205
8
Anaerobic Digestion
of Aqueous Waste for
Methane and Hydrogen
8.1 intrOdUCtiOn
The global energy usage is growing rapidly due to increasing demands from countries
like China, India, Russia, Brazil, Mexico and other developing nations. The report
from International Energy Agency (IEA [1]) predicts that global energy demand during this century will increase by two fold. Currently 86% of world’s energy demand
is supplied by fossil energy such as coal, oil, and natural gas. However, over next
several decades the supply of oil may go down and the major suppliers of oil and gas
are in the politically unstable regions of Middle East. Furthermore, fossil energy is
also causing more environmental problems due to emissions of greenhouse gases
(GHGs) such as carbon dioxide and lower volatile hydrocarbons. According to the
Intergovernmental Panel on Climate Change (IPCC) [2], GHG emissions must be
reduced to less than half of global GHG emissions level of 1990.
An alternate to fossil energy, renewable energy from biomass has a significant
potential. Biogas from wastes, residues, energy crops, and many other organic materials is a versatile renewable energy source. Methane-rich biogas can be used for
heat and power applications, as fuel for vehicles, and for the production of a variety
of chemicals and materials. Fehrenbach et al. [3] showed that biogas generated by
anaerobic digestions of numerous different types of biomass and effluent wastes is
the most energy-efficient and environment-friendly source of bioenergy. Like natural gas, methane in biogas can be used in a variety of ways. Biogas will drastically
reduce the emission of GHG compared to fossil fuels by utilizing locally available
sources of wastes and other forms of biomass. The digestate from the biogas facilities is an improved fertilizer in terms of its availability to crops than conventional
mineral fertilizers.
In Europe, biogas is the fastest growing bioenergy and it reached six million tons
of oil equivalent (Mtoe) in 2007 with a yearly increase of >20% [4]. Germany is the
biggest producer of biogas with about 4000 agricultural biogas production plants by
the end of 2008. Within the agriculture sector of the European Union, 1500 million
tons of biomass could be digested anaerobically each year, half of which will come
from energy crops [5,6]. Besides the agriculture sector, biogas coming from landfills
is also becoming more important source of power generation. Biogas is generated not
only from various wastewater effluent streams with solids concentration <10 wt%,
but also from various streams with high solids concentration (25–35 wt%) such as
municipal solid waste (MSW) and animal wastes. The amount of MSW generated
8
Anaerobic Digestion
of Aqueous Waste for
Methane and Hydrogen
8.1 intrOdUCtiOn
The global energy usage is growing rapidly due to increasing demands from countries
like China, India, Russia, Brazil, Mexico and other developing nations. The report
from International Energy Agency (IEA [1]) predicts that global energy demand during this century will increase by two fold. Currently 86% of world’s energy demand
is supplied by fossil energy such as coal, oil, and natural gas. However, over next
several decades the supply of oil may go down and the major suppliers of oil and gas
are in the politically unstable regions of Middle East. Furthermore, fossil energy is
also causing more environmental problems due to emissions of greenhouse gases
(GHGs) such as carbon dioxide and lower volatile hydrocarbons. According to the
Intergovernmental Panel on Climate Change (IPCC) [2], GHG emissions must be
reduced to less than half of global GHG emissions level of 1990.
An alternate to fossil energy, renewable energy from biomass has a significant
potential. Biogas from wastes, residues, energy crops, and many other organic materials is a versatile renewable energy source. Methane-rich biogas can be used for
heat and power applications, as fuel for vehicles, and for the production of a variety
of chemicals and materials. Fehrenbach et al. [3] showed that biogas generated by
anaerobic digestions of numerous different types of biomass and effluent wastes is
the most energy-efficient and environment-friendly source of bioenergy. Like natural gas, methane in biogas can be used in a variety of ways. Biogas will drastically
reduce the emission of GHG compared to fossil fuels by utilizing locally available
sources of wastes and other forms of biomass. The digestate from the biogas facilities is an improved fertilizer in terms of its availability to crops than conventional
mineral fertilizers.
In Europe, biogas is the fastest growing bioenergy and it reached six million tons
of oil equivalent (Mtoe) in 2007 with a yearly increase of >20% [4]. Germany is the
biggest producer of biogas with about 4000 agricultural biogas production plants by
the end of 2008. Within the agriculture sector of the European Union, 1500 million
tons of biomass could be digested anaerobically each year, half of which will come
from energy crops [5,6]. Besides the agriculture sector, biogas coming from landfills
is also becoming more important source of power generation. Biogas is generated not
only from various wastewater effluent streams with solids concentration <10 wt%,
but also from various streams with high solids concentration (25–35 wt%) such as
municipal solid waste (MSW) and animal wastes. The amount of MSW generated