitsinselectedcountries:

Country No of units Volume >100 m3

China 12,000,000 x0China 12,000,000 x0India (in 2004) 3,600,000 ?Nepal (in 2007) 200,000 ?Vietnam, Thailand, Tanzania, Bangladesh, Burundi, Brazil x,000

3,400 (2006)in Germany

Kenya, Mexico, Cuba, Guyana; x00 ?Kenya, Mexico, Cuba, Guyana; Uganda??

x00 ?

Morocco, Ghana, Zimbabwe, Nicaragua Jamaica Bolivia x0

DK, NL, S, ThailandNicaragua, Jamaica, Bolivia x0 Thailand,

99% of all systems do not use pumps, agitator, and heating

Available human excreta in India compared to the need of fertiliser the need of fertiliser

Excretaviewed Faeces 250,000 tons/day

Dry org. matter (DS) 90,000 t/day

aswaste: Urine 1,000,000 m3/day

NPK:y g ( ) , yNitrogen (N) 15,000 t/day

Phosphorus (P2O5) 5,000 t/dayorasa

N P K:X

Y

Potassium (K2O) 3,000 t/dayCarbon (C) 35,000 t/day

resource Z

Calcium (CaO) 5,000 t/dayPotential biogas 50 mil m3 day R

Slurry application in agriculture

Biogas appliances

Hydro

Hydro

THE ANAEROBIC DIGESTION PROCESS

Complex organic matterComplex organic matterCarbohydratesCarbohydratesProteinProtein FatsFats

StagStag

olysis andolysis and

Hydrolytic & Fermentative MicroorganismHydrolytic & Fermentative Microorganism

Volatile Fatty acidsVolatile Fatty acidsAlcoholsAlcohols ChetonsChetons

ge 1ge 1d A

cidogend A

cidogen

propionatepropionatebutirratebutirrate

AcetateAcetate

yy

Acetogenic BacteriaAcetogenic Bacteria

O i B iO i B iHH22+CO+CO22

nesisnesis

Stage Stage

acetogeneacetogene

FormateFormate

Omoacetogenic BacteriaOmoacetogenic Bacteria

AcetoclasticAcetoclasticbacteriabacteria

HydrogenofilicHydrogenofilicbacteriabacteria

22esisesis

StagStag

meth

anm

ethan

CHCH44+CO+CO22 CHCH44+H+H22OO

ge 3ge 3

nogenesis

nogenesis

Biochemical process of anaerobic fermentation/digestion

Step 1:Step1:Hydrolysis+Acidogenesis Step2:

Acetogenesis Step3:Methanogenesis

Organic wasteCarbohydrates

BacterialmassBacterial

massH2 , CO2,acetic acidCarbohydrates

FatsProteinWater

Bacterialmass

H CO

Methan+ CO2Propionic acid

Butyric acid H2 , CO2acetic acid

Butyric acidAlcohols, Other components

Acetogenic bacteria

Fermentativebacteria

Methanogenic bacteria

What parameters affect anaerobic digestion?

The most important determinants of good living conditions for anaerobic bacteria and therefore efficient gas production are :gas production, are :

Temperature Retention Time Retention Time pH-level Carbon/Nitrogen ratio (C/N ratio)g ( ) Proportion of dry matter in substrate = suitable

viscosity Agitation (mixing) of the substrate Agitation (mixing) of the substrate

If any one of these determinants is outside acceptable range, the digestion may be inhibited

Substrate temperature in the digesterp g

Anaerobicfermentationcanworkinanambientt t b t 3oC d 70oC d if ld thtemperaturebetween3oCand70oCand,ifcolder,thereactorhastobeinsulatedand/orheated.

Common temperature ranges for bacteria:Psychrophillic bacteria below 20oCMesophillic bacteria 20 40oCMesophillic bacteria 20 40oCThermophillic bacteria above 40oC

Methaneproductionis verysensitivetochanges intemperature

Biogas production with continuous feeding

30

Litresofbiogasper litre

20perlitreofslurry

1010

Hydraulicretentiontimeindays50 100 150

Some studies on biogas yield1000

m

l

) A BMixture proportions (C )

Treatment

400

600

800

B

i

o

g

a

s

(

m C D(CD:FW)1:0 A

0:1 B

1:1 C

0

200

4001:1 C

3:1 D

1:3 E

Treatment A B C D E

Total solids (%) 22.82 13.33 16.82 16.90 15.21

Volatile solids (%) 77.18 86.67 83.18 83.10 84.78

0 20 40t (days)

50

60

e

n

t

(

%

)

pH value 6.2 3.7 4.0 4.2 3.8

Density(g/L) 20 12 18 14 16

Moisture content (%) 95.75 97 95.5 95.5 97 20

30

40

C

H

4

c

o

n

t

e

Carbon content (%) 37.8 35.3 38.6 37.9 37.2

Nitrogen content (%) 1.62 2.54 1.81 1.92 2.48

C:N Ratio 23:1 14:1 21:1 20:1 15:1

0

10

0 2 4 6t (week)

A BC D

Some findingsThe biogas potential of cow dung (CD) alone and in

combination with food wastes (FW) at various ratios was evaluated at lab-scale, using anaerobic batch reactors operated under uncontrolled temperature for 45 days.

The mixture at CD to FW of 3 to 1 gave the highest cumulative biogas yield (730 mL) while the highest CH4content (59 2%) was attained for the FW alone Therefore content (59.2%) was attained for the FW alone. Therefore, to get high quantities and of good quality, CD should be mixed with FWs. A suitable mixture ratio should be investigated further.

Also previously, we found that Cows should feed on grass in order to get a high yields and good quality of biogas. The dung from zero grazing cows, which feed on food

t b li d th i t d t wastes, e.g. banana peelings and other mixtures does not produce good quality biogas like that from cows which feed on grass.

pH value is crucial for a good resultpH value is crucial for a good result

pH is a central parameter for controlling the anaerobic process

Optimal production when pH 7.0 7.2Inhibition (due to acids) if pH < 6.2( ) pInhibition (due to ammonia) if pH > 7.6Deviationfromtheoptimumrangeresultsin:

Lowergasyieldg y

Inferiorgasquality

C/N ratio is important

Microorganisms need N (nitrogen) and C (carbon) for their metabolism

MethanogenicorganismspreferaC/N ratio of between 10:1 and 20:1C/Nratioofbetween10:1and20:1

Nmustnotbetoolow,orelse

Recommendation:shortageofnutrient

Mixdifferentsubstrates

Nitrogen inhibitionNitrogen inhibition

If N concentration is too high (>1 700 mg/l of NH N) and pHIfNconcentrationistoohigh (>1,700mg/lofNH4N)andpHishigh,then

growth of bacteria is inhibited due togrowthofbacteriaisinhibited duetotoxicitycausedbyhighlevelsof(uncharged) ammonia

Methanogens,however,areableofadaptto5,000 7,000mg/lofNH4Ngiventheprerequisitethattheunchargedammonia(NH3controlledbypH)leveldoesnotexceed200300mg/l

Changes in dry matter (DM) concentration i id th di tinside the digester

Behaviour of the substrate the substrate inside the digester

Stirring the substrate

Stirring improves the efficiency of digestion by:

R i t b lit ( l) Removingmetabolites(gasremoval) Bringingfreshmaterialincontactwithbacteria Reducing scum formation and sedimentation Reducingscumformationandsedimentation Preventingtemperaturegradientsinthedigester Avoidingtheformationofblindspots(shortcuts)g p ( )

However,excessive stirringdisturbsthesymbioticrelationshipbetweenthedifferentbacteriaspeciesp

Simplebiogasunitsnormallydonothavemechanicalstirringdevises

Efficiency of a biogas unit

Input: 1kgofdry(95%)cattledungwillproduce2.5kWh (ruleofthumb)

1kgdry(100%)mattercangenerate2.5/0.95=2.63kWh

Slurrycontains10%drymatter,thus1litrecangenerate0.263kWh

1litreslurry(27oC,90daysretention)releases27litrebiogas

1m3 ofbiogascangenerate6kWh(ruleofthumb)

So,1litofslurrygenerates0.027*6=0.162kWh

Actual kWhEfficiency =

0.162= = 0 62

PotentialkWhEfficiency =

0.262==0.62

62%efficiencyandtheother38%energyremainsintheslurry

Checklistif gas production is lower than expectedifgasproductionislowerthanexpected

Check Response

IspH>7.5? YesAddwaterandtakepHafteronehour

No

YesIspH

Principles for design and construction

Continuous feeding

Gascollector:

Continuousfeedingor batchfeeding

fixeddome,or

floatingdome

Furthertreatment ordirectdirectuse

Fixed-dome biogas digester

12

34

Birdseyeview

4

21 slurry 3

Floating-drum unit with water-jacket

Anaerobic filter (off-plot system)( p y )

gas manhole

inflow

scumoutflow

filter mass

grillsludge

sedimentation tank filter tanks

AnaerobicBaffledReactor

gasmanholes

w

um outflow

dge

sedimentation inoculation of fresh wastewater with active sludge final settler

Publictoiletwithhiddentreatmentunit

anaerobic baffled

waste-water

toilet sectionshowersection

reactor

A public toilet with a biogas digester

Design optionDesign option Anaerobic Design optionDesign optionSingle-stage reactor: all the phases in one reactor

digester

Double-stage reactors:1st reactor : hydr.+ acedogen.2nd reactor: fermentation

D (TS > 20%)

Flow type: Batch /continuous/ sequencing batch reactor -mixed or notBiomass (microorganism): suspended growth; attachedgrowth Dry process (TS > 20%)

Semi-dry process (8

PROCESS COMPLEXITY:PROCESS COMPLEXITY:

from simple and lowfrom simple and low--costcost

Human Human excretaexcreta

Anaerobic digester

FoodFoodEffluent+Effluent+

Food Food wastewaste

solid solid residueresidue

PROCESS DRANCOPROCESS DRANCOPROCESS COMPLEXITY:PROCESS COMPLEXITY:

to highto highPROCESS DRANCOPROCESS DRANCO to highto high

T = 50-58C

Faeces Urine OrganicwasteRainwater

Systemborder

Liquidurine

Groundwaterrecharge

Material flows in the Toiletunits Biodigester

Faeces

washwater

biogas

toilet complex

&showersg

Ablutionwater

Flush

UrinedryingbedCompost

LiquidurineFaeces Slurry

AerobicPond

Slurry

LiquidfertilizerSoilconditioner Urinepowder

Challenges with the anaerobic digestionChallenges with the anaerobic digestion High cost! Management of slurry is a very big challenge. Not anything should be deposited in the digester: rugs Not anything should be deposited in the digester: rugs,

inorganic solid wastes, plastics, menstrual pads etc should be excluded.

O i lid t b i t d d i th di t b t Organic solid wastes can be introduced in the digester, but they should be chopped/shredded in small pieces, perhaps in a machine similar to a meat mincer.

When water content is low, the material may not flow, and thus, there may be blockages. TS/DM should be only about 5%-10% of WW.

Structural problems, especially for large systems. The services of a competent structural engineer, conversant with fluid dynamics should be sought!

In Summary:.In Summary:.Biogas technology is receiving increased attention from Biogas technology is receiving increased attention from officials in Developing countries, due to its potential to bring an economically viable solution to the following problems: D d i t d f Dependence on imported sources of energy Deforestation, which leads to soil erosion and to a

drop in agricultural productivityp g p y

Providing inexpensive fertilizers to increase food production

The disposal of sanitary wastes, which cause severe public health problems;

The disposal of industrial wastes, which cause water pollution.

The End

Thanks for listening

Dr. Charles B. Niwagaba, PhDDepartment of Civil and Environmental Engineering

Makerere University, Kampalacniwagaba@tech.mak.ac.ug