Nutrient and Metal Breakthrough in a Stratified Soil and Mineral Filter for Urban Runoff Treatment

The arrangement of common filter materials can influence urban runoff treatment, but initial removal does not establish whether performance persists during repeated loading. This study evaluated a proposed stratification of soil, geotextile, coarse sand, gravel, and tezontle (volcanic scoria) through nutrient and metal breakthrough curves. Nine laboratory columns, comprising three independent replicates each of the stratified configuration, soil alone, and tezontle alone, received synthetic urban runoff during 16 eight-hour feeding cycles. Feeding occurred on weekdays, with overnight and weekend interruptions; the effluent from each feeding period and 30 min of subsequent drainage was combined for analysis. The curves represent ratios of mean effluent to mean influent concentrations for the three columns per configuration. In the stratified configuration, ammonium removal ranged from 74.53% to 91.60%, and mean nitrate removal was 68.29%. Phosphate and metal removal declined over successive cycles, and effluent lead concentrations exceeded influent concentrations during part of the experiment. Soil-only columns showed broadly similar nutrient trends, whereas tezontle provided limited, transient metal removal. These results identify pollutant-specific differences in the persistence of treatment within the proposed stratification. Their main design implication is that favorable initial removal by common materials must be considered together with subsequent breakthrough and possible release. The findings apply to the tested materials and loading sequence rather than establishing field service life.