Life cycle assessment of biogas digestate processing technologies

Development of optimum substrate compositions in the methane fermentation process

“…Biogas is already effectively used to produce electricity and heat, and to feed gas networks (Bekkering et al, 2010;Esposito et al, 2012). A further source of income produced by the process of methane fermentation of organic solids is represented by the semi-solid by-product of this process -post-fermentation sludge -that thanks to its high content of nutrients can be used in agriculture directly as a fertilizer or processed into compost to increase its quality (Esposito et al, 2012;Rehl and Müller, 2011;Tambone et al, 2009). Unfortunately, methane fermentation process has substantial drawbacks.…”

Recovery of nutrients from biogas digestate with biochar and clinoptilolite

“…Therefore, adequate digestate storage capacity is required, to be able to synchronize application with crop demand. Furthermore, the high volumes of digestate to be applied on agricultural land often lead to logistic problems (Ghafoori & Flynn, 2007;Møller et al, 2009;Rehl & Müller, 2011). Transportation of digestate to wider application areas is necessary to prevent overloading of the receiving land with nutrients in excess of crop demand.…”

“…In many European Union countries, manure and digestate-spreading periods on agricultural land are restricted in order to minimize nutrient leaching and run-off, and therefore a large storage capacity for manure and digestate is needed. Storage is expensive and the transportation of large volumes of water is ineffective from both a logistical and economic point of view (Paavola & Rintala, 2008;Rehl & Müller, 2011). Moreover, environmental problems such as gaseous emissions of malodors, ammonia and greenhouse gases as well as nutrient runoff to streams and waterways may occur when digestate is applied to agricultural land (Hjorth et al, 2009).…”

“…However, nutrient balancing in the soil is important to avoid nutrient runoff to streams and waterways and protect groundwater resources and in Europe nutrient loads must remain within certain legal limits (Fuchs & Drosg, 2013). Hence long-distance transportation and storage of large volumes of liquid manure or digestate is usually necessary, which can be problematic due to high transportation costs and large storage capacity requirements (Rehl & Müller, 2011;Fuchs & Drosg, 2013;Zarebska et al, 2015). The recovery and concentration of nutrients from the liquid fraction of digestate by using sorbent materials could therefore potentially offer one solution for reducing practical and environmental issues.…”

“…However, in areas with very high animal densities or no cropping land suitable for digestate fertilisation, management and utilisation of the liquid fraction presents a challenge (Zarebska et al, 2015). Transportation of large volumes of liquids is costly and ineffective (Paavola & Rintala, 2008;Hjorth et al, 2009;Rehl & Müller, 2011). Furthermore, environmental problems, such as gaseous emissions of malodours, ammonia and greenhouse gases as well as nutrient runoff to streams and waterways, may occur when the liquid fraction of digestate is applied to agricultural land (Hjorth et al, 2009).…”