CO₂ Emission Characteristics Of UCT Process Wastewater Treatment Plant

The global carbon emission situation is getting more and more serious.China is taking on more and more carbon emission reduction pressures,and it is necessary to give due consideration to greenhouse gas emissions from various economic activities.Carbon dioxide?CO₂?is the one of the greenhouse gas leading global warming.The sewage treatment plants where the biological treatment process of sewage is an important source of direct release of CO₂ gas account for a large proportion of carbon emissions.The UCT process is a typical urban domestic sewage treatment process.Therefore,it is of great practical significance to study the space-time characteristics,influencing factors and emission reduction measures of CO₂ emissions during the treatment of urban domestic sewage by UCT process.This paper takes the UCT process wastewater treatment plant as the research object where a one-year monitoring of a sewage treatment plant in Zhenjiang City is conducted by using a portable CO₂ concentration measuring instrument.The distribution of CO₂concentration in each process unit and general area is investigated.The influence of different operating parameters and water quality parameters of the biochemistry pool on CO₂ emissions is analyzed.The main research contents and results are as follows:?1?The spatial characteristics of the carbon emissions from sewage plants are expressed as that the concentration of CO₂ near the main process unit of sewage treatment is higher,the concentration of biochemical pool is the highest,and the concentration of the rest of the plant is lower.There is a spatial positive correlation between the CO₂ concentrations of most measurement points.That is to say,the high concentration level measurement point is surrounded by the high concentration level area while the low concentration level measurement point is surrounded by the low concentration level area.The biochemical pool concentration distribution shows that the CO₂ concentration in different sections is quite different,and it also shows symmetry which is the same as the running symmetric features in different sections on the UCT pool.The time characteristics of the carbon emissions from the sewage plant are expressed as that the CO₂ concentration in the aerobic section of the biochemical pool changed quite sharply within 24 hours when the difference reached 2000×10^-6,and the night concentration was high while the daytime concentration was low.Different process units or sections have different characteristics but the overall trend is similar.Most of the measured daily variation coefficients are greater than 20%,only two times less than 20%,indicating that the difference between the CO₂ concentrations at each measurement point is very significant.Moreover,There are strong quarterly characteristics of carbon emission changes.The CO₂ concentration in spring and summer is relatively high while it is relatively low in autumn and winter.?2?The CO₂ emissions from the UCT biochemical pool have different characteristics under different process operating conditions.The person correlation and fitting results show that under different operating parameters,the CO₂ emissions in the three regions of the biochemical pool are different.Among them,the difference in aerobic zone emissions is more obvious,while the difference in anaerobic zone emissions is not obvious.The order of the operating parameters that caused the difference of characteristics of the CO₂ volume fraction in the anaerobic zone is as follows:MLVSS>ORP.The order of the operating parameters that caused the difference of characteristics of the CO₂ volume fraction in the anoxic zone is as follows:MLVSS>ORP>DO.The order of the operating parameters that caused the difference of characteristics of the CO₂ volume fraction in the aerobic zone is as follows:MLVSS>ORP>SRT>DO>SV.The order of the operating parameters that caused the difference of characteristics of the CO₂ volume fraction in the UCT pool is as follows:water volume>HRT.In general,except for SV and ORP,the CO₂ volume fraction has large differences in emission characteristics under different operating parameters.On this basis,it is proposed that adjusting the biochemical pool operating parameters may reduce direct CO₂ emissions.Under the premise of ensuring that the sewage treatment effect is not affected,the DO concentration can be appropriately lowered,or the HRT and SRT can be appropriately extended.?3?Meteorological conditions and water quality parameters have a greater impact on CO₂ emissions from wastewater treatment plants.In the impact of operating parameters on CO₂ emissions,the impact of each operating parameter on the average CO₂ concentration of the whole plant is in descending order:COD removal rate>C/N>SS>C/P;The influence of each operating parameter on the amount of CO₂accounting is in descending order:COD removal rate>C/N>SS>C/P.In general,the impact of each water quality parameter on the average CO₂ concentration of the whole plant is higher than the CO₂ accounting amount.In the impact of meteorological conditions on direct CO₂ emissions,CO₂ emissions are positively correlated with temperature and humidity and negatively correlated with wind speed.