Straw Filtration Coupled With Biomass Waste Resource Utilization Technology And Life Cycle Assessment

Agricultural biomass waste has received increasing attention in China,here a process technology is urgently needed for reasonable resource treatment.Based on the existing biogas slurry concentration and separation process of the research group,this paper aims to synergize the resource utilization of agricultural biomass waste corn straw,livestock and poultry manure,couple the biogas engineering and the high value-added resource utilization of waste,and carry out the optimization,integration and upgrading of the integrated process,which expects to provide new ideas for the resource utilization of domestic waste in the future.The total phosphorus and COD content of biogas as the index which preliminary explores the filtration conditions of corn straw,designs and develops a biogas filtration device with corn straw as the filter material.At the same time,the process route of agricultural biomass waste resource technology was designed in a modular way and the field test of small-scale installation was conducted.Finally,a dynamic assessment method and a life cycle assessment（LCA）method were used to evaluate and refine the agricultural biomass waste resourceization technology from the economic and environmental perspectives.The main research components and conclusions are as follows:（1）In the filtration experiments of biogas slurry with straw as the filter media,the filtration effect was the best with a filter height of 50 cm within a filtration cycle of 1 h.The total phosphorus content of the filtrate was below 350 mg/L,the removal rate of total phosphorus was above 65%,and the removal rate of COD remained above 25%,reaching a maximum of 34%at 60 min;in the study of the filtration effect of the granularity of the filter media,the filtrate with medium particle size filter media had a total phosphorus content below 350 mg/L after reaching stability,and was second only to the optimal fine particle size filter media.The total phosphorus content of the filtrate was below 350 mg/L after reaching stability,which was second only to the optimal fine-grain media,and the COD of the filtrate was kept below 3500 mg/L,reaching a minimum of 3167.8 mg/L at 50min,which was the best among the three grain sizes.（2）A dual-path design idea was adopted to design a straw filtering device,as well as a modular process design for agricultural waste resource utilization technology.A continuous pilot experiment with a processing capacity of 100m³/h and a running time of3600 hours was conducted for the vehicle gas and CO₂fertilizer production module,and the calorific value of the vehicle gas output reached more than 33.92 MJ/m³ after treatment by this module;a pilot experiment with a processing capacity of 30t/d and a running time of 7200 hours was conducted for the straw filtration,biogas slurry concentration and separation module.Through continuous operation,the operation works well,almost all nutrients in the biogas slurry can be recycled,and the discharge water also meets the expectation.（3）The economic estimation of the process was carried out with a daily treatment capacity of 30 t of cow manure and 0.45 t of straw.According to the experimental results such as market research and pilot test,the economic evaluation of this project process was carried out using dynamic evaluation method,and the cumulative present value of cost was7,468,700 yuan,the cumulative present value of benefit was 11,664,800 yuan,and the cumulative present value of net benefit was 4,374,100 yuan under the condition that the service life was 10 years and the benchmark discount rate i₀ was 10%.Through calculation,it can be seen that the internal rate of return of this process is 0.211,the benefit-to-capital ratio is 1.56,the dynamic payback period is 2.45 years,and the net present value of three years of operation is RMB 60.60 million.（4）Based on the life-cycle evaluation method,the environmental impacts of agricultural biomass waste resource utilization technologies under three different scenarios of biogas recycling:direct return,concentrated treatment and straw filtration+concentrated treatment were evaluated with global warming potential,environmental acidification potential,environmental eutrophication potential and fossil energy consumption potential as evaluation indicators.The results showed that all three recycling scenarios showed positive environmental benefits,and the highest percentage of the biogas slurry recycling phase in each index,with the GWP of-7469266.25 kg CO₂ eq and the fossil energy consumption potential of-8427501.37 kg oil eq for the straw filtration+concentration treatment scenario.the standardized results for the three different recycling scenarios were-3599.25,-28846.70 and-32634.94,respectively,and the straw filtration+pressure cyclone treatment process had the highest total environmental potential,indicating that the agricultural biomass waste resource utilization technology could produce better environmental benefits.