1 Introduction
Anaerobic digestion of organic wastes and by‐products from agriculture and the food industry is a process known for many years and is widely used for waste stabilization, pollution control, improvement of manure quality and biogas production (Weiland, 2006). Biogas production from manure contributes to climate protection by reducing emissions of CO2 via substitution of fossil fuels and by reducing CH4 emissions from the manure during storage (Moller et al., 2007). It is expected that biogas production will be instrumental in reaching European goals in the field of renewable energy. Due to the simultaneous advantages of avoiding greenhouse gas emissions and producing energy (Sommer et al., 2004) as well as reducing odor emissions (Hansen et al., 2006), there has been a rapid development in the use of biogas in recent years (Weiland, 2006).
In the EU, where only about 5% of the gross consumption is made up of renewables, which is lower than observed in other parts of the world, the share of renewables is expected to double by 2010, and the share of biogas, as part of it, is expected to rise to 12% (Nielsen, Al Seadi, 2006). The Dutch government, in its white paper on energy calls for a simultaneous approach of continuous energy savings, a 30% improvement of efficiency by 2020 and a 20% share of renewable energy in 2020 (Kwant, 2003). In the Netherlands, the potential of energy production from biogas has been estimated to be 49 PJ in 2020 (Nielsen, Al Seadi, 2006).
As part of the “clean and efficient” program, the Dutch dairy chain is aiming to achieve an energy‐neutral production. This new initiative, hereafter called as the energy‐neutral milk initiative, aims at bringing the whole chain, i.e. from the dairy farm to the factory, ultimately to be self sufficient in energy in 2020. This is envisaged to be achieved by building fermentation units to convert manure and food waste into biogas,