Energy from bio wastes
Energy from bio wastes:
Fundamental considerations,
data,
comparison from products
Dr. Konrad Schleiss,
UMWEKO
Dr. Jacques Fuchs
Biophyt SA
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Energy from bio wastes
Fondamentals
 The energy potential from wastes is considerable
 Depending of their treatment, it cost or produce
more or less energy
 More dry the wastes are, more easy is the energy
use by combustion
 More wet the wastes are, more easy is the energy
use by anaerobic digestion
 Important for its energy efficiency is the use of the
energy, not its global production
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Energy from bio wastes
Treatment by burning
 Burning use the complete energy capital of the
products; waste will be completely mineralized
 Products are only mineral (ashes)
 The energy content is describe by the highest calorific
value (Gross Calorific Value GCV, without water) and the
lower calorific value (Net Calorific Value - NCV)
 Wastes have a middle calorific value from NCV=3 kWh/kg
 Bio wastes with a DM from 35 - 40% have a NCV =
0,1-0,5 kWh/kg
 So the bio wastes bring not so much energy in the
incineration plants
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Energy from bio wastes
Calorific value of wood and of bio
wastes
Valeur calorifique [kWh/kg]
Teneur en eau [%]
Relation entre la valeur calorifique et la teneur en
eau (Jonas & Görtler, 1997)
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Calorific value of
bio waste is
similare to the
calorific value of
wood if we
consider only the
organic matter
content
Energy from bio wastes
Treatment by composting
 Generally, about 50% of the organic matter will be
degradated by composting
 In average, 0,03 kWh/kg of bio wastes are needed
 According to Heller, compost contain still 2,6 kWh/kg MS =
1,3/kg MF = 0,78/lt MF = approx. 50% from input GCV
 GCV from biowaste = 1,3 - 1,7 kWh/kg
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Energy from bio wastes
Treatment by anaerobic digestion
 An average of 100 m3 biogas per ton of bio
waste is produce
 It correspond to approx. 600 kWh
 If we produce fuel wit it, approx. 400 kWh can be
used
 If we produce electricity (without use of heat), we obtain
approx. 140 kWh/t or 0,14 kWh/kg
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Energy from bio wastes
Comparison of the energey balances
Composting
Anaerobic
fermentation
(solid material)
Energy used
30
Production of
usable energy
0
Balance
-30
Energy usual
used
0
140
(40 electr. + 100 heat)
600
460
(140 electr. + 280 heat)
140
Incineration
chips
25
2000
1975 (heat)
1975
Source: Kompost und Energie aus biogenen Siedlungsabfällen ATAL (Amt für technische Anlagen
und Lufthygiene) und AGW (Amt für Gewässerschutz und Wasserbau, Kz ZH) Nov 1997
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Energy from bio wastes
Comparison (canton Zurich)
2.5
Energy usable [kWh/kg
2
1.5
Minimum
Médiane
1
0.5
0
-0.5
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Moyenne
Maximum
incineration
(6)
Anaerob. Dig.
(6)
Composting
(20)
Energy from bio wastes
Comparison
 Incinerators burn normally waste with high
energy content
 New incinerators utilized very efficiently the energy
 Also if the energy content of bio wastes is twice less
important as the household wastes, the energy usable
by incineration is twice higher as by anaerobic
digestion
 The energy content in compost and digestate is here not
consider
 If we consider the organic matter, the comparison could
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be different...
Energy from bio wastes
What are the products of the
different treatments ?
Incineration:
Energie
Ashes
Anaerobic
digestion:
Energie
Digestate solid
Digestate liquide
Composts
(different qualities)
Composting:
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Energy from bio wastes
Remark:
With an appropriate
composting process, it is
possible to produce compost
out of digestate.
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Energy from bio wastes
Which differences have the
products out a agricultural
point of view.
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Energy from bio wastes
Chemical properties from
composts, digestates and wood ashes
Compost
Digestat
Eau de pressage Cendres de bois
Médiane (max./ min.)
Médiane (max./ min.)
MS[% MF]
MO[% MS]
Valeur pH
Salinité [mS]
NO3-N [g N/t TS]
NH4-N [g N/t TS]
NO3-N/NH4-N
Ntot[kg N/t TS]
P2O5 [kg/t TS]
K2O [kg/t TS]
Ca [kg/t TS]
Mg [kg/t TS]
SO4 [kg/t TS]
47,9(30,7 / 75,8)
44,7 (17,0 / 72,2)
7,9 (7,0 / 8,6)
2,5 (0,9 / 6,6)
284 (0 / 1506)
28 (0 / 482)
6,6 (0,0 / 427,1)
13,0(6,9 / 26,1)
6,2 (3,7 / 12,9)
10,5(5,6 / 25,5)
53,9 (23,8 / 148,6)
6,5 ( 3,5 / 15,2)
4,5 (2,0 / 7,5)
51,1(41,8 / 68,5)
44,9 (35,6 / 61,1)
7,8 (7,5 / 8,6)
2,7 (1,7 / 5,3)
455 (0 / 968)
913 (515 / 2001)
0,4 (0,0 / 1,2)
12,6(8,8 / 26,0)
7,2 (5,8 / 10,1)
10,3(7,4 / 24,9)
62,9 (42,2 / 154,9)
6,3 ( 4,6 / 9,0)
4,7 (3,3 / 7,0)
11,1(2,5 / 19,6)
49,0 (38,9 / 64,5)
7,7 (7,5 / 8,1)
16,0(7,3 / 22,9)
2554(995 / 5458)
13057(1288 / 38710)
0,25(0,06 / 2,87)
35,3(19,1 / 69,7)
14,3 (9,9 / 24,3)
35,1(18,1 / 90,8)
36,5 (19,1 / 71,4)
9,5 ( 7,5 / 11,6)
8,0 (5,0 / 10,2)
95
0
Cd [g/t TS] (GW: 1)
Cu [g/t TS] (GW: 100)
Ni [g/t TS] (GW: 30)
Pb [g/t TS] (GW: 120)
Zn [g/t TS] (GW: 400)
0,32 (0,12 / 0,49)
40,7 (19,1 / 724,3)
14,7 (5,9 / 29,7)
32,1(8,2 / 66,9)
123,5(71,9 / 316,9)
0,20 (0,12 / 0,62)
38,7 (24,2 / 1504,0)
10,9 (4,3 / 19,1)
27,3(17,4 / 55,2)
90,5 (42,4 / 189,6)
0,52 (0,14 / 0,66)
75,3 (38,0 / 106,8)
25,5 (9,8 / 38,5)
41,9(15,1 / 90,4)
231,7(153,6 / 355,4)
0,3-2,7
86-376
36-140
3,4-39,9
81-522
Médiane (max./ min.)
Médiane (max./ min.)
0
0
0
24
70
300
25
Source de données pour le compost, digestat et eau de pressage: Konrad Schleiss, Analysen des Kanton
Zürich, 2004
Source de données cendres: Risikoanalyse zur Abfalldüngerverwertung in der Landwirtschaft, FAL, 2001
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Energy from bio wastes
Hygienic quality of the products:
 Ashes: OK
 Compost: OK
 Digestates ?
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Energy from bio wastes
Hygienic quality of digestates:
Influence of anaerobic digestion on survival from of clubroot
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% diseased plants
Duration of
anaerobic
digestion
[days]
without
anaerobic
digestion
Test
Temp.
No.
[ °C ]
1
55
14
100
with
anaerobic
digestion
1
2
55
14
100
0
3
55
14
99
0
4
55
7
92
0
5
55
7
100
22
6
55
7
98
1
7
35
14
93
96
8
35
14
98
98
9
35
14
99
98
Energy from bio wastes
Hygienic quality of digestates:
 thermophile (55°C)
OK
 mesophile (35°C)
Temperatur assume not a
hygienisation of the digestate.
Other actions have to be done.
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Energy from bio wastes
Hygienic quality of digestates:
 thermophile (55°C)
 mesophile (35°C)
 Post-composting of solid digestate: OK
 Post-treatement liquide digestate ?
Prée-treatement of input materials?
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Energy from bio wastes
Biological quality of the products
 Ashes
● Biologically dead
● Availability of nitrogen: neutral
(bring no nitrogen in soil, but
immobilized also no nitrogen)
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Energy from bio wastes
Biological quality of the products
 Liquid digestate
● Relatively similar to liquid manure
● Can be spread only when the plants can
assimilate nitrogen (to be consider by the
calculation of the needed storage capacity)
● Concentrated N-fertilizer for the plants
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Energy from bio wastes
Biological quality of the products
 Solid digestate
● Qualitatively similar to manure
● Biologically not stable
● Phytotoxic
● Low disease suppressivity potential
● Problematic of nitrogen: depending of its storage and
its post-treatment, the digestate can bring relatively
important quantity of mineral nitrogen to the soil, but
can also immobilized the soil nitrogen.
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Energy from bio wastes
Biological quality of the products
 Compost
● Depending of its maturity stage: stabilized product,
good compatible with plants
● Influence positively the soil biology
● Influence positively the plant health
(disease suppression)
● Problematic of nitrogen: depending of its maturity
stage and of the process management, can blocked
nitrogen in the soil, or give some nitrogen free in the
soil
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Energy from bio wastes
And the organic
matter ?
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Energy from bio wastes
Importance of organic matter for the
soil fertility
 Influence the soil structure
 Influence the water management
 Protection against erosion
 Amélioration of the soil biological activity
 Influence the climat
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Energy from bio wastes
Quality of the organic matter of the
different products
 Every organic matter bring to the soil
has not the same effect. Easy degradable
organic matter can also influence
negatively the organic balance of a soil,
because it promote too much the
microorganisms responsible for the
mineralization of the organic matter.
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Energy from bio wastes
Quality of the organic matter of the
different products
 Ashes: no organic matter
Liquid digestate: organic matter very
quickly degradable
 Solid digestate: organic matter
easily degradable
 Compost: depending of its maturity stage,
organic matter middle to high stable
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Energy from bio wastes
Middle or long term influence of the
different products on the humus level
in soil
 Ashes: neutral
Liquid digestate: neutral or negativ
 Solid digestate: neutral or
slightly positive
 Compost: slightly to strong positive
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Energy from bio wastes
Conclusions:
There is more than only energy in bio
wastes. These other aspects have to be
consider when we choose a concept of
treatment for these products.
What do you mean ?
How many kilowatts do we have in a
fertile soil ?
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