Transcript The composting of sewage sludge in Tartu Waterworks Ltd Jüri Haller

The composting of
sewage sludge in
Tartu Waterworks Ltd
Jüri Haller
Head of laboratory
ESTONIA
Sigulda, 24-25 of April, 2008.
The requirements for using of sewage
sludge in agriculture, in urban landscaping
and in recultivation
Regulation No 78 of 30.Dec.2002 of the Minister of
Environment
• The sewage sludge considered treated after using
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aerobic or anaerobic stabilisation methods (incl.
composting), chemical or thermal treating or an other
methods if the organic matter inside it has not influence
on surface- and groundwater, on soil, on flora and
fauna and on human health.
In meaning of the Regulation No 78 the composting is
aerobic degradation process of sewage sludge by the
micro- and macro organisms and in adding to the
sludge the bark, the straw, the peat or some other bulk
materials. The periodical mixing of piles is necessary.
During the process the composting material has to be
over 60 0C at least 6 days
t0 and time of exposure required for
destruction of some common pathogens and
Escherichia coli
Most die within 1 hour at 550C and within
15-20 min at 600C
Salmonella typhosa
No growth beyond 46 0C; death within
30 min. at 55-60 0C; 20 min at 60 0C
Salmonella sp.
Death within1 hour at 550C and within
15-20 min at 600C
Streptococcus pyogenes
Death within 10 min. at 54 0C
The composting is the complex series
of biological, chemical and physical
processes, which needs for successful
process some requirements
Every composting
should have the
beginning, ending and
monitored intermediate
part
Requirements for composting
• t0 indicates the activity of the
• Temperature
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decomposition process
Micro-organisms release heat as
they feed and grow
Microbiological activity in the pile is
rising about 2 times in every 10 C0
temperature rising
Microbiological activity reduces on
too high and on too low t0
Optimum t0 inside the pile should be
between 45 and 55 0C
Pathogens are killed at 50-55 0C fast
Temperature development inside the
composting piles
Requirements for composting
The optimume C/N = 20-30
C
N
C/N ratio
Organisms that decompose organic matter
use
• carbon as a source of energy
• nitrogen for building cell structure
The organisms that decompose organic matter are
using carbon, as a energy source and nitrogen as
crucial component of the proteins in fixed ratio
• Small C/N ratio
(much N)
• Too much
carbon
(C/N is big)
• Biological activity of the process is going
down
• When the energy source, carbon, is less
than that required for converting
nitrogen into protein, organisms make
full use of the available C and get rid of
the excess nitrogen as ammonia.
• Smell!
• Decomposition slows when the
nitrogen is used up and some
organisms die
• Other organisms form new cell
material using their stored nitrogen
C/N ratio effects on composting
Oxygen
• The micro-organisms need oxygen so air must be
able to circulate trough the composting material
• C10H19O3N + 12,5O2  10CO2 + 8H2O +NH3
• If a compost heap gets short of air the result is an
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evil smelling slime
Optimal O2 content during aerobic composting
process is 10-20%
Mixing of the windrows
Aeration
Homogenisation
Increase or decrease
the moisture content
to optimum level
The mixing period
depends of structure
and moisture content
of the compost
Mixing or tuning
• Turning
• Mixing and breaking
Temperature inside the windrow
is uneven
Why is important to mix the windrows!
Mixing of the windrows
• You have to mix and
pile the raw
compost rapidly
• The first mixing is
during the 3-5 days
after working up the
raw compost
• Continuously after
5-12 days
Moisture content
• In connexion with intensity of biological
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degradation process and with compost material
structure
The water keeps the thermodynamic balance of
the process
In the composting materials have to be just
enough moisture
In dry environment the micro organisms will die
Over moisture will turn out the air from the
pores of material, sludge turns into the lump
and the anaerobic process is taking place
The optimum moisture content should be in the
range between 50-65% during the composting
process
pH
• Important parameter in evaluating microbial
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environment
Optimum pH = 6,5-8,0 during composting
In first few days of composting, the simple
organic acids drops the pH to 5 or less.
If the degree of aeration is not adequate,
anaerobic conditions will occur, the pile pH will
drop to about 4,5 and the composting process
will be retarded
After the temperature reaches a thermophilic
stage the pH begins to rise to 8-8,5 and falls in
mesophilic stage to 7-8
The bulking materials
• For the regulation of C/N ratio
• For guaranteed of needful porosity
of compost (aeration)
• Optimum particle size should be
between 25-75 mm
• For regulation of moisture content
inside the windrow
Used bulk materials
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shredded bark
woodchips
straw
peat
wooden building waste
park waste (leaves)
cardboard chips
municipal waste
• bark + peat
• bark + wood ash
• straw + bark
Shredded bark
Sewage sludge:bark = 1:1,5-2,0
+ t0 is rising quite fast and high
+ easy to get
+ quite good structure
+ C/N = 110-140
- Unstable quality
(structure, moisture, pH,
resin)
Mature compost
needs sieving
Woodchips
Sewage sludge:woodchips = 1:1-1,2
• Stable structure
• Good aeration
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guarantee
t0 is rising fast and stay
in high level for a long
time
C/N = 250 - 320
Dry mat. 50-60%
Composting material is
not diffusive
Wooden building waste
Sewage sludge:building waste = 1:1,5-2,0
+ cheaper as bark
+ dry mat. 80-85%
+ C/N ~ 200
+ richer of minerals
-Inadvisable
supplements may occur
-Unstable structure
The straw
Sewage sludge: straw = 1: 3 – 3,5
+ After the mixing of
pile the windrow is
very airy
+ t0 is rising very fast
+ C/N = 85 - 100
+ dry mat. 55-65%
+ high potassium
content
- The sludge content in the pile is
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very small
The braking of straw balls adds
work
The windrow falls dawn very fast
The windrow needs intensive
mixing
Water absorption of the fresh
material is not good
The turning machine blocked by
strings during combining
The sewage sludge composting with
the straw
The peat
Sewage sludge:peat = 1:1,5-2,0
- C/N = 45-50
+dry material ~ 75%
+ mature compost
looks like a soil
- Bad aeration of the pile
- Acidic pH
- t0 can`t rise over 40 0C
- The melting of frozen pile
takes long time
- The destruction time of
pathogens is slow
- Needs intensive mixing
- Good accumulator of
toxically compounds
The peat accumulates lot of
water
Park waste
Sewage sludge : park waste = 1:1,5
+ quite stable structure
+ cheap
+ mature compost like a soil
- Foreign matters, hazardous
waste
- C/N = 40-60
- t0 is rising slowly
- Needs intensive mixing
Syringes!!!
The park waste from
autumn and spring are
different
Cardboard chips
Sewage sludge :cardboard chips = 1:3
+ dry mat. 70-75%
+ free of charge
- Shredding is problematical
- Outlook and using of
mature compost is
problematical
- The big amount of bulk
+ C/N = 300-400
+ shredded material is airy
material may cause the
temperature drop under
critical level
-The content of PAH is higher
Municipal waste
Sewage sludge: municipal waste = 1:1
• C/N = 30-40
• Structure problems
• Non-biodegradable
material
• Biodegradable organic
material falls dawn during
composting
Test piles in 2006
municipal waste 
cardboard waste 
 bark
 building waste
 park waste
Temperature inside the windrows
Temperature
0
C
Temperature inside the piles
70
60
50
40
30
20
10
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3
5
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9 10 14 17 21 25 28 30 31 33 35 38 42 48 52 58
The day after mixing
straw
straw+bark
bark+ash
woodchips
bark
t0 is measured in the depht of 50 cm of the windrows
peat
Fertilization quality of mature compost
• Fertilization quality the same as in case of
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manure
The chemical and biological control more
effective as in case of manure
The manure is more dangerous by biological
parameters, because the t0 is not high enough
in anaerobic process to kill pathogens
The compost have to be mature
In case of non mature compost the
degradation process will continue in soil, the
nitrogen may taken off from the soil and the
plants may die
Sewage sludge composting
• Take the bulk material, which is right by
structure and by quality
• You have to mix and pile the raw
compost rapidly
• Aerate (mix) the piles after optimum
time
• Follow the required parameters
• Correct the compost materials content
if you need
Problems
Possible causes
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Nothing is
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happening. Pile •
dosen`t seem
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to be heating
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up at all
Not enough O2
Wrong bulkmaterial
Not enough H2O
Not enough N
Cold weather
Temperature is • Not enough O2
rising slowly
• wrong C/N ratio
and not high
• Not enough H2O
• too much H2O
Damp and
warm only in
the middle of
the pile
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Solution
Too small or too
large pile
Not homogenous
compost
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Mix the pile
Take the right bulkmaterial
Add water and mix
Add sludge
Wait for spring
• mix the pile, change the
structure
• C/N = 20-30
• add water and mix
• add dry bulkmaterial and mix
•Make the pile in a right
size
•Mix the pile
Possible causes
Problems
The
compost in
the lump
Bad odour
Attracts insects,
millipedes, slugs
etc.
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solution
Thick bulkmaterial •
The pile is too wet
Less mixing
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• not enough O2
• owe moisture
• the pile is too
compact
• C/N ratio too high
This is normal
composting
Mix the pile, wait the
piles top dries and mix
again
Add dry materials like
straw or leaves
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The same as previous
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Add bulk material
Not a
problem
Thank You!
Jüri Haller
head of laboratory
Tartu Veevärk Ltd
ESTONIA
[email protected]
+372 7306233