Abstract
One of the most serious environmental problems that household biogas project would cause is the wastewater discharges and greenhouse gas emissions. Environmental discharges to the water (COD, TN, and TP) and emissions to the air (CO2, CH4, NH3, SO2, CO, NOx, and PM10) were identified. We conducted a life-cycle impact assessment (LCIA) based on the well-established mid-point methodology, Centrum voor Milieukunde Leiden (CML). The following indicators were selected: global warming potential (GWP, in g CO2 eq), acidification potential (AP, in g SO2 eq), eutrophication potential (EP, in g PO43- eq), photochemical oxidation (POCP, in g C2H2 eq), human toxicity potential (HTP, in g 1,4-DCB eq), and abiotic depletion potential (ADP, in g Sb eq). Direct and indirect emissions are differentiated in the accounting process. The direct category includes fuel combustion in transportation, elimination of emissions from raw materials, and methane combustion as alternative household fuel, while the indirect category accounts for biogas infrastructure and equipment, digestate reuse as substitution for chemical fertilizers, machine adaptation, etc. Results show that the total greenhouse gas mitigation is 3614.157 kg CO2-eq, to which feedstock supply stage, digestate processing stage, and biogas energy utilization stage contribute most.