| China is a country with large agriculture, and the crop straws shows characteristics of large quantity, majority species and wide distribution.However, in the countryside, there are still the problems of open burning and discarding of straw, which has led problems of air pollution, agricultural non-point source pollution and economic loss. With the development of straw biogastechnology in China,straw biogas projects for central gas supply havebecome a practical way of straw utilization thatis adapted to the current level of economic development in rural areas in China.Straw biogas projects are promoted in the rural aeras where is aboundentin crop straws resources. Practices show that straw biogas technology can improve f straw resources utilization efficiency, and biogas can be used as alternative energy to substitutefossil fuels such as coal, liquefied gas. The straw biogas projects produce biogas as clean renewable energy for ruralhousehold and organic fertilizaer for agriculture. The fact is that, during the process of energy production from biomass, energy will be comsumed, pollutents will be emissioned. So, it is of great significance to have scientific and reasonable evalucation on straw biogas projects for central gas supply for its eco-economic benefit, sustainable development, and environmental impact.Considering the contribution of natural environment and resources to the system, emergy analysis convertsall inputflows of material, energy, money, labor, etc.into solar emergy as a unified measure, which provides acommon measure for the comparisionamong various inputs. This study adopts emergy analysis method and life cycle assessment method to evaluate the ecological benefits and sustainability of straw biogas projects. The main conclusions are as follows.(1)Documentresearch on energy coefficient rate, pollutant discharge coefficient, as well as transformities were done to determine the parameter values of the energy and resources input into the straw biogas projects for central gas supply. Transformites in this study were relative to the 15.83E+24sej/a emergy baseline. The transformities of wheat straw, corn straw and rural labor were calculated.The results showed that, the wheat straw transformity in Anyang County, Henan Province was 1.10E+05sej/J; the corn straw transformity in Qing County, Henbei Province was 7.55E+04sej/J; the labour transformity in rural China was 2.56E+06sej/J.(2) Taking Xijie Village straw biogas project for central gas supply in Anyang County, Henan Province as a case, this study made emergy analysis and calculation on the inputs into and outputs from the biogas project with scenarios of full load and non-full load. The results showed that, the emergy of resources purchased input amounted to 99.73% the total emergy input of the straw biogas project, of which, the wheat straw contributed 73.83%. Compared with the full load operation scenario, the transformities of biogas, biogas residueand biogas slurry were rised obviously, the eco-economic benefits and sustainability declined, the environment load rised. In order to improve the eco-economic benefits and sustainability and decline the environmental load, full load operation of the straw biogas project should be relized.(3) Taking Gengguantun straw biogas project for central gas supply in Qing County, Henbei Province as a case, this study made emergy analysis on the inputs into and outputs from the project with 3 scenarios based on the biogas manure utilization patterns, which were traditional scenario(Scenario 1), real scenario(Scenario 2), and assumption scenario(Scenario 3).The results showed that, from Scenario 1 to Scenario 3, the input ofnonrenewable emergypurchased increased obviously; the proportion ofraw material collection, trasnpotation and pretreatmentsubsystem declined, biogas manure utilization subsystem increased obviously, and the other subsystems declined. In traditional scenario(Scenario 1), the transformity of the whole system was 2.50E+05sej/J. And with the increasing utilization level of biogas manure processing, the transformities of biogas manure and the whole system showed downward trend from Scenario 1 to Scenario 3. The results also showed that, the indices including renewable emergy ratio(RER), environmental sustainability index(ESI), feedback yield emergy(FYE), emergy of waste treatment ratio(EWR), and environmental load ratio(ELR), wereno longer suitable for the comparasion before and after the adjustmenfor the same project, with the industry chain extension and system boundary change.(4) Taking Xijie Village straw biogas project for central gas supply in Anyang County, Henan Province as a case, this study made life cycle assessment on the environmrnt impact with functional unit of annual biogas yield. The environmental impact categories included global warming potential(GWP), acid potential(AP), air quality potential(AQP), photochemical ozone creation potential(POCP), human toxicity potential(HTP). The environmental emissions during the construction unit, operation unit and products use unit of the straw biogas project were calculated and analyzed. The results showed that, the global environment impact load ofXijie Village straw biogas project was-137.72 PET, showing good emission reduction effect. Coal for increasing tempeture and electricity for project operation were two important factors to straw biogas project environmental emission.Choosing low carbon way of warming anaerobic fermentation and reducing the running power consumption are importantways for the sustainable development of strawbiogas projects. |
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