Reuse of an aerobically treated wastewater effluent for the removal of SO₂ in the flue gas

Aerobically treated wastewater effluent (ATWE), intrinsically having high alkalinity, was used to remove sulfur dioxide (SO₂) in the flue gas of a coal power plant. Experimental results conducted in a four sieve-tray tower showed that ATWE absorbed SO₂ in flue gas effectively. At a gas:liquid (G:L) ratio of 110:1, the respective SO₂ removal efficiencies were 99% and 95% for flue gases containing 1,600 and 5,000 Mg/kL of SO₂. When the G:L ratio increased to 220:1, the removal efficiency was slightly lowered to 93% for the flue gas containing 1,600 Mg/kL of SO₂. ATWE had higher buffer capacity and SO₂ removal efficiencies as compared to seawater, a common SO₂ scrubbing medium serving as control. In addition, the equilibrium equation between SO₂ partial pressure and concentration of bisulfite (HSO₃-) in ATWE and the kinetic equation describing the rate of SO₂ absorption in the sieve-tray tower by ATWE were established. The absorbing coefficients in the kinetic equation were determined to be 1.96 ± 0.37 mol/(m²ásábar) for gas phase and 0.00184 ± 0.00049 m/s for liquid film. The enhancement factor of the absorbing coefficient in liquid film was 14.28 ± 1.79, resulting in 93% of the decrease of liquid film resistance. The SO₂ absorption rate in the sieve-tray tower was mainly affected by the gas film resistance, representing 96% of the total resistance. Experimental results of this study confirmed that the removal of SO₂ from the flue gas of coal power plants by ATWE was cost-effective. This process does not require the addition of any chemicals and produces no secondary pollution.