The composting of sewage sludge in Tartu Waterworks

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 • • 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 0 C at least 6 days

t 0 and time of exposure required for destruction of some common pathogens and Escherichia coli Most die within 1 hour at 550 C and within 15 -20 min at 600 C Salmonella typhosa No growth beyond 46 0 C; death within 30 min. at 55 -60 0 C; 20 min at 60 0 C Salmonella sp. Death within 1 hour at 550 C and within 15 -20 min at 600 C Streptococcus pyogenes Death within 10 min. at 54 0 C

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 • t 0 indicates the activity of the • Temperature • • • decomposition process Micro-organisms release heat as they feed and grow Microbiological activity in the pile is rising about 2 times in every 10 C 0 temperature rising Microbiological activity reduces on too high and on too low t 0 Optimum t 0 inside the pile should be between 45 and 55 0 C Pathogens are killed at 50 -55 0 C 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) • Biological activity of the process is going • • • Too much carbon (C/N is big) 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 • C 10 H 19 O 3 N + 12, 5 O 2 10 CO 2 + 8 H 2 O +NH 3 • If a compost heap gets short of air the result is an • evil smelling slime Optimal O 2 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 • • • degradation process and with compost material structure The water keeps 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

p. H • Important parameter in evaluating microbial • • environment Optimum p. H = 6, 5 -8, 0 during composting In first few days of composting, the simple organic acids drops the p. H to 5 or less. If the degree of aeration is not adequate, anaerobic conditions will occur, the pile p. H will drop to about 4, 5 and the composting process will be retarded After the temperature reaches a thermophilic stage the p. H 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 • • 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 + t 0 is rising quite fast and high + easy to get + quite good structure + C/N = 110 -140 - Unstable quality (structure, moisture, p. H, resin) Mature compost needs sieving

Woodchips Sewage sludge: woodchips = 1: 1 -1, 2 • Stable structure • Good aeration • • guarantee t 0 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 + t 0 is rising very fast + C/N = 85 - 100 + dry mat. 55 -65% + high potassium content 1. The sludge content in the pile is very small 2. The braking of straw balls adds work 3. The windrow falls dawn very fast 4. The windrow needs intensive mixing 5. Water absorption of the fresh material is not good 6. 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 p. H - t 0 can`t rise over 40 0 C - 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 - t 0 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 t 0 is measured in the depht of 50 cm of the windrows

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 t 0 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 • Nothing is • happening. Pile • dosen`t seem • to be heating • up at all Not enough O 2 Wrong bulkmaterial Not enough H 2 O Not enough N Cold weather Temperature is • Not enough O 2 rising slowly and not high • wrong C/N ratio • Not enough H 2 O • too much H 2 O Damp and warm only in the middle of the pile • • Solution Too small or too large pile Not homogenous compost • • • Mix the pile Take the right bulkmateria 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. • • • solution Thick bulkmaterial • The pile is too wet Less mixing • • not enough O 2 • 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 • The same as previous • Add bulk material Not a problem

Thank You! Jüri Haller head of laboratory Tartu Veevärk Ltd ESTONIA jyri. haller@tartuvesi. ee +372 7306233