Carbon Emission Accounting and Comprehensive Evaluation for Combination Process of Slurry Wastewater and Mechanized Sand Production in Railway Bridge Construction
The slurry wastewater generated during bridge construction is difficult to treat and meet the standards due to its high suspended solids(SS)and high pH value.The drilling slag generated by drilling pile foundations can be used to produce aggregates,but this process requires a large amount of water.In this investigation,8 near zero discharge combination processes of mud wastewater treatment and aggregate production were designed.Based on the life cycle theory,carbon emission accounting model for the combined process has been constructed,and a comprehensive evaluation method has been established.The case analysis results show that the combined process of chemical coagulation-pH adjustment-rod grinding mechanism sand production has the highest carbon emissions during its lifecycle,approximately 2974.29 tCO2e,while the combined process of mechanical separation-vertical axis impact crushing mechanism sand production has the lowest carbon emissions,about 1038.75 tCO2e.Entropy weight-Technique for order preference by similarity to ideal solution(Entropy weight-TOPSIS)comprehensive evaluation method was applied to evaluate 8 combination processes,and it was found that mechanical separation-pH regulation-rod grinding mechanism sand production combination process has the highest degree of closeness to the optimal process.The research results will support the design of a combined process for mud wastewater treatment and comprehensive utilization of drilling slag in railway bridge construction.
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