Deliverable 5 Report on quality criteria for application ... · digestate as bio-fertiliser...

Project No. 030348

AGROBIOGAS

An integrated approach for biogas production with agricultural waste

Instrument: Specific Actions for SMEs: Collective Research Projects Thematic area: Sustainable development, global change, and ecosystems

Deliverable 5

Report on quality criteria for application of AD sludge as bio-fertiliser in

agriculture

Due date: 1st of September 2006 Submission date: 30/08/2006

Start date of project: 1st of June 2006 Duration: 36 months SDU

Final Version

Project co-funded by the European Commission within the Sixth Framework Programme (2002-2006)

Dissemination Level

PU Public

PP Restricted to other programme participants (including the Commission Services)

RE Restricted to a group specified by the consortium (including the Commission Services)

CO Confidential, only for members of the consortium (including the Commission Services) X

Agrobiogas: Deliverable 5 30.08.2006

Preface This report comprises the results from the work accomplished under subtask 1.4.2 of the Collective Research project AGROBIOGAS “An integrated approach for biogas production with agricultural waste” which is co-financed by European Union’s the 6th Framework Programme. The report was elaborated under leadership of the Syddansk Universitet (SDU) with assistance from the following partners:

• AAT (Italy) • AG (Sweden) • ASAJA (Spain) • BIOAZUL (Spain) • BME (Germany) • DAAS (Denmark) • EARL (France) • ELBE (Germany) • EUBIA (Europe) • GBA (Germany) • HG (Sweden) • PAS (Greece) • PD-K (Slovak Republic) • RES (Italy) • SA (Spain)

Esbjerg, Denmark August 2006 Al Seadi T., Holm-Nielsen J. B., Madsen M. SDU Subtask leader


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CONTENTS 1. Description of digestate........................................................................................................... 2

1.1. Fertiliser market in the European Union ........................................................................... 2 1.2. Production of digestate...................................................................................................... 2

2. Storage...................................................................................................................................... 4 3. Product declaration................................................................................................................. 5 4. Sanitary and hygienic.............................................................................................................. 8 5. EU regulation/directives ......................................................................................................... 8 6. Criteria for optimum utilisation ............................................................................................ 9

6.1. Aerobic composting ........................................................................................................ 12 6.2. Influence of the compost on the soil ............................................................................... 12

7. Tendencies in digestate utilisation in some EU countries.................................................. 13 7.1. Lithuania.......................................................................................................................... 13 7.2. Latvia............................................................................................................................... 13 7.3. Sweden ............................................................................................................................ 13 7.4. Italy.................................................................................................................................. 14

7.4.1. Utilisation of digestate in Italy ................................................................................ 14 7.4.2. Criteria for optimum utilisation of digestate as bio-fertiliser.................................. 15 7.4.3. Soil-conditioner....................................................................................................... 17

7.5. Germany.......................................................................................................................... 17 7.6. Spain................................................................................................................................ 18

References ...................................................................................................................................... 20


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1. Description of digestate

1.1. Fertiliser market in the European Union

According to the European Environment Agency (EEA), the consumption of fertilisers in agriculture will increase significantly in the EU over the next 20 years, mostly due to growth in agricultural production in the 8 new Member States. The EEA predicts an increase in mineral fertiliser consumption; consequently nutrient surpluses are expected (Figure 1).

Figure 1. Environmental pressures, fertiliser use, nutrient balance, and ammonia losses 2020/2001 (Source:

European Environment Agency, 2005)

Improving management in handling of organic fertilisers can result in a decrease in ammonia losses (i.e. fully covered storage facilities, better application techniques of manure, etc.). Overall, losses of P and K can be reduced by about 80% to 95% and by 50% for N, when correct fertiliser handling is applied. The increase of organic fertilisers (60-80%) substituting mineral fertilisers is expected in the near future (European Environment Agency, 2005).

1.2. Production of digestate

Besides biogas, anaerobic digestion produces digestate, consisting of a mixture of liquid and solid fractions and having a significant fertiliser value. The quality of the digestate depends on the feedstock and the digestion conditions. The anaerobic digestion causes a destruction of dry matter and a reduction of viscosity. For that reason, when spread on the farmland and on the growing plants, it drips off easier from the plants and penetrates faster into the soil, compared to raw manure. Consequently, there is a reduction in risk of plant etches, smaller ammonia losses if immediately incorporated in soil, and less odour problems (Pfundtner, 2002). In raw manure and organic residues, most of the nitrogen is bound in proteins. Throughout anaerobic digestion, a part of the nitrogen is released into dissolved ammonium. Therefore, nitrogen in digestate is easier available for plants. Highly efficient fertiliser can be achieved from co-digestion of cow manure (high in potassium), pig manure (high in phosphorous), and suitable agricultural wastes and by-products. Due to the fact that the digestate is nutritionally defined, it can be used very efficiently. Application of digestate as bio-fertiliser decreases nutrients losses as well as pollution of water by nutrients. Additionally, it results in saving energy consumption for production of chemical fertilisers. To obtain all these benefits, it is necessary to apply what is called a “good agricultural practice”.


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Example of a typical digestate composition is presented in Table 1 and Table 2. The results were taken from Linkoeping biogas plant in Sweden (Nordberg & al., 2002).

Table 1. Typical digestate (Source: Nordberg & al., 2002)

Parameter Digestate Linkoeping

Total solids [%] 4,5 Volatile solids [%TS] 75

pH 8,1 Total-N [kg/m3] 7,2

Ammonia-N [kg/m3] 4,9 P [kg/m3] 0,7 K [kg/m3] 1,0

Pb [mg/kgTS] <5,0 Cd [mg/kgTS] 0,12 Cu [mg/kgTS] 71 Cr [mg/kgTS] 5,7 Hg [mg/kgTS] <0,05 Ni [mg/kgTS] 5,2 Zn [mg/kgTS] 309

Table 2. Average concentrations of nitrogen, ammonia, and phosphorous in digestate from Danish centralised

co-digestion plants (Source: Danish Environmental Protection Agency, 2004)

Biogas plants Total N

(kg/ton)

NH4-N/NH3

(kg/ton)

P

(kg/ton)

Blaabjerg 4,75 3,25 1,1 Blåhøj 5,3 3,8 0,84 Fangel 5,83 4,38 0,92 Filskov 4,9 3,7 0,94 Hashøj 5,05 3,9 0,78 Lemvig 4,28 3,02 1,2 Lintrup 5 3,26 1,3 Nysted 4,84 3,79 0,9 Ribe 4,6 3,2 0,9 Sinding-Ørre 2,6 2,2 1,2 Snertinge 4,3 3 1,3 Studsgård 3,86 2,79 0,86 Thorsø 4,8 3,6 0,96 Vester Hjermitslev 6,3 5,1 0,56 Vegger 4,5 3,1 0,8

The produced digestate can be applied directly to the farmland as bio-fertiliser or can be separated in a liquid and a solid/fibre phase. The fibres can be used as a nutrient-rich soil conditioner and the liquid phase can be applied in the same way as unseparated digestate, as bio-fertiliser. Efficient utilisation of these two products gives the opportunity for the AD process to become a sustainable industry. Figure 2 shows a mass balance for anaerobic digestion (Anaerobic Digestion of farm and food processing residues, 1997).


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Figure 2. Simplified mass balance for anaerobic digestion (Source: Anaerobic Digestion of farm and food

processing residues, 1997)

In Table 3, the amount of digestible biomass for EU-15 is presented.

Table 3. Status of digestible biomass in EU-15 (Source: Holm-Nielsen, Al Seadi, 1997)

Municipal waste

generation

Cattle

manure

(1993)

Pig

manure

(1993)

Total

manure

(1993)

Population

(humans)

(1993) Total waste

450

kg/capita

Org. waste

(30% of

total)

Sewage

sludge

(1990)

Industrial

org. waste

Digestible

<35%DM

100kg/capita

*

106 tons 10

6 tons 10

6 tons 10

6 tons 10

6 tons 10

6 tons 10

6 tons 10

6 tons

Austria 25 8 32 7,7 3,5 1,0 2,3** 0,8 Belgium 35 14 49 9,9 4,5 1,3 0,7 1,0 Denmark 22 22 44 5,1 2,3 0,7 1,3 0,5 Finland 14 3 17 5,1*** 3,1*** 0,7 0,1 0,5 France 211 26 238 56,5 25,5 7,6 0,6 5,7 Germany 167 51 218 62,7 28,2 8,5 1,8 6,3 Greece 6 3 9 10,0 4,7 1,4 - 1,0 Ireland 66 3 69 3,5 1,6 0,5 0,6 0,4 Italy 80 15 95 57,6 25,9 7,8 3,4** 5,8 Luxemburg

2 0,2 2 0,4 0,2 0,02 0,02 0,04

Netherlands

48 28 77 14,9 6,7 2,0 0,3 1,5

Portugal 14 6 20 10,3 3,4*** 1,0 - 1,0 Spain 53 37 89 38,9 17,5 5,3 10,0 3,9 Sweden 19 5 24 8,6 3,9 1,2 0,2 0,9 UK 125 16 141 57,3 25,8 7,7 1,0 5,7 Total

EU -15 887 237 1.124 348,5 156,8 46,9 22,32 35,04

* Estimated figures, based on fixed data from Denmark, Finland, and the Netherlands; ** 1994 data; *** 1996 data

2. Storage

At least 6 months capacity is required by law for the storage of digestate. Sufficient capacity often corresponds to 9 months supplies. The sufficient storage capacity depends on manure quantities, crop rotation plans, rules for digestate spreading and requirements concerning the utilisation of the nitrogen and phosphorous in digestate (The Danish Agricultural Advisory centre, 1999). Requirements for 6-9 months storage capacity go together with restrictions for the application period, in order to apply digestate during the plant growing season, for optimal uptake of nutrients and consequently pollution avoidance. Storage tanks for manure/digestate must have tight cover, sheltering from wind and rainwater and avoiding obnoxious odours and losses of ammonia. Figure 3 shows a storage facility for digestate in Denmark.


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Figure 3. Container with tight cover for digestate (Source: Holm-Nielsen, 2004)

Digestate can be stored in the farm or at the centralised AD plant. After cooling down, it can be stored in lagoons or tanks. It would be better to place the storage tanks close to the areas where digestate will be applied. Stirring systems are necessary to avoid sedimentation in the storage tanks and to decrease the heterogeneity of the liquid as much as possible before the application or transportation (Anaerobic Digestion of farm and food processing residues, 1997). Storage facilities for soil-conditioner are also necessary. The market is seasonal; therefore, the storage will be needed for up to six months. The accumulated fibres will compost aerobically so, careful management and monitoring will be required (Anaerobic Digestion of farm and food processing residues, 1997). Stabilising through composting seems to be the best option. The soil-conditioner must be protected from rainwater.

3. Product declaration

The control system of the quality of digestate should be based on (Joensson & al., 2002):

• Systematic sampling and analysis of the feedstock and the digestate; it should be performed at least three times per year;

• No supply of household waste or “non specified” waste, which may contain harmful compounds;

• Careful process control, with focus on pasteurisation/sterilisation processes; • Regular contacts between farmers and suppliers of raw material.

Several certification systems already exist in European countries concerning fertilisers and utilisation of digestate as a fertiliser or soil-conditioner:

• BMLFUW, 2001: Der sachgerechte Einsatz von Biogasguelle und Garruckstanden im Acker- und Gruenland. (Appropriate use of digestate on arable land) Hrsg: Fachbeirat fur Bodenfruchtbarkeit und Bodenschutz, Wien 2001 (only available in German)

• Certification system: Swedish Association of Waste Management Report 99:2 (only in Swedish)

• Quality Assurance of Digestion Residuals – Germany Table 4 gives an overview on control systems for composting plants in several European countries.


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Table 4. Range of control systems for composting plants (Source: The European Compost Network)

Range of Control Systems for Composting Plants in Europe Production monitoring Product control Austria Compost Ordinance Compost Ordinance and KGVÖ Belgium VLACO - during the

first year of operation VLACO – beginning with the second year

Denmark Usage of digestate is integrated with Danish legislation about manure application* France According to ISO 9000 principle in the

Qualorg research project According to ISO 9000 principle in the Qualorg research project

Germany BGK BGK The Netherlands KIWA KIWA Sweden RVF Certification RVF Certification UK TCA procedures and records checked

for each assessment period TCA sampling, results, product storage and labelling checked for each assessment period

*Statutory order from the Ministry of the Environment no. 1121 of 15/12/1992, on professional livestock, livestock manure, silage, etc.

German example of quality criteria and quality guidelines for digestion residuals is presented below (Table 5 and Table 6):

Table 5. Quality criteria and quality requirements for solid residues from AD process (Source: The Compost

Quality Assurance Organisation)

Quality criteria Quality requirements

Nitrogen total to be declared % DM Phosphate (P2O5) total to be declared % DM Potassium (K2O) total to be declared % DM Magnesium (MgO) total to be declared % DM Content of alkaline effective materials

to be declared % CaO DM

Nitrogen (NH4-N + NO3-N) soluble

to be declared mg/l FM

Phosphate (P2O5) soluble to be declared mg/l FM Potassium (K2O) soluble to be declared mg/l FM Magnesium (Mg) soluble to be declared mg/l FM Organic matter at least 40, to be declared % DM pH value to be declared Salt content to be declared g/l FM Dry matter dm at least 20, compact and

spreadable % FM

Bulk density to be declared g/l FM Grain size to be declared Foreign matter >2mm diameter 0,5 at maximum % DM Stones >5mm diameter ≤ 3% % DM Degree of digestion organic acids < 4.000 mg/l FM Odour free from annoying odours graduation Hygiene (a) heating of the input material on ≥ 70 °C for at least one hour, or

(b) proof to be tested on epidemic hygienic effectiveness of the process procedure or the treatment, according to Para 3 article and article 4 no.1 and 2 BioAbV, or

(c) influence of a minimum temperature of 55 °C over a period of 24 hours and a hydraulic dwell time in the vessel of at least 20 days (compare addition 2 no.2.2 article 1 sentence 1 BioAbfV), or

(d) input-output control, or


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(e) heating of the output material by heating on to ≥ 70 °C for at least 1 hour, or

(f) other procedures of hygienisation Germinable seeds and sprouting plant parts

nearly none (< 0,5) Per litre FM

Salmonellae Salmonellae not present none in 50 g FM Heavy metal contents (limit values)

Pb=150; Cd=1,5; Cr=100; Cu=100; Ni=50; Hg=1; Zn=400

mg/kg DM

Precaution benefit-ratio efficiency value index

1 : > 4 > 4

Table 6. Quality criteria and quality requirements for liquid residuals from AD process (Source: The Compost

Quality Assurance Organisation)

Quality criteria Quality requirements

Nitrogen total to be declared % DM Phosphate (P2O5) total to be declared % DM Potassium (K2O) total to be declared % DM Magnesium (MgO) total to be declared % DM Content of alkaline effective materials

to be declared % CaO DM

Nitrogen (NH4-N + NO3-N) soluble

to be declared mg/l FM

Phosphate (P2O5) soluble to be declared mg/l FM Potassium (K2O) soluble to be declared mg/l FM Magnesium (Mg) soluble to be declared mg/l FM Organic matter at least 40, to be declared % DM pH value to be declared Salt content to be declared g/l FM Dry matter at least 12, pumpable % FM Bulk density to be declared g/l FM Homogeneity visually homogenous, free from

impurities

Foreign matter >2mm diameter 0,5 at maximum % DM Stones >5mm diameter ≤ 3% % DM Degree of digestion organic acids < 4.000 mg/l FM Odour free from annoying odours graduation Plant compatibility Suitable for the use in growing

plant cultivation without the danger of etching of overground plant parts

Hygiene (a) heating of the input material on ≥ 70 °C for at least one hour, or (b) proof to be tested on epidemic hygienic effectiveness of the

process procedure or the treatment, according to Para 3 article and article 4 no.1 and 2 BioAbV, or

(c) influence of a minimum temperature of 55 °C over a period of 24 hours and a hydraulic dwell time in the vessel of at least 20 days (compare addition 2 no.2.2 article 1 sentence 1 BioAbfV), or

(d) input-output control, or (e) heating of the output material by heating on to ≥ 70 °C for at

least 1 hour, or (f) other procedures of hygienisation

Germinable seeds and sprouting plant parts

nearly none (< 0,5) Per litre FM

Salmonellae Salmonellae are not detected n.n. in 50 g FM


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Heavy metal contents (limit values)

Pb=150; Cd=1,5; Cr=100; Cu=100; Ni=50; Hg=1; Zn=400

mg/kg DM

Precaution benefit-ratio efficiency value index

1 : > 4 > 4

4. Sanitary and hygienic

Organic waste can contain infectious matters, which can result in new spreadings of pathogens and disease transmission between animals, humans and the environment. Therefore, many countries enforced their legislation regarding pathogen control in digestate. At the same time, the European Council elaborated rules and regulations that are mandatory for all the Member Countries. The most recent example is the “Animal By-Products Directive” - 1774/2002. The directive lays down health rules concerning animal by-products not intended for human consumption. Furthermore, the condition of approval for biogas and composting plants are highlighted and the concept of the AD plants “own check”. According to the Animal By-Product Directive, the animal by-products are divided into three main categories. The categories and required pre-treatments are shown in Table 7 (Kirchmayr & al., 2003). All approved Danish biogas plants follow presented procedures.

Table 7. Pre-treatment of feedstock according to Animal By-Products, EC Regulation No 1774/2002

Category Material Pre-treatment

Category 1 Specific risk materials (SRM), animals suspected of being infected with BSE, ABP with increased concentrations of environmental contaminants.

Materials of Category 1 must

not be processed in a biogas

plant!

Category 2 All ABP that are neither included in category 1 nor in Category 3. These are also manure, digestive tract content, milk not fit for human consumption, killed or fallen animals, and solid materials in wastewater streams of slaughter houses. Manure, digestive tract

content, and milk need no pre-treatment before

digestion.

Materials of Category 2 are allowed to be processed in biogas planned after sterilisation with steam pressure: 20 min., >133 ºC, 3 bar pressure

Category 3 All ABP originating from animals fit for slaughter but not intended for human consumption as well as ABP from food production and catering waste.

Materials of Category 3 must be pasteurised before treating in an approved biogas plant.

The most important substrates for the AD process, animal manure and energy crops, do not require any hygienic/sanitary pre-treatment before anaerobic digestion. According to the Regulation 1774/2002, the digested end-products should fulfil the following requirements:

• Salmonella spp – absence in 5 samples of 25 g each • Clostridium perfringens - in 5 samples of 1 g each: 3 samples: <10 CFU/g, 2 samples

<300 CFU/g 5. EU regulation/directives

There are several EU directives and regulations, which might have an influence on utilisation of digestate as a fertiliser. Annex III of the working document “Biological Treatment of Biowaste” presents requirements for compost/digestate in terms of harmful substances (Table 8) (Biological Treatment of Biowaste, 2001).


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Table 8. Requirements for digestate/compost (Source: Biological Treatment of Biowaste, 2001)

Compost/digestate* Parameter

Class 1 Class 2

Stabilised

biowaste

Cd [mg/kg DM] 0,7 1,5 5,0 Cr [mg/kg DM] 100 150 600 Cu [mg/kg DM] 100 150 600 Hg [mg/kg DM] 0,5 1,0 5.0 Ni [mg/kg DM] 50 75 150 Pb [mg/kg DM] 100 150 500 Zn [mg/kg DM] 200 400 1500

PCBs [mg/kg DM] - - 0,4 PAHs [mg/kg DM] - - 3,0 Impurities >2mm < 0,5% < 0,5% <3,0%

Gravel and stones >5mm < 5,0% < 5,0% - * normalised to an organic matter content of 30%

The above figures and requirements are based on the Working Document “Biological Treatment of Biowaste”, 2nd Draft, 2001. However, the document has been abandoned by the European Commission and for the time being, will not be followed by a legislative proposal. Some of the EU regulations relevant for digestate streams are:

• Landfill Directive 99/31/EC – The objective of this Directive is to prevent or reduce, as far as possible, negative effects on the environment from the landfilling of waste, by introducing stringent technical requirements for waste and landfills;

• Regulation (EC) No 1774/2002 of the European Parliament and of the Council of October 3rd 2002 laying down health rules concerning animal by-products not intended for human consumption;

• Sewage Sludge Directive 86/278/EEC - On the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture;

• Organic Farming Regulation (EEC) No.2092/91 - On organic production of agricultural products and indications referring thereto on agricultural products and foodstuffs;

• Eco-label for soil improvers and growing media – Commission Decision 2001/688/EC establishing ecological criteria for the award of the Community eco-label to soil improvers and growing media;

• EU Waste Management Strategy (COM(96) 399) - The management of specific waste streams represents an important element of the general EU Waste Management Strategy (COM(96) 399) by helping to reduce the impact of waste on the environment. This is done by ensuring that waste is treated in an environmentally sound manner. Action on a specific waste stream is occasioned by its volume, its hazardousness, its treatment properties, and its effects on the ecosystem.

6. Criteria for optimum utilisation

Animal manure, especially cattle manure, has been used as organic fertiliser for thousands of years. As a consequence of the unbalanced distribution and the intensification of animal production in some regions of the world, an excess of manure is produced today, compared to the available land for its optimal use. Since the application of excessive amounts of manure on land has caused severe environmental problems, an expensive transfer of the manure in excess to areas in need for organic nutrients seems to be the only solution. Due to this, in some countries regulations/restrictions on manure handling and application were implemented (storage capacities, amounts per ha, restricted periods for application, specific spreading techniques, etc.), reducing


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further the value of manure. Gradually, animal manure has turned from a valuable natural fertiliser into an environmental problem, in areas with high livestock density and intensive animal production. A good example of restriction of application of animal manure, in order to avoid pollution, is the Danish regulation known as the “harmony rules” (Statutory order from the Ministry of the Environment No. 906, of 14/10/1996, on professional livestock, livestock manure, silage etc). The harmony rules regulate the maximum input of nitrogen per hectare and per year, by prescribing the maximum allowed livestock units (LU) loading per hectare and were enforced in 1987 by the Water Environment Action Plan I (Al Seadi & al, 2000). The statutory order defines a livestock unit as “a unit of calculation” corresponding to a maximum of 100 kg of nitrogen in manure, including the quantity deposited by the animals on the field. The Danish farmers supplying their animal slurry and manure to a centralised biogas plant are helped to meet the harmony requirements, as they receive back only the amount of digested biomass they are allowed to spread on their fields, according to the harmony law. One of the main environmental functions of a centralised plant is the redistribution of manure, and the common practice is that the excess is transferred to arable farms in the area. Separation of digestate into a liquid and fibre fraction facilitates the export of the fibres (rich in P) to other areas. The Statutory order from the Ministry of the Environment No. 906, of 14/10/1996, on professional livestock, livestock manure, silage, etc. further prescribes the detection limits for heavy metals and for persistent organic compounds that are allowed to be spread on farmland with organic fertilisers (manure, organic wastes, digestate, etc.) and the sanitation requirements. The amount of heavy metals, which can be spread on the land with compost, liquid manure, and digestate, are presented in Table 9 (Amlinger & al., 2004) (Friedmann, 2002). The figures are the result of a study carried out on behalf of the Directorate-General for the Environment of the European Commission, in the context of the European waste management policy and work on the biological treatment of biodegradable waste.

Table 9. Amount of heavy metals which is allowed to be spread on the land (Source: Friedmann, 2002)

Fertiliser Heavy metal

Liquid manure 1

Compost2

Digestate3

Pb g.ha-1.year-1 22 1000 24,3 Cd g.ha-1.year-1 0,92 10 0,3 Cr g.ha-1.year-1 12 667 9,6 Cu g.ha-1.year-1 90 667 131,2 Ni g.ha-1.year-1 8,0 333 13,2 Hg g.ha-1.year-1 0,1 7,0 0,03 Zn g.ha-1.year-1 444 2667 272

(1) Liquid manure with 10% DM content, application 2t DM.ha-1.year-1

(2) Permissible amount of compost 20t DM.ha-1.3 year-1

(3) Liquid digestate, application 30t ha-1.year-1


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Some guidelines for optimal application of digestate:

• The application of digestate as bio-fertiliser must be done in accordance with the fertilisation plan of the farm, where digestate replaces chemical fertilisers;

• It is a good practice to analyse the soil and the bio-fertiliser systematically in order to achieve the best application rate as well as to quantify the amount of needed chemical fertiliser. Over-application causes vegetation scorching and water pollution (Anaerobic Digestion of farm and food processing residues, 1997);

• To minimise nitrogen leaching to the ground water, the digestate should be applied in the time period, where the maximum crop growth and nitrogen uptake take place (Pfundtner,2002);

• There is higher risk of ammonia losses during applying digestate compared to untreated slurry, because of the greater ammonium content. Nitrates are lost by leaching to the ground water, whereas ammonia by volatilisation into the atmosphere. To decrease the gaseous losses, the digestate should be applied in cold and windless days (Pfundtner, 2002) (Al Seadi);

• Minimising ammonia losses up to 95% can be done by applying close to the ground and by an immediate incorporation or injection into the ground with proper application system like soil injection and trailing hose systems (Pfundtner, 2002);

• In order to decrease ammonia liability to volatilise, the pH value can be decreased by addition of acid to the digestate (optional) (Al Seadi);

• Due to the high water content of the liquid bio-fertiliser, it has significant irrigation benefits. On agricultural land, it can be applied for so-called “fertigation”. Although, it should not be used in greenhouses because of the particles content - this could block feeder pipes (Anaerobic Digestion of farm and food processing residues, 1997);

• The fibre fraction after AD process contains rather low rate of nutrients required by plants; however, it can serve as an efficient soil conditioner. The best way to use fibres is to return them to the land. Spreading the fibres after AD process should not cause any problems and could be done using a small tractor. Specialised equipment is not necessary (Anaerobic Digestion of farm and food processing residues, 1997). Such fibres should not contain obnoxious odours;

• According to Anaerobic Digestion of farm and food processing residues (1997), in some cases, the fibres from anaerobic digestion can be applied instead of peat. One should remember that it does not have exactly the same properties as peat (which is nutrient-free);

• In order to increase the value of the fibres, further processing is possible. Composting it aerobically will produce potting compost/growing medium.

Figure 4 shows application of digestate with trailing hoses system in Denmark.

Figure 4. Fertilisation the field with digestate using trailing hoses system (Holm-Nielsen, 2004)


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6.1. Aerobic composting

Composting the fibres aerobically has several advantages. Composting is an auto-thermal aerobic process. It has the ability to convert the waste biologically into a more stable material. It is common to compost raw animal manure to obtain a less heterogeneous substance, which has better influence on air, water and land environment. According to Cronje & al. (2004), the optimum C/N ratio for composting is from 20/1 to 40/1. The optimal moisture content for the process equals to 55%-65%. However, composting with higher moisture content is possible but only if enough oxygen is available for the aerobic activity. Measurement of oxygen uptake rate will give information about aerobic activity and consequently, about decomposition of organic compounds. According to Cronje & al. (2004), the highest rate of aerobic microbial activity occurs around 60 °C, which corresponds to the greatest stability of the composted material as well. Information about compost stability is required. As an example, it will be part of the French legislation on organic amendment quality (Francou & al., 2005). The basic measures to monitor the process are temperature, humidity and aeration control. Francou & al. (2005) suggest huminification index (C-HA/C-FA) as the most correct stability indicator. More than 1-3 should be sign of good stability. From the practical tools, the self-heating test is recommended. Compost is considered stable when the temperature does not exceed 40 ºC during the test (Rotting degree IV and V). According to the above research, the stabilised organic matter of green waste, biowaste and sewage sludge was achieved after 3-4 months of composting (Francou & al., 2005). However, composting of digestate should have a shorter period, due to anaerobic digestion process conducted before composting. Application of rapid maturity test will be necessary for the compost producers to be able to follow stabilisation level during the composting. Domeizel & al. (2004) present UV spectroscopy as a promising tool for monitoring huminification.

6.2. Influence of the compost on the soil

The overview on the short-term effects of amendments would be necessary in order to develop soil-conservation strategies. The most common determining of soil organic matter concentration might be not enough. The organic content changes very slowly so, to notice significant variations in soil quality, many years of monitoring are necessary. According to Saviozzi & al. (2006), soil biochemical parameters like soil respiration and enzyme activities are efficient indicators in relation to soil quality. Consequently, long-term planning for soil-conservation strategies can be done based on those reference values. Saviozzi & al. (2006) describe the influence of the mixture of green waste compost and cattle manure on soil. The investigation showed that such a mixture decreased pH value during the first few days after application, which increased back to the initial value during the next days. pH is an important indicator; its changes have direct influence on biochemical activities in the soil. Another parameter is dissolved organic carbon (DOC), which is usually less than 1% of the total organic carbon content. DOC migration from surface to deep levels corresponds to the main way for translocation of nutrients and energetic compounds (Saviozzi & al., 2006). Addition of compost-mixture increased its value, which then decreased during the next 60 days (being still higher than initial value in the pure soil). The water-soluble carbon, energy source for the micro-organisms, was degraded in the first stage of the mineralisation.


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Microbial biomass activity can be determined by soil ATP (Adenosintriphosphate) level. The microbial activity increased after addition of cattle manure, and it decreased again when the DOC value declined (Saviozzi & al., 2006). Concluding from the research presented above, application of digestate obtained from AD process based on animal manure and agricultural waste will have significant positive influence in improving the soil conditions.

7. Tendencies in digestate utilisation in some EU countries

The short national reports below are based on replies to a questionnaire that was sent out to all

the Agrobiogas partners involved in this subtask.

7.1. Lithuania

The biogas production in Lithuania currently occurs at six facilities: two waste water treatment plants, two food industry treatment plants and two pilot plants treating animal manure. The annual production of digestate is 19.000 tons. No declaration or certification system for digestate yet exists and typical characteristics for the digestate have not been recovered.

7.2. Latvia

In Latvia, the annual production of digestate has been estimated to 28.000 tons arising from treatment of municipal sewage sludge, agricultural waste, and industrial organic waste. A certification system has not been established, and no standardised declaration for digestate has been found.

7.3. Sweden

The estimated production of digestate in Sweden is 1.000.000 tons on an annual basis. Included in this figure is 251.000 tons of bio-fertiliser. A certification system for declaration of the digestate does exist (SP 120). The typical composition of the digestate is shown in Table 10.

Table 10. Composition of digestate from Swedish biogas plants

Dry matter

[%]

Total N

[kg/ton DM]

P

[kg/ton DM]

K

[kg/ton DM]

NH4+-N

[kg/ton DM]

3,9 116 14 51 77

Among the monitored impurities in digestate, there are organic and inorganic compounds and heavy metals. Approximately 93% of the digestate is recirculated back to agricultural land as liquid fertiliser. Regarding storage of the digestate, the store has to be covered either with a solid lid or a floating lid. The cover prevents odour emissions at the same time. The average storage period is 8-10 months. The digestate is applied to grain crops in the spring and to grain crops and rape seed in the autumn. Occasionally, acid is added to the digestate to ensure the chemical stability. But this happens very rarely. No post-treatment methods are applied to the digestate. EC-legislation for sanitation of waste prior to digestion is followed, when appropriate.


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In general, farmers applying digestate are pleased with the quality of the product. They believe that an utilisation of 70-75% of the supplied NH4-N is obtained. Bio-fertiliser is not applied to ley crops intended for forage production. The application of digestate to farm land is accomplished by use of tractors and manure spreaders with dragging hoses.

7.4. Italy (Bonazzi, 2006)(Bonazzi, 2001)(Piccinini, 2005) Recently, in Italy, Environmental Regulations have been upset as a new and unique rule for all environmental topics (and primarily for waste and water management) (“T.U.”, Unique Rule). The above mentioned regulation is called D.Lgs.152/2006 (together with all the related Acts) that abrogates all the previous rules and in particular, the D.Lgs 152/99 (T.U. on water management), the D.Lgs. 22/97 (Ronchi Act), and the 748/84 Law on fertiliser control that has been replaced by the D.Lgs 217/2006 Act. In addition to that, regarding the “wastewater agronomical Use”, the recent 209/2006 Act, released by the Agriculture and Forest Department and putting into effect the abrogated art. 38 (D.Lgs. 152/99) that is currently art. 112 (D.Lgs. 152/2006), needs local updating. That means that each Region must bring up to date the local Regulation, but they have not yet carried out the updating procedure. In conclusion, the assertions mentioned below could be only temporarily meaningful, mainly when we talk about the Regional regulations on digestate use in agriculture, that are going to be reviewed in a short time. At the moment, the digestate coming from energy crops, agricultural and animal wastes and vegetable organic wastes from food industry, can be treated in two different ways:

1. it can be sold as bio-fertiliser or soil conditioner, if digestate, as it is or as output from one or more treatments (composting, drying, etc.), is suitable from a chemical, physical, and biological point of view according to the Act on fertilisers (D.Lgs. 217/2006), then

2. in all the other cases, digestate must respect the MiPAF 209/2006 Ruling principles and be disposed according to an agronomical use.

It is estimated that the annual production of digestate is close to 40 million tons. The above mentioned evaluation has been made by analysing the available data on anaerobic digesters in the food industry field and on annual Italian biogas production by anaerobic digestion plants, not including the biogas collected in landfills. When comparing this value with estimates on available biomass (CRPA- Animal Production Research Centre, Reggio Emilia, Italy) originating from animal manure, agricultural residues and agro-industry wastes (ca. 250.000.000 tons/y), then, less than 20% of the actual biomass potential is used in Italy. The most common biomass types for AD are: animal manure, industrial organic wastes (distilleries, sugar industry, juices and bakery industry, alimentary oil industry), the organic fraction of MSW, and wastewater sludge.

7.4.1. Utilisation of digestate in Italy According to the Italian Regulation (D.Lgs. 217/2006), there are the following definitions of bio-fertiliser and soil conditioner:

• Bio-fertiliser (art. 2 let. P) - a dressing coming from organic material, vegetal or animal, formed by organic compounds with the main fertility elements linked by chemical bonds or belonging entirely to the matrix.

• Soil-conditioner (art. 2 let. Z) - any material to be added to soil in situ in order to, mainly, preserve or improve the soil physical and/or chemical properties and/or its biological activity, whose types and features are described in Annex 2.


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Product declaration

In Italy, the certification procedure is only related to composted residues. In this case, the material that is regarded as compost, is allowed to receive 3 kinds of certification:

A. Ecolabel (EC/688/2001) B. CIC mark (Italian Composter Consortium) C. “Allowed for Organic Farming” (Reg. UE 1488/97, Circ. MiPAF n°8 del 13/9/1999)

In this case, the existing rule as well is only about composting. Otherwise, the organic material, digestate or not, can be sold as fertiliser in case of some particular matrices and specific chemical-physical-biological properties (D. Lgs. 217/2006; see definitions given previously). The rule does not say if and when digestate is allowed to be considered as bio-fertiliser, soil conditioner or other. In any case, the mentioned Act is so recent that its application is not yet completely clear and the changes from the previous regulation are not evident either.

The composition depends on starting matrices (animal wastes, distilling slops) and the kind of treatment used. Anyway, in order to consider the digestate, properly treated, as bio-fertiliser according to the mentioned regulation (D.Lgs. 217/2006), the digestate itself must respect the ruling limits linked to the proper category it belongs to. Some explaining categories and reference values are given in Table 11.

Table 11. Requirements for bio-fertiliser according to D.Lgs 217/2006

Dried manure Dried pigs

manure

Dried distilling

slops

Dried distilling

slops (from

molasses)

Organic carbon ≥ 25 % (s.s.) ≥ 30 % (s.s.) ≥ 20 % (s.s.) ≥ 20 % (s.s.) C/N ≤ 15 ≤ 12 / / Total nitrogen ≥ 3 % (s.s.) ≥ 2,5 % (s.s.) ≥ 3 % (s.s.) / Organic nitrogen ≥ 2 % (s.s.) / ≥ 2 % (s.s.) ≥ 3 % (s.s.) Potassium / / / ≥ 6 % K2O (s.s.) Phosphorus / ≥ 2 % P2O5 (s.s.) / / Humification rate ≥ 10 % ≥ 10 % / / Humification degree

≥ 25 % ≥ 25 % / /

In Table 12, the detection limits for copper and zinc for the two categories are given:

Table 12. Limits for Cu and Zn

Dried manure Dried pigs

manure

Copper ≤ 750 mg/kg (s.s.) ≤ 750 mg/kg (s.s.) Zinc ≤ 500 mg/kg (s.s.) ≤ 1.500 mg/kg

(s.s.)

7.4.2. Criteria for optimum utilisation of digestate as bio-fertiliser Digestate is not usually treated as fertiliser according to D.Lgs. 217/2006, but as output to be recovered in agriculture; the regulation to be followed in this case is MiPaf 209/2006 Act. The regulation above mentioned does not hold any measure related to bio-fertiliser storage; it refers indeed to CBPA (Best Farming Practice Code). In case digestate needs to be stabilised for a


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long time, it gets dried firstly by means of mechanic equipment (filter press, belt press and centrifuge) and if needed, it gets a thermal drying up to reduce the humidity rate below 15%. The mentioned treatment is not widespread because of high costs and only applications on digestate produced in food industries (distilleries) are known.

The above mentioned Act recalls the definition of a “solid fraction” (solid manure) and “not solid fraction” (liquid manure) based on the capacity to maintain the geometric shape when the material is piled up on platforms. The volume of the storage platform or tank has to be greater than the volume of solid manure produced in 90 days or the volume of liquid manure produced in 90-120 days according to the kind of livestock and other features. In both cases, the definition of minimum storage volume for small farms (with nitrogen production, considering the amount to be spread in the field, less than 3.000 kg per year) is delegated to single Regions that have not implemented the new regulation yet. Small agro-alimentary1 farms must store at least the wastewater volume produced in 90 days. Widespread practice is then respecting the minimum thresholds required by law.

In regional regulation, winter season is not considered at all. Periods taken into account are usually as follows:

• Beginning of springtime (March, April) before corn, sorghum, sugar beet, and soybean seeding. During this period, the applied fertiliser will be absorbed by plants during their growing phases;

• During spring-autumn seasons on field, after forage harvesting. In case of crops used as livestock feedstuff, digestate needs to be submitted to sanitation treatments in order to avoid the risk of developing any kind of pathologies;

• After cereals harvest and before ploughing. A better soil improvement is obtained if digestate gets buried together with stalks so that it contributes to stalks degradation. If straw has been harvested, nitrogen losses due to percolation and rill flow events are indeed more likely;

• After spring-seeded plants harvest (corn, sorghum, sugar beet). In that case, digestate use is not optimal because of low temperatures and rains that can cause nutrients runoff and leakage.

In small farms odour emissions are neither managed nor controlled. In case of zootechnical farms that are subjected to IPPC (Integrated Pollution Prevention and Control)2 regulation, esteems by using mathematic models and annual controls are actually required in order to respect initial declared values and proposed improvements, mainly in relation to ammonia emissions.

Farmers usually use tractors with a sludge spreading system for solid materials and a tank wagon for the liquid part. It came out from a study realised in Piemonte Region in 2003 that in case of liquid manure spreading by means of tank wagons, in most cases (> 80%) farmers use firstly the mechanic spreading, and after the direct burying (ca. 15%) and watering jet (ca. 5%).

In Italy, digestate is not usually used as fertiliser and the agricultural use is almost entirely just a way to sell off waste material.

1 Farms belonging to dairy, wine, fruit and vegetables sectors producing not more than 4.000 m3 of wastewater per year and 1.000 kg of Nitrogen per year 2 Intensive rearing with 40.000 places for poultry, 2.000 places for production pigs (over 30 kg) or 750 places for sows.


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Even if bio-fertilisers are commonly regarded as better than conventional fertilisers, animal manure can not compete with them because of transport costs and application troubles as it is difficult to spread the manure in a homogeneous way. In addition to that, only a small number of farms owe specific equipment like tractors with dry manure/digestate spreading systems and tractors with tank wagons for liquid manure/digestate spreading system.

Some farms carry out a kind of solid-liquid separation in order to manage the two fractions in a separate way. Some other big farms either stipulate proper agreements with composting centres and bring the digestate as it is or they compost the digestate themselves (e.g. CAVIRO). In some cases, digestate gets dried in order to maintain fertilising properties and/or be able to belong either to chemical fertiliser or to soil conditioner trade category according to D.Lgs. 217/2006.

7.4.3. Soil-conditioner In Table 13, some explaining categories and related reference values are given:

Table 13. Requirements for soil-conditioner according to D.Lgs 217/2006

Animal

manure

Green composted

soil conditioner

Green composted

soil conditioner

Humidity rate ≤ 30 % (s.s.) ≤ 50 % (s.s.) ≤ 50 % (s.s.) pH / 6 - 8.5 6 – 8,5 Organic carbon ≥ 30 % (s.s.) ≥ 30 % (s.s.) ≥ 25 % (s.s.) Fulvic and humic carbon / ≥ 2,5 % (s.s.) ≥ 7 % (s.s.) C/N ≤ 50 ≤ 50 ≤ 25 Total nitrogen / ≥ 2,5 % (s.s.) ≥ 2,5 % (s.s.) Organic nitrogen / ≥ 80 % (tot. N) ≥ 80 % (tot. N)

Usually for each organic soil conditioner category, the following thresholds related to heavy metals are to be respected (Table 14).

Table 14. Limits for heavy metal allowed in soil-conditioners

Total Lead ≤ 140 mg/kg S.S. Total Cadmium ≤ 1,5 mg/kg S.S. Total Nickel ≤ 100 mg/kg S.S. Total Zinc ≤ 500 mg/kg S.S. Total Copper ≤ 230 mg/kg S.S. Total Mercury ≤ 1,5 mg/kg S.S. Total exhavalent Chromium ≤ 0,5 mg/kg S.S.

Below, specific detection limits for Cu and Zn in the mentioned categories are shown (Table 15).

Table 15. Limits for Cu and Zn in soil conditioner

Green composted

soil conditioner

Copper ≤ 150 mg/kg (s.s.) Zinc ≤ 500 mg/kg (s.s.)

7.5. Germany

The annual production of digestate in Germany has been estimated to 8.7 million tons. If the storage container does have a lid, there is normally no odour emission. However, the emissions have to be in the scope of the “Technische Anleitung Luft” (Technical Instructions on


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Air Quality Control) and the “Bundesimmisionsschutzgesetz” (Federal Immission Control Act). According to the law, a storage capacity of 180 days is required. Nothing is done to ensure the chemical stability of the digestate. The bio-fertiliser is mostly applied with tractors with dragging hoses or with a normal slurry tanker. Afterwards, it has to be brought in the ground. There will be a particular regulation for the appliance near water in the future. Because of the high water content of the digestate, there are high appliance costs. But as nitrogen prices are rising, more and more farmers appreciate this bio-fertiliser. Spreading of diseases and pathogens are avoided following the guidelines in the Ordinance for Biowastes. The digestate has to be subjected to a temperature of 55 °C for minimum 24 h or 1 h at 70 °C. In cases where the digestate is separated, the ‘soil improver’ is especially applied for land where sugar beets are cultivated. The quality of soil improver is governed by the Federal Compost Quality Assurance Organisation.

7.6. Spain

There are two biogas plants in Spain treating cattle waste by anaerobic digestion and obtaining biogas and bio-fertiliser. There are also a number of plants belonging to the ADAP (Association of companies to remove the Environmental impact of the Purines) in Juneda (Lerida) which is in the autonomy community of Catalonia and are oriented to the treatment of purines of pig. The applied technology has been provided by the group of Sener engineering, where a specified and registered treatment is applied with the trademark VALPUREN. In summary, the process solves the problem of excessive purines, with assumed costs by the owner of the cattle, and does not produce polluting emissions or odours. The process generates biogas that reduces the cost of gas invoice and recovers a very accepted fertiliser and reasonably remunerated by the market. The technology works in continuous form, fulfilling all the expectations as proven by the two plants that work in full operation, one of them from 2001. Projects of treatment of excessive purines in operation, like the process VALPUREN, which produces a solid fertiliser product, are economically viable to have remuneration as premium of the electrical energy which they generate, in agreement with the RD436/04. Thus, 21 plants of different technologies work. This decree is in revision, and it is expected that new norms will be approved before the end of 2006. It is the intention of the Spanish government that plants of this type will be considered in the future as co-generation plants. It is still uncertain if this consideration will allow that the processes of this type will be economically attractive with the sale of electricity or if additional contributions would be necessary, such as subventions to the investment or canons in charge of the cattle owner. The process allows to recover the energy contained in purines in form of biogas and to reduce the characteristic obnoxious odours of purine, which facilitates the application of purines as fertilisers. Nevertheless, the RD436/04 does not sufficiently remunerate the electricity generated from biogas which is the reason why the modification of the RD436/04 gives hope for anaerobic biodigestion of excessive purines to become economically viable.


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The produced biogas from the anaerobic digestion is used to reduce the natural gas consumption of the annexed installations of co-generation of electricity and heat. With this heat, the water in the purine is separated by distillation and recovered. Furthermore, solid fertilising material in form of “pellets” (small sticks) is produced. The storage and handling of this product does not produce emissions of odours. This fertilising material is commercialised in bulk and, in these conditions, the fertiliser is not subjected to the regulation of chemical fertilisers, but considered like manure. The obtained fertiliser has great acceptance on the market, getting good remuneration of around 40 €/t FOB plant of purines. At the present time, there is not any system of certification or testing methods established in Spain for the application of digestate as bio-fertiliser. The treatment of purines by biodigestion does not reduce the content in N or P2O5, which is the reason why it does not solve the problem of excessive purines unless it is followed by other treatments such as evaporation-dried nitrification-dinitrification, etc., but this substantially increases the price of the treatment. The fertilising material is an organic-mineral fertiliser with 40% organic matter and 7-5-6 of mineral composition (N, P2O5, K2O). The dry matter is superior to 85%. The fertiliser also contains Cu (approx. 700 ppm) and Zn (approx. 1.800 ppm). A system of treatment and emission control was generated in the associated centres for the potentially polluting activities and classified in accordance to the Real Decree 833/1975. Based on it, the Law 38/1972 was developed concerning the protection of the atmospheric environment. The Code of Good Agrarian Practice is elaborated, on the basis of which it anticipates the R.D. 261/1996, transposition to the legislation of the State of the directive EC 91/676/CEE and its ambit of application in Catalonia. In the above mentioned centralised facilities, 95% of water is separated and can be reused as industrial or agricultural water. Furthermore, 5% of the agricultural nutrients and the contained organic matter in purine are also recovered. This 5% recovered represents a solid fertiliser, storable until the fertilising period and transportable with low costs to far agricultural zones (50-300 km), where it replaces chemical fertilisers. The two mentioned facilities produce 12.000 t/year of this fertiliser that is regularly applied throughout the year in different crops. The tests made with maize indicate a 15-20% increase of production and smaller costs compared to the use of the same level of mineral fertilisers.


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References 2001/688/EC: Commission Decision of 28 August 2001 establishing ecological criteria for the award of the Community eco-label to soil improvers and growing media (Text with EEA relevance) (notified under document number C(2001) 2597) (OJ L 242 12/09/2001 P.17-22). 79/542/EEC: Council Decision of 21 December 1976 drawing up a list of third countries from which the Member State authorize imports of bovine animals, swine and fresh meat (OJ L 146, 14/06/1979 P.0015-0017). Al Seadi, T. Good practice in Quality Management of AD residues from biogas production. IEA Bioenergy, Taks 24, Energy from Biological Conversion of Organic Waste. Amlinger, F., Pollak, M., Favoino, E. (2004). Heavy metals and Organic Compounds from Wastes used as Organic Fertilisers. Ref. No TEND/AML/2001/07/20; ENV.A.2./ETU/2001/0024; July 2004. Anaerobic Digestion of farm and food processing residues (1997). The development of a sustainable industry; Good Practice Guidelines. Biological Treatment of Biowaste (2001). 2nd draft, Working Document. European Commission. Bonazzi, G. (2006). “Dopo il digestore, deiezioni nei campi.” L’Informatore Agrario, L’Informatore Agrario, 3/2006, 36-38. Bonazzi, G. (2001). “Liquami zootecnici. Manuale per l’utilizzazione agronomica.”, Ed. L’Informatore Agrario. Commission Regulation (EC) No 1139/2003 of 27 June 2003 amending Regulation /EC) No 999/2001 of the European Parliament and of the Council as regards monitoring programmes and specified risk material (OJ L 160, 28/06/2003 P.0022-0032). Commission Regulation (EC) No 811/2003 of 12 May 2003 implementing Regulation (EC) No 1774/2002 of the European Parliament and of the Council as regards the intra-species recycling ban for fish, the burial and burning of animal by-products and certain transitional measures (OJ L 117/12, 13/05/2003 P.0012-0013). Council Directive 86/278/EEC of 12 June 1986 on the protection of the environemt, and in particular of the soil, when sewage sludge is used in agriculture (OJ L 181, 04/07/1986 P. 6-12). Council Directive 99/31/EC of 36 April 199 on the landfill of waste (OJ L 182 16/07/1999 P.1-19). Council Regulation (EEC) No 2092/91 of 24 June 1991 on organic production of agricultural products and indications referring thereto on agricultural products and foodstuffs (OJ L 198, 22/07/2001 P.1-15) Cronje, A., Turner, C., Williams, A., Barker, A., Guy, S. (2004). The Respiration Rate of Composting Pig Manure.“Compost Science & Utilization”, Vol.12, No. 2, pp. 119-129.


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Domeizel, M., Khalil, A., Prudent, P. (2004). UF spectroscopy: a tool for monitoring huminification and for proposing an index of the maturity of compost. “Bioresource Technology”, Vol.94, pp. 177-184. Environment ’99; Rules applying to Danish agriculture. The Danish Agricultural Advisory centre. Fifth edition, 1999. European Environment Agency (2005). European Environment Outlook, EEA Report, No.4. Francou, C., Poitrenaud, M., Houot, S. (2005). Stabilization of Organic Matter During Composting : Influence of Process and Feedstocks. “Compost Science & Utilization”, Vol.13, No. 1, pp. 72-83. Friedmann, H. (2002). Consequences of EU guidelines on biogas technology. European workshop: Impact of Waste Management Legislation on Biogas Technology, Tulln, Austria, September 12-14. Hjort-Gregersen, K. (1999). Centralised Biogas Plants – Integrated Energy Production, Waste Treatment and Nutrient Redistribution Facilities, Danish Institute of Agricultural and Fisheries Economics. Holm-Nielsen, J.B., Al Seadi, T. (1997). The future of biogas in Europe. Altener Programme, Final Report Phase II. Holm-Nielsen, J.B. (2004). Centre of Biotechnology and Bioenergy, European Biogas conference & workshop, Enniskillen, Northern Ireland, 21-23 October. Joensson, O., Hammar, A., Ivarsson, S. (2002). Biogas Feeding to the Natural Gas Grid and Digestate Use in the Swedish Biogas Plant of Laholm. European workshop: Impact of Waste Management Legislation on Biogas Technology, Tulln, Austria, September 12-14. Kirchmayr, R., Scherzer, R., Baggesen, D.L., Braun, R., Wellinger, A. (2003). Animal By-Products and Anaerobic Digestion. Requirements of the European Regulation EC No 1774/2002. IEA Energy, Task 37, Energy from Biogas and Landfill Gas. Nordberg, A., Edstrom, M. (2002). Waste management in northern Europe: experiences from the Linkoeping biogas plant. European workshop: Impact of Waste Management Legislation on Biogas Technology, Tulln, Austria, September 12-14. Pfundtner, E. (2002). Limits and Merits of Sludge Utilisation – Land Application. European workshop: Impact of Waste Management Legislation on Biogas Technology, Tulln, Austria, September 12-14. Piccinini, S. (2005). “L’integrazione tra la digestione anaerobica ed il compostaggio.” La

produzione di ammendante compostato in Italia, Ed. Consorzio Italiano Compostatori, 89-112. Regulation (EC) No. 1774/2002 of the European Parliament and of the Council of 3 October 2002 laying down health rules concerning animal by-products not intended for human consumption; (Official Journal L 273 10/10/2002 P.0001-0095.


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Regulation (EC) no 999/2001 of the European Parliament and the Council of 22 May 2001 laying down rules for the prevention, control and eradiction of certain transmissible spongiform encephalopathies (OJ L147, 31/05/2001 P.0001-0040) Saviozzi, A., Cardelli, R., N’kou, P., Levi-minzi, R., Riffaldi, R. (2006). Soil Biological Activity as Influenced by Green Waste Compost and Cattle Manure. “Compost Science & Utilization”, Vol.14, No. 1, pp. 54-58.

Websites http://ec.europa.eu/environment/waste/compost/index.htm - the European Commission website http://www.bgkev.de/en/news/index.htm - Bundesgutegemeinschaft Kompost e.V. The Compost Quality Assurance Organisation (BGK). http://www.compostnetwork.info - The European Compost Network, ECN. http://www.mst.dk/default.asp?Sub=http://www.mst.dk/udgiv/publikationer/2004/87-7614-282-5/html/kap04.htm - Danish Environmental Protection Agency, Danish Ministry of the Environment

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