Inemad improved Nutrient and Energy Management through Anaerobic Digestion Project/Contract number: 289712 Call identifier: fp7-kbbe-2011-5 Funding scheme: Collaborative project Document number
Agro-digestion and manure/digestate treatment processes
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Agro-digestion and manure/digestate treatment processes
In Flanders a strong correlation can be seen between the location of manure processing installations and the pressure regions. Consequently, about 65% of manure processing installations are located in the province of West Flanders (source: survey 2011 VCM)(Figure ). The same tendency can be seen for anaerobic digestion plants (Figure ). 
Figure : Overview of the graphical spread of operational manure processing installations in 2011 (source: 2011 survey VCM) 
Figure : Geographical spread of biogas installations in Flanders (red: running installations, green: in start-up phase, yellow: under construction) In the Walloon Region, the manure import, export and processing is much less important, as the manure production is much lower than in the Flemish Region. There are no follow-ups for the manure in importing, exporting or processing except for the manure’s spreading contracts. In Wallonia, manure is usually spread as such slurry, manure (poultry manure, pig slurry, cattle manure) or after composting. There are only a few agricultural biogas plants in Wallonia. Table provides information about biogas units in Wallonia, in the agricultural sector. Table : Biogas units in the agricultural sector in Wallonia (Source: IRCO)
Here, please also use common units such as tonne (for manure, organic biological waste, CO2 etc.),kg (for N and P, etc.), m3 (for biogas, etc.) and don’t forget to clearly mention the units you have used. In 2010 the nitrogen and phosphate production in Flanders amounted to 160,2 million kg N and 60,9 million kg P2O5 respectively. The total N loss by stable emissions and storage amounted to 33,0 million kg N, which leads to a nett N production of 127,2 million kg N in 2010. In this respect, pigs were the greatest contributor to loss by emission with 44%, followed by ruminants with 37% and poultry with 17%. The disposal space for animal manure in Flanders in 2010 was 105,2 million kg N and 48,6 million kg P2O5. This space was filled in mainly by animal manure (101,2 million kg N and 46,3 million kg P2O5) , artificial manure ( 40,7 million kg N and 1,4 million kg P2O5 and other fertilisers (1,4 million kg N en 0,8 million kg P2O5) (voortgangsrapport 2011, VCM). The gap between available and used N and P must be closed by processing technologies. In 2010, 26,9 million kg N and 15.5 million kg P2O5 was processed and exported in Flanders. Currently there are 112 operational manure processing installations in Flanders. The most commonly used technique is biological treatment of the thin fraction of pig manure after separation, followed by drying of pig and poultry manure and total processing of pig manure and digestate (for example co-digestion)(Voortgangsrapport 2011, VCM). Presently, data on processing systems are not available for the Walloon region. Anaerobic digestion of agricultural wastes is still not well developed. At present time, it exists only 13 biogas plants in the agricultural sector in Wallonia (South region) using pig and cattle manure, food industry wastes and energy crops as substrate. Figure compares the production of electricity and heat from different kind of biogas facilities in Wallonia, for 2007.
Figure : Comparison of electricity and heat production of differents kind of facilities biogas in Wallonia for 2007 (CRA-W, 2008) Table represents the characteristics of agricultural biogas facilities in Wallonia, for the year 2006. For that year, the total electrical power rating for the agricultural sector was about 1,000 kWh. Table : Characteristics of agricultural biogas facilities in Wallonia (Source: CRA-W, 2006) 
In the following section we will focus on classic manure processing by means of biological treatment. Furthermore also anaerobic digestion as a general processing technique (not exclusively for manure), drying and combustion will be highlighted. Classical pig manure processing: biological treatment As a first step in classic manure processing, the manure is separated in a thick and a thin fraction by means of a centrifuge, a screw press or a seef belt. The resulting thick fraction can next be composted or dried and used as an (exportable) soil enhancer conform the EG 1774/2002 (1069/2009) ordinance. The resulting thin fraction is next subjected to biological treatment. Upon biological treatment the thin fraction undergoes nitrification followed by denitrification. In the nitrification tank N is mineralised into NO3-N. In the denitrification tank the NO3-N is further converted to atmospheric N2. The resulting fraction is used as a fertiliser. In 2010, 73 manure processing installations (Flanders) used biological treatment as primary technique, accounting for the volatilisation of 1.7 million kg N in the form of N2. Anaerobic digestion Anaerobic digestion is an alternative way to process manure. However, often manure is only a part of the input of an anaerobic digester. Consequently, the following section and numbers represent global anaerobic digestion in Flanders. At present (August 2012) 39 anaerobic digestion plants are up running or in the start-up phase. This translates to a total capacity of 1 998 000 ton biomass/year and 88,06 MWe installed electric power. Furthermore 7 more installations are currently in the construction phase or in take-over. All anaerobic digesters are located in agricultural or industrial areas. The implementation of anaerobic digesters is mainly triggered by the availability of input streams, which explains the abundance of anaerobic digesters in the manure rich regions West-Flanders and the Kempen. However, also in other provinces anaerobic digesters are present, for the digestion of organic waste streams, energy crops or different kinds of manure. An upraise of a new form of small scale digestion, this is pocket digesters on farm scale, is expected the coming years. The great majority of digesters in Flanders work according to the mesophile digestion process rather than thermophile digestion (Biogas-e voortgangsrapport 2012). The most used input streams for digestion in Flanders are organic biologic waste (OBW), energy crops and manure. The total capacity of the current operational plants account for the processing of 1,998,000 ton biomass. During the last years a change in input streams has occurred, with a growing part of energy crops. In 2010, about 11% of energy crops was used for digestion (this is an equivalent of 3,800 ha maize, or 0.63% of the available agricultural area in Flanders). Simultaneously, an equivalent raise was noticed in the use of OBWs. Due to the excessive manure surplus in Flanders there is a complicated legislative framework concerning manure input streams for anaerobic digestion (see xxx), in which digesters in manure rich areas are obliged to use a minimum of xxx manure as input. However, in 2010 only 400,000 ton or 1.7% of the available manure in Flanders was digested. It is however expected that also this figure will rise in future. (Voortgangsrapport 2012, Biogas-E). As the market for industrial waste streams is getting more scarce, there is currently a tendency to look for novel sources of input streams, such as household organic waste, harvest residues, roadside cuttings,… Following anaerobic digestion different output streams are created, namely biogas ( which can be converted into electricity and heat using a co-generator) and digestate. In 2010, the total green power production amounted 300GWhe or 60% of the total installed capacity. Another important output stream is digestate, which is the residual fraction of the digested mass. Depending on the input material of the digester, the nutrient content of the digestate varies, but in general the majority of the organic N and phosphorus are converted into ammonium and phosphate. The combination of these nutrients with the recalcitrant organic matter inherent present in the digestate, makes digestate a better fertiliser than manure. Due to the complicated Flemish legislation (see further) there is however currently hardly any market for digestate on Flemish soils, so further processing is required. Different routes can be followed, and mostly include a separation step. The resulting thick fraction can next be dried and exported. The thin fraction can next be treated with (a combination of) membrane filtration, stripping, precipitation and up-concentration. Drying The primary objective of this technology is to concentrate solid manure by thermally removing water to reduce volume and mass. The secondary objectives are to produce products with improved marketability which can be exported, to kill germs and to increase shelf life. The end product of drying is solid and the moisture content is around 10%. The resulting high content of dry matter is necessary to prevent growth of micro-organisms. There are two different types of drying, based on how the heat, needed to evaporate the water, is transferred. The first type, convection, is a direct heat transfer where hot air is brought into contact with the manure directly. The second type, conduction, is an indirect heat transfer where heat is transferred from a drying medium (steam, hot water or thermic oil) to the manure via some kind of separation wall in between. In both cases, the removed liquid will need to be further processed. A study conducted by Huybrechts and Dijkmans (2001) estimated the total primary energy use (in MJ/tonne water) between 3025-4200 for indirect and 3790 for direct drying. Moreover, the thermal energy consumption (in MJ/tonne water) is 2800-3300 and 3250, and the electrical energy consumption (in kWh/tonne water) is 25-100 and 60 for indirect and direct drying respectively. The cost of this type of techniques is determined by the investment costs of the drying installations (water evaporation capacity, type of dryer, system configuration, etc.), variable costs and energy costs. As a comparison, the cost to dry dewatered sludge, a product with a similar moisture content as the thick fraction of pig manure, is around 217 euro per tonne dry matter (figures of 2007, provided by Aquafin).
Combustion is oxidation of primarily organic material with as goals energy production, formation of a possibly reusable mineral end product, reducing the mass and decreasing the bacteriological risk. During combustion, dry fuel, at a temperature of over 800°C together with oxygen, is transformed to amongst others CO2 and H2O. Due to incomplete combustion, CO will also be partly formed. Different types of combustion ovens exist. To be in conformity with Flanders’ environmental regulations, an additional flue gas purification installation is needed. The combustion value for dry matter in manure is (in MJ/kg dry matter) 15-19 for pigs, 16-19 for cattle and 14-16 for poultry. At present, only centralised combustion at a larger scale is feasible in Flanders due to the high requirements for flue gas purification and monitoring (based on the European directive for waste incineration). In 2009, a total amount of 1,811 ktonne of garbage was incinerated in Belgium, of which 99% with heat recuperation. A total amount of 1,261 ktonne garbage was composted or fermented (FOD Economie, K.M.O., Middenstand en Energie, Kerncijfers 2011).
The renewable energy sector in Flanders offers full-time employment to more than 10000 people and has a turnover of 5 billion €. There is a potential to increase full-time employment to 33000 people by 2020. It is difficult to make a proper employment estimate for the biogas sector separately as, apart from operators and manufacturers, other indirect suppliers are connected to the sector, such as engineering offices, manufacturers, suppliers of construction materials, measuring equipment and processors and suppliers of in- and output materials) (Biogas-E, Voortgangsrapport 2012). From 2008 to 2010, the anaerobic digestion capacity in Flanders doubled to 64 MWe. However, the following period (2010-2012) was characterized by a decreased growth to a stagnation of the sector with an installed capacity of 88.06 MWe in 2011. Multiple factors have contributed in the recent years to an increased uncertainty and lower financial returns: (i) availability of biomass and increase in commodity prices, (ii) more difficult marketing and higher costs for marketing and processing of digestate and other side streams, (iii) lower commodity prices for electricity on the Energy-index as compared to the previous years, (iv) insufficient support from legal frameworks for green energy from biogas, … When looking to the future it will most likely become more difficult still to set up new projects, mostly because of the limited availability of input material, ‘not in my backyard’ protests, shifting environmental legislation, connection to the mains and funding opportunities. Moreover, the uncertainty regarding protracted changes in the subsidies framework isn’t conducive either (Biogas-E, Voortgangsrapport 2012). Figure provides an overview of the potential of anaerobic digestion at maximum utilization of biomass present in Flanders. This clearly shows the potential of manure.
Vegetable, fruit and garden waste Clippings OBW
Animal waste Sewage sludge Crop residues
Figure : Potential of anaerobic digestion at maximum utilization of biomass present in Flanders (source: Biogas-E, 2011) Anaerobic digestion of pure manure is economically not viable. Co-digestion on the other hand can be profitable. There are 3 reasons to practice co-digestion:
In Wallonia, biogas production should be estimated by the diversity of the Walloon agricultural area. In the southeast of Wallonia, the main agricultural activity is the cattle breeding. Most of crops cultivated are forage crops. In this region, the potential energy is mainly coming from farm effluents. According to a study realised by Agra-Ost in 2006, bovine manure represents 85% of methane production potential; 3% comes from pig manure and 12% from poultry manure. The methane potential of the total farm manure is estimated to 98,284 tpe. Figure shows the potential of livestock waste for 2008. These data’s are provided at the municipal level by kind of farming and concern all livestock reported in the annual agricultural census. The calculated potential is the sum of the energy produced by each livestock (cattle, pigs, poultry, sheep, goat, horse). It is expressed in MWh / year. Maximum values (17,000 MWh/y) are mainly located where the number of cattle is important.
Figure : Energy potential of livestock waste by municipality (Source: CPDT - INS, 2007)
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