Waste-incorporated subbase for porous landscape detention basin design

Porous landscape detention basins (PLDBs) capture and filter storm water while taking advantage of the intrinsic quality of plants to act as water treatment systems. A two-layered subbase filtering medium is recommended for building PLDBs. The current design method creates the opportunity for incorporating waste symbiosis. In this study, the beneficial reuse of mixing urban waste stream materials into the subbase filtering media is identified. Based on the waste screening tests conducted in this study, three mixes were selected and examined for their leaching and clogging potentials over the years of service. They are (1)peat-sand mix, (2)compost-paper-sand mix, and (3)compost-paper-sand-tire mix. Laboratory tests showed no significant differences among these three mixes in infiltration capacity and leaching contents of nutrients, pathogens, and total metals. Subbase clogging tests were also conducted for these three mixes using sample storm water. The decay of clogged infiltration rate was measured as the sediment load was accumulated on and through the filtering layer using the selected mix. Three empirical formulas were derived to predict the clogging effect for these three waste-incorporated mixes. Using the recommended threshold infiltration rate of 2.5 cm/h, the life spans of these three mixes were assessed for an example PLDB built in the field. Based on a bench-scale test of dynamic infiltration rates, the waste-incorporated mix is predicted to reduce the clogging potential of PLDB by approximately 20% compared with the currently recommended mix using peat and sand. However, shredded tires were also found to float in water and can be washed out of the basin during overflow events. Based on environmental benefits, construction cost, material availability, and life-span potential, the subbase mix using compost, paper, and sand is recommended for PLDB designs.