| In recent years,people are paying more and more attention to global warming and extreme weather,and also gradually recognized the hazards of carbon emission and the importance of carbon reduction.Industries began to realize their influence on environment while pursuing progress.Wastewaster treatment plants are one of the industries which have high electricity consumption and carbon emission.While establishing various carbon emission calculation models of WWTPs,researchers have also realized that there are considerable potential energy sources in WWTPs.A portion of carbon emission can be made up by utilizing the sources which usually be neglected by people through reasonable and effective energy recovery processes.Currently,there are a wide variety of carbon emission calculation models of WWTPs,however,the scale,precision,simplicity and applicability of evaluation varies.It is relatively weak to get the carbon emission which can meet the actual situation of the WWTPs using one model,moreover,the raw materials of the energy recovery process are always the products of the processes in WWTPs(such as sludge,effluent water,etc.),and there are few researches on the utilization of waste from other sources.In this study,the material balance and energy consumption of each process unit of wastewater treatment process were carried out based on the degradation rules of pollutants in biochemical reactions,especially made measurement and correction of the key parameter in Sotemann steady state sludge anaerobic digestion to establish carbon emission calculation methods from different sources and forms.Established the method of calculating carbon compensation ability of sewage water source heat pump,sludge anaerobic digestion and carbon source of agricultural waste solid carbon source,and the carbon emission and carbon neutral ability calculation model of WWTPs are carried out.The results of this model made the carbon emission of each process unit more intuitive,and made it easy to identiy high-carbon-emission units and the major sources,providing suggestions to WWTPs for their upgrades.Aerobic tank electricity consumption and sludge anaerobic digestion energy recovery potential were defined by COD degraded in aerobic tank and methane production through mass balance calculation.Focused on discussing the key parameter in Sotemann steady state anaerobic digestion model——unbiodegradable particulate COD fraction in primary sludge(fPS' up),proposed the necessity of measuring and correcting the value of fPS'up,and carried out the measurement method and the calculation procedure of methane production.The results of mass balance are more closely related to the actual situation of the operation of WWTPs,so as to make a more intuitive understanding of the operation of important units in tWWTPs.Summarized the calculation methods of electricity and heat consumption of each unit in WWTPs.The electricity consumption of the main power equipments in the treatment process is calculated by the product of power and working time.Extra calculation of theoretical electricity consumption of sewage pumping and aeration system,which are high energy-consuming units,are carried out based on their working principles and the results of mass balance in order to diagnose their energy efficiency.The thermal consumption of WWTPs only took into account the demand of sludge anaerobic digester,and the calculation methods were referred to relevant specification.The calculation methods of C02,N20 and CH4 sources of sewage plants were summarized based on the results of mass balance and energy consumption calculation.CO2 emissions come from electricity consumption,heat consumption and medicine consumption,and emissions are the product of carbon emission coefficient and consumption of each energy sources.The carbon emission coefficient of electricity reduced from 0.998kgCO2/kW·h to 0.83kgCO2/kW h after recomputing according to the data of power supply standard coal consumption in 2016.The carbon emission of heat consumption was calculated through the carbon emission coefficient and combustion calorific value of coal and natural gas,and the result were 3.8×10-4kgC/kcal(coal)and 2.31×10-4kgC/kcal(natural gas).The carbon emission coefficient of medicine came from the reference and summary of other researches.CH4 emission only come from sludge anaerobic digester which doesn't collect methane,the emission adopted the result of mass balance of the digester.The calculation of N2O emissions was based on the empirical values of the carbon emission coefficient of N2O of different treatment processes in current studies,and its emission was the product of TN reduction and N2O emission coefficient.Emissions from CH4 and N20 could convert into carbon emission by multiplying their warming trend factors.The carbon compensation potential of three kinds of energy recovery process——agricultural waste solid carbon source,sewage source heat pump and biogas recovery process——were investigated.Summarized the data of corns,wheat,and rice on ratio of straw and grain,collection method and yield,etc.,and the denitrification carbon emission of three crop straws were 1.43kgC/kgN(corn cob),1.75kgC/kgN(corn straw)and 1.80kgC/kgN(rice straw).Energy recovered through sewage source heat pump was calculated according to national sewage source heat pump national standard and calculation method,and energy produced by methane recovery process was calculated based on the combustion calorific value of methane and the efficiency of different processes.The carbon emission and compensation calculation model was applied to Fushun Sanbaotun wastewater treatment plant.Designed sludge anaerobic digesters,the mass balance results of aerobic tank and anaerobic digester are as follows:COD degraded in aerobic tank was 12610.24kg/d,measured value of unbiodegradable particulate COD in primary sludge was 0.40,predicted methane production was 8kg/m3influent.Current carbon emission of Sanbaotun WWTP is 138778kgCO2/d,the distribution of each treatment sector is 63.16%of secondary treatment,16.49%of advanced treatment,15.86%of pretreatment and 4.49%of sludge treatment.The current maximum carbon compensation rate of sewage water source heat pump system is 12.15%,and the maximum carbon compensation rate of sewage plant will reach 85.81%after adopting three recommended energy recovery processes. |
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