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Wastewater alkalinity enhancement for carbon emission reduction and marine CO2 removal
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DOI：10.1088/1748-9326/adc1e3.png)
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Abstract
En 中文
Wastewater alkalinity enhancement is a promising approach for ocean alkalinity enhancement due to its potential to deliver strong bases with minimum secondary precipitation and its potential use of the global network of wastewater treatment plants (WWTPs). WWTPs are also significant sources of CO2 due to organic matter oxidation, and integrating alkalinity addition into treatment processes may both reduce in-plant CO2 emissions and increase downstream CO2 uptake. This study presents a modeling framework that combines a modern activated sludge model-based WWTP simulator with an integrated hydrodynamic-biogeochemical-carbonate chemistry model of coastal oceans. We evaluate the effects of adding alkalinity either upstream (UpAdd) of the biological treatment stage or downstream at the discharge location (DnAdd) on WWTP carbon emission reduction and marine CO2 removal. The carbon emission from WWTPs decreases with increasing alkalinity dosage in UpAdd and can be eliminated at a dosage level that is feasible to implement. However, carbon uptake in the surrounding oceanic water is much reduced due to elevated dissolved inorganic carbon in the discharge water. DnAdd does not affect CO2 emissions from WWTPs but enhances carbon uptake in the ocean, with the net oceanic uptake of atmospheric CO2 increasing with increasing dosage level. Across all tested dosage levels, total CO2 removal, including emission reduction at the WWTPs and enhanced carbon uptake in the ocean, is 30% greater in UpAdd than in DnAdd. WWTP treatment tanks have much higher pCO2 than in the ocean, and aeration of process tanks enhances the gas transfer. The upstream alkalinity addition leads to sharp declines in pCO2 in the treatment tanks and large reductions in carbon emission from the WWTPs. These results have implications for developing strategies to reduce global carbon emission and enhance oceanic carbon burial using WWTPs as a delivery mechanism.
Keywords:
ocean acidification
ocean alkalinity enhancement
carbon emissions
wastewater treatment plants
oceanic carbon uptake
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