4.4 biogas reactors for treatment 2010-09-05

8/16/2019 4.4 Biogas Reactors for Treatment 2010-09-05

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4.4 Biogas – a way to solve sanitation

problems

H o w m u c h b i o g a s c a n b e p r o d u c e d f r o m

e x c r e t a a n d b i o m a s s ? H o w s a f e i s t h e p r o c e s s a n d i t s s l u d g e ? ?

Learning objectives: to know about the

fundamental processes in biogas production,

and get an overview of biogas generation in

the world

Anaerobic

fermentation

is a natural

andunavoidable

process

Jam-Olof Drangert, Linköping university, Sweden


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pying on !ature –

"hat can we learn from cows?

Inlet OutletBiogas digester

Cows convert biodegradable plants and water to

milk, cow dung and urine – and gases

Pedro Kraemer, BOD!, "ndia


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# new look at the cow – and bull

Inlet

Outlet

Biogas digester

The Biogas Plant



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# biogas plant operates though

anaerobic digestion of organic material

The Biogas Plant

InletOutlet

Biogas digester

Biogas



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$ntegrating biogas in agriculture



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ome examples of biogas plants



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"here is biogas technology applied?

#pproximate numbers of biogas units in selected countries%

&ountry !o of units 'olume ()** m+

&hina ),***,*** x*

$ndia -in **4 +,/**,*** ?

!epal -in **0 **,*** ?'ietnam, 1hailand, 1an2ania,Bangladesh, Burundi, Bra2il

x,***

+,4** -**/

in 3ermany

enya, 5exico, &uba, 3uyana x** ?

5orocco, 3hana, 6imbabwe,!icaragua, 7amaica, Bolivia x*

8, !9, ,1hailand,

##$ of all systems do not use pumps, agitator, and %eating



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#vailable human excreta in $ndia compared

to the need of fertiliser

Dry org. matter (DS) 9, t!day "itrogen (N) #$, t!day

%&osp&orus (P2O5) $, t!day

%otassium (K 2O) ', t!dayCarbon (C) '$, t!day

Calcium (CaO) $, t!day

%otential biogas $ mil m'

day

… oras a

resource

Excreta viewedas waste:

Faeces $, tons!day

Urine #,, m'!day

!:;:% <

=

6

>



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lurry application in agriculture



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nergy balance – for composting and digestion

Aerobic conversion (composting ):

C6 H12 O6 + 6O2 6 CO2 +6 H2 O

∆* +', k-!mol

Anaerobic conversion (digestion):

C6 H

12 O

6 + 2H

2 O 3 CO

2 + 3CH

4 + 2H

2O

∆* + $ k-!mol

Burning of biogas:

2CH4+ 6O2 CO2 + 6 H2 O

∆ * +',/$ k-!mol Pedro Kraemer, BOD!, "ndia


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Biogas appliances



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Biochemical process of anaerobic

fermentation@digestion

ce!ogenic

bac!eria

Fer"en!a!i#e

bac!eria

$e!%anogenic

bac!eria

Organic &as!e

Carbo%'ra!es

Fa!s

Pro!ein

a!er

*ac!eria

"ass

H2 , CO2 ace!ic aci

*ac!eria

"ass

$e!%an

+ CO2

*ac!eria

"ass

Pro-ionic aci

*.!'ric acico%os,

O!%er

co"-onen!s

H2 , CO2,

ace!ic aci

Step 1:Hydrolysis + Acidogenesis Step 2 :

Acetogenesis Step 3:Methanogenesis



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"hat parameters affect anaerobic digestion?

The most imortant determinants of good livingconditions for anaerobic bacteria and therefore efficient

gas roduction! are :

– 1emperature

– >etention 1ime

– pH:level

– &arbon@!itrogen ratio -&@! ratio

– ;roportion of dry matter in substrate A suitable viscosity – #gitation -mixing of the substrate

"f any one of these determinants is outside accetablerange! the digestion may be inhibited



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ubstrate temperature in the digester

#ommon temerature ranges for bacteria%

;sychrophillic bacteria below *o&

5esophillic bacteria * – 4*o&

1hermophillic bacteria above 4*o&

#naerobic fermentation can work in an ambienttemperature between +o& and 0*o& and, if colder,

the reactor has to be insulated and@or heated.

5ethane production is very sensitive to changes in

temerature Pedro Kraemer, BOD!, "ndia


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Biogas production with continuous feeding

Hydraulic retention time in days

9itres of

biogasper litre

of slurry


)*

*

+*

C* )** )C*


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pH –value is crucial for a good result

$timal roduction when H %&' ( %&)

$nhibition -due to acids if pH D /.

$nhibition -due to ammonia if pH ( 0./

-H is a cen!ra -ara"e!er /or con!roing !%e anaerobic -rocess

8eviation from the optimum range results in%

9ower gas yield

$nferior gas Euality Pedro Kraemer, BOD!, "ndia


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&@! ratio is important

Microorganisms need * nitrogen, and# carbon, for their metabolism

Methanogenic organisms refer a

#-* ratio of between .':. and )':.

>ecommendation%

5ix different substrates

! must not be too low, or else

shortage of nutrient



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!itrogen inhibition

"f * concentration is too high -(),0** mg@l of !H4:!and pH is high, then

growth of bacteria is inhibited due to

toxicity caused by high levels of -uncharged ammonia

5ethanogens, however, are able of adapt to

C,*** : 0,*** mg@l of !H4:! given the pre:reEuisitethat the uncharged ammonia -!H+ controlled by pH

level does not exceed **:+** mg@l



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&hanges in dry matter -85 concentration

inside the digester



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Behaviour of the substrate inside the digester



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tirring the substrate

/tirring imroves the efficiency of digestion by:

>emoving metabolites -gas removal

Bringing fresh material in contact with bacteria

>educing scum formation and sedimentation

;reventing temperature gradients in the digester

#voiding the formation of blind spots -short cuts

However! excessive stirring disturbs the symbioticrelationshi between the different bacteria secies

imple biogas units normally do not have

mechanical stirring devises Pedro Kraemer, BOD!, "ndia


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fficiency of a biogas unit

"nut:

. 0g of dry 123, cattle dung will roduce )&2 04h -rule of thumb

. 0g dry .''3, matter can generate )&2-'&12 5 )&67 04h

/lurry contains .'3 dry matter! thus . litre can generate '&)67 04h

. litre slurry )%o#! 1' days retention, releases )% litre biogas

. m7 of biogas can generate 6 04h rule of thumb,

/o! . lit of slurry generates '&')%86 5 '&.6) 04h

#ctual k"h

;otential k"hfficiency A

*.)/

*./A A *./

/F efficiency and the other +GF energy remains in the slurry



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&heck:list

if gas production is lower than expected

#hec0 9esonse

$s pH (0.C ? =es #dd water and take pH after

one hour

!o

1oo much feed or of

skewed composition?

1emperature fallen? =es

=es

1ry to insulate digester,

less feed, heat substrate.

"ait one day

#dd lime -acute action

and wait one day

!o

$s pH D /.G ?

#dd urine or ash -kg@m+ and

wait ) day

=es

Drangert & Ejlertsson, Linkoping university, Sweden


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;rinciples for design and construction

as collector:

: fixed dome! or

: floating dome

&ontinuous feeding

or batch feeding

urther

treatment or

direct use



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ixed:dome biogas digester


).

;

slurry

7

BirdIs

eye view

.)

7;


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loating:drum unit with water:Jacket



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#naerobic filter -off:plot system

gas manhole

inflow

scum

outflow

filter mass

grill

sludge

sedimentation tank filter tanks



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#naerobic baffled reactor Off-plot system

gas

manholes

m outflow

ge

sedimentation inoculation of fresh wastewater with active sludge final settler

#naerobic Baffled >eactor



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toilet sectionshower

section

anaerobic baffled

reactor

waste:

water


;ublic toilet with hidden treatment unit

# bli t il t ith bi di t


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# public toilet with a biogas digester

Jan-Olof Drangert, Linköping &niversity, Sweden


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5aterial flows in the toilet complex

Toilet units

< showers

=aece

s

>rine

Bio?digester

>rine

drying?bed

9iEuid

urine

aeces washwater

#blution

water

lush

9iEuid fertili2er

comost

9iEuid urine

aeces

$rganic waste9ainwater

roundwater

recharge

biogas

oil conditioner Krine powder

lurry

Aerobic

ond

lurry

ystem border

4.4 biogas reactors for treatment 2010-09-05

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