The Capacity of Pulp-and-Paper Wastewater in the Absorption of CO2 and its removal from the gas phase

Carbon dioxide is a major contributor to the greenhouse gas (GHG) emission, mainly generated by industrial and anthropogenic activities. Numerous investigations have been conducted on the reduction of atmospheric CO2 emission with considerable attention paid to studying the applicability of gas-liquid absorption. The present research studied CO2 absorption by the wastewater of a pulp-and-paper plant in an effort to determine the capacity of wastewater to absorb CO2 as well as CO2 emission reduction. In a series of experiments, the ability of pulp-and-paper wastewater to absorb CO2 from a CO2 - air mixture was studied. The examined wastewater had an average alkalinity of 2700 mg/L and an initial pH of 6.5. The impact of operating conditions including the wastewater temperature, gas composition, and liquid and gas flow rates on CO2 absorption by the wastewater and CO2 removal efficiency was investigated. The results showed that the gas composition had a considerable impact on the final CO2(aq) concentration and removal efficiency of CO2 while temperature and flow rate had less significant effects. Higher CO2(aq) concentrations were achieved at lower temperatures and higher gas-phase CO2 concentrations, as well as lower liquid flow rates. CO2 removal efficiencies were higher at lower temperatures, lower gas-phase CO2 concentrations, and higher liquid flow rates. The gas flow rate showed to mainly affect the absorption rate. The maximum CO2 concentration during continuous mode of operation was 11.9 g/L which was obtained at the liquid flow rate of 200 mL/min and gas flow rate of 2.5 L/min. In terms of CO2 emission reduction, the maximum removal efficiency was found to be 23%. Although the capacity of wastewater in the absorption of CO2 was shown to be lower than that of conventional caustic solutions, wastewater has been proven to be an effective alternative to reducing CO2 emissions.