Case study of the application of pervious fly ash geopolymer concrete for neutralization of acidic wastewater

Abstract

Coal-fired power plants generate electricity and produce pollutants, including sulfur dioxide and nitrogen oxides in flue gases, as well as particulates, i.e., fly ash and bottom ash. In addition, the processes for removing toxic gases from flue gas and scale from boilers generate the acid wastewater, which requires treatment before release to the environment. Hence, there are many wastes generated from these power plants, and well managed waste treatment is required. Due to the alkalinity of geopolymer, therefore, this research proposes the use of fly ash for the production of pervious geopolymer concrete to neutralize the acidic wastewater. Its high surface area and porosity makes pervious geopolymer concrete suitable for use in wastewater infiltration and neutralization. Crushed limestone to fly ash mass ratios of 8, 10 and 12 were used in the mix design to produce the pore of pervious geopolymer concretes. Samples of 10-cm cube and 30 × 30 × 5 cm were fabricated, and the physical properties and acid neutralization were tested. A 0.001 M HCl solution was used to represent acidic wastewater, and batch and continuous processes of acid neutralization were compared. Results show that the density of the pervious geopolymer concrete increased with the increasing limestone content from 2.32 to 2.57 g/mL, with the percent voids of 20–30% and water flow rate through the concrete of 3.4–3.9 L/min. The compressive strength of the pervious geopolymer concrete was in the range 5.7–8.3 MPa, conforming to the requirement for pervious concrete as a permeable base and edge drain in pavement applications. With the alkaline properties of the geopolymer, neutralization of acidic wastewater from the operational processes of a power plant could be achieved. For the batch operation, concrete with a crushed limestone to fly ash mass ratio of 8 was most efficient, as it provided the highest volume of acid neutralization of 450 L. Sustainable production of pervious geopolymer concrete is proposed by using waste heat from the combustion process in a power plant.