216
Water for Energy and Fuel Production
Alves et al. [72] proposed a new reactor concept that provides the primary biomass
retention through floatation and the secondary biomass retention through settling.
The types of bacteria involved in methanogenic conversion of LCFA are known
and the biochemical mechanism of LCFA degradation by beta-oxidation is well
understood. The initial steps in the anaerobic conversion of unsaturated LCFA are,
however, unclear. Besides the obligate hydrogen-producing acetogens (OHPAs) that
degrade the unsaturated LCFA, bacteria exist which have the ability to hydrogenate
unsaturated LCFA to saturated LCFA. This conversion can be coupled to growth
and these bacteria may compete with hydrogenotrophic methanogens for hydrogen.
LCFAs require the syntrophic cooperation of OHPA and methanogens. These
synthropic communities perform optimally when they are organized in microcolonies; the interspecies hydrogen transfer is enhanced with a short intermicrobial distance. It is yet not clear how microcolonies are developed in a fatty matrix and what
is the effect of hydrogen transfer. Since hydrogen is poorly soluble in water, hydrogen
transfer is increased when the matrix is LCFA. More work in this area is needed.
8.4.8 Food And kiTChen orgAniC WASTe
Significant efforts have been made to generate biogas (biomethane) from different
types of organic wastes [64,65,68,70,71]. Anaerobic digestion is a preferred method
for energy resource recovery from organic residuals because this method (1) generates
biomethane, (2) reduces the volume of the waste, and (3) stabilizes the waste. Shin
et al. [65] showed how this method has been successfully applied to food waste
from restaurants, markets, institutions, and households. They described a multi-step
sequential batch two-phase anaerobic composting (MUSTAC) process that was stable, reliable, and effective in treating food residuals. The process can remove 82.4%
of volatile solids and convert 84.4% of biomethane potential into methane in 10 days.
The output from the posttreatment can be used as a soil amendment. The MUSTAC
process was simple to operate and had high performance. Haug et al. [66] described
the use of Los Angeles Wastewater Hyperion Treatment plant to anaerobically digest
the food residual from the Los Angeles airport and the surroundings serving airline
industry and passengers. The plant was cost effective and handled waste in an environmentally acceptable way.
Weichgrebe et al. [57] examined the energy and CO 2 reduction potentials of
anaerobic treatment of wastewater and organic kitchen wastes. They considered
three different scenarios: (1) the classical waste treatment and the composting of
the organic waste fraction, (2) the anaerobic treatment of wastewater combined
with deammonification and the digestion of the organic waste fraction, and (3) a mutual
anaerobic treatment of wastewater and waste as co-digestion with deammonification. Scenario 2 was found to be the best. With the today’s state of the art concerning the wastewater and waste treatment, both energy surplus and simultaneous
CO 2 emission reduction was accomplished for scenario 2 at 20°C without the use
of the dissolved methane into the reactor’s effluent. If in the future an economical
process for the usage of dissolved methane is developed, GHG emission can be
further lowered. A further positive effect of scenario 2 is that the dissolved nutrients can be reused. Since a small part of these nutrients is needed for the anaerobic
Water for Energy and Fuel Production
Alves et al. [72] proposed a new reactor concept that provides the primary biomass
retention through floatation and the secondary biomass retention through settling.
The types of bacteria involved in methanogenic conversion of LCFA are known
and the biochemical mechanism of LCFA degradation by beta-oxidation is well
understood. The initial steps in the anaerobic conversion of unsaturated LCFA are,
however, unclear. Besides the obligate hydrogen-producing acetogens (OHPAs) that
degrade the unsaturated LCFA, bacteria exist which have the ability to hydrogenate
unsaturated LCFA to saturated LCFA. This conversion can be coupled to growth
and these bacteria may compete with hydrogenotrophic methanogens for hydrogen.
LCFAs require the syntrophic cooperation of OHPA and methanogens. These
synthropic communities perform optimally when they are organized in microcolonies; the interspecies hydrogen transfer is enhanced with a short intermicrobial distance. It is yet not clear how microcolonies are developed in a fatty matrix and what
is the effect of hydrogen transfer. Since hydrogen is poorly soluble in water, hydrogen
transfer is increased when the matrix is LCFA. More work in this area is needed.
8.4.8 Food And kiTChen orgAniC WASTe
Significant efforts have been made to generate biogas (biomethane) from different
types of organic wastes [64,65,68,70,71]. Anaerobic digestion is a preferred method
for energy resource recovery from organic residuals because this method (1) generates
biomethane, (2) reduces the volume of the waste, and (3) stabilizes the waste. Shin
et al. [65] showed how this method has been successfully applied to food waste
from restaurants, markets, institutions, and households. They described a multi-step
sequential batch two-phase anaerobic composting (MUSTAC) process that was stable, reliable, and effective in treating food residuals. The process can remove 82.4%
of volatile solids and convert 84.4% of biomethane potential into methane in 10 days.
The output from the posttreatment can be used as a soil amendment. The MUSTAC
process was simple to operate and had high performance. Haug et al. [66] described
the use of Los Angeles Wastewater Hyperion Treatment plant to anaerobically digest
the food residual from the Los Angeles airport and the surroundings serving airline
industry and passengers. The plant was cost effective and handled waste in an environmentally acceptable way.
Weichgrebe et al. [57] examined the energy and CO 2 reduction potentials of
anaerobic treatment of wastewater and organic kitchen wastes. They considered
three different scenarios: (1) the classical waste treatment and the composting of
the organic waste fraction, (2) the anaerobic treatment of wastewater combined
with deammonification and the digestion of the organic waste fraction, and (3) a mutual
anaerobic treatment of wastewater and waste as co-digestion with deammonification. Scenario 2 was found to be the best. With the today’s state of the art concerning the wastewater and waste treatment, both energy surplus and simultaneous
CO 2 emission reduction was accomplished for scenario 2 at 20°C without the use
of the dissolved methane into the reactor’s effluent. If in the future an economical
process for the usage of dissolved methane is developed, GHG emission can be
further lowered. A further positive effect of scenario 2 is that the dissolved nutrients can be reused. Since a small part of these nutrients is needed for the anaerobic