Surrogates for herbicide removal in stormwater biofilters

Real time monitoring of suitable surrogate parameters are critical to the validation of any water treatment processes, and is of particularly high importance for validation of natural stormwater treatment systems. In this study, potential surrogates for herbicide removal in stormwater biofilters (also known as stormwater bio-retention or rain-gardens) were assessed using field challenge tests and matched laboratory column experiments. Differential UV absorbance at 254 mn (ΔUVA₂₅₄), total phosphorus (ΔTP), dissolved phosphorus (ΔDP), total nitrogen (ΔTN), ammonia (ΔNH₃), nitrate and nitrite (ΔNO₃ + NO₂), dissolved organic carbon (ΔDOC) and total suspended solids (ΔTSS) were compared with glyphosate, atrazine, simazine and prometryn removal rates. The influence of different challenge conditions on the performance of each surrogate was studied. Differential TP was significantly and linearly related to glyphosate reduction (R² = 0.75–0.98, P < 0.01), while ΔTP and ΔUVA₂₅₄ were linearly correlated (R² = 0.44–0.84, P < 0.05) to the reduction of triazines (atrazine, simazine and prometryn) in both field and laboratory tests. The performance of ΔTP and ΔUVA₂₅₄ as surrogates for herbicides were reliable under normal and challenge dry conditions, but weaker correlations were observed under challenge wet conditions. Of those tested, ΔTP is the most promising surrogate for glyphosate removal and ΔUVA₂₅₄ is a suitable surrogate for triazines removal in stormwater biofilters.

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