AGRO-ENERGY t AGRO-ENERGY t AGRO-ENERGY #PPTUJOHNBOVSFCBTFECJPHBTXJUITUSBX Agricultural residues in the form of animal manure and straw represent a significant yet under-utilised source of renewable energy and fertiliser. Increasing livestock densities and tougher environmental demands on manure management are compounded by low methane yield from manure-based biogas plants and the ligno-cellulosic nature of straw that makes it elusive to co-digest. Until now that is. Danish company Kinetic Biofuel A/S has demonstrated a patented straw pre-treatment technology that enables manure-based biogas plants to use straw as co-substrate and over double biogas output. THE BALTIC SEA REGION (BSR) is an area of intensive arable and animal husbandry production, though not without its environmental issues. Methane and ammonia emissions to the air, groundwater nitrate pollution, run-off leading to freshwater eutrophication and algae blooms in the Baltic Sea, which is one of the world’s largest brackish inland seas and a particularly sensitive marine environment regulated under the 1992 Convention on the Protection of the Marine Environment of the Baltic Sea Area. According to Baltic Manure, a recently concluded European Union (EU) funded flagship project to address manure management practices around the BSR, some 187 million tonnes of cattle, pig and poultry manure are produced annually in the BSR, excluding Russia, most of which is generated in Poland, Denmark and the northern German states. EU legislation regulates application rates of animal manure according to its nitrogen content. Especially for pig manure this can result in over-fertilisation of phosphorous since pig manure is characterised by a high content of phosphorous relative to nitrogen. Denmark is one of the world’s leading exporters of pork and, according to Statistics Denmark, the stock of pigs in 2013 numbered almost 12 8 Bioenergy International No 80, 4-2015 million. The Danish government is keen to both increase biogas production capacity while mitigating the environmental impact of its livestock industry and has set a target of digesting 50 percent of the total annual volume of animal manure by 2020. Yield hampers economics Whilst anaerobic digestion (AD) is a suitable technology to treat manure, produce biogas and use the digestate as organic fertiliser, manure-based biogas remains largely untapped compared to its potential. – For the farmer the economics of manure-based biogas production is often the most serious bottle-neck for increasing capacity, even with generous feed-in tariffs for heat and/or electricity, simply because the biogas yield per tonne of manure feedstock is very low compared to a crop-based feedstock, said Dr Torben A. Bonde, during a visit to Foulum biogas plant in Denmark where the straw pre-treatment technology has been installed and demonstrated. A specialist in microbial ecology, Dr Torben A. Bonde is a distinguished Danish entrepreneur with a long scientific R&D career. He is a founder and CTO of Biofuels Technology ApS, a company specialised in developing biofuel processes and technologies, as well as a Director and Partner of Kinetic Biofuel A/S, a newly formed company for the patented straw pre-treatment technology. Straw as substrate Cattle and pig manure at 8–10 percent dry matter content typically have a methane yield of 15–25 Nm³ per tonne whereas poultry litter does better, at 30 percent dry matter content and 30–100 Nm³ per tonne. Manure pales compared to crop-based feedstock such as maize or grass silage at 33 percent dry matter content and 160–220 Nm³ per tonne not to mention substrates such as fats and crude glycerine which can reach 1000 Nm³ methane per tonne. – Mixing livestock manure types and energy crops as co-substrate in manure-based biogas plants can improve profitability by increasing the methane yield, but results in additional organic nitrogen applied to the fields and potentially increased leaching. Furthermore additional land is needed to grow these crops or additional costs are incurred to purchase them and this eats into profitability, said Bonde. However profitability can now be considerably improved by using other residues from agricultural production such as cereal straw as co-substrate. featu re:
Bioenergy no 4 july 2015
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