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Biogas Presentation - UIPE June 2012 [Compatibility Mode].pdf
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Transcript of Biogas Presentation - UIPE June 2012 [Compatibility Mode].pdf
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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
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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
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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.
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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
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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!
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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
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Burning with a bluish flamebluish flame
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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 .
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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.
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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.
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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
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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.
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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 .
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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.
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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
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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.
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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).
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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.
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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.
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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
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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.
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F ilFamily cooking using biogas
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Ordinary pressure lamp been adapted tobeen adapted to use biogas for security lightingsecurity lighting
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Bi l b i d t li htBiogas lamp being used to light rooms
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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
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Matoke fertilized using slurry in Mukono district UgandaMatoke fertilized using slurry in Mukono district, Uganda
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A happy farmer proudly showing high yield of matoke due to slurry in Mukono district, Uganda
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Matoke being grown on hard soils due to slurry in Kitezi, Wakiso districtKitezi, Wakiso district
Sticks used to support the huge bunches
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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
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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.
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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
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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
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A new look at the cow and bull
The Biogas Plant
O tl t
The Biogas Plant
Inlet
Outlet
Biogas digester
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A biogas plant operates though anaerobic A biogas plant operates though anaerobic digestion of organic material
The Biogas Plant
InletBiogas
Inlet Outlet
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Integrating biogas in agriculture
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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
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Some examples of biogas plants
Front part Behind part
The Biolatrine at Mengo Primary School, Kampala, May 2012
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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
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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
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Slurry application in agriculture
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Biogas appliances
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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
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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
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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
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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
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Biogas production with continuous feeding
30
Litresofbiogasper litre
20perlitreofslurry
1010
Hydraulicretentiontimeindays50 100 150
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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
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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.
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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
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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
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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
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Changes in dry matter (DM) concentration i id th di tinside the digester
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Behaviour of the substrate the substrate inside the digester
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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
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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
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Checklistif gas production is lower than expectedifgasproductionislowerthanexpected
Check Response
IspH>7.5? YesAddwaterandtakepHafteronehour
No
YesIspH
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Principles for design and construction
Continuous feeding
Gascollector:
Continuousfeedingor batchfeeding
fixeddome,or
floatingdome
Furthertreatment ordirectdirectuse
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Fixed-dome biogas digester
12
34
Birdseyeview
4
21 slurry 3
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Floating-drum unit with water-jacket
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Anaerobic filter (off-plot system)( p y )
gas manhole
inflow
scumoutflow
filter mass
grillsludge
sedimentation tank filter tanks
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AnaerobicBaffledReactor
gasmanholes
w
um outflow
dge
sedimentation inoculation of fresh wastewater with active sludge final settler
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Publictoiletwithhiddentreatmentunit
anaerobic baffled
waste-water
toilet sectionshowersection
reactor
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A public toilet with a biogas digester
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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
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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
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PROCESS DRANCOPROCESS DRANCOPROCESS COMPLEXITY:PROCESS COMPLEXITY:
to highto highPROCESS DRANCOPROCESS DRANCO to highto high
T = 50-58C
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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
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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!
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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.
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The End
Thanks for listening
Dr. Charles B. Niwagaba, PhDDepartment of Civil and Environmental Engineering
Makerere University, [email protected]