18 Study on the Quantitative Evaluation of Greenhouse Gas (GHG) …
273
treatment will become an important aspect of growth. As wastewater treatment is
gradually moving towards sustainable development, it is necessary to systematically
consider GHG emissions throughout the entire process of sewage-sludge treatment.
The LCT can provide a systematic research framework for energy conservation and
GHG emission reduction of sewage-sludge treatment systems.
In previous studies, the application of LCA in sewage treatment was mostly to
evaluate the environmental impact (EI) of WWTPs or sewage treatment processes
and to compare the sewage treatment processes. Mahgoub et al. (2010) evaluated the
EI including CO 2 emissions from an urban water system in Egypt by using the LCA
approach. Rodriguez RM et al. (2016) used the LCA method to compare heterogeneous and homogenous Fenton processes for the treatment of pharmaceutical
wastewater. Frijins (2012) mentioned that the accounting boundary should include
direct and indirect CO 2 from energy consumption, direct CH 4 and N 2 O emissions
from treatment processes, and indirect CO 2 emissions from production of chemicals used in relevant processes. However, little research has been conducted on the
calculation of GHG emissions to account for direct CO 2 emissions from sewage treatment processes. In this study, the calculation of direct CO 2 emissions from sewage
treatment was analyzed based on mass balance.
18.2 Materials and Methods
18.2.1 Boundary Definition
The sewage-sludge treatment system receives domestic sewage as well as discharge
treated sewage and sludge. The sewage-sludge treatment is a complex reaction system
involved a series of biological treatment. In its Second Assessment Report (1997),
the IPCC considers that the carbon in BOD converts only into CH 4 , whereas in
the Fourth Assessment Report (2007), CO 2 generated from biomass decay is not
considered a part of GHG emissions (IPCC 2007). In the case of GHG emission
accounting, some studies state that electric energy consumption should be counted
as a part of the energy sector rather than sewage-sludge treatment system. The influent
BOD converts into CO 2 and biomass, whereas CH 4 is generated only during sludge
anaerobic digestion. Direct GHG emissions are generated by the treatment of sewage
and sludge. Indirect GHG emissions are generated by the consumption of chemicals
and electric energy in the treatment process. The evaluation boundaries are shown in
Fig. 18.1, wherein the tetragonal broken line refers to boundary of GHG emissions,
tetragonal solid line refers to the treatment process, and the oval solid line refers to
materials coming in/getting out the boundary.
273
treatment will become an important aspect of growth. As wastewater treatment is
gradually moving towards sustainable development, it is necessary to systematically
consider GHG emissions throughout the entire process of sewage-sludge treatment.
The LCT can provide a systematic research framework for energy conservation and
GHG emission reduction of sewage-sludge treatment systems.
In previous studies, the application of LCA in sewage treatment was mostly to
evaluate the environmental impact (EI) of WWTPs or sewage treatment processes
and to compare the sewage treatment processes. Mahgoub et al. (2010) evaluated the
EI including CO 2 emissions from an urban water system in Egypt by using the LCA
approach. Rodriguez RM et al. (2016) used the LCA method to compare heterogeneous and homogenous Fenton processes for the treatment of pharmaceutical
wastewater. Frijins (2012) mentioned that the accounting boundary should include
direct and indirect CO 2 from energy consumption, direct CH 4 and N 2 O emissions
from treatment processes, and indirect CO 2 emissions from production of chemicals used in relevant processes. However, little research has been conducted on the
calculation of GHG emissions to account for direct CO 2 emissions from sewage treatment processes. In this study, the calculation of direct CO 2 emissions from sewage
treatment was analyzed based on mass balance.
18.2 Materials and Methods
18.2.1 Boundary Definition
The sewage-sludge treatment system receives domestic sewage as well as discharge
treated sewage and sludge. The sewage-sludge treatment is a complex reaction system
involved a series of biological treatment. In its Second Assessment Report (1997),
the IPCC considers that the carbon in BOD converts only into CH 4 , whereas in
the Fourth Assessment Report (2007), CO 2 generated from biomass decay is not
considered a part of GHG emissions (IPCC 2007). In the case of GHG emission
accounting, some studies state that electric energy consumption should be counted
as a part of the energy sector rather than sewage-sludge treatment system. The influent
BOD converts into CO 2 and biomass, whereas CH 4 is generated only during sludge
anaerobic digestion. Direct GHG emissions are generated by the treatment of sewage
and sludge. Indirect GHG emissions are generated by the consumption of chemicals
and electric energy in the treatment process. The evaluation boundaries are shown in
Fig. 18.1, wherein the tetragonal broken line refers to boundary of GHG emissions,
tetragonal solid line refers to the treatment process, and the oval solid line refers to
materials coming in/getting out the boundary.