Invited Talk: Low Impact Development for Stormwater Treatment in Densely Populated Areas

Bioretention systems, one of the best management practices for low impact development for water recycling/reuse, are required for a substantial removal of various heavy metals for non-potable reuse. This study investigated the efficiency of food waste compost and waste wood-derived biochar for heavy metal removal from synthetic stormwater under intermittent flow. The heavy metal removals by compost and biochar were promising throughout the 84 pore volumes of stormwater infiltration. Only a small portion of heavy metals attached on the compost was remobilized during the drainage phase of intermittent flow. In comparison with geomedia sorbent, compost and biochar are effective in retarding heavy metal breakthrough. Although the biochar showed a specific surface area approximately 1.5 times of compost, a substantial increase in surface oxygen-containing functional groups was found with compost, which contributed to the higher removal capacity and persistence against drainage. The co-existing kaolinite enhanced heavy metal removal due to plentiful active sites, whereas humic acid facilitated their transport via humate-metal complexation. Nevertheless, in view of the more recalcitrant environmental stability and customable physiochemical properties, biochar appeared to give better performance in pilot- or field-scale bioretention systems for stormwater harvesting.