The composting of sewage sludge in

Tartu Waterworks LtdJüri Haller

ESTONIA

Head of laboratory

Sigulda, 24-25 of April, 2008.

The requirements for using of sewage The requirements for using of sewage sludge in agriculture, in urban sludge in agriculture, in urban

landscaping and in recultivationlandscaping and in recultivationRegulation No 78 of 30.Dec.2002 of the Minister of Regulation No 78 of 30.Dec.2002 of the Minister of

EnvironmentEnvironment

• The sewage sludge considered treated after The sewage sludge considered treated after using aerobic or anaerobic stabilisation methods using aerobic or anaerobic stabilisation methods (incl. composting), chemical or thermal treating (incl. composting), chemical or thermal treating or an other methods if the organic matter inside or an other methods if the organic matter inside it has not influence on surface- and groundwater, it has not influence on surface- and groundwater, on soil, on flora and fauna and on human health.on soil, on flora and fauna and on human health.

• In meaning of the Regulation No 78 the In meaning of the Regulation No 78 the composting is aerobic degradation process of composting is aerobic degradation process of sewage sludge by the micro- and macro sewage sludge by the micro- and macro organisms and in adding to the sludge the bark, organisms and in adding to the sludge the bark, the straw, the peat or some other bulk materials. the straw, the peat or some other bulk materials. The periodical mixing of piles is necessary.The periodical mixing of piles is necessary.

• During the process the composting material has During the process the composting material has to be over 60 to be over 60 00C at least 6 daysC at least 6 days

tt00 and time of exposure required for and time of exposure required for destruction of some common destruction of some common

pathogens andpathogens and

Escherichia coliEscherichia coli Most die within 1 hour at 55Most die within 1 hour at 5500C and C and within 15-20 min at 60within 15-20 min at 6000CC

Salmonella typhosaSalmonella typhosa No growth beyond 46 No growth beyond 46 00C; death C; death within 30 min. at 55-60 within 30 min. at 55-60 00C; 20 min C; 20 min at 60 at 60 00CC

Salmonella Salmonella sp.sp.

Death witDeath withhin1 hour at 55in1 hour at 5500C and within C and within 15-20 min at 6015-20 min at 6000CC

Streptococcus pyogenesStreptococcus pyogenes Death within 10 min. at 54 Death within 10 min. at 54 00CC

The composting is the complex The composting is the complex series of biological, chemical and series of biological, chemical and physical processes, which needs physical processes, which needs for successful process some for successful process some requirementsrequirements

Every composting should have the beginning, ending and monitored intermediate part

Requirements for compostingRequirements for composting

• TemperaturTemperaturee

• tt00 indicates the activity of the indicates the activity of the decomposition processdecomposition process

• Micro-organisms release heat as Micro-organisms release heat as they feed and growthey feed and grow

• Microbiological activity in the Microbiological activity in the pile is rising about 2 times pile is rising about 2 times inin every 10 Cevery 10 C00 temperature rising temperature rising

• Microbiological activity reduceMicrobiological activity reducess on too high and on too low ton too high and on too low t00

• Optimum tOptimum t00 inside the pile inside the pile should be between 45 and 55 should be between 45 and 55 00CC

• Pathogens are killed at 50-55 Pathogens are killed at 50-55 00C C fastfast

Temperature development inside the Temperature development inside the composting pilescomposting piles

Requirements for compostingRequirements for composting

C N

The optimume C/N = 20-30

C/N C/N ratioratio

• carbon as a source of energy carbon as a source of energy

• nitrogen for building cell structurenitrogen for building cell structure

Organisms that decompose Organisms that decompose organic organic matter usematter use

The organisms that decompose organic The organisms that decompose organic matter are using carbon, as a energy source matter are using carbon, as a energy source

and nitrogen as crucial component of the and nitrogen as crucial component of the proteins in fixed ratioproteins in fixed ratio

• Small C/N ratioSmall C/N ratio(much N)(much N)

• Biological activity of the process is Biological activity of the process is going downgoing down

• When the energy source, carbon, is When the energy source, carbon, is less than that required for converting less than that required for converting nitrogen into protein, organisms nitrogen into protein, organisms make full use of the available C and make full use of the available C and get rid of the excess nitrogen as get rid of the excess nitrogen as ammonia.ammonia.

• Smell!Smell!

• Too much Too much carbon carbon (C/N is big)(C/N is big)

• DDecomposition slows when ecomposition slows when the the nitrogen is used up and some nitrogen is used up and some organisms die organisms die• Other organisms form new cell Other organisms form new cell material using their stored material using their stored nitrogennitrogen

C/N C/N ratio effects on compostingratio effects on composting

OxygenOxygen

• The micro-organisms need oxygen so air must The micro-organisms need oxygen so air must be able to circulate trough the composting be able to circulate trough the composting materialmaterial

• CC1010HH1919OO33N + 12,5ON + 12,5O22 10CO 10CO22 + 8H + 8H22O +NHO +NH33

• If a compost heap gets short of air the result is If a compost heap gets short of air the result is an evil smelling slimean evil smelling slime

• Optimal OOptimal O22 content during aerobic composting content during aerobic composting process is 10-20%process is 10-20%

Mixing of the windrows

The mixing period depends of structure and moisture content of the compost

AerationHomogenisation

Increase or decrease the moisture contentto optimum level

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 contentMoisture content

• In connexion with intensity of biological In connexion with intensity of biological degradation process and with compost degradation process and with compost material structurematerial structure

• The water keeps the thermodynamic The water keeps the thermodynamic balance of the processbalance of the process

• In the composting materials have to be In the composting materials have to be just enough moisturejust enough moisture

• In dry environment the micro organisms In dry environment the micro organisms will diewill die

• Over moisture will turn out the air from Over moisture will turn out the air from the pores of material, sludge turns into the pores of material, sludge turns into the lump and the anaerobic process is the lump and the anaerobic process is taking placetaking place

• The optimum moisture content should be The optimum moisture content should be in the range between 50-65% during the in the range between 50-65% during the composting processcomposting process

pHpH

• Important parameter in evaluating Important parameter in evaluating microbial environmentmicrobial environment

• Optimum pH = 6,5-8,0 during compostingOptimum pH = 6,5-8,0 during composting• In first few days of composting, the simple In first few days of composting, the simple

organic acids drops the pH to 5 or less. organic acids drops the pH to 5 or less. • If the degree of aeration is not adequate, If the degree of aeration is not adequate,

anaerobic conditions will occur, the pile pH anaerobic conditions will occur, the pile pH will drop to about 4,5 and the composting will drop to about 4,5 and the composting process will be retardedprocess will be retarded

• After the temperature reaches a After the temperature reaches a thermophilic stage the pH begins to rise to thermophilic stage the pH begins to rise to 8-8,5 and falls in mesophilic stage to 7-88-8,5 and falls in mesophilic stage to 7-8

The bulking materialsThe bulking materials

• For the regulation of C/N ratioFor the regulation of C/N ratio

• For guaranteed of needful For guaranteed of needful porosity of compost (aeration)porosity of compost (aeration)

• Optimum particle size should be Optimum particle size should be between 25-75 mmbetween 25-75 mm

• For regulation of moisture For regulation of moisture content inside the windrowcontent inside the windrow

UsUseded bulk materials bulk materials

• shredded barkshredded bark

• woodchipswoodchips

• strawstraw

• peatpeat

• woodenwooden building wastebuilding waste

• park waste (leaves)park waste (leaves)

• cardboard chipscardboard chips

• municipal wastemunicipal waste

• bark + peatbark + peat

• bark + wood ashbark + wood ash

• straw + barkstraw + bark

Shredded bark

+ t0 is rising quite fast and high

+ quite good structure+ C/N = 110-140

++ easy to get

- Unstable quality (structure, moisture, pH, resin)

Mature compost needs sieving

Sewage sludge:bark = 1:1,5-2,0

WoodchipsWoodchips

• Stable structureStable structure• Good aeration Good aeration

guaranteeguarantee• tt00 is rising fast and is rising fast and

stay in high level for stay in high level for a long timea long time

• C/N = 250 - 320C/N = 250 - 320• Dry mat. 50-60%Dry mat. 50-60%• Composting material Composting material

is not diffusiveis not diffusive

Sewage sludge:woodchipsSewage sludge:woodchips = 1:1- = 1:1-1,21,2

Wooden building waste

+ cheaper as bark

+ dry mat. 80-85%

+ C/N ~ 200

+ + richer of mineralsricher of minerals

-Inadvisable Inadvisable supplements may supplements may occuroccur-Unstable structureUnstable structure

Sewage sludge:building waste = 1:1,5-2,0

The strawThe straw

+ + After the mixing of After the mixing of pile the windrow is pile the windrow is very airyvery airy

+ t+ t00 is rising very fast is rising very fast+ C/N = 85 - 100+ C/N = 85 - 100+ dry mat. 55-65%+ dry mat. 55-65%+ high potassium + high potassium

contentcontent

- The sludge content in the The sludge content in the pile is very smallpile is very small

- The braking of straw balls The braking of straw balls adds workadds work

- The windrow falls dawn very The windrow falls dawn very fastfast

- The windrow needs intensive The windrow needs intensive mixingmixing

- Water absorption of the fresh Water absorption of the fresh material is not goodmaterial is not good

- The turning machine blocked The turning machine blocked by strings during combiningby strings during combining

Sewage sludge: strawSewage sludge: straw = 1: 3 – = 1: 3 – 3,53,5

The sewage sludge composting with the straw

The peatThe peat

-- C/N C/N = 45-50= 45-50++dry madry material terial ~~

75%75%+ mature + mature compost compost

lookslooks like a soillike a soil

-- Bad aeration of the pileBad aeration of the pile- Acidic pHAcidic pH- tt00 can`t rise o can`t rise ovver 40 er 40 00CC- The melting of frozen pile The melting of frozen pile

takes long timetakes long time- The destruction time of The destruction time of

pathogens is slowpathogens is slow- Needs intensive mixingNeeds intensive mixing- Good accumulator of Good accumulator of

toxically compounds toxically compounds

The peat accumulates lot of The peat accumulates lot of waterwater

Sewage sludge:peatSewage sludge:peat = 1:1,5-2,0 = 1:1,5-2,0

Park waste

Sewage sludge : park waste = 1:1,5

+ + quite stable structurequite stable structure+ cheap+ cheap+ mature compost like a + mature compost like a soilsoil

- C/N = 40-- C/N = 40-6060- - tt00 is rising slowly is rising slowly

- - Needs intensive Needs intensive mixingmixing

- - Foreign matters, Foreign matters, hazardous wastehazardous waste

The park waste from autumn and spring are different

Syringes!!!

Cardboard chips

Sewage sludge :cardboard chips = 1:3

+ dry mat. 70-75%

+ free of charge

+ C/N = 300-400

+ shredded material is airy

- - Shredding is problematical

- The big amount of bulk material may cause the temperature drop under critical level

-The content of PAH is higher

- Outlook and using of mature compost is problematical

Municipal waste

• C/N = 30-40• Structure problems• Non-biodegradable

material• Biodegradable organic

material falls dawn during composting

Sewage sludge: municipal waste = 1:1

Test piles in 2006

bark

building waste

park waste

cardboard waste municipal wastemunicipal waste

Temperature inTemperature inside theside the windrowswindrows

t0 is measured in the depht of 50 cm of the windrows

Temperature inside the piles

0

10

20

30

40

50

60

70

0 2 3 5 6 9 10 14 17 21 25 28 30 31 33 35 38 42 48 52 58

The day after mixing

Tem

per

atu

re

0 C

straw straw+bark bark+ash woodchips bark peat

Fertilization quality of mature Fertilization quality of mature compostcompost

• Fertilization quality the same as in case of Fertilization quality the same as in case of manuremanure

• The chemical and biological control more The chemical and biological control more effective as in case of manure effective as in case of manure

• The manure is more dangerous by biological The manure is more dangerous by biological parameters, because the tparameters, because the t00 is not high is not high enough in anaerobic process to kill enough in anaerobic process to kill pathogenspathogens

• The compost have to be matureThe compost have to be mature• In case of noIn case of nonn mature compost the mature compost the

degradation process will continue in soil, degradation process will continue in soil, the nitrogen may taken off from the soil and the nitrogen may taken off from the soil and the plants may diethe plants may die

Sewage sludge compostingSewage sludge composting

• Take the bulk material, which is Take the bulk material, which is right by structure and by qualityright by structure and by quality

• You have to mix and pile the raw You have to mix and pile the raw compost rapidlycompost rapidly

• Aerate (mix) the piles after Aerate (mix) the piles after optimum timeoptimum time

• Follow the required parametersFollow the required parameters• Correct the compost materials Correct the compost materials

content if you needcontent if you need

• Not enough O2

• Wrong bulkmaterial• Not enough H2O• Not enough N• Cold weather

• Mix the pile• Take the right bulkmaterial• Add water and mix• Add sludge• Wait for spring

Problems

Nothing is happening. Pile dosen`t seem to be heating up at all

Temperature is rising slowly and not high

• Not enough O2

• wrong C/N ratio• Not enough H2O• too much H2O

• mix the pile, change the structure• C/N = 20-30• add water and mix• add dry bulkmaterial and mix

Damp and warm only in the middle of the pile

• Too small or too large pile

• Not homogenous compost

• Cold weather

•Make the pile in a right size •Mix the pile

• Wait for spring

Possible causes

Solution

• Thick bulkmaterial• The pile is too wet• Less mixing

• Mix the pile, wait the piles top dries and mix again

• Add dry materials like straw or leaves

Problems

The compost in the lump

Bad odour • not enough not enough O2

• owe moisture• the pile is too compact• C/N ratio too high

• The same as previous

• Add bulk material

Possible causes solution

Attracts insects, millipedes, slugs etc.

This is normal

composting

Not a problem

Thank You!

Jüri Hallerhead of laboratory

Tartu Veevärk Ltd ESTONIAjyri.haller@tartuvesi.ee +372 7306233