BIOGAS FROM CO-DIGESTED ANIMAL MANURE AND DIGESTED MANURE MANAGMENT

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1 BIOGAS FROM CO-DIGESTED ANIMAL MANURE AND DIGESTED MANURE MANAGMENT Abstract Holm-Nielsen, J.B.* 1 ; Al Seadi,T. 2 ; Cybulska, I. 3 1 Ph.D., jhn@aaue.dk, Head of Centre for Bioenergy; AAUE&SDU 2 M.Sc, tas@bio.sdu.dk University of Southern Denmark 3 M.Sc., Eng., iwona@bio.sdu.dk University of Southern Denmark *Aalborg University, Niels Bohrs vej 8, DK-6700 Esbjerg, Denmark There is a common tendency in European agriculture today of intensifying the animal production and of increasing the size of the production units. High livestock densities are accompanied by production of an excess of animal manure, compared with what is necessary for the crops in the area. Utilization of the manure in excess as fertilizer causes surpluses of nitrogen and phosphorus in the soil, with negative effects on the environment and the animal and human health. In these areas there is a need of better manure management, redistribution of nutrients from animal manure and optimization of their recycling by controlling the odors, greenhouse gas emissions, nutrient leaching and pathogens. Avoiding over-fertilization is not only important because of its environmental aspects, but also because of economical reasons (Holm-Nielsen, et. al, 1997). Anaerobic digestion of manure offers several benefits for manure management by improving its fertilizer qualities, reducing odors and pathogens and producing renewable energy as biogas, utilized today in Europe for CHP-generation and as vehicle fuel and, in the near future, probably as one of the cheapest hydrogen sources. Key-words: anaerobic digestion, biogas, environment upgrading, pathogen reduction, manure managment, optimal recirculation of organic fertilizers. Introduction Short overview of biogas potential, feedstock and digestible biomass resources Biogas can be produced from nearly all kind of biological feedstock originating from organic waste streams from the entire society. The major source of feedstock originates from the primary agricultural sectors. The largest resource is the animal manure and slurries from animal production units, mainly cattle and pig farms and at some level various manure types from poultry, fish, fur and other animal production. Biogas production from anaerobic digestion of animal manure and slurries is an effective way of reducing greenhouse gas emissions, in particularly ammonia and methane from manure storages. The digested matter can be further refined after the anaerobic treatment. 43

2 In the Table 1 scenarios of area utilization of arable land from the 25 EU countries for energy crop production and the potentials of energy recovery form these areas at three different crop yielding levels are shown. Main Technologies for Manure Digestion Biogas from anaerobic digestion - an integrated system and an important tool for mitigation of global warming and air pollution Biogas from anaerobic digestion is an important integrated tool for sustainable management and treatment of animal manure and other wet organic waste streams (co-digestion). The goal is to treat animal manure and other suitable organic wastes and to convert organic residues into valuable products. Co-digestion of various biomass substrates together with animal manure increases the biogas yield and makes biogas a strong and cheap tool for management of manure and organic wastes and for mitigation of green house gas (GHG) emissions. Furthermore, environmental, human and animal health benefits are quantified and integrated in the overall economic benefits. Biogas plants for anaerobic digestion of animal manure main concepts There are many types of biogas plants in Europe; however the biogas plants digesting manure are categorised as agricultural biogas plants, and they usually codigest manure and other suitable organic residues, many of them of agricultural origin as well. The most common classification of the biogas plants of this category is 1) the large scale, joint co-digestion plants and 2) the farm scale plants. There is no sharp delimitation between these two categories as elements of technology from one is common to the other. Main fermentor types are CSTR biogas plant types. The EU countries where the agricultural biogas plants are most developed are Germany, Denmark, Austria, Sweden, and United Kingdom and to certain level in the Netherlands, Belgium, France, Spain and Italy The Joint Biogas Plant concept In this form of biogas plants animal manure and slurry are collected from the farms, transported to the biogas plant, mixed and co-digested with maximum 15-25% digestible organic wastes from agriculture and food processing industries. The anaerobic digestion process takes place at mesophilic (30-40 º C) or thermophilic temperatures (50-55 º C), during days. The longest hydraulic retention time is needed in mesophilic AD-plants, min. 25d The digested biomass is transported back to the farms, utilized as a pathogen free, nutritionally defined fertiliser. They receive back only that amount of digested biomass they are allowed by law to apply on their crops. The excess is sold to arable farms in the region. The biogas produced is used for combined heat and power generation, or for up-grading and utilization as vehicle fuel, like in Sweden. The produced power is sold to the grid and the heat is distributed through the district heating system to the consumers. Part of it is used by the biogas plant as process heating. 44

3 The biogas production cycle represents an integrated system (Figure 1) of renewable energy production, resources utilisation, organic wastes treatment and nutrient recycling and redistribution, generating intertwined agricultural and environmental benefits, as listed below: Renewable energy production Cheap and environmentally healthy organic waste recycling Less greenhouse gas emission Pathogen reduction through sanitation Improved fertilization efficiency Less nuisance from odors and flies Economical advantages for the farmers. The Farm Scale Biogas Plants The farm scale biogas plants are co-digesting the slurry from one single farm or from two or three neighboring farms. The applied technology is similar to the joint biogas plants in countries like Denmark. In this case there is an increasing tendency that the biogas plants apply also some pre- or post treatment technologies, in order to separate the liquid fraction and to concentrate the nutrients. In other countries like for example Germany, the farm scale plants are somehow low tech, lowering the investment and operation costs of the plant. Lower investment costs are needed to invest in on-site farm scale biogas technology. Optimal Recycling of Crop Fertiliser and Quality Management of Digested Manure The three main components of the anaerobic digestion cycle need to be monitored: the feedstock, the digestion process, and the digestate (Figure 2). This is done by some main measures such as: Selection/excluding from AD of the unsuitable waste categories, types / loads, based on the complete declaration of each load: origin, content of heavy metals, persistent organic compounds, pathogen contamination, other potential hazards etc. Source sorting and separate collection of digestible wastes, preferably in biodegradable recipients. Periodical sampling and analyzing of the biomass feedstock. Extensive pre-treatment/on site separation (especially for unsorted waste). Pre-treatment for safe veterinary recycling, regulated through categories for biogenic waste. Process control (temperature, retention time etc.) to obtain high biogas yield and a hygienic and stabilized organic fertilizer product. 45

4 Periodical sampling, analysing and declaration of digestate (analyses for the content of macronutrients NPK, heavy metals, organic contaminants and pathogens) Handling, storage and application of digestate after an optimal fertilizer crop planning throughout good agricultural practice. Conclusions There is a great potential for biogas from anaerobic digestion of animal slurries and organic byproducts in Europe. Anaerobic digestion of manure offers several environmental, agricultural and socio- economic benefits by improving its fertilizer qualities, controlling odors and pathogens and producing renewable energy as biogas for multiple utilisations. Future development includes the use of new feedstock such as by-products from food processing industries, biofuel processing industries as well as the biological degradation of toxic organic wastes from pharmaceutical industries or other industries by safe and secure sanitation. Biogas must not only be seen as a renewable energy source, but even more as one of the promising solution to the huge environmental problems concerning waste and manure handling, water pollution, CO 2 emission etc. References Holm-Nielsen, J.B., Halberg N., Hutingford, S., Al Seadi, T. (August 1997). Joint Biogas Plant. Agricultural advantages- circulation of N,P and K. Report made for Danish Energy Agency, revised and emendated edition. Al Seadi, T. (January 2002). Quality management of AD residues from biogas production. IEA Bioenergy, Task 24-Energy from biological conversion of organic waste. Kirchmayr, R. et al. (September 2003). Animal by products and anaerobic digestion. IEA Bioenergy, Task 37- Energy from biogas and landfill gas. Braun, R., Wellinger, A. Potential of co-digestion.. IEA Bioenergy, Task 37- Energy from biogas and landfill gas. S.O. Petersen et al. (2006). Recycling of manure and organic wastes - a whole-farm Perspective. Proceedings at RAMIRAN conference, Aarhus, Denmark. Henrik B. Møller et al. (2006). Process performance of biogas plants integrating preseparation of manure. Proceedings at RAMIRAN conference, Aarhus, Denmark. Holm-Nielsen, J. B. et al. (2006). Predicted energy crop potentials for bioenergy, worldwide and EU-25. Proceeding at World Bioenergy 2006, Jönköping, Sweden. 46

5 Animal farms * Cattle manure * Pig manure * Poultry manure Other biomass suppliers * Industrial organic waste * MSW(organic) * Sewage sludge Transport System Storage facilities out in the fields Transport System Centralised Biogas Plant * Homogenisation * Digestion * Reduction of odour nuisance * Sanitation * Nutritionally defined product Fertilizer on the fields * Improved utilisation of plant nutrients * Reduction of the consumption of mineral fertilizer * Reduction of water pollution Separation of digested biomass Biogas for heat & power generation * Renewable energy source * CO 2 - neutral * Reduction of air pollution * Effective energy utilisation Figure 1. The main streams of the integrated concept of centralised co-digestion plant. Source: Al Seadi, Figure 2. Schematic representation of the closed cycle of anaerobic digestion of biogenic waste and the three main steps (A, B and C) of the quality management process. 47

6 Table 1. Scenarios of area utilization of arable land for EU-25 in PJ; Source: Holm-Nielsen, Area used for energy prod. Yield pr. ha 10 % of arable land in EU % of arable land in EU % of arable land in EU t TS pr. ha PJ PJ PJ 20 t TS pr. ha PJ PJ PJ 30 t TS pr. ha PJ PJ PJ * 1 PJ equals J Note: The total area of the arable land in the EU-25 is assumed to be in the order of ha (according to Eurostat figures 2002) 48