| Wastewater treatment plants are not only the core components of urban infrastructure but also major emitters of greenhouse gases(GHGs).The GHGs produced in the wastewater treatment process are mainly methane(CH4)and nitrous oxide(N2O),which are the fifth largest non-CO2 greenhouse gas(non-CO2 gas)emission sources in China,accounting for about 5-6%.However,it is very difficult to carry out deep mitigation of non-CO2 gases,and there is still a lack of effective technical support.The Ministry of Science and Technology’s "Carbon Neutral Technology Development Roadmap" shows that the marginal cost of Non-CO2 gas emission reductions is on a steep upward trend,and it is estimated that the emission reduction rate in 2050 can only reach 40-50%.Therefore,finding out the emission pattern of GHGs in wastewater treatment plants is the first step for reduction.At present,the GHGs emissions of the wastewater treatment industry generally have the problem of "inaccurate data and unclear sources":1)Total emissions are inaccurate:At present,the measurement of GHGs emissions from wastewater treatment plants is mostly based on the accounting method of the Intergovernmental Panel on Climate Change(IPCC),which has large errors,and the N2O gas uncertainty even exceeds 90%;2)Unclear emission sources:The emission characteristics of the whole plant and key emission units are not clear;3)The impact of organized capping is unknown:after the typical process undergoes organized capping,the research on the change of emission flux characteristics at the gas-liquid interface needs to be further improved;4)Lack of localized emission factors:There are few on-site measured data of wastewater treatment plants,and the country has not yet issued relevant monitoring technical specifications,which hinders the establishment of localized factors;5)Portable monitoring methods are yet to be developed:new technologies for monitoring GHGs emissions based on mobile vehicles are rarely reported,and their feasibility still needs to be further explored.This work taking the typical anoxic-oxic(AO)wastewater treatment process as an example,developed a set of comprehensive monitoring methods for GHGs in combination with site characteristics:disorganized and organized,emission flux and dissolved state,mobile vehicles monitoring.Based on this,measured the emissions and emission factors of the whole plant and key units;compared the monitored emission factors with the IPCC default factors,then analyzed the difference between the two in calculating the emissions of the entire plant;supplemented by mobile vehicle monitoring,to obtain the concentration of the target wastewater plant distribution.The main conclusions are as follows:Chapter 4 addresses questions 1-3 above.Sampling and measurement of GHGs emission flux was carried out with floating tanks on the disorganized open water surface,and air pump sampling was used at the organized exhaust port,and the annual direct GHGs emission of this plant was 3110 t CO2-eq(carbon dioxide equivalent).High influent load and aeration will promote the emission of CH4 and CO2,such as aerobic tanks and exhaust port corresponding to high-load lines are the main CH4 and CO2 emission units;N2O is mainly produced in anoxic unit,such as inflow water and the corresponding exhaust port of anoxic unit,whose N2O emission is the highest.The uniform pumping effect of the exhaust port after capping will promote the release of N2O,so that the balance between the production and release of N2O in the wastewater is accelerated,especially in the anoxic cell.Chapter 5 addresses the above question 4.The monitoring results show that the CH4 emission factor of this plant is 0.12%(the amount of CH4 produced per unit of COD removed),and the N2O emission factor is 0.11%(the amount of N2O produced per removed unit TN).There is a big difference from the IPCC default emission factors,and long-term testing is urgently needed to further confirm localized emission factors.Chapter 6 addresses the above question 5.The mobile vehicle monitoring method of the wastewater treatment plant has been explored.It can be known that the changes in the concentration of the emission source and the meteorological conditions will cause different responses to the concentration inside and outside of the plant,and the feasibility of the mobile vehicle monitoring method has been preliminarily verified.It can assist in the calculation of the total amount of GHGs emissions and concentration distribution,which is convenient for regulatory authorities to conduct business supervision in the future.In summary,the research on GHGs monitoring methods and technologies is still in the stage of development and innovation.It is urgent to accelerate the construction of monitoring standards,carry out continuous online monitoring simultaneously,and provide technical support for the coordinated development of pollution reduction and carbon reduction in wastewater treatment plants. |
PDF Full Text Request