| Global climate change caused by greenhouse gas emission brings great influence on human society, the idea of reduce greenhouse gas emissions has become the consensus of the international community. CO2,CH4 and N2O will be released during sewage treatment plants operation,which is considered as one of the main source of anthropogenic greenhouse gas emission.Along with increasing of sewage quantity and pressure of energy saving,the study on quantitative evaluation of carbon emission in sewage treatment process and proposal of emission reduction are of great significance for promoting low-carbon city construction.This paper focus on the transfer and transformation of organic carbon in wastewater treatment plants,summarize the transformation rules of carbon elements in the process and the quantitative calculation methods of CO2,CH4 and N2O.The study estimate the carbon emission of Xi'an fourth sewage treatment plant,and propose carbon reduction measures.The main conclusions of this study are:?1?Computing methods of quantitative evaluation of greenhouse gases and transformation rules of carbon in sewage treatment systems can be summed up by monitoring total organic carbon?TOC? and balancing of mass.The study establish the mass balance equations of CO2,CH4,N2O,and can be used for quantitative calculation of greenhouse gas emission.?2?The CO2,CH4 and N2O produced in the process of biological treatment accounted for 69.7%, 27.9%, and 2.4% of the total on-site emission.Then,according to the carbon balance equation,the monthly water intake and outlet of TOC in the sewage treatment plant was calculated, and the greenhouse gas emission coefficient is 0.230kgCO2/tH2O,and the annual quantity of on-site emission is 38130.3tCO2, accounting for 45.9% of the Xi'an fourth sewage treatment plant's total emissions.Also the off-site coefficient is 0.268kgCO2/tH2O according to the power consumption of wastewater treatment plant.And annual quantity of off-site emission is 44501.6tCO2 accounting for 53.8%.The quantity of off-site emissions is 1.16 times of on-site emissions.Among them, the greenhouse gas emissions caused by the aerating system and pump equipment, respectively, accounted for 22.1% and 25.7% of the greenhouse gas emissions of the whole wastewater treatment plant.,they are the key of carbon emissions reduction.In addition,other discharge coefficient of 0.001 kgCO2/t water, and the quantity of annual emission is 212.0tCO2.Consequently, the total amount of greenhouse gas emission was estimated 82631.9tCO2.According to carbon emission characteristics of Xi 'an fourth sewage treatment plant,mitigation measures should be adopted on pump equipment and aeration system.Programmable Logic Controller?PLC? can be adopted on pump equipment to reduce carbon emission.As for aeration system,accurate aeration can be taken to reduce carbon emissions, and the effluent discharging can be guaranteed at the same time.?3?The model and web software of carbon emissions in the sewage treatment plant was established. After input the processing scale,water quality data and operating parameters of sewage treatment plant,the on-site emissions,off-site emissions and other emissions of the sewage treatment plant can be calculated during the calculation cycle.The results provide a reference to the reduction of GHGs in sewage treatment plant. |
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