# Removal Efficiency of Bottom Ash and Sand Mixtures as Filter Layers for Fine Particulate Matter

## TL;DR

This study shows that mixing bottom ash and sand can effectively filter fine and ultrafine particles from water, making it a promising material for permeable pavements.

## Contribution

The study introduces bottom ash–sand mixtures as a novel and stable filter layer for removing fine particulate matter in permeable pavements.

## Key findings

- Bottom ash–sand mixtures showed more stable particulate matter removal efficiency over time compared to pure sand or bottom ash.
- The 50:50 bottom ash–sand mixture achieved high removal rates for particles of various sizes, including 93.92% for 10 μm particles.
- Field validation is needed to confirm the effectiveness of these mixtures in real-world permeable pavement systems.

## Abstract

Permeable pavement is a technology that allows rainwater to infiltrate into the pavement. Permeable pavements not only help reduce surface runoff by allowing rainwater to infiltrate into the pavement, but also improve water quality with the filter layer that removes particulate matter pollutants. This study evaluated the particulate matter removal efficiency of bottom ash–sand mixtures as filter layers for removing fine (≤10 μm) or ultrafine (≤2.5 μm) particulate matter in the laboratory. Five filter media were tested: silica sand, bottom ash, and bottom ash–sand mixtures with 30:70, 50:50, and 70:30 ratios. The mixed filters exhibited more consistent and stable particulate matter removal efficiency over time than either the uniform sand or bottom ash filter. The 50:50 bottom ash–sand mixture demonstrated removal rates of 58.05% for 1.8 μm particles, 93.92% for 10 μm particles, and 92.45% for 60 μm particles. These findings highlight the potential of bottom ash–sand mixtures as effective filter media for removing PM10 road dust, although field validation with actual pavement systems is necessary.