The composting of sewage sludge in Tartu Waterworks Ltd

1. The composting of sewage sludge in Tartu Waterworks Ltd Jüri Haller Head of laboratory ESTONIA Sigulda, 24-25 of April, 2008.

2. The requirements for using of sewage sludge in agriculture, in urban landscaping and in recultivationRegulation No 78 of 30.Dec.2002 of the Minister of Environment • The sewage sludge considered treated after using 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

3. Escherichia coli Most die within 1 hour at 550C and within 15-20 min at 600C t0 and time of exposure required for destruction of some common pathogens and 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

4. 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

5. Temperature t0 indicates the activity of the 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 Requirements for composting

6. Temperature development inside the composting piles

7. Requirements for composting The optimume C/N = 20-30 C N

8. C/N ratio • carbon as a source of energy • nitrogen for building cell structure Organisms that decompose organic matter use

9. Small C/N ratio(much N) 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! The organisms that decompose organic matter are using carbon, as a energy source and nitrogen as crucial component of the proteins in fixed ratio • Too much carbon (C/N is big) • Decomposition slows when the nitrogen is used up and some organisms die • Other organisms form new cell material using their stored nitrogen

10. C/N ratio effects on composting

11. 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 evil smelling slime Optimal O2 content during aerobic composting process is 10-20% Oxygen

12. 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

13. Turning Mixing and breaking Mixing or tuning

14. Temperature inside the windrow is uneven Why is important to mix the windrows!

15. 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

16. Moisture content • In connexion with intensity of biological 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

17. pH • Important parameter in evaluating microbial 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

18. 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

19. shredded bark woodchips straw peat woodenbuilding waste park waste (leaves) cardboard chips municipal waste bark + peat bark + wood ash straw + bark Used bulk materials

20. Shredded bark Sewage sludge:bark = 1:1,5-2,0 + t0 is rising quite fast and high +easy to get + quite good structure Mature compost needs sieving + C/N = 110-140 - Unstable quality (structure, moisture, pH, resin)

21. Woodchips Sewage sludge:woodchips = 1:1-1,2 • Stable structure • Good aeration 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

22. Wooden building waste Sewage sludge:building waste = 1:1,5-2,0 + cheaper as bark +dry mat. 80-85% • Inadvisable supplements may occur • Unstable structure + C/N ~ 200 + richer of minerals

23. + 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 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 straw Sewage sludge: straw = 1: 3 – 3,5

24. The sewage sludge composting with the straw

25. -C/N = 45-50 +dry material ~ 75% + mature compost lookslike 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 Sewage sludge:peat = 1:1,5-2,0 The peat accumulates lot of water

26. Park waste Sewage sludge : park waste = 1:1,5 + quite stable structure + cheap + mature compost like a soil The park waste from autumn and spring are different - Foreign matters, hazardous waste - C/N = 40-60 - t0 is rising slowly - Needs intensive mixing Syringes!!!

27. Cardboard chips Sewage sludge :cardboard chips = 1:3 + dry mat. 70-75% - Shredding is problematical +free of charge - Outlook and using of mature compost is problematical - The big amount of bulk material may cause the temperature drop under critical level + C/N = 300-400 + shredded material is airy • The content of PAH is higher

28. C/N = 30-40 Structure problems Non-biodegradable material Biodegradable organic material falls dawn during composting Municipal waste Sewage sludge: municipal waste = 1:1

29. Test piles in 2006 municipal waste bark cardboard waste building waste park waste

30. Temperature inside thewindrows t0 is measured in the depht of 50 cm of the windrows

31. Fertilization quality of mature compost • Fertilization quality the same as in case of 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

32. 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

33. 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 Possible causes Solution Nothing is happening. Pile dosen`t seem to be heating up at all • mix the pile, change the structure • C/N = 20-30 • add water and mix • add dry bulkmaterial and mix • Not enough O2 • wrong C/N ratio • Not enough H2O • too much H2O Temperature is rising slowly and not high 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

34. 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 Possible causes solution Problems The compost in the lump • not enough O2 • owemoisture • the pile is too compact • C/N ratio too high Bad odour • The same as previous • Add bulkmaterial This is normal composting Not a problem Attracts insects, millipedes, slugs etc.

35. Thank You! Jüri Hallerhead of laboratory Tartu Veevärk Ltd ESTONIA jyri.haller@tartuvesi.ee+3727306233