Retention of water contaminants by fly ash amended pervious concrete blocks

Abstract

Fly ash amended pervious concrete has been demonstrated not to leach the hazardous compounds in the fly ash and may offer additional advantages by filtering out some contaminants. A series of experiments were conducted using five different types of fly ash amended pervious concrete blocks- 0% fly ash, 20% fly ash-high carbon content, 20% fly ash-low carbon content, 30% fly ash-high carbon content and 30% fly ash-low carbon content, to investigates the potential for biodegradation improvement of motor oil by pervious concrete blocks, and to what extent the pervious concrete blocks could retain water contaminants like BOD⁻ from urban runoff. Ion Chromatography (IC) was used to measure the retention of BOD⁻. Biodegradability was measured as the ratio of biochemical oxygen demand (BOD) to chemical oxygen demand (COD).

The range of BOD₅/COD values for leachate motor oil samples were 0.7 to 0.9, suggesting good biodegradation. The BOD₅/COD ratio improved with increasing motor oil retention as the percentage of fly ash increased in pervious concrete block. Phosphate leaching studies revealed that the 20% fly ash low carbon content and the 30 % fly ash high carbon content pervious concrete block did not leach any phosphate. The 0% fly ash, 20% fly ash high carbon content and 30% fly ash low carbon content concrete blocks leached phosphate. However, all five fly ash amended concrete blocks showed the ability to remove 99% of phosphate from high concentration phosphate solution (750 ppm).