13.4.4.1 Specification of Process Potential Material Flow and Boundaries

Figure 13.10 shows the process potential material flow of the BGUS. There are three GHGs released during the course of BGUS: carbon dioxide (CO2), methane (CH4), and nitrogen monoxide (N2O). Carbon dioxide shown by the symbolCSD in the diagram is emitted due to treatment of biomass (livestock waste in this case). It is not included in the calculation of the process potential because it is considered to be released to the atmosphere in the same amount as CO2 that was absorbed and removed from the atmosphere in the short term by plants; thus, it is considered carbon neutral according to international agreements concerning emission of GHGs made by the Intergovernmental Panel on Climate Change (IPCC)[ 16]. Chemicals indicated by the following symbols and (carbon dioxide), (methane), and C51D (nitrogen monoxide) are gases produced during crop production and biogas plant operation. Please note that when the symbol «“* indicates the use of refined biogas as an alternative to fossil fuels by equipment, it is counted toward CO2 reduction. The scope of the calculation of the process potential in terms of GHG reduction evaluation is shown in Fig. 13.10.

The main sources of GHGs produced in the processing of livestock waste by the biogas plant were divided roughly into three groups: (1) combustion of fossil fuels as power and heat sources for vehicles, (2) combustion of fossil fuels for the pro­duction of electricity when using commercial electricity, and (3) GHGs produced by the livestock waste itself by fermentation or sublimation. Further analysis shows that the process of carbon load generation can be divided into the following eight categories: (1) fuel combustion by equipment to transport livestock waste into the plant, (2) combustion of fossil fuels used by the biogas plant, (3) combustion of fossil fuels by equipment within the biogas plant, (4) deposit fermentation of solids after solid-liquid separation, (5) sublimation of digestive liquid during storage, (6) fuel combustion by equipment transporting digestive liquid and compost, (7) fuel com­bustion by equipment that spreads digestive liquid and compost, and (8) sublimation from digestive liquid and compost in fields after spreading. In addition, carbon loads were generated during (1) use of commercial electricity in the process of refining surplus biogas, (2) combustion of fossil fuels by farm trucks inside the farm pro­duction system, and (3) combustion of LPG fuel by kitchen equipment inside and outside the farm production system.

The calculation of the process potential evaluation of the BGUS modeled in Town A in terms of GHG reduction per year used the emission of carbon dioxide as its single indicator. It did not use other environmental indicators such as eutrophication of water in the region or acidification of the atmosphere in its evaluation. Below are the qualifications used in this calculation.

• Because energy involved in the delivery of biogas cylinders by the gas vendor

was almost the same as that of the previous delivery system, it was not counted

as a GHG that contributes to warming in the analysis.

<Filling refined biogas cylinders, supplying by gas vendor>

Previously existing biogas plant>

• Carbon dioxide produced when biogas was created by anaerobic fermentation of livestock waste and CO2 produced by sediment fermentation were considered the same amount as CO2 absorbed by plants during their growth, so they were considered carbon neutral and were not included in the count of GHGs.

• Besides equipment in the farm production system, there was equipment in the barn that used fossil fuels, such as boilers and tractors.