jf, FiBL, CH-Frick 1

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1 Research Institute of Organic Agriculture Forschungsinstitut für biologischen Landbau Institut de recherche de l agriculture biologique to composting and anaerobic digestion How does composting work? Conclusions Biology of composting Jacques Fuchs (jacques.fuchs@fibl.org)? What means composting? The term composting describes a natural process, in which microorganisms transform organic residues in stabilized products. Products resulted from composting: - heat - compost (more or less mature) Composting. Compost? Compost? Composting shall not only be a cheap waste treatment. It shall be a way to improve soil fertility, the plant growth and the plant health in long terms. These improvements shall be approved by the process control. Compost is the solid, crumble, brownish to black brown product of an aerobic degradation of biogenic waste or organic material. There are huge numbers of microorganisms working under constant access of air (oxygen) and with enough moisture in the material mix. There is not only degradation, but also new formation. jf, FiBL, CH-Frick 1

2 What is suitable for composting? What is suitable for composting? Green waste Egg shells What is suitable for composting? manure What is suitable for composting? Theoretically all organic residues can be composted or digestated. However, not each one is easy to handle, biodegradable, and free from toxics and pathogenic germs. Depending of the system used, some residues are more or less easy to be treated Depending of the system, some input materials have to be treated before processing (e.g. pasteurization of kitchen waste before mesophilic anaerobic digestion) The start mixture is important for the success of the process Ways of degradation for organic material: Aerobic (composting) Anaerobic (anaerobic digestion) Differences between composting and anaerobic digestion? Oxygen Energy balance Degradation products Phases Utilization field Lignin (wood) can not be decomposed anaerobe! jf, FiBL, CH-Frick 2

3 The natural cycle of life Energie Mineral nutrients Humus (compost) O2 CO2 living organisms O2 CO2 Organic residues Energy (heat) microorganisms Water Two elements are especially important in the cycle of life: The cycle of carbon: Carbon (source of energy) Nitrogen (protein formation) 1 The cycle of nitrogen: The microorganisms of composting Mushrooms Actinomycetes Bacteria jf, FiBL, CH-Frick 3

4 The microorganisms of composting Bacteria aerobic / anaerobic very active at the beginning of the process responsible for the hot phase can not abolish wood efficiently The microorganisms of composting Mushrooms aerobic abolish wood creation of stabilized crumbs important during maturity stage The microorganisms of composting Actinomycetes (ray fungus) can abolish substances, which can not be abolish with bacteria or mashrooms, for example chitin responsible for decomposition of difficult decomposable materials Composting: two steps system Step 1: Process of decomposition (mostly bacteria at work) intensive microbiological activity increasing in temperature extreme loss in volume naturally hygienisation Step 2: Maturity stage (mostly mushrooms at work) creation of stable humus development of positive characteristics of compost Degradation of cellulose during hot step Degradation of proteins during hot step CO 2 + H 2 O + energie NH 3 + CO 2 + H 2 O + (H 2 S) + energie jf, FiBL, CH-Frick 4

5 Dissolution of ammonia in water Nitrification to nitrate ammonia ammonium + - ammonium + liquid ammonia - oxygen water nitrate liquid ammonia - nitric acid + Maturity stage protein (water) H 2 O gaseous losses (ammoniac) NH 3 Maturity stage Decomposition of lignin and building of humus gaseous losses air nitrogen N 2 laughing gas N O 2 NH 4 + (ammonia) OH - (basic) Nitrit NO 2 - (oxygen from air) O 2 NO (nitrate) H (acide) 2 H 2O (Wasser) nitric acid The process parameters Evolution of temperature during composting Temperature Composition of gases Nmin forms Organic substance ph-value Intensity of extract coloration jf, FiBL, CH-Frick 5

6 Evolution of gas composition during composting Evolution of N min forms during composting NH 4 + -N NO 2 - -N NO 3 - -N 20 CO O Evolution of ph during composting Evolution of organic substance during composting Evolution of water extract coloration during composting 150 Evolution of undesirable materials during the rotting process heavy metals jf, FiBL, CH-Frick 6

7 Evolution of undesirable materials during the rotting process for example 90 kg degradable material before after for example 45 kg degradable material Evolution of undesirable materials during the rotting process heavy metals other chemical compounds??? pathogenic germs and weed seeds for example 10 kg nondegradable material = 10 % = 18 % for example 10 kg nondegradable material Final product: compost organic fertilization amelioration of soil structure biological plant protection product Compost is not waste material! Process management: Factors of process management: From collecting of green waste to utilization of the final product Concept of green manure collection Composting system Mixture of raw materials Process management Storage of end-material jf, FiBL, CH-Frick 7

8 Concept of waste collection Concept of green manure collection Can influence the quality of input materials (e.g. quantity of undesirable inputs) Organizing the materials needed to become an adequate start mixture Composting system Composting system Each composting system, has its own specificities The different management operation have to be adapted to the system Mixture composition Coarseness of the start mixture Aeration and humidity management Composition of the start mixture Start mixture C:N-ratio ( available ) jf, FiBL, CH-Frick 8

9 C:N-ratio of some materials Urine: 0.8 Feathers: 4 5 Chicken manure: 8 10 Grass: 12 Mature compost: Young compost: Cows manure: Kitchen waste: 23 Ideal C:N of start mixture: Trees leaves 50 Straw Wood (sawdust): Start mixture C:N-ratio ( available ) Structure, moisture Ideal mixture : 1/3 rough wood (shredded wood, sieved rest material from compost, snipped bark) 1/3 medium-fine, fibrous material (shredded branches, wood fibers, straw, foliage, switch grass, reed, peat from consumed potting compost) 1/3 material, nearly without structure (dung, grass, rumen contents, vegetables manure) Evtl. utilization of additives powdered clay, earth, enzymes, microorganisms, fertilizer, etc. Process management: humidity Process management: humidity Enough humidity is necessary to allowed microorganism activities Too much humidity prevent a good aeration of the composting material and so a good process development At the begin of the process, an important quantity of water is need During the maturity phase, the addition of water is to performed very carefully Humidity management is one of the most difficult role of the compost manager! Process management: aeration Process management: aeration Mushrooms need oxygen to be active. Bacteria can be active without free oxygen. But then they take oxygen from other molecules, what can cause the production of toxic compounds (e.g. nitrite from nitrate) The aeration of the compost during the maturation phase is very important. The quality of the products depreciated if not enough oxygen is then available. jf, FiBL, CH-Frick 9

10 Process management: compost turning Process management: compost turning Compost turning is not only important to assure an sufficient oxygenation of the compost during the process Compost turning is important to become an homogenous product Compost turning activate also activate the biological activity of the process Process management: storage of the products Process management: storage of the products Compost is an living product. If he didn t be come oxygen, he will died! Mature compost didn t need a lot of oxygen. But a minimum has to be assure. Different factors are important: Dimensions of the storage pile Maturity stage of the products Humidity Use of additives Conclusions Process management: storage of the products jf, FiBL, CH-Frick 10

11 Conclusions Thank you very much for your attention Knowledge of the biology of composting is essential to understand and managed the process Process management is the key for a successful production quality compost Compost quality is the basic condition to improve the market for the products and so to secure the system. jf, FiBL, CH-Frick 11