The amount of greenhouse gases (GHGs), which accelerates global warmming, is increasing every year. The GHGs emission especially accounts for a large proportion in the electricity and heating sectors. The intergovernmental panel on climate change (IPCC) has reported that average temperature will exc...
The amount of greenhouse gases (GHGs), which accelerates global warmming, is increasing every year. The GHGs emission especially accounts for a large proportion in the electricity and heating sectors. The intergovernmental panel on climate change (IPCC) has reported that average temperature will exceed 1.5°C compared to the pre-industrialization level by 2040. Accordingly, countries around the world are making efforts to reduce GHGs emissions along with the Paris Agreement and the implementation of carbon neutrality. Energy saving and carbon neutrality are also urgent tasks for public sewage treatment facilities, one of the fields of GHG emission. Various attempts have been made to reduce GHGs from sewage treatment facilities, such as producing more biogas and reducing energy consumption. This study aims to analyze the energy consumption and to estimate the energy reduction on the present public sewage treatment facilities by applying low soild retention time (SRT) and high separation efficiency of primary sludge. Various scenarios for energy saving were set for the existing 280,000㎥/day sewage treatment plant, and the effects of operating factors were simulated using a numerical model (GPS-X). SRTs (5, 10, and 20 days) effects were evaluated on energy consumption (electricity) and biogas recovery by simulating sludge production at each SRT in the sewage treatment process. The lowest power consumption per day was 35,395 kWh, which occurred on SRT of 5 days, and was 43.8% lower than the 62,924 kWh simulated on SRT of 10 days (existing operating conditions). This is because the amount of waste activated sludge increases at low SRT, which can reduce aeration energy for oxidizing organic matter in the aeration tank as well as increase biogas production. The next scenario simulated changes in biogas production and aeration energy savings when a primary sludge separation efficiency of 60 to 80% was applied. The higher the separation efficiency of the primary sludge, the higher the biogas production. Biogas production increased by 25.0%, 21.4%, and 32.7% at 5, 10, and 20 days of SRT, respectively, when the primary sludge separation efficiency increased from 60% to 80%. Even if the primary sludge separation efficiency increased, the rate of change in effluent water quality did not change significantly within 5.4% and was maintained below the effluent standard concentration. The maximum energy saving occurred at scenario R7 (SRT of 5 days, primary sludge separation efficiency of 80%), which could reduce 43.7% of power consumption compared to R1 (SRT of 10 days, primary sludge separation efficiency of 60%). Biogas production in R7 was improved by 106.2% and 41.0%, respectively, compared to R1 and R2. Biogas production was 15,383 ㎥/d (9,730 kWh when converted into electricity) when primary sludge separation efficiency was 80% and 5-day SRT was applied. The daily power used for aeration under R7 condition was 35,395 kWh, which was 56.3% compared to 62,924 kWh under 10-day SRT. Total daily energy consumption was 25,665 kWh, 44.1% and 45.8% lower than the R1 and R2 scenarios, and GHG emissions could be reduced by 14,949 kgCO2eq/d and 13,947 kgCO2eq/d, respectively. Scenario R7 applied low SRT and high primary sludge separation efficiency to save energy and increase biogas production. However, under this condition, it is difficult to efficiently remove nitrogen by the conventional nitrogen removal process(integration of nitrigication with denitrification). The anaerobic ammonium oxidation (ANAMMOX) process is a method that can efficiently remove nitrogen and reduce energy consumption under conditions of low organic matter concentration. When the ANAMMOX process was applied instead of the conventional nitrogen removal process for nitrogen removal in the R7 scenario, the concentration of organic matter (TCOD) in the effluent was lower at 19.1 mg/L compared to 25.5 mg/L for R7. It was confirmed that the T-N concentration was also improved to 8.9 mg/L compared to 17.0 mg/L of R7. In addition, when the ANAMMOX process is applied, since an external carbon source for the denitrification process is not required and aeration energy can be saved, the net energy consumption is 7,557 kWh, which can save about 50,649 kWh compared to scenario R1. Since the ANAMMOX process has not yet been sufficiently developed and has been reported to be sensitive to operational factors such as temperature change, C/N ratio, and free ammonia concentration, further research is needed on the application of the ANAMMOX process for nitrogen removal from sewage.
The amount of greenhouse gases (GHGs), which accelerates global warmming, is increasing every year. The GHGs emission especially accounts for a large proportion in the electricity and heating sectors. The intergovernmental panel on climate change (IPCC) has reported that average temperature will exceed 1.5°C compared to the pre-industrialization level by 2040. Accordingly, countries around the world are making efforts to reduce GHGs emissions along with the Paris Agreement and the implementation of carbon neutrality. Energy saving and carbon neutrality are also urgent tasks for public sewage treatment facilities, one of the fields of GHG emission. Various attempts have been made to reduce GHGs from sewage treatment facilities, such as producing more biogas and reducing energy consumption. This study aims to analyze the energy consumption and to estimate the energy reduction on the present public sewage treatment facilities by applying low soild retention time (SRT) and high separation efficiency of primary sludge. Various scenarios for energy saving were set for the existing 280,000㎥/day sewage treatment plant, and the effects of operating factors were simulated using a numerical model (GPS-X). SRTs (5, 10, and 20 days) effects were evaluated on energy consumption (electricity) and biogas recovery by simulating sludge production at each SRT in the sewage treatment process. The lowest power consumption per day was 35,395 kWh, which occurred on SRT of 5 days, and was 43.8% lower than the 62,924 kWh simulated on SRT of 10 days (existing operating conditions). This is because the amount of waste activated sludge increases at low SRT, which can reduce aeration energy for oxidizing organic matter in the aeration tank as well as increase biogas production. The next scenario simulated changes in biogas production and aeration energy savings when a primary sludge separation efficiency of 60 to 80% was applied. The higher the separation efficiency of the primary sludge, the higher the biogas production. Biogas production increased by 25.0%, 21.4%, and 32.7% at 5, 10, and 20 days of SRT, respectively, when the primary sludge separation efficiency increased from 60% to 80%. Even if the primary sludge separation efficiency increased, the rate of change in effluent water quality did not change significantly within 5.4% and was maintained below the effluent standard concentration. The maximum energy saving occurred at scenario R7 (SRT of 5 days, primary sludge separation efficiency of 80%), which could reduce 43.7% of power consumption compared to R1 (SRT of 10 days, primary sludge separation efficiency of 60%). Biogas production in R7 was improved by 106.2% and 41.0%, respectively, compared to R1 and R2. Biogas production was 15,383 ㎥/d (9,730 kWh when converted into electricity) when primary sludge separation efficiency was 80% and 5-day SRT was applied. The daily power used for aeration under R7 condition was 35,395 kWh, which was 56.3% compared to 62,924 kWh under 10-day SRT. Total daily energy consumption was 25,665 kWh, 44.1% and 45.8% lower than the R1 and R2 scenarios, and GHG emissions could be reduced by 14,949 kgCO2eq/d and 13,947 kgCO2eq/d, respectively. Scenario R7 applied low SRT and high primary sludge separation efficiency to save energy and increase biogas production. However, under this condition, it is difficult to efficiently remove nitrogen by the conventional nitrogen removal process(integration of nitrigication with denitrification). The anaerobic ammonium oxidation (ANAMMOX) process is a method that can efficiently remove nitrogen and reduce energy consumption under conditions of low organic matter concentration. When the ANAMMOX process was applied instead of the conventional nitrogen removal process for nitrogen removal in the R7 scenario, the concentration of organic matter (TCOD) in the effluent was lower at 19.1 mg/L compared to 25.5 mg/L for R7. It was confirmed that the T-N concentration was also improved to 8.9 mg/L compared to 17.0 mg/L of R7. In addition, when the ANAMMOX process is applied, since an external carbon source for the denitrification process is not required and aeration energy can be saved, the net energy consumption is 7,557 kWh, which can save about 50,649 kWh compared to scenario R1. Since the ANAMMOX process has not yet been sufficiently developed and has been reported to be sensitive to operational factors such as temperature change, C/N ratio, and free ammonia concentration, further research is needed on the application of the ANAMMOX process for nitrogen removal from sewage.
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