Capturing Atmospheric Carbon Dioxide by Depleting Inorganic Carbon in Municipal Wastewater
AuthorArabi, Seyed Mohammad Saeed
AltmetricsView Usage Statistics
CO2 removal from the atmosphere is likely necessary to limit global warming to the 2 °C goal of the Paris Agreement. This work aims to leverage the embedded conveyance energy within the existing wastewater infrastructure in the U.S. to remove inorganic carbon and develop a carbon negative CO2 removal technology. Although wastewater treatment plants are designed to remove organic carbon, a total of 588 Mt of inorganic carbon also enters the plants but is not removed. To demonstrate this, a bench-scale, membrane-based wastewater carbon-capture system was optimized. Commercially available, gas-permeable membranes (PFA) and hydrophobic, porous membranes (PVDF) fabricated in-house were evaluated in the system. The effects of multiple physiochemical parameters on inorganic carbon removal were investigated, with the best-case scenario removing 15% of the inorganic carbon from the feed stream. Deploying similar full-scale systems across US wastewater infrastructure without addition of acid for pH adjustment would remove up to 12.9 Mt-C/yr. The addition of hydrochloric acid (HCl) to bring the wastewater to 5.0 (one pH unit below the bicarbonate pKa) would increase removal to 30.5 Mt-C/yr, but this is partially offset by CO2 emissions from HCl production, resulting in a net removal of 22.6 Mt-C/yr. When compared to direct air capture, a more mature technology, the new system was more sustainable at reduced feed stream pH (2.5) based on net CO2 removal.